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.     

Deformation coefficients of metal powders

Conclusions The total deformation coefficients of metal powders are determined by the ratios of the final dimensions of a porous part being deformed to the corresponding dimensions of a nonporous body of the same mass. Comparable total deformation coefficients of metal powders have been represented as the products of the partial deformation coefficients characterizing the possible deformation of a nonporous body of the same mass upon its transition into the free-flowing state and the deformation taking place during the transition from the free-flowing into the porous state under the action of pressure. The deformation coefficients of metal powders are uniquely determined by the relative densities before and after the application of pressure for all the linear principal strain schemes, for the plane schemes , when _10p = _20p ^–1 , , when _10p = _30p ^–1 , and , when _20p= _30pand the volume schemes of isostatic compression and extension when _10p ^–1 = _30p. In the determination of the deformation coefficients for the remaining principal strain schemes, it is necessary to take into account the final dimensions of the porous part being deformed.Translated from Poroshkovaya Metallurgiya, No. 11 (119), pp. 18–23, November, 1972.     

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.     

Interrelationship between the properties of powders,the conditions of pressing and sintering,and the structure of porous niobium

Conclusions With an increase in niobium powder particle size the pressability increases while the formability decreases. There is a linear relationship between the normalized radius of the pores in high-porosity niobium powder specimens and the normalized volume of the pores. This is an indication of geometric similarity of the disposition and form of the pores in specimens pressed from niobium powders with different degrees of dispersion.The product of the coefficient of side pressure and the coefficient of friction on the die wall is 0.053 ± 0.10. This means that with reasonable values of the coefficient of friction of dispersed niobium powder on the wall of the steel die is 0.14.Translated from Poroshkovaya Metallurgiya, No. 3(327), pp. 30–33, March, 1990.     

Cold shortness and nature of failure of iron-manganese powder alloys

Conclusions The level and nature of variation of impact toughness in the iron-manganese powder alloys are similar to the vacuum-melted cast alloys. The lowest cold brittleness threshold was recorded for the alloys with 20–23% Mn (determined at –253°C) containing the maximum amount of -martensite and positioned at the boundary of the + + and + regions. Brittle fracture in these alloys takes place by the intercrystalline mechanism, and the inclusions, depending on their composition, size, and distribution, can both support crack propagation and delay this process. The possible mechanisms of failure of the powder materials are proposed on the basis of the literature data and own experimental investigations.Translated from Poroshkovaya Metallurgiya, No. 12(300), pp. 77–83, December, 1987.     

Amplitude dependence of the internal friction of plasma-sprayed coatings

Conclusions An internal friction study of plasma-sprayed coatings has shown that the application of such coatings substantially changes the ADIF parameters (decreases _cr and increases tan ) of a clad specimen. The effects of the dislocation structure of a basis on the physicomechanical properties of a plasma-sprayed coating applied to it have been established.Translated from Poroshkovaya Metallurgiya, No. 2(206), pp. 30–32, February, 1980.     

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.     

A thermodynamic analysis of the formation of zirconium nitride from zirconium tetrachloride

Conclusions On the basis of a thermodynamic calculation of the heterogeneous system zirconium-nitrogen-hydrogen-chlorine the feasibility is demonstrated of obtaining zirconium nitride in the condensed state, with a virtually complete transformation of the metal into the nitride and a comparatively low expenditure of energy (about 80,000 kJ/kg), at temperatures of 2000–2400°K, a pressure of 1 bar, and a 50-fold dilution of the stoichiometric composition to a ZrNClH ratio of 1504200. Use of ammonia instead of nitrogen at the same ratio of the elements increases the amount of energy expended to 106,000 kJ/kg.Translated from Poroshkovaya Metallurgiya, No. 12 (156), pp. 1–3, December, 1975.     

Determination of the dielectric characteristics of powders at superhigh frequencies

Conclusions The measurement method described enables the dielectric characteristics of powder objects in the shf range to be determined with errors of not more than ±2% in and not more than ±15% in tan. Conversion of results of measurements on the dielectric parameters in wide ranges of particle sizes and values of can best be performed with formula (9). To obtain silicon nitride materials characterized by a low level of dielectric losses, it is necessary to reduce to a minimum their impurity content and ensure that their composition approximates as closely as possible to stoichiometric.Translated from Poroshkovaya Metallurgiya, No. 3(207), pp. 65–72, March, 1980.     

Boundaries of the single-phase side fields of the system Mo-Cu-Ni in the solid state

Conclusions It was established that the molybdenum corner of the Mo-Cu-Ni ternary system contains a singlephase field of solid solutions of copper and nickel in molybdenum with a combined Cu and Ni content of 1.5–2 wt.%. At the copper-nickel side of the constitution diagram of this system, there is a single-phase field of ternary Cu-Ni-Mo solid solutions, whose molybdenum content steadily rises with increase in nickel concentration, from 1.5 wt.% at NiCu=2080 to 3 wt.% at NiCu=4060.Translated from Poroshkovaya Metallurgiya, No. 2 (122), pp. 65–70, February, 1973.     

