Stainless steel and aluminum oxide ceramic connecting structure and process thereof

Abstract

The invention provides a stainless steel and aluminum oxide ceramic connecting structure and a process thereof. According to the process, the stainless steel to be connected and the aluminum oxide to be connected are connected through the enamel material, the process is high in production efficiency and low in cost, and the obtained connecting structure still has the good corrosion resistance effect at the high temperature (300-500 DEG C).

Description

Technical Field

[0001] The technical field involved in the present invention is the field of inorganic connection and sealing. Specifically, it is a connection structure and process between stainless steel and alumina ceramics, especially applied to ceramic packaging in fields such as sodium-sulfur batteries, sodium-nickel batteries, solid fuel cells, and chips. Background Art

[0002] Composite components made of alumina ceramics and stainless steel are often used in harsh service conditions of high temperature and corrosive environments, which is of great significance in actual engineering.

[0003] Currently, the commonly used connection technologies for alumina ceramics and stainless steel include active brazing connection, diffusion welding connection, transient liquid phase diffusion connection, etc. Among them, active brazing connection and diffusion welding connection are currently more mature connection technologies for alumina and stainless steel. Active brazing connection is a method that utilizes the melting of the filler metal between the ceramic and metal base materials at high temperature, and the active components contained therein react with the ceramic to form a stable reaction gradient layer to bond the two different materials together. This method requires metallization treatment of the ceramic, with a relatively cumbersome process and large environmental pollution. The high-temperature corrosion resistance of the active solder used is poor, and it is difficult to be used for a long time in special environments. Diffusion welding connection is a connection method for high-temperature-resistant ceramics and metals that has been studied more and is applicable to the connection of various ceramics and metals. The main advantages of diffusion welding connection are high connection strength, stable joint quality, and good corrosion resistance, especially suitable for the connection of ceramics and metals under high-temperature and corrosion-resistant conditions. However, this process also requires metallization treatment of the ceramic. In addition, diffusion welding requires a relatively high temperature (>1000 °C) and vacuum degree, with high energy consumption, and cannot operate on components with other components (such as glass) and lower temperature resistance. Summary of the Invention

[0004] The purpose of the present invention is to provide a connection structure and process between stainless steel and alumina ceramics. The process of the present invention is a high-efficiency connection process between stainless steel and ceramics with low cost. This process not only has high production efficiency and low cost, but also the obtained connection structure still has good corrosion resistance at relatively high temperatures (300 - 500 °C).

[0005] To achieve the above purpose, the present invention provides the following technical solutions: In the first aspect, the present invention provides a connection process between stainless steel and alumina ceramics, and the process includes the following steps: 1) Clean the surface to be connected of the stainless steel workpiece; 2) Prepare enamel slurry, evenly coat it on the surface to be connected of the stainless steel workpiece, and dry it; 3) Put the dried stainless steel workpiece into a kiln for heat treatment; 4) Take out the heat-treated stainless steel workpiece, stack the glass sealing frit and alumina ceramic parts on the surface to be joined in sequence to obtain an assembly, send the assembly into a furnace for heat treatment, and obtain a connector of stainless steel and alumina after cooling.

[0006] Preferably, the chromium content of the stainless steel is at least 10.5%, and the carbon content does not exceed 1.2%.

[0007] Preferably, the solid content of the enamel slurry is 30-90%, and the solvent is water.

[0008] Furthermore, the composition of the solids in the enamel slurry is: SiO2: 60%-85%; Al2O3: 3%-10%; Na2O: 3%-10%; Li2O: 0.5%-2.0%; B2O3: 0-20%, NiO: 0.3%-5%; Co2O3: 0.3-5%; MnO: 0-3%; La2O3: 0-3%.

[0009] Preferably, the drying conditions in step 2) are: drying temperature 60-120°C, drying time 10-12 min.

[0010] Preferably, the heat treatment conditions in step 3) are: furnace temperature 750-1050°C, heat treatment time: 1-30 min.

[0011] Preferably, after the heat treatment in step 3), it further includes a step of trimming the joint surface of the heat-treated workpiece, and the thickness of the enamel layer after trimming is 0.05-0.5 mm.

[0012] Preferably, the heat treatment conditions in step 4) are: the atmosphere in the furnace is vacuum or inert atmosphere, the heat treatment temperature is 400-1000°C, and the duration is 10-240 min.

[0013] Preferably, the cooling parameter in step 4) is: cooling the assembly at a rate of 1-5°C / min to 200°C, and then cooling it in the furnace to room temperature.

