HIGH-TEMPERATURE INTERNAL-FRICTION IN NI TI ALLOY

Former internal friction studies concerning NiTi alloys are currently limited to tile temperature range 300 K-400 K relative to the martensi tic transition. This paper describes results obtained by isothermal me chanical spectroscopy between 400 K and 1050 K with a sample in austen itic phase after different thermomechanical treatments: cold rolled de formed by tension, submitted to successive transition cycles or anneal ed at high temperature. Two relaxation peaks superimposed to a low fre quency (i.e. high temperature) background were found. For the first on e (520 K at 1 Hz) both, the variation of the relaxation strength with the measurement temperatures and the relaxation parameters (Ea = 1.35 eV and tau(0) = 2.5x10(-14) s) correspond to a Zener relaxation. The h igh temperature peak (870 K at 1 Hz) was associated with a relaxation due to dislocation segment motion.