Fig. 5.32 Schematic of furnace for CARBO-JONIMP glow discharge carbonitriding and carburizing: 1 - resistance/glow-discharge heating chamber; 2 - lock; 3 - quench vestibule. (From Kowalski, S., et al. [54]. With permission.) in the main stream) chemical reactions take place which have a significant effect on the rate of formation and properties of surface layers. For that reason, selection of the chemical composition of the atmosphere, its ho- mogenization and supply to direct contact with the treated load surface is one of the fundamental problems of PACVD methods. Special mention should be made of the chamber design for processes such as glow discharge carburizing and carbonitriding, developed by the Institute of Precision Mechanics in Warsaw [54]. It comprises two cham- bers, separated by a vacuum-tight baffle. The first chamber is used for carrying out the process of nitrocarburizing (atmosphere composed of H 2 + N 2 + CH 4 ) or carburizing (H 2 + CH 4 ) under glow discharge, while the second is for cooling of load (Fig. 5.32). The cooling chamber is equipped with a transport mechanism and a quench tank. 5.4 Glow discharge applications 5.4.1 Glow discharge nitriding Glow discharge nitriding is a method used in thermo-chemical treatment, yielding diffusion cases of varied structure, featuring high hardness, very good fatigue properties, good wear resistance and resistance to corrosion in some environments. In the conventional gas nitriding method, nitrogen available for diffusion is obtained as a result of dissociation of ammonia which flows continuously over the load surface, heated to process temperature. In glow discharge ni- triding, active nitrogen particles are obtained by ionization of the reactive gas (nitrogen or a mixture of nitrogen and hydrogen), brought about by the effect of glow discharge. During the flow of current around treated © 1999 by CRC Press LLC elements of the load, a strongly ionized zone is formed, known as the ca- thodic glow (see Fig. 5.2). Ions formed in this zone, as well as high energy neutral particles, bombard the load surface, heating it to the appropriate temperature and creating conditions for the diffusion of nitrogen into the superficial layer. In the nitriding process, the most important role in the for- mation of the layer is played by atomic nitrogen and nitrogen ions, i.e., N + and N 2 + . By way of example, the composition of ions in a gas atmosphere in conditions of glow discharge is the following at 1.33 hPa pressure and 800 V potential between electrodes: - for a gas mixture of 99% N 2 and 1% H 2 : N + (15.1%), N 2 + (40.0%), H 2 + (5.1%), H + (11.7%), - for a gas mixture of 75% N 2 and 25% H 2 : N + (30.0%), H 2 + (13.0%), H + (17.0%), - for an atmosphere of pure nitrogen: N + (16.8%), N 2 + (55.5%) [55]. A rise of voltage between electrodes at constant gas pressure is conductive to an increase in the concentration of active particles, e.g., a rise of voltage from 400 to 100 V ensures a 10-fold increase in the concentration of atomic nitrogen [55]. One of the advantages of glow discharge nitriding is the possi- bility of optimization of layer structure to obtain certain usable properties through a change of process parameters. In order to obtain desired results of glow discharge nitriding, four ba- sic process parameters are controlled: - chemical composition of reactive gas (from 5 to 80% H 2 - rest N 2 ), - pressure in the working chamber within the range of 1 to 13 hPa, - duration of process within the range of 3 to 16 h, depending on the type of substrate material and desired layer thickness, - temperature of load surface, dependent primarily on type of load and its material. Glow discharge nitriding features the following advantages in com- parison with the conventional method of gas nitriding in an ammonia atmosphere: 1. Possibility of obtaining, in a controlled manner, of four basic types of nitrided layer structures, both on plain carbon, as well as on alloy steels (with an alloy content of up to 10%). These are only diffusion zone, diffusion zone and the Fe 4 N ( γ ’) nitride, diffusion zone with the Fe 2-3 (C x N y ) ( ε phase) carbonitride, and finally, a diffusion zone with a surface compound zone, composed of the γ ’ and ε phases (Fig. 5.33). This