High-precision detection method for subsurface defects in two-phase structure RB-SiC materials

Abstract

The present invention relates to the field of optical element defect detection, and in particular to a high-precision detection method for subsurface defects of a two-phase structure RB-SiC material, comprising: calibrating a magnetorheological removal function; determining the material removal amount distribution of a magnetorheological polishing device, and calculating the residence time distribution, performing bevel polishing on the component to be tested, and ensuring that the deepest part of the bevel is an undamaged substrate part; marking the head and tail of the bevel to determine the generatrix, and using a contour detection device to perform contour detection along the generatrix; using a laser confocal microscope to observe along the generatrix and perform a three-dimensional contour scan of the defect cutoff field of view to obtain a three-dimensional image of the defect cutoff field of view; according to the three-dimensional image, perpendicular to the contour detection generatrix direction, calculating the difference between the sagittal height obtained by the contour detection and the sagittal height of the deepest damage, and obtaining the subsurface defect depth. The present invention can improve the subsurface defect detection accuracy of the two-phase structure RB-SiC material.

Description

Technical Field

[0001] The present invention relates to the technical field of optical element defect detection, and in particular to a high-precision detection method for sub-surface defects of a two-phase structure RB-SiC material. Background Art

[0002] The rapid development of space astronomical optics and satellite remote sensing technology has put forward higher and higher requirements on the resolution and light-gathering ability of optical systems. Increasing the aperture of a telescope can improve the resolution and light-gathering ability of a telescope, but increasing the aperture of a telescope and mass-producing large-aperture telescopes require an exponential increase in optical manufacturing capabilities.

[0003] Among the materials for large-aperture space mirrors, reaction bonded silicon carbide (RB-SiC) has the advantages of high specific stiffness, high thermal conductivity, and easy to be lightweight, making it the preferred material for preparing large-aperture space mirrors. RB-SiC material is a hard and brittle material with high hardness and low fracture toughness, which brings two problems to optical processing: low removal rate and easy generation of sub-surface defects. Sub-surface defects and the stress they generate will affect the coating quality, long-term stability, and surface accuracy of large-aperture space mirrors, thereby reducing the imaging quality and even causing the telescope to fail. Therefore, sub-surface defects need to be completely removed during the processing process.

[0004] Due to the high hardness of RB-SiC materials (second only to diamond), it is difficult to remove the material. At present, redundant processing to remove subsurface damage is a key factor hindering the further improvement of optical manufacturing capabilities. How to accurately detect subsurface defects in RB-SiC materials has become a key technology for further improving the manufacturing capabilities of low-defect, ultra-high precision optical systems.

[0005] Most of the existing nondestructive testing methods for subsurface defects are based on optical or acoustic principles to detect defects inside optical components, such as optical coherence tomography, scanning acoustic microscopy, fluorescence confocal scanning, etc. However, for RB-SiC materials, due to its complex two-phase structure and opacity in the visible light range, conventional nondestructive testing methods are not applicable.

[0006] The destructive detection methods applicable to RB-SiC materials are mainly cross-sectional microscopy and magnetorheological polishing bevel method. The principle of the cross-sectional microscopy method is: to perform a section perpendicular to the surface to be tested, to perform non-destructive polishing on the section, and to observe the sub-surface defects of the section after non-destructive polishing using a microscope and other equipment. The advantage of this method is that the morphology of sub-surface defects can be observed, which plays an important role in the exploration of the formation mechanism of sub-surface defects. However, this method can only detect the sub-surface defect depth of a cross section, and cannot fully reflect the sub-surface defect depth of the entire surface to be tested. In addition, the detection efficiency is low, and the guiding significance for the actual processing process is limited. The basic principle of the magnetorheological polishing bevel method is: to use magnetorheological polishing equipment to perform bevel polishing on the surface of the component to be tested, to expose the defects originally on the sub-surface on the surface, to use a profiler and other profile detection equipment to detect the bevel profile, to use a microscope to observe along the bevel, to find the cutoff position of the sub-surface defect, and the bevel depth corresponding to the cutoff position is the sub-surface defect depth. If the flatness of the polished bevel is good, that is, a mother line can represent the contour of the entire bevel, this method can detect sub-surface defects of the entire bevel. However, for RB-SiC materials with a two-phase structure, the hardness of the SiC phase and the Si phase are different. After long-term magnetorheological polishing, the surface shows a phenomenon of less SiC phase removal and more Si phase removal, and there are ups and downs at the sub-micron level, which has a great impact on the accurate detection of sub-surface defects. Summary of the invention

