A method for vacuum brazing connection between RBSiC ceramic homogenous materials

Abstract

The application discloses a vacuum brazing connection method between RBSiC ceramic homologous materials and belongs to the technical field of ceramic material connection. The application aims at solving the technical problems of poor interface wettability, insufficient connection layer continuity and more interface defects in the connection between existing RBSiC homologous ceramics. The method comprises the following steps: polishing, ultrasonic cleaning and drying are sequentially performed on the surfaces of two pieces of silicon carbide ceramics to be connected and the surface of a SiFe filler piece; the SiFe filler piece is arranged between the surfaces of the two pieces of silicon carbide ceramics to be connected to assemble a sandwich structure and obtain a welding assembly; then, brazing is performed under vacuum; in the brazing process, the temperature is raised in sections, then the temperature is lowered in sections, and then the furnace is cooled to room temperature, thereby obtaining a silicon carbide ceramic brazing joint. In the brazing process, the temperature rising, temperature maintaining and temperature lowering processes are controlled in sections, so that the filler is fully melted and spread, and the adverse effects of heat cycle on the joint structure and interface combination are reduced.

Description

Technical Field

[0001] This invention belongs to the field of ceramic material joining technology, specifically, it relates to a vacuum brazing joining method between RBSiC ceramic materials of the same material; specifically, it is a method of using SiFe brazing filler metal to braze and join reaction sintered RBSiC ceramics. Background Technology

[0002] Reactive sintered silicon carbide (RBSiC) is a ceramic material prepared by reactive sintering through molten silicon infiltration, using SiC particles as a framework. Its microstructure mainly consists of SiC phase and free Si phase. RBSiC is characterized by high density, high hardness, good wear resistance, excellent thermal conductivity, and relatively low cost, making it widely used in wear-resistant sealing components, optical structural components, and semiconductor equipment parts. Due to the limitations of ceramic materials—their hardness and brittleness, and the difficulty in processing large-size and complex-shaped components—RBSiC components typically require integral manufacturing through joining techniques.

[0003] However, RBSiC ceramics have high melting points, high hardness, and almost no plastic deformation, making them difficult to join using conventional fusion welding methods. Furthermore, the surface chemical properties of RBSiC are stable, and ordinary metal brazing filler metals have poor wettability, making it difficult to form a reliable bond directly at the joint interface. Therefore, the composition of the brazing filler metal, the brazing temperature, and the holding time have a significant impact on the interfacial structure and connection performance of RBSiC joints.

[0004] Currently, SiC ceramics are mostly joined using active metal solders such as Ag-Cu-Ti, relying on the reaction of active elements like Ti with the ceramic interface to improve the wettability of the solder and thus achieve the connection. However, these solders contain precious metals such as Ag, resulting in high costs; furthermore, Ag-based solders have limited high-temperature resistance, and the joint performance is easily affected under high-temperature service conditions. Alternatively, there are methods using pure Si or Si-containing materials for silicon-doping connections of SiC ceramics, but these methods have stringent requirements for connection temperature and process conditions.

[0005] For joining RBSiC ceramics, using an active brazing filler metal system containing precious metals will directly increase the joining cost. Furthermore, if the filler metal's melting temperature and brazing process are not properly controlled, the filler metal will struggle to spread sufficiently and fill the joint gaps, thus affecting the joint's forming quality. Therefore, the selection of a brazing filler metal system must consider not only its melting temperature and spreading ability but also material cost and process adaptability.

[0006] Therefore, it is necessary to develop a low-cost, process-adaptable brazing filler metal and brazing method suitable for joining RBSiC ceramics, so as to reduce the joining cost and achieve reliable joining of RBSiC ceramics while ensuring that the brazing filler metal has a suitable melting temperature and spreading ability. Summary of the Invention

[0007] This invention aims to solve the technical problems of poor interfacial wettability, insufficient continuity of the bonding layer, and numerous interface defects in the existing bonding between RBSiC ceramics, and provides a vacuum brazing bonding method for RBSiC ceramics of the same material.

[0008] To address the aforementioned technical problems, the present invention adopts the following technical solution: The purpose of this invention is to provide a vacuum brazing connection method between RBSiC ceramic materials of the same type, comprising the following steps: Step 1: Grind, ultrasonically clean, and dry the surfaces of the two silicon carbide ceramic pieces to be joined and the surface of the SiFe solder sheet in sequence. Step 2: Place the SiFe solder sheet between the two silicon carbide ceramic surfaces to be joined, assemble them into a sandwich structure, and obtain the component to be soldered. Step 3: Then brazing is performed under vacuum. During the brazing process, the temperature is first raised in sections, then lowered in sections, and then cooled to room temperature with the furnace to obtain a silicon carbide ceramic brazed joint.

