A method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics

Abstract

The present application relates to the field of tribology and material cross, in particular to a kind of surface structure preparation method for improving the wear resistance of B4C ceramic to realize self-lubrication.Firstly, B4C and Al2O3 powder are weighed, ball-milled, dried and sieved to obtain mixed powder;Then the mixed powder is hot-pressed and sintered to obtain a block;The block is ground and polished to obtain the final B4C-Al2O3 composite ceramic.The B4C-Al2O3 composite ceramic prepared by the present application can form a concave-convex relief structure in situ on the wear surface during dry sliding due to the hardness difference between B4C and Al2O3 two phases.On the one hand, the relief structure can trap the nanoscale wear debris generated during sliding, reducing abrasive wear;On the other hand, the relief structure can reduce the real contact area between B4C ceramic and the counterbody, thereby effectively reducing the adhesive wear of B4C ceramic, improving the wear resistance of B4C ceramic and realizing self-lubrication.

Description

Technical Field

[0001] This invention relates to the interdisciplinary field of tribology and materials science, and more specifically, to a method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics. Background Technology

[0002] B4C ceramics have the advantages of high hardness, high melting point and low density, so they are widely used in military, aerospace and other fields.

[0003] B4C has a hardness second only to diamond and cubic boron nitride. Its extremely high hardness makes B4C ceramics an excellent candidate material for wear-resistant components, which can be used to manufacture sliding bearings, sealing rings, sandblasting nozzles, high-speed cutting tools, etc. Although the extremely high hardness of B4C ceramics makes it a candidate material for wear-resistant components, when B4C ceramics slide against the grinding body with ceramics with similar chemical properties, adhesive wear is prone to occur (Wei Zhang, et al. Tribological properties of SiC-B4Cceramics underdry sliding condition. Journal of the European Ceramic Society, 2020, 40(8):2855-2861.), which limits its widespread application as a wear-resistant component.

[0004] Although boron carbide (B4C) ceramics possess excellent wear resistance, they still face the bottleneck of a high coefficient of friction. Under dry sliding conditions, the coefficient of friction for B4C ceramics reaches approximately 0.6. This high coefficient of friction means that the frictional work required during the sliding process is substantial, resulting in high energy consumption in the friction system. This is detrimental to energy conservation and emission reduction requirements, limiting the widespread application of B4C ceramics. While adding lubricants can reduce the coefficient of friction of boron carbide ceramics, lubricants cannot be used in certain specific environments.

[0005] Therefore, it is necessary to invent a method to improve the wear resistance and self-lubrication of B4C ceramics to solve the above problems. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics, thereby solving the problem of adhesive wear that easily occurs when B4C ceramics slide against a grinding body with ceramics of similar chemical properties. The B4C-Al2O3 composite ceramic prepared by this method has a low coefficient of friction.

[0007] The technical solution of this invention is:

[0008] A method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics includes the following steps:

[0009] Step 1: Weigh the B4C and Al2O3 powders, ball mill them together, dry them, and sieve them to obtain the mixed powder;

[0010] Step 2: The mixed powder is hot-pressed and sintered to obtain a block;

[0011] Step 3: Grind and polish the bulk material to obtain the final B4C-Al2O3 composite ceramic;

[0012] Step 4: During dry sliding, the B4C-Al2O3 composite ceramic forms an in-situ relief structure on the wear surface.

[0013] In the method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics, in step one, the mass fraction of B4C is 60%–90%, and the mass fraction of Al2O3 is 10%–40%.

[0014] In the method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics, in step one, the particle size of B4C powder is ≤0.5μm and the particle size of Al2O3 powder is ≤2.0μm.

[0015] The method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics, in step one, uses anhydrous ethanol as the milling medium, silicon carbide and nylon as the milling ball material and milling jar material, respectively, with a milling speed of 250-300 r / min, a milling time of 12-24 h and a sieve mesh size greater than 80 mesh.

