Interface-optimized high-strength silicon nitride ceramics, methods of making and applications thereof

Abstract

The application relates to an interface-optimized high-strength silicon nitride ceramic, a preparation method and application thereof, and belongs to the technical field of advanced structural ceramic materials. The silicon nitride ceramic is a layered composite structure, comprising a bottom layer and a top layer with fine-grain microstructure and an interlaced intermediate layer with low-grain-boundary-phase content or high-grain-boundary-phase crystallinity microstructure. The preparation method comprises the following steps: providing first and second sintering powders with alumina-based and magnesium oxide-based sintering aids respectively; performing layered powder laying and sintering to form a precursor; and performing flash sintering treatment on the precursor to obtain the ceramic. The prepared silicon nitride ceramic has a surface layer hardness value of greater than or equal to 2000 Hv 1.0, a fracture toughness value of greater than or equal to 5 MPa.m 1 / 2 , a bending strength of greater than or equal to 1200 MPa, a compressive strength of greater than or equal to 4000 MPa, a thermal conductivity of greater than or equal to 80 W / (m.K), and a strain rate of greater than or equal to 2%. The silicon nitride ceramic is suitable for parts with requirements of high hardness, high wear resistance, high thermal shock resistance and high structural reliability.

Description

Technical Field

[0001] This application belongs to the field of advanced structural ceramic materials technology, specifically relating to an interface-optimized high-strength silicon nitride ceramic, its preparation method and application. Background Technology

[0002] Silicon nitride ceramics, as high-performance structural ceramics, have broad application prospects in cutting-edge industrial fields requiring high hardness, high wear resistance, high thermal shock resistance, and high structural reliability. To obtain a fully dense sintered body, sintering aids are typically added to form a liquid phase to promote sintering, which inevitably introduces grain boundary phases. The properties and morphology of these grain boundary phases are key factors determining the final properties of silicon nitride ceramics.

[0003] Currently, performance optimization of silicon nitride ceramics faces the following limitations: It's difficult to achieve a balance between performance and material properties. While grain refinement is often achieved by adding specific additives or controlling processes, this frequently leads to a decrease in material toughness and thermal shock resistance. Conversely, improving fracture toughness and thermal conductivity requires reducing or crystallizing grain boundary phases, which can cause excessive grain growth, impairing surface hardness and wear resistance. Single homogeneous material designs or traditional sintering processes struggle to simultaneously achieve a gradient of hardness on the outside and toughness on the same component. Traditional post-processing techniques are inefficient and have significant side effects. Methods involving prolonged high-temperature heat treatment to crystallize grain boundary phases are energy-intensive, time-consuming, and difficult to precisely control grain size, easily leading to unwanted grain coarsening or the formation of unfavorable crystalline phases, particularly detrimental to the material's surface properties. Integrated fabrication of complex structures is also challenging. Summary of the Invention

[0004] This application addresses the technical problems existing in the morphology control of existing silicon nitride nanomaterials by providing an interface-optimized high-strength silicon nitride ceramic, its preparation method, and its application. It can achieve high thermal conductivity and high strength performance by creating a high-hardness and wear-resistant outer layer of silicon nitride ceramic and a middle layer with low grain boundary phase content or high crystallinity.

[0005] The objective of this application can be achieved through the following technical solutions.

[0006] In a first aspect of this application, an interface-optimized high-strength silicon nitride ceramic is provided, which has a layered composite structure: The layered composite structure includes a bottom layer, an intermediate layer, and a top layer. The intermediate layer is an alternating stacked structure of highly crystalline layers and fine-crystalline layers, and the bottom layer and the top layer are each independently fine-crystalline layers. The fine-grained layer is a fine-grained silicon nitride ceramic layer with a grain size of less than 200 nm; The highly crystalline layer is a silicon nitride ceramic layer with a grain boundary phase content of less than 5 vol.% and / or a grain boundary phase crystallinity of more than 80%. A composition gradient interface is formed between the fine-grained layer and the highly crystalline layer. A compressive stress region caused by lattice mismatch exists at the interface. The compressive stress region extends along the layer thickness direction on both sides of the composition gradient interface, and the thickness of the compressive stress region is 50 nm to 200 nm.

