Abstract
A study of the exothermic behavior of reactions that occur within Ni and Ti elemental powder mixtures during heating in medium vacuum (4 × 10 -3 Pa) has been conducted. In comparison with several other ordered intermetallic compound mixes, a much more violently released exothermic heat was observed in the Ti-50Ni mixture. It indicates that the difficulties associated with a common powder metallurgy process for TiNi shape memory alloy (SMA) include the possible oxygen interaction in a low vacuum condition and the large and rapidly generated exothermic heat in a medium or high vacuum condition. Therefore, a multi-stage sintering process is proposed to fabricate the TiNi SMA powder metallurgy (PM) specimens and their composites. In order to prevent the violently released exothermic heat, the sintering process was divided into several repeated cycles with intermediate cold deformation, and a relatively low sintering temperature, 1030°C (or 1080°C), was employed. Further study of the SMA composites, Ti 50 Ni 50 + 5vol%TiC and Ti 50 Ni 50 + 10vol%TiC, with this technique was presented in this article. The obtained sintering density is above 85%. In the meantime, 94.5% (50%) recovery Of Ti 50 Ni 50 + 5vol%TiC (Ti 50 Ni 50 + 10vol%TiC) after 1.0% tensile strain then heated to 80°C were observed. The results of phase transformation and microstructure examination will also be discussed.