Abstract
The present work is concerned with the investigation of methods of improving the elevated temperature oxidation resistance of Nimonic 90 by coating techniques. Two methods are considered, the use of diffusion coatings and of a flame sprayed ceramic coating. Beneficial effects wer6 observed when diffusion coatings were employed, chromium diffused coatings imparting considerable resistance to surface deterioration but aluminium diffused coatings have been shown to be unsatisfactory at temperatures above 900°C. Flame sprayed alumina coatings have been investigated and the effects of various substrates have been considered. The use of aluminised, oxidised and molybdenum sprayed substrates has been shown to be unsatisfactory but improved results have been obtained when chromised and nickel-chromium sprayed substrates were employed. Some appropriate mechanisms are proposed to explain the results observed.