Method for welding sapphire and niobium metal based on ultrafast laser

Abstract

The invention discloses a method for welding sapphire and niobium metal based on ultrafast laser. The method comprises the following steps: cleaning the surfaces of a sapphire sheet and a niobium metal sheet; the niobium metal sheet and the sapphire sheet which are sequentially stacked are clamped through a clamp; the clamp is installed on a three-dimensional moving platform of a laser system; a laser system is started, and water cooling is conducted before welding to keep the temperature; adjusting the focal point of laser emitted by the laser system to serve as a reference focal plane on the upper surface of the niobium metal sheet, and moving the focal point to the interface of the niobium metal sheet and the sapphire sheet through upward moving adjustment of the three-dimensional moving platform to form negative defocus; parameters of laser emitted by the laser system are adjusted; through plane movement of the three-dimensional mobile platform, the focal point of the laser forms a reciprocating scanning path at the interface of the niobium metal sheet and the sapphire sheet, and the scanning path is shaped like a Chinese character'gong '; sapphire and niobium metal welding is free of cracks, pores and deformation, and the effects that the surface of a welding interface is flat, stripes are clear and brightness is uniform are achieved.

Description

Technical Field

[0001] This invention relates to the field of laser welding technology, and in particular to a method for welding sapphire and niobium metal based on ultrafast laser. Background Technology

[0002] Sapphire (α-alumina single crystal) and niobium are both key strategic materials in modern high-tech industries, and are used in many cutting-edge fields due to their excellent physical and chemical properties.

[0003] Sapphire is an oxide crystal with exceptionally high properties. Its Mohs hardness is as high as 9, second only to diamond, giving it excellent wear resistance and scratch resistance. Optically, sapphire has a wide transmission band from deep ultraviolet to mid-infrared (approximately 0.15-5.5 micrometers), with high light transmittance, making it an ideal material for high-performance optical windows, lenses, and infrared radomes. Simultaneously, it possesses good chemical inertness, excellent insulation properties, high thermal conductivity, and a melting point as high as approximately 2050℃, maintaining structural stability and functional reliability even in extreme high-temperature, high-pressure, and corrosive environments. Therefore, sapphire is widely used in LED substrates, optical sensor windows, high-strength screens, laser cavities, and wear-resistant components in precision machinery.

[0004] Niobium is an important refractory metal and functional material. It has a high melting point (approximately 2468℃), good low-temperature ductility, and processability. One of niobium's most prominent properties is its excellent superconducting performance, making it a core material for fabricating high-performance low-temperature superconducting cavities (such as those used in particle accelerators) and superconducting magnets. It also exhibits excellent corrosion resistance, showing good resistance to various acids and liquid metals.

[0005] The welding of sapphire and niobium can directly fuse the optical window (sapphire) with the superconducting cavity (niobium) into one, forming an all-solid-state, organic-free, ultra-high vacuum sealed structure, greatly improving the reliability and ultimate performance of the equipment. In traditional methods, welding sapphire and niobium is prone to problems such as excessive heat-affected zone, welding deformation, and cracks. Active metal brazing requires high-temperature heating and holding, and after cooling, there is significant thermal stress and structural deformation, affecting the joint and optical performance. Thermal diffusion welding requires high temperature and high pressure for several hours, resulting in low production efficiency, high requirements for the flatness and cleanliness of the joint surface, high energy consumption, complex process, and long processing time, making it difficult to meet the needs of modern precision manufacturing. Traditional laser welding creates a wide heat-affected zone due to concentrated heat input at the interface, inducing thermal stress gradients, leading to internal cracks in the material and damaging the mechanical properties of the joint.

[0006] Therefore, the welding method needs to be optimized to avoid the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a method for welding sapphire and niobium metal using ultrafast lasers, which solves the problems of excessive heat-affected zone, welding deformation, and cracks that easily occur when welding sapphire and niobium metal using existing technologies.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] A method for ultrafast laser welding of sapphire and niobium metal is disclosed. The surfaces of the sapphire and niobium metal sheets are cleaned and wiped with a lint-free cloth. The niobium and sapphire sheets, stacked sequentially, are clamped using a fixture. The fixture is mounted on a three-dimensional moving platform of the laser system. The laser system is started and water-cooled to maintain the temperature before welding. The focal point of the laser emitted by the system is adjusted to the upper surface of the niobium metal sheet as a reference focal plane. The three-dimensional moving platform is then moved upwards to adjust the focal point to the interface between the niobium and sapphire sheets, forming a negative defocus. The laser parameters are adjusted, including a wavelength of 1030 nm, a pulse width of 500 fs, a repetition frequency of 0.5 MHz, a single pulse count of 1, and an average power of 2 W. The three-dimensional moving platform is moved planar to create a reciprocating scanning path at the interface between the niobium and sapphire sheets, forming a "bow" shape.

