Dry friction and wear of alloys of diboride-nitride systems at normal temperatures

Conclusions A study was made of the room-temperature dry friction and wear of alloys of the systems ZrB₂-ZrN and HfB₂- HfN in air. It was found that all the materials investigated possess high wear resistance. The lowest values of coefficient of friction (0.3–0.4) and increased wear resistance at a sliding speed of 1 m/sec are exhibited by composites based on hafnium diboride and those containing 40–70 mole % zirconium nitride.Translated from Poroshkovaya Metallurgiya, No. 7 (103), pp. 63–67, July, 1971.     

Prospects of raising the heat resistance of materials based on refractory metals

Conclusions The paper examines the principles underlying the effective alloying of refractory metals on the basis of the strength loss mechanism. The heat resistance of rhenium, whose strength loss occurs essentially during recrystallization, can be increased by alloying on the basis of the principles which have been utilized for developing aluminum, cobalt, and nickel alloys.Other refractory metals (tungsten, molybdenum, niobium) lose most or all of their strength before recrystallization, as a result of polygonization processes. The heat resistance of these refractory metals and their alloys can be increased by inhibiting the polygonization process. The mechanisms by which additions influence the rate of polygonization are discussed.Translated from Poroshkovaya Metallurgiya, No. 8(44), pp. 38–42, August, 1966.     

Electrical erosion of P/M composites of the silver-nickel system

Conclusions It has been established that the erosion rate of P/M Ag-Ni composite contacts between which arc discharges of 25-A current amplitude are excited is related to their composition. It is shown that materials with a nickel content of 50–75% possess adequate erosion resistance, and are not inferior in this respect to the industrial SN-30 and SN-40 alloys (sintered Ag-30% Ni and Ag-40% Ni materials). It has been found that the erosion of Ag-Ni composite anodes depends on the thermophysical properties of cathodes made of metals or composites of various kinds. It is demonstrated that certain characteristic features of m vs composition curves can be satisfactorily explained in the light of the theory postulating that an arc discharge locks itself to the least conducting phase and of the relationship between the energetic parameters of jets of eroded mass and and the thermophysical properties of electrodes. The study has also revealed that dissimilar pairs composed of Ag cathodes and Ag-Ni anodes containing up to 60% of nickel are comparable in wear resistance to pure silver contacts; use of such pairs, after they have proved their merits in practical tests, will result in a significant saving in silver consumption.Translated from Poroshkovaya Metallurgiya, No. 6(234), pp. 61–66, June, 1982.     

Optimization of the process of manufacture of diamond-containing composite materials based on titanium carbide-steel alloys

Conclusions A study was made of the conditions of production of tungsten-free composite materials by sintering in a high-pressure chamber and in vacuum. Good-quality nonporous specimens of titanium carbide-steel materials cannot be produced by hot pressing in graphite dies. The hardness of materials sintered in a HPC is higher (81–86 HRA) than that of materials sintered in vacuum (75–82 HRA.). Heat treatment slightly lowers it (to 77–85 HRA). The highest wear resistance is exhibited by vacuum-sintered materials. In alloys sintered in a HPC a directional orientation of the steel binder with titanium carbide grain inclusions was observed. In service tests the properties of composition diamond-containing materials based on titanium carbide-steel alloys were found to match those of Tvesal alloys-diamond-containing composites based on a tungsten-group hard metal.Translated from Poroshkovaya Metallurgiya, No. 7 (259), pp. 21–25, July, 1984.     

The solubility of hydrogen in molten aluminum alloys

The solubility of hydrogen in molten aluminum alloys containing copper, lithium, magnesium, and silicon has been calculated from the solubility of hydrogen in pure metals and binary metal-metal interaction parameters. For the aluminum-copper binary system, where experimental data exist, the agreement between calculated and experimental values is excellent. The solubility of hydrogen in liquid silicon was calculated from the solubility data in aluminum-silicon alloys.     

