Study Of Two-way Shape Memory Effect And Transformation Behavior In TiNiCu Shape Memory Alloy

In this paper, the influence of the aging temperature and the training deformation on the two-way shape memory effect (TWSME) and transformation behavior in TiNiCu shape memory alloy spring has been systematically studied. The TWSME of spring was thermal cycled in order to investigate the stability of the TWSME in TiNiCu shape memory alloy coil spring after training. In the heat-treated temperature range from 400°C to 600°C, the two-way shape memory recovery rate increases in the annealing temperature range from 400°C to 450°C, then decreases above 450°C after 100 training cycles and 2000 thermal cycles. Therefore, the maximum two-way shape memory recovery rate is obtained at aging temperature 450°C. During thermal cycling, the two-way shape memory recovery rate decreases rapidly in the initial 100 thermal cycles, then the two-way shape memory recovery rate is almost unaffected with the further thermal cycling. Moreover, the different precipitations in the alloy were determined by XRD. Fcc-Cu phases are precipitated in the alloy in aging temperature range from 400°C to 600°C. Cu₃Ti phases were found in the aging temperature 400°C and 450°C, but Cu₄Ti and NiTi phases were precipitated above the 450°C.TiNiCu SMA springs show various two-way shape memory recovery rates through thermomechanical training processes when five different training deformations are employed. In the range of x₁=70mm to X₄=250mm, the two-way shape memory recovery rate increases with increasing training deformations, but above the training deformation X4=250mm, the two-way shape memory recovery rate decreases. At the point of training deformation X₄=250mm, we can obtain the maximum two-way shape memory recovery rate 76% with thermomechanical training, and this two-way shape memory recovery rate still maintains 74% after thermal cycling.The transformation temperatures increase with the increase of aging temperature. However, As and Af are decrease above 500°C. For the sample of the heat-treated 450°Cx1h/WC, after thermomechanical training, the transformation temperatures Ms, Mf and Af are obviously lower than those of the untrained sample, and As rises slightly. In the initial stage of thermal cycling (100 thermal cycles), the transformation temperatures shift greatly, but are becoming stable in the further thermal cycling. The results of the experiment for the sample of heat-treated 450°Cx1h/WC show that the transformation temperatures changed little after 100 training cycles and 2000 thermal cycles when the training deformation is 250mm, which is very important for TiNiCu SMA spring to use as the actuator.