Fabrication of Fe TiB2 Nanocomposite with use of High Energy Milling Followed by in situ Reaction Synthesis and Sintering by Huynh Xuan Khoa Thesis submitted to the Graduate School, University of Ulsa.
Fabrication of Fe-TiB2 Nanocomposite with use of High-Energy Milling Followed by in-situ Reaction Synthesis and Sintering by Huynh Xuan Khoa Thesis submitted to the Graduate School, University of Ulsan in partial fulfillment of the requirement for the degree of Doctor of Philosophy In Materials Science and Engineering APPROVED: Prof Byoung-Kee Kim, Chairman Prof Young-Soon Kwon Prof Jin-Chun Kim PhD Ji-Hoon Yoo Prof Ji-Soon Kim, supervisor December, 2014 Ulsan, Republic of Korea Abstract Metal matrix composites reinforced with nano-particles are very promising materials which is suitable for a large number of applications Fe-based composites reinforced by TiB2 particulates have attracted much attention due to its excellent mechanical properties as well as low coefficient of thermal expansion In-situ formation results in the clean particle-matrix interfaces with higher interfacial strength, finer reinforcement size and better particle-size distribution Hence, the in-situ technique is the optimal choice for the synthesis of nanocomposite In this study, Fe-TiB2 nanocomposite was in-situ fabricated from titanium hydride (TiH2) and iron boride (FeB) powders by high-energy ball milling and subsequent heat-treatment High-energy ball milling was chosen for mechanical activation as an effective method to achieve the desired results subsequently The specific energy was calculated from the measured results of electrical power consumption during milling and used for discussion on the powder characteristics and the subsequent reaction behavior About 20% of the input energy were transferred into the material at the milling speed of 500 rpm and 33% at 700 rpm By increasing the milling energy, distribution of starting powders was gradually homogeneous and reduced their size to a nanoscale Moreover, the thermal behaviors such as decomposition of TiH2 and the formation reaction of TiB2 from Ti and FeB were lowered Obviously, Fe-TiB2 nanocomposite powders after reaction synthesis showed more homogeneous microstructure for powder mixture milled with higher specific energy Microstructure was characterized by smaller nm TiB2 particulate homogeneous distributed in Fe matrix I Understanding the reaction mechanism helps controlling the affecting factors to achieve the best results Phase change was analyzed by X-ray diffraction and phase distribution was observed by electron microscopy during reaction synthesis of powder mixture milled with various milling conditions in order to explore the formation mechanism of TiB2 particles in Fe matrix The result indicated that titanium reacts with boron at the interface of Ti and FeB by gradual diffusion reaction, forming TiB2 particles, reducing the amount of boron and induced phase transition of FeB to Fe2B The process ended when whole the Ti phase transfered into TiB2 phase and Fe matrix formed from the position of Fe2B left The reaction rate strongly depended on the size and distribution of FeB particles With the finer FeB, the more homogeneous microstructure of Fe-TiB composite powder formed, involving nano TiB2 particles distributed in the Fe matrix Most refractory reinforced - metal composite are used for wear resistance parts and cutting tools, so sintering is always next stage of the manufacturing process of materials A part of this study intended to examine the consolidation of nanocomposite The sintering process was performed by both pressureless (PLS) and pressure (SPS) sintering techniques The main effecting factors of sintering time and temperature were investigated The result showed that microstructure and properties of the composites strongly affected by sintering time and temperature With the dominant advantage of low sintering temperature and short sintering time, the SPSed-samples retained nano-size TiB2 particles and obtained very high density and hardness The PLSed-samples showed sub-micrometer TiB particles, but the hardness obtained also