SUPERSOLIDUS LIQUID-PHASE SINTERING OF PREALLOYED POWDERS

A model is derived for the sintering densification of prealloyed parti cles that form internal liquids when heated over the solidus temperatu re. The model considers the powder size, composition, and microstructu re, as well as the processing conditions of green density, heating rat e, maximum temperature, hold time, and atmosphere. Internal liquid for ms and spreads to create an interparticle capillary bond that induces densification during sintering. Densification is delayed until the par ticles achieve a mushy state due to grain boundary wetting by the inte rnal liquid. This loss of rigidity and concomitant densification of th e semisolid particles depends on the grain size and liquid quantity. V iscous flow is the assumed densification mechanism, where both viscosi ty and yield strength vary with the liquid content and particle micros tructure. Densification predictions are compared to experimental data, giving agreement with previously reported rapid changes in sintered d ensity over narrow temperature ranges. The model is tested using data from steels and tool steels of varying carbon contents, as well as bor on-doped stainless steel, bronze, and two nickel-based alloys.