A SiC / MCMBs composite material, its preparation method and application

Abstract

The present invention provides a SiC / MCMBs composite material, comprising a SiC matrix and mesocarbon microbeads (MCMBs) distributed in the SiC matrix; wherein, the mesocarbon microbeads are modified by a silicon carbide polymer precursor to form silicon carbide microcrystals and free carbon at the interface between the SiC and the mesocarbon microbeads. The present invention also provides a preparation method and an application of the SiC / MCMBs composite material as described above.

Description

Technical Field

[0001] The present invention belongs to the field of composite materials, and particularly relates to a SiC / MCMBs composite material, a preparation method thereof and an application thereof. Background Art

[0002] Due to its excellent high-temperature mechanical properties, ultra-high hardness and wear resistance, good oxidation resistance and chemical corrosion resistance, low thermal expansion coefficient and high thermal conductivity, excellent thermal shock resistance and thermal stability, silicon carbide materials are widely used in aerospace engine combustion chambers, nozzle heat exchanger components, high-load long-life kiln furniture, mechanical seal devices, nuclear fuel cooling reactor cladding materials, precision bearings, turbine rotors and other fields. In recent years, due to its excellent comprehensive properties, the huge application potential of silicon carbide materials in mechanical seals and wear-resistant components has gradually attracted people's attention and has now been widely used. However, under some special working conditions, such as when silicon carbide materials are used in mechanical seals and wear-resistant components under high-temperature conditions, since the device end faces are in a state of mutual contact and rotation during use, the material is required to have good wear resistance. However, general lubricating oils fail at high temperatures, and the material is exposed to dry friction or extremely little lubrication conditions. Since single silicon carbide materials have a relatively high friction coefficient under dry friction conditions, the material is prone to damage during use, causing huge losses. In addition, in some industries, such as when silicon carbide materials are used in mechanical seal components of aerospace devices and nuclear power industries, it is often impossible to add lubricating media, and the material is also required to have a low friction coefficient under dry friction conditions. Since single silicon carbide materials can no longer meet the application requirements in these special aspects, it is necessary to develop silicon carbide composite materials suitable for the above working conditions.

[0003] Patent document CN108774065A discloses a SiC / MCMBs composite material, and proposes to add mesophase carbon microspheres to the silicon carbide material. Due to its unique lamellar stacking structure, a lubricating film can be formed on the working surface of the SiC / MCMBs composite material under dry friction conditions, significantly reducing the friction coefficient of the SiC / MCMBs composite material under dry friction conditions. However, this composite material has problems such as unstable dry friction coefficient and easy shedding of hard silicon carbide particles during dry friction and wear processes, which will affect the operation reliability and service life of the seal components under actual working conditions. It is necessary to further improve the friction and wear performance of the SiC / MCMBs composite material to better suit the special working conditions of limited lubrication and short-term dry friction. Summary of the Invention

[0004] In view of the above problems, the object of the present invention is to provide a SiC / MCMBs composite material, its preparation method and application, so as to solve the problems that hard silicon carbide particles are likely to fall off and the dry friction coefficient is unstable during the friction and wear process of the existing SiC / MCMBs composite material.

[0005] In a first aspect, the present invention provides a SiC / MCMBs composite material, comprising a SiC matrix and mesocarbon microbeads (MCMBs) distributed in the SiC matrix; wherein, the mesocarbon microbeads are modified by a silicon carbide polymer precursor to form silicon carbide microcrystals and free carbon at the interface between the SiC and the mesocarbon microbeads.

[0006] In the present invention, the SiC / MCMBs composite material comprises a SiC matrix and mesocarbon microbeads (Mesocarbon Microbeans, MCMBs) distributed in the silicon carbide matrix. Among them, the mesocarbon microbeads have a unique lamellar stacking structure, which can form a lubricating film on the working surface of the SiC / MCMBs composite material under dry friction conditions, significantly reducing the friction coefficient of the SiC / MCMBs composite material under dry friction conditions. In the present invention, the mesocarbon microbeads in the SiC / MCMBs composite material are also modified by a silicon carbide polymer precursor to pyrolyze and form silicon carbide microcrystals and free carbon at the interface between the SiC and the mesocarbon microbeads, improving the interfacial strength between the two phases of SiC and MCMBs.

