Shape memory characteristics of the P/M-processed Ti-Ni-Cu alloys

Ti-Ni and Ti-Ni-Cu shape memory alloys (SMAs) were fabricated by the powder metallurgy (P/M) process using mechanical alloyed (MAed) powder. The phase transformation behavior shape memory characteristics and thermo-mechanical properties of the P/M alloys were investigated. The stress-strain curves of Ti-45.2 mol%Ni-5 mol%Cu and Ti-35.2 mol%Ni-15 mol%Cu alloys were stabilized by the thermo- mechanical training. The two-way shape memory effect appeared after the thermo-mechanical training. Only the Ti-30.2 mol%Ni-20 mol%Cu alloy showed clearly a two-step transformation. The transformation behavior of the P/M alloy was different than that of the wrought alloy because the Cu content of the P/M alloy was reduced by composition segregation. The narrowest hysteresis measured in Ti-35.2 mol%Ni-15 mol%Cu was 9K, which is as narrow as that of the wrought alloy. The Ti-30.2 mol%Ni-20 mol%Cu alloy had the highest stress for slip deformation due to solid-solution hardening by Cu addition. The plastic strain of the alloy thermal-cycled at 175 MPa was 0.06%. The Ti-35.2 mol%Ni-15 mol%Cu alloy had the lowest value of d sigma/dT and the alloy showed superelasticity in the austenite phase. Thus, it was found that the Ti-Ni and Ti-Ni-Cu SMAs with superior shape memory characteristics could be fabricated by the P/M process. (C) 2010 Elsevier B.V. All rights reserved.