Decomposition of lubricant in compacts from aluminum powder-base mixtures during heating

Conclusions To prevent rupture of interparticle contacts during the burning out of lubricants from compacts pressed from aluminum powder-base mixtures, it is necessary to ensure that the porosity of the compacts is not less than 11–13%. The optimum temperature ranges for burning out lubricants are 240–280 for stearic acid and 300–400°C for zinc stearate. The burning out of lubricants can be performed without the use of a protective atmosphere.Translated from Poroshkovaya Metallurgiya, No. 12(228), pp. 22–25, December, 1981.     

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.     

Methods of increasing the magnetic energy of sintered platinum-cobalt magnets

Conclusions A process has been developed for the production of nonporous sintered platinum-cobalt alloy specimens having a density of 15.1–15.2 g/cm³. A heat treatment schedule is proposed enabling the magnetic energy of such specimens to be increased to 34.2 kJ/m³.Translated from Poroshkovaya Metallurgiya, No. 10 (142), pp. 33–36, October, 1974.     

Permanent magnets from fine iron and iron-cobalt alloy powders

Conclusions It has been established that, to obtain the optimum, magnetic properties in isotropic materials from fine iron and iron-cobalt alloy powders, the powders should be heat-treated for 4 h at a temperature of 280°C and compacted under a pressure of 15–16 kbar. Heat treatment tends to destroy dendritic axes of the second and third orders on the powder particles, heal structural defects, and increase the flowability of particles during pressing, thereby ultimately improving the magnetic properties of the resultant components. The maximum magnetic energy is 4.6 kJ/m³ for isotropic magnets from iron powders and 8.6 kJ/m³ for magnets from iron-cobalt alloy powders.Translated from Poroshkovaya Metallurgiya, No. 10 (142), pp. 61–63, October, 1974.     

Crystal structure and magnetic properties of SmCo5 permanent magnets produced by deformation sintering

Conclusions The phase composition and structure requirements for the optimization of the magnetic properties of SmCo₅ magnets are largely fulfilled in deformation sintering. Deformation sintering of magnets from single-phase powder enables, by ensuring the formation of an optimum structure, magnets of good magnetic properties [B^HC=7.5–8 kOe, (BH)_max=21–22 MG-Oe] to be obtained. The optimum deformation sintering conditions are: deformation load P_d=0.59 GPa; sintering temperature T_d=550°C; and sintering time _d=10–30 min.Translated from Poroshkovaya Metallurgiya, No. 1(217), pp. 75–82, January, 1981.     

High-temperature x-ray equipment for the study of powder and dense objects

Conclusions The existing experimental models of both Debye cameras and camera attachments for x-ray diffraction apparatus enable the atomic and crystal structure of metals and alloys to be studied on heating to very high temperatures (occasionally of the order of 3000°C) in a vacuum of 10^–6 torr. The camera attachments currently produced by Soviet industry are suitable for operation at temperatures up to1500°C in a vacuum of about 10^–4 torr.It is now necessary to organize production in the Soviet Union of attachments with a temperature limit of 2000°C in a vacuum of 10^–6 to 10^–7 torr and high-temperature vacuum Debye cameras designed for temperatures up to 1700°C and a vacuum of 10^–5 to 10^–5 torr.Translated from Poroshkovaya Metallurgiya, No. 5(89), pp. 88–102, May, 1970.     

Properties and structure of niobium carbide heating elements

Conclusions In operation at 1900°C in a carbon-free atmosphere at a residual pressure of 10^–2-2· 10^–3 Pa a heating element of composition NbC + Nb₂C + Nb experiences a steady loss of carbon at a rate of 0.5–1 m/h from its surface, with the formation of a metallic phase. Heating elements of this composition may be recommended for service in vacuum resistance furnaces at temperatures of up to 1900°C, where they can be expected to have a useful life of the order of 1000 h. Niobium monocarbide heating elements operating at 2100–2500°C in a carbon-containing atmosphere under a pressure of 10^–2-2·10^–3 Pa experience no change in phase composition or shape and only minor changes in structure, and possess good thermal fatigue resistance. They can thus be employed in vacuum electric furnaces under these conditions. Long experience (more than two years) with the operation of a laboratory vacuum electric furnace with a niobium carbide heating element in the temperature range 1000–1500°C has demonstrated that the use of niobium carbide heating elements widens scope for new electro-thermal equipment.Translated from Poroshkovaya Metallurgiya, No. 3(231), pp. 92–97, March, 1982.     

