Preparation method of high-wear-resistance ceramic composite bearing

Abstract

The invention discloses a preparation method of a high-wear-resistance ceramic composite bearing. The preparation method comprises the following steps: S1, raw material gradient premixing preparation; s2, gradient green body forming and charging; s3, performing magnetic control SPS (spark plasma sintering) cooperative sintering; s4, activating the interface of the ceramic body; s5, preparing a / hydroxyapatite gradient transition layer; and S6, performing precise post-treatment and performance detection. The method solves the problems that the traditional ceramic bearing is difficult to meet the requirements of high-wear-resistance and high-stability harsh working conditions due to the fact that the inner and outer layers are homogenized due to homogenized mixing of the raw materials, the sintering compactness is insufficient, the coating is weak in binding force and easy to fall off due to simple interface treatment, and the post-treatment precision is low due to the fact that the coating cannot meet the requirements of high-wear-resistance and high-stability harsh working conditions.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of bearing processing, in particular to a preparation method of a high-wear-resistance ceramic composite bearing. BACKGROUND

[0002] In the field of industrial production and high-end equipment, bearings, as the core basic components for realizing the rotation transmission of mechanical parts, directly determine the operation efficiency, stability and service life of equipment. With the development of modern industry towards high precision, high load and long period continuous operation, the traditional metal material bearing has inherent defects such as low hardness, easy wear and weak corrosion resistance, and has been difficult to meet the use requirements in severe working conditions. Ceramic material has become an ideal choice for preparing high-performance bearings due to its excellent hardness, excellent wear resistance, good chemical stability and high-temperature resistance. Therefore, ceramic composite bearings have become an important research direction in the field of bearings. At present, the preparation technology of ceramic composite bearings focuses on optimizing the material formula, innovating the structure design and improving the process, so as to further improve the comprehensive performance. Among them, the gradient structure design can adapt different performance requirements of different parts of the bearing, the multi-field synergistic sintering can optimize the microstructure of the ceramic body, and the interface modification and functional transition layer preparation can enhance the surface wear resistance and bonding performance. These technical directions jointly promote the development of ceramic composite bearings towards high wear resistance and high reliability.

[0003] At present, the traditional ceramic bearing preparation technology has many deficiencies in actual application, which is difficult to meet the severe requirements of high wear resistance: 1. In the raw material processing link, the traditional process mostly adopts the homogenization mixing method, without targeted formula adjustment according to the performance difference requirements of the inner and outer layers of the bearing, so that the overall performance of the bearing is homogenized, and the requirements of the inner layer for toughness and the surface layer for high wear resistance cannot be met at the same time. In complex working conditions, the inner layer is prone to fracture or the surface layer is prone to rapid wear; 2. In the sintering process, the traditional sintering technology mostly relies on single heating mechanism and lacks the synergistic effect of multi-energy field, which easily causes the insufficient density of the ceramic body, internal defects such as pores and micro-cracks, and significantly reduces the mechanical strength and fatigue resistance of the bearing; 3. The traditional interface treatment process is simple, and the surface of the ceramic body cannot be effectively activated. The bonding force between the coating or transition layer prepared subsequently and the body is weak, and the coating is prone to falling off during use, which further aggravates the wear; 4. The precision of the traditional post-processing is low, the surface roughness control is not good, and the performance detection indexes are not comprehensive enough, which makes it difficult to ensure the consistency and stability of the ceramic bearing. These defects greatly limit the application of traditional ceramic bearings in high-end fields. SUMMARY

[0004] In view of the deficiencies of the prior art, the application provides a preparation method of a high-wear-resistance ceramic composite bearing to solve the problems of the traditional ceramic bearing, i.e., the homogenization of the inner and outer layers due to the uniform mixing of raw materials, the insufficient sintering density, the weak coating adhesion due to the simple interface treatment, the easy peeling of the coating, and the low post-processing precision, which makes it difficult to meet the requirements of high-wear-resistance, high stability and harsh working conditions.

[0005] To achieve the above-mentioned purposes, the application provides a preparation method of a high-wear-resistance ceramic composite bearing, which comprises the following steps: S1, preparing base ceramic particles, graphene and a binder, taking two portions of base ceramic particles, adding different contents of graphene and different contents of the binder into the two portions of base ceramic particles respectively and mixing to obtain inner layer premix and surface layer premix; S2, pre-pressing the inner layer premix, covering the surface layer premix with the pre-pressed inner layer premix and pre-pressing again to obtain a gradient green body; S3, loading the gradient green body into a sintering device to perform gradient sintering on the gradient green body under the action of an alternating magnetic field and a pulse current to obtain a ceramic body; S4, heat treating the ceramic body in a nitrogen-oxygen mixed atmosphere; S5, sequentially depositing a bottom layer and a hydroxyapatite composite top layer on the surface of the ceramic body by electron beam deposition technology; S6, grinding, cleaning and performance testing the ceramic body processed by the electron beam deposition technology.

[0006] The application further provides that: the base ceramic particles in step S1 are composed of 90-95% of silicon nitride powder, 3-5% of yttrium oxide powder and 1-3% of aluminum oxide powder in terms of mass percentage; the surface layer of the graphene is added in an amount of 5-10wt% based on the mass of the base ceramic particles, and the inner layer of the graphene is added in an amount of 1-3wt% based on the mass of the base ceramic particles; the binder is a composite binder composed of chitosan and hydroxyapatite in a mass ratio of 3:1, the binder is added in an amount of 2-4% in the inner layer premix, and the binder is added in an amount of 3-5% in the surface layer premix.

