Ceramic joint femtosecond laser texturing method for stainless steel-ceramic brazing

Abstract

The invention discloses a ceramic joint femtosecond laser texturing method for stainless steel-ceramic brazing. The ceramic joint femtosecond laser texturing method comprises the following steps that firstly, ceramic for texturing machining is silicon carbide ceramic with the smooth and clean surface; 2, a femtosecond laser galvanometer machining system is built, the sample is placed on a moving platform, and the sample is moved so that the machining surface can be located at the femtosecond laser focal plane; 3, under the control of a computer system, the femtosecond laser galvanometer processing system carries out low-power scanning on the surface of the ceramic sample so as to carry out preliminary polishing on the sample; then, a plurality of parallel and continuously distributed grooves are machined in the surface of the ceramic sample at high power, so that texturing machining is completed; according to the method, femtosecond laser is adopted for pretreating the brazed ceramic joint, the specific surface area of the ceramic joint is increased through laser leveling and laser groove machining on the premise that the plane quality is not damaged, the contact area of brazing filler metal and the ceramic joint in the brazing process is increased, and the performance of the stainless steel-ceramic dissimilar material brazed joint is improved.

Description

Technical Field

[0001] The invention relates to the field of brazing of dissimilar materials, and in particular to a femtosecond laser texturing method for ceramic joints used for stainless steel-ceramic brazing. Background Art

[0002] Joining dissimilar materials has long been a research focus in the field of materials processing. Specifically, when it comes to joining metals to ceramics, ceramics are often bonded covalently or ionicly, resulting in high chemical stability and low chemical compatibility with metals. Therefore, brazing is a mainstream joining method, currently the most researched and commonly used. Due to the significant differences in the physical and chemical properties of ceramics and metals, achieving reliable joining between ceramics and metals is challenging, with the poor wettability of ceramics being a major obstacle. The ability of the brazing filler metal to wet the ceramic surface is crucial for achieving a successful brazing connection. Currently, a significant amount of research and preparation has been conducted on brazing fillers with high spreadability and high wettability. However, the degree of texturization on the ceramic surface also affects the spreading area of ​​the filler metal and, ultimately, the performance of the brazed joint. After texturization, uniformly distributed pits form on the surface of the brazed ceramic joint. Assuming the filler metal has sufficient ductility, texturization can increase the surface area to increase the contact area between the ceramic surface and the filler metal, thereby improving brazing quality and joint performance. Currently, commonly used texturing methods include electrospark texturing, chemical mechanical polishing, and ultrasonic-assisted texturing. While these methods can achieve texturing, the increase in specific surface area generally does not exceed 10%. With the development of high-flow and high-wettability solders, these texturing methods are unlikely to further increase the specific surface area and maximize the excellent performance of the solder. Deep grooves can be created through conventional mechanical polishing to further increase the contact area between the ceramic joint and the solder. However, due to the high brittleness and hardness of ceramic materials, brittle fracture is very likely to occur during mechanical processing, and defects such as cracks, pits, and subsurface damage are also prone to appear on the material surface, making it difficult to guarantee processing quality.

[0003] Lasers offer advantages such as monochromaticity, good coherence, and high power density. They are also easy to guide and integrate with CNC systems, making them ideal for precision micromachining. Compared to conventional long-pulse lasers, ultrashort-pulse femtosecond lasers offer the unique advantage of low thermal effects. Consequently, they avoid thermally induced cracks and other defects on the ceramic surface during the etching process, offering unique advantages in ceramic precision machining. Summary of the Invention

[0004] Based on the fact that the texturing process of ceramic joints during stainless steel-ceramic brazing is difficult to maximize the high wettability and high ductility of existing brazing fillers, the present invention adopts a femtosecond laser to perform pre-treatment of the brazed ceramic joints before welding. Without destroying the plane quality, the specific surface area of ​​the ceramic joints is increased through laser flattening and laser grooving, thereby increasing the contact area between the brazing filler metal and the ceramic joint during the brazing process, and improving the performance of the stainless steel-ceramic dissimilar material brazing joints.

