Molecular Dynamics Simulation On Mechanical Properties Of Nanopolycrystalline Cu-Sn Alloy

Cu-Sn alloy is widely used in various fields because of its excellent properties,but the properties of traditional coarse-grained materials have been difficult to meet the needs of engineering applications.Nanocrystalline materials have better properties than traditional coarse-grained materials,and there are few reports on the research of Cu-Sn alloy in nanoscale.Therefore,the research on the mechanical properties of nanopolycrystalline Cu-Sn alloy has important practical value.Because of the grain size and different factors,the experimental research on nanopolycrystalline Cu-Sn alloy is too difficult and expensive.With the fast improvement of workstation technology,molecular dynamics simulation has become an effective method to study nanocrystalline materials.In this study,nanopolycrystalline Cu-Sn alloy is taken as the research object,and the tensile simulation is carried out by using the method of molecular dynamics simulation to explore the effects of average grain size,Sn content,strain rate and temperature on the mechanical behavior and plastic change of nanopolycrystalline Cu-Sn alloy,to provide reference and guidance for the preparation and regulation of high-performance Cu-Sn alloy.The results are as follows:(1)The mechanical behavior of nanopolycrystalline Cu-Sn alloy are serious influenced by the average grain size.The elastic modulus of the Cu-Sn increases firstly,and then decine with the rise of the average grain size.The change of elastic modulus is mainly caused by the different proportion of grain boundary atoms in nanopolycrystalline Cu-Sn alloy.The tensile strength shows a fluctuating upward trend with the increase of grain size.The flow stress appear a Hall-Petch theory for the scale of Cu-Sn model greater than 10.53 nm and an inverse Hall-Petch theory for the scale smaller than 10.53 nm.It is also found that most dislocations originate at grain boundaries,and the dislocation density is relatively higher at the triple junctions.Shockley dislocation is the main form of dislocation.(2)The elastic modulus and tensile strength of nanopolycrystalline Cu-Sn alloy are significantly affected by the content of Sn element.Research indicate that as the proportion of Sn elements increased,the elastic modulus and tensile strength initial rise and so decline.And the tensile strength is a lot of susceptible to the addition of Sn atom;Sn content has a great impact on the plastic deformation ability of nanopolycrystalline Cu-Sn alloy,and the flow stress initial rise and so decline with the increase of Sn content.The addition of Sn will inhibit the generation of dislocations and other defects,and gradually change the dislocation line from continuous and complete state to short and broken state,resulting in the inhibition of dislocation slip and extension.(3)Different strain rates were applied to the alloy model with grain size of 6.92 nm.It was found that the elastic modulus was weakly affected by the strain rate,while the strain rate had a greater impact on the tensile strength.The tensile strength increased significantly as the increase of strain rate.The results indicate that the larger the strain rate,the upper the dislocation density and the easier the atomic structure transformation.(4)The tensile simulation of nanopolycrystalline Cu-Sn alloy was carried out in the temperature range of from 100 K to 1000 K.The study found that mechanical properties of nanopolycrystalline Cu-Sn alloy were very sensitive to temperature.The elastic modulus of the alloy system decreases as the simulation temperature increasing,and the tensile strength decreases significantly.The analysis of dislocations revealed that the dislocation density is lower at higher temperatures,showing an obvious gradient distribution;At lower temperature,dislocations are easier to form and accumulate.The higher the temperature,the smaller the length of Shockley dislocation.