Preparation method of a high-hardness silicon nitride ceramic

Abstract

The present invention relates to the technical field of silicon nitride materials, and particularly relates to a preparation method of high-hardness silicon nitride ceramics, which comprises the following steps: S1, mixing a silicon source, a titanium source and a carbon source, and sintering in a nitrogen atmosphere to obtain an intermediate; S2, mixing and sintering the intermediate and a sintering aid to obtain high-hardness silicon nitride ceramics. On the one hand, the present invention improves the uniformity of the distribution of TiN in silicon nitride grains by means of in-situ synthesis, not only realizes the improvement of mechanical properties, but also improves the uniformity of the color of the sintered body. On the other hand, the generation of TiN particles occurs synchronously with the generation of silicon nitride grains, improves the interfacial bonding force between silicon nitride and the second phase, further improves the interfacial wettability, and at the same time enhances the interfacial bonding strength between silicon nitride and the second phase, realizing the improvement of the hardness of silicon nitride.

Description

Technical Field

[0001] The present invention relates to the technical field of silicon nitride materials, and particularly relates to a method for preparing high-hardness silicon nitride ceramics. Background Art

[0002] Silicon nitride ceramic materials have excellent properties such as high strength, high temperature resistance, oxidation resistance, and wear resistance, and can be applied to many scenarios with complex conditions and harsh environments. With the development of high-end equipment manufacturing and new energy, the market field has been further expanded, and the mechanical properties requirements for the silicon nitride ceramic materials used in supporting are more stringent. The traditional methods for improving the mechanical properties of silicon nitride mainly improve the heat treatment process to promote grain growth and densification. However, in fact, the optimization of process parameters does not significantly improve the mechanical properties of silicon nitride, and the process parameters are difficult to control strictly.

[0003] The prior art improves the mechanical properties of silicon nitride by introducing second-phase particles, which refine the grains and increase the resistance to crack propagation at the same time. However, problems such as the size of the introduced second-phase particles being difficult to control, the particles being unevenly dispersed, and the poor wettability between the second-phase particles and the silicon nitride matrix result in poor hardness performance of the formed silicon nitride. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the defect that the poor hardness performance of silicon nitride caused by the problems of difficult control of the size of the second-phase particles, uneven particle dispersion, and poor wettability between the second-phase particles and the silicon nitride matrix in the prior art, so as to provide a method for preparing high-hardness silicon nitride ceramics.

[0005] For this purpose, the present invention provides a method for preparing high-hardness silicon nitride ceramics, including the following steps: S1, mixing a silicon source, a titanium source, and a carbon source, and sintering in a nitrogen atmosphere to obtain an intermediate; S2, mixing and sintering the intermediate and a sintering aid to obtain high-hardness silicon nitride ceramics.

[0006] In some embodiments, the molar ratio of the titanium source to the silicon source in step S1 is 0.5 - 8:100.

[0007] Preferably, the molar ratio of the titanium source to the silicon source is 1 - 4:100, and more preferably, the molar ratio of the titanium source to the silicon source is 2:100.

[0008] The molar ratio of the total amount of the titanium source and the silicon source to the carbon source is 1:2 - 6.

[0009] In some of these embodiments, the sintering step in step S1 specifically includes raising the temperature to 1200 - 1250°C at a heating rate of 5 - 10°C / min, holding for 0.5 - 2 h, raising the temperature to 1350 - 1400°C at a heating rate of 2 - 5°C / min, holding for 10 - 20 h, lowering the temperature to 1200 - 1250°C at a cooling rate of 2 - 6°C / min, holding for 0.5 - 1.5 h, and lowering the temperature to 25 - 35°C at a cooling rate of 2 - 6°C / min.

[0010] In some of these embodiments, the sintering pressure in step S1 is 0.12 - 0.16 MPa.

[0011] In some of these embodiments, step S1 further includes a step of removing carbon from the intermediate. The specific steps include calcining the intermediate at 650 - 700°C for 1 - 4 h.

[0012] In some of these embodiments, the mixing of the silicon source, titanium source, and carbon source is carried out by ball milling. The rotation speed of the ball milling is 300 - 360 rpm, and the ball milling time is 12 - 36 h.

[0013] In some of these embodiments, the mass ratio of the intermediate to the sintering aid in step S2 is 45 - 49:1 - 5.

