A method for manufacturing a thin x-ray mirror based on additive silicon carbide

Abstract

The application belongs to the technical field of X-ray optical element manufacturing, and specifically discloses a thin X-ray mirror preparation method based on additive silicon carbide, which comprises the following steps: preparing a silicon carbide thin X-ray mirror base blank by using an additive manufacturing technology, and performing high-temperature sintering treatment; precisely grinding the back surface of the silicon carbide thin X-ray mirror base blank; low-stress upper disc; processing the working surface of the silicon carbide thin X-ray mirror base to obtain a thin X-ray mirror. The thin X-ray mirror preparation method based on additive silicon carbide is used, the mirror base and its lightweight structure and aspherical working surface are integrally near-net formed by using the additive manufacturing technology, the process flow is shortened from the source, the material and processing costs are reduced, and the subsequent integrated ultra-precision machining and modification technology is used to break through the bottleneck that efficiency and precision cannot be simultaneously achieved, so that a solution is provided for mass production of high-performance and lightweight X-ray mirrors.

Description

Technical Field

[0001] This invention belongs to the field of X-ray optical element manufacturing technology, specifically relating to a method for preparing a thin X-ray mirror based on additive silicon carbide. Background Technology

[0002] In fields such as X-ray astronomical observation, the Wolter-I optical system, with its grazing incidence principle, is a key technology for achieving high-resolution X-ray focusing imaging. The imaging performance and light-gathering area of ​​this system largely depend on the processing precision, lightweighting, and manufacturing cost of its core component—the reflecting mirror.

[0003] Early Wolter-I systems (such as the Chandra X-ray Observatory) typically employed direct polishing for lens manufacturing. While this technique achieves nanometer-level surface accuracy, its complex processes and long lead times result in extremely high costs per lens, making it unsuitable for large-scale nested lens systems or budget-constrained projects. To control costs while maintaining optical performance, the industry has developed various alternative processes, such as nickel plating replication, epoxy resin replication, micropore optics (MSO), silicon aperture optics (SPO), and thin-glass thermoforming. Among these, thin-glass thermoforming technology, due to its relatively mature process, has become the mainstream approach internationally (especially in the United States) for developing nested Wolter-I systems, and has been successfully validated in missions such as HEFT and NuSTAR.

[0004] For next-generation observation missions requiring higher resolution and larger light-gathering areas (such as LYNX and ATHENA), single-crystal silicon materials have become a research hotspot due to their excellent optical properties. However, the inherent brittleness of single-crystal silicon leads to insufficient mechanical properties, making it difficult to maintain sufficient structural stiffness and strength while achieving extreme lightweight lenses. This material bottleneck poses a severe challenge to the processing yield, production efficiency, and structural design flexibility of single-crystal silicon lenses in multi-layer nested systems, thus restricting their engineering applications.

[0005] Therefore, in view of the problems existing in the prior art, such as high manufacturing cost of lenses, difficulty in balancing lightweight and mechanical properties, and complex production process, there is a need in the field to develop a method for preparing thin X-ray mirrors based on additive silicon carbide, which can effectively solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a method for fabricating thin X-ray mirrors based on additive silicon carbide. By using additive manufacturing technology, the mirror substrate and its lightweight structure and aspherical working surface are integrated into near-net-shape form, thereby shortening the process flow and reducing material and processing costs from the source. Furthermore, by utilizing subsequent integrated ultra-precision machining and modification technologies, the bottleneck of the difficulty in achieving both efficiency and precision is overcome, providing a solution for the mass production of high-performance, lightweight X-ray mirrors.