[0016] In the method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics, in step two, hexagonal boron nitride is uniformly brushed onto a graphite mold, a graphite sleeve, a graphite gasket, and a graphite pressure head. The hot pressing sintering temperature is 1950–2000℃, the pressure is 30–35 MPa, and the maximum pressure is applied 100–200℃ before the highest temperature. The maximum temperature and pressure are maintained for 1–2 hours.

[0017] In the method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics, in step three, the surface of the B4C-Al2O3 composite ceramic is successively ground with resin diamond grinding discs of 400 mesh, 800 mesh, 1500 mesh, and 3000 mesh, and then polished with 5000 mesh diamond polishing paste to control the surface roughness of the B4C-Al2O3 composite ceramic between 0.035 and 0.055 μm.

[0018] In the method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics, in step four, the grinding media of the B4C-Al2O3 composite ceramic is a silicon carbide ball with a diameter of 8mm, a load of 5N, a sliding distance of 200m, and a sliding speed of 0.1m / s; the properties of the silicon carbide ball grinding media are: density 3.1g / cm³.3 It has a density of 96.5%, a hardness of 20–27 GPa, a flexural strength of 400 MPa, and a fracture toughness of 3–4 MPa·m. 1 / 2 .

[0019] In the method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics, in step four, the Al2O3 with lower hardness is preferentially worn by the fragments generated during the wear process to form pits, and Al2O3 and B4C are arranged alternately on the wear surface.

[0020] The design concept of this invention is:

[0021] Al2O3 has a lower hardness than B4C. Introducing a second phase, Al2O3, with a hardness different from that of B4C grains into B4C ceramics creates a B4C-Al2O3 composite ceramic. During dry sliding, due to the hardness difference between the B4C and Al2O3 phases, the lower-hardness Al2O3 is preferentially worn away by the debris generated during the wear process. This results in an in-situ relief structure on the wear surface of the B4C-Al2O3 composite ceramic, reducing its coefficient of friction and achieving self-lubrication. This relief structure is similar to pits created on the material surface using laser technology, but unlike pits that gradually disappear due to wear during sliding, this relief structure forms in situ during the sliding process. On one hand, the relief structure can trap wear debris generated during sliding, reducing abrasive wear; on the other hand, the relief structure can reduce the actual contact area between the B4C ceramic and the wear block, reducing the contact points between the composite ceramic and the wear block, thus reducing the force required to break these connections, and also reducing adhesive wear of the B4C ceramic. Therefore, adding Al2O3 particles to the B4C ceramic matrix can enable the B4C-Al2O3 composite ceramic to form an in-situ relief structure on the wear surface during dry sliding, thereby effectively reducing the wear rate of B4C ceramic under dry sliding conditions and improving the wear resistance of B4C ceramic.

[0022] The present invention has the following advantages and beneficial effects:

[0023] (1) In this invention, B4C powder and Al2O3 powder are mixed and dried by wet high-energy ball milling to obtain a mixed powder. The mixed powder is then ground and sieved. Under the protection of a flowing Ar atmosphere, the mixed powder is hot-pressed and sintered. After further grinding and polishing, B4C-Al2O3 composite ceramic is obtained. Thus, by introducing Al2O3, which is easier to sinter, relatively cheaper, and has a lower hardness than B4C, B4C-Al2O3 composite ceramic can be prepared at a relatively low temperature. On the other hand, the B4C-Al2O3 composite ceramic can form an in-situ relief structure on the wear surface during dry sliding. This structure greatly reduces the adhesive wear of B4C ceramic and improves its wear resistance. This structure also greatly reduces the friction coefficient of B4C ceramic, achieving self-lubrication, with a friction coefficient of 0.35 to 0.53.

[0024] (2) The raw materials used in this invention are inexpensive, the preparation method is simple, the cost is low, and the effect is obvious. Attached Figure Description

[0025] Other features, objects, and advantages of the invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings.

