CN116924810B - Method for preparing fiber-toughened silicon carbide ceramic valve element by liquid phase sintering and compression molding - Google Patents

Abstract

The present invention discloses a method for preparing fiber-reinforced silicon carbide ceramic valve parts by liquid phase sintering and pressing, and the specific steps include: preparation of granulation powder, debundling of chopped carbon fibers, coating of debundled carbon fibers with granulation powder, mixing of granulation powder, valve part molding, sintering and post-processing. The silicon carbide ceramic valve parts prepared by the present invention have good toughness, high strength, good performance uniformity and high service reliability; the method of the present invention has simple process, low production cost and high production efficiency, and is suitable for industrial preparation of high-performance silicon carbide ceramic valve parts.

Description

A method for preparing fiber-reinforced silicon carbide ceramic valve parts by liquid phase sintering and pressing

Technical Field

The invention relates to the technical field of silicon carbide ceramic valve component preparation, and in particular to a method for preparing fiber-reinforced silicon carbide ceramic valve components by liquid phase sintering and pressing.

Background Art

Silicon carbide ceramics have excellent properties such as high hardness, high strength, high temperature resistance, oxidation resistance, corrosion resistance, wear resistance, thermal shock resistance, and good chemical stability, making it an ideal material for preparing high-performance valves. Ceramic valves made using the excellent properties of silicon carbide ceramics have better performance than traditional metal valves and plastic valves, and are particularly suitable for harsh industrial and mining environments with strong corrosion, severe wear and erosion, and high temperatures, such as mining, thermal power, petroleum, chemical industry, papermaking, polysilicon, metallurgy, and other fields. At present, silicon carbide ceramics have been used to make valve plates, valve balls, gate discs, valve seats and other valve parts.

However, compared with metals and plastics, silicon carbide ceramics have poor toughness, especially impact resistance. When there are high-speed particles in the fluid, the impact of particles may cause impact cracks in the valve parts, which in turn leads to damage to the valve parts, reducing the service reliability of the valve parts and failing to give full play to the excellent performance of silicon carbide ceramics. Therefore, toughening silicon carbide ceramics can give full play to the excellent performance of silicon carbide ceramics and improve the service reliability of silicon carbide ceramic valve parts.

Liquid phase sintering can improve the strength and toughness of SiC ceramic materials. However, studies have shown that when YAG is used as a liquid phase sintering aid, the body cannot contain too much carbon, because a high carbon content will lead to a decrease in the density of the sample, and the higher the carbon content, the more obvious the decrease _in density. This may be because carbon will react with _Al2O3 and _Y2O3 at high temperatures, which is not conducive to the formation of YAG liquid phase and densification. This means that a large amount of organic matter should not be added _to the YAG liquid phase sintering formula, but a low organic content will reduce the strength of the green body and cannot be processed by turning. Chinese patent CN201310578016.6 discloses the use of a low-temperature debinding method to remove organic carbon from the liquid phase sintering formula to avoid the adverse effects of high carbon content. However, when the green body size is large, it is difficult to completely remove the organic matter inside the body through low-temperature insulation, and heating in the air easily leads to oxidation of SiC micropowder, affecting the densification of SiC ceramics.

Chinese patent CN202210133185.8 discloses a technical solution of this technical team, including preparing granulation powder, adding toughening fiber, pre-setting carbon fiber braid, impregnation, and then pressing, ramming, sintering and other steps. This solution does have a good toughening effect, but its cost is relatively high and the process is relatively complicated, which is suitable for products with high economic added value. For products with relatively small economic added value, this process is not conducive to improving the market competitiveness of the product.

Therefore, there is an urgent need to further study and optimize the toughening process of liquid phase sintered silicon carbide ceramics, so that the toughening of liquid phase sintered silicon carbide ceramic valve parts can be achieved in a more economical and simple way, which is of great significance to promoting the technological progress of the silicon carbide ceramic valve parts industry.

Summary of the invention

In view of this, the purpose of the present invention is to provide a method for preparing fiber-reinforced silicon carbide ceramic valve components by liquid phase sintering and pressing to address the deficiencies of the prior art, which can achieve the purpose of toughening silicon carbide ceramic valve components in an economical and simple way.

