Influence of Cu addition to improve shape memory properties in NiTi alloys developed by laser rapid manufacturing

Abstract

In recent times Ni-Ti shape memory alloy flaunts exceptional outputs in the line of MEMS, serving as actuators. An attempt has been successfully made to develop Ni-Ti structures using laser rapid manufacturing (LRM). However the occurrence of brittleness was a drawback in the attempt. As a remedial measure Cu is included along the binary alloy to form a ternary alloy. Also the inclusion of Cu has an advantage of low hysteresis generation during phase transformations. Developing NiTiCu shape memory alloy by additive manufacturing is a novel approach for this work. The substitution of Cu with Ni can be up to 15 wt% to 30 wt% to possess shape memory properties[1]. In the current investigation combination of Ti50% Ni25% Cu25% alloy formation has been done and it is represented as NiTiCu25. Investigations were carried out to determine the product's surface morphology, phase transformation temperature, crystalline nature through scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and x-ray diffraction (XRD) respectively. These results are compared with equiatomic Ni-Ti which has been manufactured using LRM. From the investigations it was observed that the inclusion of Cu gives improved surface texture and multiple phase peaks in XRD. Also the heat flow curves which had steep peaks in DSC analysis, indicate the presence of phase transformations in the samples fabricated using LRM.