Effect of graphite content on the antifriction properties of metallographite materials

Summary Metallographite materials containing not more than 50 vol.% graphite can be used for rubbing-friction applications at high velocities in conditions of limited lubrication. Further increase in the graphite content sharply reduces the strength of the material.With increase in the friction rate and loading, the coefficient of friction diminishes. This tendency occurs with increase in the graphite content in the structure, when a reduction in the strength of the material contributes to an increase in the wear and the growth in friction coefficient owing to the development of dispersion in the material being rubbed.The metallographite materials investigated, containing graphite in the range 50–90 vol.% under dry friction conditions,have a high coefficient of friction (of the order of 0.22–0.40) which means that they cannot be recommended as antifriction materials.In the case of operation with lubricant the metallographite materials can operate as antifriction materials with friction coefficients of 0.03–0.06 at velocities of up to 50 m/sec and with loads of up to 3.3–3.8 kgm/cm² · sec (PV=165–195 kgm/cm² · sec).     

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.     

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.     

Wear-resistant P/M titanium carbide - iron coatings

Conclusions In thw work described the electric contact sinter-bonding process was employed for applying, to type 45 steel, TiC-iron composite coatings exhibiting high hardness (up to 550 HV), low porosity (0.45%), and good adhesion to their bases (up to 12 · 10⁷ N/m²). The abrasive wear resistance of the materials of these coatings proved to be twice as high as that of quenched type 45 steel. The electric contact s inter-bonding method of application of coatings enables uncomminuted coarse powders to be employed and ensures high rates of coating application (the optimum sinter-bonding time is 0.16–0.18 sec, the weight rate of coating application being 5 kg/h). Coatings applied by the electric contact sinter-bonding method can be employed for building up worn surfaces of components of, e.g., agricultural machines.Translated from Poroshkovaya Metallurgiya, No. 11(215), pp. 39–42, November, 1980.     

Atomized copper powders

Conclusions For the first time in the Soviet Union pilot-plant batches of copper powder have been produced by the method of atomization of melts with water under high pressure. The powder produced is characterized by increased apparent density and flowability. The best compressibility (2–6 tons/cm²) is exhibited by the powder after annealing. The compressibility of the powder in the as-atomized condition is slightly poorer (2–4 tons/ cm²), while that of the powder subjected to pickling amounts to 2–3 tons/cm². The atomized powder can be successfully used for pressing in automatic presses, since it ensures stability of weights of batches and dimensions of parts and produces very little dust during pressing.Translated from Poroshkovaya Metallurgiya, No. 5(221), pp. 6–10, May, 1981.     

Titanonitriding kinetics of hard metals

Conclusions TiN coatings have been obtained on hard metals by heating the latter in an environment consisting of nitrogen and a titanizing mixture. The formation and growth of TiN on a preheated hard metal occur as a result of gaseous-phase transport of titanium and nitrogen to the hot surface of the metal. The formation of TiN is a chemical reaction of the first order. The rate constant of the reaction is an exponential function of process temperature, and has the following values: for VK20 alloy K=16.5 exp (–29,330/RT) and for T30K4 alloy K=0.74 exp (–19,260/RT), where R=2 cal/g · mole · degC. The time dependence of the specific weight gain of titanonitrided hard alloys is limited by the amount of the titanium carrier compound in the gaseous phase, which varies according to the exponential law C e^–kt at K=2.3, 3.2, and 3.9 h^–1 for VK20 alloy and K=3.2, 3.9, and 4.6 h^–1for T30K4 alloy.Translated from Poroshkovaya Metallurgiya, No. 6(210), pp. 53–56, June, 1980.     

Electrical resistivity of copper-graphite powder composites

Conclusions An investigation into the variation of the electrical resistivity of copper-graphite composites in the course of their compaction has shown that the electrical resistivity of such materials falls during pressing, fairly rapidly up to pressures of 1.2–1.6 tons/cm² and more slowly at pressures above this level. The electrical resistivity of composites containing copper-clad graphite granules is much less than that of composites with bare graphite. The reason for this is that the former materials have continuous copper skeletons, while the latter have continuous graphite skeletons.Translated from Poroshkovaya Metallurgiya, No. 12 (132), pp. 62–66, December, 1973.     

Influence of zirconium addition on microstructure, magnetic properties and thermal stability of nanocrystalline Nd12.3Fe81.7B6.0 alloy

Effect of Zr addition on microstructure, magnetic properties and thermal stability of Nd12.3Fe81.7B6.0 (x=0-3.0) ribbons melt-spun and annealed was investigated. Magnetic measurement using vibrating sample magnetometer (VSM) revealed that Zr addition was significantly effective in improving the magnetic properties at room temperature. The intrinsic coercivity Hci of the optimally processed rib-boris increased monotonically with increasing Zr content, from 751.7 kA/m for x=0 to 1005.3 kA/m for x=3.0. Unlike the coercivity, the re-manence polarization Jr increased first with Zr addition, from 0.898 T up to 1.041 T at x=1.5, and then decreased with further Zr addition.The maximum energy product (BH)max behaved similarly, increasing from 103.1 KJ/m3 to a maximum of 175.2 kJ/m3 at x=1.5. Microstruc-ture studies using atomic force microscopy (AFM) and transmission electron microscopy (TEM) had shown a significant microstructttre re-finement with Zr addition. The absolute values of temperature coefficients of induction and coercivity were significantly increased with in-creasing Zr content, indicating that Zr was detrimental to thermal stability of the melt-spun Nd2Fe14B-type material.     