In order to achieve the above object, the present invention adopts the following technical solutions:

A method for preparing fiber-reinforced silicon carbide ceramic valve parts by liquid phase sintering and pressing, wherein the raw materials for preparing the ceramic valve parts include silicon carbide ceramic matrix material and toughening material; the matrix material includes 100 parts of silicon carbide micropowder, 3-12 parts of mixed powder of aluminum oxide and yttrium oxide, 5-10 parts of adhesive, 3-12 parts of silicon powder, 0.5-3 parts of surfactant and 0.5-2 parts of dispersant, by weight; the toughening material is chopped carbon fiber, and the addition amount of the chopped carbon fiber is 0.1-15% of the total amount of the matrix material;

The preparation method specifically comprises the following steps:

(1) Preparation of granulated powder

The silicon carbide ceramic matrix material is weighed according to the ratio, deionized water is added, and the amount of deionized water is 0.9-1.5 times the mass of the silicon carbide micropowder, and then ball milling is performed for 8-20 hours to obtain a silicon carbide ceramic slurry; the silicon carbide ceramic slurry is spray granulated to obtain granulated powder, and sieved to take the granulated powder between 10-100 meshes for standby use; wherein the moisture content of the granulated powder is 0.5-1.2%, and the mass ratio of the granulated powder with a particle size of 60-180 meshes is greater than 90%;

(2) Pretreatment of chopped carbon fiber

Weigh the prepared chopped carbon fibers, add them into a ball mill with a polyurethane liner, add polyurethane balls into the ball mill, and perform roller milling for 1-5 hours to make the chopped carbon fiber bundles fluffy;

Add deionized water to the ball mill, continue roller milling for 1-8 hours to initially debundle the chopped carbon fiber bundles, filter, add the filtered chopped carbon fiber to a polyurethane ball mill, add anhydrous ethanol and polyurethane balls to the ball mill, roller mill for 1-8 hours to further debundle the chopped carbon fiber bundles, filter, and dry at 50-80° C. to obtain debundled chopped carbon fiber for standby use;

(3) Debundled chopped carbon fiber coated granulated powder

The debundled chopped carbon fibers prepared in step (2) are added to a coating machine, the coating machine is started, and the debundled chopped carbon fibers begin to rotate with the coating machine, and the chopped carbon fibers are sprayed with an alcohol solution containing phenolic resin, carbon black and silicon powder to humidify and thicken them, and then the 10-100 mesh silicon carbide granulated powder in step (1) is continuously added, and the alcohol solution is continuously sprayed, so that the debundled chopped carbon fibers adhere to the granulated powder during the rotation of the coating machine, to obtain silicon carbide granulated powder coated with chopped carbon fibers, and then the granulated powder coated with carbon fibers is dried at a temperature not higher than 70° C. to have a moisture content of 0.5-1.2%;

(4) Silicon carbide granulated powder mixing

The granulated powder obtained in step (3) and the other granulated powders except 10-100 mesh in step (1) are rotated in a sugar coating machine to mix evenly;

(5) Valve molding

The granulated powder obtained in step (4) is pressed and molded to obtain a valve body green body, wherein the density of the valve body green body is not less than 1.7 g/cm ³ ;

(6) Valve parts sintering

The processed valve green body is placed in a vacuum sintering furnace, and the temperature is first raised to 1450-1600°C and kept for 1-6 hours, so that the nano silicon powder and nano carbon powder sprayed on the debundled carbon fiber yarn react in situ to generate silicon carbide, thereby improving the interface bonding strength between the carbon fiber and the silicon carbide ceramic matrix, and protecting the carbon fiber yarn bundle from the erosion of the alumina and yttrium oxide liquid phase; then the temperature is continued to be raised to 1750-2000°C, and sintered for 0.5-5 hours to obtain a sintered body of the silicon carbide ceramic valve component;

(7) Post-processing of valve parts

The silicon carbide ceramic valve component sintered body is processed after grinding and polishing to obtain the silicon carbide ceramic valve component with required specifications, shapes and sizes.

Preferably, the silicon carbide powder _D50 in step (1) is 0.5±0.2 μm; the molar ratio of aluminum oxide to yttrium oxide is 5:3, and _D50 is 1-3 μm; the _D50 of the silicon powder is not greater than 500 nm. Calculated based on the theoretical carbon content of the binder, the amount of silicon powder added is greater than the theoretical carbon content of the binder, which can avoid the influence of residual carbon on liquid phase sintered silicon carbide ceramics.

Preferably, in step (1), the binder is phenolic resin, polyvinyl alcohol or carboxymethyl cellulose; the surfactant is stearic acid or fatty acid glyceride; and the dispersant is tetramethylammonium hydroxide or polyacrylic acid.

Preferably, the chopped carbon fiber in step (2) is a high-strength carbon fiber with a tensile strength of not less than 3500 MPa; wherein the length of the chopped carbon fiber is less than 5 mm and the diameter of the filament bundle is less than 500 μm.

Preferably, the diameter of the polyurethane balls in step (2) is 10-50 mm; the mass ratio of the added polyurethane balls to the chopped carbon fibers is (0.6-1.5):1; the mass ratio of the deionized water to the chopped carbon fibers is (0.8-2):1; and the mass ratio of the anhydrous ethanol to the chopped carbon fibers is (0.8-1.5):1.