[0007] In some embodiments, the silicon nitride ceramic satisfies one or more of the following conditions: Surface hardness value ≥2000 Hv 1.0; Fracture toughness value ≥5 MPa·m 1 / 2 ; Flexural strength ≥1200 MPa; Compressive strength ≥ 4000 MPa; Thermal conductivity ≥80 W / (m·K); Compressive strain ≥2%.

[0008] In a second aspect of this application, a method for preparing interface-optimized high-strength silicon nitride ceramics is provided, comprising the following steps: A first sintering powder is provided, the first sintering powder comprising silicon nitride powder and an alumina-based sintering aid; A second sintering powder is provided, the second sintering powder comprising silicon nitride powder and a silicon nitride magnesium-based sintering aid; A sintering raw material is provided, the sintering raw material comprising a first sintering powder and a second sintering powder stacked sequentially, and the sintering raw material is sintered to form a silicon nitride ceramic precursor; The silicon nitride ceramic precursor is subjected to flash calcination to obtain the interface-optimized high-strength silicon nitride ceramic. Wherein, the first sintering powder is flash-sintered to obtain a fine-grained layer; The second sintering powder is subjected to flash sintering to obtain a highly crystalline layer.

[0009] In some embodiments, the above preparation method satisfies one or more of the following conditions: the flash calcination temperature is 1600℃~1800℃, the flash calcination holding time is 5s~10s, and the flash calcination heating rate is 200℃ / s~500℃ / s; the flash calcination atmosphere includes an inert / reducing mixture, wherein the reducing gas includes at least one of carbon monoxide, methane, and hydrogen, and the volume fraction of the reducing gas in the inert / reducing mixture is 3 vol.%~8 vol.%.

[0010] The flash sintering process described in this application utilizes an instantaneous ultra-high temperature field to drive rapid densification and microstructure adjustment, while effectively suppressing grain growth through an extremely short residence time. This thermal shock treatment allows the surface layer, dominated by alumina-based additives, to complete the final stage of densification under conditions of extremely low liquid viscosity and extremely high mass transfer rate, simultaneously achieving grain refinement and thus obtaining a nanoscale fine-grained structure. For the intermediate layer, dominated by magnesium oxide-based additives, the instantaneous high temperature provides the necessary activation energy for the rapid crystallization of the grain boundary glass phase, but the extremely short time avoids grain growth or the formation of unfavorable crystalline phases.

[0011] In some embodiments, the above preparation method satisfies one or more of the following conditions: the sintering temperature is 1500℃~1650℃, the sintering time is 3min~7min, the sintering heating rate is 200℃ / min~500℃ / min, and the sintering atmosphere is nitrogen and / or vacuum atmosphere.

[0012] In some embodiments, the above preparation method satisfies one or more of the following conditions: the alumina-based sintering aid includes alumina and a first rare earth oxide; the silicon nitride magnesium-based sintering aid includes silicon nitride magnesium and a second rare earth oxide; the first rare earth oxide and the second rare earth oxide each independently include at least one of yttrium oxide, lanthanum oxide, gadolinium oxide and ytterbium oxide; the grain size of the silicon nitride powder, the first sintering aid powder and the second sintering powder are each independently 30 nm to 100 nm.

[0013] The layered design described in this application forms the physical basis for the gradient properties. During sintering, the alumina-based systems in the bottom and top layers, due to the solid solution of alumina in silicon nitride to form a solid solution phase, inhibit grain growth and promote the formation of a fine-grained layer with high surface hardness. The silicon nitride-magnesium-based system in the middle layer, due to its unique regulatory effect on grain boundary phases, tends to form a toughened microstructure. This compositional difference from the outside to the inside is solidified and strengthened through the subsequent flash sintering process, ultimately constructing a gradient of properties that continuously changes from the surface to the interior of the material.

[0014] In some embodiments, the above preparation method satisfies one or more of the following conditions: the alumina content is 1 wt.% to 3 wt.% based on the total mass of the first sintered powder; the content of the first rare earth oxide is 2 wt.% to 4 wt.% based on the total mass of the first sintered powder.

[0015] In some embodiments, the above preparation method satisfies one or more of the following conditions: the content of magnesium silicon nitride is 1 wt.% to 3 wt.% based on the total mass of the second sintered powder; the content of the second rare earth oxide is 2 wt.% to 4 wt.% based on the total mass of the second sintered powder.

