Powder Metallurgy and Metal Ceramics (v.46, #9-10)

The paper examines the geometrical evolution and particulate interaction in WC-Co alloys produced by solid-phase sintering. It is shown that solid-phase sintering actively modifies the geometric structure: carbide particles grow, become facetted and grow together, and the cobalt phase is redistributed. The WC particles grow irregularly over different temperature ranges. The low rate of growth is characteristic of temperature ranges between 1050 and 1200°C. When alloys are sintered at 1200°C and higher temperatures, the growth of tungsten carbide particles intensifies substantially (by four times). Hence, the temperature 1200°C separates two structurization areas in solid-phase sintering. At this temperature, there is a bend on the specific resistivity curve, which is evidence of higher-quality grain and phase boundaries.
Keywords: hard alloy; solid-phase sintering; structure; phase boundary

Microwave energy is highly efficient for heating and processing different materials. In recent years, this type of heat transfer has been used in sintering process. Rapid and highly efficient heating, time and energy saving, and improved properties of sintered materials are advantages of microwave sintering. In this paper, Fe and Fe-Cu powder compact samples (cylindrical and bone shapes) are sintered both in microwave and electrical tube furnaces. The microwave generator has 2.45 GHz frequency and 1 KW power. Times are selected in the range of 5–25 min for microwave sintering and 5–40 min for electrical heating. The sintering temperature is set at 1120°C. Samples are sintered in the reducing atmosphere of 95% N2 + 5% H2 mixture. The density, hardness, and tensile strength of the samples are measured. The results are compared. The results show that the microwave-sintered materials have a finer microstructure. The microwave-sintered materials have 6–8% higher density, 5–10 HV5 higher hardness, and about 10% higher tensile strength than conventionally sintered materials.
Keywords: microwave sintering; ferrous powder metallurgy; density; tensile strength

Al-Fe-Ce alloys based on water-atomized powders for high-temperature applications by O. D. Neikov; Yu. V. Mil’man; A. I. Sirko; A. V. Samelyuk; A. V. Krainikov; N. A. Efimov (429-435).
The microstructure and mechanical properties of Al-Fe-Ce alloys based on water-atomized powders between 20 and 300 °C are examined in comparison with the properties of similar alloys produced by other rapid crystallization techniques. Changes in atomization parameters vary both the cooling rate (from 104 to 106 K/sec) and powder size distribution (from 5 to 100 µm). The excellent compactability of water-atomized powders facilitates powder consolidation, which is based on hot extrusion and cold pressing of degassed powders. The mechanical properties are examined by tensile tests. The ultimate tensile strength is 500 to 550 MPa at 20 °C and 270 to 300 MPa at 300 °C at adequate plasticity. The properties achieved are comparable with those of similar alloys known from the literature.
Keywords: aluminum alloys; water-atomized powders; rapid crystallization; mechanical properties

Sintering and strength of hot-pressed ceramics based on titanium diboride by M. S. Koval’chenko; L. F. Ochkas; R. V. Litvin; D. Z. Yurchenko; V. F. Britun (436-441).
The paper examines how the grain-size composition of starting titan diboride powders and calcium silicon and calcium hexaboride additives influence the consolidation of titanium diboride in hot pressing and the structure and properties of hot-pressed materials. It is shown that 3 and 5 wt.% of calcium silicon decrease the pressing temperature by 200 °C, refine the structure, and improve the density and mechanical properties of titan diboride materials.
Keywords: titan diboride powder; calcium silicon; grinding; hot pressing; temperature; density; strength properties; structure

Electric-spark hardening of VT3-1 titanium alloy with tungsten-free composite ceramics by I. A. Podchernyaeva; V. M. Panashenko; A. D. Panasyuk; O. N. Grigor’ev; A. I. Dukhota; V. F. Labunets; V. V. Zhiginas (442-448).
The mass transfer and wear resistance of both monolayer and multilayer coatings on VT3-1 alloy are examined. The coatings are deposited by electrospark alloying (ESA) with composite titanium and zirconium refractory ceramics. It is shown that the wear resistance of these electrospark-deposited coatings is 1.6 to 3 times higher in fretting corrosion in unlubricated friction as compared with the conventional WC + 3% Co coating. In addition, the multilayer structure permits four-to fivefold increase in the coating thickness as opposed to the monolayer WC + 3% Co ESA coating.
Keywords: coating; electrospark alloying; mass transfer; wear resistance; composite ceramics; layered structure

