Effects of Y dopant on mechanical properties and electronic structures of M7C3 carbide in Fe-Cr-C hardfacing coating

In order to reduce cracking and spalling problems of M7C3 carbides in hypereutectic Fe-Cr-C hardfacing coating, the effects of Y doping on anisotropy, mechanical properties and electronic structures of M7C3 carbide were elucidated by first principles method. Nano indentation experiments were performed to compare with partial calculation results. From first principles calculation, we find that the formation enthalpy of Fe3Cr3YC3 (Y-doped M7C3) carbide is lower than that of Fe3Cr4C3 (M7C3) carbide, which shows that Fe3Cr3YC3 is more stable and it can form preferentially. No imaginary frequency appears in the phonon dispersion spectrums, which indicates that Fe3Cr4C3 and Fe3Cr3YC3 crystal models are theoretically stable. The Young's modulus is decreased from 450.62 GPa to 228.01 GPa and shear modulus is decreased from 178.44 GPa to 86.22 GPa, after Y atoms doped in Fe3Cr4C3. The intrinsic hardness H-nu is decreased from 18.83 GPa to 7.69 GPa. In addition, the anisotropy of elastic moduli of Fe3Cr3YC3 carbide is also reduced significantly. Compared with Fe3Cr4C3 carbide, the fracture elongation of Fe3Cr3YC3 (2110) crystal face is obviously increased from 7% to 14%. The indentation experiments also prove that the ductility and toughness of Y-doped M7C3 carbides are improved. Its mechanism is the electron redistribution and more stable chemical bonds formation caused by Y atoms. This can provide new ideas for cracking and spalling improvement of M7C3 carbides and design of hardfacing coatings with preferable mechanical properties.