Silicon nitride ceramic bearing ball and preparation method for improving wear resistance and self-lubricating performance of silicon nitride ceramic bearing ball

Abstract

The invention belongs to the technical field of mechanical bearings, and particularly relates to a silicon nitride ceramic bearing ball and a preparation method for improving wear resistance and self-lubricating performance thereof. The high-wear-resistance self-lubricating silicon nitride ceramic bearing ball is prepared from the following raw materials in percentage by mass: 90 to 92 weight percent of silicon nitride powder, 0.2 to 1.5 weight percent of carbon nano tube particles, 3 to 6 weight percent of aluminum oxide nano particles and 1 to 5 weight percent of yttrium oxide nano particles. The preparation method of the silicon nitride ceramic bearing ball comprises the steps of raw material preparation and mixing, spray granulation, dry pressing forming, cold isostatic pressing forming, degumming pre-sintering, hot isostatic pressing sintering, coarse grinding, fine grinding, forming of the TiN bottom layer through an ion implantation method, first accurate grinding, forming of the molybdenum disulfide layer through a vapor deposition method, second accurate grinding and finished ball obtaining. The preparation method of the silicon nitride ceramic bearing ball provided by the invention is simple and stable to operate; the prepared silicon nitride ceramic bearing ball is good in self-lubricating property and wear resistance, and the service life of the bearing ball is prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of mechanical bearings, and particularly relates to silicon nitride ceramic bearing balls and a preparation method for improving their wear resistance and self-lubricating performance. Background Art

[0002] As a core basic component of a mechanical system, the performance of a bearing directly affects the reliability and service life of the equipment. As a key component of a rolling bearing, a bearing ball undertakes the important functions of transmitting load and reducing friction in fields such as aerospace, new energy equipment, high-end precision instruments, and machinery under extreme working conditions. Traditional metal-based bearing balls (such as chrome steel, bearing steel, etc.) exhibit good comprehensive mechanical properties under normal working conditions, but they have significant defects in extreme environments (such as high temperature, high humidity, strong corrosive media, vacuum environment, etc.): the chemical activity of metal materials is high, and they are prone to electrochemical reactions or chemical corrosion with environmental media, resulting in the peeling failure of surface materials; at the same time, the friction coefficient of the metal surface is relatively high, and the friction loss is serious under high-speed and heavy-load working conditions, generating a large amount of heat and exacerbating the fatigue failure of the material.

[0003] To solve the problems of corrosion resistance and high friction loss of metal bearing balls, ceramic materials (such as zirconia, silicon nitride, etc.) are widely used in the manufacture of bearing balls due to their high hardness, low friction coefficient, and chemical corrosion resistance. However, the existing ceramic bearing balls still have the following technical pain points: insufficient wear resistance: Although ceramic materials have high hardness, their surfaces are prone to abrasive wear and fatigue wear under long-term rolling contact loads, resulting in a decrease in bearing accuracy and affecting the operating stability of the equipment. For example, in the bearings of a wind power equipment speed increaser, the surface wear of ceramic balls will cause an increase in gear meshing error and reduce the power generation efficiency. Lack of self-lubricating function: The lubrication of existing ceramic bearing balls mainly relies on an external oil supply system. In extreme environments (such as vacuum, high temperature, or enclosed spaces that are difficult to maintain), the external lubricating medium is prone to failure or cannot be replenished, resulting in a dry friction state, exacerbating wear and causing thermal failure. Risk of brittle fracture: Ceramic materials have high intrinsic brittleness and are sensitive to defects. Local microcracks or processing defects are prone to rapid propagation under impact loads, resulting in sudden fracture of the bearing ball. Especially during the start-up / shutdown process of an aeroengine, instantaneous impact loads often trigger ceramic ball fracture accidents, threatening system safety.

[0004] CN108997017A discloses a method for preparing silicon nitride ceramic bearing balls. A stabilizer is added to the silicon nitride raw powder and stirred evenly. The stabilizer is composed of 50 - 60% alcohol, 2 - 4% PVB, 1 - 3% castor oil, 0.4 - 0.6% DBP, 0.3 - 0.7% yttrium oxide, 0.3 - 0.7% cerium oxide, and 0.3 - 0.7% alumina. Spray granulation is carried out. A mixed glue is prepared with 10 - 20% DBE, 20 - 40% acetone, 20 - 30% ethyl acetate, and 30 - 40% alcohol. The total addition amount of the mixed glue is 15 - 20% of the weight of the silicon nitride granulated powder. It is placed in a ball-making machine, and the mixed glue is sprayed in to make the silicon nitride granulated powder into seed balls. Then, the silicon nitride granulated powder and the mixed glue are continuously added to the ball-making machine at the same time to make the seed balls into green silicon nitride balls. After aging, isostatic pressing, debinding, sintering, and finishing. The ceramic balls produced by this method are uneven in single weight, size, density, etc., and internal layer cracks are likely to occur in the products. Such ball products can only be used as grinding medium balls and cannot be used for bearing balls.