Effect of sintering temperature on the microstructure and mechanical properties of Ti(C, N)-based cermets by Yonglin Yan; Yong Zheng; Haijun Yu; Haijian Bu; Xin Cheng; Nengwei Zhao (449-453).
Ti(C, N)-based cermets are produced by vacuum sintering at 1420, 1430, and 1440°C. The effect of sintering temperature on the microstructure and properties of Ti(C, N)-based cermets is studied. The microstructure and fracture morphology are investigated with a scanning electron microscope; mechanical properties such as transverse rupture strength and hardness are measured. The results show that, with increasing sintering temperature, the microstructure of cermets became uniform, and the rim phase structure is gradually completed. When the sintering temperature reaches 1440 °C, the rim phase becomes thicker and more brittle, grains start growing, and the mechanical properties decrease, indicating that a sintering temperature of 1440°C is too high.
Keywords: Ti(C; N)-based cermets; sintering temperature; microstructure; mechanical properties

Alloys and phase equilibria in the Al-Ti-Rh system. I. Solidus surface of the TiRh-Rh-AlRh partial system by K. E. Kornienko; V. G. Khoruzha; P. S. Martsenyuk; A. V. Samelyuk (454-460).
The data of metallography, x-ray diffraction, electron microprobe, and differential thermal analyses are used to project the solidus surface of the partial TiRh-Rh-AlRh system onto the concentration triangle for the first time. No ternary compounds are found in this system. It is established that there are four single-phase surfaces corresponding to the rhodium solid solution, phases based on Ti3Rh5 and TiRh3 compounds, and the δ phase (continuous series of solid solutions between isostructural CsCl-type AlRh-based phases and high-temperature modification of the TiRh-based phase). The solidus surface also contains five ruled surfaces bounding two-phase volumes and two isothermal planes that are constituents of invariant four-phase equilibria reached at 1714 and 1675°C, respectively.
Keywords: aluminum; titanium; rhodium; alloy; phase equilibrium diagram; solidus surface; phase; compound; isothermal plane

The interaction of components in the V-Si-Sb system is examined at 0.7 mole% Sb using an x-ray analysis. An isothermal section of the phase diagram is constructed at 1070 K. The existence of V4SiSb2 with the W5Si3-type structure is not confirmed. Based on VSi2 (CrSi2 structure type), V5Si3 (W5Si3), VSb2 (CuAl2), VSb (NiAs) compounds, terminal solid solutions are formed. Their solubility is lower than 0.05 mole% of the third component. A continuous series of solid solutions exists between V3Si and V3Sb (Cr3Si). The interaction of components in related systems is analyzed.
Keywords: silicides; stibides; solid solutions; phase equilibrium diagrams; isothermal section

Thermodynamic evaluation of the Cu-Ni system within the CALPHAD approach is based on values of mixing enthalpies and activities of components in liquid and solid solutions, as well as parameters of phase transformations. The excess Gibbs free energy of phases is described by the following equations: ΔGL, ex = xNi(1 − xNi)(14259 + 0.45T) J/mole for liquid alloy and ΔG(Cu, Ni), ex = xNi(1 − xNi) × × (6877.12 + 4.6T + (1–2xNi)(−2450.1 + 1.87T)) J/mole for fcc solution. For the Gibbs free energy of the (Cu, Ni) phase, the magnetic effect is described by the Hillert-Jarl method. The thermodynamic model of the system generates a self-consistent description of all thermodynamic values and phase equilibria. The calculated binodale of fcc solid solution is in satisfactory agreement with experimental data. The critical point have coordinates 605 K and xNi = 0.6.
Keywords: phase diagram; thermodynamics; thermodynamic modeling; copper-based alloys

High-temperature thermodynamic characteristics of Ho5Ge3 by N. P. Gorbachuk; V. R. Sidorko; L. M. Kulikov; I. M. Obushenko; S. N. Kirienko (478-482).
The enthalpy of Ho5Ge3 is measured by drop calorimetry between 463 and 2314 K for the first time. The temperature dependences of enthalpy, heat capacity, entropy, and Gibbs free energy are plotted and, enthalpy and entropy of melting are calculated.
Keywords: thermodynamics; enthalpy; heat capacity; entropy; Gibbs free energy

