Effect of temperature on fatigue of superelastic NiTi wires

The stress induced martensitic transformation in superelastic NiTi alloy can be accompanied by a plastic deformation. In this work, NiTi wires were subjected to tensile displacement-controlled tests in the temperature range -90 degrees C to 190 degrees C and lattice defects created by the deformation were analysed by TEM. The unrecovered strain significantly increased and fatigue life decreased with increasing test temperature. The rate of the accumulation of unrecovered strain in the stabilized stage of tensile cycling was taken as an indicator of the accumulation of material damage. Fatigue life ranged from 900 cycles at 80 degrees C to 4700 cycles at 15 degrees C.