Preferably, in the alcohol solution of step (3), the mass fraction of phenolic resin is 1-10%, the mass fraction of carbon black is 1-10%, and the mass fraction of silicon powder is 1-20%; and the carbon black is nano-carbon powder with _D50 not greater than 50nm; and the molar ratio of carbon black to silicon powder is 1:(1-1.2).

The beneficial effects of the present invention are:

1) Compared with the toughening process using a preset two-dimensional or three-dimensional carbon fiber reinforcement, the technical solution of the present invention is simpler, the manufacturing cost is lower, and it still has a good toughening effect, and is particularly suitable for industrial production.

2) Compared with the toughening process of directly mixing chopped carbon fiber bundles with granulated powder, the technical solution of the present invention can improve the dispersion uniformity of carbon fibers, thereby improving the uniformity and consistency of the obtained products and increasing the service reliability of the products.

3) The carbon fiber debundling process used in the present invention is relatively mild and will not cause a significant decrease in the strength of the carbon fiber precursor, thereby being able to better exert the reinforcing and toughening effects of the carbon fiber.

4) After the carbon fiber is unbundled, the diameter of the toughened carbon fiber bundle is smaller, and the inhibitory effect on the densification of liquid-phase sintered silicon carbide ceramics is weakened, which is conducive to obtaining a higher density, thereby improving the hardness and wear resistance of the product.

5) After the carbon fiber is unbundled, it is coated on the surface of the silicon carbide granulated powder. After pressing and molding, the unbundled carbon fiber bundles can be overlapped to form a three-dimensional spatial network, which has a similar effect of toughening a preset three-dimensional braided body, but the technical solution of the present invention is relatively simple.

6) The present invention adds alumina and yttrium oxide as liquid phase additives, and pressureless liquid phase sintering can also improve the toughness and strength of silicon carbide ceramics, and can reduce the sintering temperature. Resin, carbon black and silicon powder are sprayed on the debundled chopped carbon fiber filaments, and silicon carbide can be generated by in-situ reaction when kept at 1450℃-1600℃. On the one hand, it can improve the bonding strength between the debundled carbon fiber bundle and the silicon carbide ceramic, and on the other hand, it can reduce the erosion of the carbon fiber bundle by the alumina and yttrium oxide liquid. Pre-adding silicon powder in the formula can make it react with the cracked carbon of organic matter such as the binder to generate silicon carbide, avoiding the reaction of residual carbon in the binder with alumina and yttrium oxide.

7) Compared with the existing carbon fiber toughened silicon carbide ceramic process, the process of the present invention is simple, has low production cost, high production efficiency, and has a good toughening effect. It has obvious comprehensive advantages in cost and performance and is particularly suitable for industrial pressing and molding to prepare high-performance silicon carbide ceramic valve parts.

DETAILED DESCRIPTION

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

Example 1

A method for preparing a fiber-reinforced silicon carbide ceramic valve component by liquid phase sintering and pressing, comprising the following steps:

(1) Preparation of granulated powder

Weigh the matrix materials according to the proportion: 100 parts of silicon carbide powder, 5 parts of mixed powder of aluminum oxide and yttrium oxide, 8 parts of phenolic resin, 7.5 parts of silicon powder, 0.6 parts of stearic acid, and 0.6 parts of tetramethylammonium hydroxide, wherein the molar ratio of aluminum oxide to yttrium oxide is 5:3;

Then, the weighed matrix material was added into 110 parts of deionized water, and ball-milled in a drum ball mill for 10 hours to obtain silicon carbide ceramic slurry;

The silicon carbide ceramic slurry is then sprayed and granulated using a centrifugal spray tower to obtain granulated powder; the moisture content of the granulated powder is measured to be 0.8%, and the mass ratio of the particle size of 60-180 mesh in the granulated powder is 91.2%;

The above granulated powder was sieved, and the granulated powder with mesh size between 10 and 100 was taken out, and the weight was 12.8 parts, and it was set aside.

(2) Pretreatment of chopped carbon fiber

Weigh 100 parts of 3.0 mm long chopped carbon fibers, add them into a ball mill with a polyurethane liner, weigh 30 parts of 15 mm diameter polyurethane balls, and 60 parts of 40 mm diameter polyurethane balls, and roll mill for 3 hours to make the chopped carbon fiber bundles fluffy;

Then, 120 parts of deionized water were added to the ball mill, and the ball mill was performed for 5 hours to initially debundle the chopped carbon fiber bundles.

