Oxidation protection of alloy IN 738 LC by plasma assisted vapour deposited silica coating

The benefits conferred upon the oxidation behaviour of the nickel based superalloy IN 738 LC by thin ( < 10 μm),amorphous, silica coatings, produced by plasma assisted vapour deposition, have been examined. During 5000 h tests in air, the coatings substantially reduced the extent of attack at all temperatures between 700 and 1000°C and the amount of spallation at 1000°C. A range of surface analytical techniques was deployed to establish that the protection afforded to the alloy at the highest temperatures, 900°C and particularly 1000°C, resulted from the silica coating acting in a unique dual role. While directly protecting the alloy, as at the lower temperatures, the silica coating was degraded sacrificially and an underlying, coherent, Al2O3 layer formed, which also was more protective than the oxide scale formed naturally on the uncoated alloy.MST/1019