[0007] Preferably, the silicon carbide polymer precursor is a vinyl-containing liquid polycarbosilane.

[0008] In the present invention, the vinyl-containing liquid polycarbosilane (LPVCS) is a kind of liquid polycarbosilane precursor containing active Si-H groups and -CH=CH2 groups. The vinyl-containing liquid polycarbosilane (LPVCS) is a liquid with good fluidity at room temperature, and can undergo a curing hydrosilylation reaction at 250 - 300 °C. The curing retention rate at 300 °C is about 90%. The pyrolysis product at 1200 °C shows β-SiC microcrystals and a small amount of free carbon. When it is applied to the SiC / MCMBs composite material to modify the mesocarbon microbeads (MCMBs), silicon carbide microcrystals and free carbon are pyrolyzed and formed at the interface between the SiC and the mesocarbon microbeads, improving the interfacial strength between the two phases of SiC and MCMBs.

[0009] Preferably, the SiC / MCMBs composite material further comprises a sintering aid, and the sintering aid is at least one of boron element and boron compounds, preferably at least one of boron element, boric acid and boron carbide, more preferably boron carbide; the content does not exceed 1 wt%, preferably 0.5 - 1.0 wt%.

[0010] Preferably, the density of the SiC / MCMBs composite material is ≥97%, the flexural strength is 280-450 MPa, the elastic modulus is 160-190 GPa, and the fracture toughness is 3-5 MPa·m 1 / 2 , and the dry friction coefficient is 0.16-0.31.

[0011] In a second aspect, the present invention also provides a method for preparing the SiC / MCMBs composite material as described above, comprising:

[0012] Dissolving a silicon carbide polymer precursor, mesocarbon microbeads, silicon carbide powder, and a sintering aid in an organic solvent, ball milling, drying, and sieving to obtain raw material powder;

[0013] Placing the obtained raw material powder in a hot pressing mold, and then hot pressing and sintering in a protective atmosphere to obtain the SiC / MCMBs composite material.

[0014] In the present invention, a silicon carbide polymer precursor, mesocarbon microbeads (MCMBs), silicon carbide (SiC) powder, and a sintering aid are dissolved in an organic solvent, ball milled and mixed evenly, and then the mixed slurry is dried and sieved through a 100-mesh sieve to obtain raw material powder; then the raw material powder is loaded into a hot pressing mold (for example, preferably a high-purity graphite hot pressing mold, etc.), and then hot pressed and sintered in a protective atmosphere at a pressure of 30-60 MPa and a temperature of 2000-2200 °C to obtain the SiC / MCMBs composite material. During the hot pressing and sintering process, due to the good sintering shrinkage performance and fluidity of the mesocarbon microbeads, under the action of pressure and high temperature, the mesocarbon microbeads are evenly distributed in the obtained SiC / MCMBs composite material. Among them, the mesocarbon microbeads are spherical particles formed by stacking flaky molecules before sintering, and small molecules are removed after sintering, leaving residual carbon, but still maintaining the original lamellar structure. During the hot pressing and sintering process, the silicon carbide polymer precursor, that is, vinyl-containing liquid polycarbosilane (LPVCS), cracks at the interface between SiC and mesocarbon microbeads (MCMBs) to form β-SiC microcrystals and free carbon.

[0015] Preferably, the silicon carbide polymer precursor is vinyl-containing liquid polycarbosilane; the mesocarbon microbeads are graphitized mesocarbon microbead cooked balls, the particle size of the mesocarbon microbeads is 5 μm-10 μm; the particle size of the silicon carbide powder is 0.5 μm-2.0 μm; in the raw material powder, the weight percentage of the silicon carbide polymer precursor is 1-10%, the weight percentage of the silicon carbide powder is 50-80%, and the weight percentage of the mesocarbon microbeads is 15-30%.

