Kirkendall effect expansion during sintering in Cu-Ni powder compacts

Abstract

Length changes under superposed sintering and homogenization of mixed Cu-Ni powder compacts have been measured. The results are interpreted as the superposition of shrinkage due to interparticle void filling and expansion due to Kirkendall effect porosity formation. The time—temperature behavior of both the shrinkage and the Kirkendall effect expansion is a function only of Dt ∝ t exp[−Q/RT] with Q = 42 kcal/ mole. Volume diffusion is concluded to be the primary mechanism of the length change processes. By comparing the present results with the author's previously reported X-ray determination of the degree of interdiffusion, it is found that nearly all of the Kirkendall effect created vacancies are deposited as porosity. This porosity was very stable. It is concluded that the theory of Coulomb and Friedel of cavity formation along dislocation lines is in best accord with the experimental results.