[0007] The application further provides that: the silicon nitride powder of the base ceramic particles is in an alpha phase, and the content of the alpha phase is greater than or equal to 92%; the particle size of the silicon nitride powder is 0.8-5um, and the proportion of 1-3um particles in the silicon nitride powder is greater than or equal to 80%; the median diameter of the yttrium oxide powder of the base ceramic particles is 0.95-1.05um; the purity of the aluminum oxide powder in the base ceramic particles is greater than or equal to 99.9%, and the median diameter of the aluminum oxide powder is 0.75-0.85um.

[0008] The application further provides that: the inner layer premix in step S1 is prepared by ball milling at a ball-to-material ratio of 10:1 at a rotating speed of 250-300 r / min for 8-10 h; the surface layer premix is prepared by ball milling at a ball-to-material ratio of 12:1 at a rotating speed of 280-320 r / min for 10-12 h; the inner layer premix and the surface layer premix are dried and sieved after ball milling, the inner layer premix is sieved at a mesh number of 200, and the surface layer premix is sieved at a mesh number of 300.

[0009] The application further provides that: the pre-pressing process of the inner layer premix in step S2 is that the inner layer premix is pre-pressed at 15-20 MPa for 10-15 min to form an inner layer blank; and the surface layer premix is pre-pressed at 20-25 MPa for 8-10 min after being covered to a thickness of 1.0-1.5 mm.

[0010] The application further provides that: the alternating magnetic field parameters in step S3 are 50-200 Hz and 0.1-0.5 T, and the pulse current parameters are 10-20 kA and a duty cycle of 10-30 %; and the gradient sintering process is: heating from room temperature to 500 DEG C at a rate of 5 DEG C / min, keeping the temperature for 2 h, then heating to 1200 DEG C at a rate of 20 DEG C / min, keeping the temperature for 1 h, then heating to 1550 DEG C at a rate of 3 DEG C / min, keeping the temperature for 3-4 h, and finally cooling to 800 DEG C.

[0011] The application further provides that: the alternating magnetic field parameters are adjusted according to the bearing size requirements in step S3: when the bearing inner ring diameter is 20-30 mm, the alternating magnetic field parameters are 50-70 Hz / 0.15-0.25 T; when the bearing inner ring diameter is 30-50 mm, the alternating magnetic field parameters are 70-100 Hz / 0.25-0.3 T; when the bearing outer ring diameter is 50-70 mm, the alternating magnetic field parameters are 100-150 Hz / 0.35-0.45 T; and when the bearing outer ring diameter is 70-100 mm, the alternating magnetic field parameters are 150-200 Hz / 0.45-0.5 T.

[0012] The application further provides that: the oxygen content of the nitrogen-oxygen mixed atmosphere is 1-3 %, and the total gas pressure is 0.1-0.12 MPa in step S4; and the heat treatment process is: heating to 700-900 DEG C at a rate of 3-5 DEG C / min, keeping the temperature for 0.5-1.5 h, and then cooling with the furnace.

[0013] The application further provides that: the deposition thickness of the bottom layer is 50-100 nm in step S5. The deposition thickness of the bottom layer is 50-100 nm in step S5. The deposition thickness of the / hydroxyapatite composite top layer is 100-150 nm, wherein the mass ratio of the / hydroxyapatite composite top layer to the hydroxyapatite is 2:1. The deposition thickness of the bottom layer is 50-100 nm in step S5. The deposition thickness of the bottom layer is 50-100 nm in step S5. / hydroxyapatite composite top layer is annealed at 300 DEG C for 1h in a nitrogen atmosphere after deposition.

[0014] The application further provides that: the grinding in step S6 adopts a 1200-1500 mesh diamond grinding wheel, and the surface roughness Ra is controlled to be less than or equal to 0.08 microns; the cleaning adopts ultrasonic cleaning with a mixed solution of anhydrous ethanol and nitric acid in a volume ratio of 9:1 for 15-20 minutes; and the performance detection includes density detection and hardness detection.

[0015] The above technical solution has the advantages that: in the above technology, the inner layer and the surface layer premix are prepared respectively by gradient premixing design, so that the gradient distribution of the ceramic bearing raw material composition is realized, and the gradient sintering of the green body is performed by using the synergistic effect of the alternating magnetic field and the pulse current in combination with the magnetic control SPS synergistic sintering technology, and the magnetic field parameters are adapted according to the bearing size. The use of the above process design can effectively improve the density and structural uniformity of the ceramic body, avoid the performance difference between the inside and the outside of the traditional sintering, and also improve the toughness of the inner layer and the wear resistance of the surface layer by the gradient addition of graphene. The reasonable selection of the composite binder enhances the bonding between the raw materials, provides a stable foundation for the subsequent forming and sintering links, and makes the ceramic bearing body have excellent mechanical properties and wear resistance potential from the initial stage of preparation, thereby laying a solid structural foundation for subsequent performance improvement.

