Effect of Heat Treatment on the Structural Properties and Martensitic Transformation of Ni-26.5at. %Ta High Temperature Shape Memory Alloy

Abstract

The effect of heat treatment at 450 oC, 550 oC and 650 oC temperatures for 1 hour on the structuralproperties and the transformation behaviour of Ni-26.5at. %Ta high temperature shape memoryalloy have been examined by XRD, SEM-EDX analysis and DSC measurements. The SEM-EDXinvestigations showed that microstructures of all heat-treated alloy samples consisted of Ta-richNiTa2 precipitate phase and matrix. The XRD results indicated that both numbers and intensitiesof martensite phase reflections of the alloy highly increased as a result of heat treatment at 650oC. This was indication that the structural properties of the alloy were significantly affected byheat treatment at 650 oC. The thermal measurements revealed that the high temperature shapememory behaviour of the alloy did not changed with heat treatment. However, it was seen thatheat treatment performed at 450 oC caused shifting martensitic transformation temperatures ofthe alloy and hence transformation hysteresis value of the alloy increased.