Modeling void closure in solid-state diffusion bonding of TC4 alloy

An analytical model is developed in effort to characterize the closure of interface void in the joint fabricated using solid state diffusion bonding (SSDB). Based on considering the relationship between the micro-deformation of the contact surface asperities and the macro-deformation of the joint, the model firstly quantitatively predicates the contribution of macro-deformation of joint on the bonding ratio without assuming the interface void geometries before analyzing the mechanisms of plastic and creep deformation. Furthermore, cooperating with the mechanisms of surface and interface diffusion, the correlation between the void closure (i.e. bonding ratio) and bonding parameters is investigated by the model. The results demonstrate that in the early stage of SSDB process, the void closure is mainly resulted from the contributions of the both mechanisms of plastic and creep deformation. However, with bonding time increasing, the mechanisms of surface and interface diffusion gradually become the dominated driving forces until the void elimination. The efficiency and applicability of the analytical model are verified by experimental results of diffusion bonding of TC4 titanium alloy with specially fabricated bonding surface, which demonstrates that the model can successfully forecast the effect of joining parameters on the void closure (or bonding ratio) evolution.