Effect of heat treatment on transformation behavior of Ti-49.8Ni-1.0Co superelastic alloy
Zhi-rong HE;Fang Wang
陕西理工学院材料科学与工程学院
Cite this article:
Zhi-rong HE; Fang Wang. Effect of heat treatment on transformation behavior of Ti-49.8Ni-1.0Co superelastic alloy. Acta Metall Sin, 2008, 44(1): 23-28 .
Abstract The deformation characteristics of annealed Ti-49.8Ni-1.0Co (atomic percentage) alloy at room temperature were studied with differential scanning calorimetry (DSC) and tensile testing. The effects of annealing and aging processes on transformation behaviors of the alloy were systematically investigated by DSC. Ti-49.8Ni-1.0Co alloy shows superelasticity (SE) at room temperature. After replacing Ni with Co, the R phase (R) and martensitic (M) transformation temperatures, the transformation peak area, the SE stress and the SE loop area of the alloy are all decrease. The A→R→M/M→R→A (A-parent phase) type reversible transformation occurred in the 350-450℃ annealed alloy upon cooling / heating, the A→R→M/M→A type occurred in the 500-550℃ annealed alloy, and the A→M/M→A type occurred in above 600℃ annealed alloy. With increasing aging time, the transformation type of 300℃ aged alloy transforms from A→R→M/M→R→A to A→R→M/M→A, the one of 400℃ aged alloy transforms from A→R/R→A to A→R→M/M→R→A to A→R→M/M→A, and the one of 500℃ aged alloy is A→R→M/M→A constant. The influencing regularity of annealing temperature, annealing time, aging temperature and aging time on the R, M transformation temperature and temperature hysteresis were given out.