Friction welding is classified as a solid-state welding technique, where joining takes place through intensive friction which locally heats the workpiece material into a plastic state in conjunction with an applied force. Since there is no bulk melting of the workpiece, common problems associated with fusion welding such as solidification cracking, porosity and the loss of volatile alloying elements are avoided.
Due to the high temperatures and cooling rates, as well as the extensive thermomechanical deformation associated with friction welding techniques, there are considerable changes in the microstructure and texture of the weld region leading to changes in the mechanical properties. Transient thermal cycles and mechanical deformation also lead to the development of strong residual stresses within the weld, albeit they are much lower than in conventional fusion welds.
Research work has combined microstructural characterisation using electron and optical microscopy, structural integrity (i.e. mechanical property) assessment and neutron and X-ray diffraction to improve the understanding of the process mechanisms.