[0026] Figure 1 This is a schematic diagram of the two-dimensional structure of the B4C-Al2O3 composite ceramic surface in an embodiment of the present invention.

[0027] Figure 2 The figures show the X-ray diffraction patterns of the B4C-Al2O3 composite ceramics in Examples 1, 2, and 3 of this invention. In the figures, the horizontal axis 2θ represents the diffraction angle (°), and the vertical axis Intensity represents the relative intensity (au).

[0028] Figure 3 This is a cross-sectional transmission electron microscope (TEM) image of the worn surface of the B4C-Al2O3 composite ceramic in Example 2 of the present invention.

[0029] Figure 4 This is a field emission scanning electron microscope (SEM) image of the wear surface of the B4C-Al2O3 composite ceramic in Example 3 of the present invention.

[0030] Figure 5 This is a schematic diagram of the three-dimensional structure of the B4C-Al2O3 composite ceramic surface in an embodiment of the present invention. Detailed Implementation

[0031] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that the invention will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art.

[0032] In a specific implementation, a method for preparing B4C-Al2O3 composite ceramic material is provided. First, B4C powder and Al2O3 powder are mixed in a specific ratio and then subjected to high-energy ball milling in anhydrous ethanol. After uniform mixing, a slurry is obtained, which is then dried to obtain a uniformly mixed raw material powder. The mixed powder is then ground and sieved. Next, under a flowing Ar atmosphere, the mixed powder is hot-pressed and sintered to generate the B4C-Al2O3 composite ceramic block. Finally, the block is ground and polished to obtain the finished product.

[0033] Preferably, the steps include the following:

[0034] (1) Add B4C powder and Al2O3 powder to a ball mill jar and mix them evenly to obtain a mixed slurry; dry them to obtain a mixed powder.

[0035] By mass ratio, the mixed powder contains 60%–90% B4C and 10%–40% Al2O3.

[0036] The preferred particle size of B4C powder is ≤0.5μm; the preferred particle size of Al2O3 powder is ≤2.0μm.

[0037] The preferred high-energy ball mill is the QM-BP planetary ball mill.

[0038] The grinding jar and grinding balls of the preferred high-energy ball mill are made of nylon and silicon carbide, respectively.

[0039] The preferred ball milling parameters are: anhydrous ethanol as the ball milling medium; a ball-to-material weight ratio of 3:1; a ball mill speed of 250–300 r / min; and a ball milling time of 12–24 h.

[0040] The preferred drying process is as follows:

[0041] After the ball milling process, the mixed slurry is evaporated and dried in a constant temperature chamber at 60-70℃ for 12-24 hours until the ball milling media has completely evaporated.

[0042] (2) Grind and sieve the mixed powder.

[0043] The preferred sieving process is as follows: the mixed powder is ground and crushed in an agate mortar and then passed through an 80-200 mesh sieve.

[0044] (3) Under the protection of flowing Ar atmosphere, the mixed powder is sintered in a hot pressing sintering furnace to obtain B4C-Al2O3 composite ceramic material.

[0045] The preferred sintering process is as follows:

[0046] First, the temperature is increased from room temperature to 1000℃ at a heating rate of 10-15℃ / min; then the heating rate is adjusted to 5-8℃ / min, and the temperature is increased from 1000℃ to 1950℃-2000℃; the pressure is applied at 30-35MPa, and the pressure is slowly increased from 1500℃ to the maximum value 100-200℃ before the target temperature; the temperature and pressure are maintained for 1-2 hours to obtain B4C-Al2O3 composite ceramic bulk.

[0047] The present invention will now be described with reference to specific embodiments.

