Silicon nitride ceramic ball and preparation method thereof

Abstract

The invention provides a silicon nitride ceramic ball and a preparation method thereof. The preparation method comprises the following steps: (1) mixing alpha-silicon nitride, an additive, a binder and an organic solvent, and then sequentially performing grinding, vacuum drying, sieving and dry pressing to obtain a spherical blank; (2) carrying out shaping packaging and cold molding on the spherical blank obtained in the step (1) to obtain a silicon nitride ceramic ball biscuit; and (3) sequentially carrying out degreasing treatment, air pressure sintering and hot isostatic pressing sintering on the silicon nitride ceramic ball biscuit obtained in the step (2) to obtain the silicon nitride ceramic ball. The purpose of simply and rapidly pressing the silicon nitride ceramic ball biscuit with high sphericity degree and uniform density in batches is achieved through shaping packaging, cold molding and other molding, and the silicon nitride ceramic ball with stable quality and excellent mechanical property is obtained through air pressure sintering and hot isostatic pressing sintering; and the preparation method is high in feasibility, the forming difficulty is reduced, the balling rate is increased, and the complicated procedures of subsequent shaping are reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of ceramic materials, and specifically to a silicon nitride ceramic ball and a preparation method thereof. Background Art

[0002] High-quality silicon nitride ceramic balls are usually used in high-end bearings. Dense silicon nitride (Si3N4) ceramics have excellent comprehensive properties, with an elastic modulus of up to 320GPa, a tensile strength of 1600MPa, a compressive strength of up to 3600MPa, and mechanical properties that remain almost unchanged below 900°C. They have a series of properties such as high strength, light weight, insulation, heat insulation, non-magnetic, high temperature resistance, corrosion resistance, wear resistance, small centrifugal force at high speed rotation, and low operating temperature rise. They are very suitable for working in some special environments, such as high temperature, high speed, non-magnetic, strong acid, strong alkali and other environments.

[0003] However, since the sintering temperature of silicon nitride ceramics is higher than that of other ceramics, liquid phase sintering cannot be formed when the temperature is not high enough, which will result in low density and poor mechanical properties of the final product. At too high a temperature, silicon nitride materials are prone to decomposition. Therefore, it is necessary to add sintering aids of appropriate types and mass fractions to silicon nitride ceramic balls to prepare high-quality ceramic balls. The formula of ceramic balls has a great influence on the final performance of the product. Additives are generally oxide ceramics. Too high a content will reduce the proportion of silicon nitride, thereby affecting the various properties of the ceramic ball. Too low a content will prevent the sample from being completely sintered, which will also reduce the performance of the sample. In the method for preparing large-sized silicon nitride ceramic balls for wind power generation disclosed in CN 111548163A, yttrium oxide, magnesium oxide, aluminum oxide, tungsten carbide and titanium carbide are used as additives, and the silicon nitride content is between 90-95wt%; the application of silicon nitride ceramic materials in the preparation of ceramic bearing balls disclosed in CN101538161A uses additives of yttrium oxide, aluminum oxide and one or more of zirconium oxide, cerium oxide, samarium oxide and lanthanum oxide, and the silicon nitride content is between 85-98wt%, but the additives used are rare earth oxides, which increases the production cost.

[0004] At the same time, due to the particularity of spherical samples, the molding process of ceramic balls is generally complicated and the pass rate is not high. The existing method of preparing spherical products from powder raw materials is to rely on a nearly spherical mold to combine the powder by pressure to press it into shape. The pressing molding is divided into dry pressing molding and cold isostatic pressing molding. The mold material used in dry pressing is mostly mold steel. This hard mold is usually difficult to demold due to the special large specific surface area of ​​the spherical shape. Not only are there strict requirements on parameters such as the type and content of adhesives in the powder raw materials and the moisture of the powder during the pressing process, but the pressed samples often have shortcomings such as low density, many internal defects, insufficient stability and uniformity, which leads to unstable quality of the samples after final sintering. Traditional cold-molded samples generally rely on flexible rubber sleeves. Although the samples have high density and internal uniformity after molding, the shape of the samples after pressing depends on whether the raw material powder is evenly and densely distributed in the sleeve before pressing. Generally, square products need to be machine-compacted or manually compacted when the powder is loaded into the mold, but the shape of the spherical sleeve itself makes it impossible to compact the powder in the sleeve. Therefore, the pressed samples often have poor sphericity and serious deformation. A large number of subsequent machining, grinding and other shaping steps will be required to repair the sample shape to a standard sphere. Another method of balling is to rely on equipment such as a disc balling machine to roll and form the ball. The powdered material with a certain humidity is rolled and rubbed, and then continuously combined with excess powder to form balls that grow to a certain size. The density of the rolled spheres is much smaller than that of the pressed products, and the sphericity after balling is average and there are many internal defects. Therefore, it is rarely used in the preparation of high-performance products. CN 109354503A discloses a silicon nitride ceramic ball manufacturing process that uses dry pressing to prepare ceramic balls. The pressure during dry pressing disclosed in the patent is low and uneven, and a high-density green blank cannot be obtained, thereby affecting the subsequent sintering performance; CN 110076882A discloses a cold isostatic pressing combined mold and production method for producing small and micro ceramic ball blanks, which introduces a cold isostatic rubber sleeve design suitable for spherical samples, but the rubber sleeve mold used therein has a complex structure and needs to be disassembled and assembled before use, which increases the cost of the rubber sleeve mold; CN115650732A discloses that the dry-pressed sample is laid flat between two layers of plastic film and then vacuumized. This operation easily causes the spherical sample to roll when vacuumized, and there is no way to fix the position, and it is impossible to avoid damage between samples due to mutual squeezing; the softer plastic film cannot ensure that it will not break under a large pressure during cold isostatic pressing, and the cracks will cause the product to be contaminated by oil.

