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.     

Manufacture of antifriction parts for a power saw by the powder metallurgy method

Conclusions The part, bush, of the Druzhba power saw manufactured out of cermet alloys has better service properties than the bush made of LS 59-1. When producing the bushes of the hinged frame of the Druzhba power saw it is best to use iron-graphite material ZhGr1.5, which permits producing parts with high service properties and effects an economy when manufacturing by the powder metallurgical method of about 10,000 rubles annually.Translated from Poroshkovaya Metallurgiya, No. 7 (67), pp. 95–98, July, 1968.     

Choice of grade of ferric oxide and hot-pressing conditions for the preparation of high-permeability manganese-zinc ferrites

Conclusions In the formulation of new ferrite materials for magnetic head cores starting raw materials and conditions of preparation of ferrite powders must be chosen with regard to the conditions prevailing in the hot-pressing process. The differences in the properties of the two hot-pressed ferrite batches investigated are attributable to the difference in the activities of the ferric oxide grades used (MM2 and SP) in the solid-phase synthesis and sintering reactions. Use of grade MM2 ferric oxide in the preparation of ferrite powders and hot pressing and annealing under optimum conditions (psp = 40 MPa, T_hp = 1663°K, _ih = 2.4 ksec, T_ann = 1613°K and _ann = 7.2 ksec) enable specimens to be obtained combining high values of initial magnetic permeability (_in = 10,000) and density.Translated from Poroshkovaya Metallurgiya, No. 2(230), pp. 79–82, February, 1982.     

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.     

Sintering of constructional powder materials by high-frequency currents

Conclusions The results are presented of a study into the possibility of sintering powder materials of complex composition by means of high-frequency currents. Relationships have been found between the critical temperature of specimens and the graphite and chromium contents of the starting charge. The microstructure has been investigated, and the mechanical properties determined for specimens of various compositions sintered at the critical temperatures.Presented to the Fifth Republican Scientific-Technical Conference on Powder Metallurgy, Kiev, March 29–31, 1966.Translated from Poroshkovaya Metallurgiya, No. 12, pp. 15–20, December, 1966.     

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.     

Sintering of boron carbide containing small amounts of free carbon

Conclusions A study was made of the sintering kinetics of grade ch. boron carbide, technical boron carbide cleaned of impurities, and boron carbide synthesized from the elements. An investigation was carried out also into the reactive sintering of a mixture of boron and carbon black. Reactive sintering fails to yield dense parts in boron carbide. The best sinterability is exhibited by a fine technical boron carbide powder cleaned of free carbon and other contaminants. Parts with a porosity of less than 5% can be produced from such a powder by pressing and subsequent sintering. However, it is not the presence of free carbon that controls the sintering behavior of boron carbide, since pure and synthesized boron carbide powders containing no free carbon are characterized by poor sinterability. The high activity of the technical powder is probably linked with the presence of structural defects and stresses generated in the course of its manufacture, during milling and quenching. The annealing spectrum of these defects covers a wide temperature range, and consequently the energy of activation for the densification of boron carbide steadily grows with increase in shrinkage.Translated from Poroshkovaya Metallurgiya, No. 7 (151), pp. 27–31, July, 1975.     

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.     

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.     

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 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.     

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.     

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.     

Structure,mechanical properties,and special features of failure of nickel-based detonation coatings

Conclusions Alloying nickel with chrome, aluminum, and boron, as well as the variation of the spraying conditions makes it possible to control purposefully the composition, structure, and properties of the detonation coatings. In alloying nickel with aluminum and chrome, the strength properties of the coatings are fully utilized at thicknesses not greater than 0.25 mm. The adhesion strength of these coatings to the titanium substrates is 35–150 MPa, to steel substrates 20–120 MPa, in the thickness range 0.1–0.3 mm. The ductility properties of the coating are utilized only to 40–60% in comparison with the dense material of the same composition. The ductility of the coatings is reduced most markedly by additions of aluminum and boron, whereas the addition of chrome causes the smallest reduction.Alloying nickel with chrome increases its cohesion strength and heat resistance, alloying with aluminium reduces heat resistance, creep strength, and wear resistance, and combined alloying with aluminum and boron reduces wear and heat resistance.The soft conditions are optimum for depositing coatings on titanium substrates. Under these conditions, particles are only welded without high deformation, whereas medium conditions with moderate temperature and kinetic parameters are optimum for depositing the steel components. This gradation is caused by the susceptibility of the titanium alloys to brittle failure in the presence of surface defects and cracks and also by a large difference in the coefficients of thermal failure of the materials of the coating and the substrate and higher chemical activity of titanium.Failure of coatings of alloyed nickel alloys takes place by means of intergrain delamination which is preceded by plastic deformation of the materials of the coating and the substrate. Only simultaneous alloying with aluminum and boron results in a slightly different fractographic pattern because these additions embrittle the material of the coating.Translated from Poroshkovaya Metallurgiya, No. 7(343), pp. 53–61, July, 1991.     

