“Activity” of powders in the sintering of single-component compacts

Summary A study has been made of the shrinkage characteristics of compacts obtained by pressing: 1) active powders of electrolytic origin, 2) powders thoroughly deactivated by high-temperature annealing, and 3) a mixture of equal amounts of the above two powders. It is shown that the observed shrinkage characteristics can be qualitatively explained by assuming that, in addition to the usual mechanism of deactivation operating during annealing, there is also a mechanism of activity loss resulting from defect migration from active to deactivated particles.Translated from Poroshkovaya Metallurgiya, No. 4 (64), pp. 18–21, April, 1968.     

Phase equilibria in the solidification range of alloys of the Ti-Ru-Ir system

Conclusions The processes taking place during solidification of the alloys of the Ti-Ru-Ir ternary system have been examined for the first time. The results show that the system contains three nonvariant quaternary equilibria with the liquid of the incongruent type: L + + at 2220°C, L + + at 1920°C, and L + + at 1465°C.In the region with the composition 0–50% Ti, the processes take place in the direction to the Ti-Ru side of the concentration triangle where they are also completed at the temperature of the binary eutectic L '+ equal to 1855°C. In the region with the composition 50–100% Ti the processes are completed at 1460°C at the nonvariant point corresponding to the eutectic reaction L + of the Ti-Ir binary system.Translated from Poroshkovaya Metallurgiya, No. 11(299), pp. 72–77, November, 1987.     

Densification of metal powders during heating under high pressures of up to 80 kbar

Conclusions An experimental study was made of the densification of metal powders during heating under pressures of up to 80 kbar. The character and kinetics of densification of powders during heating were found to differ markedly depending on whether the pressure applied to them was higher or lower than the critical pressure. It is demonstrated that the minimum necessary condition for attaining the density of the nonporous metal in the densification of a powder under the critical and higher pressures is the development of thermally activated dislocation motion processes in the range (0.3–0.4)T_m. The densification of powders at pressures below the critical is controlled by particle flow processes, its kinetics being strongly dependent on the applied pressure and temperature.Translated from Poroshkovaya Metallurgiya, No. 11(191), pp. 28–33, November, 1978.     

Calculation of diffusion in a binary powder mixture of metals with limited mutual solubility

Conclusions The case is analyzed of diffusion in a binary mixture of metals whose mutual solubility leads to the formation of two phases, one on the base of each of the metals. A powder-mixture model in the form of two concentric spheres is employed, and it is assumed that the lean component is present in the mixture as spherical inclusions and the rich component as spherical layers. Using formulas of the mathematical theory of diffusion, solutions are derived describing the distribution of concentrations in the spherical inclusions and spherical layers.Translated from Poroshkovaya Metallurgiya, No. 10 (70), pp. 43–46, October, 1968.     

Error in the determination of the particle-size distribution of a powder with a laser analyzer

Conclusions Simple expressions have been obtained from known parameters of a flow-type chamber for estimating errors in laser analyzer measurements of the main numerical particle size distribution characteristics of powders obeying the logarithmic normal law. It is shown that, in spite of marked errors (Fig. 1) in size measurements on single particles whose trajectories are deflected from the laser beam center, it is possible to attain high accuracy in the measurement of numerical particle distribution characteristics by suitable choice of aero or hydrodynamic particle stream focusing [5] (Table 1: maximum error in the determination of the amount of the main fraction in a powder of particle size 3/2 _f = 1.9% at 2_j = 15 and _f = 4.3% at 2_j = 72 m). Without good particle stream focusing, measurements may be very inaccurate (Table 1: _f = 24% at 2_j = 120 m and _f = 55.5% at 2_j = 170 m). The accuracy of laser analyzer measurements grows with increasing curvature (coefficient n) of analyzer calibration characteristics and vice versa. The q/qt relationships obtained may find application in the assessment of errors in particle size analyses of powders with particle distributions differing from the logarithmic normal law.Translated from Poroshkovaya Metallurgiya, No. 12(288), pp. 15–20, December, 1986.     

Thermodynamic properties of alloys of the manganese-silicon system in the ranges of existence of the silicides “Mn9Si9” and “Mn6Si”

Conclusions The Gibbs energy, enthalpy, and entropy of formation of phases based on the compounds Mn₉Si₂ and Mn₆Si at 690–850°C have been determined by measuring the emf's of concentration galvanic cells.Translated from Poroshkovaya Metallurgiya, No. 7(235), pp. 67–70, July, 1982.     

