A preparation method of toughened silicon nitride

Abstract

The present invention relates to the field of material technology, and specifically to a method for preparing toughened silicon nitride, comprising the following steps: S1, in the presence of an inert gas and an organic solvent, mixing an organic aluminum compound with metal particles, performing solid-liquid separation and annealing to obtain aluminum oxide-coated metal particles; S2, mixing silicon nitride, aluminum oxide-coated metal particles, a sintering aid, and a binder to form a mixture, and sintering the mixture to obtain toughened silicon nitride. The present invention can improve the bonding interface strength between silicon nitride and metal particles, effectively transfer stress, and disperse stress by introducing aluminum oxide-coated metal particles as a metal toughening phase on silicon nitride, thereby improving the toughness of silicon nitride.

Description

Technical Field

[0001] The invention relates to the technical field of materials, and in particular to a preparation method of toughened silicon nitride. Background Art

[0002] Silicon nitride (Si3N4) ceramics are widely used in high-performance bearings, valves, seals, etc. due to their excellent mechanical properties, chemical stability and thermal stability. However, the intrinsic brittleness of silicon nitride ceramics limits their application under extreme conditions, especially in high stress environments where they are prone to fracture. Therefore, improving the toughness of silicon nitride ceramics is an important research direction in the current field of materials science.

[0003] Particle toughening is simple and easy to implement, and it can also improve the high-temperature strength and high-temperature creep properties of ceramics. Compared with the ceramic toughening phase, the metal toughening phase has significant plastic deformation ability. The preparation of silicon nitride ceramics with metal toughening phases can help expand the application field of silicon nitride ceramics.

[0004] The prior art discloses a toughened silicon nitride ceramic material and a preparation method thereof, specifically disclosing that silicon nitride is used as a main raw material, yttrium oxide, aluminum oxide and magnesium oxide are used as sintering aids, and modified carbon nanotubes are used as modifying substances, which can effectively improve the mechanical properties of silicon nitride ceramic materials and achieve a toughening effect. However, when metal materials are introduced into silicon nitride as sintering aids, due to the high reactivity of Si3N4, it is easy to chemically react with certain metals and produce new interfaces. The generated interfaces will have an important influence on the mechanical properties of silicon nitride ceramics, thereby affecting the fracture mode of the silicon nitride material, resulting in poor overall toughness performance of the composite material. Summary of the invention

[0005] Therefore, the technical problem to be solved by the present invention is to overcome the defect of poor toughness performance of the composite material formed by metal particles and silicon nitride in the prior art, thereby providing a preparation method of toughened silicon nitride.

[0006] To this end, the present invention provides a method for preparing toughened silicon nitride, comprising the following steps: S1, in the presence of an inert gas and an organic solvent, mixing an aluminum precursor with metal particles, performing solid-liquid separation and annealing to obtain aluminum oxide-coated metal particles; S2, mixing silicon nitride, aluminum oxide-coated metal particles, a sintering aid, and a binder to form a mixture, and sintering the mixture to obtain toughened silicon nitride.

[0007] In some embodiments, in step S1, the thickness of the aluminum oxide coated on the surface of the metal particles is 0.5 μm-6 μm, and preferably, the thickness of the aluminum oxide coated on the surface of the metal particles is 1 μm-5 μm.

[0008] In some of the embodiments, in step S2, a hot isostatic pressing step is further included after the sintering, and the hot isostatic pressing temperature is 1800° C.-1850° C., the pressure is 100 MPa-2000 MPa, and the holding time is 0.5 h-1 h.

[0009] In some embodiments, in step S2, silicon nitride, aluminum oxide-coated metal particles, sintering aids, and binders are mixed by grinding in the presence of a dispersion to form a mixed slurry.

[0010] Preferably, the dispersion liquid includes at least one of ethanol, ethyl acetate, acetone and isopropanol. More preferably, the dispersion liquid is ethanol.

[0011] In some embodiments, the grinding speed is 500 rpm-1000 rpm, and the grinding time is 4 h-10 h.

[0012] In some embodiments, step S2 also includes the steps of spray granulation and pressing the mixed slurry, the outlet temperature of the spray granulation is 150°C-180°C, the average particle size of the spray granulation is 50μm-100μm, and the pressing pressure is 2MPa-5MPa.