[0007] To achieve the above objectives, the present invention provides a method for fabricating a thin X-ray mirror based on additive silicon carbide, comprising the following steps: Step S1: Using additive manufacturing technology, a thin silicon carbide X-ray mirror substrate blank with a predetermined aspherical working surface and a lightweight back structure is directly formed and then subjected to high-temperature sintering treatment. Based on the lens parameters designed for the Wolter-I type focusing optical system, the required thin X-ray mirror substrate is directly fabricated using additive manufacturing technology, and the back and working surfaces are integrated and rapidly formed, which is the silicon carbide thin X-ray mirror substrate blank. Step S2: Precision grinding of the back side of the thin silicon carbide X-ray mirror substrate blank; The back side of the additively formed silicon carbide substrate is precision ground to eliminate deformation and ensure the reference accuracy for subsequent clamping; the precision ground back side achieves the accuracy of fitting with the tooling and is then mounted on the plate with low stress to proceed to the next stage. Step S3: Low-stress upper plate; The thin silicon carbide X-ray mirror substrate is fixed to the worktable using a low-stress fixture or bonding process to avoid introducing additional stress and ensure that the thin silicon carbide X-ray mirror substrate does not deform during subsequent processing, providing stable support for subsequent precision machining; the back of the thin silicon carbide X-ray mirror substrate is fixed using a negative pressure porous ceramic adsorption device. Step S4: Process the working surface of the thin X-ray mirror substrate of silicon carbide to obtain a thin X-ray mirror; Step S41, Ultra-precision grinding; Ultra-precision grinding includes rough grinding and fine grinding stages, both of which use diamond grinding wheels. Ultra-precision grinding of integrally formed aspherical working surfaces is performed. Since additive manufacturing has brought them close to the final surface shape, the grinding allowance in this process is greatly reduced, which effectively improves the processing efficiency. Step S42, magnetorheological polishing: Using diamond abrasive with a particle size of 5μm and magnetorheological fluid with a concentration of 8~10%, magnetorheological polishing is performed under a magnetic field strength of 0.8T and a relative linear velocity between the workpiece and the polishing wheel of 10~30m / s. Magnetorheological polishing is performed on the working surface after ultra-precision grinding to efficiently remove the subsurface damage layer and further improve the surface accuracy and surface smoothness. Step S43, coating modification; a modification layer is deposited on the working surface of a thin silicon carbide X-ray mirror substrate after magnetorheological polishing using high-power pulsed magnetron sputtering (HiPMS); A modified layer was deposited on the polished silicon carbide working surface using high-power pulsed magnetron sputtering technology. This technology can effectively penetrate and cover the micro-defects left by grinding, and prepare a high-quality substrate for subsequent ultra-smooth polishing. Step S44, Ultra-smooth polishing; Ultra-smooth polishing is performed using a pneumatic flexible pressure small grinding head device, with a silica polishing slurry of 10~20nm particle size, pH value of 9~11, and linear velocity of 0.5~2m / s. The surface roughness of the working surface of the polished thin X-ray mirror substrate is better than 0.3 nm; The working surface after coating is ultra-smoothly polished to obtain an atomically smooth surface that meets the requirements for X-ray reflection; Step S45: Ion beam shaping, using an argon ion source, accelerating voltage of 1000 eV, and beam current density of 200 μA / cm. 2 The working distance is 100mm; the incident angle varies along the surface normal of the thin X-ray mirror surface, and after iterative shaping, the final surface shape and roughness accuracy requirements are met, thus obtaining the thin X-ray mirror.

[0008] Finally, ion beam shaping technology is used to perform non-contact fine finishing on the working surface, accurately correcting its surface shape error and ensuring that the required surface shape accuracy index is achieved.

[0009] Preferably, in step S1, a direct writing molding process is used; wherein, the slurry of the direct writing molding process comprises, by mass percentage, 70% silicon carbide powder with a particle size of 1μm, 0.03% polyacrylic acid, 0.08% methylcellulose, and 29.89% deionized water.

[0010] Preferably, in step S1, the high-temperature sintering treatment employs reactive melting silicon densification technology; wherein the temperature of the high-temperature sintering treatment is 1400~1600℃.