[0005] CN103011833A discloses a production process for rolling elements of silicon nitride ceramic ball bearings. The process includes two steps: ceramic sintering and grinding. The sintering step can sinter silicon nitride ceramic balls under normal pressure. The grinding agents in each grinding stage of the grinding step include rough grinding agent, fine grinding agent, and superfine grinding agent. These grinding agents are used in combination in each grinding stage. The silicon nitride ceramic balls prepared by the process have low density, high hardness, low friction coefficient, wear resistance, self-lubrication, and good rigidity, etc., and can be widely used as rolling elements of bearings. One of the requirements for bearing balls is to improve the product density as much as possible during the production process. Gas pressure or hot isostatic pressing sintering is to achieve this goal. The normal pressure sintering proposed by this method cannot meet the actual application requirements, and there is currently no precedent for qualified bearing balls sintered under normal pressure. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to overcome the above-mentioned defects existing in the prior art, and provide a method for preparing a highly wear-resistant and self-lubricating silicon nitride ceramic bearing ball, which is simple in operation and stable in conditions; the prepared silicon nitride ceramic bearing ball has good self-lubrication and wear resistance, and prolongs the service life of the bearing ball.

[0007] The highly wear-resistant and self-lubricating silicon nitride ceramic bearing ball described in the present invention is made of the following raw materials by mass percentage: 90 - 92 wt% of silicon nitride powder, 0.2 - 1.5 wt% of carbon nanotube particles, 3 - 6 wt% of alumina nanoparticles, and 1 - 5 wt% of yttrium oxide nanoparticles. Preferably: 90 - 92 wt% of silicon nitride powder, 0.2 - 1.5 wt% of carbon nanotube particles, 4.5 - 4.8 wt% of alumina nanoparticles, and 3 - 3.7 wt% of yttrium oxide nanoparticles.

[0008] The α-phase of the silicon nitride powder is >80%, the particle size is 0.5 - 1 μm, and the purity is >99.8%; the length of the carbon nanotube particles is 0.5 - 1.5 μm, and the diameter is 5 - 20 nm; the alumina nanoparticles have a purity of 99.9% and a particle size of 25 - 35 nm; the yttrium oxide nanoparticles have a purity of 99.9% and a particle size of 480 - 550 nm.

[0009] A preparation method of a silicon nitride ceramic bearing ball with improved wear-resistant self-lubricating performance, comprising the following technological steps: raw material preparation and mixing → spray granulation → dry pressing → cold isostatic pressing → debinding and pre-sintering → hot isostatic sintering → rough grinding → fine grinding → forming a TiN bottom layer by ion implantation method → fine grinding one → forming a molybdenum disulfide layer by chemical vapor deposition method → fine grinding two → bearing ball;

[0010] The technological parameters of forming the TiN bottom layer by the ion implantation method are as follows: using an ion plating equipment, injecting at a vacuum of 10 -2 ~10 -3 Pa, the acceleration voltage of ion implantation is 50 - 200 kV. After ion implantation is completed, the ceramic bearing ball is annealed at 300 - 600 °C. The thickness of the formed TiN layer is 3 - 5 μm, and the surface hardness is ≥2500 HV;

[0011] The specific operation of forming the molybdenum disulfide layer by the chemical vapor deposition method is as follows: cleaning the bearing ball sample after fine grinding one, performing chemical vapor deposition, evacuating to a vacuum of 10 -3 ~10 -4 Pa, heating the bearing ball sample to 300 - 600 °C, transporting the molybdenum source to the reaction chamber through a carrier gas, the carrier gas flow rate is 20 - 100 sccm, the sulfur source flow rate is 50 - 200 sccm, and introducing a reducing gas. The deposition temperature is 500 - 600 °C, the deposition rate is 0.1 - 1 μm / h. After deposition is completed, cooling to room temperature at a rate of 1 - 5 °C / min, annealing in an Ar or N2 atmosphere at 400 - 500 °C for 30 - 60 min, and then cooling to form a molybdenum disulfide layer with a thickness of 0.5 - 1 μm and a friction coefficient ≤0.05.

