First-principles Study Of The Strengthening Mechanism Of Fe-Cr-Al Alloy Interface

Fe-Cr-Al alloys are the only metallic materials that can possess sufficient resistance to be subjected to long-term service at the high temperature well above 1000℃, even the maximum working temperature up to 1300℃. This is due to the formation of continuous, compact and high adhesiveness alumina scale based on the surface of Fe-Cr-Al alloys. In spite of the excellent oxidation resistance, alumina scale is prone to spall off Fe-Cr-Al alloy bulk under high temperature environment, which results in the failure of whole materials system. Consequently, the keys of the research are the induction factor of alumina scale spallation and the methods of enhancing alumina scale adherence to the bulk.The effect of interfacial segregation of S and the doping of reactive elements(La、Ce、Y、Hf) on the interface strength of Fe-Cr-Al alloys is researched in this paper. All calculations were performed by the CASTEP code in MS6.0, which is a first-principles plane wave pseudopotential method based on the density functional theory.The interface bonding energies of the pure interface and the interface with the S segregation are-10.01787 e V and-5.04387 e V, respectively, which suggests the interfacial segregation of S results in the interface unstable. We can determine the segregation path of S via comparing the interface segregation energies of the different substitution positions of S. We can see from the DOS and bond overlap population, the overlap of peaks between Fe and O atoms decreased sharply and the P values of S-O reduced in various degrees comparing with that of Fe-O in the pure interface. It is clear that bonding at the interface is weakened seriously, thus the interface adhesion decreased.The interface segregation energy of RE is lower than that of S, so that the interface segregation ability of RE is stronger than that of S. In the DOS and bond overlap population, the P values of Fe-O increased, the P values of La-O and Ce-O all reduced, and that of Y-O and Hf-O increased, Which suggests that Y and Hf can enhance the interface strength, but the same effect of La and Ce is not ensure. In alloy matrix, the P values of La-S and Ce-S are negative, the P values of Y-S and Hf-S are large, and this means La-S and Ce-S form antibonding, Y-S and Hf-S come into being strong covalent bond. Y and Hf can pinning S in bulk, which prevent interfacial segregation of S.Consequently, as an alloying element, RE substantially improves the interface adhesion through two strengthening mechanism:(1) directly enhancing the interfacial bonds,(2) pinning S in Fe-Cr-Al alloy bulk to prevent the harmful interfacial segregation of S.