[0010] Preferably, the laser system integrates a half-wave plate, a polarizer, a shutter, a reflector, and a focusing objective. The laser emitted by the laser system passes through the half-wave plate, the polarizer, and the shutter in sequence, and is reflected by the reflector before entering the focusing objective. The focusing objective focuses the laser to form a spot with a diameter of 5 μm at the focal point.

[0011] Preferably, the focusing objective is a 10x microscope objective.

[0012] Preferably, the planar movement speed of the three-dimensional moving platform is 3 mm / s.

[0013] Preferably, the spacing between two adjacent scan lines on the scan path is 50 μm, and the length of a single scan line facing the direction of movement is 4 mm.

[0014] Preferably, the distance between the focal point of the negative defocus and the upper surface of the niobium metal sheet is 40 μm.

[0015] Preferably, after the niobium metal sheet and sapphire sheet are welded together, a shear test is performed on the finished product. The finished product is pulled at a speed of 0.5 mm / s using a shearing machine, and the force F at which the finished product breaks is obtained. The shear strength is then calculated based on the force F and the weld area S. .

[0016] Preferably, the water-cooled start-up time of the laser system is at least 15 minutes earlier than the welding start time.

[0017] Preferably, the fixture includes a base block and a pressure block. The base block has a positioning groove, and the pressure block has a protrusion that mates with the positioning groove. The pressure block has a square hole that communicates with the positioning groove. The size of the square hole is larger than the welding area of ​​the niobium metal sheet and the sapphire sheet. The base block and the pressure block have multiple fastening holes located on both sides of the positioning groove and spaced apart. Fasteners mate with the fastening holes to lock the pressure block and the base block.

[0018] Preferably, both the base block and the pressing block are made of aluminum.

[0019] Beneficial effects:

[0020] The laser system emits an ultrafast laser with parameters of 1030nm wavelength, 500fs pulse width, 0.5MHz repetition frequency, 1 pulse per burst, and 2W average power. Combined with a three-dimensional moving platform, the laser is focused on the interface between the niobium metal sheet and the sapphire sheet. During the planar movement of the three-dimensional moving platform, the interface is scanned and welded to form an "arch"-shaped welding path. This ensures that there is a sufficient effective fusion area at the interface. The laser parameters ensure a stable local melting and solidification state at the interface during welding, avoiding cracks, pores, and deformation.

[0021] Cleaning the welding area in a dust-free environment before welding and maintaining stable clamping during welding are also conducive to stable welding. Maintaining the internal temperature of the laser system during welding avoids the risk factor of unstable changes in laser parameters caused by temperature changes.

[0022] Therefore, the welding method proposed in this invention achieves crack-free, porosity-free, and deformation-free welding of sapphire and niobium metals, with a smooth welding interface surface, clear stripes, and uniform brightness. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of the process for welding sapphire and niobium metal using ultrafast lasers according to the present invention.

[0024] Figure 2 This is a partial schematic diagram of the scan path;

[0025] Figure 3 This is a schematic diagram of the fixture of the present invention;

[0026] Figure 4 This is a schematic diagram of the structure of the pressure block of the present invention;

[0027] Figure 5 This is a schematic diagram of the structure of the base block of the present invention;

[0028] Figure 6 This is a diagram showing the interface effect after welding using the method of the present invention;

[0029] exist Figures 1 to 6 In the diagram, the correspondence between component names or lines and the drawing numbers is as follows:

[0030] Fixture 100, base block 101, pressure block 102, positioning groove 103, protrusion 104, square hole 105, fastening hole 106. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0032] See Figure 1 As shown, an embodiment of the present invention proposes a method for welding sapphire and niobium metal using an ultrafast laser. The welding is performed using a laser system, the specific configuration of which is a mature technology. The key point is to propose a novel method adapted for laser-based welding of sapphire and niobium metal. Specifically, it includes the following steps:

[0033] S01. Clean the surfaces of the sapphire and niobium metal sheets and wipe them with a lint-free cloth.