[0011] Preferably, in step S2, the grinding precision is better than 3μm, and the surface roughness of the back side of the thin silicon carbide X-ray mirror substrate after precision grinding is Ra 0.8~1.6μm.

[0012] Preferably, step S3 specifically involves: using a low-stress fixture or bonding process to fix the thin silicon carbide X-ray mirror substrate onto the worktable to ensure that the thin silicon carbide X-ray mirror substrate does not deform during subsequent processing; the low-stress upper plate uses porous ceramic as the upper plate substrate, and the back side of the thin silicon carbide X-ray mirror substrate is fixed by adsorption with porous ceramic.

[0013] Preferably, in step S3, the negative pressure for adsorption and fixation is -0.02 to -0.05 MPa; wherein the bonding gap between the back side of the silicon carbide thin X-ray mirror substrate and the adsorption surface is less than 0.01 mm.

[0014] Preferably, in step S41, the rough grinding uses 2000-mesh abrasive with an average particle diameter of 15µm, the linear speed of the rough grinding is 15~25m / s, and the depth of the rough grinding is 1~5µm; the fine grinding uses 10000-mesh abrasive with an average particle diameter of 5µm, the linear speed of the fine grinding is 25~40m / s, and the depth of the fine grinding is 0.1~1µm. The precision of ultra-precision grinding is better than 1μm. After ultra-precision grinding, the surface roughness of the working surface of the thin X-ray mirror substrate of silicon carbide is Ra 0.1~0.3μm.

[0015] Preferably, in step S42, the magnetorheological fluid includes hydroxyl iron powder, diamond abrasive, deionized water / glycerin mixture, dispersant, and hydrogen peroxide; The surface accuracy of the working surface of the polished thin X-ray mirror substrate is better than 2μm, and the roughness is better than 2nm.

[0016] Preferably, in step S43, the voltage pulse width is 50~80μs, the frequency is 125~200Hz, and the peak voltage is 300V; when the substrate is deposited, the temperature is maintained at <300℃ to avoid high-temperature oxidation or grain coarsening; when the substrate negative bias voltage is -100V, ion migration is accelerated, the film density is increased, and residual stress is reduced. The modified layer is a Si / SiC modified layer with a thickness of 5~8μm.

[0017] Preferably, in step S45, the surface shape error RMS after iterative shaping is less than 50nm.

[0018] The present invention employs the above-mentioned method for fabricating thin X-ray mirrors based on additive silicon carbide, and has the following beneficial effects: (1) This invention innovatively applies slurry-based additive manufacturing technology to the substrate manufacturing of X-ray mirrors, using silicon carbide material to integrally form a thin-walled mirror blank with a lightweight back structure and a preliminary aspherical working surface on the front. This solution replaces the traditional block milling, glass hot bending, or replication methods from the source, directly forming the mounting surface on the back of the thin X-ray mirror and the aspherical working surface, greatly reducing the waste of raw materials and machining in the preceding processes, significantly shortening the production cycle, and reducing manufacturing costs.

[0019] (2) The present invention constructs a highly integrated short process chain of “additive near-net-shape forming → back surface reference processing → low stress clamping → working surface deterministic composite polishing → high performance coating modification → final surface shaping”. Among them, the coating modification is carried out by high power pulsed magnetron sputtering, which can effectively deal with the surface porous defect characteristics of additive silicon carbide materials, fill micro defects, and lay the foundation for obtaining an ultra-smooth mirror usable in the X-ray band.

[0020] (3) The method in this invention directly forms the required thin-walled X-ray mirror blank using additive manufacturing technology based on the lens design parameters of the Wolter-I optical system, realizing the integrated rapid manufacturing of the lightweight structure on the back of the mirror body and the geometry of the working surface. Compared with the prior art, the aspherical working surface directly formed by the process in this invention can significantly reduce the allowance of the previous machining; the subsequent surface coating and modification using high-power pulsed magnetron sputtering technology can effectively fill and cover the micro-defects on the polished silicon carbide surface, obtaining an ultra-smooth surface that meets the requirements of X-ray reflection.

