G. Yamaya, M. Tomozawa, H. Y. Kim, S. Miyazaki, University of Tsukuba, Tsukuba, Japan
Ti-Ni-Pd shape memory alloys (SMAs) are promising candidates for high-speed microactuators, because they show high transformation temperatures and narrow transformation temperature hystereses. It is also reported that substitution of Cu for Ni in Ti-Ni SMAs reduces the transformation temperature hysteresis and increases the transformation temperature. In this study, Cu was added to a Ti-27Ni-22Pd alloy in replacement of Ni and the effect of Cu on shape memory behavior and internal structure was investigated. The 51Ti-(27-x)Ni-22Pd-xCu (x = 0-27at.%) alloys were fabricated by Ar arc melting and heat-treated at 1223 K for 7.2 ks. The martensitic transformation start temperature Ms of the 51Ti-27Ni-22Pd alloy was measured to be 396 K by the differential scanning calorimetory (DSC). The Ms slightly decreased with increasing Cu-content from 0 to 10at.%, however, it increased with increasing Cu-content from 10at.% to 20at.%. The Ms of the 51Ti-7Ni-22Pd-20Cu alloy reached 443 K. Transformation peaks could not be detected in the alloys with a Cu content above 20at.%. The transformation temperature hysteresis showed an almost constant value of approximately 8 K regardless of Cu-content. Effect of Cu content on the recovery strain and critical stress for slip was investigated by thermal cycling tests under various constant stresses. The maximum recovery strain of the 51Ti-27Ni-22Pd alloy was 5.3%, and it did not change significantly by increasing Cu-content up to 20at.%. The critical stress for slip increased from 275 MPa to 400 MPa with increasing Cu-content from 0 to 20at.%.
Summary: Ti-Ni-Pd shape memory alloys (SMAs) are promising candidates for high-speed microactuators, because they show high transformation temperatures and narrow transformation temperature hystereses. It is also reported that substitution of Cu for Ni in Ti-Ni SMAs reduces transformation temperature hysteresis and increases the transformation temperature. In this study, Cu was added to a Ti-27Ni-22Pd alloy in replacement of Ni and the effect of Cu on shape memory behavior and internal structure was investigated. The 51Ti-(27-x)Ni-22Pd-xCu (x = 0-27at.%) alloys were fabricated by Ar arc melting and heat-treated at 1223 K for 7.2 ks. The martensitic transformation start temperature Ms of the 51Ti-27Ni-22Pd alloy was measured to be 396K by the differential scanning calorimetory (DSC).