[0009] Further specifying, the atomic percentage of Fe in the solder sheet is 25%~30%, with the balance being Si.

[0010] To further specify, sanding should be done sequentially using sandpaper of grits 240, 400, 800, 1200, 2000, and 3000.

[0011] Further specify that ultrasonic cleaning should be performed using anhydrous ethanol or acetone.

[0012] Furthermore, the thickness of the solder sheet is specified to be 0.3mm-1mm.

[0013] To further specify, the vacuum degree is 2.7 × 10⁻⁶. -5 Pa.

[0014] Further specifying, the temperature increase is from room temperature to 1000℃-1200℃ at a rate of 5-10℃ / min; then the temperature is increased to 1230℃-1330℃ at a rate of 5-10℃ / min, and held for 5-20 min. Further defining the method according to claim 1, the cooling is characterized in that the temperature is reduced to 600℃-800℃ at a rate of 5℃ / min to 10℃ / min; then reduced to 130℃ at a rate of 5℃ / min to 10℃ / min, and the programmed temperature control is stopped.

[0015] Another object of the present invention is to provide a silicon carbide ceramic brazing joint, which is prepared by any of the methods described above.

[0016] Based on one specific embodiment, the vacuum brazing connection method between RBSiC ceramic homogeneous materials provided by the present invention is carried out according to the following steps: Step S1: Prepare two RBSiC ceramic samples and SiFe sheet solder; the SiFe solder is a Si-Fe binary solder, wherein the atomic percentage of Fe is 25%~30%, and the balance is Si.

[0017] Step S2: Surface treatment is performed on the surfaces of the two RBSiC ceramics to be joined and the surface of the SiFe solder sheet. Specifically, the surfaces to be joined are successively ground and polished using 240-grit, 400-grit, 800-grit, 1200-grit, 2000-grit, and 3000-grit sandpaper to remove the surface oxide layer, processing damage layer, and attached impurities, making the surfaces to be joined smooth. Then, the RBSiC ceramic samples and SiFe solder sheets are ultrasonically cleaned in anhydrous ethanol, removed, and dried for later use.

[0018] Step S3: Place the SiFe solder sheet between two RBSiC ceramic samples to obtain the assembly to be soldered. The assembly to be soldered is a sandwich structure of RBSiC ceramic / SiFe solder / RBSiC ceramic, with the SiFe solder sheet corresponding to the surface of the RBSiC ceramic to be joined; no external pressure is applied during the assembly process.

[0019] Step S4: Place the component to be soldered in a vacuum brazing furnace. When the vacuum level inside the furnace reaches 2.7 × 10⁻⁶... -5 Brazing was performed after Pa. The brazing process included: heating from room temperature to 1100℃ at 10℃ / min; heating from 1100℃ to 1300℃ at 5℃ / min and holding at 1300℃ for 15 min; after holding, cooling from 1300℃ to 800℃ at 5℃ / min, and then cooling from 800℃ to 130℃ at 10℃ / min, followed by furnace cooling to room temperature to obtain the RBSiC ceramic brazed joint.

[0020] This invention uses SiFe solder as the intermediate solder. SiFe solder, with Fe and Si as its main components, is widely available and inexpensive, and does not contain precious metals such as Ag, which significantly reduces the joining cost of RBSiC ceramics. The Si-Fe binary system has a low melting temperature, allowing the solder to melt, spread, and fill the gap between two RBSiC ceramics at temperatures above 1230°C. Simultaneously, the solder, with Si as its main component, is homologous to the SiC phase and free Si phase in RBSiC ceramics, exhibiting good compatibility and facilitating its spread on the RBSiC surfaces to be joined and the formation of an interfacial bond. In this invention, two RBSiC ceramics and the SiFe solder sequentially constitute a sandwich-type welding assembly, and the connection is between the same ceramic materials. The thermophysical properties of the base materials on both sides of the joint are consistent, which helps reduce residual stress caused by thermal expansion mismatch during heating and cooling. During brazing, segmented control of the heating, holding, and cooling processes ensures sufficient melting and spreading of the brazing filler metal while minimizing the adverse effects of thermal cycling on the joint microstructure and interfacial bonding. This invention employs a sandwich-style assembly structure of RBSiC ceramic / SiFe brazing filler metal / RBSiC ceramic, where the brazing filler metal sheet size matches the dimensions of the surfaces to be joined. Furthermore, no external pressure is required during assembly, resulting in simple operation and good process repeatability.