[0021] (4) The method provided by the present invention has comprehensive advantages such as short processing cycle, low manufacturing cost, high surface accuracy and good mirror rigidity. It is suitable for mass production and high-efficiency manufacturing of X-ray mirrors in large scientific devices such as synchrotron radiation devices and X-ray telescopes.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a flowchart illustrating the fabrication process in an embodiment of a method for preparing a thin X-ray mirror based on additive silicon carbide according to the present invention. Figure 2 This is the basic composition of the Wolter-I type thin mirror in an embodiment of the method for fabricating a thin X-ray mirror based on additive silicon carbide according to the present invention. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0026] Example like Figure 1 As shown, a method for fabricating a thin X-ray mirror based on additive silicon carbide includes the following steps: Step S1: Prepare a thin silicon carbide X-ray mirror substrate blank using additive manufacturing technology and perform high-temperature sintering treatment; like Figure 2 As shown, based on the lens parameters designed for the Wolter-I type focusing optical system, a thin silicon carbide X-ray mirror blank with a predetermined aspherical working surface and a lightweight back structure was directly fabricated using additive manufacturing technology through a direct writing forming process, thereby achieving rapid one-piece forming of the mirror body.

[0027] The slurry for the direct-write molding process comprises, by mass percentage, 70% silicon carbide powder with a particle size of 1μm, 0.03% polyacrylic acid, 0.08% methylcellulose, and 29.89% deionized water. The initial blank thickness is ≤2mm, the front side is formed as an aspherical surface as designed, and the back side is formed as a cylindrical surface, with the radius of curvature fitted according to the lens parameters.

[0028] The thin X-ray mirror blank made of silicon carbide was subjected to high-temperature sintering using reactive silicon densification technology; the high-temperature sintering temperature was 1500℃.

[0029] Step S2: Precision grind the back side of the thin silicon carbide X-ray mirror substrate blank to eliminate deformation and ensure the reference accuracy for subsequent clamping; The precision grinding accuracy is less than 3μm, and the surface roughness of the back side of the thin silicon carbide X-ray mirror substrate after precision grinding is Ra 1.2μm.

[0030] Step S3: Low-stress upper plate; The thin silicon carbide X-ray mirror substrate is fixed to the worktable using a low-stress fixture or bonding process to ensure that the thin silicon carbide X-ray mirror substrate does not deform during subsequent processing; the low-stress upper plate uses porous ceramic as the upper plate substrate, and the back of the thin silicon carbide X-ray mirror substrate is fixed by adsorption with porous ceramic.

[0031] The negative pressure for adsorption fixation is -0.03 MPa; wherein, the bonding gap between the back side of the silicon carbide thin X-ray mirror substrate and the adsorption surface is less than 0.01 mm.

[0032] Step S4: Process the working surface of the thin X-ray mirror substrate of silicon carbide to obtain a thin X-ray mirror; Step S41, Ultra-precision grinding; Ultra-precision grinding includes rough grinding and fine grinding stages, both of which use diamond grinding wheels. For rough grinding, 2000-mesh abrasive with an average particle diameter of 15µm is used, the linear speed of rough grinding is 20m / s, and the depth of rough grinding is 3µm; for fine grinding, 10000-mesh abrasive with an average particle diameter of 5µm is used, the linear speed of fine grinding is 30m / s, and the depth of fine grinding is 0.5µm. Ultra-precision grinding is performed on the integrally formed aspherical working surface. Since additive manufacturing has brought it close to the final surface shape, the grinding allowance in this process is greatly reduced. The thickness of the thinned lens is ≤1.0mm, and the accuracy after ultra-precision grinding is better than 1μm; the surface shape error is ≤2μm, and the surface roughness Ra of the working surface of the silicon carbide thin X-ray mirror substrate after ultra-precision grinding is 0.2μm.

