EFFECT OF AGING AND ANNEALING ON THE ELECTRICAL-RESISTIVITY OF PROTON-IRRADIATED NITINOL

The electrical resistivity of a initinol alloy before and after irradiation with a 2 MeV proton beam, was measured in the temperature range 233-353 K. A sharp rise in resistivity, in the irradiated sample, irradiated to a fluence of 6.6 x 10(15) cm(-2) which was achieved over a period of 6 h, at the martensite transformation was detected around the transition temperature T-c. The increase in resistivity is many orders of magnitude higher than what is normally observed at T-c for pure unirradiated nitinol. It has been noted that this significant change in resistivity observed at the transition temperature occurs at a short temperature interval. It was observed in one of the irradiated samples aged at room temperature (297 K), that the electrical resistivity reaches a maximum value after 8 days aging at room temperature, then it decreases exponentially to the original value after 76 days aging. Annealing the irradiated samples at higher temperatures decreases the relative electrical resistivity but the sharpness of the transition is not affected, however annealing the irradiated samples for 2 h at 520 K removes almost completely the induced defects of irradiation.