[0014] In some of these embodiments, the sintering step in step S2 specifically includes raising the temperature to 1200 - 1250°C at a heating rate of 2 - 6°C / min, holding for 0.5 - 1.5 h, raising the temperature to 1650 - 1850°C at a heating rate of 2 - 6°C / min, holding for 2 - 10 h, lowering the temperature to 1200 - 1250°C at a cooling rate of 2 - 8°C / min, holding for 0.5 - 1.5 h, and lowering the temperature to 25 - 35°C at a cooling rate of 3 - 8°C / min.

[0015] In some of these embodiments, the specific steps of mixing the intermediate and the sintering aid include mixing the silicon nitride of the intermediate and the sintering aid by ball milling in the presence of a solvent. The rotation speed of the ball milling is 300 - 400 rpm, and the ball milling time is 12 - 36 h.

[0016] In some of these embodiments, after mixing the intermediate and the sintering aid and before sintering, it further includes steps of drying the mixed slurry and cold isostatic pressing. The drying temperature is 80 - 90°C, the drying time is 8 - 12 h, and the cold isostatic pressing pressure is 150 - 300 Mpa.

[0017] In some of these embodiments, the carbon source includes at least one of carbon powder or saccharides. Preferably, the saccharides include at least one of monosaccharides, disaccharides, and polysaccharides. More preferably, the monosaccharide includes glucose, the disaccharide is sucrose, and the polysaccharide includes starch.

[0018] In some of these embodiments, the silicon source includes at least one of silica gel and silicate. Preferably, the silicate includes organic silicate and inorganic silicate. More preferably, the organic silicate includes tetraethyl orthosilicate. More preferably, the inorganic silicate is sodium silicate.

[0019] In some of these embodiments, the titanium source includes at least one of inorganic titanium and organic titanium. Preferably, the titanium source includes at least one of titanium dioxide, tetrabutyl titanate, ethyl titanate, and isopropyl titanate.

[0020] In some of these embodiments, the sintering aid includes metal oxide.

[0021] Preferably, the sintering aid includes at least one of yttrium oxide, alumina, magnesia, ytterbium oxide, lanthanum oxide, and scandium oxide.

[0022] The technical solution of the present invention has the following advantages:

[0023] A method for preparing a high-hardness silicon nitride ceramic provided by the present invention includes the following steps: S1, mixing a silicon source, a titanium source, and a carbon source, and sintering in a nitrogen atmosphere to obtain an intermediate; S2, mixing and sintering the intermediate and a sintering aid to obtain a high-hardness silicon nitride ceramic. By sintering the silicon source, the titanium source, and the carbon source in a nitrogen atmosphere, the present invention obtains an intermediate containing titanium nitride and silicon nitride. While sintering the intermediate with the sintering aid to form silicon nitride, a crystal phase transformation from α to β occurs, and the in-situ synthesized TiN can be embedded between the formed silicon nitride grains. On the one hand, the present invention improves the distribution uniformity of TiN in silicon nitride grains by in-situ synthesis, not only achieving an improvement in mechanical properties but also improving the color uniformity of the sintered body. On the other hand, the generation of TiN particles occurs simultaneously with the formation of silicon nitride grains, improving the interfacial bonding force between silicon nitride and the second phase, further improving the interfacial wettability, and at the same time enhancing the interfacial bonding strength between silicon nitride and the second phase, achieving an improvement in the hardness of silicon nitride.

[0024] The preparation method provided by the present invention has simple steps, low cost, and pure material components, which is conducive to the large-scale production of high-hardness silicon nitride. Description of the Drawings

[0025] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0026] Figure 1 It is the microscopic morphology diagram of the silicon nitride ceramic material prepared in Example 1 of the present invention;

[0027] Figure 2 It is the microscopic morphology diagram of the silicon nitride ceramic material prepared in Comparative Example 1 of the present invention. Specific Embodiments

[0028] The following embodiments are provided to better further understand the present invention. They are not limited to the best embodiments, and do not limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior art features falls within the protection scope of the present invention.

[0029] For those embodiments where specific experimental steps or conditions are not indicated, the operations or conditions of the conventional experimental steps described in the literature in this field can be followed. For reagents or instruments whose manufacturers are not indicated, they are all conventional reagent products that can be obtained through commercial purchase.

