http://www.aa1car.com/library/ar996.htm
Try this out for some information on resurfacing. It appears that PDC is for aluminum and CNB for cast iron. I got this info off a machine tool insert site.
CNB (Cubic Boron Nitride) Inserts
These inserts provide an excellent finish on cast iron and have an exceptional cutting life. These inserts are also capable of handling the strain of high speed milling.
PDC (Poly-Crystalline Diamond) Inserts
These inserts have a thin coating of Diamond on top of a carbide insert. This insert is designed for cutting aluminum heads and blocks at very high speeds.
Ceramic Inserts
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