Pretty much all of the compressor blades we make here are left as bare metal. They are usually shot peened as a measure against fatigue, but thats all.
One exception is a compressor blade we make for land use, (it's a power gen gas turbine) and that is made from stainless steel and coated with Sermatel 5380DP, which is a inorganic corrosion resistant coating. I *think* that the particular engine this blade is destined for is used mainly on oil platforms, and this coating is used because of the corrosive marine environment it'll be used in.
I can;t think of a single compressor blade for flight use that has a coating on it though....! Corrosion isn't really a problem:most blades are made from titanium, stainless steel, or aluminium with the occasional nickle based alloy thrown in for fun.
Turbine blades are another story all together though.....
