Influence of Hf Solute Addition on the Shape Memory and Superelastic Behavior of NiTi Alloy

NiTi alloys (SMAs) are unique alloys, which have two attractive properties, shape memory effect and superelastic behaviour. Each property strongly depends on the composition, temperature and structure. The microstructure was investigated by optical microscopy, and chemical composition was analyzed using line scan analysis with energy dispersive X-ray spectroscopy. X-ray Diffraction (XRD) analysis of the bulk samples was conducted. The transformation temperatures were measured by Dilatometry. The shape memory and superelastic behavior of material were investigated using loading-unloading test and in-situ thermal cycling by applying electrical current at the end of sample and the shape changes of the bi-layers were recorded using a digital camera. The solute addition of Hf to NiTi alloy, led to a Two-way shape memory effect after tensile deformation. The Hf solute additions on NiTi alloy provides bell-curve shape memory behaviour during stress-free thermal cycling after 12 percent tensile deformation which demonstrates the acute influence of Hf additions on the material's properties.