Effects of grain size and Co addition on transformation temperatures of Ti-Ni-Zr high-temperature shape-memory alloys

摘要

Recently, the author demonstrated that a sputtering method is a powerful tool to investigate the transformation behavior and mechanical properties of shape-memory alloys (SMAs) [1]. The advantage for using a sputtering method in developing a new SMA is the prompt feedback of the test results because the test samples are easily prepared from a film; X-ray diffraction (XRD) and differential scanning calorimetry (DSC) samples, tensile specimens, and discs for electropolishing can be readily cut from a film using scissors, rotary paper trimmer, and puncher, respectively. The electropolishing only requires 10 s. Furthermore, a wide range of film composition can be obtained by simply setting the power of each element target with sufficient precision (ca. 0.3 at%). The resulting film exhibited excellent mechanical properties compared with those of bulk alloys, which enables the comprehensive study of SMAs over a wide composition range [2]. In the present study, the sputtering method was employed to explore a new high-temperature SMA. Ti-Ni-Zr alloys are known as a cost-effective, high-temperature SMA; however, their large temperature hysteresis has prevented their commercial use [3]. The present investigation using film samples revealed that the substitution of Co for Ni in Ti-Ni-Zr alloys was effective in decreasing the temperature hysteresis. The effect of Co addition was also verified in a bulk alloy.