[0030] Example 1

[0031] This example provides a preparation method for a high-hardness silicon nitride ceramic, and the specific steps and parameters are as follows:

[0032] (1) Weigh silicon dioxide (purity 99.99%, 500 nm), titanium dioxide (purity 99.99%, 300 nm) and high-purity carbon powder (purity 99.99%, 50 nm). Among them, the molar ratio of titanium dioxide to silicon dioxide is 1:50, and the molar ratio of the sum of silicon dioxide and titanium dioxide to high-purity carbon powder is 1:3;

[0033] Add the above powders into a roller mill according to the ratio for ball milling and mixing to obtain a mixed powder. The grinding medium balls are silicon nitride balls. The mass ratio of the powder to the grinding medium balls is 3:1, and the ball milling and mixing time is 24 h at a rotation speed of 300 rpm.

[0034] (2) Put the mixed powder into a silicon nitride crucible and place it in a nitriding furnace for sintering. The entire sintering process is divided into four stages. In the first stage, heat up at a heating rate of 5 °C / min to 1200 °C and hold at 1200 °C for 1 h;

[0035] In the second stage, the temperature is increased at a heating rate of 3 °C / min to 1400 °C and held at 1400 °C for 12 h;

[0036] In the third stage, the temperature is decreased at a cooling rate of 2 °C / min to 1200 °C and held at 1200 °C for 0.5 h;

[0037] In the fourth stage, the temperature is decreased to 25 °C at a cooling rate of 3 °C / min.

[0038] The entire sintering process is carried out in a nitrogen environment with the pressure maintained at 0.12 MPa.

[0039] (3) Place the sintered powder in a decarburizing furnace and calcine it at 700 °C in an air environment for 2 h to remove the carbon in the powder.

[0040] Finally, the carbon content in the powder after decarburization treatment is < 0.08 wt%.

[0041] (4) Take the powder, alumina, and yttrium oxide obtained in step (3), add the above raw materials and grinding media balls to a ball mill jar, pour in alcohol (75 vol% ethanol solution), and ball mill at a speed of 300 rpm for 16 h to obtain a slurry. Among them, the mass ratio of the powder, alumina, and yttrium oxide obtained in step (3) is 93:3:4, and the mass ratio of the above raw materials, alcohol, and grinding media balls is 1:1.5:5.

[0042] (5) Place the slurry in a vacuum drying oven for 10 h at a drying oven temperature of 80 °C to obtain the dried powder.

[0043] (6) Use an automatic tablet press to press a silicon nitride green compact disc with a diameter of φ35 mm, and perform cold isostatic pressing on the silicon nitride green compact disc with a cold isostatic pressure of 160 MPa.

[0044] (7) Place the cold isostatically pressed green compact balls in a graphite crucible, sprinkle boron nitride powder, and put them into an atmosphere pressure sintering furnace for sintering. The sintering is divided into four stages.

[0045] In the first stage, the temperature is increased to 1200 °C at a heating rate of 6 °C / min and held at 1200 °C for 1 h;

[0046] In the second stage, the temperature is increased to 1750 °C at a heating rate of 3 °C / min and held at 1750 °C for 2 h;

[0047] In the third stage, the temperature is decreased to 1200 °C at a cooling rate of 3 °C / min and held at 1200 °C for 30 min;

[0048] In the fourth stage, the temperature is decreased to 25 °C at a cooling rate of 5 °C / min.

[0049] Obtain a silicon nitride ceramic material with high hardness.

[0050] The micrograph of the silicon nitride ceramic material obtained in this example is shown in Figure 1 , it can be seen that the TiN on the silicon nitride formed by in-situ growth of TiN (the white dots in the figure are TiN) is evenly distributed, and the color of the sintered body is uniform.

[0051] Example 2

[0052] This example provides a preparation method of a high-hardness silicon nitride ceramic, and the specific steps and parameters are as follows:

[0053] (1) Weigh silicon dioxide (purity 99.99%, 500 nm), titanium dioxide (purity 99.99%, 300 nm) and high-purity carbon powder (purity 99.99%, 50 nm). Among them, the molar ratio of titanium dioxide to silicon dioxide is 1:25, and the molar ratio of the sum of silicon dioxide and titanium dioxide to high-purity carbon powder is 1:3;

[0054] Add the above powders into a roller mill according to the ratio for ball milling and mixing to obtain a mixed powder. The grinding media balls are silicon nitride balls, and the mass ratio of the powder to the grinding media balls is 3:1. Ball mill and mix at a speed of 320 rpm for 24 h.

