Method for fiber-reinforced silicon nitride-based ceramic springs

Abstract

The invention discloses a method for fiber-reinforced silicon nitride-based ceramic springs, which belongs to the technical field of ceramic springs and comprises the following steps: preparing slurry, preparing a spring preform, burning off a mold, and hanging and firing; in the slurry preparation, syringa seeds and deionized water are put into a blender, stirred at 55-65 DEG C for 5-8 hours, and filtered to obtain pectin; adding a dispersant polyacrylamide to the pectin solution, stirring evenly, and obtaining a pectin premix; adding silicon nitride powder to the pectin premix, stirring evenly, and obtaining a silicon nitride premix; stirring the silicon nitride premix at 35-45 DEG C, and adding citric acid at the same time, and obtaining slurry after the addition is completed; the fiber-reinforced silicon nitride-based ceramic spring prepared by the invention has good toughness, high strength and high stiffness.

Description

Technical Field

[0001] The invention relates to the technical field of ceramic springs, and in particular to a method for fiber-reinforced silicon nitride-based ceramic springs. Background Art

[0002] Existing ceramic springs such as silicon nitride, zirconium oxide, and aluminum oxide have poor toughness and are prone to brittle fracture during compression, which affects the service life of components such as solid oxide electrolytic cells (SOECs). It is necessary to take certain measures to improve the toughness of ceramic springs.

[0003] The commonly used method is to toughen carbon fibers, but the existing carbon fiber toughening method is to prepare ceramic springs by chemical vapor deposition of carbon fibers, which has the problem of low strength and a relatively small load value during the compression and rebound process, making it difficult to meet the needs of SOEC and aerospace fields.

[0004] Chinese patent CN110937909B discloses a method for preparing a continuous fiber reinforced C / SiC ceramic spring, which designs a special mold structure, uses 3D printing to obtain a cylindrical spring that can be opened and closed, has threads all around, and through holes are distributed between the threads. It is divided into three sections along the axial direction, and the middle mold is longer than the ceramic molds at both ends; the mold is used to prepare a spring preform, and the spring preform is toughened by chemical vapor infiltration. However, although the stiffness of the ceramic spring prepared by this method at room temperature and in air at 1000°C is low, the stiffness at room temperature is 0.984N / mm, and the stiffness in air at 1000°C is 0.351N / mm. Summary of the invention

[0005] In view of the deficiencies in the prior art, the present invention provides a method for fiber-reinforced silicon nitride-based ceramic springs. The prepared fiber-reinforced silicon nitride-based ceramic springs have good toughness, high strength and high stiffness.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is as follows:

[0007] The method for fiber-strengthening silicon nitride-based ceramic springs comprises the following steps: preparing slurry, preparing a spring preform, burning off the mold, and hanging and firing;

[0008] The slurry is prepared by putting the prickly ash seeds and deionized water into a blender, stirring at 55-65° C. and 100-150 rpm for 5-8 hours, and filtering to obtain pectin; adding a dispersant polyacrylamide to the pectin solution, stirring evenly, to obtain a pectin premix; adding silicon nitride powder to the pectin premix, stirring evenly, to obtain a silicon nitride premix; stirring the silicon nitride premix at 35-45° C., and slowly adding citric acid, controlling the addition time of the citric acid to be 5-20 minutes, and obtaining a slurry after the addition is completed;

[0009] In the prepared slurry, the mass ratio of the lychee seeds to deionized water is 1:10-40;

[0010] The mass fraction of silicon nitride powder in the silicon nitride premix is ​​40-50%;

[0011] The mass of the polyacrylamide accounts for 0.5-2% of the mass of the silicon nitride powder;

[0012] The mass of the citric acid accounts for 0.5-2% of the mass of the silicon nitride premix;

[0013] The preparation of the spring preform comprises the following steps: mold forming, mold grouting, and curing forming;

[0014] The mold forming comprises forming a ceramic spring resin mold by 3D printing to obtain a mold;

[0015] In the mold forming, the material of the mold is a high temperature resistant resin, and the mold has a spiral hollow structure;

[0016] The wall thickness of the mold is 100-200 μm;

