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Friction welding techniques are a family of solid-state joining processes in which heat is generated by mechanically rubbing two workpieces against each other under an applied compressive force, bringing the material at the interface into a plasticized state without melting, after which the relative motion is stopped and an upset force forges the parts together into a coherent bond ^[1]. In conventional rotary and inertia friction welding, one part is rotated relative to the stationary part while being pressed against it, and in friction stir welding a non-consumable rotating tool traverses along a joint, its shoulder and probe generating frictional heat that plasticizes the surrounding material and stirs it into a consolidated seam ^[2]. Because the material never fully melts, friction welding is distinguished from fusion welding by the solid-state nature of the bond, which relies on severe plastic deformation, dynamic recrystallization, and intimate contact at temperatures below the equilibrium melting point ^[1]. The process is defined by conversion of mechanical energy into interfacial heat, followed by axial forging that expels contaminated interface material as flash, so that the joint forms in the solid state and is governed by the temperature, pressure, and material flow in the stirred or rubbed region ^[2]. These techniques share the generation of interfacial heat by friction and the absence of bulk liquid formation ^[3].