[0007] In view of the above problems, the present invention proposes a detection method which combines laser confocal microscopy technology with magnetorheological polishing bevel technology to improve the detection accuracy of subsurface defects of two-phase structure RB-SiC materials.

[0008] The high-precision detection method for sub-surface defects of a two-phase structure RB-SiC material provided by the present invention comprises the following steps:

[0009] S1. Removal function calibration: Use a magnetorheological polishing device to perform single-point resident polishing on the component to be tested, and detect the removal function of the polishing to calibrate the removal function of the magnetorheological polishing device;

[0010] S2. Bevel polishing: determine the material removal distribution of the magnetorheological polishing device, and calculate the residence time distribution of the magnetorheological polishing device in combination with the removal function of the magnetorheological polishing device. The magnetorheological polishing device performs bevel polishing on the component to be tested with the residence time distribution to ensure that the deepest part of the bevel is the undamaged substrate part;

[0011] S3. Contour detection: Mark the head and tail of the bevel at the unpolished position on the component to be tested, and use a contour detection device to perform contour detection along the contour detection generatrix between the two marks to obtain the contour of the bevel;

[0012] S4. Damage detection: Use a laser confocal microscope to observe along the contour detection generatrix, record the distance between the sub-surface defect cutoff position field of view and the two marks, and perform a three-dimensional contour scan of the sub-surface defect cutoff position field of view to obtain a three-dimensional image of the sub-surface defect cutoff position field of view;

[0013] S5. Data fusion: Based on the three-dimensional image of the field of view of the sub-surface defect cutoff position, perpendicular to the contour detection generatrix direction, calculate the difference between the sagittal height of the inclined surface profile and the sagittal height of the sub-surface defect cutoff position to obtain the sub-surface defect depth.

[0014] Furthermore, if the surface roughness of the component to be measured meets the interference detection requirements, the interference method is used to detect the removal function; if the surface roughness of the component to be measured does not meet the interference detection requirements, the contour detection equipment is used to respectively detect the contours of the removal function in the major axis direction and the minor axis direction to fit the complete removal function.

[0015] Furthermore, the material removal distribution of the magnetorheological polishing equipment is determined according to the following formula:

[0016] ;

[0017] In the formula, To remove the function, is the residence time distribution, is the symbol for two-dimensional convolution.

[0018] Furthermore, microscopic observation and iterative polishing are used to ensure that the deepest part of the bevel is the undamaged substrate part.

[0019] Furthermore, after the bevel is polished by the magnetorheological polishing device, a microscope is used to observe the deepest part of the bevel. If there is damage, polishing is continued until the deepest part of the bevel is an undamaged substrate part.

[0020] Furthermore, the head and tail of the bevel are marked using an oil-based marker, a target sticker, or a scratching method.

[0021] Furthermore, the contour detection generatrix is ​​aligned with one axis of the laser confocal microscope, and the laser confocal microscope is used to observe from the head mark of the bevel to the tail mark of the bevel, while ensuring that the other axis of the laser confocal microscope is stationary, and the distance from the head mark of the bevel to the sub-surface defect cutoff position field of view is recorded, and the sub-surface defect cutoff position field of view is scanned in three dimensions to obtain a three-dimensional image of the sub-surface defect cutoff position field of view.

