Phase transformation behavior and shape memory response of a novel NiTiHfCu alloy subjected to high pressure torsion and post-deformation annealing

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: 1214-UFGNSM2021
University of Tehran
A novel Ni44.8Cu5Ti45.2Hf5 shape memory alloy was processed by high-pressure torsion (HPT) for five turns under a pressure of 6 GPa at room temperature and then subjected to post deformation annealing (PDA) at 450°C for 10 min. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) results approved that HPT processing processed by annealing significantly decreases transformation temperatures as compared with the as-cast alloy. The observation was attributed to the grain refinement during the process of severe plastic deformation. The results obtained from thermal cycling under constant stress experiments revealed that HPT followed by post-deformation annealing improved shape memory behavior of the alloy by vanishing irrecoverable strain and decreasing the width of thermal hysteresis. Shape memory strain of abour 6.5% with almost no residual irrecoverable strain was generated in the HPT+PDA-processed alloy under a tensile stress of 200 MPa.
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