Effect of Thermal Cycling on Transformation Temperatures of Ti-Ni Thin Films.

Abstract

The effect of thermal cycling on the transformation temperatures was investigated in TiNi alloys which were subjected to various types of thermo-mechanical treatments. In solution-treated specimens with various Ni-contents, the transformation temperatures were found to change with thermal cycling. However, in aged Ni-rich specimens and those annealed at a temperature lower than the recrystallization temperature after cold working, they were found to be constant even after thermal cycling. Transmission electron microscopy revealed that dislocations were introduced by thermal cycling in the solution-treated specimens and their density increased with increasing number of thermal cycles. However, in the specimens with constant transformation temperatures, no substantial change in the microstructures was observed with thermal cycling. On the basis of these results, it is concluded that the shift of the transformation temperatures with thermal cycling is due to the introduction of dislocations, but not due to any ageing effect nor due to a change in the degree of order during thermal cycling.