Being a toolmaker by trade, I make extensive use of hardcoatings to reduce friction, and heat on cutting tools. Has anyone used any coatings on internal engine parts? What results did you find?

I am considering having my new camshaft coated with titanium nitride, or another pvp coating. I was thinking the valves would also be an ideal place to coat. The thickness of the coating is only about .0002/ .0003 so an increase, or decrease in size shouldnt be much of an issue. I have found that the titanium nitride drastically reduces friction on some of the wear plates I build, and repair. For instance... I built a wear plate for a guy, and had it coated, when he sent it back for a new set of holes I was happy to see no wear at all to the parent metal. He showed me an uncoated plate that had less hours of use that had worn .003", and was made from the same base material.
Send me some thoughts on this folks, im interested in hearing what may or may not have worked for others.