[0016] Preferably, the organic solvent includes cycloalkanes (5-, 6-, 7-, 10-membered cycloalkanes), ethers (tetrahydrofuran), and aromatics (benzene, toluene, xylene); preferably, the organic solvent is cyclohexane.

[0017] Preferably, the protective atmosphere is vacuum or inert atmosphere, and the inert atmosphere is argon; the pressure of hot pressing sintering is 30 - 60 MPa, the sintering temperature is 2000 - 2200 °C, and the sintering time is 1 - 3 hours.

[0018] Preferably, before hot pressing sintering, there is also a step of debinding the raw material powder, and the debinding treatment is carried out in a protective atmosphere at 900 - 1200 °C for 0.5 - 2 hours.

[0019] In a third aspect, the present invention also provides an application of the SiC / MCMBs composite material as described above in the conditions of limited lubrication and short-term dry friction.

[0020] The present invention controls the microstructure and various properties of the material by the addition ratio of mesocarbon microbeads, so that it can be applied to different working conditions. This composite material uses silicon carbide and mesocarbon microbeads as the main raw materials and is made by a hot pressing process. In the preparation method of the mesocarbon microbead / silicon carbide composite material provided by the present invention, there is no appearance of liquid phase during the preparation process, avoiding the damage and collapse of the material in a high-temperature environment. In the preparation method of the mesocarbon microbead / silicon carbide composite material provided by the present invention, there is no free silicon during the preparation process, improving the high-temperature resistance and corrosion resistance of the material. The remarkable feature of the present invention is that due to the use of mesocarbon microbeads with good fluidity and self-sintering activity, the prepared composite material is evenly distributed in all aspects, and the material has a high density and excellent mechanical properties. In the composite material prepared by the method provided by the present invention, the carbon microbeads are widely and evenly distributed, and the content of carbon microbeads is controllable, and the mechanical properties of the material are higher than those of reaction sintered materials.

[0021] The present invention also innovatively uses liquid polycarbosilane to optimize the interfacial structure between MCMBs and SiC. First, the debinding treatment is carried out to release small molecule gases, avoiding the deformation and cracking of the green body during sintering. After high-temperature hot pressing sintering, silicon carbide microcrystals are formed at some two-phase interfaces between silicon carbide and mesocarbon microbeads, improving the interfacial bonding, which is beneficial to inhibiting the shedding of hard silicon carbide particles during the friction and wear process, making the friction coefficient of the SiC / MCMBs composite material stable under dry friction conditions. In addition, this process is simple, has good repeatability, and the prepared composite material with a high carbon content has uniform phase distribution, high density, and good comprehensive mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a microstructural diagram of the liquid polycarbosilane interfacial modified SiC / MCMBs composite material related to the present invention.

[0023] Figure 2 SEM image of the SiC / MCMBs composite material with 9 wt% liquid polycarbosilane interface modification in Example 3 of the present invention.

[0024] Figure 3 HRTEM image of the SiC and MCMBs two-phase interface of the SiC / MCMBs composite material with 9 wt% liquid polycarbosilane interface modification in Example 3 of the present invention. Detailed implementation manners

[0025] The present invention is further illustrated by the following implementation manners. It should be understood that the following implementation manners are only used to illustrate the present invention and do not limit the present invention.

[0026] In the present disclosure, a SiC / MCMBs composite material disclosed by the present invention includes a SiC matrix and mesocarbon microbeads (MCMBs) distributed in the SiC matrix. The microscopic morphology of the SiC / MCMBs composite material is that the mesocarbon microbeads are uniformly distributed in the silicon carbide matrix, and the grain size and morphology of the silicon carbide can be adjusted by the content of the mesocarbon microbeads. In an optional implementation manner, the content of the mesocarbon microbeads in the SiC / MCMBs composite material is 15 wt% to 30 wt%. Within this range, the SiC / MCMBs composite material has good self-lubricating performance while having a highly dense mechanical seal and excellent wear resistance. When the content of the mesocarbon microbeads is less than 15 wt%, although the obtained SiC / MCMBs composite material is easily densified, the friction coefficient of the material becomes higher under dry friction conditions. When the content of the mesocarbon microbeads exceeds 30 wt%, although the friction coefficient of the SiC / MCMBs composite material is lower, the material is difficult to sinter and densify, and as the content of the carbon microbeads continues to increase, the main phase of the material becomes the carbon microbeads, resulting in the deterioration of the mechanical properties of the material.