[0017] The mold grouting is to braid the inorganic fiber bundles into fiber ropes, control the twisting viscosity to be 8-12 twists / m, then insert a fiber rope into the mold, and then inject the slurry into the mold through an injection pump to ensure that the slurry completely fills the mold to obtain a grouting mold;

[0018] In the mold grouting, the inorganic fiber bundle is one of a carbon fiber bundle or a boron nitride fiber bundle;

[0019] Each inorganic fiber bundle contains 100-500 inorganic fibers;

[0020] When the inorganic fiber bundle is a carbon fiber bundle, the diameter of the inorganic fiber is 5-8 μm, and when the inorganic fiber bundle is a boron nitride fiber bundle, the diameter of the inorganic fiber is 8-13 μm;

[0021] The curing molding is to put the mold after grouting into an oven for curing molding, control the curing temperature to be 35-45°C, and the time to be 1-5h to obtain a mold after curing molding;

[0022] The mold is burned out, and the mold after solidification is placed in a sintering furnace for sintering to obtain a ceramic spring blank;

[0023] In the burn-out mold, the sintering method is: starting from room temperature, heating to 183-195°C at a heating rate of 0.4-0.6°C / min, and keeping warm for 55-65min; heating to 350-370°C at a heating rate of 0.2-0.3°C / min, and keeping warm for 110-130min; heating to 650-690°C at a heating rate of 0.7-0.9°C / min, and keeping warm for 170-190min; heating to 900-1000°C at a heating rate of 1.5-2.5°C / min, and keeping warm for 120min;

[0024] In the above-mentioned burning out of the mold, the temperature is raised to 650-690° C. in an inert gas atmosphere;

[0025] The inert gas is one of nitrogen or argon;

[0026] The hanging firing process uses carbon fiber to fix the ceramic spring blank, places a gasket at the bottom of the spring, and then sintering;

[0027] During the hanging firing, the sintering method is: starting from room temperature, heating to 950-1050°C at a heating rate of 9-11°C / min, and keeping warm for 25-35min; heating to 1480-1520°C at a heating rate of 4-6°C / min, and keeping warm for 110-130min; heating to 1700-1880°C at a heating rate of 4-6°C / min, and keeping warm for 70min, to obtain a fiber-reinforced silicon nitride-based ceramic spring.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] (1) In the method for fiber-reinforced silicon nitride-based ceramic springs of the present invention, in the slurry preparation step, schizolinone seed gum is used as a binder. The schizolinone seed gum is not only highly viscous but also environmentally friendly and non-toxic. In the mold burning step, thermal decomposition can occur to improve the compression, stiffness, strength and toughness of the ceramic spring. In the mold burning step, after the schizolinone seed gum is completely decomposed, further heat preservation is performed at 900-1000°C, which can improve the internal densification of the ceramic spring and improve the compression, stiffness, strength and toughness of the ceramic spring. In the hanging tip firing step, gradient heating is performed, which is also beneficial to the internal densification of the ceramic spring and improves the compression, stiffness, strength and toughness of the ceramic spring.

[0030] (2) The fiber-reinforced silicon nitride-based ceramic spring prepared by the method of the present invention has good toughness, high strength and stiffness. For a ceramic spring with an outer diameter of 20 mm and a height of 35 mm, the compression is 23-25%, the stiffness is 15-20 N / mm, the strength is 571-593 MPa, and the toughness is 10.2-10.9 MPa·m 1 / 2 . DETAILED DESCRIPTION

[0031] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, the specific implementation methods of the present invention are now described.

[0032] Example 1

[0033] The method for fiber-strengthening silicon nitride-based ceramic spring is specifically:

[0034] 1. Prepare slurry: put the seeds of Ligustrum lucidum and deionized water in a blender at a mass ratio of 1:10, stir at 60°C and 100 rpm for 5 hours, and filter to obtain pectin; add the dispersant polyacrylamide to the pectin solution and stir evenly to obtain a pectin premix; add silicon nitride powder to the pectin premix and stir evenly to obtain a silicon nitride premix; stir the silicon nitride premix at 35°C and slowly add citric acid at the same time, controlling the addition time of citric acid to be 5 minutes, and after the addition is completed, obtain slurry;

[0035] The mass fraction of silicon nitride powder in the silicon nitride premix is ​​40%;

[0036] The mass of the polyacrylamide accounts for 0.5% of the mass of the silicon nitride powder;

[0037] The mass of the citric acid accounts for 0.5% of the mass of the silicon nitride premixed solution;

[0038] 2. Preparation of spring preform:

[0039] (1) Mold forming: a ceramic spring resin mold is formed by 3D printing to obtain a mold;

[0040] The mold is made of high temperature resistant resin and has a spiral hollow structure to facilitate slurry injection. In order to facilitate the removal of the mold by sintering, the wall thickness of the mold is 100 μm.

