Effect of Mode of Heating on Cyclic Temperature Range during Partial Thermal Cycling under Constant Stress of a Near-Equiatomic Ni-Ti Shape Memory Alloy

The effect of different modes of heating, viz. current-controlled and temperature-controlled modes, on the upper and lower cycle temperatures during partial thermal cycling of a binary near-equiatomic Ni-Ti shape memory alloy under constant stress was experimentally investigated. The sheet specimens were subjected to partial thermal cycling (Tmin<Mf to Tmax<Af), keeping the stress constant at 100 MPa, for 1000 cycles. The heating of the sample to a predetermined temperature was done by passing an electric current by two different methods: 1. current-controlled mode (supplying a current of constant magnitude for a fixed length of time) and 2. temperature-controlled mode (fixing the upper cycle temperature using a temperature feedback mechanism). An analysis of the cycling temperature reveals that there is an increase in the lower cycle temperature during the temperature-controlled mode of heating. In contrast, both upper and lower cycle temperatures vary significantly during the current-controlled mode of heating.