CN1323146C - Borontroixide-silicon carbide self-lubricating coating and its preparing method - Google Patents

Abstract

The present invention relates to a surface self-lubricating coating with boron oxide and silicon carbide for carbon/carbon composites. The surface self-lubricating coating layer solves the problems that the friction wear property of carbon/carbon composites in the prior art is influenced by different factors, such as the environment, temperature, etc., and poor lubrication effect and high friction coefficient are caused. The present invention takes silicon carbide as a transition layer and uses a boron trioxide coating as an outer coating, and a surface self-lubricating coating taking orthoboric acid as a carbon/carbon composite is formed by way of in-situ reaction. The surface self-lubricating coating adopts the following raw materials: 70 to 85% of silicon powder, 10 to 20% of carbon powder and 5 to 15% of aluminium oxide powder, that are uniformly mixed, an embedding method is adopted to prepare the transition layer of silicon carbide, and a slurry method is used for preparing the coating of boron oxide on the surface of the silicon carbide coating. The present invention effectively reduces the friction coefficient of a carbon/carbon composite, widens the application field of carbon/carbon friction material, has the characteristics of simple process control and uniform coating, and is suitable for mass production in industry.

Description

A kind of preparation method of diboron trioxide-silicon carbide self-lubricating coating

(1) Technical field:

The invention relates to a method for preparing a boron trioxide-silicon carbide self-lubricating coating on the surface of a carbon/carbon composite material.

(two) background technology:

Carbon/carbon composite material has low density, high temperature resistance, high specific strength, thermal shock resistance, corrosion resistance, good vibration absorption and self-lubricating properties, and is a friction material with excellent comprehensive properties. As a friction material, carbon/carbon composites have been used in aircraft brake discs, self-lubricating bearings, and internal combustion engine pistons. However, the friction and wear properties of carbon/carbon composites are affected by many factors. For example, in an environment without oxygen and water vapor, carbon/carbon composites will lose their self-lubricating properties and the lubrication effect will be poor; The friction performance of carbon/carbon composites has a non-negligible effect. The carbon/carbon composite material undergoes a transition from "normal wear" to "dust wear" in the temperature range of 150-200°C. In the "normal wear" region below the transition temperature, the friction coefficient of the carbon/carbon composite material is only 0.1 ~0.2, but above the transition temperature, the coefficient of friction increases to 0.25~0.5. If carbon/carbon composites are used in lubricating systems such as space mechanical lubrication systems or pistons of internal combustion engines, in order to maintain a low coefficient of friction, a low friction coefficient coating must be prepared on its surface. It can be seen that the preparation of self-lubricating coatings with different structures on carbon/carbon composites according to different needs is one of the key technologies for its commercial application, which can further exert its huge application potential in aerospace and civil fields. The research on preparing self-lubricating coatings on the surface of carbon/carbon composites has not been reported in the literature.

Boric acid is a crystal with a layered structure, and the layers are connected by weak van der Waals force, the interlayer shear force is small, and its bonding characteristics are very similar to solid lubricants molybdenum disulfide and graphite, with a low coefficient of friction , so it can be used as a lubricant. Boron trioxide can react with water vapor in the air at room temperature to form a boric acid lubricating film on its surface, which can be indirectly used as a lubricating coating. Erdemir A. et al used the method of electron beam heating and evaporation to prepare diboron trioxide coating on iron and polycrystalline α-aluminum (Erdemir A., Fenske G.R., Erck R.A..Surface and CoatingsTechnology, 1990, 43/44 : 588-596.), the boron trioxide coating reacts with water vapor in the air to form a boric acid lubricating film, and the friction coefficient is 0.025 to 0.05. ErdemirA.et al oxidized boron carbide in a box furnace at 800°C to form boron trioxide, and then used boron trioxide in-situ reaction to prepare a boric acid lubricating film with a friction coefficient of 0.03-0.05 (Erdemir A., Bindal C., Zuiker C., et al. Surface and Coatings Technology, 1996, 86/87: 507-510.). At present, when preparing boron carbide pneumatic bearings in high-precision and long-life gyroscopes, the same method is also used to form a low friction coefficient self-lubricating boric acid film on the surface of the bearing (Wu Fang, Wang Lingsen, Zhang Jinsheng, etc. Journal of Central South University of Technology , 2001, 22(1):78-80.). At the same time, diboron trioxide still has lubricating properties at 650 ° C, and the friction coefficient is low (about 0.1) (Larsson P., Axén N., Hogmark S.. Wear, 1999, 236: 73-80.). The preparation of diboron trioxide coating by electron beam heating and evaporation requires relatively expensive equipment, and it is difficult to prepare large-scale samples. The two-step process of embedding method and slurry method is used to prepare a self-lubricating coating system on the surface of carbon/carbon composite materials with silicon carbide as the transition layer and boron trioxide coating as the outer coating, which improves the relationship between the outer coating and the surface of the carbon/carbon composite material. The binding force of carbon/carbon composites, this self-lubricating coating system has not been reported in the literature.