[0005] A femtosecond laser texturing method for ceramic joints for stainless steel-ceramic brazing, characterized by comprising the following steps: Step 1: The ceramic used for texturing is silicon carbide ceramic with a relatively smooth and clean surface; Step 2: Build a femtosecond laser galvanometer processing system, place the sample on a moving platform, and move the sample so that the processing surface is located at the focal plane of the femtosecond laser; Step 3: Under the control of a computer system, the femtosecond laser galvanometer processing system first scans the surface of the ceramic sample at low power to perform a preliminary polishing of the sample. It then uses high power to process multiple parallel and continuously distributed grooves on the surface of the ceramic sample to complete the roughening process. Furthermore, in step 1, the silicon carbide ceramic used for texturing is made by pressureless sintering, has an apparent porosity of less than 0.2%, a room temperature thermal expansion coefficient of less than 4.3×10-6 / °C, a compressive strength of more than 2200 MPa, and a hardness of 110-120 HS; Furthermore, in step 1, the surface of the silicon carbide ceramic is polished with metallographic sandpaper of not less than 1200# before the roughening treatment, and then ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively, and blown dry to obtain a relatively smooth and clean silicon carbide ceramic; Furthermore, in step 2, the constructed femtosecond laser galvanometer processing system includes a femtosecond laser, a first reflector, a λ / 2 wave plate, a beam expander, an adjustable aperture, a second reflector, a scanning galvanometer, a mobile platform, and a computer control system, wherein the computer control system is connected to the femtosecond laser, the scanning galvanometer, and the mobile platform; Furthermore, in step 2, the femtosecond laser outputs a Gaussian beam with a laser wavelength of 1030 nm, a pulse width of 240 fs, an adjustable repetition frequency of 50-300 kHz, and an adjustable output power of 1-10 W; Furthermore, in step 2, the femtosecond laser scanning speed can be adjusted by the galvanometer, and the speed is adjustable from 100 to 2000 mm / s; Furthermore, in step 3, when the surface of the ceramic sample is preliminarily polished using a femtosecond laser, the polishing parameters are: laser power 2-4 W, repetition frequency 150-200 kHz, spot diameter 40-60 μm, scanning speed 800-1000 mm / s, scanning spacing 30-50 μm, and Z-shaped scanning mode; Furthermore, in step 3, when grooves are processed on the surface of the ceramic sample using a femtosecond laser, the processing parameters are: laser power 8-10 W, repetition frequency 150-200 kHz, spot diameter 20-40 μm, scanning speed 200-400 mm / s, scanning spacing 100-130 μm, and unidirectional scanning mode; Furthermore, in step 3, the groove depth is processed to 30-50 μm, and the repetition spacing is 100-130 μm. Under the premise of ensuring the wettability of the solder, the contact area between the ceramic side and the solder can be increased by 30-40%, which is beneficial to improving the performance of the brazed joint.

[0006] The present invention has significant advantages over the prior art: The surface of the ceramic joint of stainless steel-ceramic brazing is roughened by femtosecond laser. The unique advantages of high energy density and low heat affected range when processing ceramics by femtosecond laser are utilized to achieve low stress and high-quality groove structure processing on the ceramic surface. The processed surface quality is high and the specific surface area of ​​the ceramic joint is increased by 30%-40%. Obviously, the existing methods such as electric spark texturing and mechanical grinding and polishing are conducive to giving full play to the advantages of high wettability and high ductility brazing filler metals, thereby improving the mechanical properties of stainless steel-ceramic brazing joints. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 Schematic diagram of the femtosecond laser galvanometer processing system constructed by the present invention; Figure 2 Schematic diagram of the scanning path during femtosecond laser preliminary polishing of the present invention; Figure 3 Schematic diagram of the scanning path when femtosecond laser groove machining is used to achieve roughening in the present invention.

[0008] In the figure: 1. Femtosecond laser; 2. First reflector; 3. λ / 2 wave plate; 4. Beam expander; 5. Adjustable aperture; 6. Second reflector; 7. Scanning galvanometer; 8. Moving platform; 9. Computer control system; 10. Laser beam; 11. Ceramic sample to be processed. DETAILED DESCRIPTION

[0009] The preferred embodiments of the present invention are described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more precise definition of the protection scope of the present invention.

[0010] Example 1 (1) A 50 mm × 50 mm silicon carbide ceramic sample was obtained by wire cutting. The silicon carbide ceramic sample was made by pressureless sintering, with an apparent porosity of less than 0.2%, a room temperature thermal expansion coefficient of less than 4.3 × 10-6 / ℃, a compressive strength of more than 2200 MPa, and a hardness of 110-120 HS. The silicon carbide ceramic sample was ground with 100#, 200#, 400#, 600#, 800#, 1000#, and 1200# metallographic sandpapers in sequence until only the grinding scratches of 1200# sandpaper in the same direction could be observed under an inverted metallographic microscope. The sample was then ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water, respectively, and dried to obtain a relatively smooth and clean silicon carbide ceramic.

