Powder Metallurgy and Metal Ceramics (v.57, #1-2)

Grigorii Samsonov’s Contribution in Creating and Developing of Materials Science of Refractory Compounds by M. S. Kovalchenko; L. M. Kulikov; V. I. Ivashchenko; I. I. Timofeeva (1-8).

The paper describes advances in a promising area for the development of Samsonov’s scientific school at the Igor Sikorsky Kyiv Polytechnic Institute. The main results are provided to refine the mechanisms whereby crystals nucleate and grow from melts of eutectic alloys and acquire their microstructure and phase composition and the mechanisms whereby reinforced composite materials with isotropic and anisotropic microstructure are strengthened for extreme applications involving high-speed heating and cooling, impact interaction, cyclic loading, and corrosive environments. The mechanical properties of reinforced composite materials in a wide temperature range are presented. Areas for application of the reinforced ceramics are identified.
Keywords: ceramics; directional solidification; composites; structure; properties; strengthening mechanisms; reinforced composite materials; eutectic alloys

Kinetics of Nonisothermal Pressure Sintering of Zirconium Diboride Powder with Additives of Boron and Chromium Carbides in Vacuum by V. B. Vinokurov; M. S. Kovalchenko; L. I. Klimenko; N. D. Bega; T. V. Mosina (27-37).
The analysis of the experimental data on the kinetics of nonisothermal pressure sintering of zirconium diboride-based powder mixtures with the addition of boron and chromium carbides in vacuum showed a division of the sintering temperature mode into low-temperature and hightemperature areas. The division is clearly observed when the temperature increases at a rate of 20°C/min. In low-temperature area, the densification occurs slowly and hardly depends on the temperature. In high-temperature area, the viscous flow of the matrix of the porous material is controlled by the power-law creep of the matrix forming the porous body with an activation energy of 394 kJ/mol. Twofold increase in heating rate leads to acceleration of low- and high-temperature strain of the matrix and increase in the apparent activation energy to 581 kJ/mol, indicating the series engagement of additional mechanisms of material flow. The investigation of structure and properties of materials has showed that the formation of new boron–carbide phases and eutectic that disappears during sintering activates the densification of the porous material. It is found out that under low pressure nonisothermal sintering, a superplasticity phenomenon can occur, which results in the densification of the porous body to the virtually non-porous state.
Keywords: zirconium diboride; boron and chromium carbides; pressure sintering in vacuum; densification kinetics; structure; properties

The densification of fine-grained tungsten carbide-based cermet with 25 wt.% cobalt binder during impact sintering at 1150, 1200, 1250, and 1300°C with the initial impact velocity of 5.8 and 6.2 m/s, with the initial solid-phase state of the binder, is investigated. Based on the obtained experimental data and the calculated elastic properties of the samples and the impact machine, the simulation of densification dynamics using third-order dynamic system is carried out by hit-and-miss method and the value of the shear viscosity of cermet matrix determining the energy dissipation in the system and the irreversibility of the material densification are obtained. In addition, the data on the phase trajectory of the dynamic system motion, the duration of impact loading, the time variations of the force, compression, velocity, and acceleration of the system, densification work, and the mechanical-thermal effect resulting from the energy dissipation and causing a significant increase in the temperature of the porous cermet samples are obtained. At the starting temperature of the samples close to that of eutectic formation and low starting porosity of the samples, this temperature increase can cause the liquid phase squeezing from the sample volume into the porous graphite shell that protects the samples against adhesion to the metal die. The estimated activation energy of the viscous flow of the matrix forming the porous cermet is 1.1 eV or 103 kJ/mol.
Keywords: impact sintering; densification dynamics; porous cermet; tungsten carbide; cobalt; modeling; mechanothermal effect

Interaction and Phase Formation in the WC–Fe2O3–NiO–C System Heated in Vacuum and Argon by A. V. Laptiev; O. M. Myslyvchenko; O. I. Tolochyn; M. V. Karpets; T. A. Silinska; L. N. Kuzmenko (49-56).
The interaction and phase formation in the WC–33 wt.% (80% Fe2O3 + 20% NiO) system with and without free carbon when heated in vacuum and in an argon atmosphere have been studied. Superfine soot and sucrose were used as free carbon. The powders pressed as pellets were heated by incremental temperature rise. In the absence of free carbon, the carbon contained in tungsten carbide and the oxygen contained in iron and nickel oxides actively interact in the carbide–oxide system, leading to weight loss of the samples. The intermetallic (Fe, Ni)7W6 phase, (Fe, Ni)WO4 oxide, and tungsten form as a result. The addition of free carbon allows tungsten carbide to be retained partially or completely and iron and nickel to be reduced from oxides. If there is a lack of free carbon, some part of the carbon contained in tungsten carbide begins to interact with oxygen to form complex Me6C carbide in the system, the metal phase having fcc and bcc lattices. When heating proceeds in vacuum, more carbon is spent to remove the same amount of oxygen than in heating in an argon atmosphere, but temperature of active interaction between carbon and oxygen decreases.
Keywords: tungsten carbide; iron oxide; nickel oxide; soot; sucrose; weight loss; phase formation