Influence of electrospark alloying on the heat resistance of steels

Conclusions The high-temperature oxidation of electrospark coatings on R9K5, 5KhNV, and 50 steels obtained by electrospark alloying with standard (T15K6, VK8, VK6M) and carbide-, nitride-, and boride-base tungsten-free alloys was investigated by the differential thermal analysis method. It was shown that in increase in heat resistance the refractory compound-base electrode materials used for production of coatings are in the order (by base component) boride-carbidenitride. A significant factor increasing the high-temperature oxidation resistance of the coatings is the increase in their coverage. With a high coating coverage on carbon steel its high-temperature oxidation resistance approaches that of die steel. Therefore, in a number of cases, replacement of expensive alloy steels with carbon steels is possible.Translated from Poroshkovaya Metallurgiya, No. 3(303), pp. 69–74, March, 1988.     

The eutectoid region of the Zr−Ga system

The zirconium-rich portion of the Zr?Ga phase diagram was determined by the optical examination of microstructures of isothermally annealed and quenched alloys. A deviation from binary equilibrium, was observed even though careful selection of materials and techniques held impurities to a minimum and produced alloys with a purity of at least 99.9 pct. The slopes of the α-β boundaries are depressed and the range of solubility of the solid solution phases is restricted when compared to the phase diagrams of other Group IIIB elements, apparently as a result of the large difference in atomic size between zirconium and gallium. Thea ₀ andc ₀ lattice constants of cph zirconium are contracted and the axial ratio is expanded by the addition of gallium. The change inc/a at 1 at. pct was very close to the change observed in Zr-In alloys, in agreement with general dependence of these properties in zirconium alloys upon electron to atom ratio. A eutectoid reaction occurs at 860°C with β solid solution (1.8 at. pct Ga) decomposing into α solid solution (0.8 at. pct Ga) and Zr₃Ga. Cast microstructures suggest a eutectic reaction in which liquid (21.0 at. pct Ga) decomposes into β (8.0 at. pct Ga) and Zr₅Ga₃. It is proposed that intermediate phases are formed at 25.0 at. pct Ga (Zr₃Ga), 37.5 at. pct Ga (Zr₅Ga₃), and 50.0 at. pct Ga (ZrGa) although the exact composition was not determined.     

Technological characteristics of W-Ni-Cu alloys containing dispersed zirconium dioxide inclusions

Summary The results presented demonstrate that the sintering of W-Ni-Cu alloys with dispersed zirconium dioxide inclusions at a temperature of 1785° C in hydrogen yields specimens of high density, so that alloys produced in this manner can be employed as constructional materials.Translated from Poroshkovaya Metallurgiya, No. 11(47) pp. 43–45, November, 1966.     

On the development of packing materials for steam turbines (part 1)

Summary The performance of iron and copper as packing materials for steam turbines was evaluated on the basis of their oxidation resistance in a water-vapor environment. It was shown that the rational constant of oxidation of copper at 600° C is 4–5 orders of magnitude smaller than that of iron. The influence of impurities on the susceptibility of intergranular corrosion is more pronounced in nickel than in copper and iron. A procedure is described for calculating the rational constant of oxidation of metals on the basis of Wagner's equation; using this procedure, it is possible to determine in the first approximation the oxidation resistance of metals in hightemperature corrosive environments.     

Thermodynamic modeling of the interaction of high-level element and oxygen in iron-based melt

The main reactions of calcium, cerium, lanthanum, silicon, and complex alloys with the active additive Ca–Si, Ca–Al, Ce–Si, La–Si, Ce–La, or Ce–Ca–Al are subjected to thermal analysis. On the basis of binary and ternary fusibility diagrams, the thermodynamic data are refined for the main reactions between complex alloys with rare-earth elements and the oxygen present in the liquid metal. Solubility surfaces are plotted for components of the Fe–Si–Ce–O, Fe–Si–La–O, Fe–Ce–La–O, and Fe–Ca–Al–Ce–O systems. From those diagrams, optimal compositions of complex alloys with rare-earth elements in terms of nonmetallic-inclusion formation are established by plotting the consumption of the active components. For each group of steels, the quantitative elementary composition of the active components used for reduction and modification of the nonmetallic inclusions must be calculated. The chemical and phase composition of the nonmetallic inclusions may be very complex even in the final stages of the reduction of oxides. A method is developed for taking account of the polyvalency of cerium in reduction processes. The thermodynamic data and diagrams obtained help provide a better understanding of the complex heterogeneous processes within multicomponent systems that contain liquid metals. In combination with experimental data for the solubility surfaces of the components and the consumption diagrams, it is possible to track the transitions from the nonequilibrium state of the metallurgical system to the equilibrium state. In other words, the degree of refining of the metal and the equilibrium composition of the nonmetallic inclusions may be determined.     