forms the basis for selection of the type of nitrided structure for given service conditions of a component; 2. Possibility of treatment of components with complex shapes, e.g., crank- shafts; 3. Reduction of process time, thanks to faster heating of load to treat- ment temperature and activation of the environment, as well as the treated surface of the load; 4. Possibility of control of dimensional growth of components subjected to treatment; 5. Significant economy of electric energy because only the load is sub- jected to heating. This means that heat resistant retorts and ceramic shields © 1999 by CRC Press LLC Fig. 5.35 Hardness distributions in glow discharge nitrided layers for different steel grades: 1 - N135M; 2 - 1045; 3 - 30HN2MFA* (0.3%C, 0.6 to 0.9%Cr, 2 to 2.5%Ni, 0.15 to 0.3%V); 4 - M2; 5 - 40H2MF* (0.4%C, 0.5 to 0.8Mn, 1.6 to 1.9%Cr, max. 0.3%Ni, 0.3%Mo, 0.2%V); 6 - 4140; 7 - N9E* (0.9%C, 0.15 to 0,3%Mn, 0.15 to 03%Si, max. 0.15%Cr, 0.2%Ni). (From Kowalski, S., et al. [54]. With permission.) tigue properties, suitability to service in conditions of strong dynamic loading and ductility which surpasses that of other types of nitrided lay- ers. Nitrided layers with the surface phase zone feature low ductility but high wear resistance. They are suitable for service in conditions of wear by friction when no dynamic loading occurs [54]. Glow discharge nitriding is applied in the treatment of structural alloy steels, hot work and cold work tool steels, especially those which do not suffer significant core hardness drop at typical nitriding temperatures above 500ºC, of high speed steels, e.g., M2 and 9%W grades, as well as of steels with special properties, such as acid-resistant, heat resistant and creep-resistant. It can also be used in the treatment of titanium and mo- lybdenum and their alloys. Hence, glow discharge nitriding is finding broad application in extending the service life of machine components and tools, e.g., injection mold screws and cylinders, dies, gears, punches, injection nozzles, ultrasonic wave-guides, hobs, etc. For example, the life of glow dis- charge nitrided hobs was extended significantly (from 3- to 10-fold, depend- ing on steel grade) in comparison with that of same components, nitrided by other means [54, 55]. Glow discharge, ensuring homogeneity of physico-chemical conditions at the load surface, as well as the possibility of controlling layer structure, also allows the treatment of components with big dimensions and high requirements regarding dimensional tolerance, such as crankshafts. The heat treatment of these components is encumbered with some problems, on account of the type of loading and the tendency to undergo dimen- sional changes caused by geometry and residual stresses induced by the manufacturing process. © 1999 by CRC Press LLC Fig. 5.36 Examples of distribution profiles for nitrogen, titanium, carbon and oxygen in a Ti(NCO) layer of 3 µm thickness, obtained on a prior glow discharge nitrided 1H18N9T* steel (0.1%C, 18%Cr, 9%Ni, 0.5%Ti). Fig. 5.37 Anodic polarization curves in 0.5 m NaCl solution of surface layers on Armco iron, formed in glow discharge nitriding and carbonitriding at 580°C. Glow discharge nitriding also finds application in the treatment of hot work tools, among others, forging dies, punches, die-casting dies and plastic molds. Very ductile monophase layers of 6 µm thickness produced at the surface accommodate dynamic loading occurring during forging, enhance sliding properties and reduce tendency to checking as the result of ther- mal fatigue [59]. Glow discharge nitriding is also used on a broad assortment of cutting tools, among others on milling cutters, broaches, reamers and thread taps. The process is, for those applications, carried out at 450 to 500ºC in times up to 30 min. Their core hardness (62 to 65 HRC) does not change, while surface hardness rises to 1100 to 1300 HV1. The hard nitrided layer significantly raises wear resistance without causing spalling of the cutting edge, thanks to good ductility. Glow discharge nitriding is finding increasing application in industry, and research currently carried on is aimed at developing modifications of the process, e.g., by introducing carbonitriding, oxy-carbonitriding [56, 57], ob- taining