Multi-element collaboration in Cr₂TiAl_1−xSi_xC₂ MAX for the oxide barrier formation in a 550 °C LBE environment

MAX phase ceramics have good oxidation and corrosion resistance, while the controllable formation of the protective oxide layer is still a challenge for their application in lead-cooled fast reactors. Herein, the oxide barrier formation mechanism of three Cr₂TiAl_1−xSi_xC₂ MAXs (x = 0, 0.2, 0.4) with different Si contents exposed to lead-bismuth eutectic (LBE) at 550 °C for 500-3000 hours was systematically studied. Based on the evolution of the structure and composition of the oxide layer, a diffusion rate-controlled oxide layer formation mechanism is proposed. The collaboration of Cr, Al, and Si regulates the structure and composition of the oxide layer. Particularly, the existence of Si facilitates the transport of Al across the oxide layer, which builds a continuous oxide double-layer with mainly Al₂O₃ as the outer layer in LBE. Eventually, the multi-component oxide layer regulates the corrosion resistance of the Cr₂TiAl_1−xSi_xC₂ MAXs, which paves the way for the performance-oriented design of the MAX phase.