This will tie together.
Being part of the gun community, machining goes hand and hand with the knowledge. With a barrel being the part that is most likely to wear out over time through lots of firing, people look for processes to extend their barrel life to shoot more and to keep the accuracy of the barrel longer. Two process make this possible. One is nitride and the other is meloniting which is a step over nitride. What this does is change the composition of the steel to make it a great deal stronger to the point that people get double the life time of a barrel. With harder steel comes longer life and decreased friction which leads me to this. I have been thinking of this when I get the money to take apart my car and send it though the process. Just imagine a gearbox or an engine that could take a lot more abuse just by sending the parts to have the process done. Pistons that hardly wear out, teeth on gears that don't break. Pushing a car beyond it's limits.
I am not site pimping for this next part.

Here is a company that does the process and the benefits of the process.
http://www.burlingtoneng.com/melonite.html
Melonite Processing: Melonite Q

• Improved Wear Resistance
• Improved Running Properties
• Increased Fatigue and Rolling Fatigue Strengths
• Heat Resistance
• Black Color

Melonite Processing: Melonite QP

• lncludes the properties of Melonite Q
• Lower coefficient of Friction
• Decreased surface roughness

Melonite Processing: Melonite QPQ

• lncludes the properties of Melonite Q and QP
• Low Light Reflection
• Further Decreased Coefficient of Friction
• Enhanced Corrosion Resistance (Not suitable for stainless)

 

I have this for my Barrel, and I never thought about doing this for an engine. This would actually be very beneficial for a piston. Whats even better is it doesn't add too the thickness of the material instead it penetrates and converts the material. Possible crank and wrist pins use also. You could use it on the rods to help shed the oil. Dang, if you could do it use it on sleeves too. Probably would get expensive at some point.