This review is devoted to the understanding of the recrystallization mechanisms and its role in the control of the microstructure in emerging metallic materials. Recrystallization is a very pervasive transformation phenomenon that is considered to be very important in efficient microstructure designs.
Journal of Science: Advanced Materials and Devices (2019) 19e33 Contents lists available at ScienceDirect Journal of Science: Advanced Materials and Devices journal homepage: www.elsevier.com/locate/jsamd Review Article Recrystallization mechanisms and microstructure development in emerging metallic materials: A review Kenneth Kanayo Alaneme*, Eloho Anita Okotete Department of Metallurgical and Materials Engineering, Federal University of Technology, Akure, PMB 704, Nigeria a r t i c l e i n f o a b s t r a c t Article history: Received 27 October 2018 Received in revised form 19 December 2018 Accepted 20 December 2018 Available online 28 December 2018 This review is devoted to the understanding of the recrystallization mechanisms and its role in the control of the microstructure in emerging metallic materials Recrystallization is a very pervasive transformation phenomenon that is considered to be very important in efficient microstructure designs Currently, there is hardly any work which has attempted to present a concise and systematic review of the recrystallization in emerging materials with a view to reconcile its manifestations with trends established from recrystallization studies in traditional alloys This review aims to address this by first reviewing the fundamental and nascent recrystallization mechanism concepts and then analyzing their forms in emerging metallic materials, such as high strength steels, Ti- and Mg-based alloys, as well as high-entropy and shape-memory alloys The reviews on these systems show that the classic recrystallization concepts are still relevant for explaining the recrystallization behavior and by extension to the microstructure development in the materials However, in some instances, structural factors exclusive to these materials influenced the driving force and recrystallization behavior yielding outcomes sufficiently distinct from that observed in traditional alloys Basically, deformation processing and material factors such as stress accumulation, inhomogeneous strain distribution, stored energy, available slip systems, phase composition, microstructural variability, initial grain size, texture, stacking fault and lattice distortion energies, strain path, deformation temperature, and solute clustering and diffusion rates were at play in determining the recrystallization mechanisms and kinetics in these emerging metallic materials © 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) Keywords: Recrystallization mechanisms Microstructure Deformation processing Stored energy Emerging metallic materials Introduction In the design of metallic materials, materials scientists and engineers are always conscious of the functionality which is a great determinant of technical efficiency and performance of materials in service, and a vital factor influencing materials service life Traditionally, developing high performance metallic materials was pursued by appropriate alloying and heat-treatment, which help in the development and control of microstructures to meet the target properties [1] In this regard, several transformation phenomena are explored in structure and property control in metallic materials depending on the composition and the nature of the phase constitution of the metallic system One of the most influential transformation phenomena vastly applied in the development of * Corresponding author E-mail address: kalanemek@yahoo.co.uk (K.K Alaneme) Peer review under responsibility of Vietnam National University, Hanoi microstructures in metals is the recrystallization Its prominence is due largely to its capacity to control the structure and properties, specifically structure-sensitive properties of materials [2] This has made it of great scientific interest over the years, since it can be utilized to control several physical, mechanical and technological properties of materials [3] Processes involving the development of conventional alloys, super plastic alloys, thermo-electric materials (semiconductor alloys), thermomechanical processing, powder metallurgy, metallic thin films and several other materials processing operations rely on the application of the recrystallization mechanisms [4] Although predominantly applicable for the design of metallic microstructures tailored to possess properties for specific applications, it has also been employed in polymers [5] and ceramics [6] Recrystallization refers to groups of processes which can manifest stress relaxation to varied extents in a deformed metal by releasing the stored energy generated from the deformation process when heat-treated at an appropriate temperature [2,7] https://doi.org/10.1016/j.jsamd.2018.12.007 2468-2179/© 2019 The Authors Publishing services by Elsevier B.V on behalf of Vietnam National University, Hanoi This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/) 20 K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 Understanding of the mechanisms of recrystallization evolved over time from its first mention in scientific communications recorded in 1885 [7], to the epochal works of Cahn [8,9], Cottrell [10], and a host of other eminent scholars whose contributions are detailed in several classic reviews on the subject [2,3,11] Perhaps some of the most exciting breakthroughs in recrystallization studies were the understanding of recrystallization nucleation mechanisms [11], and the unravelling of recrystallization mechanisms when influenced by intervening metallurgical reactions such as solid solution decompositions, precipitation, crystallographic phase changes, and coalescence of phases [12] Recrystallization nucleation mechanisms were subject of contention for several years It is now appreciated that the recrystallization nucleation mechanism differs from that characteristic of conventional phase transformations where classical nucleation theories are applicable [13] The nuclei which give rise to new recrystallized grains are believed to be already present in the deformed state where the deformation structures with high local orientation gradients constitute the pre-deformed nuclei [14] Recrystallization mechanisms tend to compete with other phase reactions for the stored energy from the defect structure of metallic systems, accumulated during deformation processing This stored energy serves as driving force for the recrystallization/ structural transformation to occur [15,16] The competition among the contending phase reactions can either suppress, occur concurrently with, or accelerate the recrystallization process [16] The unpredictability of the transformation process, generally creates a confused scenario, difficult for an effective and optimal microstructure design Detailed scientific explanations on how to explore effectively recrystallization occurring with intervening phase reactions to develop high strength recrystallized textures in metallic materials, have been provided by Hornbogen [17e19] and Kamma [12,20] Presently, metallic materials processing and development approaches have evolved over time with novel plastic working and forming processes such as severe plastic deformation applied in microstructure design and control Also, advanced metallic materials (such as Ti based alloys, Mg and alloys, high entropy alloys, shape memory alloys, biomedical alloys and weight saving high strength steels) characterised with unusual phase compositions and constitutions have opened new frontiers for industrial, structural, biomedical and technological applications of metallic materials [21e24] A great success in the use of these emerging metallic materials is strongly dependent on the ability to harness the rare property variety they can avail e a factor depending on the microstructure control and optimization Recrystallization processes have been observed to be important in the development of microstructures in deformation processed metallic materials [25] Several insightful reviews which are classics on recrystallization are available in literature: Doherty et al [11] covered majorly the fundamentals of recovery and recrystallization processes while Rios et al [2] focussed more on understanding the recrystallization nucleation and growth mechanisms Recent reviews by Sakai et al [3], and Huang and Loge [26] are more devoted to theories and models in dynamic recrystallization processes Few review articles exist which have discussed both fundamental and nascent recrystallization concepts - such as recrystallization in non-deformed metals subjected to electric current stressing [27], and recrystallization mechanisms in emerging metallic materials, the primary concern of the present review This review covers recrystallization mechanisms in selected deformation processing and emerging metallic materials This is preceded by a concise look at some of the fundamental concepts of recrystallization, which help in explaining the reasons for the type(s) of recrystallization behaviour observed in several metallic material systems Stored energy e driving force for recrystallization The driving force for recrystallization is the amount of stored energy within the metallic material This energy arises from the lattice strains and the crystalline imperfections generated in the material during deformation processing The bulk of the energy generated during the deformation of a metallic material is dissipated as heat with only a small fraction of the energy stored in the material Martin et al [28] reported that the greater proportion of the stored energy is contributed by the crystal imperfections (dislocations and point defects) with dislocations being the major contributor A deformation process such as cold working, is known to increase the dislocation density in a metal to an estimated 1016mÀ2 from approximately 1010À12mÀ2, which is observed in the unworked state It can then be understood why they contribute to the stored energy as each dislocation being a crystal defect generates lattice disturbances in form of strains within its vicinity The increased lattice strain is associated with the increase in strain energy in the metal [29] Several factors, both processing and material variables, have been reported to influence the amount of the stored energy in deformed metals The type and severity of the deformation including the deformation temperature, composition and metallurgical nature of the metallic system are some of the factors which will be discussed Generally, the less the complexity of the mode of deformation, the lower the stored energy Martin et al [28] adduced that this is because simpler deformation processes, involve less stress gradients with little or no friction and redundant work This has also been corroborated by several works which compared stored energy of deformation between different metal working processes [32,33] Zhang et al [34] studied the effect of strain path on deformation and recrystallization in high purity tantalum They reported the formation of different textures during unidirectional rolling and clock rolling deformation processes Workhardening rates which reflect the pace at which the dislocation density in a deformed material increases is strongly dependent on the temperature The rate of workhardening usually increases with the decreasing temperature, since the process of energy release occurring during or immediately after the deformation are suppressed to a greater extent [35] For instance, He et al [36] observed from their study on cryo-rolling and the recrystallization of the hexagonal Zr-4 alloy that the intensity of the heterogeneous deformation in cryo-rolling performed at À7 C is more severe than that in room temperature rolling Lu et al [25] reported that the dynamic recovery is normally suppressed during cyro-rolling which in the case studied, was carried out below C, resulting in a higher