Processing of porous NiTi by spark plasma sintering method

摘要

Intermediate porosity (25% - 40%) NiTi is processed by Spark Plasma Sintering (SPS) method. In order to increase the porosity, the SPS chamber setup is modified. A pair of spacers is added to the chamber punch setup so that the pressure applied on the powder is minimized. As a result, the porosity is increased. TiH_2 powder is added as a pore-forming reagent to the element powder mixture for sintering. The decomposition of TiH_2 increases the porosity efficiently. Two kinds of heat treatments are applied to convert the porous NiTi to superelastic grade. One is homogenization followed by aging treatment, the other is aging treatment only. It is found that homogenization heat treatment reduces the porosity. Compressive testing under both room temperature and temperature above the austenite transformation finish temperature are conducted. Porous NiTi specimens perform ductility and show clear superelestic loop with high flow stress and strain.