[0014] Preferably, the glass sealing frit used in step 4) is pre-pressed into a glass sealing ring.

[0015] In a second aspect, the present invention also provides a connection structure of stainless steel and alumina, which sequentially includes stainless steel, an enamel layer, a glass layer and alumina ceramics. Furthermore, the connection structure is made by the process described above.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. The connection structure and process of the present invention use enamel materials and inorganic glass materials as the connection materials for stainless steel and ceramics. The obtained connection structure of stainless steel and alumina ceramics still has good corrosion resistance at relatively high temperatures (300 - 500 °C). 2. In the process of the present invention, an enamel material with a specific composition is used to ceramicize the surface of stainless steel, forming a dense and firm enamel layer on the surface of stainless steel, which is convenient for bonding with the glass powder material. 3. In the connection structure of the present invention, glass materials with higher material strength are used, such as formed or unformed glass - sealed powder materials, which can withstand the compressive stress and tensile stress generated by the different thermal expansion coefficients of metals and ceramics. The multi - layer structure between the stainless steel and the alumina ceramic layer connection structure also makes the thermal expansion coefficient of the entire connector show a gradient distribution, increasing the stability of the system. 4. The entire process of the process of the present invention is simple, with less energy consumption and higher efficiency. Compared with traditional active brazing and diffusion welding, it greatly saves equipment, energy consumption, site and labor. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a schematic structural diagram of the connection structure obtained by the method of the present invention; Figure 2 is a photograph of the connection structure of the stainless steel and alumina ceramic tubular connector prepared in Example 1 of the present invention; Figure 3 is a photograph of the connection interface between stainless steel and enamel prepared in Example 2 of the present invention; Figure 4 is a longitudinal - section micrograph of the connection interface between stainless steel and enamel in Example 1 of the present invention; Figure 5 is a longitudinal - section micrograph of the connection interface between stainless steel and enamel in Example 2 of the present invention; Figure 6 is a longitudinal - section micrograph of the connection interface between stainless steel and enamel in Example 3 of the present invention; Figure 7 shows the connection interface between stainless steel and aluminum solder in the comparative example.

[0018] In the figure: 1. Alumina ceramic; 2. Glass layer; 3. Enamel layer; 4. Stainless steel. DETAILED DESCRIPTION OF THE INVENTION

[0019] The present invention provides a process for efficiently connecting stainless steel and alumina ceramics at low cost. This process not only has high production efficiency and low cost, but also has good corrosion resistance at relatively high temperatures (300 - 500 °C). The process of the present invention draws on the glass sealing used in the surface connection technology of inorganic non-metallic materials. Glass sealing is a relatively mature sealing mode, which is mainly applied to the connection between the surfaces of inorganic non-metallic materials. Stainless steel contains a large amount of Ni and Cr, and these elements can form a dense and firm ceramic layer on the stainless steel surface with the enamel material at relatively high temperatures, thus providing a technical basis for glass sealing.

[0020] In an exemplary embodiment, the process of the present invention adopts the following technical solutions: Step 1: Clean the surface of the stainless steel workpiece using processes such as sandblasting, magnetic polishing, and vibration polishing to remove the oil stains on the stainless steel surface, and at the same time increase the bonding area between the stainless steel surface and the enamel material. The stainless steel material used in this process, according to the definition of GB / T20878 - 2007, is steel with corrosion resistance as the main characteristic, and the chromium content is at least 10.5%, and the carbon content does not exceed 1.2% at most.

[0021] Step 2: Make the enamel powder into a slurry, evenly coat it on the surface to be welded of the stainless steel, and then dry it at 60 - 120 °C for 10 - 120 min. The main components of the enamel material used are: SiO2: 60% - 85%; Al2O3: 3% - 10%; Na2O: 3% - 10%; Li2O: 0.5% - 2.0%; B2O3: 0 - 20%, NiO: 0.3% - 5%; Co2O3: 0.3 - 5%; MnO: 0 - 3%; La2O3: 0 - 3%. The solid content in the enamel slurry is 30% - 90%, and the solvent is water.

[0022] Step 3: Put the component dried in Step 2 into a kiln for heat treatment, the kiln temperature is 750 - 1050 °C, and the heat treatment time is 1 - 30 min.

[0023] Step 4: Take out the component heat-treated in Step 3, and after cooling, place the component on the equipment for grinding. This step mainly has two purposes: one is to remove the oxide scale on the stainless steel surface; the other is to trim the uneven enamel layer on the stainless steel surface to be smooth and make its thickness uniform. The thickness of the enamel layer is controlled between 0.05 - 0.5 mm.