of composite layers, e.g., a nitride layer topped by a zone composed of titanium nitride [23] or of Ti(NCO) titanium-oxy-carbonitride (Fig. 5.36). © 1999 by CRC Press LLC In industrial practice, a tendency is observed to replace carburizing by glow discharge nitriding or carbonitriding which creates a possibility of enhancing service properties of the treated components, ensuring dimen- sional accuracy and elimination of finish grinding. Glow discharge carbonitriding (Fig. 5.37) is carried out in an atmosphere composed of H 2 + N 2 + CH 4 , and oxy-carbonitriding in N 2 +CH 4 +air. The utilization of glow discharge allows a reduction of treatment time, e.g. at 800 ºC it is possible to obtain in a time of 1 h a carbonitrided layer of 1 mm thickness and good wear resistance [56]. 5.4.2 Glow discharge boriding Formation of boride layers in a gaseous environment with the utilization of glow discharge is a new thermo-chemical treatment method, still car- ried out on laboratory or semi-technical scale. Nonetheless, specific prop- erties of boride layers on steels, their high hardness, significant resistance to wear, good resistance to the action of a number of chemical agents, notably to acids [58-60], constitute a basis for research aimed at developing new methods of obtaining such layers, methods which are economically justifiable and at the same time creating possibilities of control of structure, hence, of properties. Currently known and used methods, e.g., powder pack, salt bath, paste and gas, are not fully controllable. The most favorable conditions for obtaining a homogenous diffusion layer are those associated with the gas method. Gaseous boriding features such advantages as: lower temperatures than in other treatment methods, possibility of forming boride layers on components with complex shapes and easier process control [61]. The gas atmospheres used in such a pro- cess, however, pose hazards on account of their toxicity and strong corro- sive action against the walls of the working chamber (BCl 3 ) or their high degree of explosiveness (B 2 H 6 ). These difficulties may be eliminated by a reduction of the proportion of reactive gas in the gas mixture with H 2 or H 2 with Ar, and its more efficient utilization. Such conditions can be cre- ated by lowering the pressure in the working chamber and the introduc- tion of glow discharge [9, 34, 62-64]. This allows shortening of process time and lowering of treatment temperature, as well as reduction of reactive gas consumption. The pressure applied here is within the range of 1 to 13 hPa, while the content of BCl 3 vapours is from 2 to 10% by volume [8]. Fig. 5.38 shows examples of microstructure of boride layers on different metallic sub- strates, while Fig. 5.39 shows an example of microstructure and distribution of boron and iron in a biphase FeB+Fe 2 B boride layer on 1045 steel. Boride layers are biphase, as a rule, and comprise the borides FeB and Fe 2 B. Their microhardness oscillates within the range of 1500 to 2400 HV0.1, depending on the phase composition and their thickness reaches 200 µm after 6 h of treatment at 850ºC. The desired goal is to obtain monophase layers compris- ing only the more ductile Fe 2 B phase. The FeB phase, being harder and more brittle, spalls during service and acts as abrasive medium, thus accelerating the process of wear [9]. © 1999 by CRC Press LLC Fig. 5.40 Appearance of surface of boride layers obtained on 1045 steel by glow dis- charge boriding (a) and by the low pressure gas method (b). Process parameters same for both processes: T = 800ϒC, τ = 120 s, p = 4 hPa (H 2 + 10% BCl 3 vapours). Fig. 5.41 Microstructure and distribution of Ni, Fe, B and P in multicomponent boride layers, obtained on AISI1045 grade steel at various temperatures: 923, 1023 and 1123 K. © 1999 by CRC Press LLC Fig. 5.42 Microstructure of composite borided layers on low carbon steel (0.18%C), obtained by the combination of plasma spraying of a nickel-base alloy PMNi35 (C+B+Si - 8%, Co - max 1%, Fe - 3-5%, Cr - 5-8%, Ni - balance) with the process of glow discharge boriding. Shown also is distribution of elements in borided layers. charge process (Fig. 5.17). Electric activation of the gaseous medium, sig- nificant development of the treated