[0016] In some embodiments, the thickness of the bottom and top layers of the interface-optimized high-strength silicon nitride ceramic is independently 10% to 20% of the total ceramic thickness.

[0017] The outer layer thickness (i.e., the thickness of the bottom and top layers) needs to be sufficiently thick to provide effective surface wear resistance and protection, but it cannot be too thick to prevent the brittle fine-grained structure from dominating the overall mechanical behavior of the material and impairing its toughness. The intermediate layer adopts an alternating spreading method, the mechanism of which is to build a microscale composition and structure gradient in the intermediate layer. This can blur the sharp interface that may exist between the highly crystalline layer and the fine-grained layer, promote a smoother performance transition, thereby achieving a better distribution of residual stress inside the material, and may further improve crack propagation resistance and overall structural reliability by introducing more interface effects.

[0018] In a third aspect, this application provides the application of interface-optimized silicon nitride ceramics in components with high hardness, high wear resistance, high thermal shock resistance, and high structural reliability.

[0019] The beneficial effects of the interface-optimized high-strength silicon nitride ceramic preparation method of this application include: (1) Achieving gradient structure in one step: By designing the differentiated composition of the fine-grained layer (alumina-based) and the highly crystalline layer (silicon-magnesium nitride-based), combined with the subsequent flash firing process, a gradient composite ceramic with "super-fine-grained wear-resistant surface and strong and highly thermally conductive inner layer" is formed simultaneously in a single process.

[0020] (2) Precise control of flash burning process: Instantaneous ultra-high temperature flash burning achieves rapid densification of the surface layer and inhibits grain growth, resulting in nano-fine crystals; the intermediate layer drives the rapid crystallization of the grain boundary phase, optimizing performance.

[0021] (3) Excellent and comprehensive performance: The ceramic prepared by the method has high hardness, high toughness, high strength and good thermal conductivity, which meets the stringent requirements of high reliability components for the comprehensive performance of materials. Attached Figure Description

[0022] Figure 1 This is a macroscopic morphology image of the cross-section of the silicon nitride ceramic prepared in Example 1; Figure 2 These are microstructure images of silicon nitride ceramics prepared in Example 1, wherein (a) shows the interface of the layered combination, (b) shows the sintering microstructure of the first sintered powder, and (c) shows the sintering microstructure of the second sintered powder. Figure 3 This is a macroscopic morphology image of the cross-section of the silicon nitride ceramic prepared in Example 2; Figure 4This is a macroscopic morphology image of the cross-section of the silicon nitride ceramic prepared in Example 3; Figure 5 These are microstructure images of silicon nitride ceramics prepared in Example 4, where (a) shows the interface of the layered combination, (b) shows the sintering microstructure of the first sintered powder, and (c) shows the sintering microstructure of the second sintered powder. Figure 6 These are microscopic morphology images of silicon nitride ceramics prepared in Example 5, wherein (a) shows the interface of the layered combination, (b) shows the sintered microscopic morphology of the first sintered powder, and (c) shows the sintered microscopic morphology of the second sintered powder. Detailed Implementation

[0023] The following detailed description, with appropriate reference to the accompanying drawings, discloses the interface-optimized high-strength silicon nitride ceramic, its preparation method, and embodiments of its application. However, unnecessary details may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of essentially the same structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0024] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of the particular range. The range defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range.

[0025] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0026] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0027] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in this application is for the purpose of describing particular embodiments only and is not intended to limit this application; unless otherwise stated, the values ​​of the parameters mentioned in this application can be measured using various measurement methods commonly used in the art (e.g., they can be tested according to the methods given in the embodiments of this application).

[0028] Existing methods and technologies for achieving layered or gradient ceramic structures typically require complex multi-step molding and sintering processes, and it is difficult to guarantee the bonding strength and smoothness of the performance transition between layers. Therefore, a simple and efficient process is needed to construct a gradient microstructure with optimized interfaces in a single ceramic body in one step, thereby synergistically improving its surface hardness, wear resistance, and internal toughness, thermal conductivity, and other comprehensive properties, providing a new approach to solving the traditional bottleneck of ceramic materials being "hard but not tough".

