Effect of creep deformation on oxidation behavior of nickel-based alloy with Re-based diffusion barrier coating

摘要

Oxidation and creep behaviors of a Ni-Mo-based alloy (Hastelloy-X) with a diffusion barrier coating consisting of duplex, inner Re-based alloy, and outer β-NiAl layers were investigated at 1243 K in air with an external tensile stress of 22.5 MPa. For comparison the alloys, as-received, heat treated, and with the Ni-aluminide coating, were oxidized under creep deformation. Creep rapture time for the diffusion barrier-coated alloy was longer than those for the bare alloy and with the β-NiAl-coated alloy. After creep deformation to a strain of 3.5% for 190 h, it was found that the Re-based alloy layer has few cracks and flaws and the β-NiAl layer has the similar structure and composition before and after the creep test. The external scale mainly consisted of θ-Al{sub}2O{sub}3 at the early stage of creep, and with further oxidation the external scale became a duplex layer, inner, equi-axed α-Al{sub}2O{sub}3, and outer, plate-like θ-Al{sub}2O{sub}3, which exfoliated significantly. It was concluded that the Re-based alloy layer acts effectively as a barrier against inward Al diffusion and outward diffusion of alloy elements under creep deformation.