[0012] The raw material preparation and mixing is specifically as follows: after mixing the silicon nitride powder, carbon nanotube particles, alumina nanoparticles, and yttrium oxide nanoparticles, adding 150 - 250% of absolute ethanol and PVB solution (the addition amount of PVB is 1 - 2% of the total mass of the raw materials) based on the total mass of the above raw materials, mixing into a ceramic slurry, and then granulating in a spray granulation tower. The granulation temperature is 145 - 155 °C, and spherical powder with a particle size of 30 - 100 μm is obtained after granulation.

[0013] The pressure of the dry pressing is 1 - 10 MPa; the pressure of the cold isostatic pressing is 180 - 230 MPa.

[0014] The degumming and pre-sintering is carried out in a vacuum furnace, heated to 500 - 800 °C, and held for 2 - 4 h.

[0015] The process parameters of the hot isostatic pressing sintering are as follows: temperature 1600 - 1750 °C, nitrogen pressure 150 - 200 MPa, and sintering time 2 h - 3 h.

[0016] Rough grinding is to grind the sintered blank into the target size of +30 - 50 μm with a rough grinder, and fine grinding is to grind the rough ground material into the target size of +5 - 10 μm with a fine grinder.

[0017] The first fine grinding is to perform the first polishing, and grind the finely ground material into the target size of +1 - 2 μm with a fine grinder.

[0018] The second fine grinding is to perform the second polishing, and grind the material ground in the first fine grinding into the target size of 2 mm - 50 mm with a fine grinder.

[0019] Specifically, the preparation method of the silicon nitride ceramic bearing balls with improved wear-resistant and self-lubricating properties includes the following technological steps:

[0020] (1) Add the formulated raw material powder into anhydrous ethanol and PVB solution, mix into a ceramic slurry, and then granulate through a spray granulation tower to obtain the formulated powder.

[0021] (2) Form the ball blanks by dry pressing and cold isostatic pressing of the formulated powder.

[0022] (3) The ball blanks are degummed in a degumming furnace, pre-sintered in a gas pressure furnace, and finally sintered at 1600 - 1750 °C under the protection of a nitrogen pressure of 200 MPa for 2 hours to obtain the porcelain blank balls.

[0023] (4) Send the porcelain blank balls to the processing procedure to complete the rough grinding and fine grinding procedures.

[0024] (5) Generate a TiN bottom layer on the finely ground semi-finished bearing balls by ion implantation method, and then send them to the first fine grinding procedure to complete the first surface polishing.

[0025] (6) The bearing balls in the first fine grinding procedure are further processed by chemical vapor deposition to obtain a molybdenum disulfide top layer.

[0026] (7) Send the bearing balls after chemical vapor deposition to the second fine grinding procedure to complete the final sizing grinding and polishing of the bearing ball products to become the final products.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] (1) The bearing balls prepared by the method of the present invention significantly improve the strength and toughness of the silicon nitride matrix (the strengthening and toughening effect of carbon nanotubes) by adding carbon nanotubes and nano-scale sintering aids (aluminum oxide, yttrium oxide). At the same time, a micro oil storage cavity is formed by using the porous structure of the carbon nanotubes, and long-term self-lubrication is realized through capillary action, overcoming the defect that traditional ceramic bearings rely on external oil supply and reducing the maintenance cost.

[0029] (2) The bearing balls prepared by the method of the present invention adopt the synergistic effect of a double-layer composite coating (TiN bottom layer + MoS2 top layer). The TiN layer increases the surface hardness to ≥2500 HV (far exceeding 1500 - 1800 HV of ordinary ceramics), and the MoS2 layer reduces the friction coefficient to ≤0.05, significantly improving the wear resistance of the bearing balls.

[0030] (3) The combination of the oil cavity structure and the self-lubricating coating in the present invention enables the lubricating layer to remain intact even in a high-temperature environment of 300 °C, breaking through the lubrication failure problem of traditional ceramic bearings under extreme working conditions, and is particularly suitable for the high-reliability requirements of special fields such as aerospace and deep-sea equipment. Description of the Drawings

[0031] Figure 1 It is a schematic structural diagram of the bearing ball prepared by the present invention. Detailed Embodiments

[0032] The present invention will be further described below in conjunction with specific embodiments.

