Creep Mechanisms and Their Role in the Sintering of Metal Powders

Abstract

Material transport in sintering of loose metal powder aggregates and of powder compacts with or without an external load can be considered as creep. Creep takes place under the influence of stresses due to surface tension forces, to externally applied forces including gravity, or to internal stresses. Creep mechanisms important in sintering include slip controlled by dislocation climb and creep due to movement of vacancies from boundaries under tensile to those under compressive stress (Herring-Nabarro microcreep). The type of creep mechanism involved in any particular sintering experiment depends primarily on the temperature and the level of stress. Stresses due to surface tension forces may be calculated by applying the virtual work concept to the change in geometry of particle aggregates during sintering. By determining the rates involved in sintering, such as increase in contact area between particles or shrinkage rate, as a function of temperature and of stress, the type of creep mechanism can be identified.