Oxidation behavior of Cu–Cr environmental barrier coatings on Cu–8Cr–4Nb

Oxidation behavior of some Cu–Cr alloys (with 8.5–25.6 wt.% Cr, in both stand-alone coupons and spray coatings on Cu–8Cr–4Nb) was studied by TGA and cyclic oxidation. Judging by the more stringent cyclic oxidation results, protection of the substrate Cu–8Cr–4Nb was effective for the whole 10-h duration of testing up to 750 °C only for coatings with 21% or higher Cr. Similar protection was exhibited by Cu–17Cr only up to 650 °C, and only for <3 h at 750 °C. In all cases the Cr2O3 subscale nucleated discretely (and always under a non-adherent scale of Cu oxides), and passive protection did not start until the nuclei joined into a continuous barrier and parabolic oxidation kinetics set in. The only protection achieved before that stage of Cr2O3 coalescence was via sacrificial oxidation of the coating.