[0033] The raw materials and additives used in the following examples and comparative examples are all commercially available products. The α-phase of the silicon nitride powder is >80%, the particle size is 0.5 - 1 μm, and the purity is >99.8%; the length of the carbon nanotube particles is 0.5 - 1.5 μm, and the diameter is 5 - 20 nm; the aluminum oxide nanoparticles have a purity of 99.9% and a particle size of 25 - 35 nm; the yttrium oxide nanoparticles have a purity of 99.9% and a particle size of 480 - 550 nm. All are carried out according to the following process: raw material preparation and mixing → spray granulation → dry pressing → cold isostatic pressing → debinding and pre-sintering → hot isostatic sintering → rough grinding → fine grinding → forming the TiN bottom layer by ion implantation method → fine grinding I → forming the molybdenum disulfide layer by chemical vapor deposition method → fine grinding II → bearing ball. The schematic structural diagram of the bearing ball is as Figure 1 shown.

[0034] Example 1

[0035] 1. Formula

[0036] 92 wt% of silicon nitride powder, 0.2 wt% of carbon nanotube particles, 4.8 wt% of aluminum oxide nanoparticles, and 3 wt% of yttrium oxide nanoparticles.

[0037] 2. Process

[0038] (1) Mix silicon nitride powder, carbon nanotube particles, alumina nanoparticles, and yttrium oxide nanoparticles, then add 200% of absolute ethanol and PVB solution (the addition amount of PVB is 1.5% of the total mass of the raw materials) based on the total mass of the above raw materials, mix them into a ceramic slurry, and then granulate in a spray granulation tower at a granulation temperature of 150 °C to obtain spherical powder with a size of 30 - 100 μm after granulation.

[0039] (2) Obtain a spherical blank by dry pressing the formulated powder at 5 MPa and cold isostatic pressing at 200 MPa.

[0040] (3) Heat the spherical blank in a vacuum furnace to 700 °C, hold for 3 h for pre-sintering, and finally sinter at a hot isostatic pressing temperature of 1700 °C, nitrogen pressure of 180 MPa, and sintering time of 2 h to obtain a porcelain blank sphere.

[0041] (4) Send the porcelain blank sphere to the processing procedure, grind the sintered blank sphere to the target size of +30 - 50 μm with a rough grinder, and grind the coarsely ground sphere to the target size of +5 - 10 μm with a fine grinder to complete the rough grinding and fine grinding procedures.

[0042] (5) Generate a TiN bottom layer on the finely ground semi-finished bearing ball by ion implantation method. Using an ion coating equipment, inject at a vacuum of 10 -3 Pa, the acceleration voltage of ion implantation is 100 kV. After ion implantation is completed, anneal the ceramic bearing ball at 400 °C. The thickness of the formed TiN layer is 3 μm, and the surface hardness is 2510 HV. Then send it to the first fine grinding process to complete the first surface polishing, grinding to the target size of +1 - 2 μm.

[0043] (6) Obtain a molybdenum disulfide top layer on the bearing ball from the first fine grinding process by chemical vapor deposition method. Clean the bearing ball sample after the first fine grinding, perform chemical vapor deposition, evacuate to a vacuum of 10 -3 Pa, heat the bearing ball sample to 400 °C, transport the molybdenum source to the reaction chamber through a carrier gas, the flow rate of the carrier gas is 80 sccm, the flow rate of the sulfur source is 100 sccm, and introduce a reducing gas. The deposition temperature is 550 °C, the deposition rate is 0.5 μm / h. After deposition is completed, cool down to room temperature at a rate of 3 °C / min, anneal at 450 °C for 40 min in an Ar atmosphere, and then cool down. The thickness of the formed molybdenum disulfide layer is 1 μm, and the friction coefficient ≤ 0.05.

[0044] (7) Send the bearing ball after chemical vapor deposition to the second fine grinding process, grind the ball from the first fine grinding to the target size of 40 mm with a fine grinder to complete the final sizing grinding and polishing of the bearing ball product and become the final product.

[0045] 3. Performance Testing

[0046] Under a high-temperature environment of 300 °C, bearing lubrication tests were carried out. The lubricating layer remained intact, and the friction coefficient was 0.043. After cyclic load tests (5 × 10 6 times), the wear amount on the surface of the sphere was 0.008 mm.

