Microstructure evaluation of magnetic field-assisted dissimilar laser welding of NiTi to stainless steel

Abstract

Significant attention has been directed to the need for a strong and lightweight welding technology for joining the NiTi shape memory alloys (SMAs) to stainless steel (SS). Dissimilar NiTi/SS joints suffer from the brittle and inevitable intermetallic components (IMCs) like TiFe, TiFe2 and FeNi that are formed during the welding process. To tackle this challenge, this study explores the use of an engineered magnetic field during the dissimilar laser welding of NiTi to SS. The presence of a magnetic field delivered a remarkable improvement in tensile strength (over 452 MPa) of the joint with a notable difference in microstructure. The effect of the magnetic field on microstructure was investigated; material characterizations showed brittle IMC-free microstructure and a change in grain growth mechanism from columnar to cellular growth during the solidification. Further, fractography analysis proved a ductile failure mode at the joint.