Effect of Heat Treatment and Cyclic Strain on Shape Memory Effect and Superelasticity of TiNiZr Alloy

The effects of annealing processes, aging processes and cyclic strain on shape memory effect (SME) and superelasticity (SE) of Ti-50.8Ni-0.1Zr shape memory alloy were investigated by tensile test, optical microscopy and TEM. The alloys annealed at 350 similar to 400 degrees C and 600 similar to 700 degrees C present SE, the alloys annealed at 450 similar to 550 degrees C present SME, the alloys aged at 300 degrees C for 1 similar to 50 h and at 400 degrees C for 1 h present SE, and the alloys aged at 400 degrees C for 5 similar to 50 h and 500 degrees C for 1 similar to 50 h present SME. With increasing annealing temperature, the platform stress (sigma(M)) of the stress-strain curve in the alloy decreases firstly and then increases, and the minimum 200 MPa is obtained in the alloy annealed at 500 degrees C; the residual strain (epsilon(R)) increases firstly and then decreases, and the maximum 2.64% is obtained in the alloy annealed at 500 degrees C. With increasing aging time, the am decreases, and the epsilon(R) is small in the alloy aged at 300 degrees C; the sigma(M) decreases, and the ER increases firstly and then tends to be stable in the alloy aged at 400 and 500 degrees C. With increasing stress-strain cycle number, the alloy presenting SE transforms from partial nonlinear SE to fully nonlinear SE, and the sigma(M) and energy dissipation (Delta W) decrease firstly and then tend to be stable; the sigma(M) and Delta W decrease firstly and then tend to be stable in the alloy presenting SME.