Powder Metallurgy and Metal Ceramics (v.56, #1-2)

A New Method of Mixing Quality Assessment for Friction Material Constituents Toward Better Mechanical Properties by Fatma Makni; Mohamed Kchaou; Anne-Lise Cristol; Riadh Elleuch; Yannick Desplanques (1-13).
Friction materials used for brake lining are highly heterogeneous composites for which the link between formulation, the resulting material properties, and performances is not well understood. Their heterogeneity is induced by the variety of ingredients (morphology, size, properties etc.) and the manufacturing process which includes a succession of steps: mixing, preforming, hot molding, and post-curing. Among these steps, mixing have a great impact on the material microstructure in terms of ingredient distribution and, therefore, on its mechanical properties. However, mastering the mixing process is very difficult, since it is still based on the empirical experience of manufacturers. In this study, a new method and methodology of mixing state evaluation of friction material constituents was developed. First, it consists on studying constituents’ physical properties permitting to facilitate the investigation of mixing state evolution. This investigation includes two steps: binary and multi-constituent mixture study. This work suggests a non-time-consuming image analysis method using two statistical coefficients to evaluate the mixing state, which are Kurtosis and Coefficient of Variation (C.V). The latter enable to describe the mixing quality and state evolution at the surface of the mixing volume as well as to evaluate the mixing time.
Keywords: mixing; image analysis; heterogeneity; brake friction materials

Optimizing the Thermomechanical Processing of Spray-Formed Corrosion-Resistant Steel by O. M. Sydorchuk; K. A. Gogaev; A. K. Radchenko (14-16).
The structure and properties of spray-formed corrosion-resistant steel 95Kh18 with subsequent thermomechanical processing are investigated. The optimal conditions for steel deformation and heat treatment are established. With increasing temperature of the rolled hot forming from 800 ± ± 20°C to 1100 ± 20°C, the steel impact strength increases from 80 to 260 kJ/m2.
Keywords: spray forming; heat treatment; plastic deformation; rolling; structure; hardness

The Hot Deformation Behavior of Spray-Formed High Speed Steel by Shunli Zhao; Junfei Fan; Jieyu Zhang; Kuochih Chou (17-25).
The hot deformation behavior of spray-formed 1.28C–6.4W–5Mo–4.2Cr–3.1V–8.5Co high speed steel is investigated in the 950–1100°C temperature range at a strain rates of 0.1 to 50 sec–1 and a true strain of 1.0. The activation energy for hot deformation is obtained. The relation between the flow stress and Zener–Hollomon parameter is successfully analyzed via the hyperbolic sine function under the whole range of deformation conditions. By a microstructural analysis for the breakdown of carbide networks in the temperature range and different strain rates, the size and distributing character of carbide grains are given. The appropriate ranges of deformation temperature and strain rate are provided to obtain fine spheroidal carbide particles and their uniform distribution.
Keywords: spray forming; high speed steel; hot deformation; flow stress; strain rate; carbide

Pressure Sintering, Structure and Some Properties of SiC–Al Composite Materials by Yu. G. Tkachenko; D. Z. Yurchenko; M. S. Kovalchenko; V. F. Britun; I. I. Timofeeva (26-37).
The pressure sintering of silicon carbide powder mixtures with 15, 30, and 50 wt.% aluminum prepared by grinding in a planetary mill is investigated. A mechanochemical synthesis of new Aland Si-based phases with Fe and O admixtures during grinding is discovered. Further pressure sintering results in the formation of a fine-grained (1–2 μm) structure consisting of SiC basic phase, Al and Si oxides as well as Al oxysilicide. Oxygen and carbon atoms are uniformly distributed, while Al and Si atoms are concentrated in the structural components of the composites. According to the analysis of the compaction kinetics of the composites during nonisothermal pressure sintering, it is found out that their volume flows are controlled by a combination of non-linear creep and linear viscous flow mechanisms, providing the accommodation of the structure of forming phases. These flows are characterized by relatively low activation energies, which can be attributed to the movement of vacancies when lattice and grain-boundary diffusion run. With the exception of SiC–50% Al sintered at 1800°C, the studied materials are characterized by brittle fracture. The hardness and fracture toughness values of SiC–Al sintered composites are in agreement with literature data.
Keywords: pressure sintering; composite; silicon carbide; aluminum; structure; hardness; fracture toughness

