Oxygen diffusivity in alumina scales grown on Al-MAX phases

• Ti3AlC2, Ti2AlC, and Cr2AlC MAX phases form protective Al2O3 scales.
• Grain boundary diffusivity was calculated from a modified Wagner equation and grain size.
• Scale δDgb,O,int. for MAX compounds was comparable to that for FeCrAl alloys.

Ti3AlC2, Ti2AlC, and Cr2AlC are oxidation resistant MAX phase compounds distinguished by the formation of protective Al2O3 scales with well controlled kinetics. A modified Wagner treatment was used to calculate interfacial grain boundary diffusivity from scale growth rates and corresponding interfacial grain size, based on the pressure dependence of oxygen vacancies and diffusivity. MAX phase data from the literature yielded grain boundary diffusivity nearly coincident with that for Zr-doped FeCrAl (and many other FeCrAl alloys), suggesting similar oxidation mechanisms. The consolidated body of diffusivity data was consistent with an activation energy of 375 ± 25 kJ/mol.

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