[0055] (2) Put the mixed powder into a silicon nitride crucible and place it in a nitriding furnace for sintering. The whole sintering process is divided into four stages.

[0056] In the first stage, heat up at a heating rate of 6 °C / min to 1200 °C and hold at 1200 °C for 1 h;

[0057] In the second stage, heat up at a heating rate of 3 °C / min to 1400 °C and hold at 1400 °C for 13 h;

[0058] In the third stage, cool down at a cooling rate of 3 °C / min to 1200 °C and hold at 1200 °C for 0.5 h;

[0059] In the fourth stage, cool down to room temperature at a cooling rate of 3 °C / min.

[0060] The whole sintering process is carried out in a nitrogen environment, and the pressure is maintained at 0.12 MPa.

[0061] (3) Place the sintered powder in a decarburizing furnace and calcine it at 700 °C in an air environment for 3 h to remove the carbon in the powder.

[0062] Finally, the carbon content in the powder after decarburization treatment is < 0.08 wt%.

[0063] (4) Take the powder obtained in step (3), alumina, and yttrium oxide. Add the above raw materials and grinding balls into a ball mill tank, pour in alcohol (75 vol% ethanol solution), and ball mill for 16 h to obtain a slurry. Among them, the mass ratio of the powder obtained in step (3), alumina, and yttrium oxide is 95:2:3, and the mass ratio of the above raw materials, alcohol, and grinding balls is 1:1.5:5.

[0064] (5) Place the slurry in a vacuum drying oven for 10 h. The temperature of the drying oven is 85 °C, and after drying, a powder is obtained.

[0065] (6) Use an automatic tablet press to press a silicon nitride green compact wafer with a diameter of φ35 mm, and perform cold isostatic pressing on the silicon nitride green compact wafer. The cold isostatic pressure is 180 MPa.

[0066] (7) Place the cold isostatically pressed green compact balls in a graphite crucible, sprinkle boron nitride powder, and put them into an atmosphere pressure sintering furnace for sintering. The sintering is divided into four stages.

[0067] In the first stage, raise the temperature to 1200 °C at a heating rate of 6 °C / min and hold at 1200 °C for 1 h.

[0068] In the second stage, raise the temperature to 1750 °C at a heating rate of 3 °C / min and hold at 1750 °C for 2 h.

[0069] In the third stage, lower the temperature to 1200 °C at a cooling rate of 3 °C / min and hold at 1200 °C for 30 min.

[0070] In the fourth stage, lower the temperature to room temperature at a cooling rate of 5 °C / min.

[0071] A high-hardness silicon nitride ceramic material is obtained.

[0072] Example 3

[0073] This example provides a method for preparing a high-hardness silicon nitride ceramic, and the specific steps and parameters are as follows:

[0074] (1) Weigh silicon dioxide (purity 99.99%, 500 nm), titanium dioxide (purity 99.99%, 300 nm), and high-purity carbon powder (purity 99.99%, 50 nm). Among them, the molar ratio of titanium dioxide to silicon dioxide is 3:50, and the molar ratio of the sum of silicon dioxide and titanium dioxide to high-purity carbon powder is 1:3.

[0075] Add the above powders into a roller mill according to the ratio for ball milling and mixing to obtain a mixed powder. The grinding balls are silicon nitride balls, and the mass ratio of the powder to the grinding balls is 3:1. Ball mill and mix at a speed of 360 rpm for 24 h.

[0076] (2) Put the mixed powder into a silicon nitride crucible and place it in a nitriding furnace for sintering. The entire sintering process is divided into four stages.

[0077] In the first stage, heat at a heating rate of 8 °C / min until the temperature reaches 1200 °C, and hold at 1200 °C for 1 h.

[0078] In the second stage, heat at a heating rate of 3 °C / min until the temperature reaches 1400 °C, and hold at 1400 °C for 15 h.

[0079] In the third stage, cool at a cooling rate of 5 °C / min until the temperature reaches 1200 °C, and hold at 1200 °C for 1 h.

[0080] In the fourth stage, cool the temperature to room temperature at a cooling rate of 3 °C / min.

[0081] The entire sintering process is carried out in a nitrogen environment, and the pressure is maintained at 0.13 MPa.

