A method for pre-treating RB-SiC surface by femtosecond laser modification

Abstract

The present application relates to a kind of RB-SiC surface femtosecond laser modification pretreatment method, by femtosecond laser to the preset Si powder on RB-SiC surface is modified and handled, to improve the polishing efficiency of RB-SiC surface.The present application can directly carry out surface modification to the cutting surface of RB-SiC, Si powder prepositioned on the surface of RB-SiC is rapidly oxidized under the action of the high peak power of femtosecond laser, and with the deepening of the depth of oxidation, so that the modified layer after oxidation forms bonding with RB-SiC matrix, obtains a modified coating with high adhesion strength, high quality.The method has the advantages of simple operation, low requirement to RB-SiC matrix and working environment, can be directly carried out in air, etc., can be applied to the surface modification of RB-SiC with complex surface shape, can significantly improve its polishing efficiency.

Description

Technical Field

[0001] This invention relates to RB-SiC reflectors, and in particular to a femtosecond laser modification pretreatment method for RB-SiC surfaces, in order to solve the problem that existing RB-SiC surface modification technologies have high requirements for the surface quality of RB-SiC, resulting in long manufacturing cycles and high costs for RB-SiC reflectors. Background Technology

[0002] SiC possesses high strength and excellent thermal stability, enabling the manufacture of large-sized mirror blanks at a relatively low cost, thus achieving lightweight large-aperture mirrors. RB-SiC is currently the preferred material for preparing large-aperture, complex, and lightweight mirror blanks, capable of producing dense, intricately shaped SiC mirror blanks. However, because RB-SiC contains approximately 10%–30% free Si, it has a two-phase structure. The difference in their physical properties leads to a faster removal rate of Si during polishing compared to SiC, resulting in microsteps at the interface between the two phases, which is difficult to meet the requirements for mirror use. Currently, physical vapor deposition (PVD) and chemical vapor deposition (CVD) methods are often used to modify the surface of RB-SiC, depositing a SiC or Si film similar to the substrate material to address the diffraction problem caused by the different polishing properties of the two phases. Through surface modification, a single-component modified layer can be deposited on the RB-SiC surface, reducing the polishing difficulty of the RB-SiC substrate and effectively avoiding the microstep problem caused by its two-phase structure. Modified layers prepared on RB-SiC surfaces using physical / chemical vapor deposition methods have achieved good results in improving polishing precision. However, these methods require a certain vacuum environment during modification, leading to complex and costly preparation processes. Furthermore, both methods place high demands on the surface quality of the RB-SiC substrate before modification, and the high hardness of RB-SiC results in low polishing efficiency, causing a long preparation cycle for the RB-SiC substrate before modification.

[0003] Some researchers have used femtosecond laser irradiation to improve the chemical mechanical polishing efficiency of SiC single crystals. The results show that the SiC surface becomes graphitized after laser irradiation, and the material removal rates of the C and Si faces of the SiC single crystal samples increased by approximately 77% and 207%, respectively. While femtosecond laser modification has achieved positive results in improving the polishing efficiency of SiC single crystals, it struggles to address the diffraction problem caused by the two-phase structure of RB-SiC, making it difficult to directly apply to the surface modification of RB-SiC.

[0004] Furthermore, patent document CN102094179 discloses a surface modification layer structure and preparation method for an RB-SiC substrate mirror. Using ion implantation, the Si phase on the RB-SiC substrate surface is first carbonized into SiC, then a diamond-like carbon (DLC) buffer layer is grown on the SiC. Finally, a Si modification layer is grown on the DLC buffer layer using high-energy ion-assisted methods. The Si modification layer is relatively dense and uniform, thereby improving polishing characteristics and significantly enhancing the optical quality of the polished substrate surface. However, this method is cumbersome, has a long preparation cycle, and is costly. Before preparing the Si modification layer, a DLC buffer layer needs to be prepared on the carbonized RB-SiC surface. The carbonization pretreatment of the RB-SiC surface also requires pretreatment in a vacuum environment, and this method requires polishing pretreatment of the RB-SiC surface to meet the bonding strength requirements. Summary of the Invention

[0005] To overcome the shortcomings of existing technologies, this invention proposes a femtosecond laser modification pretreatment method for RB-SiC surfaces. This method modifies pre-placed Si powder on the RB-SiC surface using a femtosecond laser. Under the high peak power of the femtosecond laser, the pre-placed Si powder is rapidly oxidized, and as the oxidation depth increases, the oxidized modified layer bonds with the RB-SiC substrate, resulting in a modified coating with high adhesion strength and high quality. This effectively improves the processing efficiency of SiC mirrors and reduces costs, demonstrating good economic benefits. This method is simple to operate, has low requirements for the RB-SiC substrate, and is unrestricted by the working environment; it can be performed directly in air, providing a simpler process approach for the surface modification of RB-SiC.

