Achieve high oxidation resistance of nickel-based ODS superalloys at 1150℃ by adding Y₂Ti₂O₇ nanoparticles to control selective oxidation and Y segregation

The commercially available nickel-based ODS alloys with a maximum operating temperature of 1050℃ are unable to meet the poor service conditions of the advanced aircraft engines that pursue higher operating temperature to improve the thrust-to-weight ratio. Herein, a novel Ni-based ODS alloy is developed by substituting Y₂O₃ in MA6000 alloy with Y₂Ti₂O₇ nanoparticles. Remarkably, the Y₂Ti₂O₇-ODS superalloy exhibits high oxidation resistance at 1150°C for 200 h with a low mass gain of 1.76 mg/cm², thanks to a compact oxide scale. In contrast, the Y₂O₃-ODS alloy (MA6000) fails after 200 h of oxidation due to oxide scale spalling. Unlike Y₂O₃, Y₂Ti₂O₇ does not react with and deplete Al in the matrix, and the higher Al content enhances its reactivity and promotes its selective oxidation, which is proved by Thermo-Calc simulation. Additionally, the fine size and high number density of Y₂Ti₂O₇ provide more nucleation sites for rapid formation of a continuous and protective Al₂O₃ scale during initial oxidation. In prolonged oxidation of Y₂O₃-ODS alloy, precipitation of supersaturated Y initiates at the grain boundaries within the oxide scales. The precipitated yttrium-rich oxides increase oxygen diffusion and accelerate the oxidation kinetics, resulting in high growth stresses. However, the lower Y content in Y₂Ti₂O₇ reduces yttrium-rich oxide precipitation within the oxide scale, retaining beneficial yttrium segregation along grain boundaries, thus decreasing the oxidation rate and improving spallation resistance. This work offers a novel approach to accomplish high oxidation and spallation resistance of Ni-based ODS superalloy.