[0082] (3) Place the sintered powder in a decarburizing furnace and calcine it at 700 °C in an air environment for 4 h to remove the carbon in the powder.

[0083] Finally, the carbon content in the powder after decarburization treatment is < 0.08 wt%.

[0084] (4) Take the powder obtained in step (3), alumina, and yttrium oxide. Add the above raw materials and grinding balls to a ball mill tank, pour in alcohol, and ball mill for 16 h to obtain a slurry. Among them, the mass ratio of the powder obtained in step (3), alumina, and yttrium oxide is 97:1:2, and the mass ratio of the above raw materials, alcohol, and grinding balls is 1:1.5:5.

[0085] (5) Place the slurry in a vacuum drying oven for 10 h. The temperature of the drying oven is 90 °C, and dry it to obtain the powder.

[0086] (6) Use an automatic tablet press to press a silicon nitride green body disc with a diameter of φ35 mm, and perform cold isostatic pressing on the silicon nitride green body disc. The cold isostatic pressure is 200 MPa.

[0087] (7) Place the cold isostatically pressed green body balls in a graphite crucible, spread boron nitride powder, and put them into an atmosphere pressure sintering furnace for sintering. The sintering is divided into four stages.

[0088] In the first stage, heat the temperature to 1200 °C at a heating rate of 6 °C / min, and hold at 1200 °C for 1 h.

[0089] In the second stage, heat the temperature to 1750 °C at a heating rate of 3 °C / min, and hold at 1750 °C for 2 h.

[0090] In the third stage, the temperature is decreased to 1200 °C at a cooling rate of 3 °C / min and held at 1200 °C for 30 min;

[0091] In the fourth stage, the temperature is decreased to room temperature at a cooling rate of 5 °C / min.

[0092] A silicon nitride ceramic material with high hardness is obtained.

[0093] Example 4

[0094] This example provides a method for preparing a silicon nitride ceramic with high hardness, and the specific steps and parameters are as follows:

[0095] (1) Weigh tetraethyl orthosilicate (purity 99.99%), tetrabutyl titanate (purity 99.99%) and high-purity glucose powder (purity 99.99%). Among them, the molar ratio of tetrabutyl titanate to tetraethyl orthosilicate is 0.5:100, and the molar ratio of the sum of tetraethyl orthosilicate and tetrabutyl titanate to high-purity glucose powder is 1:6;

[0096] Add the above powders and solutions into a drum mill according to the ratio for ball milling and mixing to obtain a mixed powder. Silicon nitride balls are selected as the grinding media balls, and the mass ratio of the powder to the grinding media balls is 3:1. The ball milling and mixing time is 12 h at a rotation speed of 360 rpm.

[0097] (2) Put the mixed powder into a silicon nitride crucible and place it in a nitriding furnace for sintering. The whole sintering process is divided into four stages.

[0098] In the first stage, the temperature is increased at a heating rate of 10 °C / min to 1250 °C and held at 1250 °C for 0.5 h;

[0099] In the second stage, the temperature is increased at a heating rate of 2 °C / min to 1350 °C and held at 1350 °C for 10 h;

[0100] In the third stage, the temperature is decreased at a cooling rate of 6 °C / min to 1250 °C and held at 1250 °C for 1.5 h;

[0101] In the fourth stage, the temperature is decreased to 35 °C at a cooling rate of 6 °C / min.

[0102] The whole sintering process is carried out in a nitrogen environment, and the pressure is maintained at 0.16 MPa.

[0103] (3) Place the sintered powder in a decarburization furnace and calcine it at 650 °C in an air environment for 4 h to remove the carbon in the powder.

[0104] Finally, the carbon content in the powder after decarburization treatment is < 0.08 wt%.

[0105] (4) Take the powder obtained in step (3), magnesium oxide, and ytterbium oxide. Add the above raw materials and grinding balls into a ball mill jar, pour in alcohol (75 vol% ethanol solution), and ball mill at a speed of 360 rpm for 36 h to obtain a slurry. Among them, the mass ratio of the powder, alumina, and yttrium oxide obtained in step (3) is 90:5:5, and the mass ratio of the above raw materials, alcohol, and grinding balls is 1:1.5:5.

[0106] (5) Place the slurry in a vacuum drying oven for 12 h, with the drying oven temperature at 80 °C, and dry to obtain a powder.

