There are several distinct types of wear which generally fall into two main categories:
l Abrasive wear
l Sliding wear
The type of wear encountered in a particular application is an important factor that influences the selection of a wear-resistant material.
Abrasive wear is encountered when hard particles or hard projections (on a counter-face) are forced against and moved relative to a surface. The terms high and low stress abrasion relate to the condition of the abrasive medium (be hard particles or projections) after interaction with the surface. If the abrasive medium is crushed, then the high stress condition is said to prevail. If the abrasive medium remains intact, the process is described as low stress abrasion. Typically, high stress abrasion results from the entrapment of hard particles between metallic surfaces (in relative motion), while low-stress abrasion is encountered when moving surfaces come into contact with packed abrasives, such as soil and sand.
In alloys such as the cobalt-base wear alloys, which contain a hard phase, the abrasion resistance generally increases as the volume fraction of the hard phase increases. Abrasion resistance is, however, strongly influenced by the size and shape of the hard phase precipitates within the microstructure and the size and shape of the abrading species.
Sliding Wear. Of the two major types of wear, sliding is perhaps more complex, not in concept, but in the way different materials respond to sliding conditions. Sliding wear is a possibility whenever two surfaces are forced together and moved relative to one another. The chances of damage are increased markedly if the two surfaces are metallic in nature, and if there is little or no lubrication present.
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