Effects of Thermo-mechanical Processing on the Mechanical Properties and Shape Recovery of the Nanostructured Ti50Ni45Cu5 Shape Memory Alloy

The main purpose of this research is to evaluate effects of the thermo-mechanical treatment of cold rolling followed by annealing on microstructure and shape recovery of the nanostructured shape memory Ti50Ni45Cu5 alloy. Several samples were produced by the copper-boat vacuum induction melting technique. The as-solidified samples were homogenized and hot rolled at 900̊C. The hot rolled samples were then cold rolled up to 70% thickness reduction followed by annealing at 400 ̊C for 1 h. The microstructures and critical temperatures of the alloys were characterized by scanning electron microscopy, X-ray diffraction and differential scanning calorimetry, respectively. According to the results, the average grain size was decreased by increasing the thickness reduction. Microstructure of the sample with 70% thickness reduction had a bimodal size distribution of Nano-sized austenite grains within the amorphous matrix. The dislocation density was increased up to 1013mm−2 in the specimen with 70% reduction. During the annealing process, the softening processes and crystallization of the amorphous shear bands occurred together, resulting in a nanostructured austenitic microstructure. The crystallization temperature was about 330̊C. The shape recovery percentage was increased by cold rolling.