Chemical vapor deposition of ruthenium on NiCoCrAlYTa powders followed by thermal oxidation of the sintered coupons

This paper introduces spouted-bed metal-organic chemical vapor deposition, an original technique for doping by platinum group metals of commercial powders that are used as raw materials in the processing of bond coats in thermal barriers. In this context, Praxair NI-482 NiCoCrAlYTa powders were doped by ruthenium, starting from ruthenocene. The doping level, purity, microstructure and ruthenium distribution of the powders were established. Doped and undoped (reference) powders were sintered at 1473 K by uniaxial hot pressing. Isothermal oxidation tests on the coupons obtained were carried out in a thermogravimetry apparatus, at temperatures ranging between 1173 and 1423 K, in order to determine the parabolic rate constants. Microscopic and spectrometric characterization of the oxidized samples provided information on the morphology of the scale, its nature and the distribution of its components over the surface. The addition of 0.8 wt.% of ruthenium in NiCoCrAlYTa powders is not detrimental to their oxidation resistance in isothermal conditions. The present study reveals that spouted-bed metal-organic chemical vapor deposition is a convenient method for the systematic screening of raw materials used in thermal barriers doped by different elements.