[0048] Example 1:

[0049] In this embodiment, a method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramic includes the following steps:

[0050] (1) 80g of B4C powder with a particle size of 0.2μm and 20g of Al2O3 powder with a particle size of 1.0μm were placed in a ball mill jar. Grinding balls were added at a ball-to-material ratio (mass) of 3:1. The mixture was ball-milled at 285r / min for 24h using anhydrous ethanol as the ball milling medium. Then it was dried at 60℃ for 24h and passed through an 80-mesh sieve to obtain mixed powder.

[0051] (2) Place the above powder in a graphite mold, and evenly brush h-BN onto the inner wall of the graphite mold, the inside and outside of the sleeve, the upper and lower pressure heads, and the surface of the graphite gasket. Place graphite paper between the powder and the graphite gasket. First, raise the temperature from room temperature to 1000℃ at a heating rate of 10℃ / min. Then, raise the temperature from 1000℃ to 1950℃ at a heating rate of 8℃ / min. The hot pressing sintering temperature is 1950℃. The applied pressure is 30MPa, which is slowly increased from 1500℃ to the maximum value at 1850℃. The sintering time is 1h, accompanied by flowing Ar.

[0052] (3) Remove the graphite paper from the sintered material and smooth the sample by polishing the edges with 400-mesh and 800-mesh silicon carbide sandpaper. Grind the material surface sequentially using 400-mesh, 800-mesh, 1500-mesh, and 3000-mesh resin diamond grinding discs, and polish the material with 5000-mesh diamond polishing paste. During the grinding and polishing process, the resin diamond grinding disc rotates at 100 r / min and the pressure is 0.5 kg. Finally, a self-lubricating B4C-Al2O3 composite ceramic with a surface roughness between 0.035 and 0.055 μm is obtained.

[0053] like Figure 1 , Figure 5As shown, the phase composition of the composite ceramic prepared in Example 1 is B4C and Al2O3, indicating that no new phase is generated in the composite ceramic.

[0054] Example 2:

[0055] In this embodiment, a method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramic includes the following steps:

[0056] (1) 70g of B4C powder with a particle size of 0.1μm and 30g of Al2O3 powder with a particle size of 0.5μm were placed in a ball mill jar. Grinding balls were added at a ball-to-material ratio (mass) of 3:1. The mixture was ball-milled at 285r / min for 24h using anhydrous ethanol as the ball milling medium. Then it was dried at 60℃ for 24h and passed through an 80-mesh sieve to obtain mixed powder.

[0057] (2) Place the above powder in a graphite mold, and evenly brush h-BN onto the inner wall of the graphite mold, the inside and outside of the sleeve, the upper and lower pressure heads, and the surface of the graphite gasket. Place graphite paper between the powder and the graphite gasket. First, raise the temperature from room temperature to 1000℃ at a heating rate of 10℃ / min. Then, raise the temperature from 1000℃ to 1950℃ at a heating rate of 8℃ / min. The hot pressing sintering temperature is 1950℃. The applied pressure is 30MPa, which is slowly increased from 1500℃ to the maximum value at 1850℃. The sintering time is 1h, accompanied by flowing Ar.

[0058] (3) Remove the graphite paper from the sintered material and smooth the sample by polishing the edges with 400-mesh and 800-mesh silicon carbide sandpaper. Grind the material surface sequentially using 400-mesh, 800-mesh, 1500-mesh, and 3000-mesh resin diamond grinding discs, and polish the material with 5000-mesh diamond polishing paste. During the grinding and polishing process, the resin diamond grinding disc rotates at 100 r / min and the pressure is 0.5 kg. Finally, a self-lubricating B4C-Al2O3 composite ceramic with a surface roughness between 0.035 and 0.055 μm is obtained.

[0059] like Figure 2 and Figure 3 The X-ray diffraction pattern and transmission electron microscope (TEM) image of the worn surface of the B4C-Al2O3 composite ceramic in Example 2 are shown respectively. The analysis results are as follows:

[0060] according to Figure 2 It can be seen that the prepared composite ceramic only has two phases: B4C and Al2O3. According to... Figure 3It can be seen that an in-situ surface relief structure is formed on the wear surface of the B4C-Al2O3 composite ceramic after dry sliding, that is, a height difference is generated between the B4C and Al2O3 grains. The relief structure can trap the nanoscale wear debris generated during sliding, reducing abrasive wear; at the same time, the relief structure can reduce the actual contact area between the B4C ceramic and the wear block, thereby effectively reducing the adhesive wear of the B4C ceramic.

