Doctoral research on ceramic-metal joint porosity optimization

Tom's student's thesis showing strength peaks near 10% interfacial porosity for ceramic-metal joints; strain-energy framework as the diagnostic.

I had a student do a doctoral thesis ten years ago who showed through modeling and experiments that if you look at the amount of porosity at an interface in a ceramic-metal joint, you get something like this, where 10% porosity gives you the strongest joint. The residual stresses kill you with no porosity, because of the thermal mismatch. With some porosity you're losing bonded area and you've got stress concentrators, but you're reducing residual stresses. Around 10% it starts to decrease, because now the amount of bonded area is so small. So some porosity actually can be good in a dissimilar-material joint for combating residual stresses.

Brief reference. Thesis showed ~10 volume percent porosity in the proper pattern at the interface produces the strongest ceramic-metal joint. Used as theoretical follow-up to the cookware insight about porous interfaces accommodating CTE mismatch.

Based on that thought, back in the 1990s I had a student do her doctoral thesis, and she showed that you can actually get the strongest joint in ceramic-metal joints if you have about 10 volume percent porosity in the proper pattern on the interface. So you don't always want to get 100% joint, okay. But that illustrates cold bonding.