Microstructure and martensitic transformation of cast TiNiSi shape memory alloys

The martensitic transformation behavior, second phases and hardness of Ti51Ni49-xSix shape memory alloys (SMAs) with x = 0, 1 and 2 at.% are investigated. The transformation temperature of one stage martensitic reaction B2 <-> B19' is associated with the forward (M-s) and reverse (A(s)) martensitic transformations, respectively. All experimental DSC results such as martensitic transformation peaks (M*) and reverse martensitic transformation peaks (A*) are increased and became sharper with increasing Si-content. The microstructure investigation of the studied SMAs (Ti51Ni49-xSix) showed that there are two types of precipitated second phase particles. The first one is Ti2Ni which mainly located at grain boundaries and intermetallic compound of Ti-2(Ni + Si) phase distributed inside the matrix. The volume fraction of these two phases is increased with Si content. Additionally, a small amount of Si remained in solid solution of the matrix of Ti51Ni49-xSix SMAs. Moreover, hardness of Ti51Ni49-xSix SMAs is increased as the Si-content increases. (C) 2010 Elsevier B. V. All rights reserved.