Microstructure and electronic structure of Cr2C and Fe2Y in the Cr-coating prepared by pack-cementation on the surface of ODS steel

Abstract

In this study, a combination of experimental characterization and first-principles calculation was employed to systematically study the structure and electronic properties of Cr-coating prepared on the surface of oxide dispersion strengthened (ODS) steel by pack-cementation chromizing. X-ray diffraction (XRD) and energy dispersive spectrometer (EDS) results show that the Cr-coating is mainly composed of Cr2C and Fe2Y phases. The first-principles calculation results show that the Cr atoms and C atoms in the Cr2C crystal are bonded by ionic bonds, while the Fe atoms and Y atoms in the Fe2Y crystal are mainly boned by polar covalent bonds. Compared with Fe2Y, Cr2C crystal has greater elastic anisotropy. The elastic constant of Cr2C crystal increases significantly with the increase of pressure. When the pressure reaches 2.4 GPa, Cr2C undergoes a transition from ductile to brittle. The elastic modulus of Fe2Y increases slowly with increasing pressure, and always appears as a ductile phase under the pressure value of 0–6 GPa, which is considered to have a good effect on the impact properties of the Cr-coating. The average work function of Cr2C crystal electrons is greater than that of Fe2Y crystal electrons, indicating that when the coating is in a corrosive medium, the Fe2Y phase will serve as the anode in the electrode first, and will be corroded before the Cr2C phase.