surface, thus intensification of the process of chemisorption of boron cause the FeB boride to be formed first, as a rule, in an atmosphere composed of vapors of BCl 3 and H 2 [9]. Thus, depending on the amount of boron supplied, FeB or Fe 2 B borides may be formed. Due to the effect of cathodic sputtering, borides being formed in the initial stages are fine grained and have a developed surface. This favors chemisorption of boride and its diffusion into the core of the treated steel. After the formation of a compact layer of FeB and Fe2B borides, boron may diffuse from the surface in the direction of the core of the treated component along boride grain boundaries [8, 76]. The formation of a boride layer on the steel surface is based predominantly on the mecha- nism of reactive diffusion [9, 65]. Borides formed during the early stages of the boriding process are clearly oriented perpendicular to the surface and constitute a compact, tight layer (Fig. 5.17), facilitating further diffu- sion of boron along grain boundaries. Research carried out in the field of glow discharge boriding is aimed at implementation of this process in the industry, especially as part of the formation of composite and multi-compo- nent layers. Figs. 5.41 and 5.42 show examples of multi-component and com- posite boride layers, formed by the combination of processes of electroless nickel plating or plasma spraying of a nickel alloy with the process of glow discharge boriding [67, 68]. These are layers featuring good corrosion resistance (Figs. 5.43 and 5.44), as well as good wear resistance (Fig. 5.45). © 1999 by CRC Press LLC anti-abrasion and anti-corrosion layers [69-74]. These are methods which make possible the formation of such surface layers as e.g. titanium carbide (TiC) and titanium nitride (TiN), aluminum oxide (Al 2 O 3 ), silicon nitride (Si 3 N 4 ), as well as multi-component layers like Ti(C,N), Ti(NCO) or composite like TiC + TiN, nitrided layer + TiN or Ti(NCO), or boride layer + TiB 2 or Fe 2 B +(Ni,Fe)B + TiB 2 . CVD methods constitute a continuation of powder pack and salt bath methods of formation of surface layers, differing by phase structure, with a thickness up to 15 µm. In the traditional form, these are unassisted CVD processes, carried out under atmospheric pressure (Atmospheric Pres- sure CVD or APCVD) and Low Pressure CVD or LPCVD. These are high temperature processes, thus their utilization is prima- rily in the case of treatment of such materials as sintered carbides or such components where in service the only important aspect is wear by fric- tion, without major dynamic loading. In such conditions, these layers as- sure a significant increase in the service life of treated components [4, 72]. Table 5.4 shows data concerning the extension of service life of some com- ponents, made from different materials and treated by different CVD meth- ods [72, 75]. A common feature of all CVD methods is the supply of the element constituting the layer usually in the form of a halogen, e.g., TiCl 4 in the case of TiC, TiN or Ti(C,N) layers, SiCl 4 in the case of Si 3 N 4 layers and a mixture of halogens, e.g., TiCl 4 + BCl 3 in the case of TiB 2 layers. Table 5.4 Examples of application of CVD methods and extension of life of treated components The second component of the layer may come from the substrate, e.g., nitrogen or carbon in the case of TiN, TiC and Ti(C,N) layers [23] or from the atmosphere, e.g., oxygen in the case of oxide layers [76, 77]. Traditional CVD processes require the use of high temperatures, necessary for the oc- currence of chemical reactions which guarantee the formation of the layers (Fig. 5.46) which limits the scope of their application. This is because in the case of components exposed to dynamic loading in service, or Glow discharge treated components Material Type of layer Application Life extension factor after treatment Upsetting machine punches HSS TiC, Ti(C,N) low carbon steels 2.6 Deep extrusion rams NC10 TiC stainless steel 5 Rollers NC10 Ti(C,N) cold rolled steel 2.7 Small roller N9 TiC thin aluminum sheet 4.7 Pitch circle for external grinding of thread tap centers NC6 TiN abrasive material 5 Masoneylen valves in coal liquefying plants 1H18N9T flow of suspension of coal dust in oil at up