Effect of annealing process on phase transformation and deformation behavior of Ti-Ni-V shape memory alloy
The phase transformation behavior,tensile properties and shape memory behavior of the Ti-50.8Ni-0.5 V alloy annealed at 400℃ for 10-120 min and at 500℃ for 10-120 min were studied by differential scanning calorimetry and tensile test.The results show that with the change of annealing temperature and time,the transformation type,R transformation temperature TR and temperature hysteresisΔTR,martensitic transformation temperature TM and temperature hysteresis ΔTM,tensile strength Rm,elongation A,critical stress of stress inducing martensitic transformation σM,loading-unloading residual strain εR and energy consumption WDof the alloy vary as follows:both 400℃and 500℃annealed Ti-50.8Ni-0.5V alloys undergo B2→R→B19'/B19'→R→B2(B2-parent phase,CsCl-type structure;R-R phase,rhombic structure;B19'-martensite phase,monoclinic structure)type phase transformation upon cooling/heating.TR 400 ℃＞TR 500 ℃,TM 500 ℃＞TM400 ℃,ΔTM400 ℃＞ΔTM500 ℃(＞)ΔTR400 ℃ ≈ΔTR500 ℃≈4 ℃;Rm 400 ℃＞Rm 500 ℃,A500 ℃＞A400 ℃.The superelaticty TR400℃＞TR500℃,TM500℃＞TM400℃,ΔTM400℃＞ΔTM500℃(＞)ΔTR400℃≈ΔTR500℃≈4℃;Rm400℃＞Rm500℃,A500℃＞A400℃.The superelasticity(SE)stability of 400℃ annealed alloy is higher than that of 500℃ annealed alloy.With the increase of annealing time,TR400℃,TR500℃,TM400℃ and TM500 ℃ increase,ΔTM400 ℃ and ΔTM 500 ℃ decrease,ΔTR 400 ℃ and ΔTR 500 ℃ change in the range of3.5-4.6℃;the TR500℃,TM400℃and TM500℃increase,ΔTM400℃andΔTM500℃decrease,ΔTR400℃and ΔTR500℃change in the range of 3.5-4.6 ℃;the 400℃annealed alloy exhibits SE,while the 500℃annealed alloy undergoes a transition from SE to SE+SME(shape memory effect);σM400℃and σM500℃decrease,WD400℃andWD500℃increase,εR500℃decreases first and then increases,εR400℃changes in the range of 0.64％-1.36％.The Ti-50.8Ni-0.5V alloy can be annealed at 400℃to obtain a higher TR,can be annealed at 500℃to obtain a higher TM,and can be annealed at 400℃for 10-120 min or at 500 ℃ for 10-60 min to obtain SE at room temperature.
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