deformation energy storage (Fig 1) Materials variables such as melting point, alloying, grain size and orientation, and the presence of second phase particles, have also been reported to influence the amount of stored energy in deformed metallic materials [28] The effects of these variables are summarized in Table Recrystallization mechanisms If deformation processing is performed at temperatures that are low (less than 0.1) relative to the absolute melting temperatures of a metallic system, there will be a high likelihood for defect accumulation to occur resulting in an increase in the stored energy [44] The deformed state due to defect accumulation and work hardening is thermodynamically unstable It is also usually accompanied with changes in mechanical properties and other material K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 21 Fig EBDS orientation maps room temperature rolled (a, c) and cryorolled CueAg alloys (b,d) annealed at 300 C (a, b)and 400 C (c, d) (Culed from Lu et al [25] with permission from Elsevier) It shows that cryorolled CueAg alloys have local areas of recrystallized grain at low annealing temperatures compared to room temperature rolled CueAg alloys because of higher stored energy during deformation Table Influence of material variables on stored energy Variable Effect on stored energy Melting Point Foreign Atoms Grain size and Orientation Stored energy decreases with decreasing melting point (exceptions exist!) [28] Elastic stress field interactions between atoms and dislocations allows larger amount of energy to be stored [37,38] At same strain, fine grains result in greater accumulation of dislocations resulting in higher stored energy in comparison to coarse grains [25,30,39] Different grain orientations have varying slip accommodation and hence have different values of stored energy [31] High vacancy concentrations induced from high strains increase the stored energy [40] Influence dependent on volume fraction and applied strain [2] Coherent precipitates which are deformable with the matrix results in increased yield strength due to coherency strains, and several short range interactions [41,42] For non-deformable second phase particles, much higher dislocation density (reflecting higher stored energy is achieved) in comparison with single phase metals [28] Generally orientations, planes or directions which favor easy slip will result in lower stored energy because of lesser dislocation accumulation [31] Dislocations pile up easily along grain orientations, planes and directions where slip is constrained hence more stored energy will be amassed [29] Stacking fault energies influence dislocation mobility and morphology e in high stacking fault energy metals (such as Al) there is ease of dislocation movement by glide, climb and cross slip during plastic deformation, thus less dislocations are accumulated resulting in low stored energy [43] Low stacking fault energy metals (such as Mg) restrict the mobility of dislocations and as a result accumulate high dislocation densities which increases stored energy [43] Vacancy Concentration Second phase particles Crystallographic texture Stacking fault energies properties, such as electrical conductivity and corrosion resistance [45] For such an unstable system, there is a natural tendency to revert to the unworked or annealed state so as to minimize its overall energy Reverting to the unworked state will require activating the stored energy release which can eliminate the defects locked in the material These processes usually require heating, and depending on the activation energy, results in different levels of stress relaxation, namely: recovery and recrystallization Recovery is the term used to refer to multi-stage processes which result in the redistribution and annihilation of point defects and the redistribution and annihilation of dislocations either without the formation of new boundaries or with the formation and migration of low angle boundaries [26,46] Recovery processes are basically divided into two types - the processes involving the redistribution and the elimination of point defects (point defects annihilation) [47,48], and the processes resulting in the rearrangement and the partial annihilation of dense dislocation networks formed by the glide and interaction of dislocations during cold working - a phenomenon referred to as polygonization [49] Both processes generally result in the release of some of the stored energy arising from deformation The recrystallization mechanism with the capacity to eliminate almost all the deformation induced dislocations in worked metallic materials is referred to as the primary recrystallization Simply stated, it is the process of formation and growth in a deformed matrix of new grains which are distortion free and appreciably more perfect than the proper matrix and are separated from the latter by large angle boundaries [14] This process is propelled by the excess volume energy accumulated during the prior plastic deformation, and is mostly localized in the stress fields which surround the dislocations formed by deformation [50] The activation energy for the recrystallization is generally higher than that required for the polygonization and point defect annihilation The activation energy, however, changes all through the recrystallization process as the stored energy is used up [50] A critical amount of deformation is reported to be prerequisite for the primary recrystallization to occur during heating [51] Above the critical deformation, the recrystallization nuclei are postulated to appear during heating and are formed first of all in portions of the crystal lattice that have been most severely misoriented and distorted by the cold work Haasen [50] pointed out that recrystallization commences in the areas of high dislocation density, and 22 K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 at sites where the deformation is inhomogeneous The mechanism of the primary recrystallization has led to the sub-classification of the process It is often referred to as static recrystallization when the process is propelled by annealing after prior cold working The term ‘discontinuous’ static recrystallization is used when recrystallization proceeds by a two stage process of nucleation and growth of new grains within the deformed microstructure [26] However, it should be noted that the origin of a recrystallized grain is reported to always preexist in regions that are highly misoriented in relation to the material surrounding it This high degree of misorientation also gives the region from which the new grain originates the needed growth mobility [52] New recrystallized grains are also formed by a process known as continuous static recrystallization This involves gradual localized migration of subgrains formed during severe deformation when subjected to annealing [53] Some factors such as temperature, extent and complexity of deformation, grain size, melting point and purity of metallic materials, presence of foreign atoms and second phase particles, stacking fault energies and crystallographic texture which affect stored energy of deformation are well known to influence the primary recrystallization process [28] The influence of stacking fault energies, melting point and purity levels of metallic materials are summarised in Tables and Recently, it has been reported that an electric current also influences the recrystallization kinetics [57] The exposure of a coldworked metal deformed at large deformation strains to an alternating electric current during annealing is reported to accelerate the recrystallization process [58] This is because of greater sensitivity of sub grain/grain structures to the electron wind effect which helps accelerate the grain boundary motion This is coupled with the increased vacancy density facilitated by the applied current which aids the motion of sub grains [57] Liang and Lin [27] also showed that recrystallization can be induced in non deformed metals exposed to direct current stressing They discovered that direct electric current stressing produces a high dislocation density in Cu36Zn brass, based on observations from EBSD and TEM analysis The recrystallization was triggered in situ by the Joules heat generated during the electric current pulse treatment The direct current stressing followed by rapid quenching was reported to result in substantial improvement in grain size refinement and micro-hardness The extent of recrystallization was observed to depend on the period of current stressing which affected the amount of Joules heat supplied to the material The longer the current stressing period, the greater the likelihood of achieving complete recrystallization Electromigration of atoms from their lattice positions and thermal expansion during joule heating were noted as the driving force for the recrystallization This phenomenon (recrystallization in non-deformed brass) has not been corroborated by other authors, or reported for other metallic materials, so it would be fascinating to see the response of other metallic materials to such direct electric current stressing The micrographs confirming the influence of direct electric current Table Influence of stacking fault energies on stored energy and recrystallization mode [43,54,55] Stacking Fault Energy Stored Energy Recrystallization mode High (Al, b-Ti, ferritic steels) Low Low/Medium (Cu, Mg, Zn) High Dynamic recovery, Continuous dynamic recrystallization Discontinuous dynamic recrystallization stressing on the microstructure of non deformed brass is presented in Fig During the hot plastic deformation of metals and alloys, two competing processes occur in parallel, strain hardening and softening ones The strain hardening effect is due to the increase in the dislocation density under the action of external forces and to the interaction of dislocations which form dislocation pile-ups of various degrees of stability and mobility [59] The softening process consists in a decrease of the dislocation density and in the redistribution of dislocations into energetically more stable configurations The dislocation redistribution is due to the vacancy climb, the formation of recrystallization nuclei and their growth by the migration of large-angle boundaries under appropriate conditions (temperature, amount and rate of deformation) [60] When these processes occur during the high temperature deformation of materials the structures formed are taken to be formed via the dynamic recrystallization The mechanism of dynamic recrystallization has been shown to be dependent on factors, such as the temperature, the amount and rate of deformation, the stacking fault energy, the initial structural state, and the phase composition of a material [61] Since the dynamic recrystallization requires strain hardening and softening to occur in parallel, the final structure is strongly dependent on the aforementioned factors, albeit in a complicated manner Dynamic recrystallization (DRX) is classified, on the basis of the mechanism of formation of new grains, into discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) DDRX is a fast pace DRX process which proceeds by the nucleation of new grains at the expense of old deformed grains during high temperature plastic deformation DDRX mostly occurs in low stacking fault energy metals (Mg, Zn) where the dynamic recovery is suppressed [62] DDRX is usually preceded by the serration and bulging of pre-existing grain boundary and the recrystallization is confirmed by the appearance of a necklace structure [63] CDRX occurs by the migration of subgrains with low angle boundaries formed within the deformed structure into grains with high angle boundaries during straining at high temperature [64] CDRX is often preceded by the dynamic recovery and mostly occurs in high stacking fault energy metals Dynamic recovery is a phenomenon associated with the deformation processes undertaken at temperatures at which wholesale sweeping of dislocations may not be energetically favoured [65] Under such conditions the pace of defect