[0033] Step S42, magnetorheological polishing: Using diamond abrasive with a particle size of 5μm and magnetorheological fluid with a concentration of 8~10%, magnetorheological polishing is performed under a magnetic field strength of 0.8T and a relative linear velocity between the workpiece and the polishing wheel of 10~30m / s. The magnetorheological fluid includes hydroxyl iron powder, diamond abrasive, deionized water / glycerin mixture, dispersant, and hydrogen peroxide; Magnetorheological polishing is performed on the working surface after ultra-precision grinding to efficiently remove the subsurface damage layer and further improve the surface accuracy and surface smoothness; the surface accuracy of the working surface of the thin X-ray mirror substrate after polishing is better than 2μm and the roughness is better than 2nm.

[0034] Step S43: Coating modification; A modified layer was deposited on the working surface of a thin X-ray mirror substrate of silicon carbide after magnetorheological polishing using high-power pulsed magnetron sputtering. The voltage pulse width is 65μs, the frequency is 170Hz, and the peak voltage is 300V. During substrate deposition, the temperature is maintained below 300℃ to avoid high-temperature oxidation or grain coarsening. When the substrate negative bias voltage is -100V, ion migration is accelerated, the film density is improved, and residual stress is reduced. The modified layer is a Si / SiC modified layer with a thickness of 6μm.

[0035] This technology can effectively penetrate and cover the microscopic defects left by grinding, thus preparing a high-quality substrate for subsequent ultra-smooth polishing.

[0036] Step S44, Ultra-smooth polishing; Ultra-smooth polishing is performed using a pneumatic flexible pressure small grinding head device, with a silica polishing slurry with a particle size of 15nm, a pH value of 10, and a linear velocity of 1m / s. The working surface after coating is ultra-smoothly polished to obtain an atomically smooth surface that meets the requirements for X-ray reflection, with a roughness of ≤0.3nm after polishing; Step S45: Ion beam shaping; using an argon ion source, accelerating voltage of 1000 eV, and beam current density of 200 μA / cm². 2 The working distance is 100mm; the incident angle varies along the surface normal of the thin X-ray mirror surface, and after iterative shaping, the final surface shape and roughness accuracy requirements are met, thus obtaining the thin X-ray mirror.

[0037] Finally, ion beam shaping technology was used to perform non-contact fine finishing on the working surface, accurately correcting its surface shape error and ensuring that the required surface shape accuracy index was achieved. The surface shape accuracy RMS after iterative shaping was less than 50nm, thus obtaining a thin X-ray mirror.

[0038] Therefore, this invention adopts the above-mentioned method for preparing thin X-ray mirrors based on additive silicon carbide. Through additive manufacturing technology, it achieves near-net-shape integration of the mirror substrate and its lightweight structure and aspherical working surface, thereby shortening the process flow and reducing material and processing costs from the source. Furthermore, by utilizing subsequent integrated ultra-precision machining and modification technologies, it overcomes the bottleneck of the difficulty in achieving both efficiency and precision, providing a solution for the mass production of high-performance, lightweight X-ray mirrors.

