Nanometer zirconium diboride-silicon carbide composite ceramic powder based on gradient proportioning regulation and low-temperature preparation method thereof

Abstract

The application relates to the technical field of ultrahigh-temperature ceramic materials, and discloses a nano ZrB2-SiC composite ceramic powder based on gradient proportioning regulation and a low-temperature preparation method thereof; in view of the technical bottlenecks such as high reaction temperature (>=1600 DEG C), large powder particle size (>=10 mu m) and difficult two-phase proportion regulation in the prior art, the application innovatively proposes a gradient temperature-subsection proportioning preparation process. By accurately controlling the raw material proportioning of n(ZrO2):n(B4C):n(Si):n(C)=3:(1.8-2.0):1:(5.5-6.0), adopting a two-stage heating procedure (SiC crystal nuclei are preferentially generated at 1200 DEG C, and ZrB2 synthesis is completed at 1500 DEG C), the low-temperature and high-efficiency synthesis of ZrB2-SiC composite powder is realized in a single process. The complete reaction temperature is successfully reduced to 1500 DEG C, the average particle size of the obtained powder is 0.5-0.6 mu m, the oxygen content is <=0.8 wt%, and the ZrB2:SiC molar ratio can be accurately regulated in the range of 2:1 to 4:1 by adjusting the Si content. The ZrB2 (101) plane and the SiC (111) plane in the powder form a semi-coherent interface, and the crystal lattice distortion rate is <=3%.

Description

Technical Field

[0001] This invention relates to the field of ultra-high temperature ceramic materials technology, specifically to a nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method. Background Technology

[0002] Currently, the synthesis of ZrB2-SiC multiphase powder mainly relies on the traditional borothermal reduction method, which presents significant technical barriers. For example, Cao et al. prepared powder with an average particle size of 10-20 μm using zirconium silicate, boric acid, and graphite at 1650℃ for 2 hours. The excessively high reaction temperature resulted in huge energy consumption and abnormal grain growth. Although Zeng et al. reduced the temperature to 1200℃ using a molten salt-assisted method, the introduction of NaCl / KCl medium caused halogen impurity contamination, reducing the powder purity to below 95% while the average particle size remained as high as 38 μm. More importantly, the existing process lacks systematic research on raw material ratios, especially regarding the synergistic effects of multiple parameters such as the B4C overcompensation mechanism (B2O3 volatilization loss), carbon source reduction kinetics, and silicon source ratio control. This makes it difficult to simultaneously achieve the three core indicators of submicron particle size (D100 < 0.6 μm), low oxygen content ( < 1 wt%), and precise control of the two-phase ratio (ZrB2:SiC = 2:1-4:1 adjustable). At the level of powder microstructure control, existing technologies face significant challenges in interfacial bonding and morphology control. Studies have shown that insufficient B4C content results in residual ZrO2 in the product, while an excess of 30 mol% leads to unreacted B4C blocky impurities, disrupting the homogeneity of the two phases. Xie et al.'s research confirmed that when SiO2 is used as the silicon source, the product exhibits a mixed columnar and granular morphology, and residual ZrO2 results in a sintering density of only 96.75%. The fundamental reason is that traditional processes cannot coordinate the reaction kinetic sequence—SiC is completely generated at 1300℃ while ZrB2 requires 1500℃ for complete synthesis. This asynchronous reaction causes excessively high interfacial energy between the two phases, making it difficult to form a semi-coherent bond. An ideal interface requires a lattice mismatch of <5% between the ZrB2 (101) plane and the SiC (111) plane. However, interfaces obtained by existing methods often exhibit an amorphous transition layer, reducing the ceramic crack propagation resistance by approximately 30%. In the performance transfer process from powder to ceramics, existing technologies share a common problem: a decrease in densification mechanisms and a reduction in toughening effects. For example, the ceramic prepared by Roacha et al. using 2.6μm commercial powder has a relative density of only 92.5% and a flexural strength of 260MPa, far lower than the 99.24% density and 470MPa strength of the self-made powder ceramic B in the document. The fundamental reason is that the purchased powder has a wide particle size distribution (0.2-3μm) and irregular morphology, resulting in a densification mechanism dominated by plastic deformation during sintering, rather than the more efficient grain boundary slip mechanism. Ceramic A, due to its high porosity of 0.25%, has a straight crack propagation path and a fracture toughness of only 3.96MPa·m¹ / ²; while ideally, ceramic B, through fine grain strengthening and crack deflection / branching mechanisms, should achieve a toughness of 4.87MPa·m¹ / ². Existing processes struggle to achieve this level of microstructure control, severely restricting the practical application of ultra-high temperature ceramics in thermal protection systems.