[0027] In the present invention, mesophase carbon microspheres with unique self-sintering activity and good fluidity are used as carbon sources to obtain SiC / MCMBs composite materials with high carbon microsphere content, high density, and excellent mechanical and electrical properties. Moreover, the mesophase carbon microspheres of the present invention are modified by silicon carbide polymer precursors to form silicon carbide microcrystals and free carbon at the interface between the SiC and the mesophase carbon microspheres. In one embodiment, the silicon carbide polymer precursor is a vinyl-containing liquid polycarbosilane. Vinyl-containing liquid polycarbosilane (LPVCS) is a type of liquid polycarbosilane precursor containing active Si-H groups and -CH=CH2 groups. Liquid polycarbosilane (LPVCS) containing vinyl groups is a liquid with good fluidity at room temperature. It can undergo a curing hydrogenation addition reaction at 250-300°C. The curing retention rate at 300°C is about 90%. The cracking products at 1200°C show β-SiC microcrystals and a small amount of free carbon. It is applied to SiC / MCMBs composite materials to modify mesophase carbon microspheres (MCMBs), so that the interface between SiC and mesophase carbon microspheres is cracked to form silicon carbide microcrystals and free carbon (such as Figure 1 As shown in the figure), the interfacial strength between SiC and MCMBs was improved.

[0028] In the present invention, the SiC / MCMBs composite material also includes a sintering aid, which is at least one of a boron element and a boron compound, preferably includes at least one of a boron element, boric acid and boron carbide, more preferably boron carbide; the content does not exceed 1wt%, preferably 0.5-1.0wt%.

[0029] The following is an exemplary description of the preparation method of the SiC / MCMBs composite material.

[0030] The silicon carbide polymer precursor, mesocarbon microbeads (MCMBs), silicon carbide (SiC) powder and sintering aid are dissolved in an organic solvent, ball milled and mixed evenly, and then the mixed slurry is dried (the drying temperature can be 40-60°C, the time can be 6-8 hours, and the drying temperature and time can be adjusted according to the processing amount) and then passed through a 100-mesh sieve to obtain a raw material powder. Wherein, in the above steps, the organic solvent includes cyclic hydrocarbons (5, 6, 7, 10 cyclic hydrocarbons), ethers (tetrahydrofuran) and aromatics (benzene, toluene, xylene); in an embodiment of the present invention, the organic solvent is cyclohexane. In the step of obtaining the raw material powder, spray granulation can also be used to obtain a raw material powder with a suitable particle size.

[0031] In an optional embodiment, the sintering aid may be a boron source, preferably at least one of a boron element and a boron compound. The boride may be boron carbide. The amount of the sintering aid added accounts for 0 to 1.0 wt % of the total mass of the raw material powder, preferably 0.5 to 1.0 wt %.

[0032] In an alternative embodiment, preferably, the mesophase carbon microspheres may be graphitized mesophase carbon microsphere green balls, and the particle size may be 5 μm to 10 μm. The particle size of the silicon carbide powder may be 0.5 μm to 2.0 μm. In the raw material powder, the weight percentage of the silicon carbide polymer precursor may be 1 to 10%, the weight percentage of the silicon carbide powder may be 50 to 80%, and the weight percentage of the mesophase carbon microspheres may be 15 to 30%.

[0033] Then, the raw material powder is subjected to a debinding treatment in a protective atmosphere at 900 to 1200 °C for 0.5 to 2 hours, which is beneficial to the release of small molecule gases and avoids deformation, cracking of the green body and pollution of the furnace cavity during subsequent sintering.

