Abstract

FeAl coatings with yttrium (Y) doping were prepared at 600 °C on pure iron. The anti-flaking properties of Al2O3-oxide films at 1000 °C oxidation was improved significantly by Y doping in FeAl coatings. The spallation was 0.47 mg/cm2 for 200 h of oxidation and only ~1/6 of that without Y. The first principle calculation results demonstrate that the interfacial bond strength were enhanced with Y doping, that is because Y substituted primarily in the Al1 and Al2 position at the Al2O3/FeAl interfacial zone as the most negative interfacial cohesive energy of −13.94 eV and −12.72 eV. Remarkably, it is found that the maximum tensile strength of Y–FeAl/Al2O3 reaches to 20.48 GPa on uniaxial tensile strain, which is 1.33 times than that of FeAl/Al2O3 interface (15.36 GPa). Meanwhile, compared with a pure interface, Y doping would change ductile fracture on the Al2O3/FeAl interface as the strain was enhanced significantly by 49.12%. The bond length of the Al1–Y showed little change under external stress, which resulted in an increase in bonding strength of the Al2O3/FeAl interface and the inhibition of the generation and propagation of micro-cracks. The formation of a YAlO3 layer induced a release of thermal stress at the Al2O3/FeAl interface. Due to the improvement of interfacial strength, the enhancement of interfacial toughness and the formation of a YAlO3 stress-release layer between the Al2O3 film and FeAl coating, therefore, Y doping can significantly improve the anti-flaking performance of the Al2O3-oxide films in high temperature oxidation.

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