Protective Coatings for Niobium Alloys: Manufacture, Characterization and Oxidation Behaviour of (TiXCr)(7)Si-6 with X = Fe, Co and Ni
Résumé
Intermetallic single phases (TiXCr)(7)Si-6 (with X = Fe, Co or Ni) were manufactured by uniaxial hot pressing. Their full characterization (SEM + XRD) highlighted that the nature of the metal constituent X influenced the chromium content in the silicide compositions. Both isothermal and cyclic oxidation studies at a temperature as high as 1300 A degrees C evidenced very low degradation rate for all compounds and lifetime at 1100 A degrees C exceeded 4700 cycles. All phases developed a duplex protective layer of chromia and silica. It was observed that the chromia:silica ratio depended on the nature of X, and, particularly for the Ni-containing specimen, also on the temperature. Co- and Ni-containing specimens developed pure chromia during oxidation whereas Fe ones develop (CrxFe1-x)(2)O-3, reducing drastically the CrO3 volatilization during exposure at temperature higher than 1000 A degrees C.