(3) Contents of the invention:

In order to solve the problem that the friction and wear properties of carbon/carbon composite materials are affected by many factors such as environment and temperature, resulting in poor lubrication effect and increased friction coefficient, the present invention proposes a carbon/carbon composite surface diboron trioxide- Preparation method of silicon carbide self-lubricating coating.

The technical solution adopted in the invention is to use silicon carbide as a transition layer, a diboron trioxide coating as an outer coating, and in-situ reaction to form boric acid as a self-lubricating coating on the surface of the carbon/carbon composite material.

The invention adopts the two-step method of embedding method and slurry method to prepare, that is, the silicon carbide inner coating is prepared by the embedding method, and the diboron trioxide outer coating is prepared by the slurry method. The specific method is to use silicon powder, carbon powder and aluminum oxide as raw materials, and make a mixture of 70-85% silicon powder, 10-20% carbon powder, and 5-15% aluminum oxide powder. powder; the carbon/carbon composite material is ground and polished, buried in the mixed powder, placed in a protective atmosphere, sintered at a temperature of 1500-2000 ° C, and the required silicon carbide inner coating is obtained through a solidification reaction; Diboron trioxide powder and absolute ethanol are mixed into a slurry, and the slurry is painted on the silicon carbide inner coating. After the ethanol volatilizes, the obtained sample is sintered at a temperature of 500-700°C in a protective atmosphere. , down to room temperature; put the sample in the air, you can get a self-lubricating coating.

The friction coefficient of the diboron trioxide-silicon carbide self-lubricating coating is 0.065-0.083, which effectively reduces the friction coefficient of the carbon/carbon composite material and expands the application field of the carbon/carbon friction material. The particular advantage of the method used to prepare the coating is simple process control and uniform coating. Due to these advantages, this method has the potential to be developed into large-scale industrial production.

(4) Description of drawings:

Accompanying drawing 1 is the preparation process flowchart of boron trioxide-silicon carbide coating on the surface of carbon/carbon composite material;

Accompanying drawing 2 is the scanning electron micrograph of the surface of the silicon carbide coating prepared under 1600 ℃;

Accompanying drawing 3 is the X-ray diffraction figure of the silicon carbide coating prepared under 1600 ℃;

Accompanying drawing 4 is the scanning electron micrograph of the surface of diboron trioxide-silicon carbide coating on carbon/carbon composite material surface;

Accompanying drawing 5 is the X-ray diffraction figure of carbon/carbon composite material surface diboron trioxide-silicon carbide coating;

Accompanying drawing 6 is the friction coefficient of carbon/carbon composite material and diboron trioxide-silicon carbide coating;

(5) Specific implementation methods:

Example 1:

In this example, silicon powder, carbon powder and aluminum oxide are used as raw materials, and the two-step method of embedding method and slurry method is used to prepare, that is, the silicon carbide inner coating is prepared by the embedding method, and the trioxide is prepared by the slurry method. Diboron outer coating. The specific implementation steps are:

1. Prepare mixed powder. Perform ball milling and mixing treatment on silicon powder, carbon powder and aluminum oxide powder. Get 77% of silicon powder, 15% of carbon powder and 8% of aluminum oxide powder, and place them in a resin ball mill jar. At the same time, respectively take 2, 5, 24, and 50 agate balls with diameters of 25mm, 12mm, 7mm, and 2mm respectively and put them in a ball mill jar, add distilled water as a ball milling agent, and the ratio of material, balls, and water is 1: 3:0.8 (mass percentage); put the ball mill jar on the ball mill and clamp it. Turn on the ball mill, first ball mill and mix the materials at a speed of 120 rpm for 2 hours, then adjust the speed to 180 rpm, mill for 5 hours, and then rotate the ball mill in the opposite direction for 5 hours, totaling 12 hours of ball milling. The mixed slurry after ball milling was taken out and passed through a 220 mesh sieve and put into a beaker. Put the beaker containing the slurry in an oven to dry at 90°C, then use a mortar to grind the dispersed powder, and pass through a 220-mesh sieve for later use.

2. Make test pieces. Cut the carbon/carbon composite material with a density of 1.72g/cm ³ into 12×12×6mm ³ samples, grind and polish them in turn with No. 400, No. 800 and No. 1000 sandpaper respectively, wash them with distilled water, and store them at 100°C. Dry in oven.

