Supersolidus liquid-phase sintering of prealloyed powders

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