[0034] Finally, the raw material powder is placed in a special hot pressing mold (for example, a graphite mold), and the SiC / MCMBs composite material is obtained through a hot pressing sintering process. Among them, the protective atmosphere for hot pressing sintering may be a vacuum or an inert atmosphere. Among them, the inert atmosphere is argon. The sintering temperature for hot pressing sintering may be 2000 to 2200 °C. The pressure for hot pressing sintering may be 30 - 60 MPa. The time for hot pressing sintering may be 1 to 3 hours.

[0035] As an example of a method for preparing a liquid polycarbosilane interface-modified SiC / MCMBs composite material, it includes: successively adding a silicon carbide polymer precursor, mesophase carbon microspheres (MCMBs), silicon carbide (SiC) powder, and a sintering aid to cyclohexane, stirring evenly, ball milling for 3 to 5 h, drying the fully mixed slurry, screening the dried powder through a 100-mesh sieve, then performing a debinding treatment at 1200 °C for 0.5 hour, and then loading it into a high-purity graphite hot pressing mold and hot pressing and sintering at 2000 to 2200 °C to obtain the SiC / MCMBs composite material.

[0036] As a detailed example of a preparation method of a liquid polycarbosilane interface-modified SiC / MCMBs composite material, the method comprises: 1) using graphitized mesophase carbon microspheres as the second phase, and uniformly mixing them with silicon carbide, silicon carbide polymer precursor, and boron source with an organic solvent to obtain an original slurry, wherein the total mass of the raw material powder is 100%, the mesophase carbon microspheres have an energy content of 30wt%, and the content of the sintering aid is 0.5-1.0wt%; 2) ball-milling and drying the raw material obtained in step 1) and passing it through a 100-mesh sieve to obtain a raw material powder; 3) placing the raw material powder in a graphite crucible for debonding at a certain temperature; 4) placing the debonded powder obtained in step 3) in a graphite mold, and obtaining the liquid polycarbosilane interface-modified MCMBs-SiC composite material through a hot pressing sintering process. In step 1), the mesophase carbon microspheres are graphitized carbon microspheres. In step 1), the boron source is a boron element or a boron compound as a sintering aid. In step 1), the SiC polymer precursor is a liquid vinyl-containing polycarbosilane. In step 2), cyclohexane is used as a mixed solvent, and the raw materials are fully mixed, dried and sieved to prepare a raw material powder. In step 3), the raw material powder is directly placed in a graphite crucible and debonded at 1200°C; in step 4), the raw material powder is directly loaded into a special graphite hot pressing mold and sintered at high temperature and high pressure.

[0037] In the present disclosure, the density of the SiC / MCMBs composite material of the present invention is measured by the Archimedean method to be ≥97%.

[0038] In the present disclosure, the flexural strength of the SiC / MCMBs composite material of the present invention is measured by a three-point bending method and is found to be 280-450 MPa.

[0039] In the present disclosure, the fracture toughness of the SiC / MCMBs composite material of the present invention is measured by the single-edge notched beam method to be 3-5 MPa 2m 1 / 2 .

[0040] In the present disclosure, the dry friction coefficient of the SiC / MCMBs composite material of the present invention is measured to be 0.16 to 0.31 by using the block-on-ring method (test conditions are generally 49 to 98 N load, 200 r / min).

[0041] The following further examples are given to illustrate the present invention in detail. It should also be understood that the following examples are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​exemplified below.

[0042] In the following examples and comparative examples, unless otherwise specified, the particle size of the silicon carbide powder is 0.5 μm, the mesophase carbon microspheres are produced by Rongtan Technology Co., Ltd. with a particle size of 8 μm, and the silicon carbide polymer precursor is HPCS-D11 / 12 prepared by the Institute of Chemistry, Chinese Academy of Sciences.

[0043] Example 1

[0044] Raw materials such as 1 wt% liquid polycarbosilane, 68.4 wt% silicon carbide powder, 30 wt% mesophase carbon microsphere green balls, and 0.6 wt% boron carbide were successively added to cyclohexane and thoroughly mixed evenly by a planetary ball mill. The rotation speed of the planetary ball mill was 300 r / h, and the mass ratio of material:ball:cyclohexane was 1:2:1. Then it was dried in an oven at 60 °C for 8 h, passed through a 100-mesh sieve to obtain the raw material powder. The prepared raw material powder was loaded into a graphite crucible and subjected to debinding treatment at 1200 °C for 0.5 h. After secondary grinding, it was loaded into a graphite hot pressing mold and sintered under the conditions of 2100 °C, 40 MPa, and 1 h in an argon atmosphere. The prepared composite material had a uniform distribution of two phases, a strong interfacial bond, and a relative density of 97.6%.