[0013] In some embodiments, the step S2 further comprises a step of debinding the pressed silicon nitride blank, the debinding temperature is 450° C.-550° C., and the debinding time is 4 h-12 h.

[0014] In some of the embodiments, after the silicon nitride blank pressed and formed in step S2 is debinded, the step of cold isostatic pressing the debinded silicon nitride blank before sintering is also included, and the cold isostatic pressing pressure is 130MPa-300MPa, and the holding time is 300s-600s.

[0015] In some embodiments, in step S1, the organic aluminum compound and the metal particles are mixed under stirring, the stirring speed is 400 rpm-600 rpm, and the stirring time is 5 h-7 h.

[0016] In some embodiments, the solid-liquid separation in step S1 includes a drying step, the drying temperature is 100° C.-120° C., and the drying time is 6 h-8 h.

[0017] In some embodiments, the annealing temperature is 500° C.-800° C., and the annealing time is 5 h-8 h.

[0018] In some embodiments, the sintering temperature in step S2 is 1680° C.-1780° C., the holding time is 2 h-10 h, and the pressure is 1 MPa-5 MPa.

[0019] In some embodiments, the organoaluminum compound includes at least one of aluminum isopropoxide and aluminum isobutoxide.

[0020] In some embodiments, the metal particles include at least one of tungsten, molybdenum, rhenium, tantalum, chromium and zirconium.

[0021] In some embodiments, the particle size of the metal particles is 0.8-2 μm;

[0022] In some embodiments, the organic solvent includes a C1-C3 alcohol solvent. Preferably, the organic solvent includes at least one of methanol, ethanol, and isopropanol.

[0023] In some embodiments, the sintering aid includes a metal oxide.

[0024] In some embodiments, the binder includes at least one of polyvinyl butyral, polypropylene carbonate, polyvinyl alcohol, and polyvinyl acetate, preferably polyvinyl butyral.

[0025] In some embodiments, the ratio of the organoaluminum compound to the metal particles in step S1 is 0.5-2.5:1, preferably 1-2:1, in units of mol:g.

[0026] In some embodiments, the alumina-coated metal particles have a particle size of 50 mesh to 100 mesh.

[0027] In some of the embodiments, the sintering aid includes at least one of aluminum oxide, lanthanum oxide, neodymium oxide, ytterbium oxide, erbium oxide, and samarium oxide.

[0028] In some of the embodiments, in the mixture in step S2, the mass fraction of silicon nitride is 75%-95%, the mass fraction of alumina-coated metal particles is 1%-5%, the mass fraction of sintering aid is 3%-10%, and the mass fraction of binder is 3%-10%.

[0029] The technical solution of the present invention has the following advantages:

[0030] 1. A method for preparing toughened silicon nitride provided by the present invention comprises the following steps: S1, in the presence of an inert gas and an organic solvent, mixing an organic aluminum compound with metal particles, performing solid-liquid separation and annealing to obtain aluminum oxide-coated metal particles; S2, mixing silicon nitride, aluminum oxide-coated metal particles, a sintering aid, and a binder to form a mixture, and sintering the mixture to obtain toughened silicon nitride. The present invention can improve the bonding interface strength between silicon nitride and metal particles, effectively transfer stress, and disperse stress by introducing aluminum oxide-coated metal particles as a metal toughening phase on silicon nitride, thereby improving the toughness of silicon nitride.

[0031] 2. The present invention provides a method for preparing toughened silicon nitride. In step S1, the thickness of the aluminum oxide coated on the surface of the metal particles is 0.5μm-6μm, preferably 1μm-5μm. If the aluminum oxide coating layer is too thin, it will affect the toughness of silicon nitride. If the aluminum oxide coating layer is too thick, it will cause the coating layer to fall off from the surface of the metal particles, reducing the interface strength between the coating layer and the metal particles. The aluminum oxide coated on the surface of the metal particles provided by the present invention has a thickness of 0.5μm-6μm, preferably 1μm-5μm, which can significantly improve the toughness and structural integrity of silicon nitride.

