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.     

Deformation of porous sintered titanium-nickel material during uniaxial compression

Conclusions Anomalously high reversible deformation is observed during compressive cyclical deformation of titanium-nickel material, increasing with increase of acting stress. Its value increases with increase of porosity, reaching 0.071.The reversible deformation contribution to the overall relative deformation decreases with increase the acting stress and material porosity.For a porous titanium-nickel material produced by reaction sintering from a powdered mixture, simultaneous occurrence of shape memory and pseudoelastic effects is observed. This is associated with the material inhomogeneity in chemical composition.Translated from Poroshkovaya Metallurgiya, No. 1(253), pp. 76–80, January, 1984.     

Compactability of powdered copper-lanthanum hexaboride composites under hydrostatic treatment

Conclusions The compactability of powder composites copper-lanthanum hexaboride depends largely on the content of additive. Under hydrostatic pressing of powder mixtures the hard inclusions of LaB₆ hinder plastic deformation of copper particles, and thereby they hinder densification of the composite. In sintering of compacts the additive LaB₆ hinders the increase of volume of the specimens; on the other hand, an increase of content of LaB₆ hinders shrinkage of the composite material. In hydroextrusion of sintered compacts, inclusions of lanthanum hexaboride increase the deformation resistance of the material, and that increases the extrusion pressure of the composite, causing the most intense healing of pores.Almost pore-free powder materials of the system Cu-LaB₆ were obtained by hydrostatic pressing at pressures of 800–1000 MPa, sintering in hydrogen at 950°C for 2 h and subsequent hydroextrusion with reduction =80–90%.Translated from Poroshkovaya Metallurgiya, No. 5(353), pp. 18–22, May, 1992.     

Rheological and thermal activation analyses of the sintering kinetics of tungsten powders

Conclusions At any given sintering temperature the relative rate of densificaron of compacts of porosities 29–44% from reduced and atomized tungsten powders of particle sizes 1.5–5m is determined by their capillary pressure, the character of this dependence being close to linear. Densification during sintering is a threshold process, i.e., porous skeletons behave during sintering like Bingham solids. For each sintering temperature there exists a critical pore size above which the rate of densification sharply changes, approaching zero. Assessments of coefficients of Bingham viscosity have shown that at 1600 and 1900°C they are linear functions of sintering time. The energy of activation for the densification of the powders investigated during sintering in the range 1600–2000°C is equal to the energy of activation for grain-boundary self-diffusion in tungsten and amounts to 90 ± 5 kcal/mole.Translated from Poroshkovaya Metallurgiya, No. 10(262), pp. 27–32, October, 1984.     

Processing properties of reduced nickel powders obtained from Cuban ore

Conclusions Nickel powder obtained by reduction from Cuban production waste (PNVK) exhibits good compressibility. Difficult-to-reduce oxide impurities decrease its low-temperature sintering activity compared with carbonyl powder and powder reduced from pure nickel oxides. As a result, for sintering PNVK powder higher temperatures (1100–1200°C) are required.Translated from Poroshkovaya Metallurgiya, No. 5(317), pp. 4–7, May, 1989.     

Effect of sintering conditions on the structure and mechanical properties of P/M aluminum base alloys

Conclusions A magnesium addition promotes densification of Al-Cu alloy specimens sintered for short periods of time in the range 595–635C. Longer sintering at 615 and 635C results in higher specimen porosity. At a temperature above 595C Al-Cu alloys experience severe coarsening. Alloying with magnesium does not significantly affect the structure of the alloys. A magnesium addition improves the mechanical properties of an Al-Cu alloy. The extent to which magnesium alters the mechanical characteristics of heat-treated Al-Cu alloys depends on sintering conditions. The highest strength — 340 MPa and =6% — is exhibited by specimens sintered for 45 min at 595C.Deceased.Translated from Poroshkovaya Metallurgiya, No. 9(297), pp. 29–34, September, 1987.     

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.     

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.     

Cyclic sintering of cermet powders

Summary It is shown that after eleven cycles of sintering under conditions of 1200–800 °C a stage of porosity stability of the sample sets in, and a stage of exhaustion of shrinkage.Cyclic sintering has no advantages over isothermal sintering: with equal temperatures and summary durations during sintering, the magnitude of porosity of the samples is the same.     