[0045] Example 2

[0046] Raw materials such as 5 wt% liquid polycarbosilane, 64.4 wt% silicon carbide powder, 30 wt% mesophase carbon microsphere green balls, and 0.6 wt% boron carbide were successively added to cyclohexane and thoroughly mixed evenly by a planetary ball mill. The rotation speed of the planetary ball mill was 300 r / h, and the mass ratio of material:ball:cyclohexane was 1:2:1. Then it was dried in an oven at 60 °C for 8 h, passed through a 100-mesh sieve to obtain the raw material powder. The prepared raw material powder was loaded into a graphite crucible and subjected to debinding treatment at 1200 °C for 0.5 h. After secondary grinding, it was loaded into a graphite hot pressing mold and sintered under the conditions of 2100 °C, 40 MPa, and 1 h in an argon atmosphere. The prepared composite material had a uniform distribution of two phases, a strong interfacial bond, and a relative density of 98.1%.

[0047] Figure 2 The SEM image of the SiC / MCMBs composite material prepared in this example is shown. From Figure 2 It can be seen that the mesophase carbon microspheres in this example are uniformly distributed in the silicon carbide matrix. Figure 3 The HRTEM image of the two-phase interface of the SiC / MCMBs composite material prepared in this example is shown. From Figure 3 It can be seen that the liquid polycarbosilane in this example is between the mesophase carbon microspheres and the two phases of silicon carbide. Silicon carbide microcrystals and a small amount of free carbon are generated at the two-phase interface, improving the interfacial strength between SiC and MCMBs.

[0048] Example 3

[0049] 9 wt% liquid polycarbosilane, 60.4 wt% silicon carbide powder, 30 wt% heat-treated mesocarbon microbeads, 0.6 wt% boron carbide and other raw materials were sequentially added to cyclohexane and thoroughly mixed evenly by a planetary ball mill. The rotation speed of the planetary ball mill was 300 r / h, and the mass ratio of material:ball:cyclohexane was 1:2:1. Then it was dried in an oven at 60 °C for 8 h, passed through a 100-mesh sieve to obtain the raw material powder. The prepared raw material powder was loaded into a graphite crucible and subjected to debinding treatment at 1200 °C for 0.5 h. After secondary grinding, it was loaded into a graphite hot pressing mold and sintered under the conditions of 2050 °C, 40 MPa, and 1 h in an argon atmosphere. The prepared composite material had a uniform distribution of two phases, a strong interfacial bond, and a relative density of 97.0%.

[0050] Example 4

[0051] 5 wt% liquid polycarbosilane, 74.4 wt% silicon carbide powder, 20 wt% heat-treated mesocarbon microbeads, 0.6 wt% boron carbide and other raw materials were sequentially added to cyclohexane and thoroughly mixed evenly by a planetary ball mill. The rotation speed of the planetary ball mill was 300 r / h, and the mass ratio of material:ball:cyclohexane was 1:2:1. Then it was dried in an oven at 60 °C for 8 h, passed through a 100-mesh sieve to obtain the raw material powder. The prepared raw material powder was loaded into a graphite crucible and subjected to debinding treatment at 1200 °C for 0.5 h. After secondary grinding, it was loaded into a graphite hot pressing mold and sintered under the conditions of 2100 °C, 40 MPa, and 1 h in an argon atmosphere. The prepared composite material had a uniform distribution of two phases, a strong interfacial bond, and a relative density of 97.7%.