Determining equations for compressible plastic porous solids

Conclusions The scalar properties of a compressible porous solid can be characterized by a pair of equations expressing the dependence of hydrostatic pressure p and tangential stress intensity t on the ratio between the rates of volume change e and shape change , porosity, and parameters characterizing the state of the material of the powder and the porous solid. The p and functions must satisfy Eq. (14), with p being a monotonically increasing limited function of S=e/ and t increasing at S 0, attaining a maximum at S = 0, and decreasing at S 0; at ¦S¦ 0. During the plastic deformation of compressible materials, hydrostatic pressure can affect shear strains, while tangential stresses can lead to volume changes. Together with this form there exists a form of determining equations expressed by the loading surface equation (16) and the relationship (18). In the case of a rigorously convex surface these two forms are equivalent.Translated from Poroshkovaya Metallurgiya, No. 4(220), pp. 17–23, April, 1981.     

The angle parameters of the metal-powder rolling process

Summary The investigation established the regularity of variation of the angle _P as a function of the maximum specific pressure during the rolling of aluminum, iron, copper, and nickel powders, as well as the regularity of the relationship between the angle _P and strip thickness as a function of conditions of powder feed into the deformation zone. The character of variation and the value of the neutral angle during the rolling of iron, copper, and nickel powders were determined.     

Strength characteristics of matrials produced by hot forming of porous powder compacts. I. The influence of porosity,carbon content,and the method of compacting on the tensile,shear, and compressive yield strengths

Conclusions The mechanical characteristics (_t, ) of powder metallurgy steels depend upon the porosity as a weakening factor and work hardening as a strengthening one. The tensile strength is more sensitive to porosity and less susceptible to work hardening than the shear strength. The compressive yield strength depends practically only upon work hardening and the size of the metal cross section.In comparison with hot rolled of the same composition, powder metallurgy low-porosity steels possess higher characteristics _t, , and _0.2 ^comp , which may be explained by the strengthening action of work hardening.Powder metallurgy steels produced by extrusion have higher values of _t than hot formed as the result of improvement in the quality of the intergranular contacts and orientation of the nonmetallic inclusions while there is practically no difference in the characteristics and _0.2 ^comp of these materials.Translated from Poroshkovaya Metallurgiya, No. 3(279), pp. 88–91, March, 1986.     

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.     

Wear- and Scaling-Resistant Coatings Based on TiCN

The composition, structure, and properties of coatings obtained by the high-velocity gas-flame spraying of composite powders based on TiCN with additions of SiC, AlN, SiC AlN/Al₂O₃ and a binder of NiCr based alloy were investigated. The working surfaces of coatings were studied by metallographic, petrographic, x-ray diffraction, electron-probe analyses, and scanning electron microscopy. It was determined that coatings 200 m in thickness had a typical finely dispersed lamellar structure with layers enriched in titanium alternating with layers of NiCr alloy. The tribological properties of developed coatings were superior to those of the standard WC + 8% Co alloy: under dry friction at a load of 2 MPa and sliding velocities in the range 5-15 m/sec the coefficient of friction was 0.17-0.11, and wear rate 3.4-8.5 m/km. The high oxidation resistance of the coatings is due to the presence, in the outer scale layer, of refractory compounds Al₂SiO₅, (Cr, Al)₂O₃, and Al₂TiO₅, which prevent the diffusion of oxygen into the substrate. The mass gain of the coating based on TiCN SiC AlN was 1.42 mg/cm₂ at 1450°C.     

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.     

Electric-spark alloying of steels with WC-Co hard metals

Conclusions A study was made of the electroerosion and cathode weight increase accompanying the ESA of steels with WC-Co hard metals and of some properties of resultant alloyed layers. In ESA the best results are obtained with VK20 alloy under soft conditions and with VK15 alloy under hard condition. The optimum alloying time is 5–10 min/cm² in process No. 2 and 3–5 min/cm² in process No. 5. Under these conditions ESA by the soft process (with VK20 alloy) ensures the formation of a hard (2200 kgf/mm²) white layer of the same thickness (40 m).Translated from Poroshkovaya Metallurgiya, No. 8(212), pp. 67–71, August, 1980.     

