| Ion vapour deposited yttrium-free and yttrium-containing aluminide diffusion coatings on Ni-base superalloys (IN738 and Rene80) were investigated.; Subsequent heat treatments were performed at temperatures below or above 1000{dollar}spcirc{dollar}C to allow complex diffusional interactions of the coated materials with the substrate. The heat-treated coatings with thicknesses of about 95 {dollar}mu{dollar}m to 110 {dollar}mu{dollar}m comprised three zones. The outermost zone contained Cr and Ni-rich precipitates in a NiAl matrix with Y-rich protective oxides on the top; the intermediate zone contained dissolved Cr, Mo, Ti, Co in NiAl intermetallics; the interdiffusion zone consisted mainly of Cr-rich lamellae with a few carbides.; Microstructures, phase compositions, surface hardness, and fatigue behaviour of these coatings were investigated by conventional and FE-SEM, x-ray diffraction, microhardness testing, and four point cyclic bend testing. These yttrium aluminide diffusion coatings offer excellent resistance to oxidation and hot corrosion for aero gas turbine blades at elevated temperatures by enhancing the Al{dollar}sb2{dollar}O{dollar}sb3{dollar} scale adherence. |
