THE EFFECTS OF COLD-ROLLING ON THE MARTENSITIC-TRANSFORMATION OF AN EQUIATOMIC TINI ALLOY

The effects of cold rolling on the martensitic transformation of an equiatomic TiNi alloy have been studied by internal friction and shear modulus measurements, hardness test and TEM observation. The martensite stabilization can be induced by cold rolling at room temperature. A variety of deformed martensite structures has been observed. Both deformed martensite structures and deform-induced dislocations/vacancies are considered to be related to the martensite stabilization. The hardness test results also support this viewpoint. After the occurrence of the first reverse martensitic transformation of B19' --> B2, the martensite stabilization dies out and the transformation temperatures are depressed by retained dislocation on subsequent thermal cycles. Experimental results indicate that the martensite stabilization can depress the rate of martensitic transformation in the equiatomic TiNi alloy.