Functional fatigue recovery of superelastic cycled NiTi wires based on near 100 °C aging treatments

Functional fatigue affecting superelastic behaviour of NiTi wires includes an accumulation of residual strain and an uneven decrement of transformation stress on cycling. Although this evolution is observed to diminish asymptotically, it represents an important loss in the maximum recoverable strain level and in the hysteretic dissipative capacity of the material. In this work, the effect of moderate temperature aging treatment on the functionally degraded material properties was studied with two experimental setups. NiTi pseudoelastic wire samples of 0.5 and 2.46 mm diameter were subjected to different cycling programs intercalated by aging treatments of different durations up to 48 h at 100°C. Results show that important levels of recovery on the residual strains and the transformation stresses were attained after the aging treatments. The analysis indicates that the characteristics of the recovered cycles are rather independent from the treatment duration and from the reached condition before each treatment