INFLUENCE OF POWDER DEFORMATION ON ANISOTROPY OF SINTERING SHRINKAGE

Densification in cold compaction of metallic powders is due to rearrangement and plastic deformation. The two phenomena are partially overlapped during the compaction cycle, but the former prevails at the lower forces, while plastic deformation increases on increasing the compaction force. AISI 316L green cylindrical parts were compacted at different forces, corresponding to different steps of the compaction process, and sintered at 1250°C in a vacuum furnace. At the lower forces, when plastic deformation is negligible and densification is due to rearrangement, the radial shrinkage is almost isotropic. On increasing force, the increasing plastic deformation causes a progressive deviation from this behaviour, the axial shrinkage becomes larger than the radial one. An interpretation of this behaviour is proposed, based on the analysis of the multiaxial stress field acting on the powder column in the whole of the force range investigated.