[0047] Example 2

[0048] 1. Formula

[0049] Silicon nitride powder: 91 wt%, carbon nanotube particles: 0.8 wt%, alumina nanoparticles: 4.5 wt%, yttrium oxide nanoparticles: 3.7 wt%.

[0050] 2. Process

[0051] (1) After mixing silicon nitride powder, carbon nanotube particles, alumina nanoparticles, and yttrium oxide nanoparticles, add 150% of absolute ethanol and PVB solution (the addition amount of PVB is 2% of the total mass of the raw materials) based on the total mass of the above raw materials, mix them into ceramic slurry, and then granulate in a spray granulation tower. The granulation temperature is 155 °C, and spherical powder with a size of 30 - 100 μm is obtained after granulation.

[0052] (2) The formulated powder is formed into a ball blank by dry pressing at 10 MPa and cold isostatic pressing at 230 MPa.

[0053] (3) The ball blank is heated to 800 °C in a vacuum furnace, pre-sintered for 2 h, and finally sintered at a hot isostatic pressing temperature of 1750 °C, a nitrogen pressure of 150 MPa, and a sintering time of 3 h to obtain a porcelain body ball.

[0054] (4) The porcelain body ball is sent to the processing process. The sintered blank ball is ground to the target size of +30 - 50 μm with a rough grinder, and the rough ground ball is ground to the target size of +5 - 10 μm with a fine grinder to complete the rough grinding and fine grinding processes.

[0055] (5) The finely ground semi-finished bearing ball is subjected to ion implantation to generate a TiN bottom layer. Using an ion coating equipment, the injection is carried out under a vacuum of 10 -2 Pa, the acceleration voltage of ion implantation is 200 kV. After ion implantation is completed, the ceramic bearing ball is annealed at 300 °C. The average thickness of the formed TiN layer is 3 μm, and the surface hardness is 2530 HV. Then it is sent to the first fine grinding process to complete the first surface polishing, and ground to the target size of +1 - 2 μm.

[0056] (6) The bearing ball from the first fine grinding process is further subjected to chemical vapor deposition to obtain a molybdenum disulfide top layer. The bearing ball sample after the first fine grinding is cleaned, and chemical vapor deposition is carried out. The vacuum is pumped to a vacuum of 10 -4The bearing ball samples were heated to 600 °C by Pa. The molybdenum source was transported to the reaction chamber through a carrier gas with a carrier gas flow rate of 20 sccm and a sulfur source flow rate of 50 sccm. A reducing gas was introduced, the deposition temperature was 500 °C, the deposition rate was 1 μm / h. After the deposition was completed, the temperature was decreased to room temperature at a rate of 5 °C / min. In an Ar atmosphere, annealing was carried out at 500 °C for 30 min, and then the temperature was decreased. The thickness of the formed molybdenum disulfide layer was 0.5 μm, and the friction coefficient was ≤0.05.

[0057] (7) The bearing balls that had completed chemical vapor deposition were sent to the second fine grinding process. The balls ground in the first fine grinding were ground to the target size of 2 mm to 50 mm with a fine grinding machine, and the final sizing grinding and polishing of the bearing ball products were completed to become the final products.

[0058] 3. Performance testing

[0059] In a high-temperature environment of 300 °C, bearing lubrication testing was carried out. The lubricating layer remained intact, and the friction coefficient was 0.039; after the cyclic load test (5×10 6 times), the wear amount on the surface of the ball was 0.007 mm.

[0060] Example 3

[0061] 1. Formula

[0062] Silicon nitride powder 90 wt%, carbon nanotube particles 1.5 wt%, alumina nanoparticles 4.8 wt%, yttrium oxide nanoparticles 3.7 wt%.

[0063] 2. Process

[0064] (1) After mixing silicon nitride powder, carbon nanotube particles, alumina nanoparticles, and yttrium oxide nanoparticles, 250% of absolute ethanol and PVB solution (the addition amount of PVB is 1% of the total mass of the raw materials) based on the total mass of the above raw materials were added, and they were mixed into a ceramic slurry, and then granulated in a spray granulation tower. The granulation temperature was 145 °C, and spherical powders of 30 - 100 μm were obtained after granulation.

[0065] (2) The formulated powder was formed into a green compact by dry pressing at 1 MPa and cold isostatic pressing at 180 MPa.