[0041] (2) Mold grouting: The inorganic fiber bundles are braided into fiber ropes, and the twisting viscosity is controlled to be 10 twists / m. Then a fiber rope is inserted into the mold, and the slurry is injected into the mold through an injection pump to ensure that the slurry completely fills the mold to obtain a mold after grouting;

[0042] The inorganic fiber bundle is a carbon fiber bundle, each inorganic fiber bundle contains 100 carbon fibers, and the diameter of the carbon fiber is 5 μm;

[0043] (3) Curing and molding: Put the mold after grouting into an oven for curing and molding, control the curing temperature to 35°C and the time to 1 hour to obtain the mold after curing and molding;

[0044] 3. Burning out the mold: Put the mold after curing into the sintering furnace for sintering. In order to remove the mold and the organic matter in the mold, the sintering method is controlled as follows: starting from room temperature, heating up to 190°C at a heating rate of 0.5°C / min, and keeping warm for 60 minutes; heating up to 350°C at a heating rate of 0.2°C / min, and keeping warm for 120 minutes; heating up to 650°C at a heating rate of 0.8°C / min, and keeping warm for 180 minutes; heating up to 900°C at a heating rate of 2°C / min, and keeping warm for 120 minutes to obtain a ceramic spring blank;

[0045] In order to avoid oxidation of silicon nitride, the process is carried out in an inert gas atmosphere after the temperature is raised to 650°C;

[0046] 4. Hanging firing: Use carbon fiber to fix the ceramic spring blank, specifically, tie the carbon fiber to the top of the ceramic spring. The purpose of fixing is to keep the spring in an upright state during the sintering process to avoid skewing, which will cause uneven pitch of the prepared ceramic spring. Put a gasket at the bottom of the spring to prevent the spring from stretching due to its own gravity, causing uneven pitch. Then sintering is carried out, and the sintering method is controlled as follows: starting from room temperature, heat up to 1000℃ at a heating rate of 10℃ / min, and keep warm for 30min; heat up to 1500℃ at a heating rate of 5℃ / min, and keep warm for 120min; heat up to 1700℃ at a heating rate of 5℃ / min, and keep warm for 70min to obtain a fiber-reinforced silicon nitride-based ceramic spring.

[0047] Example 2

[0048] The method for fiber-strengthening silicon nitride-based ceramic spring is specifically:

[0049] 1. Prepare slurry: put the seeds of Ligustrum lucidum and deionized water in a blender at a mass ratio of 1:25, stir at 60°C and 120rpm for 6h, and filter to obtain pectin; add dispersant polyacrylamide to the pectin solution and stir evenly to obtain a pectin premix; add silicon nitride powder to the pectin premix and stir evenly to obtain a silicon nitride premix; stir the silicon nitride premix at 40°C and slowly add citric acid at the same time, controlling the addition time of citric acid to be 15min, and after the addition is completed, obtain slurry;

[0050] The mass fraction of silicon nitride powder in the silicon nitride premix is ​​45%;

[0051] The mass of the polyacrylamide accounts for 1.5% of the mass of the silicon nitride powder;

[0052] The mass of the citric acid accounts for 1.5% of the mass of the silicon nitride premix;

[0053] 2. Prepare the spring preform:

[0054] (1) Mold forming: a ceramic spring resin mold is formed by 3D printing to obtain a mold;

[0055] The mold is made of high temperature resistant resin and has a spiral hollow structure to facilitate slurry injection. In order to facilitate the removal of the mold by sintering, the wall thickness of the mold is 150 μm.