to 30 0∫C 10 © 1999 by CRC Press LLC Table 5.5 CVD method designations Table 5.6 General characteristics of selected CVD methods in the process of titanium nitride layer formation A successful future and broad application is predicted for the PACVD method, carried out in conditions of glow discharge, without prior treat- ment (Fig. 5.47) or following surface treatment (Fig. 5.48) with the appli- cation of gas atmospheres containing metal-organic compounds, e.g. va- pors of tetrapropyloxititanium - Ti(OC 3 H 7 ) 4 [8, 73, 82] or Ti[N(CH 2 CH 3 ) 2 ] 4 or Ti[N(CH 3 ) 2 ] 4 [84]. This process allows the formation of multi-compo- nent layers of the Ti(NCO), Ti(CN) and composite layers like nitrided layer topped by a layer of titanium nitride or titanium oxycarbonitride - Ti(NCO), as well as Ti(NCO) + TiN [8, 83]. Composite layers may be formed with the utilization of single stage processes, i.e. after the finished glow APCVD Atmospheric Pressure Chemical Vapour Deposition LPCVD Low Pressure Chemical Vapour Deposition DCPACVD Direct Current Plasma Assisted Chemical Vapour Deposition RFPCVD Radio Frequency Plasma Chemical Vapour Deposition MPCVD Microwave Chemical Vapour Deposition HFCVD Hot Filament Chemical Vapour Deposition EACVD Electron Assisted Chemical Vapour Deposition PhACVD Photon Assisted Chemical Vapour Deposition LCVD Laser Chemical Vapour Deposition MOCVD Metal-Organic Chemical Vapour Deposition PAMOCVD Plasma Assisted Metal-Organic Chemical Vapour Deposition General designation of method APCVD LPCVD PACVD PACVD Method of heating resistance heating of working chamber resistance heating or so-called indirect heating with the utilization of glow discharge heating by glow discharge or by glow discharge with the so-called hot anode heating by glow discharge or by glow discharge with the so-called hot anode Process temperature 1170-1220 K 1150 K 770-820 K 720-790 K Pressure inside working chamber atmospheric 10-500 hPa 3-13 hPa 3-10 hPa Gas atmospheres TiCl 4 +H 2 +N 2 TiCl 4 +H 2 +N 2 TiCl 4 +H 2 +N 2 Ti(OC 3 H 7 ) 4 + H 2 +N 2 Type of layer Ti(C,N), TiN TiC, Ti(C,N), TiN TiN, composite layer: nitrided + TiN layers of the type: Ti(OCN) or composite: nitrided + Ti(OCN) © 1999 by CRC Press LLC Fig. 5.49 Concentration profiles of nitrogen, titanium, carbon and iron in Ti(NCO) layers, obtained on Armco iron at 560ϒC (a) and 520ϒC (b) in an atmosphere com- posed of vapors of Ti(OC 3 H 7 ) 4 - H 2 - N 2 . discharge nitriding process in an atmosphere of N 2 +H 2 , the working cham- ber is filled with vapours of TiCl 4 or Ti(OC 3 H 7 ) 4 in a mixture with hydrogen and nitrogen, and by changing process parameters the Ti(NCO) type layer is formed in a controlled process. Similarly to all glow discharge treatments, by changing process parameters, and appropriate preparation of the treated surface (by e.g., cathodic sputtering) it is possible to control layer microstructure, their chemical composition and thickness (Figs. 5.49 and 5.50). Such layers feature good adhesion to the substrate because nitrogen (from initial nitriding) and carbon from the matrix actively participate in the forma- tion of titanium nitride layers or of Ti(CN), Ti(NCO) or TiC layers [7, 8, 23]. They all feature high surface hardness within 1600 to 2400 HV0.05 for Ti(NCO) layers, depending on carbon and oxygen content, approximately 200 HV0.05 for TiN layers and 3000 to 4000 HV0.5 for TiC layers [7]. Usable properties of these layers may be shaped by their microstructure. Better corrosion resistance and wear resistance are exhibited by layers with a fine grain structure which, as has been stressed, may be formed by the ap- propriate selection of chemical composition of the reactive atmosphere and the utilization of cathodic sputtering (Figs. 5.50 and 5.51). © 1999 by CRC Press LLC [...]