STUDY OF THE ANISOTROPIC MICROSTRUCTURE OF THE UNIAXIALLY COLD COMPACTED GREEN PARTS

The anisotropy of dimensional change on sintering of uniaxially cold compacted green parts is mainly caused by the inhomogeneous distribution of pressure during compaction. The difference between the axial and the radial pressure leads to an inhomogeneous deformation of the powder particles and in particular to a different extension of the interparticle contact areas. These areas are larger for contacts perpendicular to the compaction direction than for those parallel to it. This contributes to anisotropy of sintering shrinkage, since the interparticle contact area is the source of atoms diffusing towards the neck. Such an anisotropy of the neck region geometry may have an influence on anisotropy of the sintering stress, too. These features of the uniaxially cold compacted iron parts were investigated by SEM on the metallographic sections, using a geometrical model of the green parts to correct data taken from 2D images. The results were correlated to shrinkage at different temperatures measured by dilatometry.