TiPt Base High Temperature Shape Memory Alloys

TiNi is one of the most excellent practical shape memory alloys and used as eyeglass frame, micro actuator, medical devices, and so on. Recently, the demand of high-temperature shape memory alloys is increasing to use them in gas turbines, rocket engines, automotive engines, and nuclear reactor environments. However, the martensitic transformation temperature related with the shape memory effect of TiNi is below 373 K. New alloy system should be developed to suffuse the demand. We have focused on TiPt as new high-temperature shape memory alloys due to its high martensitic transformation temperature from the B2 to B19 phases above 1173 K. The effect of Ir addition to TiPt on phase transformation and the shape memory effect has been investigated for Ti-50 (Pt, Ir)(50) with Ir contents between 5 and 37. 5at%. The phase transformation temperature increased with increasing Ir contents. Relatively large strain recovery rate was obtained in Ti-50 (Pt,Ir)(50) with 10-30at%Ir. The highest shape recovery rate was 57% in Ti-25Pt-25Ir after deformation at 1123 K, followed by heating to above A(f). Strain recovery of Ti-50 (Pt, Ir)(50) is discussed along with volume change between the B2 and B19 phases during phase transformation, lattice parameter change depending on Ir contents, and microstructure.