[0056] (2) Mold grouting: The inorganic fiber bundles are braided into fiber ropes, and the twisting viscosity is controlled to be 10 twists / m. Then a fiber rope is inserted into the mold, and the slurry is injected into the mold through an injection pump to ensure that the slurry completely fills the mold to obtain a mold after grouting;

[0057] The inorganic fiber bundle is a boron nitride fiber bundle, each inorganic fiber bundle contains 300 boron nitride fibers, and the diameter of the boron nitride fiber is 10 μm;

[0058] (3) Curing and molding: Put the mold after grouting into an oven for curing and molding, control the curing temperature to 40°C and the time to 3 hours to obtain the mold after curing and molding;

[0059] 3. Burning out the mold: Put the mold after curing into the sintering furnace for sintering. In order to remove the mold and the organic matter in the mold, the sintering method is controlled as follows: starting from room temperature, heating up to 190°C at a heating rate of 0.5°C / min, and keeping warm for 60 minutes; heating up to 360°C at a heating rate of 0.2°C / min, and keeping warm for 120 minutes; heating up to 670°C at a heating rate of 0.8°C / min, and keeping warm for 180 minutes; heating up to 950°C at a heating rate of 2°C / min, and keeping warm for 120 minutes to obtain a ceramic spring blank;

[0060] In order to avoid oxidation of silicon nitride, the temperature was raised to 670°C and then carried out in an inert gas atmosphere;

[0061] 4. Hanging firing: Use carbon fiber to fix the ceramic spring blank, specifically, tie the carbon fiber to the top of the ceramic spring. The purpose of fixing is to keep the spring in an upright state during the sintering process to avoid skewing, which will cause uneven pitch of the prepared ceramic spring. Put a gasket at the bottom of the spring to prevent the spring from stretching due to its own gravity, causing uneven pitch. Then sintering is carried out, and the sintering method is controlled as follows: starting from room temperature, heat up to 1000℃ at a heating rate of 10℃ / min, and keep warm for 30min; heat up to 1500℃ at a heating rate of 5℃ / min, and keep warm for 120min; heat up to 1800℃ at a heating rate of 5℃ / min, and keep warm for 70min to obtain a fiber-reinforced silicon nitride-based ceramic spring.

[0062] Example 3

[0063] The method for fiber-strengthening silicon nitride-based ceramic spring is specifically:

[0064] 1. Prepare slurry: put the seeds of Ligustrum lucidum and deionized water in a blender at a mass ratio of 1:40, stir at 60°C and 150 rpm for 8 hours, and filter to obtain pectin; add the dispersant polyacrylamide to the pectin solution and stir evenly to obtain a pectin premix; add silicon nitride powder to the pectin premix and stir evenly to obtain a silicon nitride premix; stir the silicon nitride premix at 45°C and slowly add citric acid at the same time, controlling the addition time of citric acid to be 20 minutes, and after the addition is completed, obtain slurry;

[0065] The mass fraction of silicon nitride powder in the silicon nitride premix is ​​50%;

[0066] The mass of the polyacrylamide accounts for 2% of the mass of the silicon nitride powder;

[0067] The mass of the citric acid accounts for 2% of the mass of the silicon nitride premix;

[0068] 2. Prepare the spring preform:

[0069] (1) Mold forming: a ceramic spring resin mold is formed by 3D printing to obtain a mold;

[0070] The mold is made of high temperature resistant resin and has a spiral hollow structure to facilitate slurry injection. In order to facilitate removal of the mold by sintering, the wall thickness of the mold is 200 μm.

[0071] (2) Mold grouting: The inorganic fiber bundles are braided into fiber ropes, and the twisting viscosity is controlled to be 10 twists / m. Then a fiber rope is inserted into the mold, and the slurry is injected into the mold through an injection pump to ensure that the slurry completely fills the mold to obtain a mold after grouting;

[0072] The inorganic fiber bundle is a carbon fiber bundle, each inorganic fiber bundle contains 500 carbon fibers, and the diameter of the carbon fiber is 8 μm;

[0073] (3) Curing and molding: Put the mold after grouting into an oven for curing and molding, control the curing temperature to 45°C and the time to 5 hours to obtain the mold after curing and molding;