[0005] In summary, it is necessary to provide a method for preparing silicon nitride ceramic balls that can both improve the ball formation rate and reduce subsequent shaping. Summary of the invention

[0006] In view of the shortcomings of the prior art, the present invention aims to provide a silicon nitride ceramic ball and a preparation method thereof. The preparation method provided by the present invention has high feasibility, reduces the difficulty of forming, improves the ball forming rate, and reduces the complicated subsequent shaping process.

[0007] To achieve this object, the present invention adopts the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a silicon nitride ceramic ball, the preparation method comprising the following steps:

[0009] (1) mixing α-silicon nitride, an additive, a binder and an organic solvent, and then sequentially grinding, vacuum drying, screening and dry pressing to obtain a spherical blank;

[0010] (2) forming and packaging the spherical blank obtained in step (1) and cold forming the spherical blank to obtain a silicon nitride ceramic spherical blank;

[0011] (3) The silicon nitride ceramic ball blank obtained in step (2) is subjected to degreasing treatment, gas pressure sintering and hot isostatic pressing sintering in sequence to obtain the silicon nitride ceramic ball.

[0012] The present invention achieves the purpose of simply and quickly pressing out silicon nitride ceramic ball blanks with high sphericity and uniform density in batches through shaping packaging and cold isostatic forming, and obtains silicon nitride ceramic balls with stable quality and excellent mechanical properties through gas pressure sintering and hot isostatic pressing. The preparation method of the present invention has high feasibility, reduces the difficulty of forming, improves the ball forming rate, and reduces the complicated subsequent shaping process.

[0013] As a preferred technical solution of the present invention, the purity of the α-silicon nitride in step (1) is 93-96wt%, for example, it can be 93wt%, 94wt%, 95wt% or 96wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0014] Preferably, the particle size of the α-silicon nitride in step (1) is 0.8 to 2 μm, for example, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm or 2 μm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0015] Preferably, the additive in step (1) includes any one of silicon dioxide, silicon carbide, magnesium oxide, aluminum oxide or yttrium oxide, or a combination of at least two of them. Typical but non-limiting combinations include: a combination of silicon dioxide and silicon carbide, a combination of magnesium oxide, aluminum oxide and yttrium oxide, or a combination of silicon dioxide, silicon carbide, magnesium oxide, aluminum oxide and yttrium oxide.

[0016] Preferably, the amount of additive added in step (1) is 1 to 5 wt% of the total mass of α-silicon nitride and the additive, for example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt% or 5 wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0017] Preferably, the average particle size of the additive in step (1) is 100 to 200 nm, for example, 100 nm, 120 nm, 140 nm, 160 nm, 180 nm or 200 nm, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0018] Preferably, the binder in step (1) comprises any one of polyvinyl butyral (PVB), polyethylene glycol (PEG), phenolic resin or paraffin, or a combination of at least two of them. Typical but non-limiting combinations include: a combination of polyvinyl butyral, polyethylene glycol and phenolic resin, a combination of polyethylene glycol, phenolic resin and paraffin, or a combination of polyvinyl butyral, polyethylene glycol phenolic resin and paraffin.

[0019] Preferably, the amount of the binder added in step (1) is 1 to 5 wt% of the mass of α-silicon nitride, for example, it can be 1 wt%, 2 wt%, 3 wt%, 4 wt% or 5 wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0020] Preferably, the organic solvent in step (1) comprises any one of anhydrous ethanol, acetone or gasoline, or a combination of at least two of them. Typical but non-limiting combinations include: a combination of anhydrous ethanol and acetone, a combination of anhydrous ethanol and gasoline, a combination of acetone and gasoline, or a combination of anhydrous ethanol, acetone and gasoline.

[0021] Preferably, the amount of the organic solvent added in step (1) is 10 to 20 wt% of the mass of α-silicon nitride, for example, it can be 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt% or 20 wt%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0022] In the present invention, a small amount of silicon dioxide on the surface of the α-silicon nitride can form one or more eutectics with the additives, generate a liquid phase at a relatively low temperature, and the generated oxide glass phase is distributed at the silicon nitride grain boundaries, thereby improving the density and high-temperature strength of the silicon nitride ceramic ball. The prepared silicon nitride ceramic ball has high density and good mechanical properties.

[0023] In addition, the present invention can also improve the density and high-temperature strength of silicon nitride ceramic balls by using additives with nano-particle size; and the additives used in the present invention are all common ceramic powders, which can reduce costs while ensuring sample quality.

[0024] As a preferred technical solution of the present invention, the grinding rotation speed in step (1) is 150-300 r / min, for example, it can be 150 r / min, 180 r / min, 210 r / min, 240 r / min, 270 r / min or 300 r / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0025] Preferably, the grinding time in step (1) is 10 to 24 hours, for example, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0026] Preferably, the temperature of the vacuum drying in step (1) is 100-120°C, for example, 100°C, 104°C, 108°C, 112°C, 116°C or 120°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0027] Preferably, the vacuum drying time in step (1) is 2 to 6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0028] Preferably, the mesh size of the sieve used for sieving in step (1) is 150 to 300 meshes, for example, it can be 150 mesh, 180 mesh, 210 mesh, 240 mesh, 270 mesh or 300 mesh, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0029] Preferably, the dry pressing pressure in step (1) is 1 to 10 MPa, for example, 1 MPa, 2 MPa, 4 MPa, 6 MPa, 8 MPa or 10 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0030] Preferably, the dry pressing time in step (1) is 60 to 180 seconds, for example, 60 seconds, 90 seconds, 120 seconds, 150 seconds or 180 seconds, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0031] In the present invention, the pressure of the dry pressing molding is 1-10 MPa. Too high a pressure will result in failure to demould, while too low a pressure will result in failure to mold.