[0034] Before welding, the surfaces must be cleaned in a dust-free environment, ensuring the welding interface is free of dust. This improves laser energy coupling efficiency and prevents localized welding defects or insufficient adhesion caused by contamination at the interface. Specifically, cleaning involves spraying anhydrous ethanol onto the surfaces of the sapphire and niobium metal sheets and wiping them with a lint-free cloth.

[0035] In this embodiment, the sapphire sheet is 10mm×10mm×1mm in size, and the niobium metal sheet is 20mm×10mm×1mm in size. Of course, in actual product welding, the size is not limited to this size, and the size can be selected according to the corresponding structure.

[0036] S02. The niobium metal sheet and sapphire sheet, which are stacked in sequence, are clamped by the clamp 100.

[0037] After cleaning, the sapphire sheet is stacked on the niobium metal sheet and clamped with a fixture, allowing the laser to pass through the sapphire sheet and be focused at the interface.

[0038] Among them, such as Figures 3-5As shown, the fixture 100 includes a base block 101 and a pressure block 102. A positioning groove 103 is provided on the base block 101, and sapphire sheets and niobium metal sheets are stacked in the positioning groove 103. A protrusion 104 that cooperates with the positioning groove 103 is provided on the pressure block 102. The pressure block 102 and the base block 101 cooperate to position and press the fixture together. A square hole 105 communicating with the positioning groove 103 is provided on the pressure block 102. The size of the square hole 105 is larger than the welding area size of the niobium metal sheet and the sapphire sheet, so that the laser can enter through the square hole 105 to realize the welding operation. Multiple fastening holes 106 are provided on the base block 101 and the pressure block 102, located on both sides of the positioning groove 103 and spaced apart. Fasteners cooperate with the fastening holes 106 to lock the pressure block 102 and the base block 101, ensuring that the sapphire sheet and niobium metal sheet will not move relative to each other when the fixture 100 moves during the welding process, thus avoiding affecting the welding effect. At the same time, the base block 101 and the pressure block 102 are both made of aluminum, which is lightweight and easy to clamp and use. S03, Install the fixture onto the three-dimensional moving platform of the laser system.

[0039] The three-dimensional moving platform is integrated into the laser system, enabling movement adjustment in the X, Y, and Z directions. After the fixture 100 is mounted on the three-dimensional moving platform, the fixture 100 can be moved and adjusted in three directions via the three-dimensional moving platform. The motion program of the three-dimensional moving platform can be written in the ACS control software, all of which are integrated into the laser system, facilitating automatic operation of the three-dimensional moving platform according to preset conditions.

[0040] S04. Start the laser system and maintain the temperature with water cooling before welding;

[0041] The laser system can be started simultaneously with the cleaning of the sapphire and niobium metal sheets to preheat the laser in the laser system and to cool it down with water before the actual welding to keep the laser at a constant temperature. This ensures the stability and consistency of pulse energy during the subsequent welding process and avoids the drift of laser output power caused by temperature fluctuations.

[0042] Generally, the water-cooling start-up time of the laser system should be at least 15 minutes before the welding start time to ensure a more stable constant temperature.

[0043] S05. Adjust the focal point of the laser emitted by the laser system to the upper surface of the niobium metal sheet as the reference focal plane. Adjust the focal point by moving the three-dimensional moving platform upwards to move it to the interface between the niobium metal sheet and the sapphire sheet, thus forming negative defocus.

[0044] Negative defocusing concentrates the laser's active area near the interface between the sapphire and niobium sheets, which helps increase the weld depth and improve the weld strength. Experiments were conducted using three focal points: -40μm, -20μm, and 0μm. It was found that welding at the -40μm focal point resulted in the shallowest weld marks, the best optical transmittance, and no cracks. The welded results are shown in [link to image]. Figure 6 As shown. Therefore, the distance between the negative defocus point and the upper surface of the niobium metal sheet is 40μm. Specifically, during adjustment, after the focus is aligned with the upper surface of the niobium metal sheet, the three-dimensional moving platform is moved up 40μm to complete the focus adjustment.

