EBSD Patterns Simulation Of Dislocation Structures Based On Electron Diffraction Dynamic Theory

Dislocations have important effects on the mechanical properties,electrical properties,phase transitions and crystal growth of materials.At present,it is urgent to develop a new dislocation characterization method which can not only obtain morphology and structure simultaneously,but also have high resolution and easy operation.Electron backscattering diffraction(EBSD)is undoubtedly a suitable choice.EBSD technique is a microscopic characterization method working in scanning electron microscopy,which can provide the crystallographic information of the samples quickly and accurately.However,it can only evaluate the geometrical necessary dislocation density in crystal samples by measuring orientation information,and cannot directly analyze the dislocation structure.The key problem is that the EBSD standard patterns of the dislocation structures cannot be obtained.In order to obtain EBSD standard patterns with fine intensity information,EBSD patterns of dislocation structures are simulated by the RRS method in this thesis,and the correlation between dislocation structures and the pattern features is carefully analyzed,which will provide a theoretical basis for the resolution of the crystal dislocation structures by EBSD technology.The main research contents and results of this thesis are as follows.(1)EBSD patterns of face-centered cubic(FCC)Fe with perfect structure,1/2<110>and 1/3<(?)11>edge dislocation dipole structures in the[1(?)2],[1(?)(?)]and[(?)(?)0]orientations are simulated using the RRS method,respectively.By comparison,it is found that the presence of the edge dislocation hardly change the geometric position of the Kikuchi bands and Kikuchi poles in the patterns,but deteriorates the quality of the patterns,and has different effects on different Kikuchi bands.The edge of the Kikuchi band of the dislocation slip plane is sharp and the details in the band are very clear.The edge of the Kikuchi band of the crystal plane normal to the dislocation Burgers vector is not very sharp,but the diffraction details within the band are clearer.Other Kikuchi bands display obvious anisotropic blurring.In addition,the smaller the Burgers vector of the edge dislocation structure,the clearer the diffraction details in the EBSD pattern.These phenomena are attributed to the atomic displacements of the edge dislocation structure.Based on these analyses,it can be derived as following:when one clearer or two clearer and mutually perpendicular Kikuchi bands appear in the fuzzy EBSD pattern,it can be identified as a pattern with the edge dislocation.Among them,the Kikuchi pole at the intersection of the two clear Kikuchi bands corresponds to the direction of the dislocation line;the one with sharper edges corresponds to the slip plane of the edge dislocation,and the one with slightly fuzzy edge corresponds to the crystal plane normal to the Burgers vector.(2)EBSD patterns of FCC Fe with perfect structure,1/2<110>and 1/6<1 (?)2>quadrupole screw dislocation structures in the[(?)(?)0],[(?)1(?)]and[(?)11]orientations are simulated using the RRS method,respectively.By comparison,it is found that the presence of screw dislocations hardly change the geometric positions of the Kikuchi bands and poles in the pattern,but deteriorates the quality of the pattern and has different effects on different Kikuchi bands and poles.The screw dislocations have the least influence on the Kikuchi pole corresponding to the Burgers vector and the Kikuchi bands passing through the pole.The diffraction details at the Kikuchi pole are clear.The edges of the Kikuchi bands are sharp,and diffraction details within the band are clear in segments close to the pole and blurred in segments far from it.The diffraction details of the other Kikuchi bands and Kikuchi poles are blurred.In addition,the smaller the Burgers vector,the clearer the diffraction details in the EBSD pattern.These phenomena are also attributed to the atomic displacements caused by the screw dislocations.Based on these analyses,it can be derived that:when only one Kikuchi pole in the blurred EBSD pattern has the clearest diffraction details,and the band edges of the Kikuchi bands passing through it are clear with similar blurred details within the bands,or when only some band edges of the mutually parallel Kikuchi bands are clear,it can be identified as a pattern of screw dislocations.Among them,the clearest Kikuchi pole corresponds to the Burgers vector of the dislocation,and a series of parallel and clear band edges corresponds to the crystal plane perpendicular to the Burgers vector.