Anisotropy of mass transfer during sintering of powder materials with pore–particle structure orientation

A micromechanical model for the shrinkage anisotropy during sintering of metallic powders is
proposed and experimentally assessed. The framework developed for modeling sintering based
on the mechanism of grain boundary diffusion is extended to take into account the dislocation
pipe-enhanced volume diffusion. The studied iron powder samples are pre-shaped into their
green forms by uniaxial cold pressing before sintering step. The resultant green bodies are
anisotropic porous structures, with inhomogeneous plastic deformation at the inter-particle
contacts. These non-uniformities are considered to be the cause of the anisotropic dislocation
pipe diffusion mechanisms, and thus of the undesired shape distortion during shrinkage. The
proposed model describes the shrinkage rates in the compaction loading and transverse
directions, as functions of both structural and geometric activities of the samples. Dislocation
densities can be estimated from such equations using dilatometry and image analysis data. The
reliability and applicability of the developed modeling framework are verified by comparing the
calculated dislocation densities with outcomes of nanoindentation and electron backscatter
diffraction-derived lattice rotations.