Papers by Author: Li Li

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Authors: Li Li, Bin Xu, Mu Sen Li, Jian Hong Gong
Abstract: Large numbers of experimental results show that carbides Me3C (Me means Fe, Ni, Co, Mn) are the primary carbon source to form diamond structure under the high temperature and high pressure (HPHT). In this paper, based on the empirical electron theory of solids and molecules (EET), the valence electron structure (VES) and interface structure factors of diamond and various carbides are calculated, and the boundary condition of electron movement in the improved Thomas- Fermi-Dirac theory by Cheng (TFDC) is applied to the carbide/diamond interfaces. It is found that the electron density of crystal plane in Me3C formed by C-C bonds is continuous with that in diamond at the first order of approximation. Compared with Ni-based carbides [Ni3C, (NiMn)3C)], the electron density difference of Fe-based carbides [Fe3C, (FeNi)3C, (FeMn)3C]/diamond interfaces is lower, and that of (FeNi)3C/diamond interface is minimum. The results show that the energy needed to transform carbon atomic groups into diamond structure is lower for Fe-based carbides than Ni-based carbides.
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Authors: Bin Xu, Le Yang, Shi Bo Xing, Li Li
Abstract: In order to increase boronizing speed without decreasing the hardness of boride layer, the effect of plastic deformation at room temperature on powder RE-chrome-boronizing for a medium carbon steel (steel 45), in which boronizing plays a main role, was studied in this paper. The cold plastic deformation (CPD), whether compressing or shot-peening, can increase boronizing speed. Meanwhile, the boride layer can also retain its high microhardness (1 300―1 900HV0.1) with low brittleness. The layer depth achieved for a given heating time increases with increasing CPD degree on the steel. The analyses show that boronizing kinetics in the RE-chrome-boronizing (RE-Cr-B) samples with CPD can be enhanced.
575
Authors: Bin Xu, Li Li, Mu Sen Li, Cai Gao, Ren Hong Guo
Abstract: Despite many studies have been carried, there is no clear understanding of the growth mechanism involved in the high-pressure and high-temperature (HPHT) diamond synthesis with metal catalyst, especially the problem about carbon source. In this paper, the lattice constants of diamond, graphite and Fe3C at HPHT were calculated with the linear expansion coefficient and elastic constant. Then based on the empirical electron theory of solids and molecules (EET), the valence electron structures of them and their common crystal planes were calculated, and the boundary condition of electron movement in the Thomas-Fermi-Dirac theory modified by Cheng (TFDC) was applied to analyzing the electron density continuity of the interface. It was found that the relative electron density differences across graphite/diamond interfaces are great and discontinuous at the first order of approximation, while the relative electron density differences across Fe3C/diamond interfaces were continuous. The results show that the carbon atom cluster is easier to decompose from Fe3C than from graphite and to transform into diamond structure, so the carbon source for diamond crystal growth may come from the decomposition of Fe3C instead of graphite. Accordingly, the diamond growth mechanism was analyzed from the viewpoint of valence electron structure.
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