[0016] In the above technology, the interface activation treatment of the ceramic body is performed, the interface bonding state of the ceramic body is optimized by heat treatment in a nitrogen-oxygen mixed atmosphere, and then the / hydroxyapatite gradient transition layer is prepared by electron beam deposition technology, the gradient transition design of the bottom layer and the composite top layer effectively improves the bonding performance of the ceramic body and the outside world, reduces the interface defects, and the subsequent nitrogen atmosphere annealing further improves the structural stability of the transition layer. At the same time, the application of precision grinding and specific ratio cleaning process ensures that the bearing surface reaches high standard quality, and the performance detection link controls the density and hardness core indicators. The above whole process not only makes the ceramic bearing have excellent surface wear resistance and interface bonding force, but also has stable overall performance, effectively solves the problems of interface shedding and rapid surface wear of traditional ceramic bearings, meets the high requirements of performance stability and durability of bearings in high wear resistance scenes, and significantly improves the service life and application adaptability of the bearings. BRIEF DESCRIPTION OF DRAWINGS

[0017] Figure 1 It is a simple view of the preparation method flow of the application. DETAILED DESCRIPTION

[0018] The application provides a preparation method of a high-wear-resistant ceramic composite bearing, which comprises the following steps: S1, prepare base ceramic particles, graphene and binder, take two portions of base ceramic particles, add different contents of graphene and different contents of binder to the two portions of base ceramic particles respectively and mix to obtain inner layer premix and surface layer premix; S2, pre-press the inner layer premix, cover the surface layer premix with the pre-pressed inner layer premix and pre-press again to obtain a gradient green body; S3, load the gradient green body into a sintering device to perform gradient sintering on the gradient green body under the action of an alternating magnetic field and a pulse current to obtain a ceramic body; S4, heat treat the ceramic body in a nitrogen-oxygen mixed atmosphere; S5, sequentially deposit bottom layer and hydroxyapatite composite top layer on the surface of the ceramic body by electron beam deposition technology; S6, grind, clean and detect the performance of the ceramic body processed by electron beam deposition technology.

[0019] Further, in step S1, the base ceramic particles are composed of 90-95% silicon nitride powder, 3-5% yttrium oxide powder and 1-3% aluminum oxide powder by mass percentage; the surface layer graphene is added in an amount of 5-10wt% based on the mass of the base ceramic particles, and the inner layer graphene is added in an amount of 1-3wt% based on the mass of the base ceramic particles; the binder is a composite binder composed of chitosan and hydroxyapatite in a mass ratio of 3:1, the binder is added in an amount of 2-4% in the inner layer premix, and the binder is added in an amount of 3-5% in the surface layer premix.

[0020] Further, the silicon nitride powder of the base ceramic particles is in alpha phase and the alpha phase content is ≥92%, the particle size of the silicon nitride powder is 0.8-5μm and the proportion of 1-3μm particles in the silicon nitride powder is ≥80%; the median diameter of the yttrium oxide powder in the base ceramic particles is 0.95-1.05μm; the purity of the aluminum oxide powder in the base ceramic particles is ≥99.9% and the median diameter of the aluminum oxide powder is 0.75-0.85μm.

[0021] Further, in step S1, the inner layer premix is prepared by ball milling at a ball-to-material ratio of 10:1 at a rotation speed of 250-300r / min for 8-10h, and the surface layer premix is prepared by ball milling at a ball-to-material ratio of 12:1 at a rotation speed of 280-320r / min for 10-12h; the inner layer premix and the surface layer premix are dried and sieved after ball milling, the inner layer premix is sieved to 200 mesh, and the surface layer premix is sieved to 300 mesh.

[0022] Further, the pre-pressing process of the inner layer premix in step S2 is that the inner layer premix is pre-pressed at 15-20 MPa for 10-15 min to form an inner layer pre-embryo; and the surface layer premix is covered to a thickness of 1.0-1.5 mm and then is secondarily pre-pressed at 20-25 MPa for 8-10 min.

[0023] Further, the alternating magnetic field parameters in step S3 are 50-200 Hz and 0.1-0.5 T, and the pulse current parameters are 10-20 kA and a duty cycle of 10-30%; and the gradient sintering process is as follows: heating from room temperature to 500 ℃ at a rate of 5 ℃ / min, keeping the temperature for 2 h, then heating to 1200 ℃ at a rate of 20 ℃ / min, keeping the temperature for 1 h, then heating to 1550 ℃ at a rate of 3 ℃ / min, keeping the temperature for 3-4 h, and finally cooling to 800 ℃ and then air cooling.

[0024] Further, the alternating magnetic field parameters are adjusted according to the bearing size requirements in step S3: when the bearing inner ring diameter is 20-30 mm, the alternating magnetic field parameters are 50-70 Hz / 0.15-0.25 T; when the bearing inner ring diameter is 30-50 mm, the alternating magnetic field parameters are 70-100 Hz / 0.25-0.3 T; when the bearing outer ring diameter is 50-70 mm, the alternating magnetic field parameters are 100-150 Hz / 0.35-0.45 T; and when the bearing outer ring diameter is 70-100 mm, the alternating magnetic field parameters are 150-200 Hz / 0.45-0.5 T.