generation (dislocation increase) is greater than that of the dislocation annihilation That is, only partial elimination of dislocations occurs under such conditions In some metallic systems deformed at room temperature, dynamic recovery has been reported [28] The deformation induced store energy in such material at room temperature is observed to be lower than that when processing is carried out under cryogenic conditions such as cryo-rolling [30,66] This is because the dislocation mobility is hindered during cryogenic deformations, hence suppressing the dynamic recovery This leads to a high accumulation of dislocations and an increase in potential nucleation sites for new grains during annealing [66,67] Fig illustrates the idealised evolution of microstructure in hot deformed metals for cases where dynamic recovery and dynamic recrystallization are the activated recrystallization mechanisms Grain growth also referred to as normal grain growth or continuous grain growth normally sets in after the primary recrystallization, as the growing recrystallization nuclei begin to impinge on one another It is characterized by the growth of some new grains at the expense of other newly formed grains resulting in a microstructure with a narrow range of grain size and shape [48,68] The principal thermodynamic driving force of the grain growth is the tendency to diminish the overall grain-boundary K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 23 Table Influence of melting point and purity levels on average grain size of annealed and HPT processed metals at 300K and 100K (adapted from Edalati et al [56]) Metals Zn Mg Al Purity (%) Crystal Structure Tm (K) gSFE (mJ/m2) Grain size, ds (mm) 99.99 HCP 693 140 390 20 20 99.9 HCP 922 125 1600 1.0 2.7 99.999 FCC 933 166 >4000 3.5 3.8 Anneal HPT 300 K HPT 100 K Self -Anneal Cu 99.99 99 1000 1.3 2.2 160 0.38 0.16 99.99999 FCC 1357 45 310 0.30 0.080 1.5 Nb 99.99 150 0.29 0.073 20 99.9 BCC 2740 150 50 0.24 0.041 Fig (a) The EBSD image of the annealed as-prepared specimen shows dislocation of free grains The EBSD image in the middle of the specimen (b) h, 10 cycles (Curled from (Liang and Lin [27], with permission from Elsevier) (Larger grains exhibit prominent colour contrast, The non-uniform color is ascribed to the high dislocation density induced by current stressing) ‘surface’ energy [69] Thus as the grains grow in size and their numbers decrease, the grain boundary area diminishes and the total surface energy is lowered accordingly [69] Some abnormal grain growth, that is the exaggerated growth of some grains at the expense of others, is often observed after primary recrystallization [47] A typical microstructure of a metal that 24 K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 Fig Evolution of microstructure during hot deformation of a material showing (a) dynamic recovery (b) dynamic recrystallization (Curled from Verlinden et al [48] with permission from Elsevier) has undergone an abnormal grain growth show the growth of just a few grains to very large diameters This grain growth variant is known as discontinuous grain growth, or secondary recrystallization [43] It occurs due to anisotropic properties of emerging grain boundaries after recrystallization The grain boundary anisotropy is initially characterized by the inequigranularity, which is facilitated by factors such as disparity in grains concentration of defects (volume energy), size, crystal orientation, dispersion of precipitates, second phases and impurities, structural and topological characteristics [43] The recrystallization mechanisms discussed are drawn largely from observations in traditional metals and alloys How the recrystallization behavior is influenced by novel deformation processing and in emerging materials, has not come under much scrutiny The recrystallization behavior and how it is harnessed in the microstructure design in emerging metallic materials, are the concerns discussed in the succeeding section Recrystallization mechanisms in emerging metallic systems 4.1 Recrystallization mechanisms in high strength steels High strength steels (HSS) are steels whose composition and structure have been metallurgically modified to provide a superior combination of mechanical properties like strength, toughness, ductility and formability [70,71] These steels are modified using the microalloying technology and thermomechanical treatments and are mostly developed for the use in automotive, petrochemical and petroleum industries [72,73] Examples of HSS are high Mn alloy steels, twining induced plasticity steels, transformation induced plasticity steels, complex phase steels and martensitic steels The microalloying technology and thermomechanical treatments utilized in the development of these new generation HSS trigger metallurgical reactions (recrystallization processes inclusive) which influence the microstructures developed and ultimately the engineering properties Bracke et al [74] investigated the recrystallization behavior of the low SFE FeeMneC based alloys processed with twinning induced plasticity (TWIP) FeeMneC alloys have exceptional mechanical properties like high ultimate tensile strength (600e1000 MPa) and elongations (15e25%), which has informed its use in automotive applications where high strength is required The test material (a fully austenitic FeeMneC steel) was hot rolled and quenched in water prior to the deformation process Subsequently the material was subjected to cold rolling with total reductions between and 50% before annealing treatment at temperatures between 673 (400) and 998K (725 C) It was observed from the study that softening of the test material readily occurred at annealing temperatures above 855 K (612 C) and the full recrystallization was observed in the material subjected to 973 K (700 C) annealing temperature after 100 s These observations were attributed to the presence of microtwins in the deformed structure which hindered recrystallization at lower annealing temperatures On the other hand, the fully recrystallized structure at high annealing temperatures was characterized with the absence of microtwins but this does not mean that the microtwins served as preferential sites for the nucleation of new grains The recrystallization process was, however, associated with sweeping of boundaries of growing grains in which the deformation substructure discontinuously disappears as the process proceeds The texture of the material appeared unchanged after the recrystallization and this was attributed to the nucleation and growth of the recrystallized structure without any preferred orientation as a result of the energetically homogenous deformed structure Saha et al [75] developed a fully recrystallized nanostructured high Mn austenitic steel through conventional rolling and annealing The research was aimed at producing ultrafine grained materials which have a good balance of strength and ductility The test material was a Fe-31 wt %Mn-3wt %Al-3wt %Si TWIP austenitic steel which has a high strength and a large ductility A hot rolled plate of this steel was subjected to multiple passes of cold rolling under lubrication to about 92% reduction in thickness, and subsequently subjected to annealing treatments at 650 C for several period of time The presence of elongated regions, black points and low angle boundaries in the microstructure of test specimens annealed for 0.18 ks at 650 C was indicative of the partial recrystallization at this treatment time It was, however, observed that as the annealing time was increased to 0.3 ks and 1.8 ks very fine and equiaxed grains were observed in the microstructures depicting full recrystallization of the test specimens It was also established that the mean grain sizes (average 400 nm) observed in the fully recrystallized steel structure studied surpassed grain sizes previously reported for other metallic systems which were fully recrystallized These observations were attributed to the low stacking fault energy of the high Mn steel under study which greatly inhibits a dynamic recovery of dislocations during rolling deformations at ambient temperatures resulting in a nanosized lamellar structure with a high dislocation density Shear banding further subdivides the lamellar structure into finer length scale which introduces more misorientation, and such deformation structures enhance the formation of recrystallized grains during annealing K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 The dynamic recrystallization mechanism of the Fe-8 wt.% Al low density steel under hot rolling conditions was investigated by Castan et al [76] These steels are reported to have tendencies to exhibit surface defects referred to as roping (surface corrugations parallel to rolling direction) which originates from the inhomogeneous orientation distribution of individual grains The purpose of the research was to understand the conditions of recrystallization during hot rolling which can control the microstructure and curb the occurrence of roping in this steel The steel for the test was rolled in three successive passes which accumulated to a total deformation of The dynamic recrystallization behavior of the steel was studied by performing the hot torsion test in a direction involving a negative shear and under argon atmosphere to reduce the oxidation phenomena The test was performed within a temperature range of 900e1100 C and a strain rate range of 0.1e10 SÀ1 The deformed test samples were quenched immediately in argon to preserve the microstructure and avoid post dynamic-recrystallization It was observed from the study that the test material undergoes continuous dynamic recrystallization (CDRX) at lower temperature (1000 C) and lower strain rates (0.1 S-1) This was evident in the presence of subgrains formed close to the initial grain boundaries which gradually replaced the initial large grain structure with finer recrystallized grains The observations were linked to the simultaneous action of strain hardening and dynamic recovery which results in the redistribution of the dislocation and the formation of subgrain boundaries, which divide initial grain boundaries to subgrains On the contrary, small and equiaxed freshly recrystallized grains free of substructure were observed in the steel subjected to higher processing temperatures (1000 C) and higher strain rates (5 SÀ1 - 10 SÀ1) This is indicative of the activation of the discontinuous dynamic recrystallization (DDRX) which is not commonly associated with high stacking fault energy materials like ferritic alloys but can be a function of specific deformation conditions At these processing conditions the rate of strain hardening is very high and renders the dynamic recovery less effectively leading to accumulated dislocation densities and stored elastic energy which is the driving force for the formation of new recrystallized grains The nuclei usually appears near the original grain boundaries and is formed either by the accelerated rotation of a particular subgrain, coalescence of adjacent subgrains or local migration boundary into the interior of neighboring grain It was also noted that the grains recrystallized by DDRX had no preferred orientation (low texture intensity) which would reduce the tendency of roping in these steels The dynamic recrystallization behavior of a high strength low alloy steel during hot deformation was investigated by Wu et al [77] The aim of the study was to assess the role of strain, strain rate and temperature on the compressive deformation characteristics of the steel with a view to understanding optimum processing conditions Hot compression test was used in the study and performed within a temperature range of 950e1150 C under strain rates of 0.1, and SÀ1 up to a true strain of 0.9 using a Gleeble-500 thermosimulation machine The test specimens were heated to 1200 C at a rate of 10 C/s and held for min, then cooled to the deformation temperature within the range 950e1150 C at a rate of C/s and held for 30 s After the hot deformation, the test specimens were quenched immediately in tap water