[0011] (2) Build a femtosecond laser galvanometer processing system. The schematic diagram of the system is as follows: Figure 1 As shown, it includes a femtosecond laser 1, a first reflector 2, a λ / 2 wave plate 3, a beam expander 4, an adjustable aperture 5, a second reflector 6, a scanning galvanometer 7, a moving platform 8, and a computer control system 9; wherein, the femtosecond laser outputs a Gaussian beam with a laser wavelength of 1030nm, a pulse width of 240fs, an adjustable repetition frequency of 50-300kHz, and an adjustable output power of 1-10W; the λ / 2 wave plate 3 is mainly used to convert the light beam from linearly polarized light to circularly polarized light, thereby ensuring that the material removal rate is consistent when the focused laser scans across the material surface; the beam expander 4 can expand the laser beam diameter by 3 times, It is beneficial to obtain a laser beam with a smaller spot diameter after focusing; the adjustable aperture 5 is mainly used to adjust the size of the femtosecond laser spot and remove the low-energy area at the edge of the Gaussian beam, reducing the influence of stray light on material processing; the scanning galvanometer is mainly used to control the laser beam to process the specified area, and the scanning speed is adjustable from 100 to 2000 mm / s; the mobile platform can move in the Z direction so that the ceramic surface to be processed is located on the laser focal plane; the computer control system is connected to the femtosecond laser, the scanning galvanometer, and the mobile platform, and can respectively realize the adjustment and control of the laser power, scanning direction and speed, and the Z position of the sample to be processed.

[0012] (3) Place the silicon carbide ceramic sample on a moving platform and control the computer system to move the sample so that the processed surface is located at the focal plane of the femtosecond laser.

[0013] (4) The laser power was set to 2W, the repetition frequency was set to 200kHz, the spot diameter was set to 40μm, the scanning speed was set to 800mm / s, and the scanning interval was set to 30μm. The surface of the ceramic sample was preliminarily polished using a Z-shaped scanning method. The scanning path was as follows: Figure 2 shown.

[0014] (5) The laser power was set to 8W, the repetition frequency was set to 200kHz, the spot diameter was set to 20μm, the scanning speed was set to 200 / s, and the scanning interval was set to 100μm. The surface of the ceramic sample was grooved to achieve roughening using a unidirectional scanning method. The scanning path was as follows: Figure 3 shown.

[0015] (6) The average depth of the obtained grooves is 30 μm and the average spacing is 100 μm. Under the premise of ensuring the wettability of the solder, the contact area between the ceramic side and the solder can be increased by about 32%, which is beneficial to the improvement of the performance of the brazed joint.

[0016] Example 2 (1) A 50 mm × 50 mm silicon carbide ceramic sample was obtained by wire cutting. The silicon carbide ceramic sample was made by pressureless sintering, with an apparent porosity of less than 0.2%, a room temperature thermal expansion coefficient of less than 4.3 × 10-6 / ℃, a compressive strength of more than 2200 MPa, and a hardness of 110-120 HS. The silicon carbide ceramic sample was ground with 100#, 200#, 400#, 600#, 800#, 1000#, and 1200# metallographic sandpapers in sequence until only the grinding scratches of 1200# sandpaper in the same direction could be observed under an inverted metallographic microscope. The sample was then ultrasonically cleaned with acetone, anhydrous ethanol, and deionized water, respectively, and dried to obtain a relatively smooth and clean silicon carbide ceramic.

[0017] (2) Build a femtosecond laser galvanometer processing system. The schematic diagram of the system is as follows: Figure 1 As shown, it includes a femtosecond laser 1, a first reflector 2, a λ / 2 wave plate 3, a beam expander 4, an adjustable aperture 5, a second reflector 6, a scanning galvanometer 7, a moving platform 8, and a computer control system 9; wherein, the femtosecond laser outputs a Gaussian beam with a laser wavelength of 1030nm, a pulse width of 240fs, an adjustable repetition frequency of 50-300kHz, and an adjustable output power of 1-10W; the λ / 2 wave plate 3 is mainly used to convert the light beam from linearly polarized light to circularly polarized light, thereby ensuring that the material removal rate is consistent when the focused laser scans across the material surface; the beam expander 4 can expand the laser beam diameter by 3 times, It is beneficial to obtain a laser beam with a smaller spot diameter after focusing; the adjustable aperture 5 is mainly used to adjust the size of the femtosecond laser spot and remove the low-energy area at the edge of the Gaussian beam, reducing the influence of stray light on material processing; the scanning galvanometer is mainly used to control the laser beam to process the specified area, and the scanning speed is adjustable from 100 to 2000 mm / s; the mobile platform can move in the Z direction so that the ceramic surface to be processed is located on the laser focal plane; the computer control system is connected to the femtosecond laser, the scanning galvanometer, and the mobile platform, and can respectively realize the adjustment and control of the laser power, scanning direction and speed, and the Z position of the sample to be processed.

[0018] (3) Place the silicon carbide ceramic sample on a moving platform and control the computer system to move the sample so that the processed surface is located at the focal plane of the femtosecond laser.