Thermionic emission properties of cermets of eutectic compositions in Me(IV)-(C,B)-(Mo,Re, W) systems

Conclusions Sintered eutectic (Ti, Zr, Hf)C-(Mo, Re, W) and ZrB₂-(Mo, Re, W) cathode cermets having a quasieutectic coarse-conglomerate structure are characterized by high stability of emission, and their effective work function is lower than that of their most emission-active components. The rapid stabilization of the emission characteristics of the eutectic cathode cermet composites is linked with the specific character of electron exchange between their phases, which creates optimum conditions for the formation of a self-stabilized structure on the surface of an emitter. The relative fall in work function exhibited by the cathode cermets investigated compared with their metallike compound components grows with increasing work function of their pure metallic components. Composite emitters of the eutectic compositions of the MeC (MeB₂)-Me' (where Me' = Mo, Re, W) systems are film-type emitters, on whose surfaces thin layers of the metal Me' form during heat treatment (sintering) and actual operation. The metal surface layers adsorb atoms from the metallike compounds MeC and MeB₂, which are supplied to the surfaces of the emitters by diffusion.Translated from Poroshkovaya Metallurgiya, No. 1(205), pp. 81–87, January, 1980.     

Ternary systems nio bium-rhenium-carbon and tantalum-rhenium-carbon

Summary The systems Nb-Re-C and Ta-Re-C were investigated by the methods of x-ray and metallographic analyses. The phase equilibria in these systems at 1800°C were determined (Figs. 1 and 3). In the ascast high-rhenium alloys, a metastable -phase was detected. The -phase could not be obtained in the pure form; this phase is in equilibrium with NbC and TaC. The -phase does not exist in the system Ta-Re at 1800°C.Translated from Poroshkovaya Metallurgiya, No. 4(52), pp. 42–45, April, 1967     

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.     

Effect of phase transformation in higher iron silicide on the electrical conductivity of the multiphase system iron silicide-glass. II. Effect of structural transformation in lebeauite on the temperature dependence for composite resistivity

Annealing at the eutectoid decomposition temperature for higher iron suicide -phase is studied for its effect on the temperature dependence for resistance (T) of a composite based on cermet containing iron suicide and barium borosilicate glass. An attempt is made to distinguish the contribution of -FeSi₂ to the (T) dependence of the system on a background of the conductivity of the other phase components.Translated from Poroshkovaya Metallurgiya, No. 10, pp. 20–24, October, 1992.     

Formation of the structure in sintering and the strength properties of Al-Cu P/M alloys

Conclusions Al-Cu system P/M alloys sintered with long holds in the eutectic-solidus temperature and concentration range are characterized by a quite porous structure consisting of fine grains and precipitates of secondary -phase. The appearance of the latter is related to decomposition of the -solid solution in cooling of the alloy from the sintering temperature.Alloys sintered in the solidus-liquidus area are distinguished by low porosity and a structure consisting of polyhedral grains and boundary -phase. Its formation is related to the formation and degeneration of the nonequilibrium eutectic during cooling of the alloy. The temperature and hold in sintering determines the grain size and character of -phase precipitates. Alloys with a high degree of homogeniety, low porosity, fine-grained structure, and fine -phase precipitates uniformly distributed in the structure possess the best strength properties.Translated from Poroshkovaya Metallurgiya, No. 10(334), pp. 52–58, October, 1990.     

Creep of highly-porous iron compacts under conditions of cyclic α ↔ γ-transformations

Features of the creep of highly-porous iron compacts with cyclic -transformation are studied. Possible reasons are explored for acceleration of deformation during -transformation and sintering of compacts with -transformation.Kharkov University. Translated from Poroshkovaya Metallurgiya, Nos. 3–4, pp. 19–23, March–April, 1994.     

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.     

Consolidation and Structure Formation during the Sintering of Composites Based on Nitrides of Transition Metals of Groups IV-V. Part IV. Sintering of Composite Materials of (VN,TaN) ― Ni

A study is made of the sintering of (VN, TaN) Ni composites in argon under isothermal and nonisothermal conditions. It is shown that the sintering of these materials is characterized by a reaction between the components, which is accompanied by the release of nitrogen from the nitrides and the formation of solid solutions and intermetallides based on nickel. These processes affect the rate and sign of the consolidation process. It is established that nitrides of vanadium and tantalum are sintered with nickel considerably more rapidly and at a lower temperature than nitrides of group-IV transition metals. Isothermal sintering leads to a slowing of consolidation compared to nonisothermal sintering, which can be attributed to the release of nitrogen from the nitrides and its localization in closed pores. The sintering is accompanied by an increase in the volume content of the metallic binder and a change in its phase composition (intermetallides of nickel and nickel-based solid solutions form). TaN Ni materials are characterized by a solid phase with very fine grains (1 m).     

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.     

Ductile fracture of dispersion-hardened alloys

Conclusions Experimental data have been obtained for the Ag-MgO system demonstrating the existence of a mean critical width L of the necks between adjacent particles. It is noted that this magnitude is related to the critical degree of deformation at fracture, lfr, and to the transverse contraction of alloys with secondary particles, . The screening influence exerted by large-sized particles on the void coalescence process is described. For the alloys investigated, the critical MgO particle size, capable of inducing void nucleation, has been found to lie in the range 30–50 nm.Translated from Poroshkovaya Metallurgiya, No. 10(178), pp. 99–103, October, 1977.