Study on Microstructure and Properties of Ti-49.8Ni Shape Memory Alloy As-annealed

The effects of annealing temperature (Ta) and deforming temperature (Td) on the microstructure and shape memory behavior of Ti-49.8Ni shape memory alloy wires and springs were investigated by optical micrometry and tensile test. The results show that the microstructure of cold-worked Ti-Ni alloy is fibroid. After annealing,the microstructure of the alloy is gradually changing from fibroid to equi-axed grain,and the martensite reoriented stress of the alloy wires and springs decreases first and then increases with the annealing temperature increasing. The annealed alloy shows shape memory effect at room temperature. With the deforming temperature increasing,the martensite reoriented stress increases,the portion of shape memory effect decrease and that of superelasticity increase gradually.