Wear is defined as the action of causing deterioration through use. In materials science, wear is considered to be the errosion of material from a solid surface by the action of another solid.
Adhesive wear – also known as scoring, galling, or seizing – occurs when two solid surfaces slide over one another under pressure. Surface projections, or asperities, are plastically deformed and eventually welded toghether by the high local pressure. As sliding continues, these bonds are broken, producing cavities on the surface, projections on the second surface, and, frequently, tiny, abrasive particles, all of which contribute to future wear of the surfaces.
Fatigue wear occurs when the material fails due to contact with a non-negligible load.
Abrasive wear occurs when material is removed through contact with hard particles. The particles may either be present at the surface of a second material, or exist as loose particles between two surfaces.
Corrosive wear is the deterioration of useful properties in a material due to reactions with its environment.