A study of the diffusion and pre-oxidation treatment on the formation of Al2O3 ceramic scale on NiCrAlY bond-coat during initial oxidation process

In this study, the formation of thermally growth ceramic oxides during initial oxidation on treated NiCrAlY bond-coat was investigated. The oxidation resistance of NiCrAlY bond-coat was enhanced by two approaches: (i) an inter-diffusion treatment in a tube furnace with flowing argon at 600 degrees C for 1 h, and (ii) a pre-oxidation treatment in static air at atmospheric pressure at 1000 degrees C for 1 h. Experimental results showed that, after diffusion treatment, the content of Al in the bond-coat increased. This led to the growth of theta-Al2O3 during the pre-oxidation process, which was then helped in the formation of a dense and continuous alpha-Al2O3/Cr2O3 multilayer on the surface of the bond-coat. Results on the cyclic oxidation at 1200 degrees C (for time <= 204 h) showed that the treated NiCrAlY bond-coat exhibited better oxidation resistance than the NiCrAlY bond-coat samples without diffusion treatment and the samples pre-oxidized at 800 degrees C for 1 h. The formation of NiO, Cr2O3 and NiCr2O4 spinel oxides were suppressed due to the formation of alpha-Al2O3 scale during the initial oxidation on the surface of pre-treated NiCrAlY bond-coat. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.