The above-mentioned initially debonded chopped carbon fiber bundle is filtered, and then added to a polyurethane ball mill, 90 parts of anhydrous ethanol, 30 parts of polyurethane balls with a diameter of 15 mm, and 60 parts of polyurethane balls with a diameter of 40 mm are added to the ball mill, and roller milling is performed for 6 hours to further debond the chopped carbon fiber bundle, and then filtered and dried at 60° C. to obtain debonded chopped carbon fibers for standby use;

(3) Debundled chopped carbon fiber coated granulated powder

Weigh 4 parts of the debundled chopped carbon fibers prepared in step (2), add them into a coating machine, start the coating machine, make the debundled chopped carbon fibers start to rotate with the coating machine, spray humidify and viscosity-enhance the chopped carbon fibers with an alcohol solution containing 2% by mass of phenolic resin, 3% by mass of carbon black and 7% by mass of silicon powder, then continuously add the 10-100 mesh silicon carbide granulated powder prepared in step (1), and continuously spray the alcohol solution containing phenolic resin, so that the debundled chopped carbon fibers adhere to the granulated powder during the rotation of the coating machine, to obtain silicon carbide granulated powder coated with chopped carbon fibers, until 12.8 parts of 10-100 mesh silicon carbide granulated powder are completely added.

The granulated powder coated with the chopped carbon fiber is then dried at 55° C. to make its moisture content 0.7%.

(4) Silicon carbide granulated powder mixing

The coated granulated powder obtained in step (3) and the other granulated powders except 10-100 mesh in step (1) are rotated in a sugar coating machine and mixed evenly.

(5) Valve molding

The granulated powder obtained in step (4) was placed in a steel mold, compacted, flattened, and compression molded to obtain a disk with a diameter of 123 mm and a thickness of 25 mm. The green density was measured to be 1.81 g/cm ³ .

The pressed disc was dried at 65° C. for 10 h and set aside.

(6) Valve parts sintering

The dried valve plate green body is placed in a vacuum sintering furnace, first heated to 1500°C and kept warm for 3 hours, so that the nano-silicon powder and nano-carbon powder sprayed on the debundled carbon fiber filaments react in situ to generate silicon carbide, thereby improving the interfacial bonding strength between the carbon fiber and the silicon carbide ceramic matrix, and allowing the carbon produced by the decomposition of organic matter in the green body to react with the added silicon powder to generate silicon carbide, and then sintered at 1880°C for 3 hours to obtain a silicon carbide ceramic valve plate sintered body.

(7) Post-processing of valve parts

The valve surface is surface-grinded to obtain a silicon carbide ceramic valve plate with a diameter of 100 mm, a thickness of 20 mm, and a surface roughness of 5 microns.

After testing, the obtained silicon carbide ceramic valve plate has a relative density of 98.3%, a Vickers microhardness of 24.3 GPa, a three-point bending strength of 582.2 MPa, and a fracture toughness of 8.3 MPa·m ^1/2 .

Example 2

A method for preparing a fiber-reinforced silicon carbide ceramic valve component by liquid phase sintering and pressing, comprising the following steps:

(1) Preparation of granulated powder

The matrix materials were weighed according to the following proportions: 100 parts of silicon carbide micropowder, 3 parts of mixed powder of aluminum oxide and yttrium oxide, 10 parts of phenolic resin, 3 parts of silicon powder, 1.6 parts of stearic acid, and 1.2 parts of tetramethylammonium hydroxide; wherein the molar ratio of aluminum oxide to yttrium oxide was 5:3.

Then, the weighed matrix material was added into 120 parts of deionized water and ball-milled in a drum ball mill for 12 hours to prepare silicon carbide ceramic slurry.

The silicon carbide ceramic slurry is then sprayed and granulated using a centrifugal spray tower to obtain granulated powder; the moisture content of the granulated powder is measured to be 0.9%, and the mass ratio of the particle size of 60-180 mesh in the granulated powder is 91.6%.

The above granulated powder was sieved, and the granulated powder with mesh size between 10 and 100 was taken out, and the weight was 14.7 parts, and it was set aside.

(2) Pretreatment of chopped carbon fiber

Weigh 100 parts of 3.5 mm long chopped carbon fibers, add them into a ball mill with a polyurethane liner, weigh 35 parts of 15 mm diameter polyurethane balls, and 70 parts of 40 mm diameter polyurethane balls, and roll mill for 4 hours to make the chopped carbon fiber bundles fluffy;

Then, 130 parts of deionized water were added to the ball mill, and the ball mill was performed for 6 hours to initially debundle the chopped carbon fiber bundles.

The above-mentioned initially debonded chopped carbon fiber bundle is filtered and then added to a polyurethane ball mill. Then 100 parts of anhydrous ethanol, 30 parts of polyurethane balls with a diameter of 15 mm and 60 parts of polyurethane balls with a diameter of 40 mm are added to the ball mill. Roller ball milling is performed for 6 hours to further debond the chopped carbon fiber bundle. The chopped carbon fiber bundle is then filtered and dried at 65°C to obtain debonded chopped carbon fiber for later use.