[0003] Therefore, we propose a method for preparing nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation. Summary of the Invention

[0004] To achieve the above objectives, the present invention provides the following technical solution: a nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method, comprising the following steps: The raw material ratio adopts a molar ratio of n(ZrO2):n(B4C):n(Si):n(C) = 3:(1.8-2.0):1:(5.5-6.0), in which B4C is in excess at 20-30 mol% to compensate for the volatilization loss of the mesophase B2O3 above 450℃. Segmented temperature control: First, the temperature is increased to 1200℃ at 5℃ / min and held for 30min to preferentially complete the Si+C→SiC reaction to generate β-SiC crystal nuclei; then, the temperature is slowly increased to 1500℃ at 2℃ / min and held for 60min to complete the main reaction via B4C+ZrO2+C→ZrB2+CO. Rapid cooling process: A quenching device is used to rapidly cool to room temperature at a rate of >50℃ / min to suppress abnormal grain growth and phase separation.

[0005] Preferably, the B4C powder meets the following technical specifications: Purity ≥ 99.5%, particle size distribution D50 ≤ 500 nm, specific surface area ≥ 3.5 m² / g Oxygen content ≤ 0.5 wt%, free carbon content ≤ 0.3 wt%. The crystal structure is rhombohedral, space group R3m, and there is no surface oxide layer.

[0006] Preferably, during the 1500℃ holding stage, an argon-containing atmosphere of 5-10 vol% CH4 is introduced to form an amorphous carbon film with a thickness of 2-5 nm on the powder surface via chemical vapor deposition. This carbon film can: Inhibit surface oxidation of powders during storage and transportation It acts as an internal lubricant to promote densification during subsequent sintering. Adjusting the interfacial energy between ZrB2 and SiC promotes the formation of a semi-coherent interface.

[0007] Preferably, it possesses the following microstructural characteristics: Crystallographic characteristics: ZrB2 is hexagonal (space group P6 / mmm), and SiC is cubic β phase (space group F43m). Interface structure: The ZrB2(101) plane and the SiC(111) plane form a semi-coherent interface with a lattice mismatch of <5% and an interface distortion rate of ≤3%. Particle size distribution: Average particle size 0.5-0.6 μm, D100 < 0.71 μm, particle size distribution span [(D90-D10) / D50] < 1.0 Chemical purity: Oxygen content ≤0.8wt%, free of impurities such as ZrO2, B2O3, and free carbon.

[0008] Preferably, by adjusting the n(ZrO2):n(Si) ratio in the raw materials to within the range of 2:1 to 4:1, the ZrB2:SiC molar ratio can be precisely controlled. When n(ZrO2):n(Si) = 2:1, the ZrB2:SiC mass ratio is 83.9wt%:16.1wt%. When n(ZrO2):n(Si) = 3:1, the ZrB2:SiC mass ratio is 88.2wt%:11.8wt%. When n(ZrO2):n(Si) = 4:1, the ZrB2:SiC mass ratio is 90.4wt%:9.6wt%. The deviation between the measured value and the theoretical value is controlled within ±2 mol%.

[0009] Preferably, the sintering activity is: complete densification can be achieved at ≤1800℃, which is 100-150℃ lower than the traditional process; densification effect: the relative density of the obtained ceramic is ≥99.2%, and the apparent porosity is ≤0.15%; mechanical properties: Vickers hardness is ≥17.5GPa, flexural strength is ≥450MPa, and fracture toughness is ≥4.5MPa·m¹ / ².

[0010] Preferably, the impurity content is controlled through the following measures: High-purity graphite crucibles (purity ≥ 99.99%) are used to avoid the introduction of metal impurities. ZrO2 grinding balls are used during the ball milling process to prevent contamination by transition metals such as Fe and Cr. Maintaining a high vacuum of 10⁻²Pa before heating to 800℃ effectively removes adsorbed water and bound water.

[0011] Preferably, the powder morphology is controlled by the following combination of process parameters: Ball milling time of 10-12 hours and rotation speed of 180-220 rpm are used to obtain the best raw material mixing uniformity. During the heating phase of 1200-1500℃, the rate was controlled at 2℃ / min to promote diffusion-controlled solid-phase reactions. Quenching should be initiated within 30 seconds after the heat preservation period ends to avoid Ostwald curing.

[0012] Compared with the prior art, the present invention provides a nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method, which has the following beneficial effects: 1. This invention relates to a gradient-ratio controlled method for preparing nano-ZrB2-SiC multiphase ceramic powder at low temperatures. The technology achieves a breakthrough improvement in the comprehensive performance of ZrB2-SiC multiphase powder. By controlling the gradient temperature (preferentially generating SiC nuclei at 1200℃ and completing ZrB2 synthesis at 1500℃), the complete reaction temperature is successfully reduced from 1600-1650℃ in the traditional process to 1500℃, resulting in a reduction of energy consumption of approximately 25%. The average particle size of the obtained powder is controlled within the range of 0.5-0.6 μm, and the particle size distribution span [(D90-D10) / D50] < 1.0. More importantly, through a precise compensation mechanism of 20 mol% excess B4C, the loss of boron source caused by the volatilization of the mesophase B2O3 is effectively avoided, reducing the oxygen content of the powder to below 0.8 wt% and eliminating the residue of impurity phases such as ZrO2 and B2O3.

