Role of surface finish on interface grain boundary migration in vacuum diffusion bonding

The objective of this study was to get insight into the role of surface finish on interface grain boundary migration during vacuum diffusion bonding of stainless steel. The results showed that two types of interface grain boundary migration were observed. One was interface grain boundary migration at triple junction; and another was strain induced interface grain boundary migration. Surface finish had an obvious influence on the behavior of interface grain boundary migration. For smoother surface interface grain boundary migration mainly occurred at the triple junctions, while for rougher surface a larger number of strain induced interface grain boundary was produced. The mechanism analysis revealed that the higher surface asperities on the rougher surfaces suffered the load and deform seriously, readily leading to the inhomogeneous local deformation on opposite sides of the interface grain boundary as well as the difference in stored energies accumulated, thereby producing more strain induced interface grain boundary migration. Additionally, the shear strength of joint was consistent with the interface grain boundary migration ratio, and the higher interface grain boundary migration ratio resulted in a higher shear strength of joint.