[0029] This application proposes a high-strength silicon nitride ceramic with optimized interface by designing a layered structure and performing post-processing on silicon nitride powder, along with its preparation method and applications. The preparation method of this high-strength silicon nitride ceramic includes the following steps: A first sintering powder is provided, the first sintering powder comprising silicon nitride powder and an alumina-based sintering aid; A second sintering powder is provided, the second sintering powder comprising silicon nitride powder and a silicon nitride magnesium-based sintering aid; The first sintering powder and the second sintering powder are alternately laid in sequence, and the resulting laid product is sintered to obtain a silicon nitride ceramic precursor. The silicon nitride ceramic precursor is subjected to flash calcination to obtain the interface-optimized high-strength silicon nitride ceramic. Wherein, the first sintering powder is flash-sintered to obtain a fine-grained layer; The second sintering powder is subjected to flash sintering to obtain a highly crystalline layer.

[0030] In some embodiments, the above preparation method satisfies one or more of the following conditions: the flash calcination temperature is 1600℃~1800℃, the flash calcination holding time is 5s~10s, and the flash calcination heating rate is 200℃ / s~500℃ / s; the flash calcination atmosphere includes an inert / reducing mixture, wherein the reducing gas includes at least one of carbon monoxide, methane, and hydrogen, and the volume fraction of the reducing gas in the inert / reducing mixture is 3 vol.%~8 vol.%.

[0031] In some embodiments, the sintering powder is laid in the following order: first, the first sintering powder is laid on the bottom layer, then the second sintering powder is laid on the first sintering powder, and then the powder is laid alternately in sequence, with the first sintering powder laid on the top layer.

[0032] In some embodiments, the above preparation method satisfies one or more of the following conditions: the sintering temperature is 1500℃~1650℃, the sintering time is 3min~7min, the sintering heating rate is 200℃ / min~500℃ / min, and the sintering atmosphere is nitrogen and / or vacuum atmosphere.

[0033] In some embodiments, the above preparation method satisfies one or more of the following conditions: the alumina-based sintering aid includes alumina and a first rare earth oxide; the silicon magnesium nitride-based sintering aid includes silicon magnesium nitride and a second rare earth oxide; the first rare earth oxide and the second rare earth oxide each independently include at least one of yttrium oxide, lanthanum oxide, gadolinium oxide and ytterbium oxide.

[0034] In some embodiments, the alumina content is 1 wt.% to 3 wt.% based on the total mass of the first sintered powder.

[0035] In some embodiments, the content of the first rare earth oxide is 2 wt.% to 4 wt.% based on the total mass of the first sintered powder.

[0036] In some embodiments, the magnesium silicon nitride content is 1 wt.% to 3 wt.% based on the total mass of the second sintered powder.

[0037] In some embodiments, the content of the second rare earth oxide is 2 wt.% to 4 wt.% based on the total mass of the second sintered powder.

[0038] In some embodiments, the thickness of the bottom and top layers of the high-strength silicon nitride ceramic is independently 10% to 30% of the total thickness of the high-strength silicon nitride ceramic; the intermediate layer is formed by alternating spreading of the first sintered powder and the second sintered powder.

[0039] Example 1: A first sintered powder is provided, which is composed of silicon nitride powder, 2 wt.% alumina and 3 wt.% ytterbium oxide, accounting for 2 wt.% of the total weight of the first sintered powder.

[0040] A second sintering powder is provided, which is composed of silicon nitride powder, 2 wt.% magnesium oxide and 3 wt.% yttrium oxide, accounting for 2 wt.% of the total weight of the second sintering powder.

[0041] The initial particle size of all powders is 30nm~60nm.

[0042] Two powders were layered in a sandwich configuration, with the outer two layers being the first sintered powder and the inner layer being the second sintered powder. The mold after powder layering was sintered at 1550℃ for 5 minutes at a heating rate of 300℃ / min under a nitrogen atmosphere to form a silicon nitride ceramic precursor.

