Improvement in oxidation resistance of a Ni3Al-based superalloy IC6 by rhenium-based diffusion barrier coatings

The oxidation behavior of a Ni3Al-based superalloy IC6 coated with a duplex Re–Cr–Ni–Mo diffusion barrier layer and an Al reservoir layer was investigated in air at 1423 K for up to 1080 ks. The diffusion barrier layer was formed by electroplating Re(Ni) and Ni films on the alloy, followed by Cr pack cementation at 1573 K, and as a result, forms a continuous inner Re–Cr–Ni–Mo diffusion barrier layer and an outer Ni(Cr,Mo,Al) layer. Then a Ni film was electroplated on the Ni(Cr,Mo,Al) layer, followed by Al-pack cementation at 1273 K for 18 ks, to form an Al reservoir layer with a duplex Ni2Al3 and γ-Ni(Cr,Mo,Al) layers. After oxidation at 1423 K in air for 1080 ks, the Al reservoir layer changed to a γ-Ni–4Cr–5Mo–12Al (all in at%) layer, on which a protective α-Al2O3 scale formed. The Re–Cr(Mo)–Ni layer was stable and effectively retarded the interdiffusion between the Al reservoir layer and the alloy, as a result, the depth of the microstructural change zone of the alloy was less than 15 μm. In contrast, the bare and the coated IC6 superalloy only with an Al reservoir layer were significantly oxidized, accompanied by serious spallation of oxide scales. After oxidation at 1423 K for 1080 ks, the depth of the microstructural change zone of the alloy was about 200 μm for the bare and coated alloy only with an Al reservoir layer. These results indicate that the oxidation resistance of IC6 superalloy can be effectively improved by coating with a Re–Cr–Ni–Mo diffusion barrier layer and an Al reservoir layer.