[0032] Preferably, the density of the spherical blank in step (1) is 1.2 to 1.5 g / cm 3 , for example, it can be 1.2 g / cm 3 , 1.3g / cm 3 , 1.4g / cm 3 or 1.5g / cm 3 , but not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0033] As a preferred technical solution of the present invention, the shaping and packaging in step (2) includes: using pearl cotton to independently wrap each spherical blank obtained in step (1), and then performing vacuum sealing twice.

[0034] Preferably, the thickness of the pearl cotton is 0.5-2 mm, for example, it can be 0.5 mm, 0.8 mm, 1.1 mm, 1.4 mm, 1.7 mm or 2 mm, but it is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0035] In the present invention, the vacuum sealing process includes: firstly packing the spherical blank wrapped with pearl cotton in a packaging bag for vacuum sealing, and then performing two-layer packaging. Then, the packaged spherical blank is placed in a hollow box, the box is locked and placed in a material frame, and cold isostatic pressing is performed.

[0036] The present invention omits the molds used in cold forming in the traditional process by shaping and packaging the spherical blanks, improves the plastic film, and packages the single ball to avoid damage caused by mutual friction and extrusion between samples. The sample is wrapped with pearl cotton to make the surface of the ball smoother after pressing, thereby reducing the cost. Silicon nitride ceramic ball blanks with high sphericity and uniform density can be simply and quickly pressed in batches, reducing the difficulty of forming, improving the ball formation rate, and reducing the complicated subsequent shaping process.

[0037] As a preferred technical solution of the present invention, the cold forming in step (2) includes a first pressing, a second pressing, a third pressing and a pressure relief treatment performed in sequence.

[0038] Preferably, the pressure rise rate of the cold forming is 3 to 5 MPa / min, for example, it can be 3 MPa / min, 3.4 MPa / min, 3.8 MPa / min, 4.2 MPa / min, 4.6 MPa / min or 5 MPa / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0039] Preferably, the first pressing pressure is 100-120 MPa, for example, 100 MPa, 104 MPa, 108 MPa, 112 MPa, 116 MPa or 120 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0040] Preferably, the holding time of the first pressing is 5 to 8 minutes, for example, 5 minutes, 6 minutes, 7 minutes or 8 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0041] Preferably, the second pressing pressure is 150-200 MPa, for example, 150 MPa, 160 MPa, 170 MPa, 180 MPa, 190 MPa or 200 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0042] Preferably, the holding time of the second pressing is 10 to 12 minutes, for example, 10 minutes, 10.5 minutes, 11 minutes, 11.5 minutes or 12 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0043] Preferably, the third pressing pressure is 250-300 MPa, for example, 250 MPa, 260 MPa, 270 MPa, 280 MPa, 290 MPa or 300 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0044] Preferably, the holding time of the third pressing is 15 to 18 minutes, for example, 15 minutes, 16 minutes, 17 minutes or 18 minutes, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0045] Preferably, the pressure relief rate of the pressure relief treatment is 8 to 10 MPa / min, for example, it can be 8 MPa / min, 8.5 MPa / min, 9 MPa / min, 9.5 MPa / min or 10 MPa / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0046] It is worth noting that, in the cold forming process described in the present invention, it is necessary to limit the pressure increase rate and the pressure release rate to prevent the packaging film from rupturing due to excessively rapid pressure changes.

[0047] As a preferred technical solution of the present invention, the density of the silicon nitride ceramic ball blank in step (2) is 1.9 to 2.1 g / cm 3, for example, it can be 1.9 g / cm 3 , 1.95g / cm 3 , 2g / cm 3 , 2.05g / cm 3 or 2.1 g / cm 3 , but not limited to the listed values, other values ​​not listed within the numerical range are also applicable.

[0048] Preferably, the density of the silicon nitride ceramic ball blank in step (2) is 65-70%, for example, it can be 65%, 66%, 67%, 68%, 69% or 70%, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0049] In the present invention, preforming is first performed by dry pressing to obtain a spherical blank with good sphericity but low density; then, by wrapping pearl cotton, the packaging film is prevented from generating creases during vacuuming or pressing, resulting in uneven sample surfaces; vacuum packaging is performed in separate vacuum packaging bags by vacuum packaging machines, and after packaging twice, the samples are placed in a hollow box that can be fixed in a material frame for cold isostatic pressing, and the method of step-by-step pressure increase can make the sample shrink more uniformly and stably, and a spherical sample with good sphericity, relatively smooth surface and uniform density can be pressed out without a rubber sleeve. The cold isostatic forming method provided by the present invention can be applied to products of different diameters, greatly reducing the difficulty and cost of forming, reducing the subsequent shaping process, and successfully pressing out silicon nitride ceramic ball blanks with high sphericity and high density in batches.

[0050] The present invention also includes removing the packaging film on the silicon nitride ceramic ball blank before the degreasing treatment.

