Research On Pattern Calibration And Stress Analysis In EBSD System

Electron Backscattered Diffraction(EBSD)can be applied to almost all crystal materials and has become an important tool in the microstructure analysis of materials.As an auxiliary device installed in a scanning electron microscope,it can effectively give crystallographic information such as grain size,crystal structure and orientation,phase content texture of the material.In addition,due to its high resolution and the ability to characterize residual stress distribution,it has become the best analytical system for microstructure stress analysis.The key partof the EBSD system is to obtain the corresponding crystallographic information from the diffraction pattern,depending on its pattern calibration algorithm.The current commercial EBSD calibration software algorithms are based on Hough transform.According to the data provided by the instrument manufacturer,the angular error of the Kikuchi bands is about ±5°,and the relative error is about 10%.Based on this error,the voting algorithm is used to give a possibility of the highest crystal plane orientation.If the accuracy can be improved in the pattern calibration stage and the voting is performed under a smaller angle error,the calibration accuracy of the crystal orientation can be improved.In this paper,a high-precision EBSD pattern calibration correction method is proposed.Based on the gradient analysis,the strong and weak boundary positions of the Kikuchi bands are obtained.Then,we use the feature of Kikuchi pattern to correct the weak boundary,and complete entire calibration process.In the experimental verification stage,the single crystal silicon sample collected by the commercial system is taken as an example to verify the calibration algorithm.Firstly,we use gradient analysis method to detect the strong and weak boundary linear clusters of the Kikuchi bands,then group and weight the linear clusters to obtain the position of the strong and weak boundary of the Kikuchi zone.Compared with the theoretical value,the angle calibration error of the algorithm is about 2%-8%,compared with the commercial algorithm(about 10%),calibration accuracyhas been greatly improved;combined with the rotational symmetry feature of the Kikuchi pole,the weak boundary is corrected.For different Kikuchi bands,the corrected calibration algorithm can reduce the width calibration error by 10%-90%to different degrees,which proves the feasibility and reliability of the calibration algorithm.In addition,according to the coordinates of the Kikuchi pole center point calculated by the calibration algorithm,combined with the spin matching DIC algorithm,an EBSD residual stress analysis system is built in this paper,which can realize the residual stress state analysis of the crystal material.