[0107] (6) Use an automatic tablet press to press a silicon nitride green compact disc with a diameter of φ35 mm, and perform cold isostatic pressing on the silicon nitride green compact disc, with a cold isostatic pressure of 300 MPa.

[0108] (7) Place the cold isostatically pressed green compact balls in a graphite crucible, and put them into an atmosphere pressure sintering furnace for sintering. The sintering is divided into four stages.

[0109] In the first stage, raise the temperature to 1250 °C at a heating rate of 2 °C / min and hold for 0.5 h at 1250 °C.

[0110] In the second stage, raise the temperature to 1650 °C at a heating rate of 2 °C / min and hold for 10 h at 1650 °C.

[0111] In the third stage, lower the temperature to 1250 °C at a cooling rate of 2 °C / min and hold for 1.5 h at 1250 °C.

[0112] In the fourth stage, lower the temperature to 25 °C at a cooling rate of 3 °C / min.

[0113] Obtain a high-hardness silicon nitride ceramic material.

[0114] Example 5

[0115] This example provides a preparation method for a high-hardness silicon nitride ceramic, and the specific steps and parameters are as follows:

[0116] (1) Weigh silica gel (purity 99.99%), tetraethyl titanate (purity 99.99%), and high-purity sucrose powder (purity 99.99%). Among them, the molar ratio of tetraethyl titanate to silica gel is 2:25, and the molar ratio of the sum of silica gel and tetraethyl titanate to high-purity sucrose powder is 1:2.

[0117] Add the above powders and solutions in proportion to a roller mill for ball milling and mixing to obtain a mixed powder. The grinding balls are silicon nitride balls, and the mass ratio of the powder to the grinding balls is 3:1. The ball milling and mixing time is 12 h at a speed of 300 rpm.

[0118] (2) Put the mixed powder into a silicon nitride crucible and place it in a nitriding furnace for sintering. The entire sintering process is divided into four stages.

[0119] In the first stage, heat it at a heating rate of 5 °C / min until the temperature reaches 1200 °C, and keep it at 1200 °C for 2 h.

[0120] In the second stage, heat it at a heating rate of 2 °C / min until the temperature reaches 1400 °C, and keep it at 1400 °C for 20 h.

[0121] In the third stage, cool it at a cooling rate of 2 °C / min until the temperature reaches 1200 °C, and keep it at 1200 °C for 0.5 h.

[0122] In the fourth stage, cool the temperature to 30 °C at a cooling rate of 3 °C / min.

[0123] The entire sintering process is carried out in a nitrogen environment, and the pressure is maintained at 0.14 MPa.

[0124] (3) Put the sintered powder in a decarburizing furnace and calcine it at 700 °C in an air environment for 1 h to remove the carbon in the powder.

[0125] Finally, the carbon content in the powder after decarburization treatment is < 0.08 wt%.

[0126] (4) Take the powder obtained in step (3), lanthanum oxide and scandium oxide, add the above raw materials and grinding balls to a ball mill jar, pour in alcohol (75 vol% ethanol solution), and ball mill at a speed of 300 rpm for 12 h to obtain a slurry. Among them, the mass ratio of the powder obtained in step (3), lanthanum oxide and scandium oxide is 98:1:1, and the mass ratio of the above raw materials, alcohol and grinding balls is 1:1.5:5.

[0127] (5) Place the slurry in a vacuum drying oven for 8 h, and the temperature of the drying oven is 90 °C to dry and obtain the powder.

[0128] (6) Use an automatic tablet press to press a silicon nitride green body wafer with a diameter of φ35 mm, and perform cold isostatic pressing on the silicon nitride green body wafer, with a cold isostatic pressure of 150 MPa.

[0129] (7) Place the cold isostatically pressed green body balls in a graphite crucible, spread boron nitride powder, and put them in an atmosphere pressure sintering furnace for sintering. The sintering is divided into four stages.

[0130] In the first stage, heat the temperature to 1200 °C at a heating rate of 2 °C / min, and keep it at 1200 °C for 1.5 h.

[0131] In the second stage, heat the temperature to 1850 °C at a heating rate of 6 °C / min, and keep it at 1850 °C for 2 h.

[0132] In the third stage, the temperature is decreased to 1250 °C at a temperature decreasing rate of 8 °C / min and held at 1250 °C for 1 h.

