In general, wear is mechanically induced surface damage that results in the progressive removal of material due to relative motion between that surface and a contacting substance or substances. A contacting substance may consist of another surface, a fluid, or hard, abrasive particles contained in some form of fluid or suspension, such as a lubricant for example. As is with friction, the presence of wear can be either good or bad. Productive, controlled wear can be found in processes like machining, cutting, grinding and polishing. However, in most of the technological applications, the occurrence of wear is highly undesirable and it is an enormously expensive problem since it leads to the deterioration or even failure of components. In terms of safety it is often not as serious (or as sudden) as fracture. This is because wear is usually anticipated.
Certain material characteristics such as hardness, carbide type, and volume percent can have a decided impact on the wear resistance of a material in a given application. Wear, like corrosion, has multiple types and subtypes, is predictable to some extent, and is rather difficult to reliably test and to evaluate in the lab or in service.
Corrosive and oxidation wear
Corrosive wear is a material degradation process due to the combined effect of corrosion and wear. It is defined as the wear process in which sliding takes place in a corrosive environment. In the absence of sliding, the products of the corrosion (e.g.,, oxides) would form a film typically less than a micrometer thick on the surfaces, which would tend to slow down or even eliminate the corrosion, but the sliding action wears the film away, so that further corrosion can continue. Oxidation wear is one of the most common forms of corrosive wear, because an oxygen-rich environment is a typical environment in which this wear process occurs. Corrosive wear requires both corrosion and rubbing. Chemical corrosion occurs in a highly corrosive environment and in high temperature and high humidity environments.
Erosion – Corrosion
Erosion can also occur in combination with other forms of degradation, such as corrosion. This is referred to as erosion-corrosion. Erosion corrosion is a material degradation process due to the combined effect of corrosion and wear. Nearly all flowing or turbulent corrosive media can cause erosion corrosion. The mechanism can be described as follows:
- mechanical erosion of the material, or protective (or passive) oxide layer on its surface,
- enhanced corrosion of the material, if the corrosion rate of the material depends on the thickness of the oxide layer.
Wear is a mechanical material degradation process occurring on rubbing or impacting surfaces, while corrosion involves chemical or electrochemical reactions of the material. Corrosion may accelerate wear and wear may accelerate corrosion.