3. Preparation of silicon carbide inner coating by embedding method. Put the test piece in the graphite crucible, embed the test piece with mixed powder and seal the crucible; put the graphite crucible in the vacuum furnace, vacuumize for 30 minutes to make the vacuum degree reach -0.09MPa, and let it stand for 30 minutes; Argon to normal pressure and then vacuum, this process was repeated three times. Then raise the furnace temperature from room temperature to 1600°C, and control the heating rate at 10°C/min. After reaching the predetermined maximum temperature, keep it warm for 3 hours, then lower the temperature to 1200°C at a rate of 10°C/min, and turn off the power for natural cooling. To room temperature, the whole process was protected by argon. After opening the furnace, remove the powder attached to the surface of the sample, wash it with an ultrasonic cleaner, and dry it in an oven at 120°C for 2 hours.

4. Preparation of diboron trioxide outer coating by slurry method. Make a slurry of boron trioxide powder and absolute ethanol, and paint the slurry on the silicon carbide inner coating, allowing the ethanol to volatilize naturally, and this process needs to be repeated 4 times. Place the sample in a vacuum furnace, vacuumize for 30 minutes to make the vacuum degree reach -0.09MPa, and let it stand for 30 minutes. The process was repeated three times after passing argon to normal pressure and then vacuuming. Raise the furnace temperature from room temperature to 500 °C, and control the heating rate at 10 °C/min. After reaching the predetermined maximum temperature, keep it warm for 30 minutes, turn off the power and naturally cool to room temperature, and protect the whole process with argon.

5. In situ reaction to generate boric acid lubricating film. Take out the sample, put it in the air, and let it stand for 24 hours. It can be seen that a white boric acid lubricating film is formed on the surface of the specimen.

Example 2:

In this example, silicon powder, carbon powder and aluminum oxide are used as raw materials, and the two-step method of embedding method and slurry method is used to prepare, that is, the silicon carbide inner coating is prepared by the embedding method, and the trioxide is prepared by the slurry method. Diboron outer coating. The specific implementation steps are:

1. Prepare mixed powder. Perform ball milling and mixing treatment on silicon powder, carbon powder and aluminum oxide powder. Get 72% of silicon powder, 13% of carbon powder and 15% of aluminum oxide powder, and place them in a resin ball mill jar. At the same time, respectively take 2, 5, 24, and 50 agate balls each with a diameter of 25mm, 12mm, 7mm, and 2mm and put them in a ball milling tank, add distilled water as a ball milling agent, and control the ratio of material, balls, and water to be material:ball : water=1:3:0.8 (mass percentage), put the ball mill jar on the ball mill and clamp it. Turn on the ball mill, first ball mill and mix the materials at a speed of 120 rpm for 2 hours, then adjust the speed to 180 rpm, mill for 5 hours, and then rotate the ball mill in the opposite direction for 5 hours, totaling 12 hours of ball milling. The mixed slurry after ball milling was taken out and passed through a 220 mesh sieve and put into a beaker. Put the beaker containing the slurry in an oven to dry at 90°C, then use a mortar to grind the dispersed powder, and pass through a 220-mesh sieve for later use.

2. Make test pieces. The carbon/carbon composite material with a density of 1.75g/ ^cm3 was cut into 12×12× ^6mm3 samples with a hacksaw, polished and polished with No. 400, No. 800 and No. 1000 sandpaper respectively, and then washed with distilled water. Dry in an oven at 100°C.

3. Prepare silicon carbide inner coating by embedding method. Put the test piece in the graphite crucible, embed the test piece with mixed powder and seal the crucible; put the graphite crucible in the vacuum furnace, vacuumize for 30 minutes to make the vacuum degree reach -0.09MPa, and let it stand for 30 minutes; Argon to normal pressure and then vacuum, this process was repeated three times. Then raise the furnace temperature from room temperature to 1700°C, and control the heating rate at 10°C/min. After reaching the predetermined maximum temperature, keep it warm for 2 hours, then lower the temperature, and cool it down to 1200°C at a rate of 10°C/min, then turn off the power supply and cool naturally To room temperature, the whole process was protected by argon. After opening the furnace, remove the powder attached to the surface of the sample, wash it with an ultrasonic cleaner, and dry it in an oven at 120°C for 2 hours.

4. Preparation of diboron trioxide outer coating by slurry method. Make a slurry of boron trioxide powder and absolute ethanol, and paint the slurry on the silicon carbide inner coating, let the ethanol volatilize naturally, and repeat this process 3 times. Place the sample in a vacuum furnace, vacuumize for 30 minutes to make the vacuum degree reach -0.09MPa, and let it stand for 30 minutes. The process was repeated three times after passing argon to normal pressure and then vacuuming. Raise the furnace temperature from room temperature to 650 °C, and control the heating rate at 20 °C/min. After reaching the predetermined maximum temperature, keep it warm for 20 minutes, turn off the power supply and naturally cool to room temperature, and protect it with argon during the whole process.

