Abstract
Using pure titanium and nickele powders, a TiNi shape memory alloy was experimentally manufactured by the vacuum hot pressed powder metallurgy method. An influence of various hot pressed forming process on the homogeneity of alloy structure was investigated to fabricate practical device parts with the shape memory effect.The results are as follows.(1) The chemical diffusion of pure Ti and Ni mixed powder shows a thendency towards inferiority as compared with bulk materials. However, above 1273 K, the diffusion behavior of this powder, which has the liquid phase locally, was closer to that of bulk materials.(2) The homogeneity and density of TiNi alloy varied according to temperature and pressure as well as to the holding time. A density of 96-97% of the ideal value was obtained using a mixed powder of pure Ni and Ti processed by the vacuum hot pressed method at temperature 1323 K, pressure 35 MPa and holding time 3.6 ks.(3) The transformation temperature region (Ms-Af) shows slightly unsharpness as compared with that of molten material. But the result of mechanical and SME test confirmed that these alloys have extremely effective shape memory characteristics, that is, the recovery stress was 75-80% of that of molten material. Finally, as a practical example, we tried the fabrication of a spring washer and a pipe joint tube.
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