EFFECTS OF COLD-ROLLING AND POST-DEFORMATION ANNEALING ON THE MARTENSITIC-TRANSFORMATION OF A TINI SHAPE MEMORY ALLOY

The thermoelastic transformation of shape-memory titanium -nickel alloys is highly influenced by the microstructural state of the alloy and particularly by the plastic deformation of the metal. In this study, the influence of cold-work and annealing on martensitic and austenitic transformations is performed with ''in situ'' thermoelectric power measurements during thermal cycling. In the recrystallized state the transformations are very well defined, and the thermal hysteresis is generally less than 30 degrees. After work hardening the transformation becomes ''diffuse'' and is no longer observed if the deformation is greater than a critical value of approximately 25%. The effects of post-deformation beat treatments were also characterized using a heavily cold- worked metal within a temperature range of 300-600-degrees-C. Thermoelectric power measurements applied to the characterization of shape-memory alloy transformation proves to be a high performance tool displaying a great sensitivity to martensitic transformation.