Laser micro-welding of NiTi to stainless-steel via in-situ high entropy alloying in the fusion zone

Welding NiTi and stainless steel (SS) wires is of great importance for device fabrication within the medical industry. Production of Ni–Ti and Fe–Ti-based intermetallic compounds (IMCs) in the fusion zone (FZ) makes joining extremely challenging. This study aims to eliminate IMCs in the FZ by generating an in-situ high-entropy alloy (HEA) FZ of NiTi–SS wires. A custom Co–Cr–Ni powder was created to target a face-centred cubic (FCC) CoCrNiFe HEA FZ. Temporal pulse shaping was investigated by using different laser power/duration during the welding. It was discovered that long, low-power pulses were effective in obtaining a fully FCC HEA joint. However, IMC precipitation occurred at the NiTi–FZ interface. Results showed a 60% increase in tensile strength and a 47% increase in strain.