PORE SHAPE EFFECTS DURING CONSOLIDATION PROCESSING

Recent experimental studies [e.g. Y. Liu et nl., Acta metall. mater. 4 2(7), 2247 (1994)] have shown that final stage densification of alloy powders and metal-coated fibers occurs by the creep collapse of cusp-s haped voids at rates significantly higher than those predicted by the conventional spherical pore analyses of current consolidation models. In this paper, a strain rate potential is developed to describe the de nsification of a power-law creeping material containing aligned cylind rical pores (with axes perpendicular to the plane of deformation). The pores' cross-sections are randomly oriented (cusp-shaped) hypotrochoi ds, so the material is isotropic in the plane of deformation. The appr oach involves the computation of the incremental change in the potenti al energy of a linear creeping body due to an incremental increase in the porosity, the application of a differential self consistent scheme to obtain a potential for a linear body with an arbitrary pore concen tration and the use of a bounding principle to produce an estimate of the porous materials power-law creep potential. The results show that the presence of the cusps increases the predicted densification rates by a (sometimes large) factor that depends upon the cusp geometry, the applied load asymmetry and materials nonlinearity (i.e. its creep exp onent). Copyright (C) 1996 Acta Metallurgica Inc.