[0051] As a preferred technical solution of the present invention, the heating rate of the degreasing treatment in step (3) is 5 to 10°C / min, for example, it can be 5°C / min, 6°C / min, 7°C / min, 8°C / min, 9°C / min or 10°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0052] Preferably, the temperature of the degreasing treatment in step (3) is 500-700°C, for example, it can be 500°C, 540°C, 580°C, 620°C, 660°C or 700°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0053] Preferably, the holding time of the degreasing treatment in step (3) is 2 to 6 hours, for example, 2 hours, 3 hours, 4 hours, 5 hours or 6 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0054] Preferably, the cooling rate of the degreasing treatment in step (3) is 3 to 5°C / min, for example, it can be 3°C / min, 3.4°C / min, 3.8°C / min, 4.2°C / min, 4.6°C / min or 5°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0055] It is worth noting that when the degreasing process of the present invention is cooled to 300° C., the sample can be placed in the air for natural cooling.

[0056] In addition, the present invention needs to strictly control the cooling rate during the degreasing process. Too high a cooling rate will cause microcracks in the sample, and in severe cases may directly cause the sample to break.

[0057] As a preferred technical solution of the present invention, the gas pressure sintering described in step (3) includes nitrogen gas pressure sintering.

[0058] Preferably, the gas pressure of the gas pressure sintering in step (3) is 1 to 10 MPa, for example, 1 MPa, 2 MPa, 4 MPa, 6 MPa, 8 MPa or 10 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0059] Preferably, the temperature of the gas pressure sintering in step (3) is 1750-1850°C, for example, it can be 1750°C, 1770°C, 1790°C, 1810°C, 1830°C or 1850°C, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0060] Preferably, the heating rate of the gas pressure sintering in step (3) is 4 to 7°C / min, for example, 4°C / min, 5°C / min, 6°C / min or 7°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0061] Preferably, the holding time of the gas pressure sintering in step (3) is 4 to 6 hours, for example, 4 hours, 4.4 hours, 4.8 hours, 5.2 hours, 5.6 hours or 6 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0062] Preferably, the cooling rate of the gas pressure sintering in step (3) is 7 to 10°C / min, for example, 7°C / min, 8°C / min, 9°C / min or 10°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0063] Preferably, the pressure of the hot isostatic pressing sintering in step (3) is 180-200 MPa, for example, 180 MPa, 184 MPa, 188 MPa, 192 MPa, 196 MPa or 200 MPa, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0064] Preferably, the temperature of the hot isostatic pressing sintering in step (3) is 1750-1800° C., for example, 1750° C., 1760° C., 1770° C., 1780° C., 1790° C. or 1800° C., but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0065] Preferably, the heating rate of the hot isostatic pressing sintering in step (3) is 4 to 7°C / min, for example, 4°C / min, 5°C / min, 6°C / min or 7°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0066] Preferably, the holding time of the hot isostatic pressing sintering in step (3) is 4 to 6 hours, for example, it can be 4 hours, 4.4 hours, 4.8 hours, 5.2 hours, 5.6 hours or 6 hours, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0067] Preferably, the cooling rate of the hot isostatic pressing sintering in step (3) is 7 to 10°C / min, for example, 7°C / min, 8°C / min, 9°C / min or 10°C / min, but is not limited to the listed values, and other values ​​not listed within the numerical range are also applicable.

[0068] As a preferred technical solution of the present invention, the method for preparing the silicon nitride ceramic ball provided in the first aspect of the present invention comprises the following steps:

[0069] (1) α-silicon nitride with a purity of 93-96 wt% and a particle size of 0.8-2 μm, an additive with an average particle size of 100-200 nm, a binder and an organic solvent are mixed, and then ground at a speed of 150-300 r / min for 10-24 h, vacuum dried at 100-120° C. for 2-6 h, sieved with a 150-300 mesh screen, and dry pressed at 1-10 MPa for 60-180 s to obtain a density of 1.2-1.5 g / cm 3 Spherical billet;

[0070] The additive is added in an amount of 1 to 5 wt% of the total mass of α-silicon nitride and the additive, the binder is added in an amount of 1 to 5 wt% of the mass of α-silicon nitride, and the organic solvent is added in an amount of 10 to 20 wt% of the mass of α-silicon nitride;

[0071] (2) The spherical blanks obtained in each step (1) are wrapped separately with pearl cotton having a thickness of 0.5 to 2 mm, and vacuum-sealed twice and then cold-formed to obtain a spherical blank having a density of 1.9 to 2.1 g / cm 3 , Silicon nitride ceramic ball blank with a density of 65-70%;

[0072] The cold forming includes first pressing, second pressing, third pressing and pressure relief treatment performed in sequence; the pressure increase rate of the cold forming is 3-5MPa / min; the pressure of the first pressing is 100-120MPa, and the holding time is 5-8min; the pressure of the second pressing is 150-200MPa, and the holding time is 10-12min; the pressure of the third pressing is 250-300MPa, and the holding time is 15-18min; the pressure relief rate of the pressure relief treatment is 8-10MPa / min;

[0073] (3) sequentially performing degreasing treatment, nitrogen pressure sintering and hot isostatic pressing sintering on the silicon nitride ceramic ball blank obtained in step (2) to obtain the silicon nitride ceramic ball;

[0074] The degreasing treatment has a heating rate of 5 to 10°C / min, a temperature of 500 to 700°C, a holding time of 2 to 6 hours, and a cooling rate of 3 to 5°C / min.

[0075] The gas pressure sintering is 1-10 MPa, the temperature is 1750-1850°C, the heating rate is 4-7°C / min, the holding time is 4-6h, and the cooling rate is 7-10°C / min;

[0076] The hot isostatic pressing sintering has a pressure of 180-200 MPa, a temperature of 1750-1800° C., a heating rate of 4-7° C. / min, a heat preservation time of 4-6 hours, and a cooling rate of 7-10° C. / min.