Effect of charge fractional composition on high-speed steel powder sintering

The fractional composition of gas-atomized high-speed steel R6M5K5 is studied for its effect on the main features of activated sintering of compacts. A mixture consisting of nickel powder and 30% (wt.) boron is used as an activating addition. It is established that a reduction in average particle size increases shrinkage after sintering, but the dependence of compact shrinkage on fractional composition is different for monodispersed and polydispersed compositions. The maximum size of powder particles for polydispersed compositions has little effect on shrinkage, whereas in the case of monodispersed mixtures there is a marked increase in compact density after sintering with a reduction in particle size. There is a marked increase in density providing closed porosity (90–93%) with a sintering temperature of 1200C, whereas in order to achieve a similar density in the mixture without activator the sintering temperature should be at least 1230C.Translated from Poroshkovaya Metallurgiya, No. 10, pp. 15–20, October, 1992.     

Special features of the production of low-alloy powder steel for structural and antifriction purposes

Conclusions The use of a minimal amount of plasticizer (not more than 0.5%) in the compacted charge and molds with additional drainage make it possible with a single compaction and sintering to obtain highly dense powder products — (7.2-7.3)·10³ kg/m³ — with a compacting pressure of 1000 MPa. Sintering of highly dense powder material ZhGr0,8D2N1 for 3.6 ksec is accompanied by its decompaction in consequence of degassing; extending the sintering time to 10.8 ksec reduces the porosity and improves the mechanical porperties of the products.The combination of the processes of sintering and hardening of rollers made of powder steel ZhGr0,8D2N1 in the plant Degussa makes it possible to obtain great hardness (of the order of 50–53 HRC) of products with a porosity of 5–10% after their cooling in oil. In comparison with existing technological processes, this one is distinguished by high productivity and degree of automation and mechanization; all this meets perfectly the requirements of mass production.Study of the refrigerating capacity of compressors confirmed the possibility of successfully using porous components operating in dynamic regimes under conditions of liquid lubrication, using capillary phenomena and the effect of hydraulic obliteration of fine communicating pore channels for lubricating the surfaces of friction pairs.Translated from Poroshkovaya Metallurgiya, No. 9(297), pp. 42–47, September, 1987.     

Effect of time of sintering on some properties of SmCo5 magnets

Conclusions A study was made of the effect of time of sintering at 1120–1170°C on the magnetic characteristics of SmCo₅ magnets. It was established that the specific magnetization intensity and coercive force of these magnets change appreciably at the beginning of sintering (_s < 5 min), but subsequently vary but little with sintering time. The presence of a low-meltingpoint addition was found to have no effect on the densification rate of SmCo₅ powder compacts. The sintering of SmCo₅ magnets of optimum chemical composition occurs in the solid state irrespective of the method by which the SmCo₅ powder has been enriched in samarium. It is proposed that a Sm₂Co₇ alloy powder be employed for this purpose. Structural equilibrium in particles, which is chiefly responsible for the magnetic characteristics of sintered SmCO₅ specimens, becomes established in a short period of time thanks to a high value of coefficient of diffusion.Translated from Poroshkovaya Metallurgiya, No. 3(183), pp. 70–75, March, 1978.     

Effect of plastic deformation on the fracture energy of powder and cast iron

Conclusions Structurai evolution in powder material is subject to the laws of deformation for cast bcc metals.The fracture energy and cold-brittleness temperature are sensitive to the structural state of the material: change in this predetermines the changes in the fracture energy and cold-brittleness temperature.The nature of the change in fracture energy with degree of deformation is independent of the method of production of the material (cast or powder) and the rolling temperature (below the recrystallization temperature): at low deformations the fracture energy decreases (=0–15%); following this it increases upon formation of a cell structure (=15–30%). With further increase in the degree of deformation (=30–40%) the fracture energy decreases, upon transition to a misoriented cell structure the fracture energy in the rolling plane decreases, but in the transverse plane increases.Translated from Poroshkovaya Metallurgiya, No. 9(345), pp. 74–79, September, 1991.     

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.     

Correlation between the particle size,pore size,and porous structure of sintered tungsten

Conclusions It has been established that the maximum size of pore channel constrictions D₁ is close to the mean size of pore sections in microsections of porous skeletons (-=22–44%) from tungsten powders of 1- to 5-m mean particle size. A rapid method of assessment of an integral fineness characteristic of a tungsten powder is proposed consisting in the determination of the pore size D₁ in a compact (-_c=25–45%), followed by the calculation of the mean size of agglomerated particles with Kozeny's formula. The densification of compacts from tungsten powders of 4-m particle size at sintering temperatures of about 0.6 T_melt is a result of decrease in the number of pores and increase in the equivalent size of agglomerated particles. In this process the mean pore section size determined by the metallographic method remains unchanged during sintering, which corresponds to a statistical model of a porous solid in the rheological theory of sintering.Translated from Poroshkovaya Metallurgiya, No. 12(312), pp. 24–31, December, 1988.     

