Powder Metallurgy and Metal Ceramics (v.52, #1-2)

A compaction process using self-propagating high-temperature synthesis (SHS) has been developed. The process includes preparation of a composite powder billet in conditions that promote uniform pore distribution over the synthesized product, followed by barothermal SHS and compaction of the billet by plastic deformation. To determine the ultimate strain of the synthesized billet, a hereditary damage accumulation model is proposed to consider two competing processes during compaction: accumulation of microdamage induced by plastic deformation and partial healing of the accumulated microdamage through structural changes. Areas of theoretical studies to intensify the compaction process are identified.
Keywords: self-propagating high-temperature synthesis; powder billet; damage accumulation; hereditary model; limit state criterion

Rheological models of deformable bodies are used to develop a dynamic approach to the problem of mechanical actions on porous bodies during pressure sintering. Solutions of dynamic systems describing the force acting on porous viscoelastic bodies, either strain-hardenable or not, are presented depending on the control parameters of the systems. These parameters are determined by the inertial properties and rigidity of the machine and the rheological properties of the deformable bodies. The intensity of densification during the pressure sintering of porous bodies mainly depends on the ratio of rigidity of the system to the viscous resistance of the body. The simulation and analysis of the pressure sintering of porous bodies using the obtained solutions enable prediction of their densification conditions and functional properties depending on the machine characteristics and the sizes and rheological properties of deformable bodies.
Keywords: rheological models; pressure sintering; porous body; strain; dynamic system

Microstructural evolution of Cr–Cu composites in liquid-phase sintering by E. V. Khomenko; R. V. Minakova; N. D. Lesnik (20-31).
The paper examines the effect of temperature and volume fraction of refractory particles on the kinetics of their growth during liquid-phase sintering of Cr–Cu composites in the temperature range 1150–1350°C under a vacuum of (2–4)∙10–3 Pa. It is established that the growth kinetics of average-size particles is described by a near-cubic law and the decrease in their number is determined by a near-inverse dependence: the apparent activation energy (Q = 113 ± 10 kJ/mol) is of the order of magnitude comparable to that of diffusion in liquid metals. According to the Lifshitz–Slyozov–Wagner theory (LSW theory), diffusion coalescence is indicative of diffusion-controlled particle growth. Experimental growth constants are one order of magnitude higher than those calculated within the classical LSW theory. The increase in the growth rate constant with volume fraction of refractory particles varying from 0.4 to 0.7 and the change in the particle size distribution function after sintering for 90 min at 1200°C agree with the Ardell model, which modifies the LSW theory considering the effect of volume fraction of particles on their growth kinetics.
Keywords: liquid-phase sintering; Cr–Cu composites; growth kinetics of refractory particles; Lifshitz–Slyozov–Wagner theory; activation energy

Oxide nanomaterials with properties absent in bulk (Author Review) by M. D. Glinchuk; V. V. Khist; E. A. Eliseev; A. N. Morozovska (32-38).
A ferroelectric phase can be induced in otherwise nonferroelectric binary oxides like BaO, EuO, and Er2O3 by a strong enough intrinsic surface stress present under the curved surface in nanowires. Our analytical calculations performed within the Landau–Ginzburg–Devonshire theory prove that BaO nanowires can be ferroelectric at room temperatures. Undoped nanoparticles of incipient ferroelectrics SrTiO3 and KTaO3 without any magnetic ions can become ferromagnetic even at room temperatures due to the presence of a new type of magnetic defects, such as oxygen vacancies, inherent to nanostructures. Nanosize Eu x Sr1–x TiO3 wires and tubes are shown to be the new multiferroics with “triple” the antiferrodistortive–ferroelectric–ferromagnetic phase, which is of interest for fundamental study and can be important for their potential applications. We hope that our predictions will stimulate experimental studies of the nanosized binary oxides and perovskites.
Keywords: binary oxides; perovskites; surface stress; nanowires; antiferrodistortive–ferroelectric–ferromagnetic phase; antiferrodistortive phase

The structurization and properties of Fe–Cr–C alloys with a liquid phase vanishing during sintering by N. P. Brodnikovskii; A. A. Mikhailov; P. V. Mazur; K. S. Chirik; A. V. Samelyuk; M. S. Tkachenko; S. A. Firstov (39-46).
The possibility of increasing the wear resistance and bending strength of Fe–Cr–C alloys with a high chromium carbide content produced by powder metallurgy methods is studied. Regularities of the structurization and mechanical properties of the alloys are determined in relation to their composition and production conditions. The conditions of sintering and the composition of the alloys with a high chromium carbide content ensuring high abrasive wear resistance, which is 1.5 times greater than that of VK8 alloy, are found. The structure of the alloy represents a fine-grained chromium carbide composite formed at a certain amount of a liquid phase vanishing during sintering.
Keywords: alloys; Fe–Cr–C system; sintering; structure; wear resistance; strength

