Study On Methods Of Phase Identification And Orientation Analysis Of Electron Backscatter Diffraction(EBSD)

Electron Backscatter Diffraction(EBSD)is a complete microstructure analysis system attached to a Scanning Electron Microscope(SEM).It can simultaneously realize the functions of grain phase identification,phase content distribution,grain size measurement,orientation measurement,orientation relationship analysis,texture analysis,as well as analysis of grain boundary,dislocation,stress and strain.Since its inception,it has received extensive attention and is known as the "new weapon" for material microstructure research.EBSD has played an irreplaceable role in many research fields such as earth sciences,metal materials,and ceramic materials because of its powerful function,strong statistics,simple sample preparation and other advantages.At present,China's commercial EBSD system is completely dependent on imports.Under the background that the country is striving to overcome the "stuck neck" problems and independently researching and developing key technologies to break foreign monopolies,the research and development of domestic instruments has been paid more and more attention.The core algorithm is the key part of the whole EBSD system,but it has always been in the hands of a few foreign instrument manufacturers.In order to overcome algorithm problems,break the monopoly,and establish the EBSD analysis methods with independent intellectual property rights,this article,based on the two core functions of EBSD,namely phase identification and orientation analysis,studied the methods of phase identification and high-precision orientation calculation based on the existing methods,and proposed five new methods:method of indexing Kikuchi patterns assisted by Kikuchi bandwidth,method of identifying symmetry axis by reciprocal vectors,method for crystal structure identification by Kikuchi patterns,accuracy evaluation method for orientation calculation and method for selecting Kikuchi pole combinations.The pattern indexing method assisted by Kikuchi bandwidth uses the bandwidth as an important auxiliary condition for indexing the Kikuchi pattern.By measuring the bandwidth,the lattice plane spacing is calculated to determine the crystal plane family of the Kikuchi band,which greatly reduces the searching range of the matching of interplanar angle and improves the efficiency and accuracy of phase identification.The accurate detection of the edges of the Kikuchi band has been realized by the combination of the rotation method and the Hough transform.The relationship between the bandwidth and the interplanar spacing at any position in the Kikuchi pattern was established,and the accurate measurement of the interplanar spacing based on the bandwidth has been realized.The analysis of silicon single crystal showed that the measurement error of interplanar spacing is small,the average relative error is about 2.6% and the minimum is only 1.04%.This method is expected to provide a new idea for high precision phase identification and similar phases discrimination.The symmetry axis identification method uses the reciprocal vector as a tool to determine the symmetry axis(Kikuchi pole)in the Kikuchi pattern by judging the geometric shape of the reciprocal vectors,which makes the judgment of the symmetry axis more intuitive and convenient.Based on the essence of crystallography,the criterion for the symmetry axis identification was proposed,which provided reliable crystallographic evidence for the judgment of symmetry axis,and effectively avoided misjudgment by the naked eye.This method successfully judged the symmetry axes(including the 3-fold axis,the 4-fold axis and the asymmetric axis)in three Kikuchi patterns of single crystal silicon,and also realized the distinction between the 3-fold axis and the similar axis.This method lays a foundation for phase identification by crystal symmetry.The method of using the Kikuchi pattern to identify the crystal structure is to extract the symmetry axes from the pattern,calculate the angle between the symmetry axes,and combine the symmetry characteristics of different point groups to identify the crystal structure.The flow chart of crystal structure identification was established according to the combination law of symmetry elements of different point groups.The symmetry analysis and crystal structure identification of three unknown samples were successfully carried out.It showed that using the Kikuchi pattern to analyze the symmetry is an effective method to judge the crystal structure.Through the crystal structure identification,the selection range of phase identification has been greatly reduced,and the results that do not satisfy the crystal symmetry in the phase identification results given by the commercial EBSD has been eliminated,which improved the reliability and accuracy of EBSD phase identification.This method has good adaptability to the current commercial methods,and can be used as an important supplement to the existing interplanar angle matching method.The evaluation method of orientation calculation accuracy and the selection method of Kikuchi pole combination were proposed for the different orientation results obtained from different Kikuchi pole combinations.The precise coordinates of the Kikuchi poles were obtained by accurately positioning the lattice plane traces for orientation calculation.The positive correlation between the self-defined "deviation" and the misorientation angle was found,and the "deviation" was used as the criterion to evaluate the accuracy of orientation calculation.Based on this,a method for selecting the combination of Kikuchi poles was proposed.The first five Kikuchi pole combinations with smaller "deviation" were selected,and all of them can obtain high-precision orientation calculation results.The accuracy of orientation calculation has been greatly improved after Kikuchi pole combination selection,and the average orientation accuracy of kikuchi patterns has been improved by 60%,71% and 58%,respectively.This method can effectively eliminate the unreliable Kikuchi pole combinations,and completely eliminate the orientation calculation results with large errors.This research will help to develop a high-resolution domestic EBSD system with advanced functions and completely independent intellectual property rights,which is expected to change the situation of our country's long-term dependence on imports for this key microstructure characterization method.It is important to enhance the independent innovation ability of domestic instrument research and development,and make substantial contribution to China's material industry from large to strong.