Effect of grain boundary migration on impact toughness of 316L diffusion bonding joints

316L stainless steel was vacuum diffusion bonded under the stress of 10 MPa, the temperature ranged as 900 °C ∼ 1100 °C and the holding time varied as 45 ∼ 90 min. The joint microstructures were examined. Tensile test and Charpy impact test were performed. The bonding interface showed 'Y' intersection or boundary migration (i.e., bulging migration) effected by boundary energy balance and strain inhomogeneity. The impact toughness increased linearly with the grain boundary migration ratio. Increasing grain size by increasing bonding temperature further distorted the bonding interface that increased crack propagation resistance. The highest impact toughness of the joint was 173.1 J cm^-2 with the grain boundary migration ratio of 96%, obtained by the joint bonded at 1050 °C for 60 min.