Kinematics and stress-strain state of metal powder issuing from a hopper device. Part I

Conclusions On the basis of CM hypotheses a mathematical problem has been formulated on determining the flow parameters and stress-strain state of a powder issuing from a hopper under the action of gravity and frictional forces. In the solution of the problem incompressibility conditions, equations of motion, and kinematic boundary conditions are satisfied absolutely, while relationships between stresses and deformation speeds having a physical meaning (model of the medium, friction laws) are satisfied approximately by the mismatch minimization method.Translated from Poroshkovaya Metallurgiya, No. 9 (285), pp. 19–22, September, 1986.     

Production and properties of constructional parts from copper and copper alloy powders. A review

Conclusions Conventional methods of manufacture enable constructional copper alloy parts to be produced with a porosity of 10–15%. However, such parts do not exhibit high electrical conductivity and corrosion resistance, good brazing qualities, and stability of properties with time and at ambient temperature fluctuations. To improve their characteristics, it is necessary to reduce their porosity to not more than 3–5%. This can be achieved by employing high-energy methods of densification, in particular hot and cold forging. There is therefore an urgent need to study the processes of deformation of sintered blanks, determine optimum chemical compositions of materials, and develop methods of determining optimum blank sizes and shapes for forging.-Brasses are ductile at room temperature, but at 500–700°C they become less ductile than -brasses. At temperatures above 500°C the latter are less strong and hence more ductile than at room temperature. To obtain the best results, parts from -brass powders should be produced by cold forging and those +-brasses by hot forging. For hot forging it is best to use compacts from powders with a zinc content of 32–38%, which at room temperature are of the -modification and possess good formability. After heating for forging the -phase (an unordered solid solution) appears in their structure, which improves the workability of compacts in the hot state. Under these conditions their hightemperature ductility increases twofold. Hot-forged parts are also amenable to heat treatment (aging).Translated from Poroshkovaya Metallurgiya, No. 3(231), pp. 44–53, March, 1982.     

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.     

Diffusion processes in the sintering of nickel alloy powders with spherical particles under pressure

Conclusions Hot gasostatic pressing and subsequent annealing at 1200C result in the formation of 160–200-m diffusion zones between particles, which extend over practically the whole particle widths. During sintering under conditions of hot hydrostatic pressing, which is characterized by a shorter period of annealing at any given temperature and pressure, the widths of the diffusion zones after sintering and annealing attain 50–65m. The optimum diffusion zone width in the sintering of particles making good contact with one another (pure and even surfaces) is about 30–40m. However, the presence of oxides, carbide phases, and more complex compounds on the surfaces of particles substantially increases the optimum width of this zone. In such a case the optimum width is determined by the need for diffusion to cross interparticle contacts with diffusion-inhibiting barriers. In view of this, for particles of the nickel alloys investigated the optimum diffusion zone width may be taken to be 100m. At this width there are no areas in which the diffusion zone width is less than 40m, i.e., the minimum thickness at which strong bonds can be expected to form between particles.Translated from Poroshkovaya Metallurgiya, No. 5(233), pp. 38–41, May, 1982.     

Cold extrusion forging of sintered porous materials

Conclusions Experiments have confirmed the validity of an arbitrary division of the back extrusion process of a porous blank into two consecutive stages: I) densification of porous material under the ram face to some and density and II) flow (back extrusion proper) of the densified material into an annular gap. During the deformation of blanks of starting densities equal to or greater than their threshold values the extrusion process, as in the case of incompressible (bulk) materials, takes place in a single stage — the flow stage. In cases where ₀ < _t the maximum densification pressure of a porous material and the extrusion pressure, which is equal to it, are virtually independent of the starting blank density; the parameter determining these pressures is the threshold density, which depends on the magnitude of transverse strain. Optimum power and force conditions prevail when blanks of starting density equal to the threshold density are used. In the forging of iron powder blanks of this density the extrusion pressure is 20% less than with bulk St. 10 steel. Analytical expressions have been derived enabling the power and force parameters — pressure and work — in each stage of the extrusion forging process of porous sintered materials to be determined.Translated from Poroshkovaya Metallurgiya, No. 11(215), pp. 28–34, November, 1980.