Effect of surface roughness on interface characteristics and mechanical properties of dissimilar diffusion bonded 45 steel/additive manufactured 316L steel joints

Diffusion bonding of additive manufactured (AM) metal parts to traditionally manufactured metal parts is an effective and low-cost way to produce large-scale and multi-functional parts. In this study, diffusion bonding of casting 45 steel and AMed 316L stainless steel was conducted with four different bonding surface roughness from large to small. The interface formation mechanisms including the metallic elements diffusion layer, the carbide layer and the interfacial grain boundary (IGB) migration were investigated in detail. The results show that the interface bonding ratio improves from 43 to 96% due to void closure as the roughness of the bonding surface decreases from Ra similar to 1.5 mu m to Ra similar to 0.1 mu m. The shear strength of the joint increases from 350 to 468 MPa, and the specific shear strength increases from 58 to 94%. The type and number of grain boundary migrations are significantly affected by the bonding surface roughness. The number of IGB migrations at the "triple junction" structure increases while the number of strain-induced grain boundary migrations decreases as the bonding surface becomes smoother.