[0061] Example 3:

[0062] In this embodiment, a method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramic includes the following steps:

[0063] (1) 60g of B4C powder with a particle size of 0.1μm and 40g of Al2O3 powder with a particle size of 0.5μm were placed in a ball mill jar. Grinding balls were added at a ball-to-material ratio (mass) of 3:1. The mixture was ball-milled at 285r / min for 24h using anhydrous ethanol as the ball milling medium. Then it was dried at 60℃ for 24h and passed through an 80-mesh sieve to obtain mixed powder.

[0064] (2) Place the above powder in a graphite mold, and evenly brush h-BN onto the inner wall of the graphite mold, the inside and outside of the sleeve, the upper and lower pressure heads, and the surface of the graphite gasket. Place graphite paper between the powder and the graphite gasket. First, raise the temperature from room temperature to 1000℃ at a heating rate of 10℃ / min. Then, raise the temperature from 1000℃ to 1950℃ at a heating rate of 8℃ / min. The hot pressing sintering temperature is 1950℃. The applied pressure is 30MPa, which is slowly increased from 1500℃ to the maximum value at 1850℃. The sintering time is 1h, accompanied by flowing Ar.

[0065] (3) Remove the graphite paper from the sintered material and smooth the sample by polishing the edges with 400-mesh and 800-mesh silicon carbide sandpaper. Grind the material surface sequentially using 400-mesh, 800-mesh, 1500-mesh, and 3000-mesh resin diamond grinding discs, and polish the material with 5000-mesh diamond polishing paste. During the grinding and polishing process, the resin diamond grinding disc rotates at 100 r / min and the pressure is 0.5 kg. Finally, a self-lubricating B4C-Al2O3 composite ceramic with a surface roughness between 0.035 and 0.055 μm is obtained.

[0066] like Figure 2 and Figure 4 The X-ray diffraction pattern and field emission scanning electron microscope (SEM) microstructure of the B4C-Al2O3 composite ceramic of Example 3 are shown respectively. The analysis results are as follows:

[0067] according to Figure 2 It can be seen that the prepared composite ceramic only has two phases: B4C and Al2O3. According to... Figure 4It can be seen that there is no obvious adhesive wear on the material surface. The relief structure reduces the actual contact area between the composite ceramic and the grinding body, thereby reducing the contact points between the composite ceramic and the grinding body and thus reducing the force required to break these connections. It also effectively reduces adhesive wear when the B4C ceramic slides with the grinding body, thus demonstrating a reduced wear rate.

[0068] Comparative example:

[0069] A single-phase B4C ceramic was used as a comparative example, consisting of 91g of B4C powder, 3.6g of Al2O3 powder, and 5.4g of Y2O3 powder. At high temperature, Al2O3 reacted with Y2O3 to form yttrium aluminum garnet (Y3Al5O3). 12 This is used to promote the sintering of single-phase B4C ceramics. The preparation process of single-phase B4C ceramics is the same as in Example 1.

[0070] Test example:

[0071] The wear rate of the B4C-Al2O3 composite ceramics and single-phase B4C ceramics prepared in the examples and comparative examples was determined using a ball-disc controlled atmosphere micro tribology and wear tester (instrument model UMT-2). The test conditions were as follows: SiC ball with a grinding body diameter of 8 mm; circumferential sliding with a radius of 8 mm; sliding distance of 200 m; sliding speed of 0.1 m / s; applied load of 5 N; and friction method of dry friction in air (oil-free lubrication). The mechanical properties and wear rates of the B4C-Al2O3 composite ceramics and single-phase B4C ceramics prepared in Examples 1-3 and the comparative examples are shown in Table 1.

