Effects of annealing temperatures on transformation,microstructure and tensile properties of Ti-50.8Ni-0.1Zr alloy

Effects of annealing temperatures(Ta) on microstructure,transformation behavior and tensile behavior of Ti-50.8Ni-0.1Zr shape memory alloy were investigated by DSC,optical microscopy and tensile tests.The results show that when Ta=400 ℃,the transformation types during cooling or heating is A→R→M/M→R→A(reversible transformation with two stages),when Ta=500 ℃,the reversible transformation types is A→R→M/M→A,the R phase doesn't occur at the reverse transformation of R phase.When Ta=600-700 ℃,the reversible transformation types are A→M/M→A(one stage).The recovery,recrystallization and grain growth occur in the alloy during annealing.When Ta=350-450 ℃,the alloy is at the recovery stage,and the microstructure is fibriform.When Ta=500-600 ℃,the alloy is at the recrystallization stage,the microstructure turns to the unstrained equiaxed grains.When Ta=600-800 ℃,the alloy is at the grain growth stage,the microstructure shows larger and asymmetrical grains.With the increasing annealing temperature(Ta),the tensile strength of the alloy decreases,the critical stress of the stress-induced martensitic transformation declines at first and then rises,but the elongation of alloy increases at high annealing temperature,and then decreases due to the grain growth when Ta600 ℃.