Influence of the chemical composition and of heat-treatment regimes on the properties of the powder material 29NK

Conclusions A distinguishing feature of the production of the powder material 29NK with specified level of CLTE from powder components is the smaller amount of cobalt contained in the mechanical mixture compared with the amount required for the cast alloy. This has obviously to do with the more intense evaporation of nickel and iron in the process of structure formation occurring under conditions of lengthy vacuum sintering at 1280–1300°C.The influence of the grain size distribution of the component powders and of the sintering regimes on the CLTE of the powder material 29NK was established. It was noted that reducing the maximal grain size to 50–63 pm and simultaneously extending the sintering time to 20 h ensures the required value of the CLTE; this is due to the complete termination of the process of structure formation and the production of material with the specified chemical and phase composition.The special features of fracture by impact bending of specimens of the powder material 29NK were examined. It was shown that there is no correlation between the rupture work Ar and the number and area of oxide inclusions; this is connected with pore nucleation in the regions of intense plastic flow, independently of the connection with particles of inclusions. It was established that Ar is affected by structural inhomogeneities connected with the production technology. It was shown that Ar is dependent on the area of the bands of in-homogeneity which cause crack nucleation.Translated from Poroshkovaya Metallurgiya, No. 12(300), pp. 45–52, December, 1987.     

Effect of porosity on microplastic deformation of iron base powder materials

Conclusions By the method of subjecting beams of uniform strength to bending tests we measured the modulus of elasticity of sintered iron base materials in a broad interval of porosity (0–40%).With porosity from 10 to 25% the curves of microyield are reduced to a single curve of strain-hardening of compact material by normalization to the coefficients K = E_o/E_gq.Deviations from similarity are found in the region of small (<10%) and high (>25%) porosity. The authors bring these effects into connection with the change of the structural state of the material.In the region of microplasticity (_pl = 10^–6-10^–3) a characteristic feature of iron base sintered materials with porosity of less than 25% is parabolic strengthening: ^1/2. An analysis of the curves of microyield in coordinates -^1/2 revealed that strengthening proceeds in stages.For materials with porosity of more than 25% the yield stress and strain are correlated by a dependence of the type ln .Translated from Poroshkovaya Metallurgiya, No. 7(319), pp. 79–84, July, 1989.     

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.     

Effect of intermediate sintering temperature on the properties of domestic air conditioner components produced by double pressing

Conclusions In the pressing of parts of high density the factor of degassing of the charge being pressed acquires special significance. In the designing of die sets for pressing parts of large size and complex configuration particular attention should be given to choice, with allowance for the properties of the charge, of optimum clearances between moving forming elements. It may be desirable to incorporate in the design of die sets auxiliary elements forming additional drain clearance lines. The process of pore formation in sintered materials commences during pressing, continues during intermediate sintering as a consequence of evaporation of plasticizer and degassing of compacts, and comes to an end at a high temperature. The rate of heating of compacts can affect the density, chemical composition, and strength properties of sintered parts. For ZhGr0.8 and ZhGr0.65D2N1 rollers heated for 40 min under isothermal conditions, the optimum intermediate sintering temperature may be taken to be 900 ± 20C.Translated from Poroshkovaya Metallurgiya, No. 10(274), pp. 106–109, October, 1985.     

Properties of R6M5 steel powders of various particle sizes and the structure of the steel in the sintered condition

Conclusions An investigation was carried out into the effect of particle size of powders produced by comminution of R6M5 high-speed steel waste (swarf) on their compressibility and sinterability. It is shown that with decreasing mean particle size the compressibility of such powders deteriorates, but their sinterability improves. The finer the steel powder, the lower is the sintering temperature necessary for the attainment of a given density. Varying the powder particles size brings about marked changes in the microstructure of the steel in the sintered condition. The liquid phase (ledeburitic eutectic) appearing during the sintering of steel powders of different particle sizes varies in form and distribution. With coarse powders (d_m=100 m) the eutectic is similar to that in cast steel, but with powders of small particle size (d_m=22 m) it is finer and evenly distributed throughout the structure in the form of thin lamellae.A 0.85%C-6% W-5% Mo-4% Cr-2% V (nominal composition) high-speed steel — Translator.The authors wish to thank A. N. Nikolaev of the Gorkii Polytechnic Institute for helpful discussion in the experimental part of the work.Translated from Poroshkovaya Metallurgiya, No. 6(234), pp. 9–15, June, 1982.     

Methods of raising the density of parts from materials based on boron and aluminum nitrides

Conclusions Parts from aluminum-nitride powder with a particle size of about 40 can be produced by a technique consisting of cold pressing, sintering, filling of the pores with Al₂O₃ by impregnation with aluminum monophosphate, and final high-temperature heating. Boron-nitride parts with a porosity approaching the level of closed porosity can be obtained by vacuum pressing and subsequent high-temperature heating in a nitrogen atmosphere.Translated from Poroshkovaya Metallurgiya, No. 12 (72), pp. 22–25, December, 1968.