Influence of grain size and porosity on the high-temperature friction of titanium carbide

Conclusions It was established that in friction of a TiC-TiC pair in vacuum the coefficient of friction at 250C and the wear rate at 1250C are practically independent of grain size. At higher temperatures these characteristics have an inverse relationship to grain size.It was shown that with an increase in porosity both the wear rate and the coefficient of friction increase. With an increase in temperature the influence of porosity on the wear rate decreases.With variations in porosity in the 1–10% range, in grain size in the 1–50 m range, and in temperature in the 20–1500C range the wear rate changes within limits of 10–45% and the coefficient of friction within limits of 3–35%.Translated from Poroshkovaya Metallurgiya, No. 9(297), pp. 56–61, September, 1987.     

Some mechanical properties of silicon carbide fibers

Conclusions Electroerosion of silicon carbide fibers in contaminated mercury electrical contacts decreases their strength by between one-half and two-thirds. During prolonged holding under load at room temperature the creep of silicon carbide fibers is close to zero, while at 1173°K l/l 10^–7 l/day. X-ray structural analysis of silicon carbide fibers annealed for (1.8–10.8)·10³ sec in a hydrogen atmosphere at 1273–1773°K and for (3.6–18)·10³ sec in a nitrogen atmosphere at 1773–1973°K revealed no recrystallization in (4–5)·10^–7-m-thick layers of polycrystalline SiC deposited from a gaseous phase. A correlation was found between the strength of silicon carbide fibers and the number of flashes forming during their fracture.Translated from Poroghkovaya Metallurgiya, No. 1(253), pp. 55–59, January, 1984.     

Laser chemical production of thin iron films,powders, and fibers from the carbonyl gaseous phase

Conclusions Healing a quartz substrate in a medium of IPC to a temperature above 500 K. by pulsed (> 5·10^–1 sec) radiation of a CO₂ laser with intensity of 50–100 W·cm^–2 yields thin (up to 3 m) iron films at a rate of 2 m·sec^–1 on a surface bounded by the cross section of the laser beam.When the intensity of the radiation is increased to 250 W·cm^–2, the process of decomposition of the IPC spreads to the gaseous phase. Together with intense crystallization of iron on the surface of the substrate (the surface temperature is 1500 K) a finely disperse (0.1–0.3 m) iron powder also forms.Translated from Poroshkovaya Metallurgiya, No. 1(325), pp. 85–89, January, 1990.     

Static and cyclic strength of a uniaxially reinforced material in bending (part 1)

Conclusions A built-up degree of damage =f/f_o 8% has virtually no effect on the static strength of an AD33-B CM operating in air. The arbitrary fatigue limit corresponding to this volume of damage on a basis of 2–10⁵ cycles may be taken to be equal to (0.5–0.55) _t. Accelerated buildup of damage on a basis of 2–10⁵ cycles is observed at _a > (0.5–0.55) _t.Translated from Poroshkovaya Metallurgiya, No. 7 (259), pp. 65–67, July, 1984.     

Copper-gallium alloys containing 18–70 WT.% Ga

Conclusions A study of specimens produced by the powder metallurgy technique has demonstrated that six stable phases occur in the system gallium-copper at room temperature, namely, (31.5–33.8 wt.% Cu), ₃ (55.5–58.5 wt.% Cu), ₂ (61–62 wt.% Cu), ₁ (63–70 wt.% Cu), ₁ (77 wt.% Cu), and an solid solution of gallium in copper (80.5–100 wt.% Cu).Translated from Poroshkovaya Metallurgiya, No. 4 (124), pp. 70–74, April, 1973.     

Dependence of the mechanical properties of a P/M nickel alloy on deformation temperature and rate

Conclusions At room temperature the strength of ZhS6 nickel alloy produced by the granule metallurgy method is 1.5 times higher and its plasticity 3–4 times higher than those of the same alloy produced by the standard casting process. The P/M alloy remains superior in strength to the cast alloy up to temperatures of the order of 750–800°C, above which the strength characteristics of the P/M alloy fall below the level of properties of the cast material. The deformation of the P/M alloy varies in character depending on testing temperature, and three types of specimen fracture are possible: brittle fracture without waist formation in the temperature range 20–700°C, fracture with waist formation at 700–1000°C, and plastic deformation along the whole specimen length above 1000°C. At temperatures of 1000–1150°C the P/M alloy exhibits superplasticity: At low rates of deformation its elongation attains several hundred percent when the load is about 0.1_0.2. The elongation of the specimen, load applied, and type of stress-strain diagram depend to a large extent on the rate of deformation: As the latter is decreased, _e sharply grows and the load diminishes.Translated from Poroshkovaya Metallurgiya, No. 1(205), pp. 76–80, January, 1980.     