Hard powder alloys and carburized chromium steels in the Cr–Fe–C system by V. A. Maslyuk; R. V. Yakovenko; O. A. Potazhevskaya; A. A. Bondar (47-57).
The literature data for the Cr-Fe-C system are used to construct the Fe–Cr3C2 vertical section showing wide two-phase (αFe) + (Cr, Fe)7C3 and (γFe) + (Cr, Fe)7C3 regions. Sintering of a powder mixture of iron and chromium steels Kh17N2 and Kh13M2 with higher chromium carbide is studied, and sintering conditions are optimized. It is shown that dissolution of Cr3C2 in the metal matrix of both chromium steels is described with a series of phase transformations: Cr3C2 → → Cr7C3 → (Cr, Fe)7C3 → (Cr, Fe)23C6. The effect of structure and phase composition on the mechanical properties (bending strength, HRA hardness, impact strength, fracture toughness), tribotechnical characteristics, wear resistance, and corrosion resistance is examined for the hard alloys and carburized steels Fe–Cr3C2, Kh17N2–Cr3C2, and Kh13M2–Cr3C2. Application of the materials developed allows an increase in the service life by 7–10 times for operating elements of feed mills and high-wear parts of equipment in construction industry.
Keywords: Fe–Cr–C system; phase; hard powder alloy; carburized steel; microstructure; wear resistance; corrosion resistance

Effect of doping with refractory rare-earth metals on the structure and properties of Al–5Zn–3Mg alloys produced by powder metallurgy and casting methods by Yu. V. Mil’man; O. D. Neikov; A. I. Sirko; N. P. Zakharova; G. I. Vasil’eva; A. O. Sharovskii; R. K. Ivashchenko; V. G. Tokhtuev; N. V. Semenov (58-66).
The effect of doping with transition refractory metals on the structure and properties of Al–Zn–Mg alloys produced by different methods is studied. It is ascertained that the strength of cast alloys is increased by scandium and zirconium doping due to the modifying action of scandium that arrests recrystallization and precipitation of the fine-grained phase matrix-coherent Al3(Sc1–x Zr x ) phase; the strength of alloys obtained by powder metallurgy (P/M) methods increases to a smaller extent, in which the ultrahigh cooling rate of melt atomized by high-pressure water plays the basic role in forming the fine-grained structure. The strength of powder metallurgy alloys based on wateratomized powders is substantially higher than that of similar alloys produced by the conventional casting method (standard commercial cast alloys and alloys produced by granular technology). The advantages of P/M alloys over cast alloys are especially prominent in the absence of scandium doping. The highest strength of the P/M alloys with scandium (σb = 651 MPa and σ0.2 = 596 MPa) is shown by Al–5Zn–3Mg–0.5Mn–0.7Zr–0.3Sc. Among the P/M alloys without scandium, the highest strength is shown by Al–5Zn–3Mg–0.85Zr–0.22Cr–0.17Ni–0.15Ti alloy (σb = 618 MPa and σ0.2 = = 553 MPa).
Keywords: aluminum alloys; casting method; powder metallurgy methods; mechanical properties; recrystallization; fine-grained structure

Formation of a layered structure on SiC–Al2O3–ZrO2 ceramics during high-temperature oxidation by I. A. Podchernyaeva; V. A. Lavrenko; A. D. Panasyuk; A. P. Umanskii; I. P. Neshpor; A. G. Dovgal (67-72).
The high-temperature oxidation of SiC–Al2O3–ZrO2 composite material in air under the action of concentrated solar radiation at temperature close to the melting point leads to the formation of a three-layer wear- and corrosion-resistant protective scale with an outer layer of aluminum silicate Al2SiO5 about 180 μm in depth with fine fibrous structure. It is shown that preliminary hightemperature oxidation of the composite improves its service characteristics.
Keywords: SiC–Al2O3–ZrO2 composite ceramics; preliminary high-temperature oxidation; concentrated solar radiation; lamellar structure; service characteristics of composites

