Gravity-Induced Distortion During Liquid-Phase Sintering

Sintering is used in the production of complex-shaped engineering components from compacted powders. For most applications, a predictable sintered size is a key requirement. While the formation of a liquid phase can accelerate sintering, it also can contribute to nonuniform dimensional change resulting in component distortion. Several factors, including gravity, play a role with respect to distortion. These factors are examined using tungsten heavy alloys sintered in two gravitational environments where liquid content, pore saturation with liquid, and loss of capillarity result in distortion. A significant situation arises when the component loses structural rigidity, as occurs with a low dihedral angle and high liquid content. In microgravity sintering, where buoyancy forces are absent, pores coalesce to cause swelling, leading to incomplete densification, and in some cases extensive distortion. Sintering on Earth increases solid grain contact, resulting in greater densification and less distortion. Microgravity liquid-phase-sintering behavior is substantially different from that exhibited by Earth-based sintering trials.