Some features of the formation of A1N during the reduction-nitriding of ultrafinely divided alumina

Conclusions A study was made of the process of carbothermic reduction-nitriding of ultrafinely divided alumina in the temperature range 1200–1450C. It was established that the carbothermic reduction-nitriding of ultrafinely divided alumina is accompanied by the formation of intermediate oxycarbide and oxynitride phases. This is a result of the alumina reduction process having a stepwise character and of the formation of solid solutions in the AI-O-N system. It is shown that the resultant aluminum nitride is in the form of polycrystalline particles. The sizes of the particles and of the grains in them are 1–3 and 0.01–0.2 m, respectively. With rise in nitriding temperature, the particles decrease and the grains increase in size.Translated from Poroshkovaya Metallurgiya, No. 11(263), pp. 14–19, November, 1984.     

Ceramic coatings of high thermal-cycling resistance

Conclusions A single-component ceramic coating produced by plasma-spraying a powder mixture consisting of 85% of 5–30- particles and 15% of 70–110- particles exhibits improved thermal-cycling resistance, because the dispersed inclusions of the coarse fraction present in the coating hinder crack propagation and coating rupture. The chemical identity of the fine and coarse fractions has a beneficial effect on the properties of the coating.Translated from Poroshkovaya Metallurgiya, No. 10 (106), pp. 46–48, October, 1971.     

Electrical and thermal properties of niobium-base cermets

Conclusions Corundum-niobium cermets have temperature of transition into the superconducting state of 6–7°K at metal contents in excess of 20 vol.% and 1–2°K at metal contents of less than 20 vol.%. The volume electrical resistivity of these cermets before the transition into the superconducting state is determined by their metal concentration; it is equal to 1 -m at metal contents of less than 20 vol., and < 10^–2 -m at metal contents of more than 20 vol.%. Studies combining determinations of thermal conductivity and electrical resistivity enable an objective assessment to be obtained of the structure of these materials. The materials investigated were found to have a continuous ceramic phase.Translated from Poroshkovaya Metallurgiya, No. 11(203), pp. 63–65, November, 1979.     

Buckingham-potential parameters and relations between them for solids

Parameters m and n in the Buckingham potential in the form =[U₀mn/(m – n)]{(1/m)Y^–m – (1/n)exp[n(1–Y)]} have been calculated for 79 elements and 35 compounds, which have been compared with data on =c_v/(U₀) and =KV₀/c_v, in which U₀ is the cohesion energy, Y=(V/V₀)_1/3, V a volume with equilibrium value V₀, ... c_v the specific heat, the thermal-expansion coefficient, and K is the bulk elastic modulus. It is found that m is dependent essentially on and n on . These relationships have been approximated, and conclusions are drawn from them about the most reliable input data, particularly K because of the large spread in published values. A study is made on the relation of m and n to the positions of the elements in the periodic system and the electron structures.Institute of Problems of Materials Sciences, National Academy of Sciences of the Ukraine, Kiev. Translated from Poroshkovaya Metallurgiya, No. 5–6, pp. 118–126, May–June, 1994.     

Development of a higher-density pressing technology using gas drainage. II. Device for evaluating the efficiency of gas drainage from molding dies and experimental assessment of factors affecting it

A device designed specifically to determine the efficiency of gas drainage during ejection from a molding die and the intrapore gas pressure in compacts is described. This device was used to study how the morphology of iron powder particles, the size and shape of the molded parts, the compact rate and production run, as well as amount of plasticizer affect the parameters studied. Recommendations are made for developing technologies for pressing high-density briquets.Scientific Industrial Firm Bakkonditsioner. Translated from Poroshkovaya Metallurgiya, Nos. 7–8, pp. 19–26, July–August, 1994.     

Development of a technology for pressing high-density products using gas-draining methods

The factors that hinder the formation of high-density compacts by cold-pressing of powders are considered. The main factors are the gases present in the charge and the technological lubricant introduced to facilitate the work of the press mold. A procedure has been developed for calculating the efficiency of gas drainage from a mold and the pressure in gas pores in the compacts. Recommendations are made for increasing the density of compacts from iron powders by a single cold pressing.Scientific-Industrial FirmBakkonditsioner,Baku. Translated from Poroshkovaya Metallurgiya, No. 5–6, pp. 34–39, May–June, 1994.     

