| The echelle grating has a large blaze angle,so it has high diffraction efficiency at high diffraction orders,so it is widely used in the fields of spectrum detection and spectrum analysis.The master grating is prepared by plating an aluminum film on a glass substrate using a vacuum thermal vapor deposition process,and then using a diamond tool to scribe the aluminum film line by line to cause plastic deformation of the aluminum film to form a periodic groove structure.In the process of forming the groove,the factors affecting the quality of the grating groove shape are not only the accuracy of the scribing equipment and the scribing process,but also a very important factor-the quality of the grating aluminum film blank.According to theoretical analysis and preliminary research,it is found that there will be residual stress inside the aluminum film of the echelle grating vapor deposited by physical vapor deposition method,which seriously affects the stability of the groove quality at the initial stage of scribing;At the same time,the preliminary scribing test results show that the aluminum film with the "aluminum layer-chromium layer-base" structure prepared by a step-by-step plating process can often obtain a better groove shape when scribing.At present,there are many factors affecting the grating groove,the elastic-plastic deformation mechanism of aluminum film is not clear,and it is difficult to predict the groove profile,In this paper,combining the two research methods of finite element simulation and nanoindentation experiment,the stress transmission and distribution law of the composite layered aluminum film during plastic deformation are studied,and the influence of residual stress on the plastic deformation of the grating film is analyzed.It is of great practical significance to improve the groove quality of machine-engraved gratings.In this paper,the 79g/mm echelle diffraction grating is taken as an example to conduct metallographic experiments on aluminum films prepared by step-by-step plating and singlestep plating processes.Based on the experimental results,a finite element model of nanoindentation of grating films with different chromium layer thicknesses and aluminum film layers was established,and nanoindentation simulation experiments were carried out.Combined with the basic theory of nanoindentation testing,analyze the stress and strain transmission mechanism and distribution characteristics of different layered grating films during plastic deformation,the reason for the small springback and easy plastic deformation of the composite layered aluminum film after plastic deformation was found.Through the constant pressure depth nanoindentation simulation test,the load pressure depth curve and the stress-strain distribution of the aluminum film under various residual stress states such as tensile stress,compressive stress and shear stress are compared.It is found that the residual stress only changes the plastic yield limit and stiffness of the aluminum film.Based on this discovery,this paper analyzes the stress state and composition of the grating film combined with the Suresh model,and derives the residual stress calculation formula.The parameter fitting method is used to modify the formula,which improves the accuracy of the calculation result and provides a reference for the calculation of the residual stress of the grating aluminum film.According to the distribution law of residual stress field after plastic deformation of aluminum film obtained by simulation,a nanoindentation multi-point indentation test was designed to study the influence of residual stress on plastic deformation uplift of aluminum film.This article explains the reason for the unstable quality of the groove shape in the initial stage of scribing,explains the influence of residual stress on the plastic deformation uplift of aluminum film,it provides a reference for analyzing the deformation law of the machineengraved grating complex forming grooves,and then improving the quality of the grooves. |
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