The variation of sp3 fractions from carbon K-edge and the 3d-state occupancy on Fe–L2–3 edges in different layers of Fe-based metallic film covering on an as-grown diamond single crystal in diamond synthesis have been investigated by electron energy loss spectroscopy (EELS). It shows that from the diamond/film interface to the inner, the sp3 fractions decrease from 87.33% to 78.15%, the 3d-state occupancy for Fe increase from 4.54 to 5.64 electrons/atom. Moreover, by X-ray diffraction (XRD), only γ-Fe, Fe3C and (Fe,Ni)23C6 are found on the interface, which suggests that these carbon atoms with changed electronic configuration come from Fe3C. Based on the valence bonding theory, formation of Fe3C should make 3d occupancy increase, inconsistent with experimental observations. It can be concluded that, the 3d unpaired electrons of γ-Fe affect carbon atoms in Fe3C lattice and make them transform into sp3-like state. These sp3-like carbon atoms are separated from Fe3C and stack on the growing diamond crystal, eventually resulting in the reduction of 3d-state occupancy of Fe on the interface.Highlights► The sp3 fractions increase from the interface to the inner film. ► The 3d-state occupancy for Fe decrease from the interface to the inner film. ► The 3d unpaired electrons of γ-Fe make carbon atoms transform into sp3-like state.

The lattice constants of diamond and graphite at high pressure and high temperature (HPHT) were calculated on the basis of linear expansion coefficient and elastic constant. According to the empirical electron theory of solids and molecules (EET), the valence electron structures (VESs) of diamond, graphite crystal and their common planes were calculated. The relationship between diamond and graphite structure was analyzed based on the boundary condition of the improved Thomas-Fermi-Dirac theory by Cheng (TFDC). It was found that the electron densities of common planes in graphite were not continuous with those of planes in diamond at the first order of approximation. The results show that during the course of diamond single crystal growth at HPHT with metal catalyst, the carbon sources forming diamond structure do not come from the graphite structure directly. The diamond growth mechanism was discussed from the viewpoint of valence electron structure.

The Cr-Rare earth-boronized layers were fabricated on the steel 45 at 650°C for 6 h. The microstructure, phase composition, microhardness and tribological properties were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), microhardness tester and wear tester. The results showed the Cr-Rare earth-boronized layer was composed of single Fe2B phase. A sawtooth morphology was obtained in the Cr-Rare earth-boronized layer and the microstructure of the Cr-Rare earth-boronized layer was compact and dense. The thickness of the boride layer is about 23 μm. The boride tooth was thin and straight. The microhardness of the Cr-Rare earth-boronized layer was 1200HV∼1700HV, and first increased with the increase of distance from surface and then decreased when the distance from surface is longer than 7.5 μm. The hardness gradient of the boride layer is lessened. The wear resistance of steel 45 is greatly improved by Cr-Rare earth-boronizing.