Laser welding of TiNi shape memory alloy and stainless steel using Co filler metal

Dissimilar metal joints of TiNi shape memory alloy wire and stainless steel wire were welded by laser welding method with and without Co filler metal. Comparative microstructure and properties of laser welded joints with and without Co filler metal have been detailed investigated. The effects of Co filler metal thickness on joint microstructure and properties were also discussed. The results indicated that the addition of Co filler metal had great effect to improve joint microstructure and properties. When 20 μm thick Co filler metal was used, the joint tensile strength and elongation reached the maximum values (347 MPa and 4.2%), and the corresponding joint fracture mode changed from pure brittle feature to mixture of cleavage and dimples due to decreasing brittle intermetallic compounds such as TiFe2, TiCr2, etc. But excessive Co addition resulted in decreasing the joint properties because of forming more Co–Ti intermetallic compounds.

► Laser welding was achieved using Co filler metal between TiNi SMA and stainless steel.
► Weld composition and structure changed by adding Co filler metal.
► Increasing Co filler metal thickness caused decreasing of brittle phases (TiFe2, TiCr2, etc.).
► Excessive addition of Co results in forming more Co–Ti intermetallic compounds.