(3) Debundled chopped carbon fiber coated granulated powder

Weigh 6 parts of the debundled chopped carbon fibers prepared in step (2), add them into a coating machine, start the coating machine, make the debundled chopped carbon fibers start to rotate with the coating machine, spray humidify and thicken the carbon fibers with an alcohol solution containing 3% by mass of phenolic resin, 3% by mass of nano carbon black and 7% by mass of nano silicon powder, then continuously add the 10-100 mesh silicon carbide granulated powder in step 1, and continuously spray the above-mentioned alcohol solution, so that the debundled chopped carbon fibers adhere to the granulated powder during the rotation of the coating machine, to obtain silicon carbide granulated powder coated with chopped carbon fibers, until 14.7 parts of 10-100 mesh silicon carbide granulated powder are completely added.

The granulated powder coated with the chopped carbon fiber is then dried at 60° C. to make its moisture content 0.8%.

(4) Silicon carbide granulated powder mixing

The coated granulated powder obtained in step (3) and the other granulated powders except 10-100 mesh in step (1) are rotated in a sugar coating machine and mixed evenly.

(5) Valve molding

The granulated powder obtained in step (4) was placed in a spherical rubber mold, compacted by vibration, cold isostatically pressed, and turned to obtain a sphere with a diameter of 86 mm. The green density was measured to be 1.84 g/cm ³ .

The pressed disc was dried at 60° C. for 12 hours and set aside.

(6) Valve parts sintering

The dried valve ball green body is placed in a vacuum sintering furnace, first heated to 1550°C and kept warm for 2 hours, so that the nano-silicon powder and nano-carbon powder sprayed on the debundled carbon fiber filaments react in situ to generate silicon carbide, thereby improving the interfacial bonding strength between the carbon fiber and the silicon carbide ceramic matrix, and allowing the carbon produced by the decomposition of organic matter in the green body to react with the added silicon powder to generate silicon carbide, and then sintered at 1850°C for 3 hours to obtain a silicon carbide ceramic valve ball sintered body.

(7) Post-processing of valve parts

The valve ball surface is ground to obtain a silicon carbide ceramic valve ball with a diameter of 70 mm and a surface roughness of 1 micron.

After testing, the relative density of the obtained silicon carbide ceramic valve ball is 98.4%, the Vickers microhardness is 24.1 GPa, the three-point bending strength is 587.4 MPa, and the fracture toughness is 8.6 MPa·m ^1/2 .

Example 3

A method for preparing a fiber-reinforced silicon carbide ceramic valve component by liquid phase sintering and pressing, comprising the following steps:

(1) Preparation of granulated powder

The matrix materials were weighed according to the proportion: 100 parts of silicon carbide micropowder, 12 parts of mixed powder of aluminum oxide and yttrium oxide, 5 parts of phenolic resin, 12 parts of silicon powder, 3 parts of fatty acid glyceride, and 2 parts of polyacrylic acid; wherein the molar ratio of aluminum oxide to yttrium oxide was 5:3.

Then, the weighed matrix material was added into 120 parts of deionized water and ball-milled in a drum ball mill for 15 hours to prepare silicon carbide ceramic slurry.

The silicon carbide ceramic slurry is then sprayed and granulated using a centrifugal spray tower to obtain granulated powder; the moisture content of the granulated powder is measured to be 0.8%, and the mass ratio of the granular particles of 60-180 mesh in the granulated powder is 92.3%.

The above granulated powder was sieved, and the granulated powder with mesh size between 10 and 100 was taken out, and the weight was 13.3 parts, and it was set aside.

(2) Pretreatment of chopped carbon fiber

Weigh 100 parts of 4 mm long chopped carbon fibers, add them into a grinding jar with a polyurethane liner, weigh 30 parts of 20 mm diameter polyurethane balls, and 60 parts of 50 mm diameter polyurethane balls, and roll mill for 4 hours to make the chopped carbon fiber bundles fluffy;

Then, 130 parts of deionized water were added to the ball mill, and the ball mill was performed for 6 hours to initially debundle the chopped carbon fiber bundles.

The above-mentioned initially debonded chopped carbon fiber bundle is filtered and then added to a polyurethane ball mill. 105 parts of anhydrous ethanol, 30 parts of polyurethane balls with a diameter of 15 mm and 60 parts of polyurethane balls with a diameter of 40 mm are added to the ball mill. Roller ball milling is performed for 5 hours to further debond the chopped carbon fiber bundle. The chopped carbon fiber bundle is then filtered and dried at 60°C to obtain debonded chopped carbon fiber for later use.

