The kinetics of isostatic diffusion bonding in superplastic materials

A model has been developed to predict the time required to attain full interfacial contact during diffusion bonding under an isostatic state of stress. It has been shown that bonding occurs primarily as a result of time-dependent (super)plastic flow of material into the interfacial voids created when the two surfaces to be bonded are brought into contact. For diffusion bonding within the superplastic regime, temperature and pressure have little effect on the kinetics of bonding. However, variations in the absolute scale of the surface roughness, through the effect of surface tension, have a substantial effect on the bonding time. Discrepancies between the measured and predicted bonding times for Ti6Al4V suggest that the reduction of the long-range waviness of the surfaces plays as significant a part in the bonding process as does the closure of the short wavelength roughness.