Elastic And Thermodynamic Properties Of The Nanocrystalline Metals

Nanocrystalline(nc)metals and alloys have generally been classified as having an average grain size less than 100nm,and they are becoming a new type of materials used in various fields.Nanocrystalline metals have received considerable attention because these materials have shown many unique properties which deviate from coarse-grain with the same chemical composition,such as the increased hardness、yield stress、strong toughness and the bigger diffusion coefficient,excellent wear resistance compered with the coarse grain.Understanding thermodynamic properties of polycrystalline metals contributes to elevate the application value of nanomaterials in various fields.In this paper,we construct the initial nc samples with different size by Voronoi geometrical method,then these samples are relaxed to reduce the high energy and stress,which is caused by the unphysical grain boundaries.The structures,the average internal stresses,as well as energies are observed and we analysis the different grain samples during the relaxtion process.The initial and final structures are drawed and then by analyzing it is found that the proportion of grain boundary atoms has changed.Subsequently,by means of molecular dynamics simulation we constract the cold energy curve of single crystal with the one of polycrystalline when miniature strain is implemented,and the influence of grain size on the elastic constants and thermodynamic properties which nc metals possess was analyzed.Applying miniature tensile or compressive strain to the system,we obtain the cold energy curves of single crystal and poly crystalline.Furthermore,the figure is basically identified,which shows that our simulation method is feasible.The stress of system is found to soften with the decrease of grain size that is restrained below 10 nm,which exhibits a breakdown in the Hall-Petch relation.With the increase of grain size,on the one hand the tensile strength of the samples becomes more diffuicult,on the other hand the degree of compression is relatively easier.According to the formulas of thermodynamic parameters and unique elastic constants,we conclude that shear modulus,young’s modulus,poisson’s ratio,debye temperature value of thermodynamics,which makes us perceive further the properties of small grain size of nanometer materials such as resist deformation,plastic deformation and rigidity and so on.Through detailed analysis about the elastic and thermodynamic properties of small grain size of nanocrystalline,people can more comprehensively understand nanomaterials,which provides a powerful guarantee for better application of nanocrystalline.