2008 Volume 49 Issue 7 Pages 1650-1655
Effects of pre-strain and heat treatment on shape recovery stress and phase transformation temperature in Ti-Ni-Nb shape memory alloys with various Nb content (6, 9, and 12 mol%) were investigated by tensile testing. The recovery stress of Ti-Ni-Nb alloys increased with increasing the pre-strain and then decreased after reaching the maximum recovery stress of around 450–500 MPa at about 9% pre-strain. Martensitic transformation temperatures (Ms, As, Af) also increased with increasing the applied pre-strain, while the relation between As and pre-strain did not depend on the Nb contents and Ni/Ti ratio. Moreover, the recovery stress in the Ti-Ni-Nb alloy heat treated at 673 and 773 K after solution treatment was slightly higher than that in the solution-treated alloy. These behaviors were examined relative to the increased defect density due to pre-straining and the elimination of defects by heat treatment.