THE EFFECT OF COLD WORK, HEAT-TREATMENT, AND COMPOSITION ON THE AUSTENITE TO R-PHASE TRANSFORMATION TEMPERATURE OF NI-TI SHAPE-MEMORY ALLOYS

The influence of cold work (CW) and heat treatment (HT) on the austeni te to R-Phase (A-->R) transformation temperature (TT) of a near equiat omic and three other Ti rich NiTi SMA is examined. For the SMA having a near equiatomic composition, the A-->R TT increases with increasing CW at low HT temperatures. For the SMA having the maximum possible Ti content, the A-->R TT decreases with increasing CW at low HT temperatu res. For all compositions, the A-->R TT is not sensitive to CW at high HT temperatures. At a Ti content slightly below the maximum possible, the A-->R TT is relatively insensitive to CW and HT temperature. For all of the SMA investigated, the A-->R TT increases with increasing Ti content for a specific CW and HT temperature, and this effect is grea test at low CW and at high HT temperatures.