high temp oxidation coatings

Question 1

what is diffusion coating

Answer 1

one or more elements are diffused into the surface of the substrate to create oxidation resistant layer

Question 2

what should the coating do
what is preferred on refractory metals
what is used in super alloy as produces a subsequent oxidation.

Answer 2

➢The protective oxide coating should prevent (or strongly inhibit) attack.
➢Silicides tend to be preferred on refractory metals as they have a better
thermal expansion match. The coatings can also be modified, with various
additions, to promote “self healing” if the coating is damaged.
➢In superalloys, aluminides, ie. NiAl or CoAl, are usually produced and
subsequent oxidation produces a spall resistant Al2O3
coating.

Question 3

what are overlay coatings

Answer 3

group of coating that does not rely on diffusion as primary method for producing a coating.