Influence of Aging Temperature on Functional Fatigue Behavior of a Ti50Ni45Cu5 Shape Memory Alloy

Smart actuators, using materials with a memory, are an attractive alternative to conventional actuators due to their unique properties, such as high energy density, low power-to-weight ratio, simplicity of design, and miniaturization of size. However, the continuous cyclic operation of such devices, within their transformation temperature range, leads to the degradation of their functional properties. In this paper, the degradation of functional properties, such as recovery strain, permanent strain, and critical transition temperatures, of an Ni 45 Ti 50 Cu 5 (at.%) shape memory alloy, aged at four different temperatures, ranging from 450 to 600 °C, was experimentally investigated under constant stress. The results reveal that all alloys underwent a single-step transition from B2 → B19’ at all aging temperatures. The aging temperature has a significant impact on recovery strain and permanent strain. The permanent strain accumulation after every cycle is minimized as the temperature of aging is raised to 550 °C due to the strengthening of the matrix by precipitate particles. Above this temperature, it starts to increase due to the coarsening of the precipitate particles. Aging treatment also helps to achieve faster cyclic stability during thermomechanical cycling.