[0043] The precursor was placed in a flash furnace and rapidly heated to 1700°C at a heating rate of 400°C / s under a mixed atmosphere of nitrogen and hydrogen (5 vol%), held for 8 s, and then rapidly cooled to obtain a high-strength silicon nitride ceramic with optimized interface. The macroscopic morphology of the layered structure cross-section is as follows. Figure 1As shown, the bottom and top layers are fine-grained layers, and the middle layer is highly crystalline.

[0044] The high-strength silicon nitride prepared in this embodiment has the following microstructure: Figure 2 As shown; the surface hardness is 2050 Hv1.0; the fracture toughness value is 5.2 MPa·m. 1 / 2 The bending strength is 1114 MPa; the compressive strength is 4050 MPa; the thermal conductivity is 82 W / (m·K); and the compressive strain is 2.1% (the specific data of each indicator are shown in Table 1).

[0045] Example 2 A first sintered powder is provided, which is composed of silicon nitride powder, 2 wt.% alumina and 3 wt.% ytterbium oxide, accounting for 2 wt.% of the total weight of the first sintered powder.

[0046] A second sintering powder is provided, which is composed of silicon nitride powder, 2 wt.% magnesium oxide and 3 wt.% yttrium oxide, accounting for 2 wt.% of the total weight of the second sintering powder.

[0047] The initial particle size of all powders is 50nm~100nm.

[0048] An alternating powder spreading method was adopted: first, the first sintered powder was spread at the bottom of the mold, then the second sintered powder was spread, then the first sintered powder was spread again, and the spreading of the second and first sintered powders was repeated to form a green body with five alternating layers. The mold after powder spreading was sintered at 1600℃ for 4 min, with a heating rate of 400℃ / min, under a nitrogen atmosphere to form a silicon nitride ceramic precursor.

[0049] The precursor was placed in a flash furnace and rapidly heated to 1750°C at a heating rate of 450°C / s in a mixed atmosphere of argon and carbon monoxide (3 vol%), held for 6 s, and then rapidly cooled to obtain a high-strength silicon nitride ceramic with optimized interface. The macroscopic morphology of the layered structure cross-section is as follows. Figure 3 As shown in the figure. The bottom and top layers are fine-grained layers, and the middle layers are alternating layers of highly crystalline and fine-grained layers.

[0050] The high-strength silicon nitride surface layer prepared in this embodiment has a hardness of 2100 Hv 1.0 and a fracture toughness of 5.5 MPa·m. 1 / 2 The bending strength is 1249 MPa; the compressive strength is 4119 MPa; the thermal conductivity is 81 W / (m·K); and the compressive strain is 2.4% (the specific data of each indicator are shown in Table 1).

[0051] Example 3 A first sintered powder is provided, which is composed of silicon nitride powder, 2 wt.% alumina and 3 wt.% ytterbium oxide, accounting for 2 wt.% of the total weight of the first sintered powder.

[0052] A second sintering powder is provided, which is composed of silicon nitride powder, 2 wt.% magnesium oxide and 3 wt.% yttrium oxide, accounting for 2 wt.% of the total weight of the second sintering powder.

[0053] The initial particle size of all powders is 30nm~80nm.

[0054] An alternating powder spreading method was adopted: first, the first sintered powder was spread at the bottom of the mold, then the second sintered powder was spread, then the first sintered powder was spread again, and the spreading of the second and first sintered powders was repeated twice to form a green body with seven alternating layers. The mold after powder spreading was sintered at 1620℃ for 6 minutes, with a heating rate of 350℃ / min, under a nitrogen atmosphere to form a silicon nitride ceramic precursor.

[0055] The precursor was placed in a flash furnace and rapidly heated to 1780°C at a heating rate of 500°C / s under a mixed atmosphere of nitrogen and methane (8 vol%), held for 5 s, and then rapidly cooled to obtain a high-strength silicon nitride ceramic with optimized interface. The macroscopic morphology of the layered structure cross-section is as follows. Figure 4 As shown in the figure. The bottom and top layers are fine-grained layers, and the middle layers are alternating layers of highly crystalline and fine-grained layers.

[0056] The high-strength silicon nitride surface layer prepared in this embodiment has a hardness of 2236 Hv 1.0 and a fracture toughness of 5.4 MPa·m. 1 / 2 The bending strength is 1328 MPa; the compressive strength is 4368 MPa; the thermal conductivity is 86 W / (m·K); and the compressive strain is 2.7% (the specific data of each indicator are shown in Table 1).