[0022] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0023] Combining the two-dimensional magnetorheological polishing bevel method with the three-dimensional cross-sectional microscopy method, the sub-surface defect detection is upgraded from the original two-dimensional to three-dimensional, so as to overcome the sub-surface defect depth detection problem caused by the magnetorheological differential removal of the two-phase structure RB-SiC material. Through the precise positioning of the bevel head mark and tail mark, the contour detection and damage detection data are integrated, thereby improving the sub-surface defect detection accuracy of the two-phase structure RB-SiC material. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a schematic flow chart of a high-precision detection method for sub-surface defects of a two-phase structure RB-SiC material provided in accordance with an embodiment of the present invention;

[0025] Figure 2 is a schematic diagram of an undamaged substrate of a RB-SiC material provided according to an embodiment of the present invention;

[0026] Figure 3 Schematic diagram of sub-surface defect detection of a two-phase structure RB-SiC material according to an embodiment of the present invention;

[0027] Figure 4 Schematic diagram of a slope contour line provided according to an embodiment of the present invention.

[0028] Reference numerals: component to be tested 1 , polished bevel 2 , head mark 3 , contour detection generatrix 4 , sub-surface defect cutoff position field of view 5 , deepest damage 6 , tail mark 7 . DETAILED DESCRIPTION

[0029] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In the following description, the same modules are represented by the same reference numerals. In the case of the same reference numerals, their names and functions are also the same. Therefore, the detailed description thereof will not be repeated.

[0030] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and do not constitute a limitation of the present invention.

[0031] The embodiment of the present invention provides a high-precision detection method for sub-surface defects of a two-phase structure RB-SiC material, comprising the following steps:

[0032] S1. Removal function calibration: Use a magnetorheological polishing device to perform single-point dwell polishing on the component to be tested, and detect the removal function of the polishing to calibrate the removal function of the magnetorheological polishing device.

[0033] If the size of the component to be tested is large enough and the operating space is large enough, the component to be tested can be used directly to calibrate the removal function. If the size of the component to be tested is not large enough, a component with the same surface roughness as the component to be tested can be used to calibrate the magnetorheological removal function.

[0034] If the surface roughness of the component to be tested is good and meets the interference detection requirements and reaches the interference detection level, the interference method is used to detect the removal function; if the surface roughness of the component to be tested is poor and does not meet the interference detection requirements, only a contour detection device (such as a profilometer) can be used to detect the removal depth, then the contour detection device is used to detect the contours of the removal function in the major and minor axis directions respectively to fit the complete removal function.

[0035] S2. Bevel polishing: Determine the material removal distribution of the magnetorheological polishing equipment, and calculate the residence time distribution of the magnetorheological polishing equipment in combination with the removal function of the magnetorheological polishing equipment. The magnetorheological polishing equipment performs bevel polishing on the component to be tested with the residence time distribution to ensure that the deepest part of the bevel is the undamaged substrate part.

[0036] The material removal distribution of the magnetorheological polishing equipment is determined according to the following formula:

[0037] (1);

[0038] In the formula, To remove the function, is the residence time distribution, ” is the symbol for two-dimensional convolution.

[0039] The width of the bevel is determined by the required detection efficiency and repeatability, the angle of the bevel is determined by the detection accuracy and efficiency requirements, and the deepest depth of the polished bevel is determined based on experience, which should exceed the expected sub-surface defect depth.

[0040] Substitute the determined material removal amount distribution (width, angle and depth of the polishing bevel) of the magnetorheological polishing device and the removal function calibrated in step S1 into formula (1) to calculate the residence time distribution, and use the magnetorheological polishing device to polish the bevel of the component to be tested with the residence time distribution. After polishing, use a microscope to observe the deepest part of the bevel. If there is no damage, mark the head and tail of the bevel. If there is still damage, continue to use the magnetorheological polishing device to polish until the deepest part of the bevel is the undamaged substrate part.

[0041] In other words, use a microscope to observe whether the bottom of the bevel is an undamaged substrate. If so, mark the head and tail of the bevel; if not, deepen the polished bevel until the bottom of the bevel is an undamaged substrate. For RB-SiC material, the microscopic image of the undamaged substrate is as follows: Figure 2 shown.

[0042] S3. Contour detection: Mark the head and tail of the bevel at the unpolished position on the component to be tested, and use a contour detection device to perform contour detection along the contour detection generatrix between the two marks to obtain the bevel profile.

