Chemically driven growth of tungsten grains during sintering in liquid nickel

Abstract

Spherical tungsten particles of 200–250μm size were sintered in liquid nickel at 1640°C. Many of the tungsten spheres grow into their neighbours as reported earlier by Huppmann, Riegger and Petzow. The growing regions etch differently from the original pure tungsten spheres and consist of a tungsten alloy phase saturated with 0.15 wt.% Ni. It is therefore suggested that the driving force for this process is the chemical potential difference between the equilibrium W-Ni alloy and the pure tungsten phase being dissolved. The growth is a linear function of sintering time. The measured growth rate is 1.1 μm/min, the activation energy is (3.7 ± 0.5) × 10 5 J/mole. The kinetics appear to be controlled mainly by the solution-reprecipitation reaction at the moving boundaries. This chemically driven solution-reprecipitation process is expected to enhance the coalescence and growth of grains during sintering in the presence of liquid or solid elements which form alloys with the major component.