[0057] Example 4 A first sintered powder is provided, which is composed of silicon nitride powder, 2 wt.% alumina and 4 wt.% yttrium oxide.

[0058] A second sintering powder is provided, which is composed of silicon nitride powder, 2 wt.% magnesium oxide and 3.5 wt.% of a mixture of gadolinium oxide and ytterbium oxide (molar ratio 1:1).

[0059] The initial particle size of all powders is 30nm~60nm.

[0060] The first sintered powder was spread on the bottom of the mold to form an outer layer accounting for 30% of the total ceramic thickness. Subsequently, the second sintered powder was spread on the outer layer to form an inner layer with a thickness of 7 mm. The mold after powder spreading was sintered at 1580°C for 7 min with a heating rate of 250°C / min under a nitrogen atmosphere to form a silicon nitride ceramic precursor.

[0061] The precursor was placed in a flash furnace and rapidly heated to 1650°C at a heating rate of 300°C / s in a mixed atmosphere of nitrogen and hydrogen (3 vol%), held for 10 s, and then rapidly cooled to obtain a high-strength silicon nitride ceramic with optimized interface.

[0062] The high-strength silicon nitride ceramic prepared in this embodiment has a surface hardness of 2144 Hv 1.0 and a fracture toughness of 5.8 MPa·m. 1 / 2 The bending strength is 1269 MPa; the compressive strength is 4117 MPa; the thermal conductivity is 83 W / (m·K); and the compressive strain is 2.4% (the specific data of each indicator are shown in Table 1).

[0063] Example 5 A first sintered powder is provided, which is composed of silicon nitride powder, 3 wt.% alumina and 2 wt.% yttrium oxide, accounting for 3 wt.% of the total weight of the first sintered powder.

[0064] A second sintering powder is provided, which is composed of silicon nitride powder, 1 wt.% magnesium oxide and 2.5 wt.% gadolinium oxide, accounting for 1 wt.% of the total weight of the second sintering powder.

[0065] The initial particle size of all powders is 30nm~60nm.

[0066] The first sintered powder was spread on the bottom of the mold to form an outer layer with a thickness of 2.5 mm. Then, the second sintered powder was spread on the outer layer to form an inner layer with a thickness of 7.5 mm. The mold with powder spread was sintered at 1650°C for 3 min at a heating rate of 500°C / min under vacuum to form a silicon nitride ceramic precursor.

[0067] The precursor was placed in a flash furnace and rapidly heated to 1800°C at a heating rate of 500°C / s in a mixed atmosphere of nitrogen and methane (8 vol%), held for 5 s, and then rapidly cooled to obtain a high-strength silicon nitride ceramic with optimized interface.

[0068] The high-strength silicon nitride ceramic prepared in this embodiment has a surface hardness of 1953 Hv 1.0 and a fracture toughness of 5.1 MPa·m. 1 / 2The bending strength is 1175 MPa; the compressive strength is 4009 MPa; the thermal conductivity is 91 W / (m·K); and the compressive strain is 2.0% (the specific data of each indicator are shown in Table 1).

[0069] Comparative Example 1 Except for the absence of flash firing, all other steps and conditions were exactly the same as in Example 1. The sintered precursor was cooled in the furnace.

[0070] The silicon nitride ceramic prepared in this comparative example has a surface hardness of 1650 Hv 1.0 and a fracture toughness of 4.0 MPa·m. 1 / 2 The bending strength is 974 MPa; the compressive strength is 3117 MPa; the thermal conductivity is 59 W / (m·K); and the compressive strain is 1.2% (the specific data of each indicator are shown in Table 1).

[0071] Comparative Example 2 A sintered powder is provided, comprising silicon nitride powder, 2 wt.% alumina, and 2 wt.% magnesium oxide by weight of the total sintered powder. No rare earth oxides are added. The same layered powder structure and the same sintering and flash firing process conditions as in Example 1 are used.

