Friction welding of mild steel and titanium: Optimization of process parameters and evolution of interface microstructure

The present investigation deals with the efforts to form a defect free bonded interface between mild steel (MS) and titanium (Ti) using the rotation friction welding process. The conditions were optimized based on several trials by varying friction welding parameters like frictional force, upset force, burn-off length and rotational speed. It has been established that only fine FeTi particles formed in isolated regions at the interface of 'as welded' MS/Ti joints. The evolution of interface microstructure has been studied by diffusion annealing heat treatments in the temperature range of 500-800. °C for a duration of 100. h. Plastic deformation during friction welding reduced the recrystallisation temperature of MS. The variation in microchemistry was measured across the weld interface, which was used as input to predict the formation of various phases and the consequent change in the mechanical properties using the JMatPro® software. Intermetallics were present only as fine isolated particles in bcc-Fe matrix at the interface even after heat treatment at 800. °C for 100. h. The growth kinetics was found to be much slower in friction welded joints as compared to diffusion bonded and explosive clad joints.