[0133] In the fourth stage, the temperature is decreased to 25 °C at a temperature decreasing rate of 8 °C / min.

[0134] A silicon nitride ceramic material with high hardness is obtained.

[0135] Comparative Example 1

[0136] This comparative example provides a method for preparing a silicon nitride ceramic with high hardness. The specific steps and parameters are as follows:

[0137] (1) Weigh silicon nitride, alumina, yttrium oxide and TiN. Add the above raw materials and grinding media balls into a ball mill jar, pour in alcohol, and ball mill for 16 h to obtain a slurry. Among them, the mass ratio of silicon nitride, alumina and yttrium oxide is 93:3:4, the addition amount of TiN is 0.3 wt% of the total mass of silicon nitride, alumina and yttrium oxide, and the mass ratio of the total mass of silicon nitride, alumina, yttrium oxide and TiN, alcohol and grinding media balls is 1:1.5:5.

[0138] (2) Place the slurry in a vacuum drying oven for 10 h. The temperature of the drying oven is 80 °C, and after drying, a powder is obtained.

[0139] (3) Use an automatic tablet press to press a silicon nitride green body disc with a diameter of φ35 mm, and perform cold isostatic pressing on the silicon nitride green body disc. The cold isostatic pressure is 160 MPa.

[0140] (4) Place the green body balls after cold isostatic pressing in a graphite crucible, sprinkle boron nitride powder, and put them into an atmosphere pressure sintering furnace for sintering. The sintering is divided into four stages. In the first stage, the temperature is increased to 1200 °C at a temperature increasing rate of 6 °C / min and held at 1200 °C for 1 h. In the second stage, the temperature is increased to 1750 °C at a temperature increasing rate of 3 °C / min and held at 1750 °C for 2 h. In the third stage, the temperature is decreased to 1200 °C at a temperature decreasing rate of 3 °C / min and held at 1200 °C for 30 min. In the fourth stage, the temperature is decreased to room temperature at a temperature decreasing rate of 5 °C / min.

[0141] A silicon nitride ceramic material is obtained.

[0142] The microscopic morphology diagram of the silicon nitride ceramic material obtained in this comparative example is shown in Figure 2 , and it can be seen that the distribution of TiN on silicon nitride is uneven ( Figure 2 the white dots in represent TiN), and the color of the sintered body is non-uniform.

[0143] Comparative Example 2

[0144] This comparative example provides a method for preparing high-hardness silicon nitride ceramics, and the specific steps and parameters are as follows:

[0145] (1)Weigh silicon nitride, alumina, yttrium oxide and TiN. Add the above raw materials and grinding balls into a ball mill tank, pour in alcohol, and ball mill for 16 h to obtain a slurry. Among them, the mass ratio of silicon nitride, alumina and yttrium oxide is 95:2:3, and the addition amount of TiN is 0.6 wt% of the total mass of silicon nitride, alumina and yttrium oxide. The mass ratio of the total mass of silicon nitride, alumina, yttrium oxide and TiN, alcohol and grinding balls is 1:1.5:5.

[0146] (2)Place the slurry in a vacuum drying oven for 10 h. The temperature of the drying oven is 80 °C, and after drying, a powder is obtained.

[0147] (3)Use an automatic tablet press to press a silicon nitride green body disc with a diameter of φ35 mm, and perform cold isostatic pressing on the silicon nitride green body disc. The cold isostatic pressure is 160 MPa.

[0148] (4)Place the cold isostatic pressed green body balls in a graphite crucible, spread boron nitride powder, and put them into an atmosphere pressure sintering furnace for sintering. The sintering is divided into four stages. In the first stage, the temperature is raised to 1200 °C at a heating rate of 6 °C / min and held at 1200 °C for 1 h; in the second stage, the temperature is raised to 1750 °C at a heating rate of 3 °C / min and held at 1750 °C for 2 h; in the third stage, the temperature is lowered to 1200 °C at a cooling rate of 3 °C / min and held at 1200 °C for 30 min; in the fourth stage, the temperature is lowered to room temperature at a cooling rate of 5 °C / min.

[0149] A silicon nitride ceramic material is obtained.

[0150] Experimental example

[0151] Detect the density and hardness of the silicon nitride ceramic materials prepared in Examples 1-5 and Comparative Examples 1-2. The results are shown in Table 1.

