Residual stress and microstructural evolution in rotary friction welded Ti-6Al-4V alloy joints

This study investigates the development of residual stress and microstructural evolution in rotary friction welded (RFW) Ti-6Al-4V alloy joints fabricated under varying process parameters. RFW is a solid-state joining technique that enables defect-free welds without the use of filler materials, thereby avoiding melting-related defects such as segregation. Despite these advantages, the intense frictional heating and plastic deformation inherent to the process can induce significant residual stresses, which may adversely affect mechanical performance, corrosion resistance, and long-term structural integrity.

Neutron diffraction (ND) and X-ray diffraction (XRD) were employed to quantify residual stresses and confirm phase composition in Ti-6Al-4V dog-bone samples produced under different combinations of rotational speed, friction/forging forces, and dwell times. Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) were used for microstructural characterisation.

Residual stress analysis via ND revealed that among the process parameters investigated, friction force had the most significant impact. Axial residual stress was highest in samples welded under lower friction forces, a trend that correlated with localized hardness measurements. XRD confirmed titanium as the primary phase, with Ti₆Al₄V and other minor phases present, and no new phases formed during welding. SEM and EDX analyses revealed a predominance of the martensitic α′ phase at the weld center, transitioning to an α + β microstructure approximately 5 mm from the weld.

These findings underscore the strong influence of RFW process parameters on both residual stress development and microstructural evolution in Ti-6Al-4V alloy joints.