[0072] The silicon nitride ceramic prepared in this comparative example has a hardness of 1750 Hv 1.0 and a fracture toughness of 4.0 MPa·m. 1 / 2 The flexural strength is 1050 MPa; the compressive strength is 3500 MPa; the thermal conductivity is 60 W / (m·K); and the compressive strain is 0.8%. Its density and various properties are significantly lower than those of Example 1, demonstrating that the addition of rare earth oxides is indispensable for promoting sintering densification, controlling the composition and crystallinity of grain boundary phases, and thus achieving excellent properties such as high strength and high thermal conductivity.

[0073] Comparative Example 3 Using the same preparation process as in Example 1, only the overall fine-grained layer was sintered to prepare a uniform silicon nitride ceramic.

[0074] The silicon nitride ceramic prepared in this comparative example has a surface hardness of 2050 Hv 1.0 and a fracture toughness of 3.1 MPa·m. 1 / 2 The bending strength is 457 MPa; the compressive strength is 2648 MPa; the thermal conductivity is 21 W / (m·K); and the compressive strain is 0.9% (the specific data of each indicator are shown in Table 1).

[0075] Comparative Example 4 Using the same preparation process as in Example 1, only the overall highly crystalline layer is sintered to prepare a uniform silicon nitride ceramic.

[0076] The silicon nitride ceramic prepared in this comparative example has a surface hardness of 1759 Hv 1.0 and a fracture toughness of 4.4 MPa·m. 1 / 2 The bending strength is 842 MPa; the compressive strength is 3157 MPa; the thermal conductivity is 109 W / (m·K); and the compressive strain is 1.3% (the specific data of each indicator are shown in Table 1).

[0077] Performance testing Surface hardness: The surface hardness of high-strength silicon nitride ceramic with optimized interface was obtained by testing with a hardness tester under a load of 1 Kgf.

[0078] Fracture toughness: A hardness tester was used to pre-create a crack under a 1 Kgf load, and the fracture toughness of the interface-optimized high-strength silicon nitride ceramic was calculated based on the crack length.

[0079] Bending strength, compressive strength and compressive strain: The compressive strength and bending strength of the interface-optimized high-strength silicon nitride ceramic were tested according to GB / T 50081-2019 standard.

[0080] Thermal conductivity: The front side of the sample is heated by pulsed laser, and the temperature rise on the back side is detected by infrared. The thermal diffusivity α is calculated, and the thermal conductivity λ is then converted according to λ=α·ρ·Cp, where ρ is the density of the test sample and Cp is the specific heat capacity at constant pressure.

[0081] Table 1 Summary of comparative performance data for each embodiment

[0082] As can be seen from the above-described Examples 1 and Comparative Examples 3 and 4, Example 1, while maintaining high hardness, exhibits significantly better fracture toughness, flexural strength, compressive strength, thermal conductivity, and compressive strain than Comparative Examples 3 and 4. This indicates that the present application, through the layered composite structure design of the outer fine-grained layer and the inner highly crystalline layer, combined with the flash firing process, achieves a synergistic improvement in the comprehensive performance of the material, overcoming the inherent technical contradiction that single-structure ceramics cannot simultaneously achieve hardness, toughness, strength, and thermal conductivity.

[0083] The embodiments herein do not exhaustively cover the points not covered by the technical scope claimed in this application, and new technical solutions formed by equivalent substitutions of one or more technical features in the technical solutions of the embodiments are also within the scope of protection claimed in this application. At the same time, in all the listed or unlisted embodiments of the solution in this application, each parameter in the same embodiment merely represents an instance of its technical solution (i.e., a feasible solution), and there is no strict matching or limiting relationship between the parameters. The parameters can be substituted for each other without violating axioms and the claims of this application, unless otherwise stated.

[0084] The technical means disclosed in this application are not limited to those described above, but also include technical solutions composed of any combination of the above technical features. The above descriptions are specific embodiments of this application. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this application, and these improvements and modifications are also considered within the scope of protection of this application.

[0085] The specific embodiments described herein are merely illustrative examples of the spirit of this application. Those skilled in the art to which this application pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of this application or exceeding the scope defined by the appended claims.