[0032] 3. The present invention provides a method for preparing toughened silicon nitride, which further comprises a hot isostatic pressing step after sintering, wherein the hot isostatic pressing temperature is 1800°C-1850°C, the pressure is 100 MPa-2000 MPa, and the holding time is 0.5h-1h. The present invention can improve the compactness and uniformity of the aluminum oxide-coated metal particles on the silicon nitride surface by adding the hot isostatic pressing step after the sintering step, and further improve the toughness of the composite material.

[0033] 4. The present invention provides a method for preparing toughened silicon nitride, wherein after the silicon nitride blank pressed and formed in step S2 is debinded, the step of cold isostatic pressing the debinded silicon nitride blank before sintering is also included, and the pressure of the cold isostatic pressing is 130 MPa-300 MPa, and the holding time is 300s-600s. The present invention can improve the consolidation degree of the alumina-coated metal particles and silicon nitride by adding the step of cold isostatic pressing to the debinded silicon nitride blank, further improve the mechanical strength of the composite material, and achieve enhanced toughness.

[0034] 5. The present invention provides a method for preparing toughened silicon nitride, wherein the metal particles include at least one of tungsten, molybdenum, rhenium, tantalum, chromium and zirconium. The present invention can reduce the impact of cracks and improve the toughening effect of silicon nitride by selecting a material with a thermal expansion coefficient close to that of silicon nitride as the raw material of the metal toughening phase. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0036] Figure 1 This is a microscopic morphology of toughened silicon nitride obtained in Example 1 of the present invention. DETAILED DESCRIPTION

[0037] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to 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 arts shall fall within the protection scope of the present invention.

[0038] If no specific experimental steps or conditions are specified in the examples, the conventional experimental steps or conditions described in the literature in the field can be used. If no manufacturer is specified for the reagents or instruments used, they are all conventional reagent products that can be obtained commercially.

[0039] Example 1

[0040] This embodiment provides a method for preparing toughened silicon nitride, and the specific steps and parameters are as follows:

[0041] (1) Dissolve aluminum isopropoxide in 1 L of anhydrous ethanol. The molar concentration of aluminum isopropoxide in anhydrous ethanol is 2 mol / L. Slowly add 1 g of molybdenum metal powder (d 50 =1 μm), stirred at 500 rpm for 6 h under nitrogen, transferred to an oil bath and stirred and dried at 100 °C for 8 h to obtain a mixture.

[0042] The mixture was then annealed at 550°C for 5.5 h under oxygen to obtain alumina-coated metal particles, which were ground and sieved to about 100 mesh.

[0043] The thickness of the aluminum oxide coated on the surface of the metal particles was measured to be 1 μm by transmission electron microscopy (TEM).

[0044] (2) According to 91 wt% silicon nitride powder, 1 wt% alumina-coated molybdenum metal particles, 2 wt% alumina, 1 wt% ytterbium oxide, and 5 wt% polyvinyl butyral, the above materials and 1 L of anhydrous ethanol were transferred to a drum mill at a speed of 1000 rpm and ground for 8 h to obtain a mixed slurry.

[0045] (3) The mixed slurry was spray granulated using a spray granulation tower. The outlet temperature was 150°C. The average particle size of the granulated powder was 80 μm. The granulated powder was pressed into a silicon nitride blank at a molding pressure of 3 MPa.

[0046] (4) Debinding was performed under air at a temperature of 500 °C, a heating rate of 2 °C / min, and a debinding time of 8 h.

[0047] Subsequently, the debinding green blank was subjected to cold isostatic pressing at 250 MPa with a holding time of 600 s to obtain an intermediate.

[0048] (5) The intermediate is pressure sintered under nitrogen at a sintering temperature of 1700°C, a holding time of 6 h, and a pressure of 3 MPa.

[0049] Then, the toughened silicon nitride was obtained by further hot isostatic pressing sintering at 1800°C and 150 MPa with a holding time of 0.8 h.

[0050] The microscopic morphology of toughened silicon nitride prepared in this embodiment is shown in Figure 1 .

[0051] Example 2

[0052] This embodiment provides a method for preparing toughened silicon nitride, and the specific steps and parameters are as follows:

[0053] (1) Dissolve aluminum isopropoxide in 1 L of anhydrous ethanol. The molar concentration of aluminum isopropoxide in anhydrous ethanol is 2 mol / L. Slowly add 1 g of molybdenum metal powder (d 50 =1 μm), stirred for 6 h under nitrogen, transferred to an oil bath and stirred and dried at 100 °C for 8 h to obtain a mixture.

