Molecular Dynamics Simulation Study Of Thermal Stability And Phase Transformation In Nanocrystalline V And Zr

Nowadays nanocrystalline materials have become very popular due to their special properties. The phase transition of nanocrystalline Zr and thermal stability of nanocrystalline V, including the effect of temperature and grain size, are calculated by means of the modified analytic embedded-atom method (MAEAM) and molecular dynamics (MD) in this paper. The samples are generated with Voronoi cell method. The radius distribution function (RDF), common neighbor analysis method (CNA), nanocrystalline section and potential energy curve are used to analysis the simulation process.Simulating the initial structure, it shows that the percentage of grain boundary atom increases as the reducing of mean grain size. Especially for the sample with a mean grain size of 2.8nm, the fraction of boundary atoms exceeds 50%. With reducing grain size, the lattice parameter of intergrain increases. Comparing the potential energy of atoms, there're no change for boundary atoms, while increase for the intergrain atoms with the reducing of mean grain size. That is to say, the boundary structure has no change while the intergrain lattice is distorted.The simulation result of thermal stability of nanocrystalline V indicates that the stability temperature reduces clearly as the reducing of mean grain size. Especially for the sample with an average grain size of 2.8nm, its thermal stable temperature is only 500K. After having studied the microstructure of nanocrystalline V, we think that the reasones which causes the grain growth of nanocrystalline V mainly comes from the high percentage and high distorted crystal boundaries structure. In addition, the distorted lattice in the intergrain can't be neglected. The expanse of the nanocrystalline V below the thermal stable temperatures, is higher than that of coarse crystalline, it's about twice as many. In addition the thermal expansion of intergrain is higher than that of conventional crystals. The grain growth phenomenon studied above stability temperatures, is reflected mainly in grain boundary migration. Taking into account the small grain size and grain number, it is difficult to observe the grain rotation-induced growth phenomenon.The phase transition of nanocrystalline Zr with an average grain size of 7.05nm has been simulated. The radius distribution function, the fraction of different type atoms differentiated by the common neighbor analysis method and...