[0077] In a second aspect, the present invention provides a silicon nitride ceramic ball, which is obtained by the preparation method provided in the first aspect.

[0078] The numerical range described in the present invention not only includes the point values ​​listed above, but also includes any point values ​​between the above numerical ranges that are not listed. Due to space limitations and for the sake of simplicity, the present invention no longer exhaustively lists the specific point values ​​included in the range.

[0079] Compared with the prior art, the present invention has the following beneficial effects:

[0080] (1) A small amount of silicon dioxide on the surface of α-silicon nitride in the silicon nitride ceramic ball provided by the present invention can form one or more low eutectic products with additives, generate a liquid phase at a lower temperature, which is more conducive to sintering, and obtain a silicon nitride ceramic ball with high density and good mechanical properties;

[0081] (2) The additive in the silicon nitride ceramic ball provided by the present invention is a common ceramic powder, which can reduce the cost while ensuring the quality of the silicon nitride ceramic ball;

[0082] (3) The shaping and packaging method provided by the present invention avoids the mutual friction and extrusion damage between the spherical blanks, making the surface of the pressed blank smoother, reducing the difficulty of forming, improving the ball forming rate, and reducing the complicated subsequent shaping process;

[0083] (3) The preparation method provided by the present invention has high feasibility, reduces the difficulty of molding, improves the ball forming rate, and reduces the complicated subsequent shaping process. DETAILED DESCRIPTION

[0084] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0085] Example 1

[0086] This embodiment provides a silicon nitride ceramic ball, and the preparation method of the silicon nitride ceramic ball comprises the following steps:

[0087] (1) α-silicon nitride with a purity of 93 wt% and a particle size of 1.4 μm, an additive with an average particle size of 150 nm, a binder and an organic solvent were mixed, and then ground at a speed of 225 r / min for 17 h, vacuum dried at 110° C. for 4 h, sieved with a 200-mesh screen, and dry pressed at 5 MPa for 120 s to obtain a density of 1.3 g / cm 3 Spherical billet;

[0088] The additive is added in an amount of 3wt% of the total mass of α-silicon nitride and the additive, the binder is added in an amount of 3wt% of the mass of α-silicon nitride, and the organic solvent is added in an amount of 15wt% of the mass of α-silicon nitride; the additive is silicon dioxide;

[0089] (2) The spherical blanks obtained in each step (1) are wrapped separately with pearl cotton having a thickness of 0.5 mm, and vacuum-sealed twice and then cold-formed to obtain a density of 2.0 g / cm 3 , Silicon nitride ceramic ball blank with a density of 67%;

[0090] The cold forming includes first pressing, second pressing, third pressing and pressure relief treatment in sequence; the pressure increase rate of the cold forming is 4MPa / min; the pressure of the first pressing is 110MPa, and the holding time is 6.5min; the pressure of the second pressing is 175MPa, and the holding time is 11min; the pressure of the third pressing is 275MPa, and the holding time is 16.5min; the pressure relief rate of the pressure relief treatment is 9MPa / min;

[0091] (3) sequentially performing degreasing treatment, nitrogen pressure sintering and hot isostatic pressing sintering on the silicon nitride ceramic ball blank obtained in step (2) to obtain the silicon nitride ceramic ball;

[0092] The degreasing treatment has a heating rate of 7.5°C / min, a temperature of 600°C, a holding time of 4h, and a cooling rate of 4°C / min.

[0093] The gas pressure sintering is 5 MPa, the temperature is 1800°C, the heating rate is 5.5°C / min, the holding time is 5h, and the cooling rate is 8.5°C / min;

[0094] The hot isostatic pressing sintering process has a pressure of 190 MPa, a temperature of 1775° C., a heating rate of 5.5° C. / min, a heat preservation time of 5 h, and a cooling rate of 8.5° C. / min.

[0095] Example 2

[0096] This embodiment provides a silicon nitride ceramic ball, and the preparation method of the silicon nitride ceramic ball comprises the following steps:

[0097] (1) α-silicon nitride with a purity of 95 wt% and a particle size of 0.8 μm, an additive with an average particle size of 100 nm, a binder and an organic solvent were mixed, and then ground at a speed of 150 r / min for 24 h, vacuum dried at 100° C. for 6 h, sieved with a 150-mesh screen, and dry pressed at 1 MPa for 180 s to obtain a density of 1.2 g / cm 3 Spherical billet;

[0098] The additive is added in an amount of 1wt% of the total mass of α-silicon nitride and the additive, the binder is added in an amount of 1wt% of the mass of α-silicon nitride, and the organic solvent is added in an amount of 10wt% of the mass of α-silicon nitride; the additive is silicon carbide;

[0099] (2) Each spherical blank obtained in step (1) is wrapped separately with pearl cotton having a thickness of 1 mm, and vacuum-sealed twice and then cold-formed to obtain a spherical blank having a density of 1.9 g / cm 3 , Silicon nitride ceramic ball blank with a density of 65%;

[0100] The cold forming includes first pressing, second pressing, third pressing and pressure relief treatment in sequence; the pressure increase rate of the cold forming is 3MPa / min; the pressure of the first pressing is 100MPa, and the holding time is 8min; the pressure of the second pressing is 150MPa, and the holding time is 12min; the pressure of the third pressing is 250MPa, and the holding time is 18min; the pressure relief rate of the pressure relief treatment is 8MPa / min;

[0101] (3) sequentially performing degreasing treatment, nitrogen pressure sintering and hot isostatic pressing sintering on the silicon nitride ceramic ball blank obtained in step (2) to obtain the silicon nitride ceramic ball;

[0102] The degreasing treatment was carried out at a heating rate of 5°C / min, a temperature of 500°C, a holding time of 6h, and a cooling rate of 3°C / min.