[0043] In order to make the contour detection and damage detection along the same generatrix and the starting detection position consistent, and to ensure the correctness of the later data fusion, the head and tail of the polished bevel are marked. It should be noted that the mark should be at the position that has not been magnetorheologically polished, and the mark height / depth should exceed the surface roughness of the position by a lot, so as to avoid the mark being indistinguishable in the contour detection data.

[0044] In order to make the contour detection and damage detection along the same generatrix and the starting detection position consistent, and to ensure the correctness of the later data fusion, the head and tail of the inclined surface need to be marked. It should be noted that the mark should be at the position of the inclined surface that has not been magnetorheologically polished, and the height / depth of the mark should exceed the surface roughness of the position by a lot, so as to avoid the mark being indistinguishable in the contour detection data.

[0045] There are many ways to achieve marking, such as using oil-based markers, target stickers, and various scoring methods.

[0046] Since the paint of the oil-based marker has a certain height when it dries on the surface of the component to be tested, it is easy to distinguish if the surface roughness of the component to be tested is not particularly bad.

[0047] like Figure 3 As shown in FIG. 1 , the line between the head mark 3 and the tail mark 7 of the bevel is the contour detection generatrix 4. Therefore, by marking the head and tail of the bevel, the sub-surface defect cutoff position field of view 5 of the laser confocal microscope can be accurately located in the contour detection generatrix 4. The contour detection device is used to perform contour detection on the bevel along the contour detection generatrix 4. After the detection data is processed, the following is obtained: Figure 4 The outline shown.

[0048] S4. Damage detection: Use a laser confocal microscope to observe along the contour detection master line, record the distance between the sub-surface defect cutoff position field of view and the two marks, and perform a three-dimensional contour scan of the sub-surface defect cutoff position field of view to obtain a three-dimensional image of the sub-surface defect cutoff position field of view.

[0049] Align the contour detection generatrix 4 with one axis of the laser confocal microscope, observe from the head mark 3 of the inclined surface to the tail mark 7, ensure that the other axis of the laser confocal microscope does not move during the observation process, record the distance from the head mark 3 to the sub-surface defect cutoff position field of view 5, and perform a three-dimensional scan of the sub-surface defect cutoff position field of view 5 to obtain a three-dimensional image of the sub-surface defect cutoff position field of view 5.

[0050] For example, the contour detection busbar 4 is aligned with the x-axis of the laser confocal microscope. During the detection process, the laser confocal microscope is ensured to move along the aligned x-axis, while the y-axis remains stationary. Another example is that the contour detection busbar 4 is aligned with the y-axis of the laser confocal microscope. During the detection process, the laser confocal microscope is ensured to move along the aligned y-axis, while the x-axis remains stationary.

[0051] Of course, the present invention can record the distance from the tail mark 7 of the bevel to the sub-surface defect cutoff position field of view 5. The head mark 3 and the tail mark 7 of the bevel can, on the one hand, make the contour detection and the microscopic detection the same area as much as possible, and on the other hand, align the contour detection data with the microscopic detection data. In this way, the depth of the microscopic detection area corresponding to the component surface can be found in the contour detection data, thereby realizing the detection of the sub-surface defect depth.

[0052] The three-dimensional scanning of the laser confocal microscope refers to the scanning along the x, y, and z axes of the laser confocal microscope. The z axis direction is the depth direction. The laser confocal microscope can scan each point in the field of view along the depth direction to obtain a three-dimensional morphology.

[0053] S5. Data fusion: Based on the three-dimensional image of the field of view of the sub-surface defect cutoff position, perpendicular to the contour detection generatrix direction, calculate the difference between the sagittal height of the inclined surface profile and the sagittal height of the sub-surface defect cutoff position to obtain the sub-surface defect depth.

[0054] The laser confocal microscope has the function of three-dimensional scanning, which can perform three-dimensional scanning of the field of view with sub-surface damage cutoff. Through the scanned three-dimensional morphology, the position and depth of the deepest damage in the field of view can be confirmed.

[0055] According to the three-dimensional image of the sub-surface defect cutoff position field of view 5, the vertical contour detection generatrix 4 direction is calculated to calculate the difference between the sagittal height obtained by contour detection and the sagittal height of the deepest damage 6 (i.e., the sub-surface defect cutoff position), thereby obtaining the sub-surface defect depth.