[0025] Further, the oxygen content of the nitrogen-oxygen mixed atmosphere in step S4 is 1-3%, and the total gas pressure is 0.1-0.12 MPa; and the heat treatment process is as follows: heating to 700-900 ℃ at a rate of 3-5 ℃ / min, keeping the temperature for 0.5-1.5 h, and then cooling with the furnace.

[0026] Further, in step S5 The deposition thickness of the bottom layer is 50-100 nm, the deposition thickness of the The deposition thickness of the / hydroxyapatite composite top layer is 100-150 nm, wherein the mass ratio of the / hydroxyapatite composite top layer to the hydroxyapatite is 2:1; and the deposition thickness of the / hydroxyapatite composite top layer is 100-150 nm. The mass ratio of the / hydroxyapatite composite top layer to the hydroxyapatite is 2:1; and the deposition thickness of the / hydroxyapatite composite top layer is 100-150 nm. The deposition thickness of the bottom layer and The / hydroxyapatite composite top layer is deposited and then is annealed at 300 ℃ in a nitrogen atmosphere for 1 h.

[0027] Further, in step S6, a 1200-1500 mesh diamond grinding wheel is used for grinding, and the surface roughness Ra is controlled to be ≤0.08 μm; anhydrous ethanol and a mixed solution of nitric acid with a volume ratio of 9:1 are used for ultrasonic cleaning for 15-20 min; and the performance detection includes density detection and hardness detection.

[0028] Embodiment 1 of the present application is as follows: Preparation of high wear-resistant ceramic composite bearing with inner ring diameter of 25 mm and outer ring diameter of 60 mm.

[0029] S1, select silicon nitride powder 93%, yttrium oxide powder 4%, and aluminum oxide powder 3% by mass percentage to form the base ceramic particles, wherein the silicon nitride powder is alpha phase and the alpha phase content is 93%, the particle size range is 0.8-5 μm, and the particle size range of 1-3 μm accounts for 82%. The silicon nitride powder with the above parameters can lay a foundation for forming a dense ceramic body during subsequent sintering and reduce internal voids of the finished product. The median diameter of the yttrium oxide powder is 1.0 μm, which can help adjust the grain growth rate during ceramic sintering to avoid performance degradation caused by excessively large grains. The aluminum oxide powder has a purity of 99.95% and a median diameter of 0.8 μm, which can fill the small gaps between silicon nitride particles and optimize the ceramic microstructure. Then add graphene, the graphene addition amount in the inner layer premix is 1.5wt% based on the mass of the base ceramic particles, which can ensure the tightness of the inner layer premix and the surface layer premix, and avoid separation between the layers. The graphene addition amount in the surface layer premix is 7wt% based on the mass of the base ceramic particles, which can significantly enhance the wear resistance of the subsequent bearing surface layer and prolong the service life of the bearing. The binder is a composite binder composed of chitosan and hydroxyapatite in a mass ratio of 3:1, the addition amount in the inner layer premix is 3%, which can avoid the inner layer premix being too hard due to excessive binder and affecting the subsequent forming operation; the addition amount in the surface layer premix is 4%, which can improve the forming stability of the surface layer premix and reduce the risk of cracking after forming. Then perform ball milling, the inner layer premix is ball milled at a ball-to-material ratio of 10:1 and a rotation speed of 270 r / min for 9 h, and the surface layer premix is ball milled at a ball-to-material ratio of 12:1 and a rotation speed of 300 r / min for 11 h. The ball milling parameters can ensure that the raw material particles are fully mixed, eliminate composition segregation, and ensure uniform composition in each region; after ball milling, the powder is dried, the inner layer premix is sieved through a 200 mesh sieve after drying, and the surface layer premix is sieved through a 300 mesh sieve, the powder particle size is controlled by sieving to avoid affecting the subsequent forming density of large particles and ensure uniform density of the gradient green body in each layer.

[0030] S2, the inner layer premix is placed in a special forming mold, and is pre-pressed at a pressure of 18 MPa for 12 min, the pressure and time can make the inner layer premix preliminarily formed and have certain strength, so as to avoid deformation or collapse when the surface layer premix is covered subsequently; then the surface layer premix is uniformly covered on the surface of the inner layer pre-billet, and the thickness of the surface layer premix covered is controlled to be 1.2 mm, the thickness can meet the demand of wear resistance of the bearing surface layer, and meanwhile, material waste or difficulty in interlayer combination caused by too large thickness is avoided; after the covering is completed, the whole is pre-pressed for the second time, the pressure is set to be 22 MPa, and the pre-pressing time is 9 min, the second pre-pressing parameters can make the surface layer premix closely combined with the inner layer pre-billet, reduce the interlayer gap, and improve the overall structural integrity of the gradient green billet; finally, the prepared gradient green billet is carefully loaded into the designated station of the sintering equipment, so as to ensure that the green billet is placed stably in the equipment, and displacement of the green billet in the sintering process is avoided to cause product size deviation or structural damage.