Examination of the physical properties of ZrC-W carbide-metallic alloys

Conclusions The heat conductivity of the two-phase alloys of ZrC-W system increases with an increase of the tungsten content and with increase in temperature. This is caused by the electron contribution to the heat conductivity of the crbide phase.The electrical resistance of these alloys decreases with increase in tungsten content and increases with increase in temperature. At a mass constant of ZrC > 25% the temperature dependence of the electrical resistance of the alloys is nonlinear as a result of slight overlapping of the valency band by the conduction band in the carbide phase.The mean coefficient of thermal expansion ZrC-75% (wt.) W alloy increases with increase in temperature from 5.5·10^–6 in the range 300–600 to 7.05·10^–6 K^–1 in the range 300–2300°K.The spectral emission factor =0.65 mm of the ZrC-W alloys increases with an increase of the zirconium carbide content. With increase in temperature decreases for tungsten, zirconium alloy, and alloys with a mass content of W < 40%. For the alloys with a tungsten content of 45–75% depends only slightly on temperature. This can be explained by the presence of tungsten carbides in the subsurface layer. The critical wavelength of these carbides (_X=500–600 nm) is close to the wavelength in pyrometric measurements.The fracture tensile stress of the specimens of the alloys with a mass constant of tungsten of 75% increases with increase in temperature as a result of utilization of a certain ductility margin of the brittle material.Translated from Poroshkovaya Metallurgiya, No. 6(330), pp. 93–100, June, 1990.     

Investigation of the heat resistance and thermal stability of micaceous ceramic materials with additions of boron nitride

Conclusions On the basis of complex investigations it has been established that Brand UMB-5KT materials, having a high heat resistance and satisfactory thermal stability, can be recommended for use in the flowthrough parts of high-head compressors, with a temperature of the gas flow equal to 600–700°C, and in certain types of turbines with a working temperature up to 950–1000°C.It has been established that the requirements for densified materials are most fully satisfied by Brand UMB-5KT material with 4–8% boron nitride.Special graphite K70/30-3 and aluminum-asbestos-graphite layers have sufficient heat resistance only up to 500°C, and cannot be recommended for long-term operation at higher temperatures.Deceased.Translated from Poroshkovaya Metallurgiya, No. 9 (81), pp. 80–86, September, 1969.     

Thermodiffusional treatment of chromium carbide hard metals

Conclusions It has been established that the cementing phases of P/M chromium carbide and titanium carbide hard metals can be superficially hardened by thermodiffusional impregnation with phosphorus. Treatment of these alloys for 3–7 h at 1000°C in an alumina filler containing 30–70% of nickel phosphide and subsequent 1-h annealing at 400°C increase the surface hardness of their binder phases by 1.5–3 GPa. Thermodiffusional treatment doubles the wear resistance of KKhN35 alloy operating under hydroabrasive wear conditions.Translated from Poroshkovaya Metallurgiya, No. 12(240), pp. 69–73, December, 1982.     

Addition of vanadium to silicide master alloys for plasma-deposited coatings

Conclusions An investigation was carried out into the effect of vanadium on the structure and phase composition of some alloys of the Si-Ti-Cr system. The microstructure of resultant alloys is the same as that of similar vanadium-free materials. Vanadium is concentrated in the refractory phase, entering into the composition of a complex (Cr, Ti, V)Si₂ disilicide. The remaining structural components are, as in the vanadium-free ternary alloys, free silicon and a eutectic. A study was made also of the effect of vanadium on the oxidation kinetics of alloys of the Si-Ti-Cr system exposed for 100 h to air at 1300C. Alloying with vanadium substantially slows down the rate of oxidation of these alloys and changes the law of oxidation from parabolic, characterizing the ternary alloys, to logarithmic for the vanadium-containing alloys. The 100-h rate of oxidation of an alloy of optimum composition at 1300C is 0.04 mg/cm² · h. The optimum particle size of Si-Ti-Cr-V alloy powders intended for the application of coatings by gasothermic spray-deposition has been established.Translated from Poroshkovaya Metallurgiya, No. 5(233), pp. 46–50, May, 1982.     