[0019] (4) The laser power was set to 4W, the repetition frequency was set to 200kHz, the spot diameter was set to 60μm, the scanning speed was set to 1000mm / s, and the scanning interval was set to 50μm. The surface of the ceramic sample was preliminarily polished using a Z-shaped scanning method. The scanning path was as follows: Figure 2 shown.

[0020] (5) The laser power was set to 10W, the repetition frequency was set to 200kHz, the spot diameter was set to 40μm, the scanning speed was set to 400 / s, and the scanning interval was set to 130μm. The surface of the ceramic sample was grooved to achieve roughening using a unidirectional scanning method. The scanning path was as follows: Figure 3 shown.

[0021] (6) The average depth of the obtained grooves is 50 μm and the average spacing is 130 μm. Under the premise of ensuring the wettability of the solder, the contact area between the ceramic side and the solder can be increased by about 38%, which is beneficial to the improvement of the performance of the brazed joint.

[0022] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A femtosecond laser texturing method for ceramic joints used in stainless steel-ceramic brazing, characterized by: The following steps are involved: Step 1: The ceramic used for texturing is silicon carbide ceramic with a relatively smooth and clean surface; Step 2: Build a femtosecond laser galvanometer processing system, place the sample on a moving platform, and move the sample so that the processing surface is located at the focal plane of the femtosecond laser; In step 3, under the control of the computer system, the femtosecond laser galvanometer processing system first performs a low-power scan on the surface of the ceramic sample to perform preliminary polishing of the sample; then, multiple parallel and continuously distributed grooves are processed on the surface of the ceramic sample at high power to complete the roughening process.

2. The femtosecond laser texturing method for ceramic joints for stainless steel-ceramic brazing according to claim 1, characterized in that: In step 1, the silicon carbide ceramic used for texturing is made by pressureless sintering, with an apparent porosity of less than 0.2%, a room temperature thermal expansion coefficient of less than 4.3×10-6 / °C, a compressive strength of more than 2200 MPa, and a hardness of 110-120HS.

3. The femtosecond laser texturing method for ceramic joints for stainless steel-ceramic brazing according to claim 1, characterized in that: In step 1, the surface of the silicon carbide ceramic needs to be polished with metallographic sandpaper of not less than 1200# before the roughening treatment, and then ultrasonically cleaned with acetone, anhydrous ethanol and deionized water respectively, and blown dry to obtain a relatively smooth and clean silicon carbide ceramic surface.

4. The femtosecond laser texturing method for ceramic joints for stainless steel-ceramic brazing according to claim 1, characterized in that: In step 2, the constructed femtosecond laser galvanometer processing system includes a femtosecond laser, a first reflector, a λ / 2 wave plate, a beam expander, an adjustable aperture, a second reflector, a scanning galvanometer, a mobile platform, and a computer control system, wherein the computer control system is connected to the femtosecond laser, the scanning galvanometer, and the mobile platform.

5. The femtosecond laser texturing method for ceramic joints for stainless steel-ceramic brazing according to claim 1, characterized in that: In step 2, the femtosecond laser outputs a Gaussian beam with a laser wavelength of 1030 nm, a pulse width of 240 fs, an adjustable repetition frequency of 50-300 kHz, and an adjustable output power of 1-10 W.

6. The femtosecond laser texturing method for ceramic joints for stainless steel-ceramic brazing according to claim 1, characterized in that: In step 2, the femtosecond laser scanning speed can be adjusted by the galvanometer, and the speed is adjustable from 100 to 2000 mm / s.

7. The femtosecond laser texturing method for ceramic joints for stainless steel-ceramic brazing according to claim 1, characterized in that: In step 3, when using a femtosecond laser to perform preliminary polishing on the surface of the ceramic sample, the polishing parameters are: laser power 2-4W, repetition frequency 150-200kHz, spot diameter 40-60μm, scanning speed 800-1000mm / s, scanning spacing 30-50μm, and Z-shaped scanning method.

8. The femtosecond laser texturing method for ceramic joints for stainless steel-ceramic brazing according to claim 1, characterized in that: In step 3, when grooves are processed on the surface of the ceramic sample using a femtosecond laser, the processing parameters are: laser power 8-10 W, repetition frequency 150-200 kHz, spot diameter 20-40 μm, scanning speed 200-400 mm / s, scanning spacing 100-130 μm, and unidirectional scanning.

9. The femtosecond laser texturing method for ceramic joints for stainless steel-ceramic brazing according to claim 1, characterized in that: In step 3, the groove depth is 30-50 μm, and the repetition spacing is 100-130 μm. Under the premise of ensuring the wettability of the solder, the contact area between the ceramic side and the solder can be increased by 30-40%, which is beneficial to improving the performance of the brazed joint.

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