5. In situ reaction to generate boric acid lubricating film. Take out the sample, put it in the air, and let it stand for 30 hours. It can be seen that a white boric acid lubricating film is formed on the surface of the specimen.

Example 3:

In this example, silicon powder, carbon powder and aluminum oxide are used as raw materials, and the two-step method of embedding method and slurry method is used to prepare, that is, the silicon carbide inner coating is prepared by the embedding method, and the trioxide is prepared by the slurry method. Diboron outer coating. The specific implementation steps are:

1. Prepare mixed powder. Perform ball milling and mixing treatment on silicon powder, carbon powder and aluminum oxide powder. Get 82% of silicon powder, 12% of carbon powder and 6% of aluminum oxide powder, and place them in a resin ball mill jar. At the same time, respectively take 2, 5, 24, and 50 agate balls with diameters of 25mm, 12mm, 7mm, and 2mm respectively and put them in a ball mill jar, add distilled water as a ball milling agent, and the ratio of material, balls, and water is 1: 3:0.8 (mass percentage); put the ball mill jar on the ball mill and clamp it. Turn on the ball mill, first ball mill and mix the materials at a speed of 120 rpm for 2 hours, then adjust the speed to 180 rpm, mill for 5 hours, and then rotate the ball mill in the opposite direction for 5 hours, totaling 12 hours of ball milling. The mixed slurry after ball milling was taken out and passed through a 220 mesh sieve and put into a beaker. Put the beaker containing the slurry in an oven to dry at 90°C, then use a mortar to grind the dispersed powder, and pass through a 220-mesh sieve for later use.

2. Make test pieces. Cut the carbon/carbon composite material with a density of 1.80g/cm ³ into 12×12×6mm ³ samples, grind and polish them in turn with No. 400, No. 800 and No. 1000 sandpaper respectively, wash them with distilled water, and store them at 100°C. Dry in oven.

3. Prepare silicon carbide inner coating by embedding method. Put the test piece in the graphite crucible, embed the test piece with mixed powder and seal the crucible; put the graphite crucible in the vacuum furnace, vacuumize for 30 minutes to make the vacuum degree reach -0.09MPa, and let it stand for 30 minutes; Argon to normal pressure and then vacuum, this process was repeated three times. Then the furnace temperature was raised from room temperature to 1800°C, and the heating rate was controlled at 10°C/min. After reaching the predetermined maximum temperature, it was kept for 1 hour, and then the temperature was lowered to 1200°C at a rate of 10°C/min, and the power was turned off for natural cooling. To room temperature, the whole process was protected by argon. After opening the furnace, remove the powder attached to the surface of the sample, wash it with an ultrasonic cleaner, and dry it in an oven at 120°C for 2 hours.

4. Preparation of diboron trioxide outer coating by slurry method. Make a slurry of boron trioxide powder and absolute ethanol, and paint the slurry on the silicon carbide inner coating, allowing the ethanol to volatilize naturally, and this process needs to be repeated 4 times. Place the sample in a vacuum furnace, vacuumize for 30 minutes to make the vacuum degree reach -0.09MPa, and let it stand for 30 minutes. The process was repeated three times after passing argon to normal pressure and then vacuuming. Raise the furnace temperature from room temperature to 600°C, and control the temperature rise rate at 15°C/min. After reaching the predetermined maximum temperature, keep it warm for 30 minutes, turn off the power and naturally cool to room temperature, and protect it with argon during the whole process.

5. In situ reaction to generate boric acid lubricating film. Take out the sample and place it in the air for 36 hours. It can be seen that a white boric acid lubricating film is formed on the surface of the specimen.

Claims (1)

1. the preparation method of a Borontroixide-silicon carbide self-lubricating coating is characterized in that adopting the preparation of entrapping method and slurry process two-step approach, promptly prepares the silicon carbide undercoat with entrapping method, is equipped with the boron trioxide external coating (EC) with the slip legal system, and its detailed process is:

A. being respectively 70～85%, 10～20%, 5～15% high purity silica flour, carbon dust and aluminium sesquioxide with mass percent does former abrasive lapping and sieves and make mixed powder;

B. will be embedded in the mixed powder behind the carbon/carbon compound material sanding and polishing, place the protective atmosphere sintering;

C. boron trioxide powder and dehydrated alcohol furnishing slip are painted on the silicon carbide undercoat, treating that ethanol volatilization is placed on carries out sintering in the protective atmosphere, and sintering temperature is 500～700 ℃;

D. sample is placed air, to obtain self-lubricating coat in use.

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