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.     

Hot pressing and vacuum sintering of fine titanium nitride powder

Conclusions Increasing the specific surface of titanium nitride from 18 to 90 m²/g lowers the initial recrystallization temperature of loosely poured powder from 1300 to 600°K. The temperature at which blanks attain practically 100% density in the hot pressing of finely divided titanium nitride (a starting powder particle size of 0.05–0.07 m) is 1600°K, which is 500–700°K below the temperature level of full sintering of relatively coarsegrained powders (a particle size of about 0.5 m). At hot-pressing temperatures above 1800°K a fall in the density of sintered compacts is observed, which is apparently attributable to the beginning of nitrogen evolution from the nitride and also to the formation of microcracks. In vacuum sintering without a plasticizer, crack formation lowering the density of specimens by 3–4% is characteristic of the whole sintering temperature range. The grain size in hot pressing and vacuum sintering is practically the same, being determined chiefly by the sintering temperature and time. At the maximum specimen density the maximum grain size is 20 m.Translated from Poroshkovaya Metallurgiya, No. 12(204), pp. 27–32, December, 1979.The authors wish to thank V. I. Berestenko, T. N. Miller, and D. I. Medvedev for the provision of titanium nitride specimens.     

Structural state and mechanical properties of the material in the sialon-titanium nitride system after radiant heating

Conclusions Short-term radiant heating of the material of the Sialon-titanium nitride system in the temperature range 1230–2300°C is accompanied by oxidation of the titanium nitride with oxidation of rutile and titanium oxynitride (the lattice spacing of these compounds increases with increasing temperature) and also by the breakdown of '-Si₃N₄ to -Si₃N₄ and '-phase with a higher aluminum and oxygen content. The formation of rutile reduces the hardness of the material whereas formation of the oxynitride increases this parameter. A liquid phase consisting mainly of silicon and titanium disilicate appears on the surface of the specimens at temperatures above 1500°C. The material retains satisfactory strength in air at temperatures of up to 1200°C.Translated from Poroshkovaya Metallurgiya, No. 5(305), pp. 60–66, May, 1988.The authors are grateful to V. V. Kovylyaev and V. V. Traskovskii for help in the experiments.     

Electrical resistivity of hot-pressed TiC-SiC-C composite materials

Conclusions In hot-pressed TiC-SIC-C materials the effect of the carbon phase manifests itself in anisotropy of electrical resistivity and in the existence of an inflection point on the electrical resistivity vs temperature curve in the range 900–1200°K. The addition of silicon carbide is responsible for the high electrical resistivity of the materials. At high silicon carbide contents the presence of free carbon inhibits the process of reduction of the fraction of titanium carbide contributing to electrical conduction by the composite material. This results in a nonunique character of electrical resistivity vs composition curves.Translated from Poroshkovaya Metallurgiya, No. 11(239), pp. 44–49, November, 1982.     

Interfacial reaction and mass transport of the components in the Al2O3-TiN system during sintering

Conclusions Results of x-ray phase analyses have shown that Al₂O₃-TiN composites produced by nitrogen and vacuum heat treatment and hot pressing retain a two-phase structure at temperatures of up to 2300°K. The changes exhibited by the Al₂O₃ and TiN lattice parameters may be indicative of oxidation and subsequent dissolution of the resultant titanium oxides both in alumina and in titanium nitride. The extent of this reaction depends on the method and conditions of heat treatment.Translated from Poroshkovaya Metallurgiya, No. 11(275), pp. 32–38, November, 1985.     

Structural studies of ceramics based on detonation-wave-treated graphite-like boron nitride

The formation of a structure during pressureless sintering of graphite-like boron nitride (BN) powders pretreated in detonation waves was studied. The treated powders contained 10–12% wurtzite BN phase and 2–3% sphalerite phase. During sintering at just 1200 °C a reverse transformation from dense BN phases to graphite-like phases and primary recrystallization of highly fragmented BN_g occur as a result of the pretreatment. Accretive recrystallization of BN_g begins at 1500 °C and at T=1700–1950 °C platy grains with a size of 1–3 µm are formed in the developed surface. At 1700 °C the density of the specimens reach 0.95 of the theoretical value. The specimens produced at 1950 °C have a higher compressive strength and radiation resistance than do those made without pretreatment.Deceased.Institute of Materials Science, Ukrainian Academy of Science, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5/6, pp. 75–80, May–June, 1995.     