... refractory metals are also used, such as titanium, zirconium, hafnium, vanadium, niobium, tantalum, molybdenum and tungsten – Alloys and coating composites: steels (particularly alloyed, corrosion and heat resistant), brasses as well as alloys of metals: Pb-Sn-Cu, SnNi, W-Co, W-Ni, Ni-Fe, Co-Mo, Zn-Al, Zn-Fe, Zn-Ni, Zn-Mn, Zn-Ce, ZnSn, Al-Si, Ni-Cr, Co-Cr, Ni-Al, Pb-Zn, Ni-B-Si, Ni-Cr-B-Si, Ni-Cr-B-Si-C, Co-Mo-Cr-Si,... process control and automation; - energy and material economy of modern CVD processes, utilizing, among others, the effect of glow discharge, for reduced energy and gas consumption through shortening of process time, lowering of process temperature and the heating of only treated surfaces; - relatively low capital cost of equipment for CVD processes, as well as their versatility For example, equipment for... al.: Investigations of zones of glow discharge near the cathode in a mixture of vapours of BCl3 + H2 and BCl3 + Ar (in Polish) Report by the Institute of Flow-through Machines, No 169 /83, Gdansk-Wrzeszcz 1983 20 Roliñski, E.: Ion nitriding of titanium and its alloys (in Polish) Warsaw University of Technology Publications, Mechanics, Vol 112, 1988 21 Teer, D.G.: The energies of ions and neutrals in ion... variety of asphalts, surface engineering uses only few, mainly for the manufacture of asphalt (bituminous) varnishes and for the insulation of pipelines [22, 23] Lubricants - a general name given to all greasy substances which have the properties of diminishing friction between surfaces, as well as those which protect the surface From the point of view of consistence, we distinguish solid, semi-liquid and. .. lubricants; from the point of view of application - anti-friction lubricants and protective greases All types of lubricants are used in surface engineering, lubricants being used in the overwhelming majority of cases, to alleviate friction of the superficial layer, while protective greases - to develop coatings, deposited on the superficial layer Solid lubricants, of solid or semi-solid (semi-liquid) consistence,... Indiarubbers, particularly synthetic, are used for lining and in the manufacture of anti-corrosion coatings, e.g., butadiene-styrene, butyl and chloride indiarubber; and for anticorrosion paints, e.g., chlorinated rubber rustproof varnishes, obtained by chlorination of natural indiarubber It can also be used in the manufacture of some paints and varnishes [4 3-4 5] Rubbers are products of vulcanization (curing -. .. PN-83/H-04302, 1983 Polish Standard Specification Strength testing of metals Friction test in three-rollers-cone system 90 Boman, M., and Carlsson, D.: Laser-assisted chemical vapour deposition of hard and refractory binary compounds Surface and Coatings Technology, 49, 221, 1991 91 Jones, A.C., Houlton, D.J et al.: A new route to the deposition of Al 2O 3 by MOCVD Journal de Physique IV Vol 5, C 5-5 57, 1995 92 Bastianini,... some items of everyday use The external chromium layer gives the coating a shiny appearance and does not tarnish The internal nickel layer binds it to the substrate Products made from steel and zinc alloys are sometimes coated with three layer coatings of copper-nickel-chromium or four layer coatings of nickel-chromium-nickel-chromium with a particularly high corrosion resistance [1, 3-8 ] Heat-resistant... sandwich coating - comprising several layers of different materials, with at least one of them occurring twice and not directly on top of same material, e.g., Ni-Cr-Ni-Cr [3] – self-stratifying paint - deposited in the form of a liquid (or powder) mixture, stratifying during drying (or melting) into a bottom sublayer with strong adhesion to substrate which is usually metallic, and a top sublayer (surface) ,... control of gas flow rate distribution, all constitute the basis for optimization of the CVD process Among the most significant advantages of CVD treatments are the following: - possibility of formation of heterogeneous superficial layers with desired structure and properties at temperatures of 400ºC and above (including multi-component and composite layers) with good usable properties; - possibility of . (particularly alloyed, corro- sion and heat resistant), brasses as well as alloys of metals: Pb-Sn-Cu, Sn- Ni, W-Co, W-Ni, Ni-Fe, Co-Mo, Zn-Al, Zn-Fe, Zn-Ni, Zn-Mn, Zn-Ce, Zn- Sn, Al-Si, Ni-Cr,. Zn- Sn, Al-Si, Ni-Cr, Co-Cr, Ni-Al, Pb-Zn, Ni-B-Si, Ni-Cr-B-Si, Ni-Cr-B-Si-C, Co-Mo-Cr-Si, Ni-Cr-Al-Y. Metallic coatings are usually deposited on expensive, precision compo- nents, rather small. Microstructure of composite borided layers on low carbon steel (0.18%C), obtained by the combination of plasma spraying of a nickel-base alloy PMNi35 (C+B+Si - 8%, Co - max 1%, Fe - 3-5 %, Cr - 5-8 %, Ni -