Martensite Stabilization Effect in the Ni50Ti50 Alloy After Preliminary Deformation by Cooling Under Constant Stress

The martensite stabilization effect was studied in Ni − 50.0 at% Ti alloy after cooling under stress and compared to the same observed effect after deformation in the martensite state. After cooling under stress, three peaks of heat release were observed during the first heating, and an increase in the residual strain significantly increased the temperature of the third peak. The existence of three peaks was attributed to the formation of both non-oriented and oriented martensite upon cooling under stress. The way of the preliminary deformation hardly affected the shift in the finish temperature of the reverse transformation. Thus, the reason for the martensite stabilization effect did not depend on the type of deformation. It was assumed that the damaged intermartensite interfaces, which formed when the oriented martensite plates touched each other during growth, lost their mobility and overheating was needed to provide their movement upon subsequent heating. It was found that the way of the preliminary deformation influenced the martensite stabilization effect for the start temperature of the reverse transformation. It was assumed that this effect might be caused by different variations in the stored elastic energy during the active deformation in martensite or on cooling under stress.