Microstructural evolution and mechanical response of micro-deformation diffusion bonding Ti-6Al-4V with designed interface morphology

Abstract

This study explicates the microstructural evolution and mechanical response of the Ti-6Al-4 V joints diffusion-bonded with a micro-deformation less than 1%, assisted by pre-designed interface morphology. The interfaces composed of interfacial voids and bonded zones were developed, exhibiting varying bond rates. The interfacial voids evolved from valleys of bonding surfaces, and the bonded zones were derived from comparatively deformed ridges mainly depending on dynamic recrystallization, strain-induced migration of grain boundaries, and diffusion mechanism. The recrystallized α grains was generated due to the nucleation and rotation of sub-grains driven by pile-up of dislocations. Additionally, the diffusion of elements was significantly activated at the deformed zones (herein, referring to the bonded zones), promoting the metallurgical bonding of α / β phase interfaces. The formation of bonded zones supported for sound joining equivalent to the substrate in mechanical properties, confirmed by the void-free joint. Nevertheless, the mechanical properties of the joints were decreased when interfacial voids led to premature failure, and deteriorated more severely with narrowing void spacing. The concentration of stress and strain at void tips induced untimely initiation of cracks, and propagation guided by the trajectory of high stress. The interaction of stress field surrounding adjacent voids was enhanced under narrow spacing (less than 4 times of void length), leading to acceleration of crack initiation and propagation.