[0006] The technical solution of the present invention is as follows:

[0007] A femtosecond laser modification pretreatment method for RB-SiC surface, characterized by including:

[0008] ① The cut surface of the RB-SiC workpiece is ultrasonically cleaned to serve as a modified matrix;

[0009] ② Take alcohol with a concentration greater than 99.97% and Si powder with a particle size of 8μm, mix them at a weight ratio of 1.35 to 1.6:1, and grind them for half an hour until they become a slurry.

[0010] ③ The ground Si powder is evenly pre-placed on the surface of the RB-SiC workpiece, ensuring that the thickness of the pre-placed powder is 0.2 to 0.8 mm, and the RB-SiC workpiece with the powder is fixed on the two-dimensional moving platform of the femtosecond laser modification pretreatment device for the RB-SiC surface.

[0011] ④ Adjust the objective lens position to achieve focus;

[0012] ⑤ Set the femtosecond laser modification pretreatment process parameters;

[0013] ⑥ Move the two-dimensional moving platform to determine the processing starting point, turn on the laser and the two-dimensional moving platform, and perform femtosecond laser modification pretreatment on the Si powder pre-placed on the surface of the RB-SiC workpiece. Under the action of the high peak power of the femtosecond laser, the pre-placed Si powder on the RB-SiC surface is rapidly oxidized. As the oxidation depth continues to increase, the oxidized modified layer eventually forms a bond with the substrate.

[0014] ⑦ After the modification pretreatment is completed, turn off the laser beam, return the two-dimensional moving platform to zero, and turn off the two-dimensional moving platform (1). Take out the RB-SiC workpiece with the surface modification completed.

[0015] Preferably, the femtosecond laser modification pretreatment process parameters include: a focused spot size of 0.01–0.06 mm; a femtosecond laser wavelength of 1030–1064 nm, a pulse width of 290–400 fs, a single pulse energy of 70–90 μJ, and a repetition frequency of 200–800 kHz; a grating scanning path for the femtosecond laser, a scanning speed of 1–4 mm / s, and a scanning interval of 0.002–0.005 mm.

[0016] Compared with existing technologies, the beneficial effects of this invention are:

[0017] It can directly modify the cut surface of RB-SiC, eliminating the need for pretreatment of the RB-SiC substrate. It offers advantages such as ease of operation and low requirements for the working environment, and can be applied to the modification of complex RB-SiC surfaces, significantly improving polishing efficiency. Only when the oxidation depth of the pre-placed Si powder under femtosecond laser irradiation exceeds its thickness can a modified coating with high adhesion strength and high quality be obtained.

[0018] It can eliminate the need for polishing pretreatment of RB-SiC, and its process is simple, convenient and low-cost. The modified layer prepared by it can solve the diffraction problem caused by the two-phase structure of RB-SiC and effectively improve the polishing efficiency of RB-SiC surface. Attached Figure Description

[0019] Figure 1 Schematic diagram of the femtosecond laser modification mechanism of RB-SiC surface;

[0020] Figure 2 Schematic diagram of a femtosecond laser modification pretreatment device for RB-SiC surface;

[0021] Figure 3 Schematic diagram of femtosecond laser modification pretreatment process for RB-SiC surface.

[0022] Figure 4 : Surface morphology of RB-SiC before and after femtosecond laser modification pretreatment.

[0023] The markings in the figure are: 1. Two-dimensional moving platform; 2. RB-SiC workpiece; 3. Pre-placed Si powder; 4. Objective lens; 41. Laser beam; 5. Pressure plate; 6. Bolt; 61. Gasket; Ф, diameter of RB-SiC workpiece; X and Y, size of modified area. Detailed Implementation

[0024] To provide a clearer understanding of the technical features, objectives, and effects of this invention, the invention will be further described in detail below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the scope of protection of this invention.

[0025] Example

[0026] like Figure 1 As shown, a femtosecond laser modification pretreatment method for RB-SiC surface is based on the principle that the pre-placed Si powder on the RB-SiC surface is rapidly oxidized under the action of the high peak power of the femtosecond laser, and as the oxidation depth increases, the oxidized modified layer eventually bonds with the substrate.

[0027] like Figure 2 and Figure 3 As shown, the femtosecond laser modification pretreatment method for RB-SiC surface of the present invention includes the following steps:

[0028] Step 1: Ultrasonic cleaning is performed on the cut surface of RB-SiC workpiece 2 to serve as a modified substrate.

[0029] Step 2: Mix ethanol with a concentration greater than 99.97% and Si powder with a particle size of 8μm at a weight ratio of 1.35 to 1.6:1, and grind for half an hour until it becomes a slurry.

