Preparation method of silicon nitride-based ceramic titanium-coated silicon alloy

Abstract

The invention discloses a preparation method of a silicon nitride-based ceramic titanium-coated silicon alloy, and relates to the field of connection of silicon nitride-based ceramics and similar / dissimilar materials. The invention aims to solve the problem of poor wettability between a welding flux and a base material caused by poor physical and chemical compatibility between the ceramic base material and the welding flux in the silicon nitride-based ceramic connecting process. The preparation method of the silicon nitride-based ceramic titanium-coated silicon alloy comprises the following steps: 1, grinding and polishing the surface of silicon nitride-based ceramic, cleaning in acetone, and drying; 2, cutting the titanium-silicon alloy into slices and polishing the slices to be smooth; and 3, placing the titanium-silicon alloy on the surface of the silicon nitride-based ceramic to carry out a wetting and spreading experiment. The method is simple in process, low in cost, high in efficiency and capable of being applied on a large scale. The wettability of the titanium-coated silicon alloy on the silicon nitride-based ceramic is greatly improved, the thermophysical compatibility of a connected sample interface can be improved, the residual stress of a joint is relieved, and the performance of the joint is well strengthened.

Description

Technical Field

[0001] The invention relates to a method for preparing a silicon nitride-based ceramic titanium-coated silicon alloy, and belongs to the field of connection between ceramics and homogeneous or heterogeneous materials. Background Art

[0002] BN / Si3N4 composite ceramics combine the high strength and high temperature oxidation resistance of Si3N4 ceramics with the low dielectric constant, low dielectric loss and good machinability of BN ceramics, showing excellent chemical stability, high thermal shock resistance and low and stable dielectric constant and dielectric loss in a wide temperature range. Therefore, BN / Si3N4 composite ceramics have become one of the most promising candidates for wave-transmitting materials for high Mach number aircraft radomes in the world. In order to meet the broadband wave-transmitting characteristics of the components, some pores are generally introduced into the material, and the material is designed into a porous structure to further reduce the dielectric constant and dielectric loss of the material. However, the intrinsic brittleness of ceramic materials and the limitations of the preparation process limit their application in large-sized and complex-shaped components. Therefore, realizing the assembly connection of porous BN / Si3N4 ceramics themselves and with other materials is an effective means to solve this problem. At present, the use of commercial Ag-Cu-Ti solder can basically achieve the connection of Si3N4-based composite ceramics. However, the thermal expansion coefficient of the brazing filler metal system is quite different from that of the Si3N4-based composite ceramics, and the service temperature of the joint after connection is relatively low (about 500°C), which cannot meet the service requirements of porous BN / Si3N4 ceramics in the application of radomes for aerospace vehicles. In addition, during the connection process, due to the mismatch of the physical and chemical properties between the welded materials, the residual thermal stress of the joint after welding is large, which will cause the joint to peel off from the connection interface and crack, resulting in low bonding strength of the connection interface and poor reliability of the welded components. Therefore, it is crucial to develop a high-temperature connection method suitable for porous ceramics and achieve reliable connection with metal materials for their application in practical engineering.

[0003] The present invention promotes the infiltration of solder into the pores of the ceramic by alloying the porous BN / Si3N4 ceramic, forms a wetting layer of a certain thickness during the brazing process, widens the connection joint, and the solder infiltrates into the pores of the ceramic to form a mechanical interlocking effect with the ceramic, which can not only relieve the residual thermal stress after welding, but also increase the area of ​​the interface reaction bonding region. This dual interface action mechanism will definitely be beneficial to the improvement of the joint performance. Summary of the invention

[0004] The purpose of the present invention is to utilize the advantages of porous ceramics themselves, increase the interface reaction bonding area during the brazing process through metallization treatment, help alleviate the residual thermal stress of the joint after welding, and provide a method for preparing silicon nitride-based ceramics coated with titanium silicon alloy.

[0005] A method for preparing a silicon nitride-based ceramic titanium-silicon alloy is achieved by the following steps:

[0006] Step S1, surface treatment of silicon nitride-based ceramics. First, the silicon nitride-based ceramics are cut into corresponding sizes as required. The silicon nitride-based ceramics used in the present invention are porous ceramics with a size of 10mm×10mm×3mm. Secondly, the cut ceramic blocks are polished with 800#, 2000#, and 3000# diamond sandpapers in succession, and then the polished surface is polished with a 10μm diamond polishing agent. Finally, the silicon nitride-based ceramics are ultrasonically cleaned in acetone for 5 times, about 10min / time, and dried at 60°C for 3h before use.

