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

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 2 O 3 at the early stage of creep, and with further oxidation the external scale became a duplex layer, inner, equi‐axed α ‐Al 2 O 3 , and outer, plate‐like θ ‐Al 2 O 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.