High temperature corrosion behaviour of a gradient NiCoCrAlYSi coating I: Microstructure evolution

A gradient NiCoCrAlYSi coating was prepared by a combined method of arc ion plating and subsequent diffusion treatment. The microstructure of the gradient coating was investigated in the as-annealed condition and after oxidation at 1000 °C. During the oxidation, an in situ diffusion barrier composed of Cr(W)-rich σ phases was formed in the interdiffusion zone, resulting in an effective inhibition of inward diffusion of Al. The formation of the in situ diffusion barrier layer is also discussed.