Nano-experimental Mechanics Study On Dislocation Core In Face-centered Cubic Metal Au

With the development of electronic microscopy,the authenticity and sharpness of the electronic microscopic images are becoming higher and higher.At the same time,the nano mechanics analysis method,that is,the nano scale resolution experimental measurement technology,plays an important role in promoting the research of materials.There is inconsistent or even contradictory situations between many dislocation theories models.This is due to the lack of experimental data measured around the core of the dislocation to verify and improve various models.Therefore,the experimental determination of the core deformation field is expected to promote the development of dislocation theory.In this paper,the dislocation core in the face centered cubic metal Au is taken as the main object.This paper combines the high resolution transmission electron microscopy,molecular dynamics simulation and geometric phase analysis technology to study the reaction between mixed dislocation,the quantitative measurement of the strain field in the nanometer scale around the dislocation core,and the characterization of the interaction between dislocation.The experimental results are compared with various dislocation models and dislocation interaction models,and their applicable ranges are given.The main progress and conclusions are as follows:(1)A new type of sessile dislocation was found,and the Burgers vector was a/2[1 10].Molecular dynamics simulations show that the sessile dislocation can be formed by two 45°,45° and 60° dislocation reaction.This new type of sessile dislocation has been observed in Au with high resolution transmission electron microscopy,confirms the existence of the dislocation.(2)There is a significant difference in the strain field of sessile dislocation and glissile dislocation:the Burgers vector direction strain(εxx)image of sessile dislocation is butterfly like,and the strain(εxx)image of the glissile dislocation is oblique 8,and sessile dislocation has a very large positive strain(εyy)in the vertical direction of the Burgers vector,while the corresponding strain(εyy)of glissile dislocation tends to zero.Compared with the dislocation core strain field observed by the experiment,it is found that the Peierls-Nabarro dislocation model is consistent with the glissile dislocation core,and the linear elastic theory model is consistent with the sessile dislocation core.None of the dislocation models conforms to the sessile dislocation and glissile dislocation simultaneously.(3)The dislocation wall in the small angle grain boundary acts as a "wall" to isolate the strain field,which can hinder the expansion of the strain field and store larger residual strains.The residual strain observed in the small angle grain boundary strain concentration region is as high as 4.9%.When the strain passes,the dislocation core strain field on the dislocation wall will be stretched and deformed.(4)The data of the dislocation core strain field in a large number of two-dislocation systems are obtained by a large number of high resolution transmission microscopical experiments of polycrystalline Au.It is found that with the proximity of two dislocations,the strain field will increase near each dislocation core,but when the two dislocation distance is less than 2nm,the strain field becomes smaller.The comparison between the statistical results and the two dislocation interaction models shows that the two dislocation interaction theory based on continuum theory is remotely effective,and is invalid when the two dislocation distance is less than 3 nm.