[0007] Step S2, preparation of titanium silicon alloy sheet. First, the titanium silicon alloy block (component SiTi22 (wt.%)) was cut into 800 μm thin slices by wire cutting machine, and polished with 800#, 2000#, and 3000# diamond sandpaper in sequence, and the thickness of the final alloy sheet was about 600 μm. Secondly, the alloy sheet was ultrasonically cleaned in acetone for 3 times, about 10 minutes per time, and dried at 60°C for 30 minutes before use.

[0008] Step S3, wetting and spreading process of titanium-silicon alloy on silicon nitride-based ceramic surface. First, cut the titanium-silicon alloy sheet into small pieces of 4 mm × 4 mm × 600 μm and place them on the surface of silicon nitride-based ceramic. Then, put the assembled sample into a vacuum welding furnace and evacuate it. When the vacuum degree reaches 7.0×10 -2 Pa~1.5×10 -2 Pa, start the heating program: first heat from room temperature to 400℃ at 20℃ / min; keep warm for 5min, then heat to 1330~1420℃ at 10℃ / min, and keep warm for 10-20min. After the insulation, first reduce the temperature to 400℃ at a rate of 10℃ / min, then reduce it to 100℃ at a rate of 15℃ / min, turn off the heating program, and take out the sample after it cools to room temperature.

[0009] The preparation method of the present invention has the following advantages:

[0010] (1) The actual melting point of the SiTi22 active metal brazing filler metal used in the present invention is 1340°C, and it has good wetting and spreading properties on the surface of porous silicon nitride-based ceramics, which provides a feasible basis for realizing high-temperature connection of porous silicon nitride-based ceramics. The operating temperature of the joint obtained after connection is relatively high.

[0011] (2) The Ti element in the SiTi22 metal brazing filler metal can act as an active element that can react with the porous silicon nitride-based ceramic at the interface to achieve chemical connection. It is also a transition metal that can act as a catalyst. In the presence of a carbon source, it can in situ generate a SiC nanowire reinforcement phase in the joint to achieve a strengthened connection of the joint.

[0012] (3) The process of the present invention is simple, highly repeatable, and the composition of the brazing material is controllable. It can perform surface carburization treatment on large-sized and complex-shaped samples. This method is used to connect porous ceramics, and the joint structure is simple and the interface bonding force is strong. It can also simultaneously improve the problems of poor wettability, low joint strength, and low operating temperature. It is suitable for industrial production and has excellent industrial application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 Flow chart for the preparation of silicon nitride-based ceramics covered with titanium-silicon alloy;

[0014] Figure 2 SEM photos of the interface morphology of SiTi22 alloy coated with porous BN / Si3N4 ceramics at different temperatures. Figure 2 (a) is 1360°C, (b) is 1380°C, (c) is 1400°C, and (d) is 1420°C; DETAILED DESCRIPTION

[0015] The present invention will be further described below in conjunction with the embodiments.

[0016] Embodiment 1:

[0017] This embodiment is used for self-connection of porous Si3N4 ceramics, which is specifically implemented by the following method.

[0018] 1.1. Use acetone as the medium to perform ultrasonic cleaning on porous Si3N4 ceramics for 3 times, 10 min / time;

[0019] 1.2. Place the SiTi22 alloy sheet on the porous Si3N4 ceramic surface and put the two sets of samples into the welding furnace until the vacuum reaches 1.5×10 -2 Pa, the temperature was raised to 1360°C at a rate of 20°C / min and kept for 10 min, then cooled to 400°C at a rate of 10°C / min, and then naturally cooled to room temperature to obtain a porous Si3N4 ceramic connection specimen.

[0020] Embodiment 2:

[0021] This embodiment is used for self-connection of carbon-containing porous Si3N4 ceramics after heat treatment, and is specifically implemented by the following method.