Production and properties of diamond-metal sheet materials

Conclusions The tensile strength of diamond-metal sheet materials bonded with a tin-nickel bronze can be increased by raising the nickel content of the binder, employing aging after quenching and cold working, and decreasing the grain size of the diamond powder. A study was made of the operating performance of diamond disks in the cutting of brittle nonmetallic materials. The size of cleavages on the work materials was found to be 11–21 m at diamond powder grain sizes of 3–20 m.Translated from Poroshkovaya Metallurgiya, No. 11(203), pp. 90–92, November, 1979.     

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.     

Free upsetting of heated porous cylindrical specimens

Conclusions When compacts with = 90–92% are upset, they become more compact up to some critical degree of axial deformation _z, beyond which the mean density in volume practically does not increase, or even decreases. In compacts with = 78–82% density increases in upsetting up to the instant of the appearance of cracks on the lateral surfaces. The permissible degrees of transverse deformation corresponding to the critical values of _z lie within the limits 25–35%.Reduction of the ratio of the height of the compact to its diameter increases compaction and decreases radial deformation for the same values of _z. Deformability of compacts before failure increases with increasing ratio of the height of the specimen to the diameter and with its increasing initial density.Translated from Poroshkovaya Metallurgiya, No. 7(307), pp. 33–37, July, 1988.     

Effect of milling conditions on properties of intermetallic SmCo5 powder

We present the results of a study of the milling process for preparing intermetallic SmCO₅ powder. From the curves we obtained representing the dependence of the particle size distribution and the oxygen uptake on milling time together with the results from x-ray diffraction, we determined the optimal milling times with respect to the required particle size of the SmCo₅ powder 7.7–8.3 m and the permissible oxygen content 2250–2520 ppm.Belgrade University. Translated from Poroshkovaya Metallurgiya, Nos. 5–6, pp. 100–103, May-June, 1996. Original article submitted August 31, 1995.     

Sintering kinetics of tantalum carbide

Conclusions Tantalum carbide sinters at a temperature above 2500C. Decreasing the powder particle size activates the sintering process, but even with a powder of 0.17-m particle size specimens sintered at 2700C have a porosity of 11%. Coarse powders (> 7–8 m) sinter, without densification, at 2000–2200C by a surface self-diffusion mechanism. Fine powders (<7–8 m) undergo densification already at temperatures above 1400C by a diffusion-viscous flow and a volume self-diffusion mechanism during long holding periods and also probably by an activated grain-boundary sliding mechanism in the initial stage of sintering after rapid heating.Translated from Poroshkovaya Metallurgiya, No. 10(238), pp. 16–19, October, 1982.     

Heat treatment of highly dispersed electrolytic iron and Fe-Co alloy powders with a composite coating

Conclusions A necessary condition for improving the magnetic properties of powers is improvement of the metal phase structure, elimination of nonmagnetic impurities, and destruction of a chemisorbed coating. Annealing in hydrogen at 633–653 K makes it possible to retain the main geometric size of particles within the limits 0.8–1.0 m, to reduce dendrites and to increase the coercive force by a factor of 1.5–2 and the residual specific magnetization of iron and Fe-Co alloy powders up to 95 and 105 A·m²/kg, respectively.Translated from Poroshkovaya Metallurgiya, No. 4(340), pp. 74–78, April, 1991.     

Filamentary and Tubular Silicon Carbide Nanocrystals

Filamentary crystals and nanotubes of 3C-SiC containing -SiC are prepared. The nanostructures of SiC are synthesized from a mixture of hydrocarbons, chlorosilane and hydrogen in the presence of iron (Fe(CO)₅) at 1250° C. The average nanofilament diameter is 30 nm. The nanotube diameter ranges from 10 to 200 nm.__________Translated from Poroshkovaya Metallurgiya, Nos. 1–2(441), pp. 3–7, January–February, 2005.     

Assessment of the effectiveness of compaction of ShKh15 steel powders by hot extrusion

Conclusions Hot extrusion enables high-density steel to be obtained from an ShKh15 powder at a reduction = 2.15 (degree of deformation 33%). The strength of P/M ShKh15 steel after extrusion and annealing lies in the range 720–780 MPa, and thus surpasses the strength of the same steel produced by casting (650–700 MPa), while the ductility characteristics of the two steels are comparable.Translated from Poroshkoyaya Metallurgiya, No. 1(289), pp. 25–28, January, 1987.A 1.0% C-1. 5% Cr ball-bearing stell grade — Publisher.Deceased.