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

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  • Uchida Kazunari
    Nuclear Plant Service Dept., Hitachi Ltd.
  • Shigenaka Naoto
    Nuclear Plant Service Dept., Hitachi Ltd.
  • Sakuma Toshio
    Faculty of Engineering, Ooita University
  • Sutou Yuji
    Tohoku University Biomedical Engineering Research Organization, TUBERO Aobayama Material Science Branch
  • Yamauchi Kiyoshi
    Tohoku University Biomedical Engineering Research Organization, TUBERO Aobayama Material Science Branch

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Abstract

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.

Journal

  • MATERIALS TRANSACTIONS

    MATERIALS TRANSACTIONS 48 (3), 445-450, 2007

    The Japan Institute of Metals and Materials

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