[0024] Step 5: Combine the trimmed enamel parts and alumina ceramic structural parts, and put a glass powder material such as a glass seal ring made of glass seal glass powder between them. Then, place the assembly into a vacuum furnace or an atmosphere furnace for heat treatment. The atmosphere in the furnace is an inert gas such as vacuum, N2, or AR. The heat treatment temperature is 400 - 1000 °C, and the duration is 10 min - 240 min. Then, cool the assembly to 200 °C at a rate of 1 - 5 °C / min, and then cool it to room temperature in the furnace. In this way, an alumina ceramic and stainless steel connector with good mechanical properties and corrosion resistance is obtained.

[0025] In the enamel material raw materials used in the present invention, high-purity industrial ceramic powders are used as raw materials with less impurity content. In the enamel materials used, silicon oxide and boron oxide are glass network formers, and their main function is to construct the glass network and improve the strength of the material. Alumina is a network intermediate, and its addition can improve the stiffness of the material and adjust the thermal expansion coefficient of the material. Sodium oxide and lithium oxide are network modifiers, and their main function is to lower the melting point of the material and improve the glass sealing efficiency. There are also rare earth elements such as lanthanum oxide in the material system, which is important for stabilizing the structure of the material. In addition, there are cobalt oxide, nickel oxide, and manganese oxide in the enamel material, and their main function is to react with the stainless steel surface oxide layer to form a strong ceramic connection layer, increasing the connection between the enamel layer and the metal layer.

[0026] In the connection structure of the present invention, the glass connection between the stainless steel and the alumina ceramic has a two-layer structure. One layer is the enamel layer on the stainless steel surface, and the other layer is the glass layer, while the glass connection of ordinary inorganic non-metallic materials has only one glass layer. The multi-layer connection of the present invention has the following advantages: 1. The enamel layer and the stainless steel are combined relatively tightly, which increases the strength of the whole material; 2. The multi-layer structure makes the thermal expansion coefficient of the whole connector show a gradient distribution, increasing the stability of the system.

[0027] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the specific embodiments and the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0028] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "front end", "back end", "both ends", "one end", "the other end", etc. is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on the present invention. In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0029] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installed", "provided with", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] Example 1: Bonding of 304 stainless steel and alumina ceramic Step 1: Place the surface to be connected of the 304 stainless steel tubular part in a magnetic polishing machine for magnetic polishing to remove the oil stain on the surface of the stainless steel workpiece, and at the same time increase the bonding area between the stainless steel surface and the enamel material. The magnetic polishing time is 40 min and the rotation speed is 400 r / min.

[0031] Step 2: Mix the enamel powder and water to prepare a slurry with a solid content of 90 wt%, evenly coat it on the surface to be welded of the stainless steel, and then dry it at 80 °C for 120 min.

[0032] The main components of the enamel material are: SiO2: 60%; Al2O3: 10%; Na2O: 6%; Li2O: 2.0%; B2O3: 10%, NiO: 2%; Co2O3: 4%; MnO: 3%; La2O3: 3%.

[0033] Step 3: Put the component dried in Step 2 into a kiln for heat treatment. The kiln temperature is 950 °C and the heat treatment time is 5 min.

[0034] Step 4: Take out the component heat-treated in Step 3, and after cooling, place the component on a grinding and polishing fixture for grinding. The thickness of the enamel layer is controlled to be 0.2 mm.

[0035] Step 5: Combine the trimmed enameled parts and alumina structural parts, put a glass-sealed ring formed by pressing glass-sealed glass powder between them, and then heat-treat the assembly in an N2 atmosphere at a heat-treatment temperature of 850°C for 60 minutes. Then cool the assembly to 200°C at a rate of 5°C / min and then cool it in the furnace to room temperature. In this way, we obtain an alumina ceramic and stainless steel connector with good mechanical properties and corrosion resistance.

[0036] Figure 1 Shows a schematic diagram of the connection structure prepared by this method, which includes four layers, namely, alumina ceramic 1, glass layer 2, enamel layer 3, and stainless steel 4. Figure 2 Shows a photo of the connection structure prepared in this embodiment. The internal white part is the alumina ceramic, the middle layer is the glass layer and the enamel layer (the shiny part in the picture), and the outermost black part is the stainless steel. The stratification of the glass layer and the enamel layer in the middle layer can be Figures 4 - 6 distinguished in the cross-sectional micrograph.

