Anisotropy of dimensional change and its corresponding improvement by addition of TiH2 during elemental powder sintering of porous NiTi alloy

The paper deals with the influence of TiH2 content and sintering conditions (sintering temperature and sintering time) on the dimensional changes and the radial/axial shrinkage (R/A)-ratio of powder compacts. The purpose was to try to find out how to make precision porous products using a conventional powder metallurgical process. It was found that the dimensions of the compact shrink and anisotropy of dimensional change (ADC) occurs during sintering. Addition of TiH2 markedly minimizes ADC and makes it possible to manufacture the desired final product shape. An R/A-ratio less than 1 is supposed to be attributed to the differences in the degree of mechanical deformation, which occurs on the surface of powder particles parallel to and perpendicular to the direction of pressing during the pressing process. A model of the pore changes during pressing and sintering is proposed.