Structural and mechanical properties of TIN/BCN coatings by P. L. Skrinskii; A. I. Kuzmichev; V. I. Ivashchenko; L. A. Ivashchenko; I. I. Timofeeva; O. O. Butenko; O. Yu. Khizhun; T. V. Tomila; S. N. Dub (73-82).
Monolayer TiN and a-BCN and nanolayer TiN/BCN coatings are deposited by dual magnetron sputtering. The effect of discharge power, flow rates of gases, and substrate bias voltage on the mechanical properties of the deposited nanolayer coatings is studied. The structure, chemical bonding, mechanical properties, adhesion, and friction coefficient of the coatings are analyzed. It is established that the deposited nanolayer coatings have nc-TiNx/a-BNO+a-C structure. The Knoop hardness of the nanolayer TiN/BCN coatings is found to reach 45 GPa on average. The nanohardness is lower than the Knoop hardness (by 20–30%). The deposited nanolayer coatings can be recommended as wear-resistant and protective coatings for mechanical engineering.
Keywords: magnetron sputtering; wear-resistant coating; nanolayer coating; mechanical properties; friction coefficient; adhesion

Microstructure and properties of detonation-sprayed thermal barrier ZrO2 coatings by V. E. Oliker; S. A. Abdurashitova; I. S. Martsenyuk; E. F. Grechishkin; A. A. Bondarenko (83-89).
The formation of detonation-sprayed thermal barrier ZrO2 coatings is studied. The influence of spraying modes on the structure and mechanical properties of the coatings is determined. It is established that the microstructure of the coatings and thus their mechanical properties can be improved by controlling the weight of ZrO2–7%Y2O3 powder sprayed per shot. A quantitative evaluation of the mechanical properties of thermal barrier coatings by indentation method has shown good results.
Keywords: thermal barrier coatings; detonation spraying; microstructure; fracture toughness

Solidus and liquidus surfaces of the Al2O3–HfO2–Er2O3 phase diagram by Ya. S. Tishchenko; S. M. Lakiza; L. M. Lopato; M. S. Glabai (90-101).
Phase equilibria during solidification of alloys in the Al2O3–HfO2–Er2O3 system are studied, and liquidus and solidus surfaces of the Al2O3–HfO2–Er2O3 phase diagram are constructed for the first time. It is established that interaction in the system is eutectic. No ternary compounds or appreciable regions of solid solutions based on components or binary compounds are found in the ternary system.
Keywords: ceramics; hafnia; alumina; erbia; interaction; isothermal section; phase diagram; eutectic materials

Sintering in incompletely sealed containers without gas flows by L. A. Sosnovskii; G. A. Baglyuk; O. V. Vlasova (102-108).
The paper presents an analytical review of published data and the authors’ data on the use of incompletely sealed steel containers for the sintering of iron-powder products in air. Consideration is given to additional techniques for removing oxidation products during sintering such as introduction of protective gas microgenerators into containers or use of a fill. It is concluded that it is reasonable and possible to sinter small and medium batches of powder products and to remelt powder waste at existing thermal stations.
Keywords: sintering; powder material; container; liquid seal; fill

Granular periclase–spinel vibration castables are studied. The range of their service characteristics (vibrating activity not less than 3 h) is determined depending on the type of dispersant: flow is 80–190% at 4.5–6.2% castable moisture for polyethyleneglycol dispersant, 80–180% at 5.2–6.5% castable moisture for polycarboxylic acid dispersant, and 80–190% at 5.5–7.0% castable moisture for polyelectrolyte dispersant. The range of service characteristics is assessed taking into account quality of the effective (melting) crucible surface. The studies have allowed the minimization of possible rejects during vibration casting and the production of high-refractory crucibles with smooth surface without defects to be used for induction melting of oxidation- and heat-resistant alloys.
Keywords: vibration casting; periclase; alumina–magnesia spinel; moisture; flow; periclase–spinel crucibles

The structure and phase composition of boride coatings on sintered powder steels by G. A. Baglyuk; A. A. Mamonova; S. G. Pyatachuk; L. A. Sosnovskii (113-117).
Results of metallographic and X-ray diffraction analyses of boride coatings produced by saturation of porous blanks from iron–carbon powder alloys are provided. It is established that the structure and phase composition of boride coatings made of iron–carbon powder alloys depend on the composition of borating mixtures: the amount of diffusion activator AlF3 in the borating mixture essentially influences the structure, phase composition, and hardness of the coating and a higher amount of the activator intensifies the borating process, leading to the formation of a very hard coating and borocarbides in the transition zone.
Keywords: borating; iron boride; carboboride; microhardness