Multi-stage transformation in annealed Ni-rich Ti49Ni41Cu10 shape memory alloy

Multi-stage transformation (MST) in 500 degrees C annealed Ni-rich Ti49Ni41Cu10 shape memory alloy (SMA) is investigated by differential scanning calorimetry (DSC), dynamic mechanical analyzer (DMA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). The as solution-treated alloy undergoes B2 <-> B19 <-> B19' two-stage transformations. Ti(Ni,Cu)(2) precipitates are formed in 500 degrees C annealed specimens. Alloy annealed at 500 degrees C for 6-24 h exhibits MST. This MST is confirmed by DMA tests and is composed of B2(1) <-> B19(1) <-> B19'(1) and B2(2) <-> B19'(2) <-> B19'(2) transformations corresponding to the regions near and far from Ti(Ni,Cu)2 precipitates, respectively. Experimental results show that the more the annealing time, the more the B2(1) <-> B19(1) <-> B19'(1) transformations and finally only B2(1) <-> B19(1) <-> B19'(1) transformations retain with the transformation temperatures close to those of Ti50Ni40Cu10 SMA. (C) 2009 Elsevier Ltd. All rights reserved.