Sprayed coatings hard facing

Hard facing of various components in the aircraft gas-turbine engine and in industrial apphcations for textile machinery parts, oil and gas machinery parts, paper-shtting knives, etc, is estimated at 1 x 10 in 1995 with an estimated growth rate of 5% annually. The mix is approximately 45% aerospace apphcations, 55% industrial apphcations. Additionally, repair coatings for gas-turbine blades and vanes is estimated at 500 x 10 . These coatings are primarily deposited by plasma spray, arc-wire, HVOF, and detonation gun techniques. 

In recent years, the spraying process has been adapted for hard facing, using the chromium-nickel-boron alloys which have become known as Colmonoy. More recently still, the cobalt-base Stellite alloys have also been used. These materials in powder form are sprayed on to the surface in the usual way. The deposit is afterwards heat treated by a torch, so that fusion takes place. The process is often known as spray-welding. Such coatings are primarily used for hard facing under wear conditions, but as the Anal surface is nickel-chromium or cobalt-chromium they exhibit very high anticorrosive properties. 

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