Electrochemical Corrosion Inhibition of Cr2AlC MAX Phase Coatings via Mo Solid Solution: Comprehensive Experimental and Simulation Study

The Cr2AlC MAX phase has gained increasing interest as a protective coating used in harsh high-temperature oxidation and molten-salt corrosion. However, these coatings are easily apt to fail at room temperature due to the poor electrochemical corrosion resistance. Taking the concept of M-site solid solution, herein, (Cr0.9, Mo0.1)2AlC solid solution coatings were specially fabricated by a combined technique composed of magnetron sputtering and subsequent heat treatment. The dependence of electrochemical behavior on the structural evolution was focused by comprehensive simulations and experiments. Results showed that the structure of (Cr, Mo)2AlC solid solutions was stable regardless of the Mo concentration. Moreover, compared to pristine Cr2AlC coating, the corrosion current density was reduced and the electric impedance was enhanced by almost 1 order magnitude in 3.5 wt % NaCl solution, respectively. This was mainly ascribed to the accelerated passivation layer rich in aluminum oxides on the coating surface. Based on density functional theory simulation, the partial substitution of Mo for Cr in Cr2AlC favored the stronger mobility of Al atoms because of the reduction in vacancy formation energy, leading to the rapid growth of passivation of aluminum oxides substantially. The observations not only provide conducive evidence of Mo solid solution for the enhanced corrosion inhibition in Cr2AlC MAX phase coating but also offer an alternative strategy to enable the electrochemical performance of protective coatings with extended long-life serving.