Molecular Dynamic Simulation Of Energy And Structural Stability On Grain Boundary In Bicrystal Copper

Metal materials have been widely used as the form of polycrystalline, and the study on grain boundaries (GB) of polycrystalline materials was an important subject in the field of materials science. GB was a kind of defect structure and contained GB energy, it has the trend of development to low energy state. Thus, the character of GB which is different from the bulk grain would even change the macroscopic properties of materials. The grain boundary character distribution (GBCD) could be controlled by specific thermo-mechanical treatment in order to improve the performance of materials—Grain Boundary Engineering (GBE). However, the micro-mechanism of GBCD optimization is not very clear at present. With the development of computer simulation techniques, Computational Materials Science which is an independent new subject is widely used in the study of material microstructure. Molecular dynamic simulation is one of the most important methods in Computational Materials Science, it could reveal the internal mechanism of microstructure changes by showing the atoms movement configuration.In this dissertation, molecular dynamic simulation was first used to calculate the static GB energies of different kinds of bicrystal copper. Then tensiling and annealing simulations were carried out on several typical kinds of bicrystal copper. The mechanism of GB evolution and structural stability was analyzed in detail. The simulation results showed:1) The energies of Coincidence Site Lattice GBs with low∑value were always the local minimum points in energetic curves. (111)-∑3-twist GB has the lowest GB energy in all the simulation results;2) (111)-Σ3-twist GB has the best mechanical properties with the highest stress and strain limitations. Only (111)-∑3-twist GB could keep complete structure and intergranular cracking happened when the bicrystal copper was tensiled to failure. (111)-∑3-twist GB was the most stable structure during the tensiling simulation.3) The melting point of bicrystal copper obtained by simulation was 1355K which was more close to true value. Simulation annealing temperature was set to 1250K according to the melting point 1355K. All the GBs showed the pre-melting with different degree during annealing process except (111)-∑3-twist GB. After annealing, most GB structures changed, only (111)-∑3-twist GB could go back to the initial structure. (111)-∑3-twist GB was the most stable structure during the annealing simulation.