Molecular Dynamics Study On Mechanical Properties Of Metal Tantalum

Nanomaterials have a series of excellent chemical and physical properties,and have been widely used in environmental,chemical,medical,energy and other fields.However,there are still many doubts about their mechanical properties at the nanometer scale,especially the plastic deformation mechanism.The tantalum has good stability,high strength and high melting point,and has broad application prospects in biomedical products,high temperature resistant devices,aerospace devices.Based on the molecular dynamics(MD)method,the deformation behavior of tantalum under uniaxial tensile load was simulated.The mechanical properties and plastic deformation mechanism of single crystal and nanocrystalline tantalum were studied with different size or grain size at different strain rate and temperature.The specific work of the thesis is as follows:Firstly,the research background and significance of nanometer metal tantalum are introduced.The research status of nanomaterials is summarized and analyzed.The basic principles,calculation processes and related mechanisms of molecular dynamics are summarized.The basic theory of mechanical and plastic deformation testing is introduced.Then,the Voronoi method used in nanocrystalline simulation modeling is introduced.The simulation models of single crystal and nanocrystalline tantalum are respectively established,and Ravelo-EAM and Zhou-EAM used in molecular dynamics tensile simulation are based on elastic constants.The two types of potential function are analyzed and compared.Next,based on the principle of molecular dynamics,the simulation process and condition setting in single crystal tantalum tensile simulation are described,and the feasibility analysis of the relaxation of the simulation is carried out.The stress-strain curve and energy variation curve are drawn and quantitative analysis is carried out.The mechanical properties such as the elastic modulus and peak stress of single crystal tantalum are combined with the atomic motion trajectory to qualitatively analyze the plastic deformation mechanism of single crystal tantalum.In addition,the single crystal tantalum was subjected to tensile simulation at different strain rates and temperatures,and the effects of size,strain rate and temperature on the mechanical properties of single crystal tantalum were investigated.Finally,nanocrystalline tantalum with various grain sizes was simulated at different strain rates and temperatures.The effects of grain size,strain rate and temperature on the mechanical properties and plastic deformation mechanism of nanocrystalline tantalum were investigated.The simulation results show that the flow stress and grain size of nanocrystalline tantalum always conform to the mixed Hall-Petch relationship.When the grain size is larger than the critical grain size,the plastic deformation is dominated by deformation twinning and dislocation activity.At the time of grain boundary behavior,a small amount of deformed twins was found.In addition,we found that the strain rate and temperature only affect the mechanical properties of nanocrystalline tantalum and the critical grain size of plastic deformation.The main plastic deformation mechanism is still determined by the grain size.In addition,the temperature mainly affects the dislocation activity in the plastic deformation of nanocrystalline tantalum,and has little effect on the deformation twins and grain boundary behavior.Through the molecular dynamics simulation of the uniaxial stretching process of single crystal and nanocrystalline tantalum,the mechanical properties and plastic deformation mechanism and influencing factors of single crystal tantalum were investigated.The grain size,strain rate and temperature were completely discussed.The plastic deformation mechanism of nanocrystalline tantalum and the influence of critical grain size provide a theoretical reference for the future application of nanometer metal tantalum in biomedical and high temperature resistant devices.