[0037] Example 2: Bonding of 316 stainless steel and alumina ceramic Step 1: Place the surface to be connected of the 316 stainless steel disc-shaped part in a sandblasting machine for sandblasting to remove the oil on the surface of the stainless steel workpiece and at the same time increase the bonding area between the stainless steel surface and the enamel material. The sandblasting time is 20 minutes.

[0038] Step 2: Mix the enamel powder and water to prepare a slurry with a solid content of 60 wt%, evenly coat it on the surface of the stainless steel to be welded, and then dry it at 80°C for 120 minutes.

[0039] The main components of the enamel material are: SiO2: 85%; Al2O3: 5%; Na2O: 3.0%; Li2O: 1.0%; NiO: 1.5%; Co2O3: 2.5%; MnO: 1%; La2O3: 1%.

[0040] Step 3: Put the assembly dried in Step 2 into a kiln for heat treatment. The kiln temperature is 1050°C and the heat treatment time is 30 minutes.

[0041] Step 4: Take out the assembly heat-treated in Step 3, and after cooling, place the assembly on a grinding and polishing fixture for grinding. The thickness of the enamel layer is controlled to be 0.05 mm.

[0042] Step 5: Stack the glass powder material for glass sealing on the trimmed enamel parts, then stack the alumina structural parts on top and combine them together. Then heat-treat the assembly under vacuum at a heat treatment temperature of 900 °C for 60 min. Then cool the assembly to 200 °C at a rate of 5 °C / min and then cool it in the furnace to room temperature. In this way, we obtain alumina ceramics and stainless steel connectors with good mechanical properties and corrosion resistance.

[0043] Example 3: Bonding of 310s stainless steel and alumina ceramics Step 1: Place the 310s stainless steel parts in a vibrating polishing machine to remove the oil on the surface of the stainless steel workpieces, and at the same time increase the bonding area between the stainless steel surface and the enamel material. The magnetic polishing time is 120 min.

[0044] Step 2: Mix the enamel powder and water to prepare a slurry with a solid content of 30 wt%, evenly coat it on the surface to be welded of the stainless steel, and then dry it at 80 °C for 120 min.

[0045] The main components of the enamel material are: SiO2: 72%; Al2O3: 8%; Na2O: 3%; Li2O: 2.0%; B2O3: 2%, NiO: 5%; Co2O3: 3%; MnO: 2%.

[0046] Step 3: Put the components dried in Step 2 into a kiln for heat treatment. The kiln temperature is 1000 °C and the heat treatment time is 15 min.

[0047] Step 4: Take out the components heat-treated in Step 3, and after cooling, place the components on a grinding and polishing fixture for grinding. The thickness of the enamel layer is controlled to be 0.1 mm.

[0048] Step 5: Stack the glass sealing rings formed by pressing glass powder for glass sealing on the trimmed enamel parts, then stack the alumina structural parts and combine them together. Then heat-treat the assembly in an N2 atmosphere at a heat treatment temperature of 900 °C for 60 min. Then cool the assembly to 200 °C at a rate of 3 °C / min and then cool it in the furnace to room temperature. In this way, we obtain alumina ceramics and stainless steel connectors with good mechanical properties and corrosion resistance.

[0049] Comparative example: Diffusion bonding of 316 stainless steel and alumina ceramics This example uses the currently common connection method for stainless steel and alumina ceramic materials, which is diffusion welding with pure aluminum as the welding raw material. The connection process is as follows: Step 1: Use processes such as sandblasting, magnetic polishing, and vibrating polishing to clean the surface of the stainless steel workpieces to remove the oil on the stainless steel surface, and at the same time clean the pure aluminum solder by pickling and alkali washing. Step 2: Fabricate a component using stainless steel, aluminum alloy solder, and alumina. Apply continuous pressure to the welding area and place the component under high vacuum conditions at 580 - 660 °C for hot press welding. Step 3: Remove the hot press component after cooling.

[0050] Performance Detection Example 1 - Mechanical Property Detection Internal Hydrostatic Pressure Test Example This example uses the internal hydrostatic pressure test equipment commonly available on the market for metal and ceramic pipes. The principle of this equipment is to inject water into the cavity of the test piece and increase the pressure of the water body through a gas source to achieve a uniformly increasing pressure inside the entire cavity of the test piece to be measured, and test the physical strength of the cavity wall and weld of the test piece. The test steps are as follows: Step 1: Connect the test piece to the internal hydrostatic pressure tester, ensure that the entire pipeline is tightly connected, then inject water into the entire pipeline, and connect the gas source. Step 2: Input the test curve, including the pressure increase rate, pressure holding time, etc. Step 3: Conduct the test and record the data.

