A comprehensive review on non-conventional machining of Nickel-Titanium alloys: Techniques and surface integrity

Abstract

• Review focuses on NCM of NiTi alloys like WEDM, EDM, ECM, and laser machining. • Voltage, PON, and POFF are key inputs affecting SR, MRR, and recast layer. • Brass and tungsten electrodes are widely used, with varying surface effects. • High discharge energy increases cracks, craters, and oxide layer formation. • Oxides like TiO₂ and NiTiO₃ raise hardness but can impact SME properties. • Mo electrodes and ECAM are suggested for improved machining and surface quality. Nickel-Titanium (NiTi) shape memory alloys (SMAs) are widely used in biomedical implants, aerospace structures, and precision robotics due to their unique properties such as pseudo-elasticity, shape memory effect (SME), and corrosion resistance. However, their poor machinability limits the use of conventional techniques. This review critically evaluates major non-conventional machining (NCM) processes, including WEDM, EDM, ECM, laser-based, and hybrid techniques, with a focus on their influence on surface integrity, material removal rate (MRR), and electrode-tool interaction. The analysis reveals that while WEDM and EDM are popular, they often compromise SME due to thermal effects, whereas ECM and ECAM offer superior surface finish with minimal thermal damage. Notably, molybdenum electrodes reduce surface contamination, enhancing suitability for biomedical applications. The study provides actionable insights for selecting and optimizing NCM processes tailored for high-performance NiTi SMA components in medical, aerospace, and micro-mechanical systems.