[0103] The gas pressure sintering is 1 MPa, the temperature is 1750°C, the heating rate is 4°C / min, the holding time is 6h, and the cooling rate is 7°C / min;

[0104] The hot isostatic pressing sintering process has a pressure of 180 MPa, a temperature of 1750° C., a heating rate of 4° C. / min, a heat preservation time of 6 h, and a cooling rate of 7° C. / min.

[0105] Example 3

[0106] This embodiment provides a silicon nitride ceramic ball, and the preparation method of the silicon nitride ceramic ball comprises the following steps:

[0107] (1) α-silicon nitride with a purity of 96 wt% and a particle size of 2 μm, an additive with an average particle size of 200 nm, a binder and an organic solvent are mixed, and then ground at a speed of 300 r / min for 10 h, vacuum dried at 120° C. for 2 h, sieved with a 300-mesh screen, and dry pressed at 10 MPa for 60 s to obtain a density of 1.5 g / cm 3 Spherical billet;

[0108] The additive is added in an amount of 5wt% of the total mass of α-silicon nitride and the additive, the binder is added in an amount of 5wt% of the mass of α-silicon nitride, and the organic solvent is added in an amount of 20wt% of the mass of α-silicon nitride; the additive is a combination of magnesium oxide, aluminum oxide and yttrium oxide;

[0109] (2) The spherical blanks obtained in each step (1) were wrapped separately with pearl cotton having a thickness of 2 mm, and vacuum-sealed twice and then cold-formed to obtain a density of 2.1 g / cm 3, Silicon nitride ceramic ball blank with a density of 70%;

[0110] The cold forming includes the first pressing, the second pressing, the third pressing and the pressure relief treatment performed in sequence; the pressure increase rate of the cold forming is 5MPa / min; the pressure of the first pressing is 120MPa, and the holding time is 5min; the pressure of the second pressing is 200MPa, and the holding time is 10min; the pressure of the third pressing is 300MPa, and the holding time is 15min; the pressure relief rate of the pressure relief treatment is 10MPa / min;

[0111] (3) sequentially performing degreasing treatment, nitrogen pressure sintering and hot isostatic pressing sintering on the silicon nitride ceramic ball blank obtained in step (2) to obtain the silicon nitride ceramic ball;

[0112] The degreasing treatment was carried out at a heating rate of 10°C / min, a temperature of 700°C, a holding time of 2h, and a cooling rate of 5°C / min.

[0113] The gas pressure sintering is 10MPa, the temperature is 1850°C, the heating rate is 7°C / min, the holding time is 4h, and the cooling rate is 10°C / min;

[0114] The hot isostatic pressing sintering is performed under a pressure of 200 MPa, a temperature of 1800° C., a heating rate of 7° C. / min, a heat preservation time of 4 h, and a cooling rate of 10° C. / min.

[0115] Example 4

[0116] This embodiment provides a silicon nitride ceramic ball. The preparation method of the silicon nitride ceramic ball is different from that of Embodiment 1 only in that:

[0117] In this embodiment, the amount of the additive added in step (1) is adjusted to 7 wt % of the total mass of α-silicon nitride and the additive.

[0118] Example 5

[0119] This embodiment provides a silicon nitride ceramic ball. The preparation method of the silicon nitride ceramic ball is different from that of Embodiment 1 only in that:

[0120] In this embodiment, the pressure of the dry pressing molding in step (1) is adjusted to 12 MPa.

[0121] Example 6

[0122] This embodiment provides a silicon nitride ceramic ball. The preparation method of the silicon nitride ceramic ball is different from that of Embodiment 1 only in that:

[0123] In this embodiment, the pressure of the dry pressing molding in step (1) is adjusted to 0.5 MPa.

[0124] Example 7

[0125] This embodiment provides a silicon nitride ceramic ball. The preparation method of the silicon nitride ceramic ball is different from that of Embodiment 1 only in that:

[0126] This embodiment omits the process of step (2) of wrapping the spherical blank with pearl cotton.

[0127] Example 8

[0128] This embodiment provides a silicon nitride ceramic ball. The preparation method of the silicon nitride ceramic ball is different from that of Embodiment 1 only in that:

[0129] In this embodiment, the number of vacuum sealing in step (2) is adjusted to 1 time.

[0130] Example 9

[0131] This embodiment provides a silicon nitride ceramic ball. The preparation method of the silicon nitride ceramic ball is different from that of Embodiment 1 only in that:

[0132] In this embodiment, the cold forming in step (2) is adjusted as follows: increasing the pressure to 275 MPa at a pressure increasing rate of 4 MPa / min, maintaining the pressure for 20 minutes, and then reducing the pressure to normal pressure at a pressure reducing rate of 7.5 MPa / min.

[0133] Example 10

[0134] This embodiment provides a silicon nitride ceramic ball. The preparation method of the silicon nitride ceramic ball is different from that of Embodiment 1 only in that:

[0135] In this embodiment, the cooling rate during the degreasing process in step (3) is adjusted to 8°C / min.

[0136] Comparative Example 1

[0137] This comparative example provides a silicon nitride ceramic ball, and the preparation method of the silicon nitride ceramic ball is different from that of Example 1 only in that:

[0138] In this comparative example, the nitrogen pressure sintering process described in step (3) was omitted.