Effect of surface-active agents on the properties of a copper powder produced by the autoclave method

Conclusions Carboxyl-containing water-soluble polymers have the strongest influence on the properties of copper powders and are the most effective in reducing their deposits on the inside reactor surface. The optimum SAA consumption rate is 0.003–0.007 g per 1 g of copper. Higher consumption rates intensify the flocculatton of powder particles and increase the carbon content of the powder, which is undesirable, since it makes the latter's subsequent processing more difficult. The carboxyl-containing substances currently produced by industry can be used as SAAs, but, because of their low carboxyl-group content (not more than 45–60%), powders produced in their presence become fairly severely contaminated with carbon owing to destruction of inert radicals. By suitable choice of type of carboxyl-containing SAA it is possible to vary the properties of powders in the following ranges: specific surface 0.02–0.18 m²/g, apparent density 0.9–2.9 g/cm³, mean particle size 20–42m, and flowability 0–2.6 g/sec.Translated from Poroshkovaya Metallurgiya, No. 7(283), pp. 5–8, July, 1986.     

Production of metal powders from melts by centrifugal atomization

Conclusions A study was made of centrifugal atomization of molten metals in argon at low argon consumption rates [(5.2–7.5) · 10^–3 NTP m³/kg]. Output with a single injector attained 30–40 kg/h. Increasing the molten metal head to 0.6–0.8 MPa and decreasing the nozzle diameter to 0.3 mm substantially increased the fineness of the powders. Raising the head still further influenced the effectiveness of atomization to a smaller extent, and decreasing the nozzle diameter to less than 0.3 mm coarsened the powders. Powders of magnesium, aluminum, and Br020 alloy. (20% Sn-Cu bronze) produced by centrifugal atomization of superheated (by about 30–50°K) melts in an inert atmosphere (argon) had spherical particle shapes, which imparted to them good flowability. The oxygen content of the powders was low (less than 0.08%).Translated from Poroshkovaya Metallurgiya, No. 12(276), pp. 5–10, December, 1985.     

Microstructure, Chemical and Phase Composition of Chromium Silicide Diffusion Coatings on Carbon Steels

The microstructure, chemical and phase composition of chromium silicide diffusion coatings on steels 20, 45, U8, and U10 are studied. It is established that the phases Cr²³C⁶ and Cr⁷C³ with a silicon content in them of up to 0.25 at.% form at the surface of chromium silicide coatings. The maximum silicon content at 7% in steels 20 and 45 is observed beneath the carbide layer at a depth of 40–50 µm, but for steel U10 it is 1.9% at the carbide layer-matrix boundary. It is shown that the corrosion resistance of chromium silicide diffusion coatings increases markedly compared with uncoated specimens: by a factor of 15–30 depending on the acid used (H₂SO₄, HCl, H₃PO₄, HNO₃, CH₃COOH). There is also an increase in the cavitation resistance of articles with chromium silicide coatings in water and 3% NaCl solution.__________Translated from Poroshkovaya Metallurgiya, Nos. 1–2(441), pp. 23–30, January–February, 2005.     

Equation of pressing of nickel powders

Conclusions It was shown experimentally that compaction of different nickel powders during pressing in the 29–490 MN/m² range cannot be described by any one of the investigated equations of pressing.In this pressure range pressing of carbonyl powder is described by Lipson's Eq. (4), whereas pressing of enlarged carbonyl and spherical electrolytic powders in the 98–490 MN/m² is described by a polytropic type Eq. (1). The constants involved in these equations were found.Translated from Poroshkovaya Metallurgiya, No. 2 (74), pp. 11–14, February, 1969.     

Densification of porous powder preforms during hot forging. I. Processing lubricant for transverse hot forging

Conclusions Use of lubricants 2, 3, 4 and 5 (Table 1) in transverse hot densification does not prevent buildup formation on the tool. By contrast, the specially developed molybdenum disulfide and graphite base lubricant 1 [13] exhibits excellent friction- and wear-reducing characteristics. With this lubricant it is possible to produce high-density P/M parts of considerable length by transverse hot forging without buildup formation on the tool and with little nonuniformity of deformation in the surface layers of the material.Translated from Poroshkovaya Metallurgiya, No. 1(289), pp. 22–25, January, 1987.