[0031] S3, according to the size characteristics of the bearing inner ring with a diameter of 25 mm and the outer ring with a diameter of 60 mm, the alternating magnetic field parameters are set as follows: the inner ring corresponds to a magnetic field frequency of 60 Hz and a magnetic field strength of 0.2 T, and the outer ring corresponds to a magnetic field frequency of 120 Hz and a magnetic field strength of 0.4 T, the targeted magnetic field parameters can ensure that the magnetic field uniformly acts on the inner ring and outer ring areas of the green billet, and avoid uneven sintering caused by size difference; the pulse current parameters are set to be 10-20 kA and the duty cycle is 20%, the current parameters can provide sufficient energy for the raw material particles in the sintering process, promote particle diffusion and reaction, and accelerate the sintering process. Start the sintering program, first heat from room temperature to 500℃ at a heating rate of 5℃ / min, and keep the temperature for 2h after reaching the temperature, slow heating can gradually remove the water and binder volatiles remaining in the green billet, and avoid rapid heating to cause bubbles or cracking in the green billet; then heat to 1200℃ at a heating rate of 20℃ / min, and keep the temperature for 1h, the rapid heating in this stage can accelerate the preliminary reaction between the raw materials, and prepare for subsequent high-temperature sintering; then heat to 1550℃ at a heating rate of 3℃ / min, and keep the temperature for 3.5h, slow heating combined with long time keeping can promote the ceramic particles to be fully sintered, form a dense ceramic structure, and improve the strength and hardness of the ceramic body; after the sintering and keeping are completed, stop heating when the temperature in the equipment decreases to 800℃, and let the ceramic body naturally air cool to room temperature in the sintering equipment, slow cooling can avoid internal stress of the ceramic body caused by too large temperature difference, prevent cracking or deformation, and finally obtain a ceramic body with complete structure.

[0032] S4. Place the sintered ceramic body into a heat treatment furnace and introduce a nitrogen-oxygen mixed atmosphere into the furnace. Control the oxygen content of the mixed atmosphere to be 2% and the total pressure to be 0.11 MPa. These atmosphere parameters can form a thin and uniform oxide layer on the surface of the ceramic body, enhancing the bonding force between the subsequent gradient transition layer and the ceramic body, while avoiding excessive oxidation that would lead to a decline in the surface properties of the ceramic. Set the heat treatment program to heat to 800℃ at a heating rate of 4℃ / min, and hold at this temperature for 1 hour. The gentle heating rate and holding time can moderately activate the ceramic surface, optimize the surface microstructure, and avoid damage to the ceramic surface caused by excessively high-temperature and rapid treatment. After the holding time is completed, turn off the heating device of the heat treatment furnace and allow the ceramic body to cool to room temperature with the furnace. Cooling with the furnace can further stabilize the chemical state and microstructure of the ceramic surface, providing good surface conditions for the subsequent deposition of the gradient transition layer.

[0033] S5. Using electron beam deposition technology, first deposit electron beam deposition on the surface of the ceramic substrate after interface activation treatment. The bottom layer is controlled to have a deposition thickness of 70nm. The bottom layer provides a stable adhesion base for the subsequent composite top layer, ensuring a strong bond between the gradient transition layer and the ceramic body, preventing detachment. After the bottom layer deposition is completed, the process continues... Substrate surface deposition / hydroxyapatite composite top layer, in which The mass ratio of the composite top layer to hydroxyapatite is 2:1, and the thickness of the composite top layer is 120nm. This ratio and thickness can take into account both the wear resistance and surface compatibility of the gradient transition layer, thereby improving the overall performance of the bearing. After the deposition process, the ceramic body with the gradient transition layer is transferred to a nitrogen-protected furnace and annealed at 300℃ for 1 hour in a nitrogen atmosphere. The annealing treatment can eliminate the internal stress generated inside the gradient transition layer during the deposition process, improve the structural stability of the transition layer, and avoid delamination or cracking during subsequent use.

[0034] S6. A 1300-mesh diamond grinding wheel is used to grind the ceramic body with a gradient transition layer. This grit size allows for precise control of the surface finish of the ceramic body, ensuring a surface roughness of Ra≤0.08μm, reducing frictional resistance during bearing use and improving smooth operation. After grinding, a cleaning solution of anhydrous ethanol and nitric acid in a 9:1 volume ratio is prepared. The ceramic body is then immersed in the cleaning solution for 18 minutes of ultrasonic cleaning. Ultrasonic cleaning effectively removes residual debris and surface impurities from the grinding process, preventing impurities from adhering and affecting the bearing's wear resistance and service life. After cleaning and natural drying, the ceramic composite bearing undergoes density and hardness testing. Density testing verifies whether the ceramic body meets the designed density requirements, while hardness testing ensures the bearing has sufficient wear resistance, ultimately guaranteeing that the product performance meets the usage standards.

[0035] To sum up, the embodiment is aimed at a high-wear-resistant ceramic composite bearing with an inner ring diameter of 25 mm and an outer ring diameter of 60 mm, which is prepared strictly according to the file parameters. In S100, the raw materials are mixed in a specific ratio and differentiated graphene and binder are added, and after corresponding ball milling and screening, the uniformity of the raw materials and the interlayer bonding basis are ensured; in S200, the forming is carried out by adapting the pressure and time, so as to ensure the integrity of the green body structure; in S300, the magnetic field parameters are set in combination with the bearing size, and the pulse current and gradient temperature sintering are matched to form a dense ceramic body; in S400, the interface is activated under a specific nitrogen-oxygen atmosphere to create conditions for the deposition of the transition layer; in S500, a gradient transition layer of hydroxyapatite with a specified thickness is deposited and annealed to improve the bonding stability; in S600, the bearing is finally obtained by grinding with a 1300-mesh grinding wheel and ultrasonic cleaning with a specific cleaning solution, combined with performance testing.

