Study On The Electronic Structure, Mechanical And Thermodynamic Properties Of Binary Phase Formation In Steel By Si, P And

Iron and steel materials are widely used in basic industries. Because of their good comprehensive mechanical properties, stable quality, rich resources, which make the steel as one of the used most widely structural materials. Si, P, S and other non-metallic elements as gene fragments exist in the iron and steel materials, the properties of complex alloy is difficult to test by experimental measurements, which cause we can only explore the behavior and function of non metallic elements in iron and steel depend upon the experience estimation for a long time, so far is still lack of the study of the hard phase’properties. To thoroughly understand the important role of non metal elements in iron and steel, this paper deep study of FexSiy, FexPy and FexSy by first principles calculation and part of experiment, gaining the mechanical properties, electronic structure and thermodynamic properties of these compounds, in order to provide a theoretical foundation for steel performance modification, the research results are as follows:The calculated cohesive energy and formation enthalpy of studied Fe-Si, Fe-P and Fe-S binary compounds is negative, which shows these compounds are thermodynamically stable, and the calculated elastic constants of each Fe-Si, Fe-P and Fe-S compounds satisfy the mechanical stability criterion, which implying all the compounds are elastically stable. The calculated elastic constants are used to calculate the elastic modulus, including bulk modulus (B), shear modulus (G), Young’s modulus (E) and Poisson’s ratio (o), the ratio of B/G and Poisson’s ratio can be used as an indicator for the ductility or brittleness of the compounds. FenSis and Fe2Si belong to the ductile phase, and the other Fe-Si binary compounds belong to the brittle phase, Fe3P, Fe2P belongs to the ductile material, o-FeP4 belongs to the brittle material. We study the hardness of the Fe-Si binary compounds by the theoretical calculated and experimental methods, and calculate the hardness of some Fe-P binary compounds. The anisotropy of the compounds were study through the universal anisotropic index AU and the percent anisotropy AB and AG, and three-dimensional (3D) surface contour, Fe11Sis and Fe2Si show strong anisotropy of Young’s modulus and Fe3P, FeP2 and o-FeP4 show strong anisotropy of shear modulus, a-FeS show strong anisotropy of bulk modulus.Through analyzing the compounds’s density of states(DOS), electron density and electron density difference, we found chemical bonds of the compound is composed of metal bond, covalent bond and ionic bond, the different compounds contain different proportions of three kinds of chemical bonds.Finally we calculated and discussed the thermodynamic properties of compounds, including the Debye temperature, low temperature heat capacity at constant pressure and high temperature heat capacity, thermal conductivity, high temperature formation enthalpy and entropy of vibration. Through the analysis, we found that the temperature of the compound in the near Ok, heat capacity is mainly affected by dominant electron; in the slightly high temperature, heat capacity is mainly affected by the dominant phonon. For Fe-Si binary compounds, the maximum thermal conductivity belongs to FeSi (2.27 wm-1k-1). The minimum thermal conductivity belong to Fe11Si5 (1.81 wm-1k-1); For Fe-P binary compounds, the maximum thermal conductivity belong to Fe2P (2.26 wm-1k-1) and the minimum thermal conductivity beong to Fe3P (1.63 wm-1k-1).