[0139] Comparative Example 2

[0140] This comparative example provides a silicon nitride ceramic ball, and the preparation method of the silicon nitride ceramic ball is different from that of Example 1 only in that:

[0141] In this comparative example, the hot isostatic pressing sintering process described in step (3) was omitted.

[0142] Comparative Example 3

[0143] This comparative example provides a silicon nitride ceramic ball, and the preparation method of the silicon nitride ceramic ball is different from that of Example 1 only in that:

[0144] In this comparative example, the degreasing process described in step (3) was omitted.

[0145] Performance testing:

[0146] The ball formation rate, density, room temperature fracture toughness and hardness of the silicon nitride ceramic balls provided in the above embodiments and comparative examples were tested, and the results are shown in Table 1.

[0147] Table 1

[0148] Balling rate / % Density / % Crushing load / KN Hardness / HV Example 1 100 98 17.2 1522 Example 2 95 97.5 16.26 1457 Example 3 100 98.3 18.46 1503 Example 4 95 98 16.58 1483 Example 5 60 98 17.36 1531 Example 6 50 95 13.47 1448 Example 7 90 98 16.9 1475 Example 8 95 98 17.56 1495 Example 9 90 97 15.13 1449 Example 10 100 92.5 12.96 1430 Comparative Example 1 100 92 12.68 1438 Comparative Example 2 100 92.7 13.31 1453 Comparative Example 3 100 85.5 11.8 1403

[0149] According to Table 1, we can know the following points:

[0150] (1) Comprehensive analysis of Examples 1-3 shows that the preparation method provided by the present invention has high feasibility, reduces the difficulty of molding, improves the ball formation rate, and reduces the complicated steps of subsequent shaping; and the prepared silicon nitride ceramic balls have excellent density and mechanical properties;

[0151] (2) Comprehensive analysis of Example 1 and Example 4 shows that the content of additives in the formula of the silicon nitride ceramic ball of the present invention will affect the product performance. An appropriate content of additives can improve the density, but when the content is too high, the silicon nitride content in the product will be reduced, thereby reducing the mechanical properties of the final product.

[0152] (3) Comprehensive analysis of Example 1 and Examples 5-6 shows that the pressure of the dry pressing molding will affect the forming of the ball blank. Too much pressure will lead to the inability to demold, and too little pressure will lead to the inability to form, thereby reducing the ball forming rate;

[0153] (4) Comprehensive analysis of Example 1 and Examples 7-8 shows that the shaping and packaging process provided by the present invention can effectively protect the integrity of the spherical blank obtained in step (1), improve the ball formation rate, and reduce the complicated subsequent shaping process;

[0154] (5) Comprehensive analysis of Example 1 and Example 9 shows that the step-by-step pressure increase and pressure-maintaining cold forming is more conducive to uniform force forming of the sphere, so that the pressed sphere shrinks more evenly in the subsequent sintering process, thereby improving the mechanical properties of the final product;

[0155] (6) Comprehensive analysis of Example 1 and Example 10 shows that the excessively high cooling rate during the degreasing process causes excessive temperature changes, resulting in microcracks in the sample, which may directly lead to sample breakage in severe cases.

[0156] In summary, the present invention achieves the purpose of simply and quickly pressing out silicon nitride ceramic ball blanks with high sphericity and uniform density in batches through shaping packaging and cold isostatic forming, and obtains silicon nitride ceramic balls with stable quality and excellent mechanical properties through gas pressure sintering and hot isostatic pressing. The preparation method has high feasibility, reduces the difficulty of forming, improves the ball formation rate, and reduces the complicated subsequent shaping process.

[0157] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a silicon nitride ceramic ball, characterized in that: The preparation method comprises the following steps: (1) mixing α-silicon nitride, an additive, a binder and an organic solvent, and then sequentially grinding, vacuum drying, screening and dry pressing to obtain a spherical blank; (2) forming and packaging the spherical blank obtained in step (1) and cold forming the spherical blank to obtain a silicon nitride ceramic spherical blank; (3) The silicon nitride ceramic ball blank obtained in step (2) is subjected to degreasing treatment, gas pressure sintering and hot isostatic pressing sintering in sequence to obtain the silicon nitride ceramic ball.

2. The preparation method according to claim 1, characterized in that: The purity of the α-silicon nitride in step (1) is 93-96 wt %; Preferably, the particle size of the α-silicon nitride in step (1) is 0.8 to 2 μm; Preferably, the additive in step (1) includes any one of silicon dioxide, silicon carbide, magnesium oxide, aluminum oxide or yttrium oxide, or a combination of at least two thereof; Preferably, the additive added in step (1) is 1 to 5 wt% of the total mass of α-silicon nitride and the additive; Preferably, the average particle size of the additive in step (1) is 100 to 200 nm; Preferably, the binder in step (1) comprises any one of polyvinyl butyral, polyethylene glycol, phenolic resin or paraffin, or a combination of at least two thereof; Preferably, the amount of the binder added in step (1) is 1 to 5 wt% of the mass of α-silicon nitride; Preferably, the organic solvent in step (1) comprises any one of anhydrous ethanol, acetone or gasoline, or a combination of at least two thereof; Preferably, the amount of the organic solvent added in step (1) is 10 to 20 wt % of the mass of α-silicon nitride.

3. The preparation method according to claim 1 or 2, characterized in that: The grinding speed in step (1) is 150-300 r / min; Preferably, the grinding time in step (1) is 10 to 24 hours; Preferably, the temperature of the vacuum drying in step (1) is 100-120°C; Preferably, the vacuum drying time in step (1) is 2 to 6 hours; Preferably, the mesh size of the sieve used in step (1) is 150 to 300 meshes; Preferably, the pressure of the dry pressing in step (1) is 1 to 10 MPa; Preferably, the dry pressing time in step (1) is 60 to 180 seconds; Preferably, the density of the spherical blank in step (1) is 1.2 to 1.5 g / cm 3 .