[0036] Embodiment 2 of the application: Preparation of a high-wear-resistant ceramic composite bearing with an inner ring diameter of 40 mm and an outer ring diameter of 80 mm: ​S1, select 95% silicon nitride powder, 3% yttrium oxide powder, and 2% aluminum oxide powder by mass percentage to form the base ceramic particles, wherein the silicon nitride powder is alpha phase and the alpha phase content is 94%, the particle size range is 0.8-5μm and the 1-3μm particle proportion is 85%, higher alpha phase content and particle proportion can further improve the density and mechanical strength of the ceramic body after subsequent sintering, and reduce the performance deficiency of large size bearing due to loose structure; the median diameter of yttrium oxide powder is 0.95μm, which can better integrate into the silicon nitride particle system and assist in inhibiting abnormal grain growth during sintering; the purity of aluminum oxide powder is 99.9% and the median diameter is 0.75μm, high purity and fine particle size can further fill the gap between silicon nitride particles, optimize the ceramic microstructure, and improve the overall uniformity. When adding graphene, the graphene addition amount in the inner layer premix is 2.5wt% based on the mass of the base ceramic particles, which can properly enhance the strength of the inner layer while ensuring the adhesion of the inner layer and the surface layer, and adapt to the stress requirements of large size bearings; the graphene addition amount in the surface layer premix is 9wt% based on the mass of the base ceramic particles, which can significantly enhance the wear resistance of the surface layer of the large size bearing to cope with the large wear pressure during use. The binder is a composite binder composed of chitosan and hydroxyapatite in a mass ratio of 3:1, the addition amount in the inner layer premix is 2.5%, which can balance the formability and strength of the inner layer premix, and avoid the difficulty in forming large size inner layer blanks due to excessive hardness or softness; the addition amount in the surface layer premix is 4.5%, which can improve the forming stability of the large size surface layer premix and reduce the risk of cracking after forming due to excessive size. Ball milling treatment is carried out, the inner layer premix is ball milled at a ball-to-material ratio of 10:1 and a rotation speed of 250r / min for 8h, and the surface layer premix is ball milled at a ball-to-material ratio of 12:1 and a rotation speed of 320r / min for 12h, the ball milling parameters are set according to the different requirements of the inner layer and the surface layer, which can ensure uniform mixing of the raw materials and avoid composition segregation of large size premix; after drying the milled powder, the inner layer premix is sieved through a 200 mesh sieve and the surface layer premix is sieved through a 300 mesh sieve, the particle size of the powder is controlled by sieving to ensure uniform density of each layer of the large size gradient green body and avoid unstable structure after forming due to uneven particle size.

[0037] S2, the inner layer premix is put into a large-size special forming mold, and is pre-pressed at a pressure of 15 MPa for 15 min, the pressure and time can make the large-size inner layer premix fully formed, have enough strength to support the covering of the subsequent surface layer premix, avoid the deformation of the pre-billet due to the too large size; then the surface layer premix is evenly covered on the surface of the inner layer pre-billet, and the thickness of the surface layer premix is controlled to be 1.5 mm, which can meet the higher demand of the large-size bearing surface layer on wear resistance, and at the same time ensure that the combination ratio of the surface layer and the inner layer is reasonable; after the covering is completed, the whole is pre-pressed again, the pressure is set to 25 MPa, and the pre-pressing time is 8 min, the higher secondary pre-pressing pressure can make the surface layer premix and the inner layer pre-billet tightly combined, reduce the interlayer gap of the large-size green body, and improve the overall structural integrity; the prepared gradient green body is slowly loaded into the sintering equipment suitable for large-size products, to ensure that the green body is accurately positioned and stably placed in the equipment, and prevent the displacement of the green body during sintering from causing too large size deviation of the large-size product.

[0038] S3, according to the large-size characteristics of the bearing inner ring diameter of 40 mm and the outer ring diameter of 80 mm, the alternating magnetic field parameters are set: the inner ring corresponds to a magnetic field frequency of 85 Hz and a magnetic field strength of 0.28 T, and the outer ring corresponds to a magnetic field frequency of 180 Hz and a magnetic field strength of 0.48 T, which can adapt to different parts of the large-size bearing, ensure that the magnetic field uniformly acts on the whole green body, and avoid the sintering difference of the large-size green body due to uneven magnetic field; the pulse current parameters are set to 18 kA and the duty cycle is 25%, higher current and duty cycle can provide more sufficient energy for sintering of the large-size green body, and promote the full diffusion reaction of the raw material particles. Start the sintering program, heat from room temperature to 500℃ at a heating rate of 5℃ / min, and keep the temperature for 2h, slow heating can gradually remove the moisture and binder in the large-size green body, avoid rapid heating to cause bubbles or cracking in the green body; then heat to 1200℃ at a heating rate of 20℃ / min, keep the temperature for 1h, accelerate the preliminary reaction between the raw materials, lay a foundation for high temperature sintering; then heat to 1550℃ at a heating rate of 3℃ / min, keep the temperature for 4h, longer holding time can ensure that the large-size ceramic green body is fully sintered to form a dense structure, avoid insufficient sintering inside due to too large size; after the sintering holding is completed, stop heating when the temperature in the equipment decreases to 800℃, and let the ceramic body air cool to room temperature in the equipment, slow cooling can avoid the generation of internal stress in the large-size ceramic body due to too large temperature difference, prevent cracking or deformation, and finally obtain a large-size ceramic body with complete structure.