[0072] Table 1: Mechanical properties and wear rates of B4C-Al2O3 composite ceramics and single-phase B4C ceramics prepared in Examples 1-3 and the comparative examples

[0073]

[0074] The friction coefficients of the B4C-Al2O3 composite ceramics and single-phase B4C ceramics prepared in the examples and comparative examples were determined using a ball-disc controlled atmosphere micro tribology and wear tester (instrument model UMT-2). The test conditions were as follows: SiC ball with a grinding body diameter of 8 mm; circumferential sliding with a radius of 8 mm; sliding distance of 200 m; sliding speed of 0.1 m / s; applied load of 5 N; and friction method of dry friction in air (oil-free lubrication).

[0075] Table 2: Relative density and steady-state friction coefficient of B4C-Al2O3 composite ceramics and single-phase B4C ceramics

[0076] Example number relative density steady-state friction coefficient Example 1 96.1％ 0.46 Example 2 98.8％ 0.35 Example 3 98.5％ 0.53 Comparative Example 98.4％ 0.58

[0077] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics, characterized in that, Includes the following steps: Step 1: Weigh the B4C and Al2O3 powders, ball mill them together, dry them, and sieve them to obtain a mixed powder; the mass fraction of B4C is 60%~90%, the mass fraction of Al2O3 is 10~40%, the particle size of B4C powder is ≤0.5 μm, and the particle size of Al2O3 powder is ≤2.0 μm; Step 2: Under the protection of flowing Ar atmosphere, the mixed powder is hot-pressed and sintered to obtain a bulk material; the hot-pressing and sintering temperature is 1950~2000 ℃, the pressure is 30~35 MPa, the maximum pressure is applied 100~200 ℃ before the highest temperature, and the temperature and pressure are held at the highest temperature for 1~2 h. The phase composition of the composite ceramic is B4C and Al2O3. Step 3: Grind and polish the bulk material to obtain the final B4C-Al2O3 composite ceramic, and control the surface roughness of the B4C-Al2O3 composite ceramic between 0.035 and 0.055 μm; Step 4: During dry sliding, the B4C-Al2O3 composite ceramic forms an in-situ relief structure on the wear surface. The Al2O3 with lower hardness is preferentially worn by the fragments generated during the wear process, forming pits. The Al2O3 and B4C are arranged alternately on the wear surface, and their friction coefficient is 0.35~0.

53.

2. The method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics according to claim 1, characterized in that, In step one, the grinding media is anhydrous ethanol, and the grinding balls and grinding jar are made of silicon carbide and nylon, respectively. The grinding speed is 250~300 r / min, the grinding time and drying time are both 12~24 h, and the sieve mesh is greater than 80 mesh.

3. The method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics according to claim 1, characterized in that, In step four, the grinding media of the B4C-Al2O3 composite ceramic is a silicon carbide ball with a diameter of 8 mm, a load of 5 N, a sliding distance of 200 m, and a sliding speed of 0.1 m / s; the properties of the silicon carbide ball grinding media are: density 3.1 g / cm³. 3 It has a density of 96.5%, a hardness of 20-27 GPa, a flexural strength of 400 MPa, and a fracture toughness of 3-4 MPa·m. 1 / 2 .

4. The method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics according to claim 1, characterized in that, In step two, the graphite mold, graphite sleeve, graphite gasket, and graphite pressure head are evenly brushed with hexagonal boron nitride.

5. The method for preparing a self-lubricating surface structure to improve the wear resistance of B4C ceramics according to claim 1, characterized in that, In step three, the surface of the B4C-Al2O3 composite ceramic is ground sequentially with resin diamond grinding discs of 400 mesh, 800 mesh, 1500 mesh, and 3000 mesh, and then polished with 5000 mesh diamond polishing paste.

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