(3) Debundled chopped carbon fiber coated granulated powder

Weigh 5 parts of the debundled chopped carbon fibers prepared in step (2), add them into a coating machine, start the coating machine, make the debundled chopped carbon fibers start to rotate with the coating machine, spray humidify and viscosity-enhance the chopped carbon fibers with an alcohol solution containing 4% by mass of phenolic resin, 6% by mass of nano carbon black and 14% by mass of nano silicon powder, then continuously add the 10-100 mesh silicon carbide granulated powder prepared in step (1), and continuously spray the alcohol solution containing phenolic resin, so that the debundled chopped carbon fibers adhere to the granulated powder during the rotation of the coating machine, to obtain silicon carbide granulated powder coated with chopped carbon fibers, until 13.3 parts of 10-100 mesh silicon carbide granulated powder are completely added.

The granulated powder coated with the chopped carbon fiber is then dried at 55° C. to make its moisture content 0.8%.

(4) Silicon carbide granulated powder mixing

The coated granulated powder obtained in step (3) and the other granulated powders except 10-100 mesh in step (1) are rotated in a sugar coating machine and mixed evenly.

(5) Valve molding

The granulated powder obtained in step (4) was loaded into a rubber mold, compacted, isostatically pressed, and turned to obtain a valve sleeve with an outer diameter of 86 mm, an inner diameter of 62 mm, and a height of 74 mm. The green density was measured to be 1.82 g/cm ³ .

The pressed disc was dried at 70° C. for 15 hours and set aside.

(6) Valve parts sintering

The dried valve sleeve green body is placed in a vacuum sintering furnace, first heated to 1550°C and kept warm for 2 hours, so that the nano-silicon powder and nano-carbon powder sprayed on the debundled carbon fiber yarn react in situ to generate silicon carbide, thereby improving the interfacial bonding strength between the carbon fiber and the silicon carbide ceramic matrix, and allowing the carbon produced by the decomposition of organic matter in the green body to react with the added silicon powder to generate silicon carbide, and then sintered at 1850°C for 4 hours to obtain a silicon carbide ceramic valve sleeve sintered body.

(7) Post-processing of valve parts

The inner and outer surfaces of the valve sleeve were surface ground to obtain a valve sleeve with an outer diameter of 70 mm, an inner diameter of 50 mm, a height of 60 mm, and a surface roughness of 5 microns.

After testing, the relative density of the obtained silicon carbide ceramic valve sleeve is 98.2%, the Vickers microhardness is 24.2 GPa, the three-point bending strength is 578.8 MPa, and the fracture toughness is 8.5 MPa·m ^1/2 .

Comparative Example 1:

A method for preparing fiber-reinforced silicon carbide ceramic valve components by liquid phase sintering and pressing, the steps are as follows:

The technical solution refers to Example 1.

The difference is that no chopped carbon fiber is added for toughening.

The rest is the same as Example 1.

After testing, the relative density of the obtained silicon carbide ceramic valve plate is 98.8%, the Vickers microhardness is 24.6 GPa, the three-point bending strength is 443.6 MPa, and the fracture toughness is 5.0 MPa·m ^1/2 .

Comparative Example 2:

A method for preparing fiber-reinforced silicon carbide ceramic valve components by liquid phase sintering and pressing, the steps are as follows:

The technical solution refers to Example 1.

The difference is:

The pretreatment of the carbon fiber in step 2 is removed, the silicon carbide granulated powder is not coated with the carbon fiber, and the chopped carbon fiber and the granulated powder are simply mechanically mixed.

The rest is the same as Example 1.

After testing, the relative density of the obtained silicon carbide ceramic valve plate is 97.6%, the Vickers microhardness is 23.5 GPa, the three-point bending strength is 516.1 MPa, and the fracture toughness is 6.1 MPa·m ^1/2 .

Comparative Example 3:

A method for preparing fiber-reinforced silicon carbide ceramic valve components by liquid phase sintering and pressing, the steps are as follows:

The technical solution refers to Example 1.

The difference is that the chopped carbon fiber with a length of 3.0 mm is replaced with the chopped carbon fiber with a length of 30 mm.

The rest is the same as Example 1.

After testing, the relative density of the silicon carbide ceramic valve plate is 98.0%, the Vickers microhardness is 23.9GPa, the three-point bending strength is 571.0MPa, and the fracture toughness is 6.6MPa.m ^1/2 .

Comparative Example 4:

A method for preparing fiber-reinforced silicon carbide ceramic valve components by liquid phase sintering and pressing, the steps are as follows:

The technical solution refers to Example 1.

The difference is that when the silicon carbide granulated powder is coated with the debonded carbon fiber, the sprayed alcohol solution contains nano carbon black and resin, but does not contain nano silicon powder.

The rest is the same as Example 1.

After testing, the relative density of the silicon carbide ceramic valve plate is 97.2%, the Vickers microhardness is 22.4GPa, the three-point bending strength is 465.3MPa, and the fracture toughness is 5.6MPa.m ^1/2 .

