The effect of carbon content on the mechanical properties of tungsten carbide-cobalt hard alloys

Summary A study was made of the effect of graphite and-phase contents on the properties of VK8 alloy. It was found that, in the presence of the-phase in the alloy in the form of lakes or dendrites (lace), indicating carbon deficiency, the strength of the alloy is greatly reduced. Slight decarburization, taking the form of-phase formation along the interphase boundaries, has practically no effect on the strength of VK8 alloy. The presence of graphite in an amount of less than 0.5 vol. % has little effect on the wear resistance of VK8 alloy, and slightly raises its strength. A high graphite content substantially lowers both strength and wear resistance.     

Regulation and determination of the phase composition of tungsten hard metals

Conclusions The two-frequency magnetic method can be employed for detecting the presence of additional phases (free carbon and the ₁-phase) in tungsten hard metals. The degree of carburization of tungsten hard metals and hence the presence and amount of free carbon and the ₁-phase can be regulated with sufficient accuracy for practical purposes by adding graphite or tungsten powder to electrocorundum packing material and varying the rate of hydrogen flow. Control over this process may be exercised by the magnetic method. The carbon content of tungsten hard metals grows when the concentration of graphite in packing material is raised, the concentration of tungsten in packing material is lowered, and the rate of hydrogen flow is decreased. The hard metals can thus change in structure from three-phase WC + Co + ₁ to two-phase WC + Co and then to three-phase WC + Co + C alloys.Translated from Poroshkovaya Metallurgiya, No. 4(220), pp. 46–50, April, 1981.     

Reactions of TiNi with Oxygen

X-ray diffraction and metallography have been applied to study the formation conditions for the phase in Ti₄Ni₂O in the reaction of TiNi with oxygen. The phase diagram for the Ti Ni O system indicates that the phase (Fe₃W₃C structure type) is a solid solution of oxygen in Ti₂Ni. For TiNi made in an oxygen-bearing medium or from initial materials contaminated with oxygen, one gets the phase and Ni₃Ti. Those phases are formed also in surface oxidation as products from the initial interaction of the alloy with oxygen. They occur when there is a low oxygen partial pressure, as on annealing TiNi powder in a vacuum given by a rotary pump or in a layer under scale formed on a cast TiNi specimen on oxidation in air. The layer under the scale is formed because of the preferential loss of titanium from the TiNi and consists of Ti₄Ni₂O, Ni₃Ti, and an Ni(Ti) solid solution, which in turn occurs because of preferential loss of titanium from Ni₃Ti. In the subsequent oxidation stages, there is selective oxidation of Ti₄Ni₂O to lower titanium oxides. The decomposition of TiNi alloy containing oxygen when the composition is varied near the equiatomic one can be used for practical purposes. For example, the segregation of the hydride-forming phase may improve the hydrogen uptake by the alloy, while the dispersed segregation of Ni₃Ti and the lower oxides may favor hardening.     

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.     

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     

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.     

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).     

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.     

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.     

Mechanical treatment of powders of refractory carbides

Conclusions The model of mechanical treatment constructed in this work makes it possible to reduce all the parameters of this treatment to three generalized parameters: the mean energies of movement of the spheres_s, particles _p, and the fraction of absorbed energy . The main input parameters of the conditions are the vibrational speed V_a = A and the flow of the powder qv.On the basis of calculations of the energy characteristics of mechanical treatment of the powders of the tantalum carbides and semicarbides we can estimate the contribution of mechanical energy of this treatment to the activation of the processes of synthesis of the semiand subcarbides of these metals. Specifically, the effect of synthesis of the refractory tantalum semicarbide directly in the chamber of the vibratory mill during mechanical treatment can be explained.Translated from Poroshkovaya Metallurgiya, No. 4(280), pp. 91–96, April, 1986.     

Extrusion of a viscoplastic powder mixture

Summary It has been established that, in the extrusion of a viscoplastic mixture through a cylinder-confuser-cylinder space, the relationship between the rate of flow Q and the pressure dropp is described by the expression: {ie691-01} where the coefficients depend on geometrical parameters and the rheological properties of the mixture, a being proportional to {ie691-02} and {ie691-03} is the yield strength and the plastic viscosity).Translated from Poroshkovaya Metallurgiya, No. 9 (57), pp. 6–9, September, 1967.     

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.     

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.     

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.     