Oxidizability of materials based on TiC and TiN at elevated temperatures

Conclusions The addition of titanium nitride and niobium carbide to the alloys based on TiC with the nickel-molybdenum binder (TN type) increases their oxidation resistance in air at high temperatures (1173–1273°K). The alloys based on the titanium carbide and nitride and alloyed with the niobium carbide with the nickel-molybdenum binder (NTN) have higher oxidation resistance in air than the commercially produced TN20 and T15K6 alloys.The equations of the kinetic curves of oxidation in air of the TN20 and NTN alloys were derived; at temperatures of 1173 and 1273°K, the curves are almost linear, starting at a holding time of 10 min.Translated from Poroshkovaya Metallurgiya, No. 4(304), pp. 76–78, April, 1988.     

Thermographic study of the contact melting of metals. II. Binary systems with intermediate phases

Differential thermal analysis, metallography, and local x-ray spectral analysis were used to study the heat effects and structural changes occurring upon heating powder mixtures of pairs of elements whose binary phase equilibrium diagrams contain one or more intermediate phases. It was found that contact melting in these mixtures is accompanied by exothermal heat effects in both the solid and liquid states, related to the formation of intermetallic compounds. The temperatures at which strong exothermal effects were observed coincide with the melting temperatures of eutectics in the various systems. The magnitudes of the heat effects are determined by the differences between the exothermal heats of formation of the intermediate phases and the endothermal heats of formation of the liquid phases which formed simultaneously. In the systems containing phosphorous, interaction was controlled by the sublimation of this component. Phosphides were formed at low temperatures as a result of the rapid exothermal reaction of phosphorous vapor with the metals.Institute of Metal Physics, National Academy of Sciences of the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 114–123, July–August, 1994.     

Corrosion resistance of materials of the A1N-Si3N4 system

Conclusions An investigation was carried out into the high-temperature oxidation kinetics of materials of the Si₃N₄-AlN system in oxygen and in air at 800–1400°C. The resultant oxidation products were determined by x-ray phase and petrographic analyses. It has been established that the components exert a mutual influence on their oxidation parameters and that the materials investigated surpass the individual nitrides in oxidation resistance right up to 1400°C.Translated from Poroshkovaya Metallurgiya, No. 1(241), pp. 53–56, January, 1983.     

Heat treatment of exteuded corrosion- and oxidation-resistant alloy fibers and their strength properties

Conclusions It is shown that fibers of corrosion- and oxidation-resistant nickel-base alloys can be obtained by subjecting viscose fibers filled with nickel, chromium, and molybdenum powders to heat treatment. It has been established that alloy formation in such fibers and the mechanical properties attained in them as a result of this operation depend on heat-treatment parameters controlling the amount of residual carbon in the fibers after the thermal destruction of the polymer binder (cellulose) and also on the final sintering temperature. After two-stage heat treatment — preoxidation in air at 400–450°C and final sintering in hydrogen at 1200°C — extruded Ni-20 Cr, Ni-30 Mo, and M-15 Cr-15 Mo alloy fibers (of 12- to 24-m diameters) were found to have ultimate tensile strengths of 40–52 kgf/mm².Translated from Poroshkovaya Metallurgiya, No. 2(218), pp. 1–5, February, 1981.     

Effect of niobium,molybdenum, and tungsten on some properties of iron-boride materials

Conclusions A study was made of some key physicomechanical properties of iron-boride materials alloyed with Nb, Mo, and W. The greatest strengthening effect (_t = 62–75 kgf/mm² at 30–33 HRC) is achieved with iron-tungsten matrices infiltrated, using alloyed powders produced by coreduction from oxides, with eutectic Fe-Mo-B or Fe-Nb-Mo-B alloys. The presence of Fe(Nb, Mo)_xB_y type borides in the eutectic alloys substantially increases the heat resistance of the infiltrated materials.Translated from Poroshkovaya Metallurgiya, No. 2(206), pp. 79–82, February, 1980.