Abstract
Turbine blades are protected against surface degradation by the use of overlay MCrAlY (M=Ni and/or Co) coatings or Al diffusion coatings of β-NiAl, β-Ni(Pt)Al, and γ-(Ni,Pt)_3Al. The degradation of coatings is due to spallation of Al_2O_3 scales and precipitation of topologically close-packed (TCP) phases. Furthermore, the Ni-aluminide coated alloys can suffer significant degradation of mechanical properties under creep conditions. Novel coatings as EQ coating, Pt-modified γ'-Ni_3Al coating, and diffusion barrier coating system were critically reviewed, and establishment of compatibility of anti-oxidation and mechanical properties were discussed. Diffusion-barrier coating systems with an inner Re-based alloy layer and an outer Ni-aluminide layer were introduced in detail and anti-oxidation properties and creep behavior of the coated alloys were investigated It was found that Re-based alloys such as σ(Re(W), Cr,Ni) are very promising candidates as a diffusion barrier between alloy substrates and Ni-aluminides, resulting in improvement of both the anti-oxidation property and creep-rupture life.
