Mitigation of cracks in laser welding of titanium and stainless steel by in-situ nickel interlayer deposition

Abstract

• Fusion joining of SS-Ti by directed energy deposition of Ni interlayer demonstrated. • Ni interlayer restricted brittle intermetallic formation of Fe and Ti. • Ni between SS and Ti formed joint with graded thermal expansion coefficient. • Thus, Ni interlayer eliminated longitudinal and transverse cracks in SS-Ti joint. • Directed energy deposition of Ni interlayer improved the weld strength. In-situ laser deposition of Ni powder as an interlayer has been exploited to join dissimilar metals, titanium and stainless steel. Direct fusion joining of these materials often suffers from longitudinal cracks due to the formation of hard and brittle intermetallics of Ti and Fe, and also transverse cracks because of large difference in their thermal expansion coefficients. The Ni-interlayer mitigated the longitudinal cracks by acting as an effective barrier to elemental diffusion, thus restricting the growth of brittle intermetallics. As the thermal expansion coefficient of Ni lies between that of SS and Ti, this acted as a functionally graded layer to reduce the thermal residual stresses, thus preventing the formation of transverse cracks across the joint. Maximum ultimate tensile strength of the weld joints obtained was 375 MPa. Results were analyzed by performing various microstructural characterizations using scanning electron microscopy, x-ray diffraction, and energy-dispersive X-ray spectroscopy. The novelty of this method is its easy adaptability in three dimensions contour welding any dissimilar metals using an interlayer of a compatible material.