Coating techniques
Ceramic coating technology encompasses a bewildering array of coating types and deposition processes. Coatings that are frequently used include many oxide, carbide, and nitride ceramic types, deposited by commercial processes that are tailored to a specific ceramic material and a desired set of coating properties. They can, however, be divided into three very broad categories: vapour deposition, thermal spraying and wet processes. In turn these can be sub-divided into a number of generic techniques, as shown by Fig.1.
Fig.1. Deposition techniques for ceramic coatings |
Vapour Deposition
Sol-gel Metallisation Thermal Spraying |
The vapour phase processes, such as those based on the various PVD and CVD techniques, are regarded as thin coating processes. They rely on atom by atom deposition from a gas phase, which is necessarily slow, and as a consequence economically attainable thicknesses rarely exceed 100µm. On the other hand, thermal spraying techniques deposit a heated powder, at high velocity, and build up a thick coating as individual particles deform and adhere on impact. This is regarded as a thick coating technique, producing coatings from a few tens of microns to several millimetres.
Numerous other techniques fall into the category of wet processing, and one of particular interest is sol-gel. This 'wet' technique offers a route to thin ceramic coatings using colloidal or complex organic solutions as ceramic precursors.
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Staff papers
- Ceramic coatings - a growing technology (Bulletin, March/April 1992) Industrial Members Only
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