The machining characteristics and surface integrity of Ni-rich NiTi shape memory alloy using wire electric discharge machining

Owing to the increasing demand for Ni-rich shape memory alloys in various sectors such as biomedical, aerospace, and robotics, the efficient machining of shape memory alloys is vital for their productive exploitation. The aim of this experimental investigation is to explore the influence of wire electric discharge machining process parameters such as spark gap voltage, wire tension, spark off time, wire speed, and spark on time, on the cutting efficiency and surface roughness of Ni50.89Ti49.11 SMA using one factor at a time approach. The results reveal that cutting efficiency and surface roughness are strongly influenced by spark off time, spark on time, and spark gap voltage, whereas wire speed and wire tension have the inconsequential effect. The presence of many microcracks, craters, voids, bulges of debris, and the re-solidified layer of molten material on the machined surface have been detected in scanning electron micrographs. The results of phase analysis using energy-dispersive X-ray spectroscopy and X-ray diffraction divulge the migration of foreign elements from the brass wire and dielectric to the machined surface. Due to the formation of recast layer and various oxides, the hardening effect near the machined surface was also observed. The hardness near the machined surface has been increased several times in comparison to bulk hardness.