The Molecular Simulation Study Of The Low Surfaces Thermodynamic Melting Of Refractory Metals (V,Nb,W)

Surfaces have a great effect on the performance of materials. In the present paper, the molecular dynamic (MD) simulations have been performed to study the relation between their microstructures and temperature of the low-index faces (111), (110) and (001) for refractory metals V Nb and W with the modified analytic embedded-atom method (MAEAM).At first, the bulk melting points of the perfect crystals of these three refractory metals have been determined by calculating their atomic average energies, and the obtained results are in good agreement with their con-esponding experimental data. The calculated thermal expansion coefficient for each metal in the lower temperature range is approximately equal to the referenced one.The interlayer relaxation varies with temperature by the surface tension. The interlayer relaxation of the (111) face is larger than the other two faces at the same temperature and its premelting temperature is the lowest in the three low-index surfaces. The relaxation of the (110) face, which become blur difficultly among the three low-index surfaces, is the least one. and remains stable up to the melting point. The relaxation and premelting temperature of (001) surface are between that of (111) and (110). For V and Nb, the relaxation of all the three low-index surfaces shows contraction with the increase of temperature.By investigating atomic position, mean-square vibration amplitude, layer density profiles, layer structure factors, radial distribution function, the results of all the three low-index planes reveal that there establish a thin quasiliquid film in the surface region and appear premelting phenomena below the melting temperature. The (111) surface disorders first, then the (100) surface, the (110) surface comes disordering at last. As the temperature increases, at the (111) and (001) surfaces of V, Nb and W, the surface disordering state spreads from the surface layer into the bulk, yet for the (110) face the premelting phenomena is no evidence and become out-of-order near the melting temperature. The different premelting phenomena of these low-index surfaces are original from that there are the discrepancies of atomic arrangement, layer atomic density, the asymmetry of the surface and the anharmonic effects. On the other hand, the obtained results also show that all the low-index surfaces of V and Nb, including...