It was observed from the study that the dynamic recrystallization (DRX) occurs easily with the increase in the deformation temperature and the decrease in the strain rate This is because these processing conditions support the softening process by increasing the mobility of grain boundaries and providing longer time for the dislocation annihilation and the occurrence of DRX The study further established that work hardening dominated the initial stages of straining during the high temperature deformation However, as the deformation temperature is increased the softening rate equalled and surpassed work hardening DRX was summed up to occur at a critical level of stress 25 accumulation during the deformation and this corresponds to a critical strain value Layus et al [35] studied the recrystallization based formation of the uniform fine grained austenite structure in high strength steels for artic applications This study was necessitated by the need to develop low cost high strength steels with excellent low temperature properties for artic marine construction The test material was a cold resistant high strength F620 steel micro-alloyed with Nb and V to improve the aforementioned properties of the steel Dynamic recrystallization was observed to be hindered in the steels studied (Nb and V micro-alloyed steels) and this was a function of the micro-alloying constituents which restricted the threshold strains for the deformation during processing at temperatures between 950 and 1150 C The effect of the micro-alloying constituents on the dynamic recrystallization behavior of F620 high strength steel was observed to be sensitive to higher deformation temperatures and DRX ceased in both steels at 950 C The observations imply that a uniform fine grained austenite structure cannot be formed during high temperature processing of the modified F620 steels since the strain accommodation is hindered in the steels Consequently, the stress relaxation method was used to investigate the static recrystallization behavior of the steels using the Gleeble 3800 simulator The test specimens were subjected to five sequential strains with unregulated pauses and regulated pauses in the first and second treatment steps, respectively, and the pause duration was selected to give room for the complete primary static recrystallization Uniform fine grained recrystallized austenite was observed in specimens subjected to treatment with regulated pauses Thus, it is necessary to gradually increase the pause duration during the successive deformation within the process temperature for both steels to ensure complete static recrystallization The studies reviewed show that the recrystallization in high strength steels is basically influenced by factors, such as the amount of stored energy, the defect structure, the amount of strains, the annealing temperature and time Some defects, such as microtwins when present in the deformed structure can hinder the recrystallization at low temperatures while shear bands in the deformed structure contribute to more misorientation in the deformed structure, thus, facilitating the recrystallization Also, low stacking fault energies observed in some of these steels inhibit the dynamic recovery of dislocations, thereby contributing to high dislocation densities However, some deformation modes can readily activate the DDRX in high stacking fault energy materials, even when conventional thought supports the contrary That is, the deformation modes where the rate of strain hardening is very high can suppress the dynamic recovery resulting in an accumulation of dislocations with the corresponding increase in the stored energy which facilitates the recrystallization of new grains The increase in the deformation temperature and the decrease in the strain rate of high strength steels favors the dynamic recrystallization as both conditions help the softening process by increasing the mobility of grain boundaries and providing longer time for the dislocation annihilation to occur Lastly, the presence of some micro-alloying elements, such as V and Nb in high strength steels can hinder the formation of the dynamic recrystallization, as they restrain the strain accumulation, a critical amount of which is required for the dynamic recrystallization to occur 4.2 Recrystallization mechanisms in Ti based alloys Ti and Ti based alloys are currently of growing engineering interest attributed to their light weight and good engineering properties (such as good fatigue strength, good anticorrosion and biocompatibility, relatively low modulus and high specific strength 26 K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 to weight ratio) [78,79] Thus, these alloys are attractive for materials selection in biomedical, aerospace and automotive applications [80] TieAl based alloys are among the most amenable Ti based alloys for use in high temperature applications because of the excellent combination of low density, high strength, good creep and oxidation resistance they possess [22,81] Lately, TieAl based alloys are being alloyed with Nb to stabilize the beta phase and refine the microstructure, giving rise to a new TieAleNb (TNB) alloy The TieAleNb (TNB) alloys are now being considered as the substitute for the nickel based superalloys in high temperature applications [82] However, the poor plasticity at ambient temperature which is associated with the specific crystal structure of Ti and its alloys remains a major setback to the use of the TNB alloys [22,83] Grain refinements via thermomechanical treatment have been explored to reduce the deformation resistance of TNB alloys In view of this, several studies have been embarked on to understand the dynamic recrystallization behavior of TNB and other TieAl based alloys Li et al [84] investigated the effect of hot forging on the microstructure and the mechanical behavior of a high Nb content containing TieAl based alloy This study was centered on using pack forging for processing of the Ti e 45Al e 7Nb e 0.3W alloy Prealloyed powders of predetermined compositions were prepared using plasma rotating electrode processing The pre-alloyed powders were compacted into cylindrical billets and then quasiisothermal forging was carried out on the billets at a temperature of 1280 C and at the strain rate of 0.1 S-1 with a total strain of 80% It was observed that the recovery preceded the recrystallization followed by the rearrangement of dislocations to form a low energy configuration A mixture of fine dynamically recrystallized (DRX) grains, small refined lamellar colonies and other particles present along the grain boundaries were observed at the centre area of the TieAl pancake On the other hand, the incomplete DRX microstructure with coarse and lamellar colonies was observed in the microstructure at the edge of the pancake These observations were attributed to the temperature drop and the inhomogeneous plastic flow (strain variation) during hot forging across positions of the TieAl pancake, 1.9 at centre area and at the edge The microstructure showing the grain distribution of three sections of the TieAl pan cake in the hot forged Tie45Ale7Nb-0.3W alloy is presented in Fig Zhang et al [35] studied the deformation behavior of a high Nb content containing TieAl based alloy in the a ỵ g two phase region Studies have shown that the thermal deformation of the high Nb content containing TieAl based alloy (TNB) takes place in the a ỵ g two phase eld region The deformed structure in the TNB alloys is usually inhomogeneous containing the remnant lamellar structure which is detrimental to the mechanical properties of the alloy The test material (Tie44Ale8Nbe0.2We0.2Be0.1Y alloy) was produced with a Vacuum Arc Remelting furnace and subsequently hot isostatic pressed at 1300 C/130 MPa for h under argon atmosphere The thermo-physical simulation was carried out using the Gleeble 1500D at temperatures 1225 C and 1275 C to 70% total reduction at a strain rate of 0.05 S-1 A common tube-type heattreatment furnace was adopted to assess the high-temperature phase composition through water quenching It was observed that the as-cast and heat treated microstructures had near lamellar structure - consisting of g phase and a2 phase The deformed structure is observed to possess blended lamellar and fine recrystallized grains at the investigated temperatures (1225 and 1275 C) However, at higher temperatures the volume fraction of the a2 phase increased along with the coarsening of a2 laths On the other hand, g laths break down to form recrystallized grains at the deformation temperatures and not require high local strain for the dynamic recrystallization to occur This is because the stacking fault energy of the g phase in the alloy is lower than that of the a2 phase, hence, the dynamic recrystallization is favored in the g phase and the dynamic recovery favored in the a2 phase The results show that even at high deformation temperature, the TNB alloy would still contain remnant lamellar since the a2 laths not break into recrystallized grains after the deformation It was therefore proposed that reducing the deformation resistance by a multistep processing where the deformation proceeds from high to low temperatures can help produce a fine and homogeneous microstructure High deformation temperatures would form relatively fine microstructure, while grain boundary sliding promotes the homogeneity of microstructure; and further refinement could be achieved by processing at lower deformation temperatures Experimental study and numeric simulation of the dynamic recrystallization behavior of TieAl based alloy was investigated by Wan et al [83] This was achieved by subjecting a Ti - 47Al e2Nb e 2Cr alloy produced via powder metallurgy to thermomechanical simulations The compression test samples were deformed by the hot compression carried out in a Gleeble 1500D simulator at temperatures of 1223e1473 K (949.85e119.85 C) at a strain rate of 0.001 S-1 to 0.1 S-1 The samples were subjected to 55% reductions (3 ¼ 0.8), and immediately quenched in water to preserve the deformed microstructure The initial microstructure was composed of equiaxed strain free grains with large volume of high angle boundaries The alloys deformed at 1323K (1049.85 C)/0.05 S-1 were characterized with a mixture of coarse un-recrystallized grains and fine dynamic recrystallized grains at a strain of 0.3 The microstructure was also observed to have a necklace structure, typical for the dynamic recrystallization, and bulging grain boundaries which indicate that new grains nucleate at the grain boundaries This implies that the nucleation mechanism is by the discontinuous dynamic recrystallization (DDRX) The grain boundary bulging was attributed to the rapid strain hardening as a result of the increase in the dislocation density at the early stages of hot deformation At 0.8 strain and the same deforming temperature and strain rate (1323K (1049.85 C)/0.05 S-1), the deformed grains were completely replaced by the fine and equiaxed DRX grains, however, work hardened recrystallized grains were still present It was also observed that at higher deformation temperatures (1473 K) (1199.85 C), constant strain (0.8) and varying strain rates the microstructure of the alloy was characterized with larger grain size and heterogeneity The DRX grain size and volume fraction decrease with increase strain rate It was also noted that deformation twinning of the g-phase during the hot deformation created the nucleation sites for DDRX and promoted the occurrence of DRX grains for alloys deformed at 1473 K (1199.85 C)/0.001 S-1/0.8 The studies show that the increase in deformation strain and temperature favor the recrystallization in TieAl based alloys However, the temperature drop and the inhomogeneous plastic flow across the TieAl based alloy can influence the recrystallization kinetics Also the difference in stacking fault energies between the g and the a2 phase which constitutes the microstructure of the alloys can influence the recrystallization kinetics if deformed in the two-phase region The g phase which has