Experimental investigations on the effect of copper on the microstructure and shape memory characteristics of NiTi alloys

Shape memory alloys are fascinating materials, which have exclusively been studied over the last three decades owing to their distinctive functional properties, such as shape memory effect (thermal memory) and superelasticity (mechanical memory). These materials have a unique capability to react to external stimuli, such as heat and stress, because of the reversible martensitic transformation, when subjected to appropriate thermomechanical processing. They find applications in various sectors and are in particular used as actuators and sensors. Among SMAs, NiTi-based alloys are more common and have proven their utility in many practical applications. However, there is still a scope for improvement of the alloys in terms of their shape memory characteristics if they are to be exploited in several other critical applications. In this context, addition of copper proves to be an appropriate element to enhance the transformation characteristics and biocompatibility of NiTi SMAs. Hence, in this work NiTiCu ternary alloys were synthesized by vacuum induction melting followed by subjecting them to suitable thermomechanical treatment. These alloys were then characterized by X-ray diffraction, differential scanning calorimetry and optical microscopy in order to study the influence of copper addition on phases present, transformation temperatures and microstructure of NiTi SMAs. The results are discussed in detail in the paper.