[0074] 3. Burning out the mold: Put the mold after curing into the sintering furnace for sintering. In order to remove the mold and the organic matter in the mold, the sintering method is controlled as follows: starting from room temperature, heating up to 190°C at a heating rate of 0.5°C / min, and keeping warm for 60 minutes; heating up to 370°C at a heating rate of 0.2°C / min, and keeping warm for 120 minutes; heating up to 690°C at a heating rate of 0.8°C / min, and keeping warm for 180 minutes; heating up to 1000°C at a heating rate of 2°C / min, and keeping warm for 120 minutes to obtain a ceramic spring blank;

[0075] In order to avoid oxidation of silicon nitride, the temperature was raised to 690°C and then carried out in an inert gas atmosphere;

[0076] 4. Hanging firing: Use carbon fiber to fix the ceramic spring blank, specifically, tie the carbon fiber to the top of the ceramic spring. The purpose of fixing is to keep the spring in an upright state during the sintering process to avoid skewing, which leads to uneven pitch of the prepared ceramic spring. Put a gasket at the bottom of the spring to prevent the spring from stretching due to its own gravity, causing uneven pitch. Then sintering is carried out, and the sintering method is controlled as follows: starting from room temperature, heat up to 1000℃ at a heating rate of 10℃ / min, and keep warm for 30min; heat up to 1500℃ at a heating rate of 5℃ / min, and keep warm for 120min; heat up to 1880℃ at a heating rate of 5℃ / min, and keep warm for 70min to obtain a fiber-reinforced silicon nitride-based ceramic spring.

[0077] Comparative Example 1

[0078] On the basis of the method of Example 2, in the first step of preparing the slurry, the addition of the lychee seeds is omitted, and a common slurry formula for gel casting is used. Specifically, the first step of preparing the slurry is changed to:

[0079] Mix polymethyl methacrylate, polyethylene glycol 600, anhydrous ethanol, and silicon nitride powder in a mass ratio of 15:6:20:100, stir evenly, and obtain a slurry;

[0080] The remaining operations are the same as those in Example 2.

[0081] Comparative Example 2

[0082] Based on the method of Example 2, in the third step of burning off the mold, the step of keeping warm at 950° C. is omitted. Specifically, the third step of burning off the mold is changed to:

[0083] The solidified mold is placed in a sintering furnace for sintering. In order to remove the mold and organic matter in the mold, the sintering method is controlled as follows: starting from room temperature, the temperature is increased to 190°C at a heating rate of 0.5°C / min and kept at this temperature for 60 minutes; the temperature is increased to 360°C at a heating rate of 0.2°C / min and kept at this temperature for 120 minutes; the temperature is increased to 670°C at a heating rate of 0.8°C / min and kept at this temperature for 180 minutes to obtain a ceramic spring blank;

[0084] In order to prevent oxidation of silicon nitride, the temperature was raised to 670° C. and then the process was carried out in an inert gas atmosphere.

[0085] Comparative Example 3

[0086] On the basis of the method of Example 2, in the fourth step of hanging and firing, the gradient heating process is omitted. Specifically, the third step of burning off the mold is changed to:

[0087] The ceramic spring blank is fixed by using carbon fiber, specifically, the carbon fiber is tied to the top of the ceramic spring. The purpose of fixation is to keep the spring in an upright state during the sintering process to avoid skewing, which leads to uneven pitch of the prepared ceramic spring. A gasket is placed at the bottom of the spring to prevent the spring from stretching due to its own gravity, resulting in uneven pitch. Then sintering is carried out, and the sintering method is controlled as follows: starting from room temperature, heating up to 1800°C at a heating rate of 10°C / min, and keeping warm for 220 minutes to obtain a fiber-reinforced silicon nitride-based ceramic spring.

[0088] Performance Testing

[0089] Using the same specification of mold, fiber-reinforced silicon nitride-based ceramic springs were prepared according to the methods of Examples 1-3 and Comparative Examples 1-3, and the outer diameter, height, compression, stiffness, strength, and toughness of the ceramic springs were tested. The test results are as follows:

[0090]

[0091] It can be seen from the above results that the compression, stiffness, strength and toughness of the ceramic springs prepared in Comparative Examples 1-3 are worse than those of the ceramic springs prepared in Examples 1-3.