Formation and high-temperature oxidation of thermal-barrier coatings with Ti-Al-Cr binding layer by V. E. Oliker; A. A. Pritulyak; V. L. Syrovatka; E. F. Grechishkin; T. Ya. Gridasova (483-491).
The behavior of TiAlCr detonation coatings with an outside thermal barrier layer in high-temperature oxidation in air is examined. It is established that the efficiency of thermal-barrier coatings with a zirconia external layer on substrates of Ti-rich alloys and γ-TiAl depends on the oxidation of the binding TiAlCr layer and the diffusion at the coating-substrate interface. It is shown that the presence of a ceramic layer has no fundamental effect on the oxidation of γ-TiAl-based coatings. The behavior of TiAlCr coatings in high-temperature oxidation depends on the substrate structure, which determines the nature of diffusion at the coating-substrate interface. If the substrate is made of titanium-rich alloys, there is active diffusion of Al and Cr from and of Ti into the coating. Since the Al/Ti activity ratio changes, a mixed layer of TiO2 and Al2O3 forms on the surface. In case of the γ-TiAl substrate, a layer on the TiAlCr surface consists of Al2O3 alone.
Keywords: thermal barrier coating; titanium aluminides; oxidation

Interaction of titanium hydride and boron nitride at temperature gradient by V. S. Zenkov; V. P. Stetsenko; I. V. Khobta; I. I. Timofeeva; A. S. Petukhov; A. V. Ragulya (492-498).
The paper examines chemical transformation in the mixture of BN and TiH2 powders, which is compacted in a graphite die into cylinders, in a temperature-gradient system under the impact of solar energy on the edge of the sample. The research shows how starting particles transform in different temperature zones and at different temperature increase rates in reaction volumes. It is established that the temperature increase rate significantly contributes to chemical transformations when a gaseous phase forms. It determines the kinetic parameters and transformation mechanism for the starting compounds and the fraction of gas components that may leave the reaction volume with a gaseous flow because of the smaller duration and probability of their contact with the particles involved in chemical processes.
Keywords: titanium hydride; boron nitride; titanium nitride; titanium diboride; solar energy; temperature gradient; x-ray phase analysis

The change in the structure of amorphous TiB2 thin films ∼40 nm thick in heating in an electron diffraction column is studied. Amorphous films are produced by magnetron sputtering a titanium diboride target prepared by powder metallurgy method in argon. It is determined that crystal borides (from lower to higher) appear with increasing heating temperature. The correlation is established between the crystallization temperature and Ti-B bonding energy.
Keywords: thin films; crystallization; borides; phase

Sintered antifriction materials by A. G. Kostornov; O. I. Fushchich (503-512).
Some classes of sintered antifriction materials that form the basis for the development of new materials are discussed. Metal-and nonmetal-based materials with high wear resistance, low friction coefficient, and maximum lifetime are described. They differ in composition, structure (microheterogeneous, macroheterogeneous, layered, fibrous), carrying capacity, and potential for operation under various loads, at sliding rates, and in various conditions (high and low temperatures, corrosive and aggressive media, i.e., in water, acids, alkalis, melted metals, burning-hot gases, with and without lubrication, under high vacuum), in different friction modes (light, medium, heavy, and extremely heavy). The above materials are intended for application in the aviation, motorcar, chemical, oil, metallurgical, transportation, nuclear, textile, and food industries, in cryogenic, rocket, missile, and turbine engineering. Sintered antifriction materials are developed at the Frantsevich Institute for Problems of Materials Science, in particular, under the guidance of I. M. Fedorchenko, a famous materials scientist and academician.
Keywords: sintered antifriction materials; classes of materials; composition; structure; microheterogeneous structure; macroheterogeneous structure; layered structure; fibrous structure; carrying capacity; loading; sliding rate; friction conditions; friction coefficient; wear resistance; application

Effect of chromium and binder on diamond-matrix contact strength by V. P. Umanskii; T. B. Konovalenko; V. A. Evdokimov; A. A. Bugaev (513-516).
The vacuum production of diamond drill bits is considered. The effect from the concentration of an adhesive-active element (chromium) on the diamond-tool contact strength is analyzed. It is examined how the binder affects the dependence of diamond-retaining force on the chromium content.
Keywords: vacuum process; diamond drill bits; adhesive-active element; diamond-retaining force; binder