[0066] (3) The green compact was heated to 500 °C in a vacuum furnace and pre-sintered for 4 h. Finally, it was sintered at a hot isostatic pressing temperature of 1600 °C, a nitrogen pressure of 200 MPa, and a sintering time of 2 h to obtain a sintered ceramic blank ball.

[0067] (4) The sintered ceramic blank balls were sent to the processing process. The sintered blank balls were ground to the target size of +30 - 50 μm with a rough grinding machine, and the rough ground balls were ground to the target size of +5 - 10 μm with a fine grinding machine to complete the rough grinding and fine grinding processes.

[0068] (5) The finely ground semi-finished bearing balls are subjected to ion implantation to produce a TiN bottom layer. Using an ion plating equipment, the vacuum degree is 10 -3 Pa for implantation. The acceleration voltage of ion implantation is 50 kV. After ion implantation is completed, the ceramic bearing balls are annealed at 600 °C. The thickness of the formed TiN layer is 5 μm, and the surface hardness is 2600 HV. Then they are sent to the first fine grinding process to complete the first surface polishing, grinding to the target size of +1 - 2 μm.

[0069] (6) The bearing balls from the first fine grinding process are further processed by chemical vapor deposition to obtain a molybdenum disulfide top layer. The bearing ball samples after the first fine grinding are cleaned, and then chemical vapor deposition is carried out. The vacuum is pumped to a vacuum degree of 10 -3 Pa, and the bearing ball samples are heated to 300 °C. The molybdenum source is transported to the reaction chamber through a carrier gas, with a carrier gas flow rate of 100 sccm and a sulfur source flow rate of 200 sccm. A reducing gas is introduced, the deposition temperature is 600 °C, the deposition rate is 0.1 μm / h. After deposition is completed, it is cooled to room temperature at a rate of 1 °C / min. In an Ar atmosphere, it is annealed at 400 °C for 60 min and then cooled. The thickness of the formed molybdenum disulfide layer is 1 μm, and the friction coefficient is ≤0.05.

[0070] (7) The bearing balls that have completed chemical vapor deposition are sent to the second fine grinding process. Using a fine grinding machine, the balls from the first fine grinding are ground to the target size of 2 mm - 50 mm, completing the final sizing grinding and polishing of the bearing ball products to become the final products.

[0071] 3. Performance Testing

[0072] In a high-temperature environment of 300 °C, bearing lubrication testing is carried out. The lubricating layer remains intact, and the friction coefficient is 0.036; after cyclic load testing (5×10 6 times), the wear amount on the surface of the ball is 0.009 mm.

[0073] Comparative Example 1

[0074] 1. Formula

[0075] Silicon nitride powder 92 wt%, carbon nanotube particles 0.2 wt%, alumina nanoparticle 4.8 wt%, yttrium oxide nanoparticle 3 wt%.

[0076] 2. Process

[0077] (1) After mixing silicon nitride powder, carbon nanotube particles, alumina nanoparticles, and yttrium oxide nanoparticles, 200% of absolute ethanol and PVB solution (the addition amount of PVB is 1.5% of the total mass of the raw materials) based on the total mass of the above raw materials are added, and they are mixed into a ceramic slurry. Then spray granulation is carried out in a spray granulation tower at a granulation temperature of 150 °C, and spherical powders of 30 - 100 μm are obtained after granulation.

[0078] (2) The formulated powder is formed into a spherical blank by dry pressing at 5 MPa and cold isostatic pressing at 200 MPa.

[0079] (3) The spherical blank is heated to 700 °C in a vacuum furnace, pre-sintered for 3 h, and finally sintered at a hot isostatic pressing temperature of 1700 °C, a nitrogen pressure of 180 MPa, and a sintering time of 2 h to obtain a sintered ceramic blank sphere.

[0080] (4) The sintered ceramic blank sphere is sent to the processing process. The sintered blank sphere is ground to the target size of +30 - 50 μm with a rough grinder, and the fine grinding is to grind the roughly ground sphere to the target size of +5 - 10 μm with a fine grinder to complete the rough grinding and fine grinding processes.

[0081] (5) The finely ground semi-finished bearing ball is subjected to TiN bottom layer formation by ion implantation method. Using an ion coating equipment, the injection is carried out under a vacuum of 10 -3 Pa, the acceleration voltage of ion implantation is 100 kV. After ion implantation, the ceramic bearing ball is annealed at 400 °C. The thickness of the formed TiN layer is 3 μm, and the surface hardness is 2550 HV. Then it is sent to the first fine grinding process to complete the first surface polishing, grinding to the target size of +1 - 2 μm.

