Effect of Nb Content on Martensitic Transformation Temperatures and Mechanical Properties of Ti-Ni-Nb Shape Memory Alloys for Pipe Joint Applications

Several Ti-Ni-Nb shape memory alloys (SMAs) with various Nb contents (0� 15 mol%) or Ni/Ti atomic ratios (1:0� 1:1) were tested to investigate the martensitic transformation temperatures and mechanical properties. The martensitic transformation temperatures (Ms, Mf, As and Af ) of the solution-treated Ti-Ni-Nb alloys at 1173 K for 300 seconds with Ni/Ti ratio of 1.0 decrease with increasing the Nb content. These transformation temperatures also depend on the Ni/Ti ratio, heat treatment condition and cold working rate. Furthermore, in the alloy with Nb content of 6 mol% and Ni/Ti atomic ratio being less than 1.05, the fracture stress and fracture strain reached about 1,000 MPa and over 20%, respectively. Based on the obtained results, several processing conditions such as the chemical composition, fabrication process and heat treatment are optimized for the Ti-Ni-Nb SMAs to develop SMA pipe joints. [doi:10.2320/matertrans.48.445]