Effects of aluminum diffusion on the oxide of the FeCrAl alloys surface: A first-principles study

The oxide structure on a FeCrAl alloy containing a mixture of Al2O3 and Cr2O3 or a layer of Al2O3 was observed in experiments. Given that its atomistic mechanisms remain unclear, the formation mechanism of the layer structure of FeCrAl/(Cr2O3, Al2O3)/Al2O3 was explored based on Al atom diffusion using first-principles calculation. The energy of Al diffusion and the work of separation of the FeCrAl/Cr2O3 interface show that Al atoms tend to diffuse into Cr2O3 and enhance the bonding strength of the interface when the concentration of Al in the Cr atoms layer of Cr2O3 is lower than or equal to 50 %. The separation work of the interface is 2.43 J/m2 and 3.46 J/m2 for no Al and Al diffuse, respectively. Electronic structure analysis shows that more electrons of Al atoms participate in the formation of Al-O bonds and that reduces the system energy when Al atoms diffuse into Cr2O3. Hence, the Al atom tends to diffuse into Cr2O3, and the structure of FeCrAl/(Cr2O3, Al2O3) is formed. When the concentration of Al atoms in the Cr atoms layer of Cr2O3 is more than 50 %, Al atoms diffuse close to the surface and the FeCrAl/(Cr2O3, Al2O3)/Al2O3 structure may be formed. The crystal orbital Hamilton popu-lation (COHP) of Al-O bonds indicates that Al diffusing close to the surface of Cr2O3 can reduce local lattice distortion and restore the strength of the Al-O bond. The average bond length of the Al-O bond changes from 1.923 angstrom to 1.945 angstrom, and then returns to 1.926 angstrom, and the -COHP of the Al-O bond changes from 4.483 to 4.740.

Automated summary

The formation mechanism of the FeCrAl/(Cr2O3, Al2O3) layer structure was explored using first-principles calculation. It was found that when the concentration of Al in the Cr atoms layer of Cr2O3 is lower than or equal to 50%, Al atoms tend to diffuse into Cr2O3 and enhance the bonding strength of the interface. When the concentration of Al atoms exceeds 50%, Al atoms diffuse close to the surface and the FeCrAl/(Cr2O3, Al2O3)/Al2O3 structure may be formed.