a lower stacking fault energy than a2 phase, is favoured to undergo dynamic recrystallization while the a2 phase with relatively higher stacking fault energy, dynamic recovery 4.3 Recrystallization mechanisms in Mg based alloys Mg alloys are becoming the most preferred light weight alloy for several structural and commercial applications because of their low density, good castability, high specific strength and good damping properties [85,86] However, the major hindrance to the widespread utilization of Mg alloys for engineering is the limited plastic K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 27 Fig Microstructures of the as-forged Tie45Ale7Nbe0.3W alloy: (a) effective strain distributions along the radius direction simulated by DEFORM-3D software, (b) near the edge of the forged pancake, (c) at the midpoint of the radius, and (d) in the central area (Curled from Li et al [84] with permission from Elsevier) formability of these alloys at room temperature This is attributed to their HCP crystal structure and low stacking fault energy [85] Over the years, research efforts have been channeled into improving the formability of Mg alloys by grain refinement through alloying and thermomechanical processing Recrystallization processes have been established to play a key role in microstructural changes during thermomechanical processing (TMP) of Mg alloys Grain refinement and improvement in mechanical properties during TMP of Mg alloys are often attributed to dynamic recrystallization because of their low stacking fault energy Currently, studies are still ongoing to understand the recrystallization mechanisms of Mg alloys with a view to tailor the microstructure for improved engineering properties Ebrahimi et al [87] investigated the flow behavior and the microstructural evolution of an AZ91 alloy subjected to thermomechanical testing The test alloy was homogenized at 420 C for 24 h and water quenched Subsequently, compression test specimens were machined with a height to diameter ratio of 1.5 The hot compression test was carried out at temperatures ranging between 350 and 420 C at a strain rate of 0.1 S-1 under strains of 0.3 and 0.5 The deformed specimens were water quenched for less than s to preserve the deformed microstructure It was observed that all the test specimens had microstructures that showed a necklace grain structure of dynamically recrystallized grains around the initial grain boundaries However, these observations were subject to changing strains and temperatures The size of the recrystallized grain was observed to increase with the increasing temperature, while the volume fraction of the recrystallized grains decreased under the same temperature condition The increase in strain rate was also observed to correlate with the increase in the volume fraction of recrystallized grains The presence of unclear wavy boundaries and near-bulging boundaries which create new recrystallized grains along these boundaries indicates a discontinuous dynamic recrystallization as the primary mechanism of recrystallization This mechanism is also evident in the dependence of DRX on the strain intensity, since larger strains would result in increased grain boundary distortion (bulging) giving room for a larger fraction of new recrystallized grains Fig shows the necklace structure which is an evidence of the dynamic recrystallization in the AZ91 Mg alloy Xu et al [21] studied the deformation behavior and dynamic recrystallization of the AZ61 Mg alloy Dynamic recrystallization during hot deformation has been reported to play a key role in the improvement of the grain structure and mechanical properties of Mg alloys This study was therefore embarked on to study the effect of different strain rates and temperatures on the 28 K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 Fig Necklace structure obtained after hot deformation of AZ91 Mg alloy at 325 C at peak strain (Curled from Ebrahimi et al [87] with permission from Elsevier) microstructural behavior of AZ61 alloys The test material (AZ61) with cylindrical compression specimens was subjected to a test on a Gleeble-1500 thermo-mechanical simulator The test was conducted within a temperature range of 220 and 380 C at intervals of 40 C and strain rate of 0.001e1 sÀ1 All test specimens were quenched in water after thermomechanical testing The microstructural variability of the studied alloy at 380 C/ 0.01 sÀ1 under various strains was observed using optical microscopy It was reported that small amount of dynamic recrystallized (DRX) grains appear near the initial grain boundaries at 0.1 strain, but as the strain increases to 0.22, a mixture of fine DRX and coarse grains form a necklace around the initial grain boundaries At 0.5 strain the coarse grains were almost completely replaced with fine recrystallized grains Further increase in strain (0.9) eliminated all coarse grains previously present and resulted in the creation of wavy boundaries in the microstructure It was also established from the studies that high temperatures and low strain rates favored full evolution of the DRX homogenous structure in the alloy Stanford et al [88] studied the effect of rare earth (RE) elements on the hot deformation behavior of two Mg based alloys RE elements are known to improve the mechanical properties of Mg alloys by causing changes in the texture and enhancing slip in this alloy system Despite the recorded success of incorporating RE into Mg alloy systems, there have been little reported on the effect of RE elements on the hot deformation characteristics of Mg alloys The study was carried out using two Mg alloys (AZ31 and Mg-1.5Gd) with the similar static recrystallization kinetics Test samples from the alloys were machined and the test was carried out at different temperatures and strain rates in the plane strain compression condition using a Gleeble-3500 thermo-mechanical simulator Microstructures of test samples from the two alloys subjected to the same testing conditions (400 C and 0.001 S-1, 0.1 S-1, 10 SÀ1) were observed to have fractions of hot deformed grains surrounded by necklace structures associated with dynamic recrystallization The only exception was the MgeGd sample subjected to the lowest strain rate which had a large fraction of dynamically recrystallized grains with well-defined sub-boundaries However, at a lower deformation temperature (300 C) and same strain rate of 0.1 S-1, there were no recrystallized grains in the MgeGd alloy while the AZ31 alloy showed a necklace of DRX structure at grain boundaries Extremly fine DRX grains were observed in the MgeGd alloy after a deformation at 400 C and 10 SÀ1 strain rate, indicating that the dynamic recrystallization commences at higher temperatures in this alloy Also, substructures formed in the alloys during hot deformation were used to quantify the stored energy for deformation in the alloys It was established that at high strain rates MgeGd had higher stored energy while AZ31 alloy had higher stored energy at lower strain rates This indicates that the dynamic recrystallization is enhanced in Mg alloys with RE additions when subjected to high strain rates Biswas et al [89] studied the property enhancement attainable for pure Mg subjected to room temperature equal channel angular extrusion (ECAE) The pure Mg was hot rolled to a thickness of mm, then processed with an ECAE die of 90 inter-channel angle The processing was done at a speed of mm SÀ1, and at a temperature of 250 C for the first passes The processing temperature was, however, reduced for subsequent passes (200 C for the 5th pass, 150 C for the 6th pass, 100 C for the 7th pass and 25 C for the 8th pass) It was observed that the microstructure of the Mg processed at 250 C had equiaxed grains with serrated grain boundaries depicting the occurrence of dynamic recrystallization This observation was associated with the migration of low angle boundaries into high angle boundaries in the prismatic and pyramidal planes consistent with the continuous dynamic recrystallization (CDRX) However, the new grains on the basal plane were associated with the nucleation on prior deformed grains which indicates the transformation from CDRX to the discontinuous dynamic recrystallization (DDRX) in this plane At lower processing temperatures (less than 250 C), a mixture of equiaxed and elongated grains were observed in the microstructure indicating a partial dynamic recrystallization This is attributed to the occurrence of the recovery alongside the recrystallization during deformation at these temperatures Recovery associated with strain softening was mostly observed in the prismatic and pyramidal planes as the processing temperature reduced The fraction of recrystallized grains and the recovery reduced with the decreasing processing temperatures in the basal plane The studies show that Mg alloys though possessing HCP structure and limited slip systems, can be grain refined because of its low stacking fault energy and capacity to undergo dynamic recrystallization However, the dynamic recrystallization mechanism could depend on the plane of deformation e deformation along the basal plane would likely yield DDRX compared to when deformation is along the prismatic and pyramidal planes where CDRX is a greater likelihood The size of the recrystallized grains generally increases with the increasing temperature, while the volume fraction of recrystallized grains increase with the strain rate Also, RE additions depending on particular strain rates, can affect the temperatures at which the dynamic recrystallization occurs in Mg alloys 4.4 Recrystallization mechanisms in high entropy alloys High entropy alloys (HEAs) are metallic systems which have more than one principal element in the alloy mixture giving them more significant entropies of mixing resulting in superior engineering properties compared to conventional alloys [90] These alloys solidify as simple solid solutions with single phases despite the presence of multiple elements attributed to the overwhelming effect of entropies of mixing of the principal elements to the enthalpy of the compound formation [23,91] These properties have made high entropy alloys ((HEAs) of great interest to material scientists for use in advance coatings, solder and brazing fillers, electronics and other specialized high and low temperature applications [92] Currently, studies are ongoing to understand the mechanical behavior of the HEAs and related phase transformation phenomena in these alloys with a view to enhance its applicability in service K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 Sathiaraj et al [93] studied the effect of heavy cryorolling on the evolution of the microstructure and texture during annealing of equiatomic CoCrFeMnNi high entropy alloy The high entropy equiatomic as-cast alloy was homogenized at 1100 C for h to enhance the chemical homogeneity Samples from the homogenized alloy were cold rolled to a 50% reduction to get a wrought microstructure and subsequently full annealed at 800 C for h in a salt bath furnace After that they were subjected to both cold and cryorolling to a total of 90% reduction in thickness in about 10e11 passes The cold-rolled and cryorolled samples were isochronally annealed for h in the temperature range between 700 and 1200 C Fully recrystallized state was observed in cold-rolled and cryorolled annealed samples at 700 C and discernible grain growth was observed in both samples at higher annealing temperatures (1000 and 1200 C) It was also observed that the cryorolled samples had a lower average grain size (1.3 mm) compared to the cold-rolled samples (1.6 mm) after annealing at 700 C; and the absolute difference in the average grain size of both samples increased with the increase in the annealing temperature The finer microstructure of the cryorolled sample is attributed to the retention of the high dislocation density and nano-twins formation during cryorolling of the high entropy alloy This is because the significantly fragmented structure and the twin boundaries associated with the nano-twins formation