[0021] Compared with the prior art, the present invention has the following beneficial effects: The SiFe solder used in this invention uses inexpensive Fe and Si as raw materials and does not contain precious metals or active elements such as Ag, Cu, and Ti. The solder is low in cost and easy to obtain, which solves the problem of high cost of active solders such as Ag-Cu-Ti and helps to reduce the connection cost of RBSiC ceramic components.

[0022] The SiFe brazing filler metal of the present invention uses Si as the main component, which is homologous to the SiC phase and free Si phase in RBSiC ceramic and has good compatibility. After the brazing filler metal melts, it is easy to spread on the RBSiC surface to be joined and fill the connection gap, which is beneficial to obtaining a well-bonded brazed joint.

[0023] This invention is used for self-joining of RBSiC ceramic materials. The thermal expansion coefficient and other thermophysical properties of the base materials on both sides of the joint are consistent. The SiFe brazing filler metal is a silicon-based brazing filler metal with good compatibility with the base material. This helps to alleviate the residual stress caused by thermal expansion mismatch in heterogeneous joints and reduces the risk of cracking of the joint during the cooling process.

[0024] The brazing temperature of this invention can be selected in the range of 1230~1330℃, the holding time can be selected in the range of 5~20 min, and the heating rate and cooling rate can be selected in the range of 5~10℃ / min, with a wide process window. At the same time, the temperature control method of segmented heating and segmented cooling is adopted, and a lower heating rate is used above 1100℃, which helps to reduce the adverse effects of sudden temperature changes on the joint.

[0025] This invention adopts a sandwich-type assembly structure of RBSiC ceramic / SiFe solder / RBSiC ceramic. The size of the solder sheet matches the size of the surface to be connected, and no external pressure is required during the assembly process. It is easy to operate and has good process repeatability.

[0026] For a deeper understanding of the features and technical content of this invention, please refer to the accompanying detailed description and drawings. It should be noted that the drawings are provided for illustrative purposes only and are not intended to limit the scope of the invention. Attached Figure Description

[0027] Figure 1 It is an SEM image of the brazed joint; Figure 2 This is the process curve in the embodiment. Detailed Implementation

[0028] The present invention will be described in detail below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but should not be considered as limiting the present invention. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0029] Example 1: In this example, two RBSiC ceramics are connected using SiFe solder. The RBSiC ceramic is a reaction-bonded silicon carbide ceramic; the SiFe solder is designed based on the SiFe binary eutectic point, where the atomic ratio of Si to Fe is 73.5:26.5.

[0030] Step 1, Sample preparation: Two RBSiC ceramics were processed into block samples with dimensions of 4 mm × 8 mm × 3 mm and 4 mm × 4 mm × 3 mm, respectively; the SiFe brazing filler metal was processed into sheet brazing filler metal with dimensions of 4 mm × 4 mm × 0.5 mm.

[0031] Among them, the RBSiC sample with dimensions of 4 mm × 4 mm × 3 mm has a 4 mm × 4 mm surface to be joined that corresponds to the size of the SiFe solder sheet, so that the solder sheet can cover the area to be joined and is stacked on the surface of the RBSiC sample with dimensions of 4 mm × 8 mm × 3 mm.

[0032] Step 2, Surface Treatment: The surfaces to be joined on the two RBSiC ceramic samples and the surface of the SiFe solder sheet were ground and polished respectively.

[0033] During polishing, use sandpaper of 240 grit, 400 grit, 800 grit, 1200 grit, 2000 grit, and 3000 grit in sequence to polish the surfaces to be joined, so as to make the surface flat and remove the oxide layer, processing damage layer and attached impurities.

[0034] The two polished RBSiC ceramic samples and the SiFe solder sheet were placed in acetone and ultrasonically cleaned for 20 minutes at an ultrasonic frequency of 40 kHz. After ultrasonic cleaning, they were taken out and dried in the same direction and set aside for later use.

