Modeling of solid-state hot press bonding and its application to the fabrication of titanium alloy joints

Solid-state hot press bonding is an advanced joining process wherein two specimens can be joined under high pressure for a period of time at an elevated temperature. The main step in hot press bonding is the void closure process. In the present study, a three-dimensional theoretical model for describing the void closure process is developed. In the model, the void closure process is divided into two stages: in the first stage, surface asperities are flattened by the time-independent local plastic flow mechanism, and isolated voids form at the bonding interface; in the second stage, the void closure is accomplished by three time-dependent mechanisms, namely, the viscoplastic flow mechanism, surface source diffusion mechanism, and interface source diffusion mechanism. The initial and ending conditions of these mechanisms are proposed. The model also includes an analysis of the effect of macroscopic deformation on void closure. Hot press bonding experiments of Ti-6Al-4V alloy are conducted to validate the model. The modeling predictions show good agreement with the experimental results.