Microstructural development during Linear Friction Welding of titanium alloys

The application of Linear Friction Welding (LFW) to aerospace Ti-alloys components offers significant weight reduction and cost saving advantages. The severe thermomechanical deformation associated with LFW results in a localised, yet complex microstructural development, which is the subject of the present investigation. In this work, the microstructural and microhardness developments due to LFW of β-forged Ti-6246 were investigated. Metallurgical characterisation of the welds was performed using scanning electron microscopy (including electron backscatter diffraction) and microhardness. It was found that the thermomechanical deformation in the weld resulted in the formation of dynamically recrystallised metastable β-phase in the weld, which indicates that welding at the weld line occurred above the β-transus regardless of welding parameters. The width of the dynamically-recrystallised β-region, and the β-grain size was found to decrease with the increase in the consolidation (forging) pressure applied during LFW. Following post-weld heat treatment, fine α-precipitates were found to form in the weld line, resulting in a sharp increase in hardness.