Originally posted by inspyral
Molybdenum 
I dunno about it being heat resistent, but it's an anti-friction coating.
Are we talking about the piston skirt or the top of the pistons?
Moly is normally on the skirt, which makes sense, but if it's a piston top coating, it's almost certainly a ceramic-type material.
By the way, I wouldn't suggest cryo-treating ANY internal item that has a factory coating of any kind on it.