[0054] The mixture was then annealed at 550°C for 5.5 h under oxygen to obtain alumina-coated metal particles, which were ground and sieved to about 100 mesh.

[0055] The thickness of the aluminum oxide coated on the surface of the metal particles was measured by TEM method and was 1 μm.

[0056] (2) According to 88 wt% silicon nitride powder, 3 wt% alumina-coated molybdenum metal particles, 2 wt% alumina, 1 wt% ytterbium oxide, and 5 wt% polyvinyl butyral, the above materials and 1 L of anhydrous ethanol were transferred to a drum mill at a speed of 1000 rpm and ground for 8 h to obtain a mixed slurry.

[0057] (3) The mixed slurry was spray granulated using a spray granulation tower. The outlet temperature was 150°C. The average particle size of the granulated powder was 80 μm. The granulated powder was pressed into a silicon nitride blank at a molding pressure of 3 MPa.

[0058] (4) Debinding was performed under air at a temperature of 500 °C, a heating rate of 2 °C / min, and a debinding time of 8 h.

[0059] Subsequently, the debinding green blank was subjected to cold isostatic pressing at 250 MPa with a holding time of 600 s to obtain an intermediate.

[0060] (5) The intermediate is pressure sintered under nitrogen at a sintering temperature of 1700°C, a holding time of 6 h, and a pressure of 3 MPa.

[0061] Then, it was further hot isostatically pressed and sintered at 1800°C and 150 MPa with a holding time of 0.8 h to obtain toughened silicon nitride.

[0062] Example 3

[0063] This embodiment provides a method for preparing toughened silicon nitride, and the specific steps and parameters are as follows:

[0064] (1) Dissolve aluminum isobutoxide in 1 L of isopropanol. The molar concentration of aluminum isopropoxide in isopropanol is 1 mol / L. Slowly add 1 g of molybdenum metal powder (d 50 =0.8 μm), stirred at 400 rpm for 7 h under nitrogen, transferred into an oil bath and stirred and dried at 120 °C for 6 h to obtain a mixture.

[0065] The mixture was then annealed at 500°C for 8 h under oxygen to obtain alumina-coated metal particles, which were ground and sieved to about 100 mesh.

[0066] The thickness of the aluminum oxide coated on the surface of the metal particles was measured by TEM method and was 1 μm.

[0067] (2) According to 75 wt% silicon nitride powder, 5 wt% alumina-coated molybdenum metal particles, 5 wt% alumina and 5 wt% lanthanum oxide, and 10 wt% polypropylene carbonate, the above materials and 1 L of ethyl acetate were transferred to a drum mill at a speed of 500 rpm and ground for 10 h to obtain a mixed slurry.

[0068] (3) The mixed slurry was spray granulated using a spray granulation tower, the outlet temperature was 180°C, the average particle size of the granulated powder was 100 μm, and the granulated powder was pressed into a silicon nitride blank at a molding pressure of 2 MPa.

[0069] (4) Debinding was performed under air at a temperature of 450 °C, a heating rate of 2 °C / min, and a debinding time of 12 h;

[0070] Subsequently, the debinding green blank was subjected to cold isostatic pressing at 130 MPa with a holding time of 600 s to obtain an intermediate.

[0071] (5) The intermediate is pressure sintered under nitrogen at a sintering temperature of 1680°C, a holding time of 10 h, and a pressure of 5 MPa.

[0072] Then, it was further hot isostatically pressed and sintered at 1850℃ and 200 MPa with a holding time of 0.5h to obtain toughened silicon nitride.

[0073] Example 4

[0074] This embodiment provides a method for preparing toughened silicon nitride, and the specific steps and parameters are as follows:

[0075] (1) Dissolve aluminum isopropoxide in 1 L of anhydrous ethanol. The molar concentration of aluminum isopropoxide in anhydrous ethanol is 2 mol / L. Slowly add 1 g of molybdenum metal powder (d 50 =2μm), stirred at 600rpm for 5 h under nitrogen, transferred into an oil bath and stirred and dried at 100°C for 7 h to obtain a mixture.