[0039] S4, the sintering of large size ceramic body is put into the heat treatment furnace, the furnace is ventilated with nitrogen oxygen mixed atmosphere, the oxygen content of the mixed atmosphere is controlled to be 3%, and the total gas pressure is 0.12 MPa, the slightly high oxygen content can form a more uniform oxide layer on the surface of the large size ceramic body, enhance the binding force of the subsequent gradient transition layer and the ceramic body, and adapt to the stress requirement of the large size bearing; the heat treatment program is set, the temperature is raised to 900 DEG C at a heating rate of 5 DEG C / min, and the temperature is kept for 0.5 h after reaching the temperature, the faster heating rate and the appropriate holding time can efficiently complete the surface activation of the large size ceramic body, and optimize the surface microstate; after the holding is finished, the heating device is turned off, and the ceramic body is cooled to room temperature with the furnace, and the ceramic surface state can be stabilized by cooling with the furnace, so that good conditions are provided for the subsequent gradient transition layer deposition.

[0040] S5, using electron beam deposition technology, first depositing bottom layer on the surface of the ceramic body treated by interface activation, controlling the deposition thickness of the bottom layer to be 100 nm, and the thicker bottom layer can provide a more stable adhesion basis for the gradient transition layer of the large size ceramic body, and ensure firm combination; after the deposition of the bottom layer is completed, the surface of the bottom layer is deposited with hydroxyapatite composite top layer, wherein the mass ratio of hydroxyapatite is 2:1, and the deposition thickness of the composite top layer is 150 nm, and the thicker composite top layer can enhance the wear resistance and surface protection ability of the large size bearing, and cope with the use pressure of the large size bearing; after the deposition process is completed, the ceramic body with the gradient transition layer is transferred to a nitrogen protection furnace, and is annealed at 300 DEG C for 1 h in a nitrogen atmosphere, the annealing treatment can eliminate the internal stress in the large size gradient transition layer, improve the structural stability of the transition layer, and avoid delamination in the subsequent use process.

[0041] S6, using a 1500 mesh diamond grinding wheel to grind the large size ceramic body with the gradient transition layer, a finer mesh grinding wheel can more accurately control the surface precision of the large size ceramic body, ensure that the surface roughness Ra is less than or equal to 0.08 microns, reduce the friction resistance of the large size bearing during operation, and improve the operation stability; after the grinding is completed, a mixed cleaning solution with a volume ratio of anhydrous ethanol to nitric acid of 9:1 is configured, the ceramic body is put into the cleaning solution, and ultrasonic cleaning is performed for 20 min, a longer cleaning time can more thoroughly remove the grinding debris and impurities on the surface of the large size ceramic body, and avoid that the impurities affect the bearing performance; after the cleaning is completed and dried, the density and hardness of the large size ceramic composite bearing are detected, the density and hardness of the large size product are verified to meet the standard, so that the large size product has sufficient strength and wear resistance, and meets the use requirements of the large size bearing.

[0042] In summary, the embodiment is directed to a large-size bearing with an inner ring diameter of 40 mm and an outer ring diameter of 80 mm, and is prepared in accordance with the file parameters. S100 adjusts the raw material ratio and the amount of graphene and binder added, and through corresponding ball milling and screening, adapts to the demand of large-size green body; S200 is formed with higher secondary pre-pressing pressure to ensure the large-size green body to be adhered between layers; S300 sets a higher frequency and strength of the magnetic field according to the size, adapts the current, prolongs the high-temperature holding time, and ensures the large-size ceramic body to be fully sintered; S400 activates the interface with a slightly higher oxygen content of nitrogen-oxygen atmosphere; S500 increases the deposition thickness of the transition layer to improve the wear resistance and protection ability of the large-size bearing; S600 grinds with a 1500-mesh grinding wheel and cleans with ultrasonic for a longer time, and combines detection to ensure that the large-size bearing has sufficient strength and wear resistance.

[0043] The basic principles and main features of the present application and the advantages of the present application are shown and described above. It should be understood by those skilled in the art that the present application is not limited by the above embodiments, and the above embodiments and descriptions in the specification are only to illustrate the principles of the present application. Without departing from the spirit and scope of the present application, various changes and improvements can be made to the present application, and these changes and improvements all fall within the scope of the present application. The scope of protection of the present application is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high wear-resistant ceramic composite bearing, characterized in that: Includes the following steps: S1. Prepare basic ceramic particles, graphene and binder. Take two portions of basic ceramic particles, add different amounts of graphene and different amounts of binder to the two portions of basic ceramic particles respectively and mix them to obtain inner layer premix and surface layer premix. S2. The inner layer premix is ​​pre-compressed, and the pre-compressed inner layer premix is ​​covered with the surface premix and pre-compressed again to obtain a gradient green embryo. S3. The gradient green body is loaded into the sintering equipment to perform gradient sintering under the action of alternating magnetic field and pulsed current to obtain the ceramic body. S4. Heat-treat the ceramic body in a nitrogen-oxygen mixed atmosphere. S5. Sequentially deposited on the surface of the ceramic body using electron beam deposition technology. bottom layer and / Hydroxyapatite composite top layer; S6. Grind, clean, and test the performance of the ceramic body processed by electron beam deposition technology.