Thermodynamics of Component Interactions in Liquid Alloys of the Ternary Systems Ge(Al,Si) ― Ga ― Gd

The concentration dependence of the integral enthalpy of mixing in liquid alloys of the ternary systems Ge(Al, Si) Ga Gd at 1760 K, determined by the method of isoperibolic calorimetry and calculated using the surrounded atom model, was analyzed. Good agreement between H values obtained by both methods is noted. It was established that the interaction of gadolinium with components of the adjoining binary systems, which are characterized by the presence of intermetallic compounds, have a defining effect on the thermodynamics of alloy formation in the ternary systems Ge(Al, Si) Ga Gd.     

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.     

Properties of iron powders obtained from high-carbon melts by air atomization with subsequent decarburization

Conclusion The article examines the physical and processing characteristics of iron powders obtained by atomization and subsequent decementation. Experimental data, obtained by x-ray diffraction investigation, are presented on the influence of compaction pressure on the fine structure (second-type microdistortions, dislocation density, and mosaic-block size) of the powder particles.Translated from Poroshkovaya Metallurgiya, No. 10 (70), pp. 11–14, October, 1968.     

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.     

A methodology for investigating the effectiveness of magnetic-abrasive powders

Conclusions The optimal polishing speed in the range covered by our experiments was 3.05 m/sec for both magnetic-abrasive powders and both steels.The removed mass increases linearly with the increase of oscillation frequency and decrease of linear gap; for the ShKh15 ferromagnetic steel the removed mass is roughly five times that for the nonmagnetic Kh18N10 steel. When held between the electromagnet poles of the magnetic-abrasive polisher, the ferromagnetic steel increases the magnetic flux, the magnetic-abrasive particles are pressed more firmly against the surface, and the shearing forces increase (compared with those on a nonmagnetic material under the same current parameters).The maximum removal of mass is observed with the Zh15KT composition powder, but the maximum change in surface roughness in the MAP process is attained with the POLIMAM-T1 cast magnetic-abrasive powder, fractions — 01: from 7c to 12a (for ShKh15 steel) and from 8c to 10a (for Kh18N10 steel).A distinctive feature and main advantage of the proposed methodology is that it allows comparing magnetic-abrasive powders of different composition and structure under optimal operating conditions for each powder (and not under constant conditions for a fixed material, as in the traditional methods). It is thus possible to obtain in a single series of experiments a more objective assessment of the effectiveness of several magnetic-abrasive powders for different materials and to find a functional dependence between the MAP optimization parameters, e.g., the mass removed from the part being polished, and the process parameters. The experiments can be completed in a much shorter time, 1/10–1/100 of the time needed for traditional methods (depending on the number of factors studied).Translated from Poroshkovaya Metallurgiya, No. 4 (220), pp. 73–79, April, 1981.     

The phase equilibria in W-Fe-Co-Ni system alloys. II. Isotherms of the solidus and the phase composition of alloys containing 10 and 20% (Fe + Co + Ni) at temperatures above 1200°C

Conclusions The isostructural intermediate -phases Fe₇W₅ and Co₇W₆ in the W—Fe—Co system form a continuous series of -solid solutions. In the 1640–1630°C range the L + (Fe₇W₆) peritectic equilibrium in this system changes to a similar L + (Co₇W₆) equilibrium, where is the tungsten-base boundary solution.In the W-Fe-Co-Ni polythermal tetrahedron in the 1470–1460°C range conversion of the L +(Fe₇W₆)+, peritectic equilibrium into the similar L + (Co₇W₆) + , where is the nickel-, -ironcobalt-base boundary solution, occurs.Upon completion of crystallization at 1400°C, the W-Fe-Co system alloys with 10–20% (Fe + Co) have a + phase composition, while the W-Fe-Co-Ni system alloys with 10–20% (Fe + Co + Ni) accordingly have + , + + or + . At temperatures below 1215°C in alloys rich in iron, FeW may be formed instead of -phase and therefore the alloys may have an + FeW, + + FeW, + + + FeW and + + FeW phase composition.Translated from Poroshkovaya Metallurgiya, No. 5(281), pp. 86–89, May, 1986.