Claims

1. A high-strength silicon nitride ceramic with optimized interface, characterized in that, It is a layered composite structure: The layered composite structure includes a bottom layer, an intermediate layer, and a top layer. The intermediate layer is an alternating stacked structure of highly crystalline layers and fine-crystalline layers, and the bottom layer and the top layer are each independently fine-crystalline layers. The fine-grained layer is a fine-grained silicon nitride ceramic layer with a grain size of less than 200 nm; The highly crystalline layer is a silicon nitride ceramic layer with a grain boundary phase content of less than 5 vol.% and / or a grain boundary phase crystallinity of more than 80%. A composition gradient interface is formed between the fine-grained layer and the highly crystalline layer. A compressive stress region exists at the composition gradient interface. The compressive stress region extends along the layer thickness direction on both sides of the composition gradient interface. The thickness of the compressive stress region is 50 nm to 200 nm.

2. The interface-optimized high-strength silicon nitride ceramic according to claim 1, characterized in that, One or more of the following conditions must be met: Surface hardness value ≥2000 Hv 1.0; Fracture toughness value ≥5 MPa·m 1 / 2 ; Flexural strength ≥1200 MPa; Compressive strength ≥ 4000 MPa; Thermal conductivity ≥80 W / (m·K); Compressive strain ≥2%.

3. A method for preparing the interface-optimized high-strength silicon nitride ceramic according to claim 1 or 2, characterized in that, Includes the following steps: A first sintering powder is provided, the first sintering powder comprising silicon nitride powder and an alumina-based sintering aid; A second sintering powder is provided, the second sintering powder comprising silicon nitride powder and a silicon nitride magnesium-based sintering aid; The first sintering powder and the second sintering powder are alternately laid in sequence, and the resulting laid product is sintered to obtain a silicon nitride ceramic precursor. The silicon nitride ceramic precursor is subjected to flash calcination to obtain the interface-optimized high-strength silicon nitride ceramic. Wherein, the first sintering powder is flash-sintered to obtain a fine-grained layer; The second sintering powder is subjected to flash sintering to obtain a highly crystalline layer.

4. The method according to claim 3, characterized in that, One or more of the following conditions must be met: The flash burn temperature is 1600℃~1800℃. The holding time for the flash burning treatment is 5s to 10s. The heating rate of the flash burn treatment is 200℃ / s to 500℃ / s; The atmosphere for the flash combustion treatment includes an inert / reducing mixture, wherein the reducing gas includes at least one of carbon monoxide, methane, and hydrogen, and the volume fraction of the reducing gas in the inert / reducing mixture is 3 vol.% to 8 vol.%.

5. The method according to claim 3, characterized in that, One or more of the following conditions must be met: The sintering temperature is 1500℃~1650℃; The sintering time is 3 min to 7 min; The sintering heating rate is 200℃ / min to 500℃ / min.

6. The method according to claim 3, characterized in that, One or more of the following conditions must be met: The alumina-based sintering aid includes alumina and a first rare earth oxide; The silicon nitride magnesium-based sintering aid includes silicon nitride magnesium and a second rare earth oxide. The first rare earth oxide and the second rare earth oxide each independently include at least one of yttrium oxide, lanthanum oxide, gadolinium oxide and ytterbium oxide; The grain sizes of the silicon nitride powder, the first sintering aid powder, and the second sintering powder are all independently 30nm to 100nm.

7. The method according to claim 6, characterized in that, One or more of the following conditions must be met: Based on the total mass of the first sintered powder, the alumina content is 1 wt.%~3 wt.%; Based on the total mass of the first sintered powder, the content of the first rare earth oxide is 2 wt.%~4 wt.%; Based on the total mass of the second sintered powder, the content of the magnesium silicon nitride is 1 wt.% to 3 wt.%; Based on the total mass of the second sintered powder, the content of the second rare earth oxide is 2 wt.% to 4 wt.%.

8. The method according to claim 3, characterized in that, The thickness of the bottom layer and the top layer of the interface-optimized high-strength silicon nitride ceramic are each independently 10% to 20% of the total thickness of the high-strength silicon nitride ceramic.

9. The method according to claim 5, characterized in that, The sintering atmosphere is nitrogen and / or a vacuum atmosphere.

10. The application of an interface-optimized silicon nitride ceramic as described in claim 1 or 2, or an interface-optimized silicon nitride ceramic prepared by the method described in any one of claims 3-8, in components with high hardness, high wear resistance, high thermal shock resistance, and high structural reliability.

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