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. 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 technological applications, the occurrence of wear is highly undesirable, and it is an enormously expensive problem since it leads to the deterioration or failure of components. In terms of safety, it is often not as serious (or as sudden) as a fracture, and this is because the 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 that are predictable to some extent and are rather difficult to test and evaluate in the lab or service reliably.
Corrosive and oxidation wear
Corrosive wear is a material degradation process due to the combined effect of corrosion and wear. It is the wear process in which sliding occurs 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 highly corrosive environments and 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.