Millennium cookware hydrogen cracking and Teflon coating

Two-part teaching unit using the pot as prop. (1) The aluminum/stainless cold-bonded base illustrates that a deliberately weak bond (10% bonded area) is correct design for dissimilar-CTE joints — porosity accommodates thermal strain. (2) The plasma-sprayed inner surface for Teflon adhesion introduced hydrogen (95% argon / 5% hydrogen gas), which caused delayed cracking after shipping from Brooklyn to Japan. Martensite transformation in deformed 304 stainless was the susceptible microstructure.

Another type of mechanical interlocking — several of you who've taken parts of the class before have seen this prop. [Tom produces a piece of Millennium cookware.] This is Millennium cookware by Farberware. It illustrates a number of things. It illustrates forming, if you take my deformation processing course. It's actually an example of cold bonding. They have a layer of aluminum at the bottom of the stainless steel. They draw the stainless steel, they heat up the aluminum in a furnace, they put the pot over a die — a guy by hand takes some tongs, puts the aluminum on top, and there's a steel die holding it, and a 5,000-ton press comes down, goes wham, and just with pure normal pressure bonds it. There's a little bit of shear, because this thing does have some rounded edges after it comes out of the die.