Aluminum: Pistons, piston pin plugs, bearings and the case (fretting).
Chromium: Rings, (replacement) cylinders, a trace element in steel.
Iron: Cylinders, rotating shafts, the valve train, and any steel part sharing the oil.
Copper: Brass or bronze parts, bushings, bearings and oil coolers.
Lead: Primarily leaded gas blow-by, (traces from) bearings.
Tin: Bearings, bronze parts (with copper), anti-wear coatings.
Molybdenum: Traces of anti-wear coatings, some cylinder types.
Nickel: Valve guides, trace element in steel.
Manganese : Grease additive.
Silver: Trace element in some types of bearings.
Titanium/Potassium: Trace elements.
Boron/Sodium: Contamination, common to antifreeze.
Silicon: Abrasive dirt (via intake air), silicone sealers and gaskets.
Calcium/Magnesium: Oil additives, rare in aircraft engine oils.
Phosphorus: Common anti-wear additive in aircraft oils.
Zinc: Component of brass (with copper), oil additive common to auto engine oils.
Barium : Additive used in some synthetic oils, not common to aircraft oils.