Comparative Example 5:

A method for preparing fiber-reinforced silicon carbide ceramic valve components by liquid phase sintering and pressing, the steps are as follows:

The technical solution refers to Example 1.

The difference is: remove the pre-added silicon powder in the formula.

The rest is the same as Example 1.

After testing, the relative density of the silicon carbide ceramic valve plate is 96.3%, the Vickers microhardness is 21.1GPa, the three-point bending strength is 440.4MPa, and the fracture toughness is 5.3MPa.m ^1/2 .

Result analysis:

1. By comparing Example 1 with Comparative Examples 1-3, it can be seen that the technical solution of the present invention, by introducing short-cut carbon fibers of suitable sizes, debundling the carbon fibers, and spraying an alcohol solution containing resin, silicon powder and carbon black on the debundled carbon fibers, can achieve a good toughening effect.

2. By comparing Example 1 with Comparative Example 2, it can be seen that compared with simply mixing the chopped carbon fiber feather granulation powder directly, the technical solution of the present invention, which de-bundles the chopped carbon fiber and coats the de-bundled carbon fiber filaments on the surface of the silicon carbide granulation powder, can improve the density of the valve parts, improve the uniformity of fiber distribution, and achieve better strengthening and toughening effects. Directly mixing the granulation powder with the chopped carbon fiber reduces the product density, and the strengthening and toughening effects become worse.

3. By comparing Example 1 with Comparative Example 3, it can be seen that the technical solution of the present invention uses a carbon fiber bundle of appropriate size, which can be better coated on the surface of the granulated powder after being unbundled. If the carbon fiber is too long, even after being unbundled, its length far exceeds the circumference of the granulated powder, making the carbon fiber bundle too long, resulting in poor coating effect, reduced density of the valve part, and poor strength and toughness.

4. By comparing Example 1 with Comparative Example 4, it can be seen that the technical solution of the present invention, spraying an alcohol solution containing nano carbon black, nano silicon powder and resin on the debundled carbon fiber filaments, can react to generate silicon carbide, form a protective layer for the carbon fiber filaments, and avoid the reduction of the performance of the carbon fiber by the liquid phase generated by aluminum oxide and yttrium oxide. However, the density, hardness, strength and toughness of the comparative sample sprayed with an alcohol solution without nano silicon powder are significantly reduced. This should be because the resin and the added carbon black react with aluminum oxide and yttrium oxide, and the carbon fiber tow is corroded by the liquid phase generated by aluminum oxide and yttrium oxide, resulting in the deterioration of the performance of the carbon fiber filaments, thereby worsening the strengthening and toughening effects.

5. By comparing Example 1 with Comparative Example 5, it can be seen that the technical solution of the present invention, in which silicon powder is pre-added in the formula, can react with the carbon produced by the cracking of the binder in the formula, prevent the residual carbon from reacting with alumina and yttrium oxide, consume alumina and yttrium oxide, and reduce the effect of liquid phase sintering and toughening. However, the density, hardness, strength and toughness of the comparative sample without pre-added silicon powder are significantly reduced. This should be because the carbon produced by the cracking of the binder reacts with alumina and yttrium oxide, consumes alumina and yttrium oxide, reduces the effect of liquid phase sintering and toughening, and thus the strengthening and toughening effects become worse.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Other modifications or equivalent substitutions made to the technical solution of the present invention by ordinary technicians in the field should be included in the scope of the claims of the present invention as long as they do not depart from the spirit and scope of the technical solution of the present invention.

Claims (6)

