High temperature strength of sintered tungsten alloys

Tensile tests of sintered tungsten alloys at elevated temperatures were carried out in air and vacuum atmospheres in order to study the temperature dependency of mechanical properties. Liquid-phase-sintered 93.0W-4.9Ni-2.1Fe and 97.2W-2.0Ni-0.8Fe (by wt%) alloy specimens were prepared. The 0.2% proof stress and tensile strength of the sintered tungsten alloys, which decreased with increasing temperature, were higher than those of conventional high temperature structural steels. From the fractographic observations, cleavage fracture of tungsten grains was dominant in the range from room temperature to 500°C, and the area fraction of decohesion of tungsten-tungsten boundary increased in the temperature range above 600°C. For the material with a high volume fraction of tungsten particles and with direct contact of tungsten particles, lower strength was observed at elevated temperatures in air compared with the material with low tungsten content and Ni-Fe layer around tungsten particles, which may result from oxidation through the boundary of tungsten-tungsten particles.