[0039] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for fabricating a thin X-ray mirror based on additive silicon carbide, characterized in that, Includes the following steps: Step S1: Prepare a thin silicon carbide X-ray mirror substrate blank using additive manufacturing technology and perform high-temperature sintering treatment; Based on the lens parameters designed for the Wolter-I type focusing optical system, the required thin X-ray mirror substrate is directly fabricated using additive manufacturing technology, and the back and working surfaces are integrated and rapidly formed, which is the silicon carbide thin X-ray mirror substrate blank. Step S2: Precision grinding of the back side of the thin silicon carbide X-ray mirror substrate blank; Step S3: Low-stress upper plate; The thin silicon carbide X-ray mirror substrate is fixed on the worktable using a low-stress fixture or bonding process to ensure that the thin silicon carbide X-ray mirror substrate does not deform during subsequent processing. The low-stress upper plate uses porous ceramic as the upper plate substrate, and the back of the thin silicon carbide X-ray mirror substrate is fixed by adsorption with porous ceramic. The negative pressure for adsorption fixation is -0.02 to -0.05 MPa; wherein, the bonding gap between the back side of the silicon carbide thin X-ray mirror substrate and the adsorption surface is less than 0.01 mm; Step S4: Process the working surface of the thin X-ray mirror substrate of silicon carbide to obtain a thin X-ray mirror; Step S41, Ultra-precision grinding; Ultra-precision grinding includes rough grinding and fine grinding stages, both of which use diamond grinding wheels. For rough grinding, 2000-mesh abrasive with an average particle diameter of 15µm is used, the linear speed of rough grinding is 15~25m / s, and the depth of rough grinding is 1~5µm; for fine grinding, 10000-mesh abrasive with an average particle diameter of 5µm is used, the linear speed of fine grinding is 25~40m / s, and the depth of fine grinding is 0.1~1µm. The precision of ultra-precision grinding is better than 1μm. After ultra-precision grinding, the surface roughness of the working surface of the thin silicon carbide X-ray mirror substrate is Ra 0.1~0.3μm. Step S42, magnetorheological polishing: Using diamond abrasive with a particle size of 5μm and magnetorheological fluid with a concentration of 8~10%, magnetorheological polishing is performed under a magnetic field strength of 0.8T and a relative linear velocity between the workpiece and the polishing wheel of 10~30m / s. The magnetorheological fluid includes hydroxyl iron powder, diamond abrasive, deionized water / glycerin mixture, dispersant, and hydrogen peroxide; The surface accuracy of the working surface of the polished thin X-ray mirror substrate is better than 2μm, and the roughness is better than 2nm. Step S43, coating modification: A modification layer is deposited on the working surface of a thin silicon carbide X-ray mirror substrate after magnetorheological polishing using high-power pulsed magnetron sputtering; The voltage pulse width is 50~80μs, the frequency is 125~200Hz, and the peak voltage is 300V. During substrate deposition, the temperature is maintained below 300℃ to avoid high-temperature oxidation or grain coarsening. When the substrate negative bias voltage is -100V, ion migration is accelerated, the film density is improved, and residual stress is reduced. The modified layer is a Si / SiC modified layer with a thickness of 5~8μm. Step S44, Ultra-smooth polishing; Ultra-smooth polishing is performed using a pneumatic flexible pressure small grinding head device, with a silica polishing slurry of 10~20nm particle size, pH value of 9~11, and linear velocity of 0.5~2m / s. The surface roughness of the working surface of the polished thin X-ray mirror substrate is better than 0.3 nm; Step S45: Ion beam shaping; using an argon ion source, accelerating voltage of 1000 eV, and beam current density of 200 μA / cm². 2 The working distance is 100mm; the incident angle varies along the surface normal of the thin X-ray mirror surface, and after iterative shaping, the final surface shape and roughness accuracy requirements are met, thus obtaining the thin X-ray mirror. The RMS surface shape error after iterative reshaping is less than 50 nm; In step S2, the precision grinding accuracy is better than 3μm, and the surface roughness of the back side of the thin silicon carbide X-ray mirror substrate after precision grinding is Ra 0.8~1.6μm; The thin X-ray mirror is a Wolter-I type thin X-ray mirror.

2. The method for fabricating a thin X-ray mirror based on additive silicon carbide according to claim 1, characterized in that: In step S1, a direct writing molding process is used; wherein, the slurry of the direct writing molding process includes, by mass percentage, 70% silicon carbide powder with a particle size of 1μm, 0.03% polyacrylic acid, 0.08% methylcellulose, and 29.89% deionized water.

3. The method for fabricating a thin X-ray mirror based on additive silicon carbide according to claim 1, characterized in that: In step S1, the high-temperature sintering treatment employs reactive melting silicon densification technology; wherein, the high-temperature sintering temperature is 1500℃.

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