[0082] (6) The bearing ball after the first fine grinding is sent to the second fine grinding process. The ball ground in the first fine grinding is ground to the target size of 40 mm with a fine grinder to complete the final sizing grinding and polishing of the bearing ball product to become the final product.

[0083] 3. Performance testing

[0084] Under a high-temperature environment of 300 °C, the bearing lubrication test is carried out, and the friction coefficient is 0.36; after the cyclic load test (5 × 10 6 times), the wear amount of the sphere surface is 0.0328 mm.

[0085] Comparative example 2

[0086] 1. Formula

[0087] Silicon nitride powder 92 wt%, carbon nanotube particles 0.2 wt%, alumina nanoparticle 4.8 wt%, yttrium oxide nanoparticle 3 wt%.

[0088] 2. Process

[0089] (1) After mixing silicon nitride powder, carbon nanotube particles, alumina nanoparticles, and yttrium oxide nanoparticles, 200% of absolute ethanol and PVB solution (the addition amount of PVB is 1.5% of the total mass of the raw materials) based on the total mass of the above raw materials are added, mixed into a ceramic slurry, and then granulated in a spray granulation tower at a granulation temperature of 150 °C to obtain spherical powder with a size of 30 - 100 μm.

[0090] (2) The formulated powder is formed into a ball blank by dry pressing at 5 MPa and cold isostatic pressing at 200 MPa.

[0091] (3) The ball blank is heated to 700 °C in a vacuum furnace and pre-sintered for 3 h. Finally, it is sintered by hot isostatic pressing at a temperature of 1700 °C, a nitrogen pressure of 180 MPa, and a sintering time of 2 h to obtain a porcelain ball blank.

[0092] (4) The porcelain ball blank is sent to the processing procedure. The sintered blank ball is ground to the target size of +30 - 50 μm with a rough grinder, and the fine grinding is carried out with a fine grinder to grind the rough ground ball to the target size of +5 - 10 μm, completing the rough grinding and fine grinding procedures.

[0093] (5) Then it is sent to the first fine grinding process to complete the first surface polishing, grinding to the target size of +1 - 2 μm.

[0094] (6) The bearing ball after the first fine grinding process is coated with a molybdenum disulfide top layer by chemical vapor deposition. The bearing ball sample after the first fine grinding is cleaned, and chemical vapor deposition is carried out. The vacuum is pumped to a vacuum degree of 10 -3 Pa, the bearing ball sample is heated to 400 °C, the molybdenum source is transported to the reaction chamber through the carrier gas, the carrier gas flow rate is 80 sccm, the sulfur source flow rate is 100 sccm, and a reducing gas is introduced. The deposition temperature is 550 °C, the deposition rate is 0.5 μm / h. After the deposition is completed, it is cooled to room temperature at a rate of 3 °C / min. In an Ar atmosphere, it is annealed at 450 °C for 40 min and then cooled. The thickness of the formed molybdenum disulfide layer is 1 μm, and the friction coefficient is ≤0.05.

[0095] (7) The bearing ball that has completed chemical vapor deposition is sent to the second fine grinding process. The ball ground in the first fine grinding is ground to the target size of 40 mm with a fine grinder, completing the final sizing grinding and polishing of the bearing ball product to become the final product.

[0096] 3. Performance Testing

[0097] In a high-temperature environment of 300 °C, the bearing lubrication test is carried out. The lubricating layer disappears in 5 - 10 min, and the friction coefficient is 0.18; after the cyclic load test (5×10 6 times), the wear amount of the sphere surface is 0.02 mm.

Claims

1. A silicon nitride ceramic bearing ball, characterized in that: It is made from raw materials with the following mass percentages: 90 - 92 wt% of silicon nitride powder, 0.2 - 1.5 wt% of carbon nanotube particles, 3 - 6 wt% of alumina nanoparticles, and 1 - 5 wt% of yttrium oxide nanoparticles.

2. The silicon nitride ceramic bearing ball according to claim 1, wherein: The α-phase of the silicon nitride powder > 80%, the particle size is 0.5 - 1 μm, and the purity > 99.8%; the length of the carbon nanotube particles is 0.5 - 1.5 μm, and the diameter is 5 - 20 nm; for the alumina nanoparticles, the purity is 99.9% and the particle size is 25 - 35 nm; for the yttrium oxide nanoparticles, the purity is 99.9% and the particle size is 480 - 550 nm.

