XRD Diffraction Simulation And Analysis Of Subsurface Damage Defects In CaF₂ Single Crystal Processing

CaF₂ single crystal is widely used in the field of aerospace to make prisms and lenses because of its stable physical,chemical and mechanical properties.In the actual processing,CaF₂ single crystal inevitably produces different damage types.These damages seriously reduce the service life and accuracy of CaF₂ optical devices.In order to reduce the damage of CaF₂ single crystal in the process of processing,it is necessary to analyze the influence of sub-surface damage types on crystal structure after crystal processing,and more importantly,to accurately characterize the damage.Therefore,the core purpose of this paper is to accurately characterize the damage types on the surface/sub-surface of CaF₂ single crystal after machining,and the basic means are GIXD nondestructive testing and XRD simulation testing based on the results of molecular dynamics simulation.Through the test results and simulation results,the types of defects on the surface/sub-surface of CaF₂ single crystal after machining are analyzed.Molecular dynamics indentation simulation can describe the deformation process of materials.After the indentation simulation,there are different types of defects on the sub-surface of the system,resulting in different degrees of lattice distortion.First of all,through the XRD diffraction simulation results of the system after the indentation simulation,the change of the diffraction simulation spectrum is connected with the change of the material microstructure,which proves the feasibility of XRD diffraction simulation analysis of the crystal structure change.Secondly,XRD diffraction simulation is carried out for the system with different single defect types,and the characteristic law of XRD diffraction simulation line change caused by different single defect types is obtained.Finally,GIXD test is carried out on the actual processed samples,and the difference and connection between GIXD diffraction line and XRD diffraction simulation line are analyzed.Combined with XRD simulation diffraction correlation theory,it is analyzed that the change of GIXD diffraction line is mainly caused by the change of crystal plane orientation and crystal plane spacing after sample processing.According to the results of GIXD diffraction and XRD simulation diffraction,the types of defects on the surface/sub surface of the machined samples were characterized and verified by TEM.In this paper,GIXD detection is used to detect the damage types on the surface/sub-surface of the processed sample.Combined with the results of molecular dynamics simulation,the influence of different types of defects on the diffraction lines of GIXD is analyzed.Based on the research in this paper,it is concluded that the phenomenon of"drift peak"of a certain crystal surface in the sample’s GIXD diffraction line means that there are micro-cracks on the sample’s sub-surface,and the multi peak diffraction of the diffraction line means that there are dislocation structures on the sample’s sub-surface.