Many components are used for extended periods and then finally wear out and are replaced, which can be expensive. The thermal spray coating process can extend the life of components by many years.
Building a Hard Wear-Resistant Surface
Tungsten carbide and chromium carbide coatings are sprayed onto steel components to produce a surface that is harder than the component itself. Such coatings are typically in the region of 1,000-1,200 HV (hardness value) and provide excellent resistance to abrasive wear and fretting as well as to sliding contact.
Restoring Worn Parts to Correct Dimensions
The thermal spray process can be used to re-mach weakened parts to their original dimensions. A shaft or bore that has worn slightly can be restored to its original size and tolerance by the thermal spray process. For example, for process detail on HVOF thermal spraying the HVOF process is used to build up a wear surface of low porosity that can be machined to the required dimensions. Typical build up thicknesses are in the order of 0.1mm up to a few mm.
Acting as a Thermal or Chemical Barrier
Thermal Spray coatings can also be made from ceramic materials, which can protect parts that are exposed to high temperatures or to chemicals. The ceramic coating acts as a thermal barrier, and can slow down the oxidation of parts such as combustion components, or wear parts in pump housings, for example.
Bonding Without Distorting the Part
It is also important to note that thermal spraying involves the deposition of a material at relatively low temperatures and therefore does not cause distortion of thin sections or can alter the critical metallurgical characteristics of heat-treated components. For Thermal Spray Coating, see Poeton.
Matching Coating Material to the Wear Mode
The wrong material can create a coating which looks good but fails quickly. This is why identifying the correct wear mechanism prior to specification is crucial. As an example, abrasive wear is often best tackled with a tungsten carbide coating, corrosion with a nickel-chrome alloy coating and wear caused by adhesive action between parts in contact may require a lubricating coating containing molybdenum disulphide.
So long as the correct material is selected for the wear it encounters then a coating will offer a long and useful ‘life extension’.
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