Recent Progress in Laser Welding of NiTi Based Shape Memory Alloys

Successful adoption of NiTi based shape memory alloys (SMAs) in engineering designs requires metallurgical joining, where current mechanical joining techniques are unfavourable or even impossible. There are a number of joining methods that have been investigated for use with NiTi alloys, which include resistance, friction and laser welding. Laser welding has been identified as the most promising joining method, capable of achieving up to 80% joint efficiency. Difficulty in joining these NiTi SMAs is not limited to achieving acceptable joint strength but also includes maintaining the shape memory and pseudoelastic properties required in application. Given that the underlying mechanism responsible for their unique properties is a reversible thermo-mechanical diffusionless phase transformation; these alloys are extremely sensitive to alloy composition and past processing history. In this review, current insight into how laser welding processes affect the mechanical and functional properties of the NiTi SMAs is presented. Issues in laser welding including solidification cracking, brittle intermetallic formation, modification of functional properties, and dissimilar material combinations are discussed. In addition the development of novel laser technologies, stemming from laser welding know-how, capable of locally altering performance will be discussed. The information presented in this review outlines the status of current laser welding and processing technologies and techniques as applied to NiTi based SMAs, facilitating increased future applications.