[0045] Through controlled variable experiments, -40μm was determined to be the optimal defocus amount. Under this parameter, the optical transmittance of the weld joint was optimal, and no cracks were generated. The experiment fixed core welding process parameters such as laser power, scanning speed, and pulse frequency. Three sets of parallel samples were prepared for each defocus gradient to ensure experimental repeatability. The optical transmittance of the weld area was measured using a spectrophotometer, and the weld morphology was observed using an optical microscope and a scanning electron microscope to determine defects such as cracks. Simultaneously, the focus was required to be precisely located at the interface between the niobium metal sheet and the sapphire sheet, with a negative defocus of 40μm set. This scheme uses a CCD vision positioning system to identify the interface position of the two dissimilar materials, niobium metal sheet and sapphire sheet, ensuring interface recognition accuracy. Based on the CCD vision calibration results, the overlap between the focus and the interface was calibrated. Furthermore, to address the possibility of focus shift caused by material thickness tolerances and clamping tilt, real-time alignment compensation using CCD vision was used to avoid the impact of focus shift on the welding effect. The specific focusing method is built into the existing laser system and can be directly applied.

[0046] Specifically, the laser system integrates a half-wave plate, a polarizer, a shutter, a reflector, and a focusing objective. The laser emitted by the system passes through the half-wave plate, the polarizer, and the shutter in sequence, and is reflected by the reflector before entering the focusing objective. This achieves optical path processing during the laser's emission from the inside to the outside. The focusing objective focuses the laser to form a spot diameter of 5μm at the focal point. The focusing objective is a 10x microscope objective, ensuring that the laser spot diameter at the focal point covers the interface and guarantees the stability of the weld.

[0047] S06. Adjust the laser parameters emitted by the laser system. The laser parameters include a wavelength of 1030nm, a pulse width of 500fs, a repetition frequency of 0.5MHz, a single pulse number of 1, and an average power of 2W.

[0048] The laser parameters were finally determined through a series of combined experiments. They are the optimal parameters for laser welding of sapphire and niobium metal sheets. The welding conditions under average power of 2W, 3W, and 4W were verified. Only when the average power is 2W can the weld interface surface be guaranteed to be smooth, with clear stripes and uniform brightness. No obvious cracks or pores were observed, indicating that the laser energy density is moderate and can achieve stable local melting and solidification at the interface. After shear strength testing, the maximum strength can be achieved. Therefore, the average power was determined to be 2W.

[0049] Once the laser parameters are determined during the welding of sapphire and niobium metal sheets, they are not changed.

[0050] S07. The three-dimensional moving platform moves in a plane to make the laser focus form a reciprocating scanning path at the interface between the niobium metal sheet and the sapphire sheet. The scanning path is in the shape of an "arch".

[0051] Scan path diagram as follows Figure 2 As shown, after adjusting the laser focus position and determining the laser parameters, the three-dimensional moving platform moves the fixture to achieve laser welding at the interface between the sapphire sheet and the niobium metal sheet. The planar movement speed of the three-dimensional moving platform is 3mm / s, which can ensure the continuity of the welding process.

[0052] Specifically, the spacing between two adjacent scan lines (two parallel scan lines) on the scanning path is 50 μm, and the length of a single scan line (a spaced-apart scan line) facing the direction of movement is 4 mm, thereby achieving an effective welding area and ensuring that the interface has sufficient bonding area.

[0053] In this embodiment, a "bow"-shaped scanning path is adopted. Compared with spiral and parallel line scanning, this path can achieve uniform heat input and gradient heat conduction in the welding area, avoiding material thermal damage caused by local heat accumulation. In terms of stress control, the continuous and non-sharp-angled scanning trajectory of the bow shape can effectively disperse the thermal stress generated during the welding process, reducing defects such as microcracks and warping caused by stress concentration. Compared with the unidirectional heat accumulation of parallel lines and the central heat accumulation problem of spirals, it is more suitable for the welding characteristics of dissimilar materials such as niobium metal sheet and sapphire sheet.

[0054] After welding is completed, shear strength testing can be performed. Generally, only the sample needs to be tested to obtain the shear strength limit value at the weld joint of the sapphire sheet and niobium sheet welded by the above welding method, so as to understand the application scenarios of the product.

[0055] Specifically, after the niobium metal sheet and sapphire sheet are welded together, a shear test is performed on the finished product. The finished product is pulled at a speed of 0.5 mm / s using a shearing machine, and the force F at which the finished product breaks is obtained. The shear strength is then calculated based on the force F and the weld area S. .

[0056] in, The force F is obtained by measuring it when the shearing machine breaks the weld, while the welding area S is the area of ​​the fusion zone, which can be calculated based on the specific fusion zone formed during the welding process.

