Nd:YAG laser processing of thick NiTi wires to locally alter transformation properties towards achieving multiple memory shape memory alloys

Every commercial NiTi (Nitinol) Shape Memory Alloy (SMA) has its own transformation temperatures, which may cause limitations in ever-growing demands for the application of these alloys in novel engineering design. Among various methods proposed to achieve multiple functional characteristics, laser processing offers effective solutions in locally controlling the transformation properties of NiTi parts. The current work describes the application of laser technique followed by post processing to locally alter transformation temperatures and impose phase transition for thick NiTi wires. To this end, various laser parameters are applied, and the influences of peak power and pulse width on the functional, microstructural and mechanical properties of laser processed samples are studied. A four-sided laser processing protocol is proposed to process almost the whole cross section of thick Nitinol wires. It is also shown that post-processing heat treatment is required to recover the shape memory properties of as-processed Nitinol specimen. The transformation temperatures of final processed Nitinol wire increase by about 50 °C compared to those of the unprocessed base material.