[0022] 2.1. Use acetone as the medium to perform ultrasonic cleaning on the porous Si3N4 ceramics for 3 times, 5 min / time;

[0023] 2.2. Weigh 20 ml of phenolic resin and 20 ml of acetone to prepare a 50% phenolic resin organic solution;

[0024] 2.3. The porous Si3N4 ceramic was placed in a phenolic resin organic solution for vacuum infiltration for 30 min and then placed in a 120°C oven for pre-curing for 2 h;

[0025] 2.4. The solidified porous Si3N4 ceramics are placed in a sintering furnace for heat treatment until the vacuum degree reaches 1.5×10 -2 Pa and then heated to 1000℃ at a rate of 20℃ / min and kept warm for 20min. Then naturally cooled to room temperature to obtain the carburized porous Si3N4 ceramic sample.

Claims

1. A method for preparing a silicon nitride-based ceramic titanium-silicon alloy, characterized in that The method for coating silicon nitride-based ceramic with alloy is carried out in the following steps: Step S1, surface treatment of silicon nitride-based ceramics. First, the silicon nitride-based ceramics are cut into corresponding sizes as required. The silicon nitride-based ceramics used in the present invention are porous ceramics with a size of 10mm×10mm×3mm. Secondly, the cut ceramic blocks are polished with 800#, 2000#, and 3000# diamond sandpapers in succession, and then the polished surface is polished with a 10μm diamond polishing agent. Finally, the silicon nitride-based ceramics are ultrasonically cleaned in acetone for 5 times, about 10min / time, and dried at 60°C for 3h before use. Step S2, preparation of titanium silicon alloy sheet. First, the titanium silicon alloy block (component SiTi22 (wt.%)) was cut into 800 μm thin slices by wire cutting machine, and polished with 800#, 2000#, and 3000# diamond sandpaper in sequence, and the thickness of the final alloy sheet was about 600 μm. Secondly, the alloy sheet was ultrasonically cleaned in acetone for 3 times, about 10 minutes per time, and dried at 60°C for 30 minutes before use. Step S3, wetting and spreading process of titanium-silicon alloy on silicon nitride-based ceramic surface. First, cut the titanium-silicon alloy sheet into small pieces of 4 mm × 4 mm × 600 μm and place them on the surface of silicon nitride-based ceramic. Then, put the assembled sample into a vacuum welding furnace and evacuate it. When the vacuum degree reaches 7.0×10 -2 Pa~1.5×10 -2 Pa, start the heating program: first heat from room temperature to 400℃ at 20℃ / min; keep warm for 5min, then heat to 1330~1420℃ at 10℃ / min, and keep warm for 10-20min. After the insulation, first reduce the temperature to 400℃ at a rate of 10℃ / min, then reduce it to 100℃ at a rate of 15℃ / min, turn off the heating program, and take out the sample after it cools to room temperature.

2. The method for preparing a silicon nitride-based ceramic titanium-silicon alloy according to claim 1, characterized in that The ceramic used in step 1 is a silicon nitride-based ceramic, and the porosity of the ceramic is 2% to 45%.

3. The method for preparing a silicon nitride-based ceramic titanium-silicon alloy according to claim 1, characterized in that The porous ceramic described in step 1 can be in any shape and size as long as it meets the requirements of the furnace of the brazing furnace.

4. The method for preparing a silicon nitride-based ceramic titanium-silicon alloy according to claim 1, characterized in that The composition of the titanium silicon alloy block in step 2 is SiTi22 (wt.%).

5. The method for preparing a silicon nitride-based ceramic titanium-silicon alloy according to claim 1, characterized in that In step 2, the titanium silicon alloy is in the form of flakes, and the size of the flakes is proportional to the size of the ceramic.

6. The method for preparing a silicon nitride-based ceramic titanium-silicon alloy according to claim 1, characterized in that The vacuum degree of the welding furnace in step 3 is 7.0×10 -2 Pa~1.5×10 -2 Pa, heating rate 15~30℃ / min.

7. The method for preparing a silicon nitride-based ceramic titanium-silicon alloy according to claim 1, characterized in that In step 3, the wetting and spreading temperature is 1330-1420° C., and the insulation time is 10-30 minutes.

8. The method for preparing a silicon nitride-based ceramic titanium-silicon alloy according to claim 1, characterized in that In step three, the alloy is placed in a single layer.

9. A method for preparing a silicon nitride-based ceramic titanium-silicon alloy, characterized in that: The titanium-silicon alloy-coated silicon nitride-based ceramic is prepared by the method for preparing the titanium-silicon alloy-coated silicon nitride-based ceramic as described in any one of claims 1 to 8.

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