Purification of Aluminum Nitride Powder with Heat Treatment in Hydrogen

Thermodynamic modelling is provided for heat treatment of AlN powder in a hydrogen atmosphere. According to the results of modelling treatment of AlN containing impurities of O, C, S, Si, Fe, and Ti in a hydrogen atmosphere at a pressure of 0.2 MPa and at 1200–1500 K should lead to purification of nitride from S, Si, and C. It is recommended that purification is not carried out below 1300 K.__________Translated from Poroshkovaya Metallurgiya, Nos. 1–2(441), pp. 112–116, January–February, 2005.     

Reaction between carbon fibers and nickel through a zirconium nitride or titanium carbide diffusion barrier

Conclusions Carbon fibers in contact with nickel suffer a pronounced loss of strength at temperatures above 600°C as a result of surface attack by the nickel (at temperatures of 800–900°C and treatment times of 10–20 h) or recrystallization (during heating for more than l h at 1000°C). There is no unique correlation between fiber structure and strength. A zirconium nitride coating fails to prevent carbon fibers from reacting with nickel. A titanium carbide coating reduces, even at high temperatures, the strength loss experienced by carbon fibers by decreasing the rate of dissolution of the material of the fibers in nickel and by slowing down the fiber recrystallization process.Translated from Poroshkovaya Metallurgiya, No. 7(175), pp. 32–35, July, 1977.     

Carbidization of spherical titanium particles in a solid-liquid state

Conclusions A mathematical model of the carbidization process of titanium in a solid-liquid state and optimum conditions of carbidization of titanium are proposed. Data yielded by model experiments are in qualitative agreement with results of calculations. An investigation, involving microhardness measurements on specimen sections, was carried out into the carbidization kinetics of spherical titanium specimens at temperatures of 2073–2573°K.Translated from Poroshkovaya Metallurgiya, No. 9(249), pp. 28–33, September, 1983.     

Stability of refractory compounds in fused basalt

Summary A study was made of the reaction of titanium, zirconium, niobium, molybdenum, and tungsten carbides, aluminum, zirconium, and silicon nitrides, titanium, zirconium, chromium, and molybdenum borides, molybdenum disilicide, chromic oxide, and refractories based on silicon nitride and carbide with molten basalt at a temperature of 1400°C. It has been established that molybdenum disilicide exhibits the highest stability in molten basalt.Translated from Poroshkovaya Metallurgiya, No. 2 (50), pp. 47–49, February, 1967.     

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.     

Effects of conditions of preparation on the superconducting properties of niobium nitride

Conclusions Niobium nitride produced by nitriding niobium wire is brittle, which makes it unsuitable for many practical applications. By comparison, nitride specimens produced by nitriding niobium powder compacts of 20% porosity (treatment under a nitrogen pressure of 5 atm for 3 h at 1400°C) seem to hold considerable promise. The superconducting characteristics attainable with such specimens are T_c=15.4°K and T= 0.1°K.Translated from Poroshkovaya Metallurgiya, No. 12 (144), pp. 76–78, December, 1974.     

State of oxygen in fine titanium nitride powders

Conclusions Oxygen in fine titanium nitride powders produced by the plasma-chemical method can exist in three forms — replacing the nitrogen in the nitride, forming oxide films, and adsorbed on the surface. In the course of the plasma-chemical synthesis of titanium nitride 1–5 wt. % of oxygen from the starting reactants becomes statistically distributed throughout the particles, forming homogeneous titanium oxynitrides. Contact with humid air results in the formation, on the surfaces of small particles, of thin ( 1-nm) oxide films characterized by activation-type conduction and in adsorption of some oxygen. The composition of the main volume of each particle remains unchanged.Translated from Poroshkovaya Metallurgiya, No. 9 (225), pp. 6–9, September, 1981.     