4. The preparation method according to any one of claims 1 to 3, characterized in that The shaping and packaging in step (2) comprises: using pearl cotton to wrap each spherical blank obtained in step (1) independently, and then performing vacuum sealing twice; Preferably, the thickness of the pearl cotton is 0.5-2 mm.

5. The preparation method according to any one of claims 1 to 4, characterized in that: The cold forming in step (2) includes a first pressing, a second pressing, a third pressing and a pressure relief process performed in sequence; Preferably, the pressure increase rate of the cold forming is 3-5 MPa / min; Preferably, the first pressing pressure is 100-120 MPa; Preferably, the holding time of the first pressing is 5 to 8 minutes; Preferably, the second pressing pressure is 150-200 MPa; Preferably, the holding time of the second pressing is 10 to 12 minutes; Preferably, the third pressing pressure is 250-300 MPa; Preferably, the holding time of the third pressing is 15 to 18 minutes; Preferably, the pressure relief rate of the pressure relief treatment is 8-10 MPa / min.

6. The preparation method according to any one of claims 1 to 5, characterized in that: The density of the silicon nitride ceramic ball blank in step (2) is 1.9 to 2.1 g / cm 3 ; Preferably, the density of the silicon nitride ceramic ball blank in step (2) is 65-70%.

7. The preparation method according to any one of claims 1 to 6, characterized in that: The heating rate of the degreasing treatment in step (3) is 5 to 10°C / min; Preferably, the temperature of the degreasing treatment in step (3) is 500-700°C; Preferably, the holding time of the degreasing treatment in step (3) is 2 to 6 hours; Preferably, the cooling rate of the degreasing treatment in step (3) is 3 to 5°C / min.

8. The preparation method according to any one of claims 1 to 7, characterized in that: The gas pressure sintering in step (3) includes nitrogen gas pressure sintering; Preferably, the gas pressure of the gas pressure sintering in step (3) is 1 to 10 MPa; Preferably, the temperature of the gas pressure sintering in step (3) is 1750-1850°C; Preferably, the heating rate of the gas pressure sintering in step (3) is 4 to 7°C / min; Preferably, the holding time of the gas pressure sintering in step (3) is 4 to 6 hours; Preferably, the cooling rate of the gas pressure sintering in step (3) is 7 to 10°C / min; Preferably, the hot isostatic pressing sintering pressure in step (3) is 180-200 MPa; Preferably, the temperature of the hot isostatic pressing sintering in step (3) is 1750-1800°C; Preferably, the heating rate of the hot isostatic pressing sintering in step (3) is 4 to 7°C / min; Preferably, the holding time of the hot isostatic pressing sintering in step (3) is 4 to 6 hours; Preferably, the cooling rate of the hot isostatic pressing sintering in step (3) is 7 to 10° C. / min.

9. The preparation method according to any one of claims 1 to 8, characterized in that: The preparation method comprises the following steps: (1) α-silicon nitride with a purity of 93-96 wt% and a particle size of 0.8-2 μm, an additive with an average particle size of 100-200 nm, a binder and an organic solvent are mixed, and then ground at a speed of 150-300 r / min for 10-24 h, vacuum dried at 100-120° C. for 2-6 h, sieved with a 150-300 mesh screen, and dry pressed at 1-10 MPa for 60-180 s to obtain a density of 1.2-1.5 g / cm 3 Spherical billet; The additive is added in an amount of 1 to 5 wt% of the total mass of α-silicon nitride and the additive, the binder is added in an amount of 1 to 5 wt% of the mass of α-silicon nitride, and the organic solvent is added in an amount of 10 to 20 wt% of the mass of α-silicon nitride; (2) The spherical blanks obtained in step (1) are individually wrapped with pearls having a thickness of 0.5 to 2 mm, and vacuum-sealed twice before cold forming to obtain a spherical blank having a density of 1.9 to 2.1 g / cm 3 , Silicon nitride ceramic ball blank with a density of 65-70%; The cold forming includes first pressing, second pressing, third pressing and pressure relief treatment performed in sequence; the pressure increase rate of the cold forming is 3-5MPa / min; the pressure of the first pressing is 100-120MPa, and the holding time is 5-8min; the pressure of the second pressing is 150-200MPa, and the holding time is 10-12min; the pressure of the third pressing is 250-300MPa, and the holding time is 15-18min; the pressure relief rate of the pressure relief treatment is 8-10MPa / min; (3) sequentially performing degreasing treatment, nitrogen pressure sintering and hot isostatic pressing sintering on the silicon nitride ceramic ball blank obtained in step (2) to obtain the silicon nitride ceramic ball; The degreasing treatment has a heating rate of 5 to 10°C / min, a temperature of 500 to 700°C, a holding time of 2 to 6 hours, and a cooling rate of 3 to 5°C / min. The gas pressure sintering is 1-10 MPa, the temperature is 1750-1850°C, the heating rate is 4-7°C / min, the holding time is 4-6h, and the cooling rate is 7-10°C / min; The hot isostatic pressing sintering has a pressure of 180-200 MPa, a temperature of 1750-1800° C., a heating rate of 4-7° C. / min, a heat preservation time of 4-6 hours, and a cooling rate of 7-10° C. / min.

10. A silicon nitride ceramic ball, characterized in that: The silicon nitride ceramic ball is obtained by the preparation method described in any one of claims 1-9.