Farberware cooking pot thermal warping

Brief callback. Used as the everyday analogue for deliberately incomplete bonding in turbine coatings — aluminum-to-stainless cold bond with 10% bonded area to allow for thermal mismatch.

Remember the Farberware pot I showed you the other day. They didn't really want 100% bonding in that cold bonding of the aluminum base to the stainless steel pan, because if it was 100%, the difference between aluminum and steel when you go up 600 or 700° would cause warping. If you actually get only a 10% bonded joint — what's the stress on that aluminum at the bottom of a cooking pot? There's not a lot of stress compared to the area of bonding. You actually want porosity at that interface. They want porosity in the bond coat of these turbine coatings too, because what has a better ability to absorb strain than empty space? Voids are wonderful.

Brief reference. Tom's pot had varying ferrite content from bottom to top — 5–10% ferrite at the bottom, ~80–90% martensite (transformed by deformation) at the top, making the top magnetic. Used to illustrate that "zero ferrite" super-austenitic specifications can be misleading.

The problem is, with the super-austenitics, you can have zero ferrite, because that was what the Navy wanted. They wanted super-austenitic; it had zero ferrite so it wouldn't be magnetic. I showed you what would happen with that, my little Farberware pot. It was like five or ten percent ferrite down at the bottom. It had been deformed some and transformed some, and you get up to the top and it was probably close to eighty or ninety percent — actually in that case martensite, but magnetic steel.