V. I. Nizhenko, V. Ya. Petrishchev, and V. V. Skorokhod UDC 621.762 The kinetics of compaction with liquid-phase sintering for pseudoalloys of the system W − Ni − Sn are studied with molten Ni − Sn as the liquid phase. Experimental data are satisfactorily described by a kinetic equation on porosity − time coordinates. Time dependencies for compaction rate and viscosity are established for these alloys.There are systems within which a small addition of alloying admixture rapidly accelerates compact shrinkage in the initial stage of solid-phase sintering. This effect is observed most clearly on adding nickel to a compact made from tungsten powder [1][2][3][4][5]. It is interesting to study the effect of nickel on compaction kinetics for tungsten compacts during sintering in the presence of a liquid phase whose appearance temperature is markedly lower than that for nickel.Compaction kinetics have been studied [6] during liquid-phase sintering of composites of the system W − Ni − Sn containing from 3 to 10 mass% liquid phase of eutectic composition (67.5 mass% Ni + 32.5 mass% Sn). The Ni − Sn system has another eutectic (57 mass% Ni + 43 mass% Sn) with a melting temperature of 1160°C formed with intermetallics Ni 3 Sn and Ni 3 Sn 2 . We have studied compaction kinetics for W − Ni − Sn pseudoalloys within which this

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V. I. Nizhenko, V. Ya. Petrishchev, and V. V. Skorokhod UDC 621.262 Compaction kinetics during liquid-phase sintering of W − Co − Sn powder composites containing 90 mass% refractory component and 10 mass% readily-melting component is studied. It is established that compaction kinetics depends markedly on cobalt content in the melt. Specimens with a cobalt content up to 3 mass% at 1200°C (in the nonisothermal heating stage) undergo an increase in volume, and then they are compacted at a rate typical for liquid-phase sintering. The nonuniform nature of compaction is observed with an increase in cobalt in the test composites. Specimens with a cobalt mass fraction of more than 2% (cobalt content with three-phase equilibrium) experience considerable additional growth due to formation of the intermetallic compound W 6 Co 7 whose decomposition temperature exceeds the liquid-phase sintering temperature.The composite W − Co − Sn differs from pseudoalloys of the system W − Ni − Sn studied previously by us [1,2] in the nature of reaction between the components of the liquid phase. In the Co − Sn system, comprising the base of the liquid phase, for cobalt as for nickel in Ni − Sn alloys, there are typical negative deviations from the ideal behavior almost over the whole range of composite compositions [3], although they are less clearly defined, and in alloy melts rich in tin there is tendency towards the values γ Co > 1 (γ Co is the activity coefficient for cobalt in the melt). In addition, intermetallic W 6 Co 7 that forms in the W − Co system decomposes at a higher temperature (1630°C) compared with the decomposition temperature (about 970°C) for intermetallic WNi 4 [4] that exists in the W − Ni system.