Wear is the progressive loss or damage of material from a surface caused by relative motion between contacting surfaces or by interaction with moving particles or substances. Wear is an important consideration in the design of bearings, gears, shafts, seals, guides and other machine components having surfaces in relative motion.
Lubrication is one of the principal methods used to reduce wear by separating contacting surfaces with a lubricant film. Surface condition and material properties are also important. In particular, increasing surface hardness can improve resistance to abrasive and other forms of mechanical wear while allowing the underlying component to retain the properties required for its structural function.
Wear resistance can therefore be improved through material selection, surface hardening, surface treatment or the application of a suitable coating or replaceable wear surface. Methods of providing a surface with desirable wear properties include:
The most appropriate method of wear reduction depends on the wear mechanism, the materials in contact, surface loading, relative velocity, lubrication and the operating environment. Common forms of wear include:
In practical machine design several wear mechanisms may occur simultaneously. Material hardness alone should therefore not be used as the sole criterion for selecting a wear-resistant surface.
Wear results from interaction between surfaces or substances in relative motion. The mechanism may involve abrasion, adhesion, surface fatigue, erosion, fretting or a combination of these effects.
Wear can be reduced by suitable material selection, lubrication, controlling surface finish and contact conditions, increasing surface hardness where appropriate, or using treatments such as carburising, nitriding and protective coatings.
Increased surface hardness often improves resistance to abrasive wear, but hardness alone does not determine wear performance. The wear mechanism, counterface material, lubrication, contact pressure, toughness and operating environment must also be considered.
Abrasive wear occurs when hard asperities or particles remove material from a surface. Adhesive wear results from localised bonding between contacting surfaces followed by material transfer or removal during relative movement.