in the cryorolled sample act as potential nucleation sites for recrystallization in the alloy Sluggish diffusion was also reported to be responsible for minor changes in the microstructure of the cold rolled and cryorolled alloy samples at lower annealing temperatures Discontinuous recrystallization was concluded to be the primary mechanism for the recrystallization in the cryorolled high entropy alloy after annealing since the new fine recrystallized microstructure was formed by the nucleation and growth Tsai et al [94] studied the deformation and annealing behavior of a ductile Al0.5CoCrCuFeNi HEA subjected to hot forging and cold rolling They observed that the deformed (50% cold rolled) Al0.5CoCrCuFeNi was softened after annealing at 900 C for five (5) hours and this was attributed to the recovery and the recrystallization However, the recrystallization time in the HEA was longer than in traditional alloys and the recrystallization temperatures exceeded estimates of empirical formula used for traditional alloys, indicative of the high recrystallization resistance of the Al0.5CoCrCuFeNi HEA The resistance of the HEA studied to the recrystallization was attributed to the low twin boundary energy which reduces the driving force of the recrystallization, and sluggish diffusion which makes the grain boundary migration slow and the movement of dislocation difficult Bhattacharjee et al [95] investigated the effect of annealing on the microstructure and texture evolution of severely deformed CoCrFeMnNi HEA in the temperature range of 650e1000 C The test alloy after production was subjected to the homogenization treatment at 1100 C for h The homogenized samples were cold rolled to 50% reduction in thickness and subsequently annealed The annealed samples were afterwards cold rolled to 90% reduction in thickness at room temperature It was observed from the study that the test material subjected to 90% cold rolling had averagely recrystallized grains when annealed at 650 C, and the degree of recrystallization increased with the increasing annealing temperature Discontinuous recrystallization was observed for the HEAs studied, and the microstructures were completely recrystallized at higher annealing temperatures and had shown strong resistance to the grain growth which is in agreement with observations from other low SFE materials [96] The observations made are attributed to the high lattice distortion energy inherent in the whole solute matrix of HEAs which is a result of the individual strain energy possessed by every atom 29 in the matrix due to the atomic size differences This severe lattice distortion energy reduces the driving force for the nucleation and growth of new grains in the deformed matrix The sluggish diffusion of atoms as a result of the whole solute matrix also reduces the grain boundary migration rate since the effective migration of boundaries depends on the effective diffusion of atom in the matrix and the effective jumping of boundaries [94] The whole solute matrix also results in a low stacking fault energy (SFE) of HEAs which promotes the deformation of twins during cold working and increases the nucleation sites for new grains during annealing High temperature deformation behavior and dynamic recrystallization of CoCrFeMnNi HEA were similarly studied by Stepanov et al [97] The test material was subjected to an uniaxial compression test to 75% height reduction (z 1.4 true strain) in the temperature interval 600e1100 C In the study the discontinuous dynamic recrystallization (dDRX) was observed to be associated with the microstructural evolution in the CoCrFeMnNi HEA for all deformation temperatures and was noted to agree well with the low SFE of the alloy At temperatures above 800 C dDRX was linked to intensive bulging of initial grain boundaries and the nucleation of new grains along the initial grain boundaries which gradually consume the old deformed grains The dDRX at temperatures below 800 C was associated with the shear band formation and the intensity of shear deformation decreased along with volume fraction of material undergoing the shear straining as the deformation temperature decreased Guo et al [98] studied the hot deformation characteristics of a refractory HEA (MoNbHfZrTi) using isothermal compression tests with varying strain rates in the temperature range of 800e1200 C MoNbHfZrTi HEA have low density, low cost and structural ability at high temperatures, which are the major attractions for materials suitable for high temperature applications A study of this nature is, hence, essential for understanding the deformation behavior of the refractory HEA at high temperatures It was observed from the study that the microstructural evolution in the MoNbHfZrTi was dependent on both the strain rate and the deformation temperatures Low strain rates and high deformation temperatures were observed to favor the dynamic recrystallization of the grains in the alloy This is because these conditions promote the decrease in the critical dislocation density and consequently the critical strain for DRX in the alloy Also low strain rates and high deformation temperatures can provide time and energy for the grain boundary migration, which aids the occurrence of DRX The DRX which occurred during the microstructure evolution of MoNbHfZrTi HEA after the hot deformation was observed to be discontinuous (DDRX) and continuous (CDRX) At 800 C, extensive bulging grain boundaries with high angles which are closely related to strain induced grain boundary orientation was observed, indicative of the DDRX nucleation mechanism Also, numerous subgrain boundaries with low angle ones, were observed at the same temperature (800 C) as typical features of CDRX However, the mechanism of CDRX reduced with the increasing deformation temperatures (between 100 and 1200 C) and the decreasing strain rates and this was evident in the accelerated transformation of low angle grain boundaries to high angle ones It can be summed up from the works on HEAs that low strain rates and high deformation temperatures favor the dynamic recrystallization However, the recrystallization kinetics in HEAs is generally slower than in the traditional alloys This is noted to be largely due to either the low twin boundary energy observed in the deformed HEAs, which reduces the driving force for the recrystallization or/and the sluggish diffusion of the whole solute matrix of HEAs, which generally makes the grain boundary migration slow and the movement of dislocations difficult 30 K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 4.5 Recrystallization mechanisms in shape memory alloys Shape memory alloys (SMAs) are metallic materials which have the ability to recover their dimensional integrity after being deformed to certain strain levels when subjected to temperatures [99,100] These alloys have two important characteristics which qualify their suitability for both engineering and commercial applications, namely the shape memory effect (temperature sensitivity) and the pseudoelasticity (stress sensitivity) [101] Several alloys have displayed the key characteristics aforementioned in addition to inherent engineering properties, but NiTi, Cu based and Fe based alloys have been the key alloys of interest in these fields due to their approachable levels of strain recoveries [102,103] These alloys are presently used in fire safety alarms, pipe coupling, biomedical (stents and surgical instruments) and other domestic applications [100] Recently, a lot of research has been focused on achieving nanostructured SMAs to meet certain requirements for advanced applications Therefore, studies focussing on the effect of thermomechanical processing on the microstructure and properties of SMAs are of significant importance to the present day material scientists Jiang et al [103] investigated the dynamic recovery and dynamic recrystallization of NiTi SMA subjected to hot compression deformation A NiTi bar of the study material was solution treated at 850 C for h and then quenched in ice Samples were then cut for the hot compressive tests at different working temperatures (600e1000 C) and strain rates (0.001 S-1 and SÀ1) It was observed that the samples deformed at 600 C was characterized with a combination of dynamic recovery and dynamic recrystallization, the dynamic recovery was, however, dominantly evident from the presence of high fractions of elongated grains At 700 C working temperature, almost complete dynamic recrystallization was observed in the microstructure of the NiTi samples at low strain rates (0.001 S-1 and 0.01 S-1) while dynamic recovery was prevalent at higher strain rates (0 SÀ1 and SÀ1) Above 700 C, the microstructures of the NiTi samples were characterized with the complete dynamic recrystallization The authors have conlcuded that the low strain rates and high working temperatures, both favor the recrystallization because these conditions provide time for the accumulation of the energy and facilitate the higher interface migration for the nucleation and growth of new grains and thus, for the dislocation annihilation Low strain rates and higher working temperatures also favor the formation of fine equiaxed grains in hot deformed NiTi SMA Zhang et al [24] reported on the simulation of the dynamic recrystallization in NiTi SMA subjected to hot compression A NiTi bar was heated to 850 C and held for h, before being quenched into ice water The NiTi samples were then cut from the solutiontreated NiTi bar for the compression tests The compression experiments were carried out at strain rates ranging from 0.001 to s-1 and temperatures ranging from 800 to 1000 oC The samples were compressed to a total deformation degree of 70% at the true strain of 1.2, while one NiTi sample was compressed to a deformation degree of 40%, where the true strain was 0.5 All the samples were quenched into ice water immediately after the compression to retain the deformed microstructure A cellular automation model was used to simulate and predict the microstructural evolution, the dislocation density evolution, the flow stress and the grain size during the DRX of the NiTi alloy It was deduced from the study that dislocation density propels nucleation of new recrystallized grains at pre-existing grain boundaries in the initial microstructure The mean dislocation density was observed to be dependent on the strain rate and the deformation temperature, as it decreases at high deformation temperatures and low strain rates These processing conditions (high deformation temperatures and low strain rates) also have an influence on the mean grain size during the dynamic recrystallization The mean grain size increases with the increase in the deformation temperature at a given strain rate, while it decreases with the increase in the strain rate at a given temperature Basu et al [104] studied the effect of the dynamic recrystallization in the austenite e martensite phase transformation in Ni eTi e Fe shape memory alloys subjected to hot working The studied alloy was homogenized at 1000 C for 12 h and then furnace cooled Hot compression tests were subsequently conducted on the alloy samples which were deformed to approximately 50% reductions at temperatures 750, 850 and 950 C; and strain rates of 10 and 100 SÀ1 The deformed samples were quenched immediately after the test It was observed that the strain localization was dominant in the alloys deformed at lower temperatures, while serrations of grain boundaries and relatively fine, nearly equiaxed grains were observed in alloys deformed at higher temperatures The nearly equiaxed grains were present surrounded by the high angle grain boundaries with large orientation spread and also grain misorientations compared to the other recrystallized grains It was also observed that the size and fraction of dynamic recrystallized grains increased with the increase in the strain rate and working temperature This was evident from the decrease in dislocation densities in the alloy as working temperature increased The dynamic recrystallization was, however noted to suppress