[0030] Step 3: The ground Si powder 3 is evenly pre-placed on the surface of the RB-SiC workpiece, ensuring that the thickness of the pre-placed powder is 0.2 to 0.8 mm. The RB-SiC workpiece 2 with the powder is placed on the two-dimensional moving platform 1 of the RB-SiC surface femtosecond laser modification pretreatment device and fixed by the pressure plate 5, bolts 6 and gaskets 61.

[0031] Step 4: Adjust the position of objective lens 4 to perform focusing;

[0032] Step 5: Power on the laser and the two-dimensional moving platform 1, and set the femtosecond laser modification pretreatment process parameters;

[0033] Step 6: Move the two-dimensional moving platform 1 to determine the processing starting point, turn on the laser beam 41 and the two-dimensional moving platform 1, and perform femtosecond laser modification pretreatment on the surface of the RB-SiC workpiece 2 with Si powder 3 pre-placed on it.

[0034] Step 7: After the modification pretreatment is completed, turn off the laser beam 41, return the two-dimensional moving platform 1 to zero, turn off the two-dimensional moving platform 1, and take out the RB-SiC workpiece 2 with the surface modification completed.

[0035] Furthermore, to ensure that the oxidation depth of the pre-placed Si powder 3 is greater than its thickness, thereby achieving high adhesion strength and high-quality modified coating preparation, the femtosecond laser modification pretreatment process parameters are set as follows:

[0036] 1) The focused spot size of laser beam 41 is 0.03 mm;

[0037] 2) The parameters of the femtosecond laser are: wavelength 1030nm, pulse width 290fs, single pulse energy 70μJ, and repetition frequency 200kHz.

[0038] 3) Set the femtosecond laser scanning path to raster scanning, such as... Figure 3 As shown, Ф is 30mm, X and Y are both 15mm, the scanning speed is 1mm / s, and the scanning interval is 0.005mm.

[0039] Under the conditions of this embodiment, the bonding strength between the modified layer formed after modifying the pre-placed Si powder and the substrate is approximately 55 N, which is superior to existing processes. Furthermore, the modified layer has a single component, effectively solving the diffraction problem caused by the two-phase structure of RB-SiC. In addition, the surface roughness of the modified RB-SiC reaches 4.5 nm after only about 4.5 hours of polishing, significantly improving the polishing efficiency of RB-SiC. The surface morphology before and after polishing is as follows: Figure 4 As shown.

[0040] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. At the same time, the above description should be clear and implementable by those skilled in the art. Therefore, any equivalent changes or modifications made without departing from the spirit disclosed in the present invention should be included in the scope of the patent application.

Claims

1. A method for femtosecond laser modification pretreatment of RB-SiC surface, characterized in that, include: ① The cut surface of the RB-SiC workpiece is ultrasonically cleaned to serve as a modified matrix; ② Take alcohol with a concentration greater than 99.97% and Si powder with a particle size of 8μm, mix them at a weight ratio of 1.35 to 1.6:1, and grind them for half an hour until they become a slurry. ③ The ground Si powder is evenly pre-placed on the surface of the RB-SiC workpiece, ensuring that the thickness of the pre-placed powder is 0.2 to 0.8 mm, and the RB-SiC workpiece with the powder is fixed on the two-dimensional moving platform of the femtosecond laser modification pretreatment device for the RB-SiC surface. ④ Adjust the objective lens position to achieve focus; ⑤ Set the femtosecond laser modification pretreatment process parameters; ⑥ Move the two-dimensional moving platform to determine the processing starting point, turn on the laser and the two-dimensional moving platform, and perform femtosecond laser modification pretreatment on the Si powder pre-placed on the surface of the RB-SiC workpiece. Under the action of the high peak power of the femtosecond laser, the pre-placed Si powder on the RB-SiC surface is rapidly oxidized. As the oxidation depth continues to increase, the oxidized modified layer eventually forms a bond with the substrate. ⑦ After the modification pretreatment is completed, turn off the laser beam, return the two-dimensional moving platform to zero, and turn off the two-dimensional moving platform (1). Take out the RB-SiC workpiece with the surface modification completed.

2. The femtosecond laser modification pretreatment method for RB-SiC surface according to claim 1, characterized in that, The femtosecond laser modification pretreatment process parameters include: the focused spot size of the laser beam is 0.01–0.06 mm; the femtosecond laser wavelength is 1030–1064 nm, the pulse width is 290–400 fs, the single pulse energy is 70–90 μJ, and the repetition frequency is 200–800 kHz; the femtosecond laser scanning path is a grating scan, the scanning speed is 1–4 mm / s, and the scanning interval is 0.002–0.005 mm.

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