[HawgRyder]

I remember seeing a chart long ago that had a comparison (sort of) of the "hardness" of one material rubbing against a different "hardness" material and the resultant friction and wear.
It appeared to me at the time that there were combinations of materials that had almost no wear (when lubricated) and others that would be considered grinding.
The one glaring thing about the chart was that you needed to have dissimilar hardness on mating surfaces.
Bob