Assessing the Internal Structure of Cross-Linked Carbon Nanofibers by Chemical Methods by V. V. Garbuz; V. P. Sergeiev; L. S. Suvorova; V. A. Petrova; L. N. Kuzmenko; T. M. Terentieva; T. M. Silinska (38-44).
The structure of cross-linked carbon nanofibers of DNIPRO industrial carbon fabric produced by pyrolysis of hydrated cellulose is assessed, and their oxidation temperature (Tox = 923 ± 10 K) is found. Fractionated extraction of carbon (as CO2) in a purified oxygen flow is measured by coulometry of the extracted CO2 versus time at Tox. A selective chemical procedure for qualitative identification and determination of cross-linked carbon nanofibers in carbon nanomaterials of arbitrary composition is developed for the first time.
Keywords: cross-linked carbon nanofibers; chemical determination; content

The effect of the powder matrix base (Ti and TiH2) and the type of reinforcing additives (5 wt.% TiC, TiB2, B, and B4C) on the structurization features and some properties of metallic matrix composites sintered hereof is investigated. It is shown that the application of titanium hydride powder with TiC and TiB2 additives as the starting powder base allows obtaining sintered materials with lower porosity (≤2%) and higher hardness, compared to the composites produced based on commercial titanium powder. The microstructure of sintered composites considerably depends on the type of reinforcing additives. TiC particles hardly interact with the matrix phase and they are relatively equilibrium, while the TiB inclusions (as it is in the case of TiB2 additive) are acicular 1–5 μm in dia. and 10–25 μm long. The microstructure of the composites sintered from the mixture of titanium hydride and boron carbide powders has conglomerates 20–50 μm in size, consisting of highly dispersed acicular particles of titanium boride phases and unimportant number of TiC equilibrium particles.
Keywords: titanium hydride; metal matrix composite; sintering; carbides; borides; powder addition; powder metallurgy; microstructure

Mechanical and Fatigue Properties of Powder Titanium Strips, Obtained by Asymmetric Rolling by K. A. Gogaev; V. S. Voropaev; Yu. N. Podrezov; Yu. F. Lugovskoi; V. A. Nazarenko; A. Yu. Koval; Ya. I. Yevych (53-59).
The mechanical properties of titanium powder strips obtained by asymmetric rolling technique are investigated. It is found out that the use of asymmetric rolling during the consolidating and repeated compacting rolling allows obtaining a strip with better mechanical properties than that obtained by conventional technique. The fracture surface of a titanium strip obtained by symmetric rolling has a significant ratio of the interparticle fracture. After asymmetric rolling, the fracture surface is totally dimpled. It is shown that the asymmetric rolling improves the quality of interparticle contact and, consequently, the ductility and fatigue resistance increase significantly.
Keywords: powder titanium strips; asymmetric and symmetric rolling; mechanical properties; fatigue resistance