[0052] Example 5

[0053] 5 wt% liquid polycarbosilane, 69.4 wt% silicon carbide powder, 25 wt% heat-treated mesocarbon microbeads, 0.6 wt% boron carbide and other raw materials were sequentially added to cyclohexane and thoroughly mixed evenly by a planetary ball mill. The rotation speed of the planetary ball mill was 300 r / h, and the mass ratio of material:ball:cyclohexane was 1:2:1. Then it was dried in an oven at 60 °C for 8 h, passed through a 100-mesh sieve to obtain the raw material powder. The prepared raw material powder was loaded into a graphite crucible and subjected to debinding treatment at 1200 °C for 0.5 h. After secondary grinding, it was loaded into a graphite hot pressing mold and sintered under the conditions of 2100 °C, 40 MPa, and 1 h in an argon atmosphere. The prepared composite material had a uniform distribution of two phases, a strong interfacial bond, and a relative density of 97.9%.

[0054] Example 6

[0055] 5 wt% liquid polycarbosilane, 64.4 wt% silicon carbide powder, 30 wt% of heat-treated mesocarbon microbeads, 0.6 wt% boron carbide and other raw materials were added to cyclohexane in sequence and thoroughly mixed by a planetary ball mill. The rotation speed of the planetary ball mill was 300 r / h, and the mass ratio of material:ball:cyclohexane was 1:2:1. Then it was dried in an oven at 60 °C for 8 h, passed through a 100-mesh sieve to obtain the raw material powder. The prepared raw material powder was loaded into a graphite crucible and degreased at 900 °C for 0.5 h. After secondary grinding, it was loaded into a graphite hot pressing mold and sintered under the conditions of 2150 °C, 40 MPa and 1 h in an argon atmosphere. The prepared composite material had a uniform distribution of two phases, a strong interfacial bond, and a relative density of 97.4%.

[0056] Example 7

[0057] 5 wt% liquid polycarbosilane, 64.4 wt% silicon carbide powder, 30 wt% of heat-treated mesocarbon microbeads, 0.6 wt% boron carbide and other raw materials were added to cyclohexane in sequence and thoroughly mixed by a planetary ball mill. The rotation speed of the planetary ball mill was 300 r / h, and the mass ratio of material:ball:cyclohexane was 1:2:1. Then it was dried in an oven at 60 °C for 8 h, passed through a 100-mesh sieve to obtain the raw material powder. The prepared raw material powder was loaded into a graphite crucible and degreased at 1200 °C for 0.5 h. After secondary grinding, it was loaded into a graphite hot pressing mold and sintered under the conditions of 2200 °C, 40 MPa and 1 h in an argon atmosphere. The prepared composite material had a uniform distribution of two phases, a strong interfacial bond, and a relative density of 98.4%.

[0058] Comparative Example

[0059] 69.4 wt% silicon carbide powder, 30 wt% of heat-treated mesocarbon microbeads, 0.6 wt% boron carbide and other raw materials were added to absolute ethanol in sequence and thoroughly mixed by a planetary ball mill. The rotation speed of the planetary ball mill was 300 r / h, and the mass ratio of material:ball:absolute ethanol was 1:2:1. Then it was dried in an oven at 60 °C for 8 h, passed through a 100-mesh sieve to obtain the raw material powder. It was loaded into a graphite hot pressing mold and sintered under the conditions of 2150 °C, 40 MPa and 1 h in an argon atmosphere. The prepared composite material had a uniform distribution of two phases, a general interfacial bond, and a relative density of 97.4%.

[0060] Performance Test:

[0061] The test items include:

[0062] 1. The relative density of the SiC / MCMBs composite materials of Examples 1-7 and the comparative example of the present invention was measured by the Archimedes method.

[0063] 2. The flexural strength of the SiC / MCMBs composites of Examples 1-7 of the present invention and the comparative examples was measured by the three-point bending method.

[0064] 3. The fracture toughness of the SiC / MCMBs composites of Examples 1-7 of the present invention and the comparative examples was measured by the single-edge notched beam method.

[0065] 4. The dry friction coefficient of the SiC / MCMBs composites of Examples 1-7 of the present invention and the comparative examples was measured by the ring-block method (the test conditions are generally 49-98 N load and 200 r / min).

[0066] The test data are listed in Table 1 below.

