High strength welds in titanium & nickel based alloys by impact welding – A practical method

Abstract

Joining titanium-based alloys to nickel-based superalloys is of great interest for applications in aerospace propulsion. Direct welding of these materials using conventional welding methods is very difficult as they are prone to heat affected zone and formation of strain-aged cracking. The purpose of this study is to produce multiple weld combinations of Ni-based superalloys (Ni-230, Ni-718, and Ni-625) to a near-alpha Ti-based alloy (6242), Ti to Ti, and Ni to Ni welds using Vaporizing foil actuator welding (VFAW) technique. The bonding quality of the joints was evaluated by mechanical lap shear and peel tests. The microstructural characterization of the weld interface was analyzed by scanning electron microscopy and energy dispersive spectroscopy (EDS). The VFAW technique was successfully used to create 6 dissimilar and 4 similar combinations presented at various levels in this work. The Ni-Ti joints displayed mixed failure modes in both lap shear and peel tests, whereas nugget failure was observed for similar weld and dissimilar Ni-Ni joints. EDS maps of the peel surfaces showed both ductile and brittle facets that signified the material transfer between both parent materials. Irrespective of weld combinations, the microstructure showed a transition from a smooth bonding interface at the weld center to a wave profile showing a natural spatial progression as the weld forms. The VFAW process can be of interest in aerospace industries to join different exotic grade alloys, difficult to weld using conventional welding methods.