Martensitic Transformation of NiTi and NiTi-TiC Composites

Calorimetry and internal friction were used to study the martensitic phase transformation of shape-memory metal matrix composites consisting of nearly equiatomic NiTi with up to 20 vol.% TiC particles. The start and final temperatures for the austenite-martensite transformation (M s , Mf) and martensite-austenite transformation (A s , A f ) arc lower when measured by internal friction than when measured by calorimetry. In composites, TiC particles lower M f and A s but do not affect M s and A f . It is concluded that dissipative work due to twinning takes place to accommodate internal stresses.