[0076] The mixture was then annealed at 800°C for 5 h under oxygen to obtain alumina-coated metal particles, which were ground and sieved to about 50 mesh.

[0077] The thickness of the aluminum oxide coated on the surface of the metal particles was measured by TEM method and was 1 μm.

[0078] (2) According to 91 wt% silicon nitride powder, 3 wt% alumina-coated molybdenum metal particles, 2 wt% neodymium oxide, 1 wt% erbium oxide, and 3 wt% polyvinyl alcohol, the above materials and 1 L of anhydrous ethanol were transferred to a drum mill at a speed of 1000 rpm and ground for 8 h to obtain a mixed slurry.

[0079] (3) The mixed slurry was spray granulated using a spray granulation tower, the outlet temperature was 150°C, the average particle size of the granulated powder was 80 μm, and the granulated powder was pressed into a silicon nitride blank at a molding pressure of 5 MPa.

[0080] (4) Debinding was performed under air at a temperature of 550°C, a heating rate of 2°C / min, and a debinding time of 4 h;

[0081] Subsequently, the debinding green blank was subjected to cold isostatic pressing at 300 MPa with a holding time of 300 s to obtain an intermediate.

[0082] (5) The intermediate is pressure sintered under nitrogen at a sintering temperature of 1780°C, a holding time of 2 h, and a pressure of 1 MPa.

[0083] Then, the toughened silicon nitride was obtained by further hot isostatic pressing at 1800°C and 150 MPa and holding the pressure for 1 hour.

[0084] Example 5

[0085] This embodiment provides a method for preparing toughened silicon nitride, and the specific steps and parameters are as follows:

[0086] (1) Dissolve aluminum isopropoxide in 1 L of anhydrous ethanol. The molar concentration of aluminum isopropoxide in anhydrous ethanol is 2 mol / L. Slowly add 1 g of molybdenum metal powder (d 50 =1 μm), stirred at 500 rpm for 6 h under nitrogen, transferred into an oil bath and stirred and dried at 100 °C to obtain a mixture.

[0087] The mixture was then annealed at 550°C for 5.5 h under oxygen to obtain alumina-coated metal particles, which were ground and sieved to about 100 mesh.

[0088] The thickness of the aluminum oxide coated on the surface of the metal particles was measured by TEM method and was 1 μm.

[0089] (2) According to 91 wt% silicon nitride powder, 1 wt% alumina-coated molybdenum metal particles, 2 wt% alumina, 1 wt% samarium oxide, and 5 wt% polyvinyl acetate, the above materials and 1 L of acetone were transferred to a drum mill at a speed of 1000 rpm and ground for 8 h to obtain a mixed slurry.

[0090] (3) The mixed slurry is spray granulated using a spray granulation tower, the outlet temperature is 150°C, the particle size of the granulated powder is 50-100 μm, and the granulated powder is pressed into a silicon nitride blank at a molding pressure of 3 MPa.

[0091] (4) Debinding was performed under air at a temperature of 500 °C, a heating rate of 2 °C / min, and a debinding time of 8 h.

[0092] Subsequently, the debinding green blank was subjected to cold isostatic pressing at 250 MPa with a holding time of 600 s to obtain an intermediate.

[0093] (5) The intermediate is pressure sintered under nitrogen at a sintering temperature of 1700°C, a holding time of 6 h, and a pressure of 3 MPa.

[0094] Then, the toughened silicon nitride was obtained by further hot isostatic pressing sintering at 1800°C and 150 MPa and holding the pressure for 1 hour.

[0095] Example 6

[0096] This embodiment provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those in Embodiment 1, except that tungsten metal powder of equal mass is used to replace the molybdenum metal powder in step (1).

[0097] Example 7

[0098] This embodiment provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those in Embodiment 1, except that an equal mass of rhenium metal powder is used to replace the molybdenum metal powder in step (1).

[0099] Example 8

[0100] This embodiment provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those in Embodiment 1, except that an equal mass of tantalum metal powder is used to replace the molybdenum metal powder in step (1).

[0101] Example 9

[0102] This embodiment provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those in Embodiment 1, except that an equal mass of chromium metal powder is used to replace the molybdenum metal powder in step (1).