[0067] Table 1

[0068]

[0069] As can be seen from Table 1, by comparing the comparative example with Example 2, it is found that under the same preparation process, although the flexural strength of the SiC / MCMBs self-lubricating composite material modified by adding liquid polycarbosilane interface decreases, and the elastic modulus is not much different, the density and fracture toughness of the composite material are improved to a certain extent. When the comparative example and Experimental Example 2 were respectively paired with a self-prepared friction pair for rubbing, after the running-in period, at a load of 98 N, the μ of the comparative example was between 0.16 and 0.22, while the μ of Example 2 varied between 0.16 and 0.19. The low and stable μ can be attributed to the formation of a continuous and lubricating film with a certain thickness by graphitized MCMBs. In addition, the worn surface is almost completely covered by the tribochemical film. Compared with the comparative example, the brittle debris on the worn surface of Experimental Example 2 is significantly reduced, which is beneficial to preventing the lubricating film from being damaged by abrasive wear. It can be seen that the dry friction coefficient μ of the SiC / MCMBs self-lubricating composite material of the present invention is more stable, and the problem of the shedding of hard silicon carbide particles during the friction and wear process is significantly improved.

Claims

1. A SiC / MCMBs composite material, characterized in that, The invention comprises a SiC matrix and mesophase carbon microspheres MCMBs distributed in the SiC matrix; wherein the mesophase carbon microspheres MCMBs are graphitized carbon microspheres; the mesophase carbon microspheres MCMBs are modified by a silicon carbide polymer precursor to form silicon carbide microcrystals and free carbon at the interface between the SiC and the mesophase carbon microspheres MCMBs, and the silicon carbide polymer precursor is a liquid polycarbosilane containing vinyl; and the preparation method of the SiC / MCMBs composite material comprises: Dissolving a silicon carbide polymer precursor, mesophase carbon microspheres MCMBs, silicon carbide powder, and a sintering aid in an organic solvent, ball milling, drying, and sieving to obtain a raw material powder; in the raw material powder, the weight percentage of the silicon carbide polymer precursor is 1-5%, the weight percentage of the silicon carbide powder is 50-80%, and the weight percentage of the mesophase carbon microspheres MCMBs is 15-30%; The raw material powder is subjected to a debonding treatment, the debonded raw material powder is placed in a hot pressing mold, and then hot-pressed and sintered in a protective atmosphere to obtain the SiC / MCMBs composite material.

2. The SiC / MCMBs composite material according to claim 1, wherein The mass ratio of the silicon carbide polymer precursor to the mesophase carbon microspheres MCMBs is 0.03-0.

67.

3. The SiC / MCMBs composite material according to claim 1, wherein The sintering aid is at least one of a single substance of boron and a boron compound, and the content thereof does not exceed 1 wt %.

4. The SiC / MCMBs composite material according to claim 3, wherein The sintering aid is at least one of boron, boric acid and boron carbide, and the content thereof is 0.5-1.0 wt %.

5. The SiC / MCMBs composite material according to claim 1, wherein The dry friction coefficient of the SiC / MCMBs composite material is 0.16-0.

31.

6. The SiC / MCMBs composite material according to claim 1, wherein The particle size of the mesophase carbon microspheres MCMBs is 5 μm to 10 μm; the particle size of the silicon carbide powder is 0.5 μm to 2.0 μm.

7. The SiC / MCMBs composite material according to claim 1, wherein The organic solvent is cyclohexane, tetrahydrofuran, benzene, toluene or xylene.

8. The SiC / MCMBs composite material according to claim 1, characterized in that, The protective atmosphere is a vacuum or an inert atmosphere, and the inert atmosphere is argon; the pressure of hot pressing sintering is 30-60 MPa, the sintering temperature is 2000-2200° C., and the sintering time is 1-3 hours.

9. The SiC / MCMBs composite material according to claim 1, wherein The debonding treatment is carried out in a protective atmosphere at 900-1200° C. for 0.5-2 hours.

10. Use of the SiC / MCMBs composite material according to any one of claims 1 to 9 in limited lubrication and short-time dry friction working conditions.

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