Kinetics of hafnium nitride formation in nitrogen and ammonia streams

Conclusions A study was made of the kinetics of hafnium nitride formation in nitrogen and ammonia streams. It was established that the kinetics of the reaction of hafnium powder of 30- particle size with nitrogen and ammonia is described by a pseudo-topokinetic equation. Calculations have shown that, owing to the formation and subsequent decomposition of intermediate products (nitrohydrides), the rate of nitride formation is less in ammonia than in nitrogen. It was found that the range of homogeneity of hafnium nitride is represented by the compositions HfN_0.80-HfN_1.0. No signs of formation of a lower hafnium nitride (of the Me₂N type) were detected in the temperature range 600–1200°C.Translated from Poroshkovay Metallurgiya, No. 9 (141), pp. 6–10, September, 1974.     

Conditions of formation of lanthanum and samarium nitrides

Conclusions An investigation was carried out into the kinetics of the reactions of solid lanthanum and samarium specimens with nitrogen and ammonia. On the basis of data obtained in the present and earlier studies an examination is made of the mechanism operative in the chemical reactions of rare-earth metal nitride formation in nitrogen and ammonia streams and of optimum conditions for the bulk synthesis of rare-earth metal nitrides. It has been established that synthesis in nitrogen enables lanthanum and samarium nitrides to form at temperatures closeto T_m of the metals, i.e., 900 and 1100°C, respectively. The nitration of solid metal specimens in an ammonia stream is accompanied by the formation of intermediate products — hydrides, whose thermal stability leads to a significant difference in the synthesis temperatures of lanthanum and samarium nitrides (600–700 and 1200°C, respectively).Deceased.Translated from Poroshkovaya Metallurgiya, No. 8(200), pp. 71–78, August, 1979.     

Wettability of aluminum nitride by molten metals

The sessile drop method has been used with a vacuum of 2.10^–3 Pa to examine the wettability of aluminum nitride by fourteen molten pure metals as well as the effects of adding chromium, vanadium, niobium, tantalum, and titanium to the liquids on the wetting angle in systems containing aluminum nitride and liquid tin, copper, and germanium. Aluminum nitride is wetted only by molten silicon and aluminum. Out of the elements examined, titanium is the most adhesion-active for this ceramic. The results are examined from the viewpoint of thermodynamic wetting theory.Materials Science Institute, Ukrainian Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 74–78, May—June, 1996. Original article submitted June 29, 1994.     

Preparation of powders of titanium boronitrides in superhigh-frequency discharge plasma

Conclusions It is shown that alloys of the system titanium-boron-nitrogen can be prepared by the simultaneous reduction and nitriding of titanium and boron chlorides during their very brief residence time in a plasma type chemical reactor. The dissolution of about 6 wt.%of boron in titanium nitride lowers the temperature coefficient of electrical resistivity of titanium boronitrides by a factor of 2.5 compared with pure titanium nitride.Translated from Poroshkovaya Metallurgiya, No. 11 (131), pp. 6–9, November, 1973.     

Thermal and electrical properties of porous titanium

Conclusions The thermal conductivity, coefficients of thermal expansion and thermo-emf, and electrical resistivity of porous titanium have been determined in the temperature range from ambient to 800–1200°C. The effect of specimen porosity on the character of the thermal and electrical conductivities of porous titanium has been established. A study has been made of the effect of the- phase transformation on the electrical conductivity and thermo-emf of porous titanium. The thermal conductivity may be evaluated from the electrical conductivity with the aid of an experimentally established value of Lorentz number.Translated from Poroshkovaya Metallurgiya, No. 8 (92), pp. 35–38, August, 1970.     

Investigation of the magnetic properties of strip made from iron powder

Conclusions Strip with a porosity of 25%, when sintered at a temperature of 1200°C in hydrogen with a dewpoint of –30°C, is refined with respect to carbon and oxygen. At the lower sintering temperatures of 1000 and 1100°C, the carbon content is reduced to 0.03–0.02%; the quantity of not easily reducible oxides remains unaltered.With regard to the kinetics of grain growth, nonporous strip made from iron powder may be classed with steels which are coarse-grained by their prehistory.Porosity substantially affects the value of coercivity. Each 2% of pores increases the coercivity approximately by 0.1 oersted.If temperatures of 1200°C and above, with holding times of 2–3 hr are used for presintering, and temperatures of 900–1000°C for the final heat treatment of the nonporous strip, the magnetic properties of the strip can satisfy the requirements of GOST 3836-47 for low-carbon, electrical engineering thin sheet steel.