[0057] All weld area S used in the shear strength calculations is based on the nominal design area of ​​the laser scanning path. For the “1×1 mm² bow-shaped” scanning path strategy, the theoretical coverage area is 1 mm², confirming that the scanning trajectory is continuous and completely covers the target area.

[0058] Therefore, after determining the scanning path and the scanning line spacing, the corresponding welding area S is basically determined, and the corresponding shear strength can be obtained by measuring the applied force F using a shearing machine.

[0059] Shear strength can be measured to test samples welded by different welding methods, so as to obtain the laser parameters, negative defocus parameters, etc. that need to be selected. Finally, the above-mentioned welding method is determined, which can stably, well and with high quality weld sapphire sheets and niobium metal sheets.

[0060] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0061] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship commonly used when the product of this invention is in use. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. In addition, the terms "first," "second," etc., are only used to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0062] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for welding sapphire and niobium metal using ultrafast lasers, characterized in that: Clean the surfaces of the sapphire and niobium metal sheets and wipe them with a lint-free cloth; The niobium metal sheets and sapphire sheets, which are stacked in sequence, are clamped together using a clamp. Install the fixture onto the three-dimensional moving platform of the laser system; Start the laser system and maintain the temperature with water cooling before welding; The focal point of the laser emitted by the laser system is adjusted to be at the upper surface of the niobium metal sheet as the reference focal plane. The focal point is moved to the interface between the niobium metal sheet and the sapphire sheet by moving the three-dimensional moving platform upwards and adjusting it to form negative defocus. Adjust the laser parameters emitted by the laser system, including wavelength of 1030nm, pulse width of 500fs, repetition frequency of 0.5MHz, number of pulses per burst of 1, and average power of 2W. The laser is focused at the interface between the niobium metal sheet and the sapphire sheet by moving the three-dimensional moving platform in a plane, forming a back-and-forth scanning path in the shape of an "arch".

2. The method for welding sapphire and niobium metal based on ultrafast laser according to claim 1, characterized in that: The laser system integrates a half-wave plate, a polarizer, a shutter, a mirror, and a focusing objective. The laser emitted by the laser system passes through the half-wave plate, the polarizer, and the shutter in sequence, and is reflected by the mirror before entering the focusing objective. The focusing objective focuses the laser to form a spot with a diameter of 5 μm at the focal point.

3. The method for welding sapphire and niobium metal based on ultrafast laser according to claim 2, characterized in that: The focusing objective is a 10x microscope objective.

4. The method for welding sapphire and niobium metal based on ultrafast laser according to claim 1, characterized in that: The planar movement speed of the three-dimensional moving platform is 3 mm / s.

5. The method for welding sapphire and niobium metal based on ultrafast laser according to claim 4, characterized in that: The distance between two adjacent scan lines on the scan path is 50 μm, and the length of a single scan line facing the direction of movement is 4 mm.

6. The method for welding sapphire and niobium metal based on ultrafast laser according to claim 5, characterized in that: The distance between the focal point of the negative defocus and the upper surface of the niobium sheet is 40 μm.

7. The method for welding sapphire and niobium metal based on ultrafast laser according to claim 5, characterized in that: After the niobium metal sheet and sapphire sheet are welded together, a shear test is performed on the finished product. The finished product is pulled at a speed of 0.5 mm / s using a shearing machine to obtain the force F at which the finished product breaks. The shear strength is then calculated based on the force F and the weld area S. .

8. The method for welding sapphire and niobium metal based on ultrafast laser according to claim 1, characterized in that: The water-cooled start-up time of the laser system should be at least 15 minutes before the welding start time.

9. A method for welding sapphire and niobium metal based on ultrafast laser according to any one of claims 1-8, characterized in that: The fixture includes a base block and a pressure block. The base block is provided with a positioning groove, and the pressure block is provided with a protrusion that mates with the positioning groove. The pressure block is provided with a square hole that communicates with the positioning groove. The size of the square hole is larger than the size of the welding area between the niobium metal sheet and the sapphire sheet. The base block and the pressure block are provided with a plurality of fastening holes located on both sides of the positioning groove and spaced apart. The fasteners cooperate with the fastening holes to lock the pressure block and the base block.

10. A method for welding sapphire and niobium metal based on ultrafast laser according to claim 9, characterized in that: Both the base block and the pressing block are made of aluminum.

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