SHAPE-MEMORY TINI SYNTHESIS FROM ELEMENTAL POWDERS

Commercially, the shape memory alloy TiNi is produced either by vacuum induction melting or by vacuum are remelting of the pure metal ingots. Powder metallurgy techniques provide an alternative fabrication route but problems arise in achieving chemical homogeneity. In this study TiNi compacts were cold-pressed from the blended elemental powders and sintered in vacuum for varying times at temperatures from 800 degrees C to 1000 degrees C. Two heating rates were used, 5 K min(-1) and 10 K min(-1). A TiNi microstructure could be produced after annealing at 1000 degrees C for 6 h, although some TiNi3 was still observed. This is likely to be difficult to completely remove as TiNi3 is thermodynamically more stable than TiNi. Thus, homogenization is unlikely to be completed by solid-state diffusion processes. The martensitic B19' structure was observed to be highly oriented after processing.