high, equivalent to some WC-Co systems II Acknowledgements It is my great pleasure that I am in a position to express my deep gratitude to some persons without their help the present research work could have not taken final shape Foremost, I express my cordial gratitude, thanks and regards to my supervisor Professor Ji-Soon Kim I am extremely grateful for his sincere help, valuable suggestions and constant encouragement and unique guidance during the four years of my Ph.D course in the University of Ulsan I would like to express my sincere gratitude to Korean students, Mr G P Ahn, B H Lee, Y H Lee, Sang-W Bae, Sun-W Bae, W J Kim and J Y Joe for their many valuable suggestions, encouragement and assistance during my research work I am expressing my gratitude to the Korea Institute of Ceramic Engineering and Technology for helping in measurement of mechanical properties A special thanks to Mr Sang-Ha Park of Deagu Machinery Institute of Components & Materials for the use of their equipment and advice I am also thankful to all staffs of UOU Research Facilities Center for their enthusiasm in the investigation of my specimens I would like to thank my committee members: Prof Ji-Soon Kim (Advisor), Prof Young-Soon Kwon, Prof Byoung-Kee Kim, Prof Jin-Chun Kim and PhD JiHoon Yoo for their support and advice in developing this document Finally, I am grateful to my wife and my daughter for their constant inspiration to carry out the research work Date: University of Ulsan, Ulsan city, Republish of Korea Huynh Xuan Khoa III Table of Contents Abstract .I Acknowledgements III List of Figures IV List of Tables VII Chapter Introduction Reference Chapter Theoretical Background 2.1 Metal matrix nano-composites (MMnCs) 2.1.1 Processing techniques for metal matrix nano-composites (MMnCs) 2.1.2 Strengthening in particulate reinforced metal matrix composites 17 2.1.3 Previous works on production process of Fe-TiB composite 19 2.2 Mechanical activation by high-energy ball milling 26 2.2.1 Mechanical activation 26 2.2.2 High-energy milling equipments 27 2.2.3 Planetary high-energy ball milling and processing variables 27 2.2.4 Energetic of mechanical activation process 30 2.2.5 Effect of mechanical activation on properties of solid 38 2.3 Synthesis reaction mechanisms and reactions in the solid state 40 2.4 Sintering process 46 2.4.1 Presureless sintering 46 2.4.2 Spark plasma sintering – Outstanding method for sintering MMnCs 47 Reference 54 Chapter Experimental procedure 58 3.1 Materials 58 3.2 High-energy ball milling Process 59 3.3 Heat-treatment process 62 3.4 Sintering of nanocomposite powder 63 3.4.1 Pressureless sintering 63 3.4.2 Spark plasma sintering 65 3.5 Characterization 65 3.5.1 Particle size analysis 67 3.5.2 XRD analysis 67 3.5.3 SEM and TEM analysis 67 3.5.4 Thermal analysis 68 I 3.5.5 Density and hardness measurement 68 3.5.6 Wear test, and transverse rupture strength test (TRS) 69 Reference 71 Chapter Energetics of high-energy ball milling process 72 4.1 Indirect approach – Calculation of milling energy by collision model 73 4.1.1 Calculation of milling energy by collision model 73 4.1.2 Measuring the power consumption and comparison with measurement 79 4.2 Direct measurement of total energy during high-energy ball milling of FeB and TiH2 powder mixture 81 4.3 Summary 82 Reference 84 Chapter High-energy ball milling process of initial FeB-TiH2 powder mixture 85 5.1 The state of the powder mixture during High-energy ball milling 85 5.2 Effect of milling energy on mixing homogeneity and size of powder 85 5.3 Effect of Milling Energy on Reaction Behavior of Powder mixture 90 5.4 Sumamry 92 Reference 93 Chapter Fabrication of Fe-40 wt% TiB2 nanocomposite powder from FeB and TiH2 powders - Powder synthesis and formation behavior of TiB2 particulates in Fe-matrix during reaction synthesis 94 6.1 Reaction synthesis of milled powders by heat treatment 94 6.1.1 Shape and Particle Size of Fe- TiB2 nanocomposite powder 94 6.1.2 Phase analysis of Fe- TiB2 nanocomposite powder 94 6.1.3 Microstructure of Fe- TiB2 nanocomposite powder 98 6.2 Formation behavior of TiB2 particulates in the Fe - matrix during reaction synthesis 101 6.2.1 Phase change during reaction synthesis 101 6.2.2 Composite Microstructure and Analysis 103 6.2.3 Discussion 108 6.3 Summary 112 Reference 113 Chapter Combination of Synthesis and Sintering for Consolidation of Fe-TiB Nanocomposite from FeB and TiH2 114 7.1 Sintering Behaviors (sintering conditions vs shrinking) 114 7.2 Phases change during sintering 119 7.3 Microstructure evolution during sintering 121 II 7.4 Relation of density and hardness 125 7.5 Transverse rupture strength (TRS) and abrasive wear of the Fe-TiB2 composites 127 7.5.1 Transverse rupture strength 127 7.5.2 Abrasive wear 130 7.6 Summary 138 Reference 138 Chapter Conclusions 140 8.1 Energetics of high-energy ball milling 140 8.2 High-energy ball milling process of initial FeB-TiH2 powder mixture 141 8.3 Powder synthesis and formation behavior of TiB2 particulates in Fe-matrix during reaction synthesis 142 8.4 Combination of Synthesis and Sintering for Consolidation of Fe-TiB2 Nanocomposite from FeB and TiH2 143 III List of Figures Fig 2.1 Scheme of planetary disk with movement in a counter direction; Rp and Wp - revolution radius and speed, Rv and Wv - rotation radius and speed, Hv pot height 29 Fig 2.2 A snapshot of the ball motion inside the planetary ball mill with set of forces on a ball from video introducing Pulverisette classic line – FRITSCH GmbH 29 Fig 2.3 High-energy ball milling parameters of a planetary mill and cylindrical vial 30 Fig 2.4 The various possible energy dissipation processes that can occur when mechanical energy is input into a solid 31 Fig 2.5 Energy dissipated per hit versus the rotation speed of the planetary ball mill (Fritsch “Pulverisette 5” (left) and AGO-2 (right)) 33 Fig 2.6 Milling map showing the Pe-nv relationship with typical planetary mill rotation speeds 35 Fig 2.7 The milling map of MoSi2 at different conditions 36 Fig 2.8 Scheme of the planetary mill using for the electrical power measurements 37 Fig 2.9 Electrical power absorption measured vs the rotation speed of the mill for the Fe-Zr powder system (a), and experimental (full triangles) and calculated (full lines) power absorption for the Fe-Zr (99balls, db = 10, 40g powder, BPR:10) and the Ti-Al (70 balls db= + 13 balls db = 10, 20g powder, BPR: 9.3) experiments(b) 38 Fig 2.10 Two solids will react only when in close proximity 43 Fig 2.11 Formation of phase boundary 44 Fig 2.12 A “hopping” mechanism in the reaction A + B → AB 44 Fig 2.13 SPS system configuration 53 Fig 2.14 DC pulse current flow through the particles 53 Fig 3.1 Morphology of starting powders; a –TiH2, b - FeB powders and c - powder mixture of FeB-TiH2 (2:1.1) 60 Fig 3.2 Structure of planetary high energy ball mill (AGO-2) 61 Fig 3.3 Schematic illustration of the AGO-2 mill with the electric power meter (3) 61 Fig 3.4 General view of the tube furnace (up), alumina boat was tied by W wire (middle) and illustration of alumina boats in the furnace (below) 64 Fig 3.5 General view of SPS apparatus (up) and Parameters of graphite die and punches (below) 66 Fig 3.6 (a) Schematic of pin-on-disk wear test system according to the standardized method ASTM G99 – 95a F is the normal force on the pin, d is the pin or ball diameter, D is the disk diameter, R is the wear track radius, and w is the rotation velocity of the disk (b) Wear tester and (c) pin holder (H) 69 Fig 3.7 Illustration for TRS test 70 IV Fig 4.1 Structure modeling of an AGO-2 planetary mill 74 Fig 4.2 Hindering factor vs nv = Nb/Nb,tot for different ball diameters 76 Fig 4.3 Kinetic energy released per hit as a function of the rotation speed of the mill and the mass of the ball 77 Fig 4.4 The results of powder calculation for WC ball 5mm 78 Fig 4.5 Electrical power absorption measured vs the rotation, nv = 0.1 80 Fig 4.6 Electrical power absorption measured vs the rotation, nv = 0.2 80 Fig 4.7 Electrical power absorption calculated (full lines with triangles and circles) and measured (full triangles and circles) vs the rotation speed of the mill for the FeB, TiH2 powder system 81 Fig 4.8 Change in milling energy with rotational speed and milling time 