Effect of the Structure of TiB2–(Fe–Mo) Plasma Coatings on Mechanical and Tribotechnical Properties by M. S. Storozhenko; A. P. Umanskii; A. E. Terentiev; I. M. Zakiev (60-69).
The structure, mechanical properties, and wear-resistance of TiB2–(Fe–Mo) plasma coatings are investigated. Composite powders in the TiB2–(Fe–Mo) system with 20, 40, 60, and 80 wt.% of the Fe–13 wt.% Mo alloy were produced by vacuum sintering with subsequent grinding. The developed powders are conglomerates that contain both refractory and metallic phases. During plasma spraying of developed coatings, a coating with heterophase structure, which consists of Fe-based metal alloy and titanium diboride grains, is formed. The effect of the microstructure of plasmasprayed coatings on the wear-resistance under abrasive wear and dry sliding friction conditions is studied. The scratch hardness testing revealed an insufficient strength of TiB2–20 wt.% (Fe–13 wt.% Mo) coatings and their poor adhesion to the coating base, resulting in the extremely gross wear, when friction. It is found out that, due to the optimal ratio of refractory and metallic phases, the TiB2–40 wt.% (Fe–13 wt.% Mo) coating possesses high wear-resistance under abrasive wear and dry sliding friction conditions.
Keywords: plasma spraying; coating; titanium diboride; iron-molybdenum alloy; structure; wearresistance

A layer of FeCrBSi coating was prepared on H13 hot work steel using a high-velocity oxygen fuel spraying (HVOF). The morphologies and distribution of chemical elements and phases in the obtained coatings were analyzed using a field emission scanning electron microscopy (FMSEM), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD), respectively. The friction-wear performance of FeCrBSi coating was examined using a wear test, and the wear mechanism was also discussed. The results show that the coating is primarily composed of Fe, Cr, B, and Si elements, which are uniformly distributed in the coating, enriched in the coating, and poor in the substrate at the coating interface. Among them, the Fe content decreases gradually in the substrate–coating direction, the Fe content of the coating is 40% lower than that of the substrate. The Cr, B, and Si contents in the coating are higher than those in the substrate, which form compounds and diffusion at the interface; as a result, the coating is combined with the substrate in the form of metallurgical bonding. The coating has a good friction reduction and wear resistance, the average COF (coefficient of friction) is 0.2126, the wear rate is 1.5 ∙ 10–6 mm3/sec ∙ N, and the wear mechanism consists abrasive wear and spalling.
Keywords: high-velocity oxygen fuel (HVOF); FeCrBSi coating; surface–interface morphology; friction and wear

Phase Equilibria in the Cu–Ti–Zr System at 750°C. I. The Isothermal Section with Copper Content from 0 to 50 at.% by A. M. Storchak-Fedyuk; L. V. Artyukh; L. A. Duma; P. G. Agraval; M. A. Turchanin; T. Ya. Velikanova (78-87).
Optical and scanning electron microscopy, electron microprobe analysis, and X-ray diffraction are employed to examine alloys in the Cu–Ti–Zr ternary system, annealed at 750°C, with copper content from 0 to 50 at.%. A partial isothermal section of the phase diagram is constructed at 750°C in the composition range in question. The existence of a continuous series of solid solutions between CuTi2 and CuZr2 isostructural compounds (γ phase, MoSi2 type) is confirmed. The homogeneity ranges of Cu2TiZr ternary compound (τ1, MgZn2 type) and β-(Ti, Zr), (CuTi) (CuTi type), and CuZr (CsCl type) solid solutions are determined.
Keywords: Cu–Ti–Zr system; isothermal section; lattice parameters

Isothermal Section of the Al2O3–TiO2–Gd2O3 Phase Diagram at 1400°C by Ya. S. Tishchenko; S. M. Lakiza; V. P. Red’ko; O. V. Dudnik (88-93).
An isothermal section of the Al2O3–TiO2–Gd2O3 phase diagram is constructed at 1400°C. No new phases or appreciable solubility regions based on components or binary compounds are found in the system. Triangulation of the system is determined by the Gd2Ti2O7 phase, being in equilibrium with Al2TiO5 and GdAlO3 compounds and TiO2 and Al2O3 components. At 1400°C, the system is triangulated into six secondary triangles; three-phase eutectics are expected to exist in some of them. Quasibinary eutectics are likely to exist in three quasibinary sections of the system.
Keywords: ceramics; titania; alumina; gadolinia; interaction; isothermal section; phase diagram

