Modelling solid-state diffusion bonding

The increasing use of diffusion bonding as a commercial process has, over the last 15 years, been paralleled by a series of progressively more complex attempts to model the mechanisms and processes occurring during bonding. This paper describes a theoretical model for diffusion bonding which proposes a new and simplified void geometry. The mechanisms operating during diffusion bonding are based on those derived from pressure sintering studies, although the driving forces and rate terms for these mechanisms have been altered to allow for the quite different geometries of the two processes. Also included in this work is an analysis of the effect of grain size which can lead to an enhancement in the contribution to bonding from additional grain boundary diffusion and so may be particularly relevant when joining materials of fine grain size. The extent to which this new model offers significant developments over existing models is discussed; an initial comparison between experimental results and predictions from this new model shows that there is good agreement between practice and theory.