[0092] Unless otherwise specified, all percentages used in the present invention are by mass.

[0093] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for fiber-toughening a silicon nitride-based ceramic spring, characterized in that: The method comprises the following steps: preparing slurry, preparing spring preform, burning out the mold, hanging and firing; The slurry is prepared by putting the prickly ash seeds and deionized water into a blender, stirring at 55-65° C. for 5-8 hours, and filtering to obtain pectin; adding a dispersant polyacrylamide to the pectin solution, stirring evenly, to obtain a pectin premix; adding silicon nitride powder to the pectin premix, stirring evenly, to obtain a silicon nitride premix; stirring the silicon nitride premix at 35-45° C., while adding citric acid, to obtain a slurry after the addition is completed; In the prepared slurry, the mass fraction of silicon nitride powder in the silicon nitride premix is ​​40-50%; The mass of the polyacrylamide accounts for 0.5-2% of the mass of the silicon nitride powder; The mass of the citric acid accounts for 0.5-2% of the mass of the silicon nitride premix; The preparation of the spring preform comprises the following steps: mold forming, mold grouting, and curing forming; The mold grouting is to braid the inorganic fiber bundle into a fiber rope, control the twisting twist to be 8-12 twists / m, then insert a fiber rope into the mold, and then inject the slurry into the mold through an injection pump to obtain a mold after grouting; The mold is burned out, and the mold after solidification is placed in a sintering furnace for sintering to obtain a ceramic spring blank; In the burn-out mold, the sintering method is: starting from room temperature, heating to 183-195°C at a heating rate of 0.4-0.6°C / min, and keeping warm for 55-65min; heating to 350-370°C at a heating rate of 0.2-0.3°C / min, and keeping warm for 110-130min; heating to 650-690°C at a heating rate of 0.7-0.9°C / min, and keeping warm for 170-190min; heating to 900-1000°C at a heating rate of 1.5-2.5°C / min, and keeping warm for 120min; The hanging firing process uses carbon fiber to fix the ceramic spring blank, places a gasket at the bottom of the spring, and then sintering; During the hanging firing, the sintering method is: starting from room temperature, heating to 950-1050°C at a heating rate of 9-11°C / min, and keeping warm for 25-35min; heating to 1480-1520°C at a heating rate of 4-6°C / min, and keeping warm for 110-130min; heating to 1700-1880°C at a heating rate of 4-6°C / min, and keeping warm for 70min, to obtain a fiber-reinforced silicon nitride-based ceramic spring.

2. The method for fiber-toughening silicon nitride-based ceramic spring according to claim 1, characterized in that: In the prepared slurry, the mass ratio of the lychee seeds to deionized water is 1:10-40; The citric acid is added for 5-20 minutes.

3. The method for fiber-toughening silicon nitride-based ceramic spring according to claim 1, characterized in that: The mold forming comprises forming a ceramic spring resin mold by 3D printing to obtain a mold; In the mold forming, the material of the mold is a high temperature resistant resin, and the mold has a spiral hollow structure; The wall thickness of the mold is 100-200 μm.

4. The method for fiber-toughening silicon nitride-based ceramic spring according to claim 1, characterized in that: In the mold grouting, the inorganic fiber bundle is one of a carbon fiber bundle or a boron nitride fiber bundle; Each inorganic fiber bundle contains 100-500 inorganic fibers; When the inorganic fiber bundle is a carbon fiber bundle, the diameter of the inorganic fiber is 5-8 μm. When the inorganic fiber bundle is a boron nitride fiber bundle, the diameter of the inorganic fiber is 8-13 μm.

5. The method for fiber-toughening silicon nitride-based ceramic spring according to claim 1, characterized in that: The curing molding is to put the mold after grouting into an oven for curing molding, control the curing temperature to be 35-45° C., and the time to be 1-5 hours to obtain a mold after curing molding.

6. The method for fiber-toughening silicon nitride-based ceramic spring according to claim 1, characterized in that: In the above-mentioned burning out of the mold, the temperature is raised to 650-690° C. in an inert gas atmosphere; The inert gas is nitrogen or argon.

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