Materials Science Forum Vol. 749

Abstract: ndenter size effect on the incipient plasticity of Al (001) surface is studied by using the quasicontinuum simulation method. Two cylindrical indenters with the radii 2.5nm and 40nm are used to penetrate the surface respectively, and in displacement-control in steps of 0.02 nm. Results show that the plasticity under the small indenter is activated by discrete dislocation nucleation events, while the plasticity under the large indenter is dominated by a collective dislocation activity. Contact pressure calculations reveal that reversible incipient plasticity occurs under the small indenter, i.e. the plastically deformed surface can completely recover upon withdrawal of the indenter, while the incipient plasticity under the large indenter seems to be irreversible.

Abstract: Based on the full process 3D elastic-plastic thermal mechanical coupled simulation of large size H-Beam, the relevant issues about the residual stress distribution of H-Beam has been systematically analyzed, which include the formation and control of residual stress. In addition, based on the conclusion of the large size H-Beam residual stress analysis, the method of cooling for the control of residual stress has been provided and experiments about the outside cooling of the flange has been implemented. The result of the experiments proved that the coercive water cooling for the outside surface of flange largely reduced the residual stress of the web, which can avoid the web wave after cooling and crack phenomenon during utility. At the same time, on the basis of the whole rolling process finite element simulations, with the help of model of austenite evolution, phase transition and microstructure and property prediction, the simulation of 3D microstructure evolution and property prediction has been fulfilled. By means of microstructure research, it has been proved that the simulation result meet the genuine microstructure very well, which has revealed the feasibility of this method.

Abstract: To investigate the fatigue property of carbon structural steel in theory, the microstructure and properties of quenched martensite must be studied in detail. In this paper, the electronic structure and mechanical properties of carbon structural steel in quenched state were calculated by the empirical electron theory of solids and molecules (EET). The relationship between electronic structure parameters and mechanical properties of martensite was investigated. The mechanical properties of quenched carbon structural steel were calculated theoretically, and the result of theoretical calculation is consistent with the experiment result.

Abstract: An innovative sand cementation method of bio-mineral carbonate formation in sand spacing through urea hydrolysis inspired by microbial urease was introduced in the present investigation. A sand column prepared for experimental data and a set of engineering equations for 1-D numerical modeling data of the sand cementation process were adopted. Important characteristic of CaCO3 weight vertically along the sand column and the urea concentration variation under the effect of microbial urease was investigated based on the experiment and the modeling. Future study was suggested to focus on the models parameters modification in order to construct an applicable model for industrial up-scaling application in sand or soil strengthening.

Abstract: A modified Voronoi model is established based on the Richards method to generate 2D non-equiaxed initial microstructure for Monte Carlo simulation. Microstructures produced by the ordinary Voronoi model are isotropic and cannot reflect the effects of the deformed grain shape on the annealing process. The modified Voronoi model based on ellipse set can be used to construct the deformed microstructure. The initial microstructure reflects the mean strain and the grain size distribution follows lognormal distribution.

Abstract: The Explicit Finite Difference (EFD) method is used for calculating the energy conservation equation during solidification. In order to improve the computational efficiency, the equivalent specific heat method is adopted to calculate the latent heat and the high order Alternating Direction Implicit (ADI) method is also applied, which is fourth order in space and second order in time. The degree of similarity between the simulation results and experimental results is analyzed quantitatively by the Hamming Distance (HD) for the first time, and results show that this high order mathematical model based on the equivalent specific heat method and the high order ADI method is faster and more accurate than the EFD method.

Abstract: First principles calculation for optical properties of a tetragonal BC₃ (t-BC₃) are performed through the pseudopotential density functional method. The exchange correlation potential is treated by the Perdew-Burke-Eruzerhof form of generalized gradient approximation. The basic optical constants including the real and imaginary parts of the dielectric function, the optical absorption coefficient, the reflectivity and the energy loss function were calculate in detail by this method. The results indicate that the t-BC₃ is an optical anisotropic crystal and its electron-deficiency characteristic can cause some features in low energy region.

Abstract: Based on the galvanic corrosion experiment for U-Nb alloy and 45-steel in the 3.5 mass percent NaCl solutions, the galvanic corrosion electric field has been calculated by finite element method. The electric potential and the current density evolution during galvanic corrosion have been obtained. The results show that the electric potential drop between cathode and anode had obvious difference. The electric potential drop in the U-Nb alloy cathode is higher than that in the 45-steel anode, which makes the electric field in the U-Nb alloy higher than that in the 45-steel. A rather high current density exists at the ends and corners of the specimen. The permittivity of the corrosion medium only has a little effect on the corrosion electric potential, but has obvious effects on the corrosion current density. The electrode size has obvious effects on the corrosion electric potential and current density.

Abstract: The nitrogen concentration effects on electronic structures and optical properties of N-doped SrTiO3 have been investigated on the basis of density functional theory (DFT) calculations. Through band structure calculation, a direct band gap is predicted in SrTiO3-xNx. Electronic structure analysis shows that the doping N could substantially lower the band gap of SrTiO3 by the presence of an impurity state of N 2p on the upper edge of the valence band. When the doping level rises, the energy gap has little further narrowing compared with that at lower doping levels. The calculations of optical properties indicate a possible optimum N-doping level in SrTiO3 with a high photo response for visible light. These conclusions are in agreement with the recent experimental results.

Abstract: The local structures of Zn and Y in the long period stacking order (LPSO) phase in Mg-Zn-Y system were investigated by first principles calculations in details. The clustering of Zn and Y atoms ranging from single stacking fault layer to four consecutive layers was explicitly demonstrated. The calculations indicate that Zn and Y atoms prefer clustering in the form of Zn₆Y₉ embedding in ABCA-type building block to the random or ordered arrangements of Zn and Y atoms being enriched in two stacking fault layers. The cluster of Zn₆Y₉ can be regarded as the ideal stoichiometric component of LPSO and it plays a predominant role in the LPSO phases. The formation of LPSO phases is highly associated with the Zn₆Y₉ cluster and its derivatives.