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

Abstract

The oxide structure on a FeCrAl alloy containing a mixture of Al 2 O 3 and Cr 2 O 3 or a layer of Al 2 O 3 was observed in experiments. Given that its atomistic mechanisms remain unclear, the formation mechanism of the layer structure of FeCrAl/(Cr 2 O 3, Al 2 O 3 )/Al 2 O 3 was explored based on Al atom diffusion using first–principles calculation. The energy of Al diffusion and the work of separation of the FeCrAl/Cr 2 O 3 interface show that Al atoms tend to diffuse into Cr 2 O 3 and enhance the bonding strength of the interface when the concentration of Al in the Cr atoms layer of Cr 2 O 3 is lower than or equal to 50%. The separation work of the interface is 2.43 J/m 2 and 3.46 J/m 2 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 Cr 2 O 3 . Hence, the Al atom tends to diffuse into Cr 2 O 3 , and the structure of FeCrAl/(Cr 2 O 3 , Al 2 O 3 ) is formed. When the concentration of Al atoms in the Cr atoms layer of Cr 2 O 3 is more than 50%, Al atoms diffuse close to the surface and the FeCrAl/(Cr 2 O 3 , Al 2 O 3 )/Al 2 O 3 structure may be formed. The crystal orbital Hamilton population (COHP) of Al–O bonds indicates that Al diffusing close to the surface of Cr 2 O 3 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 Å to 1.945 Å, and then returns to 1.926 Å, and the –COHP of the Al–O bond changes from 4.483 to 4.740.