EQUILIBRIUM PORE SURFACES, SINTERING STRESSES AND CONSTITUTIVE-EQUATIONS FOR THE INTERMEDIATE AND LATE STAGES OF SINTERING .2. DIFFUSIONAL DENSIFICATION AND CREEP

Constitutive equations for the intermediate and late stages of sintering are derived assuming grain boundary diffusion to be the controlling transport mechanism. The surface of the pore space is assumed to be in equilibrium. Numerical results for the shape of equilibrium surfaces are taken from a companion paper [J. Svoboda, H. Riedel and H. Zipse, Acta metall. mater. 42, 435 (1994)]. For open porosity the contacts between grains turn out to be nearly circular in all cases, so that the diffusion problem in the contact areas can be solved readily. The macroscopic response of the powder compact can then be built up of the mechanical and the surface tension forces acting across the contacts. The analysis is carried out for a random, or homogeneous distribution of contacts around each particle, and for simple cubic, body-centered cubic, and face-centered cubic grain arrangements. The cubic viscosities are averaged using various methods, the best of which appears to be the self-consistent method.