[0103] Example 10

[0104] This embodiment provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those in Embodiment 1, except that zirconium metal powder of equal mass is used to replace the molybdenum metal powder in step (1).

[0105] Embodiment 11

[0106] This embodiment provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those in Example 1, except that the molar concentration of aluminum isopropoxide in step (1) is 2.5 mol / L.

[0107] The thickness of the aluminum oxide coated on the surface of the metal particles was measured by TEM method and was 6 μm.

[0108] Example 12

[0109] This embodiment provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those in Example 1, except that the molar concentration of aluminum isopropoxide in step (1) is 0.5 mol / L.

[0110] The thickness of the aluminum oxide coated on the surface of the metal particles was measured by TEM method and was 0.5 μm.

[0111] Embodiment 13

[0112] This embodiment provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those in Embodiment 1, except that step (4) does not contain a cold isostatic pressing step, that is, (4) debinding is performed in air at a debinding temperature of 500°C, a heating rate of 2°C / min, and a debinding time of 8 h to obtain an intermediate.

[0113] The remaining steps and parameters are the same as those in Example 1.

[0114] Embodiment 14

[0115] This embodiment provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those in Embodiment 1, except that step (5) does not include a hot isostatic pressing step, that is, (5) the intermediate is pressure sintered under nitrogen at a sintering temperature of 1700°C, a holding time of 6 h, and a pressure of 3 Mpa to obtain toughened silicon nitride.

[0116] The remaining steps and parameters are the same as those in Example 1.

[0117] Comparative Example 1

[0118] This comparative example provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those of Example 1, except that step (1) is not included, and the alumina-coated molybdenum metal particles in step (2) are replaced by an equal mass of silicon nitride powder, that is, in step (2), 92 wt% of silicon nitride powder, 2 wt% of alumina, 1 wt% of ytterbium oxide, and 5 wt% of polyvinyl butyral are mixed, and the above materials and 1 L of anhydrous ethanol are transferred to a drum mill at a rotation speed of 1000 rpm and ground for 8 h to obtain a mixed slurry.

[0119] Comparative Example 2

[0120] This comparative example provides a method for preparing toughened silicon nitride. The specific steps and parameters are the same as those of Example 1, except that the mixture in step (1) is not annealed. That is, (1) aluminum isopropoxide is dissolved in 1 L of anhydrous ethanol, wherein the molar concentration of aluminum isopropoxide in the anhydrous ethanol is 2 mol / L, and 1 g of molybdenum metal powder (d 50 =1 μm), stirred at 500 rpm for 6 h under nitrogen, transferred into an oil bath and stirred and dried at 100 °C to obtain a mixture.

[0121] (2) According to 91 wt% of silicon nitride powder, 1 wt% of the mixture obtained in step (1), 2 wt% of aluminum oxide, 1 wt% of ytterbium oxide, and 5 wt% of polyvinyl butyral, the above materials and 1 L of anhydrous ethanol were transferred to a drum mill at a speed of 1000 rpm and ground for 8 h to obtain a mixed slurry.

[0122] The remaining steps and parameters are the same as those in Example 1.

[0123] Experimental example

[0124] The Vickers hardness and fracture toughness of the toughened silicon nitride obtained in Examples 1-14 and Comparative Examples 1-2 were measured. The results are shown in Table 1.

[0125] Among them, hardness detection method: the test method refers to GB∕T 31703-2015.

[0126] Fracture toughness test method: The test method refers to GB∕T 31703-2015.

[0127] Table 1 Silicon nitride performance test results

[0128]

[0129] According to Table 1, compared with Comparative Example 1 in which no alumina-coated metal particles are added, and Comparative Example 2 in which a mixture of alumina and metal particles is used to replace the silicon nitride prepared by the alumina-coated metal particles, the embodiments of the present invention introduce alumina-coated metal particles as a metal toughening phase on the silicon nitride, thereby improving the bonding interface strength between the silicon nitride and the metal particles, effectively transferring stress, dispersing stress, and thus improving the toughness of the silicon nitride.

[0130] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled 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 list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the invention.

