Unravelling the impact of CoNiCrAlY coating microstructure and composition on the formation of duplex oxide scales
João P. Martins, Ying Chen, Kerui Wei, Zhaohe Gao, Shiying Qin, Gyn Brewster, Ping Xiao
Abstract
The formation process of Al2O3-based duplex oxide scales growing on high velocity oxygen fuel (HVOF) CoNiCrAlY alloy was investigated at 1135 oC. The dual-phase nature of the alloy originated a site-specific oxidation behaviour that facilitated the formation of an inhomogeneous duplex oxide scale with widespread embedded mixed oxides. The early-stage formation of these oxides was explained by a modified Gaussian diffusion model where grain boundary proximity is the main variable. The subsequent nucleation/growth of mixed oxides with oxidation time was attributed to continuous cationic diffusion of non-aluminium elements across the scale enabled by the presence of cationic impurities in the scale.