High temperature corrosion behaviour of coated F17Ti stainless steel

The effect of chromia and alumina coatings on the high temperature behavior of the F17Ti stainless steel was investigated. The films were deposited on the alloy surface by metal-organic chemical vapor deposition (MOCVD). Rare earth element oxides (REO) can also be prepared using this technique. This led us to envisage the formation of "REO-doped" chromia or alumina scales, either by successive depositions, or by codeposition of chromia or alumina and of a rare earth element oxide, followed by a post-annealing treatment. The so-formed coatings have been characterized by Scanning Electron Microscopy (SEM), EDAX, X-ray diffraction and SIMS. Thicknesses were first estimated by highly accurate weighing, then verified by profilometry after a laser impact. High temperature oxidation tests were performed at 1273 K in isothermal conditions and at 1223 K in cyclic conditions, in air under atmospheric pressure. An amelioration of the steel behavior was observed in every case, and especially for codeposited Nd2O3-Cr2O3 and Nd2O3-Al2O3: the weight gain was decreased during oxidation, compared with that for an uncoated sample, and the scale spallation phenomenon, generally observed under cyclic conditions, disappeared.