Dissimilar laser welding of superelastic NiTi and CuAlMn shape memory alloys

Dissimilar joining of advanced engineering alloys is fundamental for the development of new applications. However, joining two distinct materials poses difficulties owing to the several metallurgical and thermo-physical problems that can arise. This paper describes the work performed on dissimilar laser welding of NiTi and CuAlMn shape memory alloys, superelastic at room temperature. Detailed microstructural characterization was performed. The complex microstructure of the dissimilar joint is explained based on the characteristics of laser welding, namely material and heat flow, high cooling rates and thermal gradients within the fusion zone. Cycling tensile testing revealed that the joints preserved the superelastic behaviour despite the unfavourable microstructure of the fusion zone which translates into an irrecoverable strain of 2% when cycled at 5% strain. These results may open the possibilities for new applications based on this dissimilar combination which can combine superelasticity and higher thermal and electrical conductivity (with the latter two characteristics arising for the CuAlMn shape memory alloy).