Thermodynamic Properties of Co–Pr Alloys by V. S. Sudavtsova; M. O. Shevchenko; V. G. Kudin; L. O. Romanova; M. I. Ivanov (94-101).
The mixing enthalpies of the Co–Pr liquid binary alloys are determined by isoperibol calorimetry in the composition ranges 0 < x Pr < 0.23 and 0.4 < x Pr < 1 at 1500–1820 K. The thermodynamic properties of the Co–Pr liquid binary alloys are calculated for the entire composition range using the model of ideal associated solutions. The thermodynamic activities of components show negative deviations from the ideal behavior; the mixing enthalpies are characterized by moderate exothermic effects. The minimum mixing enthalpy of melts is –12.0 kJ/mol at x Pr = 0.46.
Keywords: thermodynamic properties; cobalt; praseodymium; calorimetry

Lead-Free Solders for Copper Alloy Wire Mesh by V. P. Krasovskii; L. R. Vishnyakov; V. A. Kokhanyi; N. A. Krasovskaya; I. N. Obodeeva (102-107).
The wetting of compact materials made of pure copper and copper bronzes (tin, beryllium, aluminum) by low-temperature tin-based solders is studied with the sessile drop method with drop melt capillary purification in the experiment. The Sn–Ag–Cu solders wet the bronzes more actively than Sn–Pb (POS-61) and Sn–Bi alloys. The wetting of vacuum-annealed copper and bronze substrates by POS-61, O-2, Sn–Bi, CASTIN, and SAC alloys show that copper and beryllium bronze are wetted by solder alloys better. The Sn–Ag–Cu solders and Sn–Bi alloys are used for metallization and soldering of copper mesh structures. Soldered copper wire 0.1 mm in diameter is obtained to produce mesh representing a knitted soldered structure. The resistivity of O-2, SAC, Sn–Bi, and POS-61 alloys and the surface resistivity of the knitted soldered copper mesh are determined. The metallization of copper wire and soldering of mesh knots substantially influence the mesh surface resistivity.
Keywords: knitted soldered mesh; mesh structure; bronze; copper; lead-free solders; resistivity; wetting; metallization

Sn–Ag–Cu based alloys are well known as an important series of lead-free solders. Gallium has been found to be beneficial for the melting point of the Sn–Ag–Cu solders. In the present work, interfacial reactions between Sn–3.0Ag–0.5Cu–xGa (x = 0, 0.1, 0.5, 1.5 in wt.%) solders and Cu substrates have been examined. The solder and substrate couples were annealed at 80°C for 2, 4, 6, 12, 18, and 24 days, respectively. Various layers of intermetallic compounds have been observed to form using scanning electron microscopy. It has been found that only Cu6Sn5 phase forms when Ga additions are 0, 0.1 and 0.5 in wt.%; but Cu3Sn and Cu9Ga4 form if Ga addition reaches 1.5 wt.%. Thicknesses of these intermetallic compounds have been measured at different annealing stages in order to study the growth kinetics. The growth of all the intermetallic compounds follows the parabolic rule.
Keywords: lead-free solder; Sn–Ag–Cu–Ga; intermetallic compounds; interfacial reaction; growth kinetics

Laboratory Electron-Beam Multipurpose Installation L-2 for Producing Alloys, Composites, Coatings, and Powders by N. I. Grechanyuk; G. A. Baglyuk; P. P. Kucherenko; A. G. Melnik; I. N. Grechanyuk; V. G. Grechanyuk; Yu. A. Smashnyuk (113-121).
The design of universal laboratory electron-beam installation L-2 is proposed and its prototype model is manufactured. The installation allows implementation of the following processes: melting of metals and alloys, deposition of protective coatings, and production of composite materials and powders.
Keywords: electron-beam installation; melting of metals and alloys; deposition of protective coatings; production of composite materials and powders