Formation of compounds in the system Al-Ni during vaccum sintering and some of their properties

Conclusions A study was made of the intermetallic compounds of the system Al-Ni produced by sintering pressed powder compacts in a vacuum at 800°C. The synthesis of these compounds is promoted by a self-heating effect brought about by an exothermic reaction between the metallic components at the melting temperature of aluminum, which in the composition range 20–70 at.% Ni leads to instantaneous partial melting of specimens. The existence was established of a metastable nickel-base solid solution at 75 at.% (86.71 wt.%) Ni, and a metastable widening was observed of the ranges of existence of the (Al₃Ni₂) and (AlNi) phases in the direction of higher nickel contents.Translated from Poroshkovaya Metallurgiya, No. 11(155), pp. 98–103, November, 1975.The author wishes to thank Academician Professor G. V. Samsonov for valuable assitance in the choice of subject for investigation and experimental procedure.     

Influence of grain size and porosity on the high-temperature friction of titanium carbide

Conclusions It was established that in friction of a TiC-TiC pair in vacuum the coefficient of friction at 250C and the wear rate at 1250C are practically independent of grain size. At higher temperatures these characteristics have an inverse relationship to grain size.It was shown that with an increase in porosity both the wear rate and the coefficient of friction increase. With an increase in temperature the influence of porosity on the wear rate decreases.With variations in porosity in the 1–10% range, in grain size in the 1–50 m range, and in temperature in the 20–1500C range the wear rate changes within limits of 10–45% and the coefficient of friction within limits of 3–35%.Translated from Poroshkovaya Metallurgiya, No. 9(297), pp. 56–61, September, 1987.     

Effect of heat treatment on the structural state and mechanical properties of polycrystals based on the superhard boron nitride modifications

Conclusions An investigation was carried out into the effect of thermal cycling on the structural state of polycrystals based on the high-density boron nitride modifications. It is shown that a two-phase material is characterized by a high level of macro- and microstresses, which control its brittle rupture behavior and mechanical properties. In particular, microcracking processes initiated by internal stresses after the application of external load promote stress relaxation at the tip of a propagating macrocrack, thereby imparting high fracture toughness (K_c 16–18 MN/m^3/2) to the material. During heat treatment (performed in this work at T 800°C) internal stress relaxation takes place, which is accompanied by a fall in fracture toughness to the level characteristic of unstressed single-phase sintering (K_c 10–14 MN/m^3/2) and changes in hardness and rupturing stress.Translated from Poroshkovaya Metallurgiya, No. 1(217), pp. 53–61, January, 1981.     

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.     

An X-ray diffraction study of the oxidation of Ni3Ti

Conclusions A layer-by-layer x-ray diffraction phase analysis was made of the scale formed on Ni₃Ti during atmospheric oxidation over the temperature range 600–1000°C. The scale was found to contain the oxides NiO, NiO · TiO₂, TiO₂ (rutile), Ti₃O₅, and Ti₂O₃ as well as two nickel phases — pure nickel and a nickel solid solution. The pattern of distribution of these phase constituents in consecutive scale layers is outlined.Translated from Poroshkovaya Metallurgiya, No. 5 (137), pp. 57–62, May, 1974.     

Electric-spark alloying of steel with tungsten-free hard metals

Conclusions A study was made of the ESA of steel with tungsten and tungsten-free TN type hard metals in different units and under different conditions, with and without anode dressing. It has been established that in alloying under finishing conditions the erosion of a dressed TN-20 alloy anode is greater than that of an undressed one; this is due to the formation of stable oxide films on the electrode surfaces. In contrast to this, in treatment under rough conditions the erosion of an undressed anode is greater because the oxide films cannot withstand the higher thermal stress generated during alloying. In ESA with tungsten alloys maximum erosion under both finishing and rough conditions is observed with undressed specimens. This is attributable to the formation of a defective zone promoting periodic brittle disintegration in the course of treatment. Removing the defective zone decreases the erosion of the material. The most favorable conditions for the formation of a reinforced layer are created in the alloying of a dressed cathode surface, and consequently it is best to perform ESA with a specific time of not more than 1 min/cm². Use of treatment conditions with large thermal loads increases the thickness and hardness of the reinforced layer. Reinforcement with TK type alloys sets up a stress which is greater on the specimen surface and extends to a greater depth than the stress generated in alloying with TN type hard metals. Electrodes made of the tungsten-free TN-20 hard metal can be used instead of tungsten alloy electrodes for the ESA of processes V and VI. The resultant reinforced layer is sufficiently thick and continuous.Translated from Poroshkovaya Metallurgiya, No. 11(239), pp. 64–69, November, 1982.