[0152] The detection method of density is determined by the Archimedes drainage method, and the detection method of hardness is determined according to the method of GB / T 16534-2009.

[0153] Table 1 Performance determination of silicon nitride ceramic materials

[0154]

[0155] According to the data in Table 1, compared with the silicon nitride ceramics formed by using titanium nitride, silicon nitride and sintering aids in Comparative Examples 1 and 2, the present invention uses a silicon source, a titanium source and a carbon source to sinter in a nitrogen atmosphere to obtain an intermediate containing titanium nitride and silicon nitride. While the intermediate is sintered with a sintering aid to form silicon nitride, a silicon nitride ceramic formed by a phase transformation exhibits good density and hardness.

[0156] Obviously, the above embodiments are merely examples for clear illustration and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. The obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A method for preparing high-hardness silicon nitride ceramics, characterized in that: The following steps are included: S1, mixing a silicon source, a titanium source and a carbon source, and sintering them in a nitrogen atmosphere to obtain an intermediate, The silicon source comprises at least one of silicon dioxide, silica gel and silicate, The carbon source includes at least one of carbon powder or sugars, The molar ratio of the titanium source to the silicon source is 0.5-8:100, and the molar ratio of the total molar amount of the titanium source and the silicon source to the carbon source is 1:2-6. The titanium source includes at least one of titanium dioxide, tetrabutyl titanate, ethyl titanate, and isopropyl titanate. The sintering step in step S1 specifically includes raising the temperature to 1200-1250°C at a heating rate of 5-10°C / min, maintaining for 0.5-2h, raising the temperature to 1350-1400°C at a heating rate of 2-5°C / min, maintaining for 10-20h, lowering the temperature to 1200-1250°C at a cooling rate of 2-6°C / min, maintaining for 0.5-1.5h, lowering the temperature to 25-35°C at a cooling rate of 2-6°C / min, The step S1 also includes a step of decarbonizing the intermediate, and the specific steps include calcining the intermediate at 650-700° C. for 1-4 hours; S2, mixing the intermediate and the sintering aid, and sintering to obtain high-hardness silicon nitride ceramics, The sintering aid comprises a metal oxide, The sintering step in step S2 specifically includes increasing the temperature to 1200-1250°C at a heating rate of 2-6°C / min, maintaining for 0.5-1.5h, increasing the temperature to 1650-1850°C at a heating rate of 2-6°C / min, maintaining for 2-10h, reducing the temperature to 1200-1250°C at a cooling rate of 2-8°C / min, maintaining for 0.5-1.5h, and reducing the temperature to 25-35°C at a cooling rate of 3-8°C / min.

2. The method for preparing high-hardness silicon nitride ceramics according to claim 1, characterized in that: The sintering pressure in step S1 is 0.12-0.16 MPa.

3. The method for preparing high hardness silicon nitride ceramics according to claim 2, characterized in that: The silicon source, titanium source and carbon source are mixed by ball milling, the rotation speed of the ball mill is 300-360rpm, and the ball milling time is 12-36h.

4. The method for preparing high-hardness silicon nitride ceramics according to claim 3, characterized in that: In step S2, the mass ratio of the intermediate to the sintering aid is 45-49:1-5.

5. The method for preparing high-hardness silicon nitride ceramics according to claim 1, characterized in that: The specific step of mixing the intermediate and the sintering aid includes mixing the silicon nitride of the intermediate and the sintering aid by ball milling in the presence of a solvent, the rotation speed of the ball milling is 300-400 rpm, and the ball milling time is 12-36 hours.

6. The method for preparing high-hardness silicon nitride ceramics according to claim 5, characterized in that: After the intermediate and the sintering aid are mixed, before sintering, the mixed slurry is dried and cold isostatically pressed. The drying temperature is 80-90° C. and the drying time is 8-12 hours. The cold isostatic pressing pressure is 150-300 MPa.

7. The method for preparing high-hardness silicon nitride ceramics according to claim 6, characterized in that: The silicate comprises at least one of an organic silicate and an inorganic silicate; and / or, The organic silicate comprises tetraethyl orthosilicate; and / or, The inorganic silicate is sodium silicate; and / or, The sugar includes at least one of monosaccharide, disaccharide and polysaccharide; and / or, The sintering aid includes at least one of yttrium oxide, aluminum oxide, magnesium oxide, ytterbium oxide, lanthanum oxide, and scandium oxide.

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