Claims

1. A method for preparing toughened silicon nitride, characterized in that: The following steps are included: S1, in the presence of an inert gas and an organic solvent, mixing an aluminum precursor with metal particles, performing solid-liquid separation, and annealing to obtain aluminum oxide-coated metal particles; S2, mixing silicon nitride, alumina-coated metal particles, a sintering aid, and a binder to form a mixture, and sintering the mixture to obtain toughened silicon nitride.

2. The method for preparing toughened silicon nitride according to claim 1, characterized in that: In step S1, the thickness of aluminum oxide coated on the surface of the metal particles is 0.5 μm-6 μm; and / or, In step S2, after sintering, a hot isostatic pressing step is further included, wherein the hot isostatic pressing temperature is 1800° C.-1850° C., the pressure is 100 MPa-2000 MPa, and the holding time is 0.5 h-1 h.

3. The method for preparing toughened silicon nitride according to claim 2, characterized in that: In step S1, the thickness of aluminum oxide coated on the surface of the metal particles is 1 μm-5 μm; and / or, In step S2, in the presence of a dispersion liquid, silicon nitride, aluminum oxide-coated metal particles, a sintering aid, and a binder are mixed by grinding to form a mixed slurry. The dispersion liquid comprises at least one of ethanol, ethyl acetate, acetone and isopropanol, The grinding speed is 500 rpm-1000 rpm, and the grinding time is 4 h-10 h.

4. The method for preparing toughened silicon nitride according to claim 3, characterized in that: The step S2 also includes the steps of spray granulation and compression molding of the mixed slurry, wherein the outlet temperature of the spray granulation is 150° C.-180° C., the average particle size of the spray granulation is 50 μm-100 μm, and the compression molding pressure is 2 MPa-5 MPa.

5. The method for preparing toughened silicon nitride according to claim 4, characterized in that: The step S2 also includes a step of debinding the pressed silicon nitride blank, wherein the debinding temperature is 450° C.-550° C., and the debinding time is 4 h-12 h.

6. The method for preparing toughened silicon nitride according to claim 5, characterized in that: After the silicon nitride blank pressed and formed in step S2 is debinded, the debinded silicon nitride blank is subjected to cold isostatic pressing before sintering. The cold isostatic pressing pressure is 130 MPa-300 MPa, and the holding time is 300 s-600 s.

7. The method for preparing toughened silicon nitride according to claim 1, characterized in that: In step S1, the organoaluminum compound and the metal particles are mixed under stirring, the stirring speed is 400 rpm-600 rpm, and the stirring time is 5 h-7 h; and / or, The solid-liquid separation in step S1 includes a drying step, wherein the drying temperature is 100° C.-120° C. and the drying time is 6 h-8 h; and / or, The annealing temperature is 500°C-800°C, and the annealing time is 5h-8h; and / or, In step S2, the sintering temperature is 1680°C-1780°C, the holding time is 2 h-10 h, and the pressure is 1 MPa-5 MPa.

8. The method for preparing toughened silicon nitride according to claim 7, characterized in that: The organoaluminum compound comprises at least one of aluminum isopropoxide and aluminum isobutoxide; and / or, The metal particles include at least one of tungsten, molybdenum, rhenium, tantalum, chromium and zirconium; and / or, The particle size of the metal particles is 0.8 μm to 2 μm; and / or, The organic solvent includes a C1-C3 alcohol solvent.

9. The method for preparing toughened silicon nitride according to claim 1, characterized in that: The sintering aid comprises a metal oxide; and / or, The binder includes at least one of polyvinyl butyral, polypropylene carbonate, polyvinyl alcohol, and polyvinyl acetate; and / or, In step S1, the ratio of the organoaluminum compound to the metal particles is 0.5-2.5:1, in units of mol:g.

10. The method for preparing toughened silicon nitride according to claim 9, characterized in that: The ratio of the organoaluminum compound to the metal particles in step S1 is 1-2:1, in mol:g; and / or, The particle size of the alumina-coated metal particles is 50 mesh to 100 mesh; and / or, The sintering aid comprises at least one of aluminum oxide, lanthanum oxide, neodymium oxide, ytterbium oxide, erbium oxide and samarium oxide; and / or, In the mixture in step S2, the mass fraction of silicon nitride is 75%-95%, the mass fraction of aluminum oxide-coated metal particles is 1%-5%, the mass fraction of sintering aid is 3%-10%, and the mass fraction of binder is 3%-10%.

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