[0051] Performance Detection Example 2 - Corrosion Resistance Detection Corrosion Resistance Detection Example Immerse the heat-treated alumina ceramics and stainless steel connectors in Examples 1 - 3 and the comparative example in corrosive sulfur liquid at 350 °C for 2 weeks.

[0052] Since complex intermetallic compounds will form between metallic aluminum and stainless steel at high temperatures, the mechanical properties and corrosion resistance to substances such as sulfur of this compound are poor, and the welding area is extremely prone to fracture and is difficult to use.

[0053] Results of mechanical property detection: The product of the comparative example fractures at the joint when the maximum internal hydrostatic pressure is less than 0.5 MPa, while the products prepared according to the example methods can withstand internal hydrostatic pressures of 4.2 MPa / 5.0 MPa / 3.8 MPa (Example 1 / 2 / 3) respectively.

[0054] Figures 3 - 7 Shows the connection interface after soaking in the corrosive liquid at 350 °C for 2 weeks. After separating the connectors after soaking under the above-mentioned conditions, since the compatibility between ceramics and enamels is good, the combination is tight and particularly corrosion-resistant, so only the connection interfaces between stainless steel and enamel and between stainless steel and aluminum solder need to be microscopically detected. From Figures 3 - 6 it can be seen that the connection interface between stainless steel and enamel has better denseness, while there are more cracks at the connection interface between stainless steel and aluminum solder. As Figure 7 shown, it indicates that the alumina ceramics formed after forming an enamel layer on the stainless steel surface and then undergoing treatment and the stainless steel connectors have good mechanical properties and corrosion resistance.

[0055] Where the present invention is not described in detail, it is common knowledge to those skilled in the art.

[0056] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention rather than to limit them. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified and equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A connection process between stainless steel and alumina ceramics, characterized in that The process includes the following steps: 1) Clean the surface to be joined of the stainless steel workpiece; 2) Prepare the enamel slurry, evenly coat it on the surface to be joined of the stainless steel workpiece, and dry it; 3) Put the dried stainless steel workpiece into a kiln for heat treatment; 4) Take out the heat-treated stainless steel workpiece, sequentially stack a glass sealing frit and an alumina ceramic part on the surface to be joined to obtain an assembly, send this assembly into a furnace for heat treatment, and after cooling, obtain a connector of stainless steel and alumina ceramic.

2. The stainless steel and alumina ceramic connection process according to claim 1, characterized in that, The solid content of the enamel slurry is 30% - 90%, and the solvent is water.

3. The stainless steel and alumina ceramic connection process according to claim 2, characterized in that, The composition of the solids in the enamel slurry is: SiO2: 60% - 85%; Al2O3: 3% - 10%; Na2O: 3% - 10%; Li2O: 0.5% - 2.0%; B2O3: 0 - 20%, NiO: 0.3% - 5%; Co2O3: 0.3 - 5%; MnO: 0 - 3%; La2O3: 0 - 3%.

4. The stainless steel and alumina ceramic connection process according to claim 1, characterized in that, The drying conditions in step 2) are: drying temperature 60 - 120°C, drying time 10 - 12 min.

5. The stainless steel and alumina ceramic connection process according to claim 1, characterized in that, The heat treatment conditions in step 3) are: kiln temperature 750 - 1050°C, heat treatment time: 1 - 30 min.

6. The stainless steel and alumina ceramic connection process according to claim 1, wherein, After the heat treatment in step 3), it also includes a step of trimming the joint surface of the heat-treated workpiece, and the thickness of the trimmed enamel layer is 0.05 - 0.5 mm.

7. The stainless steel and alumina ceramic connection process according to claim 1, wherein, The heat treatment conditions in step 4) are: the atmosphere in the furnace is vacuum or inert atmosphere, heat treatment temperature 400 - 1000°C, duration 10 - 240 min.

8. The stainless steel and alumina ceramic connection process according to claim 1, characterized in that, The cooling parameters in step 4) are: cool the assembly at a rate of 1 - 5°C / min to 200°C, and then cool it in the furnace to room temperature.

9. The stainless steel and alumina ceramic connection process according to claim 1, characterized in that, The glass sealing frit used in step 4) is pre-pressed into a glass sealing ring.

10. A connection structure between stainless steel and alumina ceramic, characterized in that The connection structure sequentially includes stainless steel, an enamel layer, a glass layer, and alumina ceramic.

11. The stainless steel and alumina ceramic connection structure according to claim 10, characterized in that, The connection structure is made by using the process described in any one of claims 1 to 9.

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