3. A method for preparing the silicon nitride ceramic bearing ball according to claim 1 or 2, which improves wear resistance and self-lubricating performance, characterized in that: It includes the following technological steps: raw material preparation and mixing → spray granulation → dry pressing forming → cold isostatic pressing forming → debinding and pre-sintering → hot isostatic pressing sintering → rough grinding → fine grinding → forming a TiN bottom layer by ion implantation method → fine grinding one → forming a molybdenum disulfide layer by chemical vapor deposition method → fine grinding two → bearing balls; The process parameters for forming the TiN bottom layer by the ion implantation method are as follows: an ion coating equipment is used, and the vacuum degree is 10 -2 ~10 -3 Pa for implantation, the acceleration voltage of ion implantation is 50 - 200 kV. After the ion implantation is completed, the ceramic bearing balls are annealed at 300 - 600 °C, the thickness of the formed TiN layer is 3 - 5 μm, and the surface hardness is ≥ 2500 HV; The specific operation of forming a molybdenum disulfide layer by chemical vapor deposition is as follows: Clean the bearing ball sample after fine grinding, perform chemical vapor deposition, evacuate to a vacuum degree of 10 -3 ~10 -4 Pa, heat the bearing ball sample to 300 - 600 °C, transport the molybdenum source to the reaction chamber through a carrier gas, with the carrier gas flow rate of 20 - 100 sccm and the sulfur source flow rate of 50 - 200 sccm, and introduce a reducing gas. The deposition temperature is 500 - 600 °C, the deposition rate is 0.1 - 1 μm / h. After the deposition is completed, cool down to room temperature at a rate of 1 - 5 °C / min. Anneal at 400 - 500 °C for 30 - 60 min in an Ar or N2 atmosphere, and then cool down. The thickness of the formed molybdenum disulfide layer is 0.5 - 1 μm, and the friction coefficient ≤ 0.

05.

4. The preparation method of the silicon nitride ceramic bearing ball with improved wear resistance and self-lubricating performance according to claim 3, characterized in that: The specific raw material preparation and mixing is as follows: After mixing the silicon nitride powder, carbon nanotube particles, alumina nanoparticles, and yttrium oxide nanoparticles, 150 - 250% of the total mass of the above raw materials of anhydrous ethanol and PVB solution is added, mixed into a ceramic slurry, and then granulated in a spray granulation tower. The granulation temperature is 145 - 155 °C, and spherical powder with a size of 30 - 100 μm is obtained after granulation.

5. The preparation method of the silicon nitride ceramic bearing ball with improved wear resistance and self-lubricating performance according to claim 4, characterized in that: The pressure for the dry pressing forming is 1 - 10 MPa; the pressure for the cold isostatic pressing forming is 180 - 230 MPa.

6. The preparation method of the silicon nitride ceramic bearing ball for improving wear resistance and self-lubricating performance according to claim 5, characterized in that: The debinding and pre-sintering is carried out in a vacuum furnace, heated to 500 - 800 °C, and held for 2 - 4 h.

7. The preparation method of the silicon nitride ceramic bearing ball with improved wear resistance and self-lubricating performance according to claim 6, characterized in that: The technological parameters of the hot isostatic pressing sintering are: temperature 1600 - 1750 °C, nitrogen pressure 150 - 200 MPa, and sintering time 2 h - 3 h.

8. The preparation method of the silicon nitride ceramic bearing ball for improving wear resistance and self-lubricating performance according to claim 7, characterized in that: Rough grinding is to grind the sintered blank with a rough grinder to a target size +30 - 50 μm, and fine grinding is to grind the rough ground blank with a fine grinder to a target size +5 - 10 μm.

9. The preparation method of the silicon nitride ceramic bearing ball with improved wear resistance and self-lubricating performance according to claim 8, characterized in that: Fine grinding one is to perform the first polishing, and grind the fine ground blank with a fine grinder to a target size +1 - 2 μm.

10. The preparation method of the silicon nitride ceramic bearing ball with improved wear resistance and self-lubricating performance according to claim 9, characterized in that: Fine grinding two is to perform the second polishing, and grind the fine ground one blank with a fine grinder to a target size of 2 mm - 50 mm.

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