Design and Oxidation Resistance Mechanism of NiMoAlY Alloy.

Aiming at the thermal corrosion issue of Cr-containing MCrAlY (M = Fe, Co, Ni) materials used in marine gas turbine hot-end components in a humid marine environment with highly corrosive chloride salts, Mo is anticipated to replace Cr, thereby enhancing the corrosion resistance and mechanical properties. However, excessive Mo facilitates oxidation and creates volatile metal oxides, ultimately jeopardizing the integrity of the oxide film. The alloy composition in the FCC_Ll₂+BCC_B2+Ni₅Y ternary phase region was designed according to the calculated phase diagrams of the Ni-Mo/Cr-Al-Y system. The influence and mechanism of replacing Cr with minor Mo on phase composition and high-temperature oxidation resistance were investigated. The high-temperature oxidation mass-gain experiments at 750 t indicate that a small amount of Mo (atomic fraction of 0. 5%) promotes the formation of BCC_B2 phase and facilitates the transformation of surface oxide films on the alloy from θ-Al₂O₃ to stable αα-Al₂O₃, which is conducive to the formation of dense α-Al₂O₃ oxide layer during long-term service, thus improving the oxidation resistance performance of the alloy. However, the addition of atomic fraction of 2. 5% Mo causes the transformation of ordered BCC_B2 phase to Mo-rich BCC_A2 phase, which is not conducive to the improvement of oxidation resistance performance. Thus, the present work indicate that the combination of theoretical calculations and experimental verification may provide a effective guidance for the composition design of novel materials with customized structures and properties. [ABSTRACT FROM AUTHOR]