[0056] The present invention combines two-dimensional contour detection with three-dimensional damage detection, so that sub-surface defect detection is upgraded from the original two-dimensional to three-dimensional, so as to overcome the sub-surface defect depth detection problem caused by magnetorheological difference removal of two-phase structure RB-SiC material. Through the precise positioning of the bevel head mark and the tail mark, the contour detection and damage detection data are fused, thereby improving the sub-surface defect detection accuracy of the two-phase structure RB-SiC material.

[0057] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0058] The above specific implementations do not constitute a limitation on the protection scope of the present invention. It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and substitutions can be made according to design requirements and other factors. Any modification, equivalent substitution and improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high-precision detection method for subsurface defects of two-phase structure RB-SiC materials, characterized in that: The steps include: S1. Removal function calibration: Use a magnetorheological polishing device to perform single-point resident polishing on the component to be tested, and detect the removal function of the polishing to calibrate the removal function of the magnetorheological polishing device; S2. Bevel polishing: determine the material removal distribution of the magnetorheological polishing device, and calculate the residence time distribution of the magnetorheological polishing device in combination with the removal function of the magnetorheological polishing device. The magnetorheological polishing device performs bevel polishing on the component to be tested with the residence time distribution to ensure that the deepest part of the bevel is the undamaged substrate part; S3. Contour detection: Mark the head and tail of the bevel at the unpolished position on the component to be tested, and use a contour detection device to perform contour detection along the contour detection generatrix between the two marks to obtain the contour of the bevel; S4. Damage detection: Use a laser confocal microscope to observe along the contour detection generatrix, record the distance between the sub-surface defect cutoff position field of view and the two marks, and perform a three-dimensional contour scan of the sub-surface defect cutoff position field of view to obtain a three-dimensional image of the sub-surface defect cutoff position field of view; S5. Data fusion: Based on the three-dimensional image of the field of view of the sub-surface defect cutoff position, perpendicular to the contour detection generatrix direction, calculate the difference between the sagittal height of the inclined surface profile and the sagittal height of the sub-surface defect cutoff position to obtain the sub-surface defect depth.

2. The high-precision detection method for sub-surface defects of two-phase structure RB-SiC materials according to claim 1 is characterized in that: If the surface roughness of the component to be tested meets the interference detection requirements, the interference method is used to detect the removal function; if the surface roughness of the component to be tested does not meet the interference detection requirements, the contour detection equipment is used to detect the contours of the removal function in the major axis direction and the minor axis direction respectively to fit the complete removal function.

3. The high-precision detection method for sub-surface defects of two-phase structure RB-SiC material according to claim 1 is characterized in that: The material removal distribution of the magnetorheological polishing equipment is determined according to the following formula: ； In the formula, To remove the function, is the residence time distribution, is the symbol for two-dimensional convolution.

4. The high-precision detection method for sub-surface defects of two-phase structure RB-SiC material according to claim 1 is characterized in that: Microscopic observation and iterative polishing ensure that the deepest part of the bevel is the undamaged substrate part.

5. The high-precision detection method for sub-surface defects of two-phase structure RB-SiC material according to claim 4, characterized in that: After the bevel is polished by the magnetorheological polishing equipment, the deepest part of the bevel is observed with a microscope. If there is damage, polishing is continued until the deepest part of the bevel is the undamaged substrate part.

6. The high-precision detection method for sub-surface defects of two-phase structure RB-SiC material according to claim 1, characterized in that: Mark the head and tail of the bevel using a permanent marker, target stickers, or by scoring.

7. The high-precision detection method for sub-surface defects of two-phase structure RB-SiC material according to claim 1, characterized in that: Align the contour detection generatrix with one axis of the laser confocal microscope, use the laser confocal microscope to observe from the head mark of the bevel to the tail mark of the bevel, ensure that the other axis of the laser confocal microscope does not move, record the distance from the head mark of the bevel to the sub-surface defect cutoff position field of view, and perform a three-dimensional scan of the sub-surface defect cutoff position field of view to obtain a three-dimensional image of the sub-surface defect cutoff position field of view.

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