1. A method for preparing fiber-reinforced silicon carbide ceramic valve parts by liquid phase sintering and pressing, characterized in that the raw materials for preparing the ceramic valve parts include silicon carbide ceramic matrix material and toughening material; the matrix material includes 100 parts of silicon carbide micropowder, 3-12 parts of mixed powder of aluminum oxide and yttrium oxide, 5-10 parts of adhesive, 3-12 parts of silicon powder, 0.5-3 parts of surfactant and 0.5-2 parts of dispersant by weight; the toughening material is chopped carbon fiber, and the addition amount of the chopped carbon fiber is 0.1-15% of the total amount of the matrix material; the length of the chopped carbon fiber is less than 5 mm, and the diameter of the filament bundle is less than 500 μm; The preparation method specifically comprises the following steps: (1) Preparation of granulated powder Weigh the silicon carbide ceramic matrix material according to the ratio, add deionized water, the amount of deionized water is 0.9-1.5 times the mass of the silicon carbide micropowder, and then ball mill for 8-20 hours to obtain silicon carbide ceramic slurry; then spray granulate the silicon carbide ceramic slurry to obtain granulated powder, wherein the moisture content of the granulated powder is 0.5-1.2%, and the mass percentage of the granulated powder with a particle size of 60-180 mesh is greater than 90%; then sieve the granulated powder, and take the granulated powder with a mesh size of 10-100 for standby use; (2) Pretreatment of chopped carbon fiber Weigh the prepared chopped carbon fibers, add them to a ball mill with a polyurethane liner, add polyurethane balls to the ball mill, and perform roller milling for 1-5 hours to make the chopped carbon fiber bundles fluffy; then add deionized water to the ball mill, continue roller milling for 1-8 hours to preliminarily debundle the chopped carbon fiber bundles, filter, then add the filtered chopped carbon fibers to the ball mill, add anhydrous ethanol and polyurethane balls to the ball mill, perform roller milling for 1-8 hours to further debundle the chopped carbon fiber bundles, then filter, and dry at 50-80° C. to obtain debundled chopped carbon fibers for standby use; (3) Debundled chopped carbon fiber coated granulated powder The debundled chopped carbon fibers prepared in step (2) are added to a coating machine, the coating machine is started, and the debundled chopped carbon fibers begin to rotate with the coating machine, and the chopped carbon fibers are sprayed with an alcohol solution containing phenolic resin, carbon black and silicon powder to humidify and thicken them, and then the silicon carbide granulated powder with a mesh size of 10-100 in step (1) is continuously added, and the alcohol solution is continuously sprayed, so that the debundled chopped carbon fibers adhere to the granulated powder during the rotation of the coating machine, to obtain silicon carbide granulated powder coated with chopped carbon fibers, and then the silicon carbide granulated powder coated with chopped carbon fibers is dried at a temperature not higher than 70° C. to make its moisture content be 0.5-1.2%; (4) Silicon carbide granulated powder mixing The chopped carbon fiber-coated silicon carbide granulated powder obtained in step (3) and the other granulated powders except 10-100 mesh in step (1) are rotated in a sugar coating machine to mix evenly; (5) Valve molding The granulated powder obtained in step (4) is pressed and molded to obtain a valve green body, wherein the density of the valve green body is not less than 1.7 g/cm ₃ ; (6) Valve parts sintering The processed valve green body is placed in a vacuum sintering furnace, first heated to 1450-1600°C and kept warm for 1-6 hours, then continued to heat to 1750-2000°C, and then sintered for 0.5-5 hours to obtain a sintered body of silicon carbide ceramic valve parts; (7) Post-processing of valve parts The silicon carbide ceramic valve component sintered body is processed after grinding and polishing to obtain the silicon carbide ceramic valve component with required specifications, shapes and sizes. 2. The method for preparing fiber-reinforced silicon carbide ceramic valve components by liquid phase sintering and pressing according to claim 1 is characterized in that the _D50 of the silicon carbide powder in step (1) is 0.5±0.2 μm; the molar ratio of aluminum oxide to yttrium oxide in the mixed powder of aluminum oxide and yttrium oxide is 5:3, and the _D50 of the mixed powder of aluminum oxide and yttrium oxide is 1-3 μm; the _D50 of the silicon powder is not greater than 500 nm, and the amount of silicon powder added is greater than the theoretical carbon content of the binder, calculated based on the theoretical carbon content of the binder. 3. The method for preparing fiber-reinforced silicon carbide ceramic valve parts by liquid phase sintering and pressing molding according to claim 1 is characterized in that the adhesive in step (1) is phenolic resin, polyvinyl alcohol or carboxymethyl cellulose; the surfactant is stearic acid or fatty acid glyceride; and the dispersant is tetramethylammonium hydroxide or polyacrylic acid. 4. The method for preparing fiber-reinforced silicon carbide ceramic valve components by liquid phase sintering and pressing according to claim 1 is characterized in that the chopped carbon fibers in step (2) are high-strength carbon fibers having a tensile strength of not less than 3500 MPa. 5. The method for preparing fiber-reinforced silicon carbide ceramic valve components by liquid phase sintering and pressing according to claim 1 is characterized in that the diameter of the polyurethane balls in step (2) is 10-50 mm; the mass ratio of the added polyurethane balls to the chopped carbon fibers is (0.6-1.5):1; the mass ratio of the deionized water to the chopped carbon fibers is (0.8-2):1; the mass ratio of the anhydrous ethanol to the chopped carbon fibers is (0.8-1.5):1. 6. The method for preparing fiber-reinforced silicon carbide ceramic valve parts by liquid phase sintering and pressing according to claim 1 is characterized in that the mass fraction of phenolic resin in the alcohol solution in step (3) is 1-10%, the mass fraction of carbon black is 1-10%, and the mass fraction of silicon powder is 1-20%; and the carbon black is nano-carbon powder with _D50 not greater than 50nm; the molar ratio of carbon black to silicon powder is 1:(1-1.2).