Modeling the hot consolidation of ceramic and metal powders

Abstract

Modeling of the consolidation of ceramic and metal powders by sintering, hot pressing, and hotisostatic pressing (HIP) was conducted using a continuum yield function and associated-flow rule modified to incorporate microstructure effects such as grain growth, pore size, and pore geometry. It was shown that consolidation behavior can be described over the entire range of densities through two parameters, the stress intensification factor and Poisson’s ratio, which are readily measured using uniaxial upset tests. Both parameters are functions of relative density, whose exact dependence varies from one material to another. Furthermore, it was demonstrated that in sinter forging of ceramics, an “apparent” Poisson’s ratio depending on stress level (relative to the sintering stress) gives a quantitative measure of the compctition between sintering and creep deformation. The accuracy of the microstructure-sensitive yield function was established through finite-element modeling (FEM) simulations of the isothermal sintering of a soda-lime glass, sinter forging of alumina, and die pressing of an alpha-two titanium aluminide alloy.