[0035] Step 3, Sample assembly: An RBSiC ceramic sample with dimensions of 4 mm × 8 mm × 3 mm, a SiFe solder sheet, and an RBSiC ceramic sample with dimensions of 4 mm × 4 mm × 3 mm are stacked in sequence, with the SiFe solder sheet sandwiched between the two RBSiC ceramic samples, forming a sandwich-type assembly to be soldered of RBSiC ceramic / SiFe solder / RBSiC ceramic.

[0036] During assembly, the SiFe solder sheet should be aligned perfectly with the 4 mm × 4 mm surface of the RBSiC ceramic to be joined, and the two RBSiC ceramic samples should be kept in relative position with the solder sheet; no external pressure should be applied during the assembly process.

[0037] Step 4, Vacuum Brazing: The components to be soldered are placed in a vacuum brazing furnace, and a vacuum is drawn until the vacuum level inside the furnace reaches 2.7 × 10⁻⁶. -5 Brazing is performed after Pa. The brazing thermal cycle process is as follows: The temperature was increased from room temperature to 1100℃ at a rate of 10℃ / min; then increased from 1100℃ to 1300℃ at a rate of 5℃ / min, and held at 1300℃ for 15 min.

[0038] After the heat preservation is completed, the temperature is reduced from 1300℃ to 800℃ at a rate of 5℃ / min; then reduced from 800℃ to 130℃ at a rate of 10℃ / min; when the furnace temperature drops to 130℃, the programmed temperature control is stopped, and the furnace is cooled to room temperature to obtain the RBSiC ceramic brazed joint.

[0039] The SEM image of the brazed joint in this embodiment is as follows: Figure 1As shown in the scanning electron microscope image, the SiFe solder and RB-SiC are tightly bonded together without obvious through cracks. The center of the solder joint consists of light gray Fe-rich silicide and dark gray Si-rich matrix, while the sides are typical SiC particles and free Si networks. However, due to the large difference in the coefficient of thermal expansion (CTE) between the SiFe solder and the RB-SiC base material, large residual stress is easily generated during the cooling process. Therefore, the residual stress at the joint will be alleviated by adding alloying elements such as Ni and Cr and preparing composite solder.

[0040] The specific embodiments of the present invention have been described in detail above. It should be noted that the present invention is not limited to the specific embodiments described above. Various modifications or alterations can be made by those skilled in the art without departing from the scope of protection defined by the claims, and all such modifications or alterations fall within the scope of the present invention.

Claims

1. A vacuum brazing method for connecting RBSiC ceramic materials of the same type, characterized in that, Includes the following steps: Step 1: Grind, ultrasonically clean, and dry the surfaces of the two silicon carbide ceramic pieces to be joined and the surface of the SiFe solder sheet in sequence. Step 2: Place the SiFe solder sheet between the two silicon carbide ceramic surfaces to be joined, assemble them into a sandwich structure, and obtain the component to be soldered. Step 3: Then brazing is performed under vacuum. During the brazing process, the temperature is first raised in sections, then lowered in sections, and then cooled to room temperature with the furnace to obtain a silicon carbide ceramic brazed joint.

2. The method according to claim 1, characterized in that, The atomic percentage of Fe in the solder sheet is 25%~30%, with the balance being Si.

3. The method according to claim 1, characterized in that, The atomic ratio of Si to Fe in the solder sheet is 73.5:26.

5.

4. The method according to claim 1, characterized in that, During sanding, use sandpaper of 240 grit, 400 grit, 800 grit, 1200 grit, 2000 grit, and 3000 grit in sequence for sanding.

5. The method according to claim 1, characterized in that, Use anhydrous ethanol or acetone for ultrasonic cleaning.

6. The method according to claim 1, characterized in that, The thickness of the brazing filler metal sheet is 0.3mm-1mm.

7. The method according to claim 1, characterized in that, The vacuum degree is 2.7 × 10⁻⁶. -5 Pa.

8. The method according to claim 1, characterized in that, The temperature is increased from room temperature to 1000℃-1200℃ at a rate of 5~10℃ / min; then increased to 1230℃-1330℃ at a rate of 5℃~10℃ / min, and held for 5~20 min.

9. The method according to claim 1, characterized in that, The temperature is reduced to 600℃-800℃ at a rate of 5~10℃ / min; then reduced to 130℃ at a rate of 5~10℃ / min, and the programmed temperature control is stopped.

10. A silicon carbide ceramic brazing joint, characterized in that, It is prepared by any one of claims 1 to 9.

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