TABLE OF CONTENTS Corrosion occurs in normal environments with virtually all materials except those termed noble, i.e., gold, platinum, etc. The most common form of corrosion is oxidation. Most metals react with the oxygen in air or water to form oxides. Elevated temperatures greatly increase the rate of all chemical reactions.
Corrosion wear adds to the chemically corrosive environment a mechanical disruption of the surface layer due to a sliding or rolling contact of two bodies. This surface contact can act to break up the oxide (or other) film and expose new substrate to the reactive elements, thus increasing the rate of corrosion. If the products of the chemical reaction are hard and brittle (as with oxides), flakes of this layer can become loose particles in the interface and contribute to other forms of wear such as abrasion.
Some reaction products of metals such as metallic chlorides, phosphates, and sulfides are softer than the metal substrate and are also not brittle. These corrosion products can act as beneficial contaminants to reduce adhesive wear by blocking the adhesion of the metal asperities. This is the reason for adding compounds containing chlorine, sulphur, and other reactive agents to create EP (extreme pressure) oils. The strategy is to trade a slow rate of corrosive wear for a more rapid and damaging rate of adhesive wear on metal surfaces such as gear teeth and cams, which can have poor lubrication due to their nonconforming geometry.
The phenomenon variously called corrosion fatigue or...