2. The method for preparing a high wear-resistant ceramic composite bearing according to claim 1, characterized in that: In step S1, the basic ceramic particles are composed of 90-95% silicon nitride powder, 3-5% yttrium oxide powder, and 1-3% alumina powder by mass percentage; the amount of graphene added to the surface layer is 5-10 wt% based on the mass of the basic ceramic particles, and the amount of graphene added to the inner layer is 1-3 wt% based on the mass of the basic ceramic particles; the binder is a composite binder composed of chitosan and hydroxyapatite in a mass ratio of 3:1, and the amount of binder added to the inner layer premix is ​​2-4%, and the amount of binder added to the surface layer premix is ​​3-5%.

3. The method for preparing a high wear-resistant ceramic composite bearing according to claim 2, characterized in that: The silicon nitride powder in the basic ceramic particles is α phase with an α phase content ≥92%, the silicon nitride powder has a particle size of 0.8-5μm and the proportion of 1-3μm particles in the silicon nitride powder is ≥80%; the median diameter of the yttrium oxide powder in the basic ceramic particles is 0.95-1.05μm; the alumina powder in the basic ceramic particles has a purity ≥99.9% and a median diameter of the alumina powder is 0.75-0.85μm.

4. The method for preparing a high wear-resistant ceramic composite bearing according to claim 1, characterized in that: In step S1, the inner layer premix is ​​prepared by ball milling at a ball-to-material ratio of 10:1 at a speed of 250-300 r / min for 8-10 h, and the surface layer premix is ​​prepared by ball milling at a ball-to-material ratio of 12:1 at a speed of 280-320 r / min for 10-12 h. After ball milling, the inner layer premix and the surface layer premix are dried and sieved. The inner layer premix is ​​sieved through a 200-mesh sieve, and the surface layer premix is ​​sieved through a 300-mesh sieve.

5. The method for preparing a high wear-resistant ceramic composite bearing according to claim 1, characterized in that: In step S2, the pre-compression process of the inner layer premix is ​​as follows: the inner layer premix is ​​pre-compressed at 15-20MPa for 10-15min to form an inner layer preform; the surface premix is ​​covered to a thickness of 1.0-1.5mm and then pre-compressed again at 20-25MPa for 8-10min.

6. The method for preparing a high wear-resistant ceramic composite bearing according to claim 1, characterized in that: In step S3, the alternating magnetic field parameters are 50-200Hz and 0.1-0.5T, and the pulse current parameters are 10-20kA and 10-30% duty cycle. The gradient sintering process is as follows: the temperature is increased from room temperature to 500℃ at 5℃ / min and held for 2 hours, then increased to 1200℃ at 20℃ / min and held for 1 hour, then increased to 1550℃ at 3℃ / min and held for 3-4 hours, and finally cooled to 800℃ and air-cooled.

7. The method for preparing a high wear-resistant ceramic composite bearing according to claim 6, characterized in that: In step S3, the alternating magnetic field parameters are adjusted according to the bearing size requirements: when the inner ring diameter of the bearing is 20-30mm, the alternating magnetic field parameters are 50-70Hz / 0.15-0.25T; when the inner ring diameter of the bearing is 30-50mm, the alternating magnetic field parameters are 70-100Hz / 0.25-0.3T; when the outer ring diameter of the bearing is 50-70mm, the alternating magnetic field parameters are 100-150Hz / 0.35-0.45T; when the outer ring diameter of the bearing is 70-100mm, the alternating magnetic field parameters are 150-200Hz / 0.45-0.5T.

8. The method for preparing a high wear-resistant ceramic composite bearing according to claim 1, characterized in that: In step S4, the oxygen content of the nitrogen-oxygen mixed atmosphere is 1-3% and the total pressure is 0.1-0.12 MPa; the heat treatment process is as follows: heat up to 700-900℃ at 3-5℃ / min and hold for 0.5-1.5h, then cool with the furnace.

9. The method for preparing a high wear-resistant ceramic composite bearing according to claim 1, characterized in that: In step S5 The thickness of the bottom layer deposition is 50-100 nm. The deposition thickness of the hydroxyapatite composite top layer is 100-150 nm, of which The mass ratio of hydroxyapatite to hydroxyapatite is 2:1; bottom layer and The hydroxyapatite composite top layer was deposited and then annealed at 300°C for 1 hour in a nitrogen atmosphere.

10. The method for preparing a high wear-resistant ceramic composite bearing according to claim 1, characterized in that: In step S6, grinding is performed using a 1200-1500 mesh diamond grinding wheel, and the surface roughness Ra is controlled to be ≤0.08μm; the cleaning is performed using an anhydrous ethanol and nitric acid mixture in a volume ratio of 9:1, which is ultrasonically cleaned for 15-20 minutes; the performance testing includes density testing and hardness testing.

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