Precipitation stability and micro-property of (Nb, Ti)C carbides in MMC coating

Multiple particles reinforced composite coatings have been noticed by many researchers due to its excellent wear resistance. In this work, (Nb,Ti)C multiple carbide reinforced Fe matrix composite coating was prepared. The microstructure and phase structure of the coatings were analyzed by scanning electron microscope (SEM) equipped with an energy-dispersive spectroscopy (EDS), X-ray diffractometer (XRD) and transmission electron microscopy (TEM). The stability, mechanical parameters (Elastic modulus, Bulk modulus and Shear modulus), hardness, brittleness, bonding structures of (Nb,Ti)C and misfit between carbide and Fe matrix were calculated by first principles method. The experimental results show that, core-shell (Nb,Ti)C can be observed in Ti-1 (0.52 wt% Ti) coating and compared to Ti-0 (0 wt% Ti), the morphology of carbides in Ti-1 coating is improved. The calculation results show that, the lattice constants, formation energy of (Nb,Ti)C (Nb0.75Ti0.25C, Nb0.5Ti0.5C and Nb0.25Ti0.75C) and misfit between carbide and Fe matrix are decreased with the decrease of Ti content in the carbide. Moreover, the hardness and brittleness of (Nb,Ti)C carbides are increased. The NbC covalent bonds in (Nb,Ti)C carbides act as a dominant factor for their high hardness.