Predicting the Composition Ranges of Amorphization for Multicomponent Melts in the Framework of the Calphad Method by M. A. Turchanin; P. G. Agraval; T. Ya. Velikanova; A. A. Vodopyanova (57-70).
Theoretical bases for the calculation of metastable phase transformations with the participation of supercooled multicomponent melts in the framework of the CALPHAD method are considered. A database with parameters for models of thermodynamic properties of phases in the Cu–Ni–Ti–Zr–Hf system for such calculations is presented. The excess term of the Gibbs energy of liquid alloys is described using the associated solution model, and bcc and fcc solid solutions with a mathematical model with Redlich–Kister polynomials. The diagrams of metastable phase transformations with the participation of supercooled liquid alloys and boundary solid solutions are calculated. The composition ranges for obtaining rapidly quenched and bulk amorphous ternary, quaternary, and quinary alloys of the Cu–Ni–Ti–Zr–Hf system are theoretically assessed.
Keywords: CALPHAD method; copper; nickel; titanium; zirconium; and hafnium alloys; rapidly quenched amorphous alloys; bulk amorphous alloys (BAA)

Mechanism of High-Temperature Oxidation of ZrB2-Based Composite Ceramics in the ZrB2–SiC–AlN System by O. N. Grigoriev; A. D. Panasyuk; I. A. Podchernyaeva; I. P. Neshpor; D. V. Yurechko (71-74).
The paper examines the oxidation of the ZrB2–SiC–AlN composite at high temperatures (1550–1700°C) and focuses on the structure and phase composition of the starting ceramic material and scale layer. The oxide layer develops in two stages. At the low-temperature stage (1170–1250°C), an intermediate layer forms, consisting of ZrB2 and involving solid solutions in the AlON–SiC/SiO2 system. The high-temperature stage (1250–1350°C) gives rise to the main protective layer consisting of xAl2O3–ySiO2 mullite solid solutions and colonies of zirconium oxide crystals, located at the grain boundaries of the mullite phase. The resultant oxide layer is an effective potential barrier to the diffusion of oxygen into the sample.
Keywords: zirconium boride; mullite solid solution; silicon carbide; aluminum nitride; high-temperature oxidation

Dielectric Properties of Sr-Doped Na0.5Bi0.5TiO3–Ba(1–x)Sr x Ti0.995Zr0.005O3 Ceramics Synthesized by Wet Solid-State Method by Haiyan Cheng; Aizhen Song; Miao Liang; Jiali Li; Ruijie Duan; Xianling Wang; Chunxia Zhao; Jing Wang (75-81).
New dielectric composite ceramics Na0.5Bi0.5TiO3–Ba(1–x)Sr x Ti0.995Zr0.005O3 (NBT–BSTZ) ( x= 0.05, 0.1, 0.2, 0.3) have been fabricated by the wet solid-state route. The effect of Sr content on phase structure and electrical properties has been studied in detail. The X-ray diffraction analysis illustrates that the composites consist of tetragonal perovskite. With increasing Sr content, the ceramic capacitors display larger dielectric constant, better temperature stability, and lower dielectric loss in dielectric behavior. The ceramics with composition x = 0.3 possess a large dielectric constant (εr) of 2522. The temperature coefficient of capacitance of NBT–BSTZ varies from –39% to 36% in the temperature range between 0 and 200°C. The dielectric loss of capacitance is below 0.07 while the Sr content is 0.3 in the whole range of measured temperatures. The results indicate that Sr-doping is an effective method to modulate the temperature stability and dielectric loss of the NBT– BSTZ dielectric ceramics.
Keywords: ceramics; dielectric materials; dielectric loss

Thermal Barrier Coatings: Current Status, Search, and Analysis by S. M. Lakiza; M. I. Grechanyuk; O. K. Ruban; V. P. Redko; M. S. Glabay; O. B. Myloserdov; O. V. Dudnik; S. V. Prokhorenko (82-113).
The principles for selecting materials to be used as thermal barrier coatings (TBCs) are presented. The advantages and disadvantages of new methods for TBC deposition are briefly described. After measurement of the thermal conductivity and thermal expansion coefficient, it is required to ascertain that such materials do not interact with the thermally grown aluminum oxide and then to determine their strength, fracture toughness, hardness, and Young’s modulus. The thermal conductivity of TBC can be reduced by increasing its porosity and suppressing its sintering. The need for and drawbacks of multilayer coatings are shown. If TBC meets all the requirements, then TBC corrosion resistance to Na2SO4, V2O5, P2O5, sand, and volcanic ash in operation and ways to protect TBC against damage need to be determined. The prospects and areas for development of these techniques are outlined.
Keywords: thermal barrier coating; bond coating; thermally grown oxide; thermal conductivity; mechanical properties; corrosion; zirconia; pyrochlores

Phase Equilibria in the Aluminum Corner of the Al–Ti–Pt System by O. V. Zaikina; V. G. Khoruzha; K. E. Kornienko; T. Ya. Velikanova (114-126).
A series of physicochemical analysis techniques are employed to study the phase equilibria in the aluminum corner of the Al–Ti–Pt system at subsolidus temperatures and in the alloy crystallization process. It has been established for the first time that a ternary τ1 phase (AuCu3 structural type) forms by peritectic reaction L + 2Al5> + ⇄ τ1 at 1405°C. On the solidus surface in the studied composition range at 1405, 1310, 1275, 1060, 925, 820, and 660°C, there are seven isothermal planes that participate in invariant four-phase equilibria involving the liquid phase, three of them being peritectic and the others transitional.
Keywords: phase equilibria; solidus surface; isothermal plane; crystallization; ternary compound; invariant equilibrium