83 Fig 5.1 XRD pattern of the FeB-TiH2 (2:1.1) powder mixture after high-energy ball milling under various milling conditions 86 Fig 5.2 SEM-SEI images of FeB-TiH2 powder mixtures milled at different milling energy levels 87 Fig 5.3 Morphology and the mapping images of Fe and Ti for various milling time 88 Fig 5.4 Results of particle size analysis of starting powder mixture and the powders milled at 700rpm/15, 60 & 180min 89 Fig 5.5 SEM-BSE images show cross-section of as-milled powders (from a to f) and TEM image (g) shows the distribution of powder mixture of (f) powder 91 Fig 5.6 DSC curves of FeB-TiH2 (2:1.1) powder mixtures milled under various conditions 92 Fig 6.1 SEM-SEI images of the Fe-TiB2 composite powder after synthesis 96 Fig 6.2 XRD-patterns of the Fe-TiB2 composite powder after synthesis 97 Fig 6.3 SEM-BSE images show the microstructure of Fe-TiB composite powder after synthesis 99 Fig 6.4 TEM images show microstructure of the composite powder (a) and TiB2 size and shape (b) 100 Fig 6.5 XRD-pattern of the FeB-TiH2 powder mixture after milling 700rpm/180min 101 Fig 6.6 XRD-pattern of the FeB-TiH2 powder mixture after milling 700rpm/60min 102 Fig 6.7 XRD-patterns of the FeB-TiH2 powder mixture after milling 500rpm/120min 102 Fig 6.8 SEM-BSE images show microstructure of Fe-TiB composite powder after milling 500rpm/120min and heat treatment at 900oC/ 00 to 120min 104 Fig 6.9 EDS-line scanning on Fig 6.8 105 Fig 6.10 Microstructure of Fe-TiB2 composite powder after milling 700r/60min 106 Fig 6.11 SEM-BSE images show microstructure of Fe-TiB2 composite powder after milling 700rpm/180min and heat treatment 750oC/ 00, 05, 15 & 30min 107 V Fig 6.12 DSC curves of the as-milled powders 110 Fig 6.13 Illustrating the formation of microstructure of the Fe-TiB2 nanocomposite 111 Fig 7.1 Shrinkage of samples sintered at the various sintering condition by PLS technique 115 Fig 7.2 Shrinkage of sample sintered at 11500C was recorded continuously by SPS 116 Fig 7.3 The densification rate of sample sintered at 11500C vs relative density 116 Fig 7.4 Broken surfaces of sample sintered at before and after densification rate peaks 117 Fig 7.5 Broken surfaces of sample enlarged from the square in Fig 7.4 118 Fig 7.6 XRD pattern of some samples sintering by PLS 120 Fig 7.7 XRD pattern of some samples sintering by SPS 120 Fig 7.8 Microstructure evolution during sintering at 1350oC by PLS (left: x 3,000, right: x 10,000) 122 Fig 7.9 Microstructure evolution during sintering at 1400oC by PLS (left: x 3,000, right: x 10,000) 123 Fig 7.10 Microstructure of some samples sintering at various sintering condition by SPS 124 Fig 7.11 Density and Hardness of some sample sintered by PLS 125 Fig 7.12 Density and Hardness of some sample sintered at various sintering condition by SPS 126 Fig 7.13 Displacement - load relation of Fe – 40wt% TiB2 composite fabricated by PLS (left) and SPS (right) during TRS test (5 specimens: 1, 2, 3, 4, 5) 128 Fig 7.14 Fractured surfaces of Fe – 40wt% TiB2 composite fabricated by PLS (above) and SPS (below) after TRS test 129 Fig 7.15 Variation of volume loss with sliding distance for all specimens 131 Fig 7.16 Volume loss for all specimens tested under an applied load of 18N and 23N 132 Fig 7.17 Wear rate (volume loss per unit sliding distance) for all specimens tested under an applied load of 18N and 23N and a sliding velocity of 1.4 m/s 132 Fig 7.18 Wear rate versus hardness for all specimens tested under an 134 Fig 7.19 SEM-SEI micrograph showing the worn surface of all specimens tested 136 VI ... powder mixture during High- energy ball milling 85 5.2 Effect of milling energy on mixing homogeneity and size of powder 85 5.3 Effect of Milling Energy on Reaction Behavior of Powder mixture... 113 Chapter Combination of Synthesis and Sintering for Consolidation of Fe- TiB Nanocomposite from FeB and TiH2 114 7.1 Sintering Behaviors (sintering conditions vs shrinking) 114 7.2... and properties of the composites strongly affected by sintering time and temperature With the dominant advantage of low sintering temperature and short sintering time, the SPSed-samples retained