How does corrosion worm its way around like that? Is it something in the manufacturing process that provides a path of least resistance or something along those lines?
Maybe it’s not that corrosion is worming around it, but instead there’s an outer coating material that’s expanded and contracted numerous times over the years, and those cracks are where it eventually split from the contractions
I could be wrong, but there’s a decent chance the corrosion is just following grain boundaries of the metal. When liquid metal cools, or is otherwise deposited (like galvanization), the atoms stack up into a crystal structure. Depending on the exact procedure, this process starts in comparatively many or few places. As more atoms stack up, the crystals run into each other, but they are usually not lined up right to just merge, so they have awkward borders. All the “impurities” get pushed into the borders.
The crystals are called grains, and controlling their size and shape is basically the most important factor in determining the strength of a metal. When a blacksmith quenches something, it’s to cool it down really quick so those grains are really small, which makes the metal really hard. Heat treating later lets some of the grains merge to soften the metal up a bit so it’s less brittle.
In this case, the corrosion is just in a coating, probably nickel, but the principle of having grains is the same. All the stuff that’s more susceptible to corrosion is confined to the borders.
The craziest application of metal crystal structures I know of is in jet turbine blades. The entire turbine blade is made of a single metal crystal structure. This is part of the reason they can operate at temperatures that would normal weaken and deform the metal.
AFAIK, that’s also how microprocessors are made; single crystals of silicon, though that’s a metalloid not a metal.
This is also a big part of why manufacturing in space has huge potential. In micro-gravity, crystal formation is less effected. I risk it’s a bigger deal for things like proteins, optics, and other non-metal things, though.
How does corrosion worm its way around like that? Is it something in the manufacturing process that provides a path of least resistance or something along those lines?
Maybe it’s not that corrosion is worming around it, but instead there’s an outer coating material that’s expanded and contracted numerous times over the years, and those cracks are where it eventually split from the contractions
This and every coating technique sprays the particles so it maybe never will be completely equally coated
Not every coating is sprayed. Electroplating and anodizing are both very common. And neither of those are sprayed on applications.
I don’t think it’s the case here, but this is exactly how lead coatings crack. This looks almost exactly like old lead paint.
I could be wrong, but there’s a decent chance the corrosion is just following grain boundaries of the metal. When liquid metal cools, or is otherwise deposited (like galvanization), the atoms stack up into a crystal structure. Depending on the exact procedure, this process starts in comparatively many or few places. As more atoms stack up, the crystals run into each other, but they are usually not lined up right to just merge, so they have awkward borders. All the “impurities” get pushed into the borders.
The crystals are called grains, and controlling their size and shape is basically the most important factor in determining the strength of a metal. When a blacksmith quenches something, it’s to cool it down really quick so those grains are really small, which makes the metal really hard. Heat treating later lets some of the grains merge to soften the metal up a bit so it’s less brittle.
In this case, the corrosion is just in a coating, probably nickel, but the principle of having grains is the same. All the stuff that’s more susceptible to corrosion is confined to the borders.
The craziest application of metal crystal structures I know of is in jet turbine blades. The entire turbine blade is made of a single metal crystal structure. This is part of the reason they can operate at temperatures that would normal weaken and deform the metal.
AFAIK, that’s also how microprocessors are made; single crystals of silicon, though that’s a metalloid not a metal.
This is also a big part of why manufacturing in space has huge potential. In micro-gravity, crystal formation is less effected. I risk it’s a bigger deal for things like proteins, optics, and other non-metal things, though.
Much too large to be grain boundaries - if you had steel with grains this large you’d be able to pull it apart with your bare hands
Yeah, thats why I specified it was just in the coating. Like the spangle in galvanized metal where you see grains with the naked eye.