Refinement of M7C3 in hypereutectic Fe-based hardfacing coating and interface behavior of (Ti, Nb)(C,N)/M7C3 from first-principles

Abstract

Hypereutectic Fe–Cr–C–Ti–Nb coatings with and without N additive were developed by harden-surface welding (hardfacing) respectively. The micro-morphologies of M7C3 and (Ti, Nb)(C,N) in coatings were observed by field emission scanning electron microscopy (FESEM). The compositions of (Ti, Nb)(C,N) were determined by energy dispersive spectrum (EDS). The crystal structure of primary M7C3, (Ti, Nb)(C,N) and γ-Fe were determined by transmission electron microscopy (TEM). On the basis of experimental research, the interface behavior of (Ti, Nb)(C,N)/M7C3 carbides was investigated by first-principles calculation. The experimental results show that, the primary M7C3 carbides are obviously refined in the coating by N additive. From the micro-morphologies of M7C3 and (Ti, Nb)(C,N), it is found that (Ti, Nb)(C,N) exists inside primary M7C3 carbide and they are tightly combined. Therefore, (Ti, Nb)(C,N) may be the heterogeneous nucleus of primary M7C3. The calculation results show that the M7C3(0001)/(Ti, Nb)(C,N)(111) interface is theoretically stable. The Fe3Cr4C3(0001)/TiC(111) interface is well jointed by covalent bond, ionic bond and metallic bond. Therefore, the preferentially precipitated (Ti, Nb)(C,N) in Fe–Cr–C–Ti–Nb coating is the heterogeneous nucleus of primary M7C3 carbide and thereby refines the primary M7C3 carbide.