SI-C FILMS ON ALLOYS - CHARACTERIZATION OF AGING BEHAVIOR IN AIR

Coatings of silicon rich silicon carbide are obtained in a plasma assi sted device from tetramethylsilane and argon mixture, around 760K unde r reduced pressure on metallic alloys: FeCrAl and NiCrAl.The atomic co mposition of the deposits is determined by microprobe analysis and adh erence is evaluated by scratch test measurements. These results are di scussed in relation with previous determinations obtained when identic al films are deposited on low carbon steel substrates. All samples exh ibit a similar behavior which denotes a good adherence. The formation of a diffusion zone is responsible for this trend. The qualitative beh avior of the coated substrate in air at high temperature (1273 K) is i nvestigated in comparison with the uncoated substrate through cross se ction examinations by different analysis (EDS mapping, WDS profiles). The heat treatment (10h, 100h) induces a strong diffusion which is dis cussed. It is evidenced that the silicon carbide based films drastical ly change the oxidation mechanism (mainly in the case of NiCrAl) and t end to improve the resistance of the substrate against an oxidizing at mosphere. Futhermore, some solutions to improve the lifetime of such m etal/ceramic junctions are suggested. As for example, the interest of an alumina interlayer between SiC coating and FeCrAl substrate is expe rimentally shown.