Surface topographical effects in the diffusion bonding of 316 stainless steel

Samples with two different surface topographies were diffusion bonded to chemomechanically-polished surfaces showing significantly greater departure from conventional pore elimination models than for samples bonded with two roughened surfaces. These findings suggest differences in the way faying surfaces interact during early plastic deformation. Ground and cold-rolled samples were characterized and bonded to polished samples, simplifying faying surface interactions for finite element analysis. Conventional diffusion bonding models were found to significantly overestimate the percent bonded area for both ground and cold-rolled samples, with the overestimation more severe for the ground samples. Finite element analyses of the initial plastic deformation reveal 50 % more contact area for the cold-rolled surface with one-quarter the amount of strain compared with ground samples with nearly equivalent root mean square surface roughness. This was attributed to the coldrolled surface being dominated by a few deep pits with smoother regions in between. Comparison of the ground sample results with the technical literature suggests that the surface asperities of ground surfaces may interleave during diffusion bonding.

Automated summary

By studying the different surface topographies and interactions between ground and cold-rolled samples with polished samples during diffusion bonding, it was found that conventional models tend to overestimate the bonded area, especially for ground samples. The analyses also revealed that cold-rolled surfaces have more contact area with less strain compared to ground samples, due to the presence of deep pits and smoother regions. This study suggests that the surface asperities of ground surfaces may intertwine during diffusion bonding.