the austenite to the martensite phase transformation in NieTieFe SMAs Yin et al [105] studied the mechanism of the continuous dynamic recrystallization in a 50Tie47Nie3Fe SMA during hot compressive deformation Samples were cut from a hot forged TiNiFe rod for the hot compression tests The samples were processed to 50% overall height reductions at different temperatures between 750 and 1050 C and strain rates between 0.01 S-1e10 SÀ1 using a Gleeble 3500 thermo mechanical simulator It was observed that the recrystallized grain region is located between the deformed grain boundaries of deformed grains surrounded with low angle grain boundaries created from the compression at low working temperatures and high strain rates The point to the original misorientation in the deformed metals was over 15 and the typical boundary rotating angle values corresponded to the high angle grain boundaries Point to point misorientations indicative of low angle grain boundaries were also observed around the vicinity of the grain boundary These observations were the delineates of the gradual transition of low angle grain boundaries to high angle grain boundaries during deformation of the samples indicating the continuous dynamic recrystallization mechanism in the SMAs studied It was concluded from the study that the DRX process benefits from the decrease in the strain rate and higher temperatures as these conditions allow greater time for the movement of the boundaries and dislocations Zhang et al [106] studied the effect of local canning compression on the dynamic recrystallization behavior of the NiTi SMA The study was aimed at investigating the effect of three dimensional compression stresses from local canning on the dynamic recrystallization of NiTi SMA A NiTi SMA bar was used as the starting material and test samples were obtained by electro-discharge machining from the bar The samples were locally canned using low carbon steel cans of known dimensions The cans were subsequently subjected to hot compression testing at a fixed strain rate of 0.05 S-1 and varying temperatures of 600, 700 and 800 C The canned NiTi samples were subjected to a total of 75% reduction in height, and thereafter quenched in water at room temperature The authors reported the presence of low angle grain boundaries and changes in texture in the compressed NiTi samples It was observed that the fraction of recrystallized grains, sub boundaries and deformed structure varied with different treatment temperatures Dynamic recovery and dynamic recrystallization were the dominant softening mechanisms during local canning at lower working K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 temperatures (600 and 700 C), while dynamic recrystallization was the principal mechanism at 800 C Two recrystallization mechanisms were reported for local canning of NiTi SMA at 600 and 700 C, namely discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) DDRX was evident from the nucleation of recrystallized grains at regions (grain interiors and grain boundaries) with local high dislocation density The pile up of these dislocations known as statistically stored dislocations (SSDs) acts as a driving force for the DDRX during local canning of NiTi SMA samples These SSDs can subsequently be transformed into geometrically necessary dislocations (GNDs) which constitute subgrain boundaries The subgrain boundaries progressively transform into high angle boundaries by absorbing GNDs to form new recrystallized grains through the CDRX mechanism Generally it is noted from the above highlighted works that the recrystallization mechanisms in hot compression processed NieTi based SMAs are dependent on the strain rate and the hot deformation temperature Low strain rate and high deformation temperatures favor the dynamic recrystallization and hence the formation of well-defined equiaxed grains This is due to the greater time for movement of boundaries and dislocations High strain rates and relatively lower working temperatures preferably favor the dynamic recovery Also, there was no significant difference in the recrystallization behavior of NiTi based SMAs to that in conventional metallic materials It is noteworthy to state that most recent publications on recrystallization behavior of SMAs are limited to NiTi systems Observations for Cue and Fe-based SMAs would be enlightening for a comprehensive position on recrystallization behavior of SMAs to be drawn Conclusion A summary of fundamental recrystallization mechanism concepts and their priceless utility in microstructure control for the property optimization in emerging metallic materials such as high strength steels, Ti based alloys, Mg based alloys, high entropy alloys, and shape memory alloys was highlightedly dicussed in this review The traditional concepts of recrystallization were found to be still applicable in explaining the recrystallization behavior in these materials Some exceptions were however noted, where deviations from the conventional recrystallization patterns, due to the exclusive structural constitution of the materials, were observed Basically, the peculiarity of both structural and deformation variables were established to govern the recrystallization mechanisms and kinetics in these emerging metallic materials Acknowledgements The lead author wishes to acknowledge the immense contribution to recrystallization studies of his Masters' and PhD mentor, Prof Celestine Munde Kamma of blessed memory who passed on October 2007 His tenth year remembrance anniversary in 2017 inspired the writing of this review article References [1] D.A Porter, K.E Easterling, M.Y Sherif, Phase Transformation in Metals and Alloys, third ed., CRC Press (Taylor and Francis Group), Unites States, 2009 [2] P.R Rios, F Siciliano, H.R.Z Sandim, R.L Plaut, A.F Padilh, Nucleation and growth during recrystallization, Mater Res (3) (2005) 225e238 [3] T Sakai, A Belyakov, R Kaibyshev, H Miura, J.J Jonas, Dynamic and postdynamic recrystallization under hot, cold and severe plastic deformation conditions, Prog Mater Sci (2013) https://doi.org/10.1016/j.pmatsci.2013.09.002 [4] D Fabregue, B Mouawad, C.R Hutchinson, Enhanced recovery and recrystallization of metals due to an applied current, Scripta Mater 92 (2014) 3e6 31 [5] M Al-Hussein, G Strobl, On the mechanisms of recrystallization after melting in semicrystalline polymers: the effect of the initial melt state, J Macromol Sci Part B: Phys 42 (3e4) (2003) 77e685 [6] S.G Oleinik, N.V Danilenko, Primary recrystallization mechanisms in ceramic materials, Powder Metall Met Ceram 37 (1e2) (1998) 56e66 [7] J.E Burke, D Turnbull, Recrystallization and grain growth, Prog Met Phys (1952) 220e292 [8] R.W Cahn, Recrystallization of single crystals after plastic bending, J Inst Met 76 (2) (1949) 121e143 [9] R.W Cahn, A new theory of recrystallization nuclei, Proc Phys Soc 63 (364) (1950) 323e336 [10] A.H Cottrell, in: B Chalmers (Ed.), Theory of Dislocations Progress in Metal Physics, vol 4, Pergamon Press, London, 1953, pp 251e255 [11] R.D Doherty, D.A Hughes, F.J Humphreys, J.J Jonas, D Juul Jensen, M.E Kassner, W.E King, T.R McNelley, H.J McQueen, A.D Rollett, Current issues in recrystallization: a review, Mater Sci Eng A238 (1997) 219e274 [12] C.M Kamma, E Hornbogen, Recrystallization mechanism in carbon steels, Can Metall Q 23 (2) (1984) 249e257 [13] R.D Doherty, Recrystallization and texture, Prog Mater Sci 42 (1997) 39e58 [14] F.J Humphreys, Nucleation in recrystallization, Mater Sci Forum 467e470 (2004) 107e116 [15] K.K Alaneme, C.M Kamma, Phase transformation studies of a low alloy steel in the (a ỵ g) phase region, Mater Res 13 (1) (2010) 113e117 [16] K.K Alaneme, Influence of tempered microstructures on the transformation behaviour of cold deformed and intercritically annealed medium carbon low alloy steel, Mater Res 13 (2) (2010) 203e209 [17] E Hornbogen, Inhibition of recrystallization in supersaturated solid solutions by large amounts of cold work, J Mater Sci 12 (1977) 1565e1572 €ster, in: F Haessner (Ed.), Recrystallization of Two-phase [18] E Hornbogen, U Ko Alloys Recrystalization of Metallic Materials, Dr Riederer Verlag, Stuttgart, 1978, pp 159e194 [19] E Hornbogen, Combined reactions, Metall Trans A 10A (8) (1979) 947e972 [20] C.M Kamma, K.K., Alaneme design of high strength microstructures in carbon steel by thermomechanical treatment, in: Proceedings of the Annual Conference of Materials Science and Technology (MS & T 05’), USA, 2005, pp 139e149 [21] Y Xu, L Hu, Y Sun, Deformation behaviour and dynamic recrystallization of AZ61 magnesium alloy, J.Alloys Compds 580 (2013) 262e269 [22] H Liu, R Rong, F Gao, Z Li, Y Liu, Q Wang, Hot deformation behavior and microstructural evolution characteristics of Ti-44Al-5V-1Cr alloy containing (g ỵ a2 ỵ B2) phases, Metals (2016) 305, https://doi.org/10.3390/ met6120305, 1-10 [23] J Hou, M Zhang, H Yang, J Qiao, Deformation behavior of Al0.25CoCrFeNi high-entropy alloy after recrystallization, Metals (2017) 111, https:// doi.org/10.3390/met7040111, 1-11 [24] Y Zhang, S Jiang, Y Liang, L Hu, Simulation of dynamic recrystallization of NiTi shape memory alloy during hot compression deformation based on cellular automaton, Comput Mater Sci 71 (2013) 124e134 [25] Y Lu, R Ma, Y Wang, Texture evolution and recrystallization behaviors of CuÀAg alloys subjected to cryogenic rolling, Trans Nonferrous Metals Soc China 25 (2015) 2948e2957 [26] K Huang, R.E Loge, A Review on Dynamic Recrystallization, Phenomena in Metallic Materials, 2016, https://doi.org/10.1016/j.matdes.2016.09.012 [27] P Liang, K Lin, Non-deformation recrystallization of metal with electric current stressing, J Alloy Comp 722 (2017) 690e697 [28] J.W Martin, R D Doherty, B Cantor, Stability of Microstructure in Metallic Systems, second ed., Cambridge University Press, UK, Cambridge, 1997 [29] N Hansen, New discoveries in deformed metals, metal, Mater Trans 32A (12) (2001) 2917e2919 [30] C.H.J Davies, W.Q Cao, C.F Gu, R.Y Lapovok, E.V Pereloma, Texture and boundary characteristics of severely deformed and recrystallized copper, Mater Sci Forum 558e559 (2007) 177e182 [31] T Konkova, S Mironov, A Korznikov, G Korznikova, M.M Myshlyaev, S.L Semiatin, Annealing behavior of cryogenically-rolled Cu-30Zn brass, J Alloy Comp (2015), https://doi.org/10.1016/j.jallcom.2015.05.287 [32] W Oliferuk, M Maj, K Zembrzycki, Distribution of energy storage rate in area of strain localization during tension of austenitic steel, IOP Conf Ser Mater Sci Eng 71 (2015) 012055, https://doi.org/10.1088/1757-899X/71/1/012055 [33] Y.C Lin, X Chen, A critical review of experimental results and constitutive descriptions for metals and alloys in hot working, Mater Des 32 (2011) 1733e1759 [34] Z Zhang, D Chen, H Zhao, S Liu, A comparative study of clock rolling and unidirectional rolling on deformation/recrystallization microstructure and texture of high purity tantalum plates, Int J Refract Metals Hard Mater 41 (2013) 453e460 [35] S.Z Zhang, C.J Zhang, Z.X Du, Z.P Hou, P Lin, F.T Kong, Y.Y Chen, Deformation behavior of high Nb containing TiAl based alloy in a ỵ g two phase eld region, Mater Des 90 (2016) 225e229 [36] W He, X Chen, N Liu, B Luan, G Yuan, Q Liu, Cryo-rolling enhanced inhomogeneous deformation and recrystallization grain growth of a zirconium alloy, J Alloy Comp 699 (2017) 160e169 _ [37] D Grygier, M Rutkowska-Gorczyca, A Zak, The effectiveness of recrystallization of pearlitic steels in the regards of the change the annealing time, Int J New Techn Res (IJNTR) (3) (2016) 15e19 32 K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 [38] V.C Moreira, A.P Tschiptschin, A dilatometric study of the influence of residual iron content on the annealing behavior of cartridge brass, Mater Res 19 (2) (2016) 483e489 [39] M Jiang, B Devincre, G Monnet, Effects of the grain size and shape on the flow stress: a dislocation dynamics study, Int J Plast 113 (2019) 111e124 [40] K Hajizadeh, S Ghobadi Alamdari, B Eghbali, Stored energy and recrystallization kinetics of ultrafine grained titanium processed by severe plastic deformation, Physica B 417 (2013) 