Mo-Regulating element diffusion and oxide formation in Cr₂TiAlC₂ MAX with boosted corrosion resistance in static liquid lead-bismuth eutectic

Generation-IV lead-cooled fast reactor (LFR) requires the promising structural material MAX phase ceramics possessing high anti-corrosion resistance towards its liquid coolant lead-bismuth eutectic (LBE). As complex and competing reactions such as element out-diffusion, oxidation and element/mass dissolution simultaneously occur on MAXs and are compositionally correlated, challenges remain in the controllable growth of dense and continuous Al₂O₃-based oxide scale with high shielding property. Herein, the potential candidate Cr₂TiAlC₂ 312-MAX ceramic is doped with an ascending Mo concentration to regulate its element diffusion kinetics as well as the Al₂O₃ formation thermodynamics. Specifically, in Cr₂TiAlC₂, a fast Al leaching rate and sluggish Al₂O₃ formation lead to peeling off of oxide particles, delamination and pulverization of the MAX matrix. Mo doping decreases the Gibbs free energy and accelerates the formation of Al₂O₃ with two orders of magnitude less oxygen required, and the simultaneous out-diffusion of Mo and Al leads to the decomposition of 312 MAX phase to corrosion-resistant metal carbides and 211 MAX phases. When these two paces are coordinated in CrTiMoAlC₂ with optimized Mo content, a continuous Al-rich oxide scale is achieved with high anti-corrosion property.