Protective coatings for wear resistance
Wear can happen in more than one way. The primary mechanisms are abrasive wear, adhesive wear and erosion.Adhesive wear - wear brought about by welding under pressure of surface asperities and subsequent shearing of such welds to give surface damage. Adhesive wear often happens between two unlubricated metallic surfaces of the same or similar composition.
Abrasive wear - loss of metal from a surface by the mechanical cutting action (rubbing or friction) of a secondary material which is in relative motion to that surface, e.g. silica (sand) and many other minerals.
Erosion - mechanical removal of material from a surface caused by the flow of a liquid or gas containing particulate matter or liquid droplets.
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Adhesive wear on a gate valve face |
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Gate valve erosion |
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Close-up view of gate valve erosion |
Abrasive wear and erosion are prevented generally by applying a coating containing hard particles or phases. Adhesive wear can be prevented by applying a coating material significantly different to the rubbing surfaces, e.g. a ceramic coating on a steel substrate. All the surface engineering facilities at TWI can be used to apply wear resistant coatings.
Examples of materials used for wear resistance include:
- Tungsten carbide cobalt
- Ceramics (alumina, chromium oxide)
- Cobalt alloys
- Nickel alloys
- Ferro chromium chrome carbide
- High speed steels
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