33e38 [41] M.J Jones, F.J Humphreys, Interaction of recrystallization and precipitation: the effect of Al3Sc on the recrystallization behaviour of deformed aluminium, Acta Mater 51 (2003) 2149e2159 [42] P Matusiewicz, W Ratuszek, A Zielinska-Lipiec, Recrystallization of ferrite in spheroidite of Fe-0.67%C steel, Arch Metall Mater 56 (1) (2011) 63e69 [43] D Raabe, Recovery and recrystallization: phenomena, physics, models, simulation, in: D.E Laughlin, K Hono (Eds.), Physical Metallurgy, 2014, pp 2291e2397 ka, L Eí.ek, ~ ski, [44] I Schindler, M Janosec, E Místecký, M Rù.ie L.A Dobrzan S Rusz, P Such anek, Effect of cold rolling and annealing on mechanical properties of HSLA steel, Arch Mater Sci Eng 36 (1) (2009) 41e47 [45] F.J Humphreys, M Hatherly, Recrystallization and Related Annealing Phenomena, second ed., Elsevier Ltd, 2004 https://doi.org/10/1016/B978-0-08044164-1.X5000-2 [46] T Yu, N Hansen, X Huang, Recovery by triple junction motion in heavily deformed metals, IOP Conf Ser Mater Sci Eng 89 (2015) 012014, https:// doi.org/10.1088/1757-899X/89/1/012014 [47] S.S Gorelik, Recrystallization in Metals and Alloys, second ed., Mir Publishers, Moscow, 1981, p 479 [48] B Verlinden, J Driver, I Samadjar, R.D Doherty, Softening mechanisms, in: Thermo-mechanical Processing of Metallic Materials, vol 11, 2007, pp 86e108 [49] E Nes, Recovery revisited, Acta Metall Mater 43 (6) (1995) 2189e2207 [50] P Haasen, Physical Metallurgy, third ed., 1997 Cambridge, Great Britain [51] K.K Alaneme, Recrystallization Studies of a Low Alloy Steel in the (aỵg) Phase Region, M Eng Thesis, Federal University of Technology, Akure, 2002, pp 1e96 [52] H Hallberg, Approaches to modeling of recrystallization, Metals (2011) 16e48 [53] H Jazaeri, F.J Humphreys, The transition from discontinuous to continuous recrystallization in some aluminium alloys II e annealing behaviour, Acta Mater 52 (2004) 3251e3262 [54] S Gourdet, F Montheillet, A model of continuous dynamic recrystallization, Acta Mater 51 (2003) 2685e2699 [55] H.E Hu, L Zhen, B.Y Zhang, L Yang, J.Z Chen, Microstructure characterization of 7050 aluminum alloy during dynamic recrystallization and dynamic recovery, Mater Char 59 (2008) 1185e1189 [56] K Edalati, J.M Cubero-Sesin, A Alhamidi, I.F Mohamed, Z Horita, Influence of severe plastic deformation at cryogenic temperature on grain refinement and softening of pure metal s: investigation using high-pressure torsion, Mater Sci Eng A 613 (2014) 103e110 , The surprising influence of continuous [57] K Huang, C Cayron, R.E Loge alternating electric current on recrystallization behaviour of a cold-rolled Aluminium alloy, Mater Char (2017), https://doi.org/10.1016/ j.matchar.2017.04.036 [58] Y.Z Zhou, S.H Xiao, J.D Guo, Recrystallized microstructure in cold worked brass produced by electropulsing treatment, Mater Lett 58 (12e13) (2004) 1948e1951 [59] S Huang, D Shu, C Hu, S Zhu, Effect of strain rate and deformation temperature on strain hardening and softening behavior of pure copper, Trans Non Met Soc China 26 (2016) 1044e1054 [60] C Shi, J Lai, X Chen, Microstructural evolution and dynamic softening mechanisms of Al-Zn-Mg-Cu alloy during hot compressive deformation, Materials (2014) 244e264, https://doi.org/10.3390/ma7010244 [61] D.G Cram, X.Y Fang, H.S Zuro, Y.J.M Brechet, C.R Hutchinson, The effect of solute on discontinuous dynamic recrystallization, Acta Mater 60 (2012) 6390e6404 [62] M.E Kassner, S.R Barrabes, New developments in geometric dynamic recrystallization, Mater Sci Eng A 410e411 (2005) 152e155 [63] D Ponge, G Gottstein, Necklace formation during dynamic recrystallization: mechanisms and impact on flow behavior, Acta Mater 46 (1) (1998) 69e80 [64] A Momeni, G.R Ebrahimi, M Jahazi, P Bocher, Microstructure evolution at the onset of discontinuous dynamic recrystallization: a physics-based model of subgrain critical size, J Alloy Comp 587 (2014) 199e210 [65] H.J McQueen, C.A.C Imbert, Dynamic recrystallization: plasticity enhancing structural development, J Alloy Comp 378 (2004) 35e43 [66] Y Wang, T Jiao, E Ma, Dynamic processes for nanostructure development in Cu after severe cryogenic rolling deformation, Mater Trans 44 10 (2003) 1926e1934 [67] J Das, Evolution of nanostructure in a-brass upon cryorolling, Mater Sci Eng A 530 (2011) 675e679 [68] H Kim, C Kang, M Huh, Olaf Engler, Effect of primary recrystallization texture on abnormal grain growth in an aluminum alloy, Scripta Mater 57 (2007) 325e327 [69] P.R., G Rios, L.S Gottstein, Shvindlerman, An irreversible thermodynamic approach to normal grain growth with a pinning force, Mater Sci Eng 332 (1 e 2) (2002) 231e235 [70] S Shanmugam, N.K Ramisetti, R.D.K Misra, J Hartmann, S.G Jansto, Microstructure and high strengthetoughness combination of a new 700MPa Nb-microalloyed pipeline steel, Mater Sci Eng A 478 (2008) 26e37 [71] G Wu, C Zhou, X Liu, Dynamic recrystallization behavior and kinetics of high strength steel, J Cent South Univ 23 (2016) 1007e1014 [72] R Kuziak, R Kawalla, S Waengler, Advanced high strength steels for automotive industry, Arch Civil Mech Eng (2) (2008) 104e117 [73] J Yang, Q Liu, D Sun, X Li, Recrystallization behavior of deformed austenite in high strength microalloyed pipeline steel, J Iron Steel Res Int 16 (1) (2009) 75e80 [74] L Bracke, K Verbeken, L Kestens, J Penning, Microstructure and texture evolution during cold rolling and annealing of a high Mn TWIP steel, Acta Mater 57 (2009) 1512e1524 [75] R Saha, R Ueji, N Tsuji, Fully recrystallized nanostructure fabricated without severe plastic deformation in high-Mn austenitic steel, Scripta Mater 68 (2013) 813e816 [76] C Castan, F Montheillet, A Perlade, Dynamic recrystallization mechanisms of an Fee8% Al low densitysteel under hot rolling conditions, Scripta Mater 68 (2013) 360e364 [77] G Wu, C Zhou, X Liu, Dynamic recrystallization behavior and kinetics of high strength steel, J Cent South Univ 23 (2016) 1007e1014 [78] K Niespodziana, K Jurczyk, M Jurczyk, The synthesis of titanium alloys for Biomedical applications, Rev Adv Mater Sci 18 (2008) 236e240 [79] J Oak, A Inoue, Formation, mechanical properties and corrosion resistance of TiePd base glassy alloys, J Non-Cryst Solids 354 (2008) 1828e1832 [80] Y Wu, H Kou, Z Wu, B Tang, J Li, Dynamic recrystallization and texture evolution of Ti-22Al-25Nb alloy during plane-strain compression, J Alloy Comp 749 (2018) 844e852 [81] H Matsumoto, V Velay, Mesoscale modeling of dynamic recrystallization behavior, grain size evolution, dislocation density, processing map characteristic, and room temperature strength of Ti-6Al-4V alloy forged in the (aỵb) region, J Alloy Comp (2017), https://doi.org/10.1016/ j.jallcom.2017.02.285 [82] J Li, Y Liu, Y Wang, B Liu, Y He, Dynamic recrystallization behavior of an ascast TiAl alloy during hot compression, Mater Char 97 (2014a) 169e177 [83] Z Wan, Y Sun, L Hu, H Yu, Experimental study and numerical simulation of dynamic recrystallization behavior of TiAl-based alloy, Mater Des 122 (2017) 11e20 [84] J Li, Y Liu, B Liu, Y Wang, X Liang, Y He, Microstructure characterization and mechanical behaviors of a hot forged high Nb containing PM-TiAl alloy, Mater Char 95 (2014b) 148e156 [85] J.D Robson, Critical assessment 9: wrought magnesium alloys, Mater Sci Technol 31 (3) (2015) 257e264 [86] M.A Kumar, I.J Beyerlein, C.N Tome, A measure of plastic anisotropy for hexagonal close packed metals: application to alloying effects on the formability of Mg, J.Alloys Comp 695 (2016a) 1488e1497 [87] G.R Ebrahimi, A.R Maldar, H Monajati, M Haghshenas, Hot deformation behavior of AZ91 magnesium alloy in temperature ranging from 350 C to 425 C, Trans Nonferrous Metals Soc China 22 (2012) 2066e2071 [88] N Stanford, M.D Callaghan, B deJong, The effect of rare earth elements on the behaviour of magnesium-based alloys: Part1dhot deformation behaviour, Mater Sci Eng A 565 (2013) 459e468 [89] S Biswas, S.S Dhinwal, S Suwas, Room-temperature equal channel angular extrusion of pure magnesium, Acta Mater 58 (2010) 3247e3261 [90] M Tsai, J Yeh, High-entropy alloys: a critical review, Mater Res Letts (2014), https://doi.org/10.1080/21663831.2014.912690 [91] C.E Slone, J Miao, E.P George, M.J Mills, Achieving ultra-high strength and ductility in equiatomic CrCoNi with partially recrystallized microstructures, Acta Mater 165 (2019) 496e507 [92] K.K Alaneme, M.O Bodunrin, S.R Oke, Processing, alloy composition and phase transition effect on the mechanical and corrosion properties of high entropy alloys: a review, J Mater Res Techn (2016) https://doi.org/10 1016/j.jmrt.2016.03.004 [93] G.D Sathiaraj, P.P Bhattacharjee, C Tsai, J Yeh, Effect of heavy cryo-rolling on the evolution of microstructure and texture during annealing of equiatomic CoCrFeMnNi high entropy alloy, Intermetallics 69 (2016) 1e9 [94] C Tsai, Y Chen, M Tsai, J Yeh, T Shun, S Chen, Deformation and annealing behaviors of high-entropy alloy Al0.5CoCrCuFeNi, J Alloy Comp 486 (2009) 427e435 [95] P.P Bhattacharjee, G.D Sathiaraj, M Zaid, J.R Gatti, C Lee, C Tsai, J Yeh, Microstructure and texture evolution during annealing of equiatomic CoCrFeMnNi high-entropy alloy, J Alloy Comp 587 (2014) 544e552 [96] R Saha, R Ueji, N Tsuji, Fully recrystallized nanostructure fabricated without severe plastic deformation in high-Mn austenitic steel, Scripta Mater 68 (2013) 813e816 [97] N.D Stepanov, D.G Shaysultanov, N.Yu Yurchenko, S.V.Zherebtsov, A.N Ladygin, G.A Salishchev, M.A Tikhonovsky, High temperature deformation behavior and dynamic recrystallization in CoCrFeNiMn High entropy alloy, Mater Sci Eng A, https://doi.org/10.1016/j.msea.2015.03.097 [98] N.N Guo, L Wang, L.S Luo, X.Z Li, R.R Chen, Y.Q Su, J.J Guo and H.Z Fu, Hot deformation characteristics and dynamic recrystallization of the MoNbHfZrTi refractory high-entropy alloy, Mater Sci Eng A, https://doi.org/10.1016/j msea.2015.10.113 [99] C.A Canbay, A Aydogdu, Thermal analysis of Cu-14.82 wt.% Al-0.4 wt.% Be shape memory alloy, J Therm Anal Calorim 113 (2013) 731e737 K.K Alaneme, E.A Okotete / Journal of Science: Advanced Materials and Devices (2019) 19e33 [100] K.K Alaneme, E.A Okotete, Reconciling viability and cost-effective shape memory alloy options e a review of copper and iron based shape memory metallic systems, Eng Sci Tech Int J 19 (2016) 1582e1592 [101] C Fang, M.C.H Yam, A.C.C Lam, Y Zhang, Feasibility study of shape memory alloy ring spring systems for self-centring seismic resisting devices, Smart Mater Struct 24 (2015) 075024 [102] R Dasgupta, A look into Cu-based shape memory alloys: present scenario and future prospects, J Mater Res 29 (16) (2014) 1681e1698 [103] S Jiang, Y Zhang, Y Zhao, Dynamic recovery and dynamic recrystallization of NiTi shape memory alloy under hot compression deformation, Trans Nonferrous Metals Soc China 23 (2013) 140e147 33 [104] R Basu, L Jain, B Maji, M Krishnan, Dynamic recrystallization in a NieTieFe shape memory alloy: effects on austeniteemartensite phase transformation, J Alloy Comp 639 (2015) 94e101 [105] X.-Q Yin, C.-H Park, Y.-F Li, W.-J Ye, Y.-T Zuo, S.-W Lee, J.-T Yeom, X.-J Mi, Mechanism of continuous dynamic recrystallization in a 50Ti-47Ni-3Fe shape memory alloy during hot compressive deformation, J Alloy Comp 693 (2017) 426e431, https://doi.org/10.1016/j.jallcom.2016.09.228 [106] Y Zhang, S Jiang, S Wang, D Sun, L Hub, Influence of partial static recrystallization on microstructures and mechanical properties of NiTiFe shape memory alloy subjected to severe plastic deformation, Mater Res Bull 88 (2017) 226e233 ... boundaries at 0.1 strain, but as the strain increases to 0.22, a mixture of fine DRX and coarse grains form a necklace around the initial grain boundaries At 0.5 strain the coarse grains were almost... rolling had averagely recrystallized grains when annealed at 650 C, and the degree of recrystallization increased with the increasing annealing temperature Discontinuous recrystallization was... conventional rolling and annealing The research was aimed at producing ultrafine grained materials which have a good balance of strength and ductility The test material was a Fe-31 wt %Mn-3wt %Al-3wt