[0013] 2. This patented method for preparing nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control achieves precise control of the two-phase interface and morphology in terms of microstructure control. By optimizing the ratio range of n(ZrO2):n(Si) = 2:1-4:1, the ZrB2:SiC molar ratio can be precisely controlled to be continuously adjustable between 2:1 and 4:1, with the deviation between the measured and theoretical values ​​controlled within ±2mol%. HRTEM analysis shows that the ZrB2(101) crystal plane and the SiC(111) crystal plane form a semi-coherent interface with a lattice distortion rate ≤3%. This low-distortion interface lays the foundation for the high-temperature structural stability of the material. In addition, the "pinning points" formed by SiC particles at the ZrB2 grain boundaries effectively inhibit abnormal grain growth, making the powder exhibit a near-equiaxed morphology and avoiding the common problem of columnar and granular mixing in traditional processes.

[0014] 3. This invention relates to a gradient-proportion-controlled nano-ZrB2-SiC multiphase ceramic powder and its low-temperature preparation method. The ceramics prepared from this self-made powder exhibit superior comprehensive performance. Ceramic B achieves a relative density of 99.24% and an apparent porosity of only 0.12%, significantly improving upon ceramic A (97.15% density) prepared from commercially available powder. In terms of mechanical properties, it achieves a Vickers hardness of 17.93 GPa, a flexural strength of 470.00 MPa, and a fracture toughness of 4.87 MPa·m¹ / ², representing improvements of 15%, 45%, and 23% respectively compared to ceramic A. This performance optimization stems from the fine-grain strengthening effect and a unique toughening mechanism—uniformly distributed SiC particles induce crack deflection and branching, significantly extending the crack propagation path. Simultaneously, the higher sintering activity of the self-made powder transforms the densification mechanism from plastic deformation to more efficient grain boundary slip, providing a reliable guarantee for the application of ultra-high temperature ceramics in extreme environments. Detailed Implementation

[0015] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0016] An Example of a Gradient-Proportion-Controlled Nano-ZrB2-SiC Multiphase Ceramic Powder and its Low-Temperature Preparation Method A method for preparing nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation includes the following steps: The raw material ratio adopts a molar ratio of n(ZrO2):n(B4C):n(Si):n(C) = 3:(1.8-2.0):1:(5.5-6.0), in which B4C is in excess at 20-30 mol% to compensate for the volatilization loss of the mesophase B2O3 above 450℃. Segmented temperature control: First, the temperature is increased to 1200℃ at 5℃ / min and held for 30min to preferentially complete the Si+C→SiC reaction to generate β-SiC crystal nuclei; then, the temperature is slowly increased to 1500℃ at 2℃ / min and held for 60min to complete the main reaction via B4C+ZrO2+C→ZrB2+CO. Rapid cooling process: A quenching device is used to rapidly cool to room temperature at a rate of >50℃ / min to suppress abnormal grain growth and phase separation.

[0017] Specifically, the B4C powder meets the following technical specifications: Purity ≥ 99.5%, particle size distribution D50 ≤ 500 nm, specific surface area ≥ 3.5 m² / g Oxygen content ≤ 0.5 wt%, free carbon content ≤ 0.3 wt%. The crystal structure is rhombohedral, space group R3m, and there is no surface oxide layer.

[0018] Specifically, during the 1500℃ holding stage, an argon-containing atmosphere of 5-10 vol% CH4 is introduced, and an amorphous carbon film with a thickness of 2-5 nm is formed on the powder surface through chemical vapor deposition. This carbon film can: Inhibit surface oxidation of powders during storage and transportation It acts as an internal lubricant to promote densification during subsequent sintering. Adjusting the interfacial energy between ZrB2 and SiC promotes the formation of a semi-coherent interface.

[0019] Specifically, it possesses the following microstructural characteristics: Crystallographic characteristics: ZrB2 is hexagonal (space group P6 / mmm), and SiC is cubic β phase (space group F43m). Interface structure: The ZrB2(101) plane and the SiC(111) plane form a semi-coherent interface with a lattice mismatch of <5% and an interface distortion rate of ≤3%. Particle size distribution: Average particle size 0.5-0.6 μm, D100 < 0.71 μm, particle size distribution span [(D90-D10) / D50] < 1.0 Chemical purity: Oxygen content ≤0.8wt%, free of impurities such as ZrO2, B2O3, and free carbon.

[0020] Specifically, by adjusting the n(ZrO2):n(Si) ratio in the raw materials to within the range of 2:1 to 4:1, the ZrB2:SiC molar ratio can be precisely controlled. When n(ZrO2):n(Si) = 2:1, the ZrB2:SiC mass ratio is 83.9wt%:16.1wt%. When n(ZrO2):n(Si) = 3:1, the ZrB2:SiC mass ratio is 88.2wt%:11.8wt%. When n(ZrO2):n(Si) = 4:1, the ZrB2:SiC mass ratio is 90.4wt%:9.6wt%. The deviation between the measured value and the theoretical value is controlled within ±2 mol%.

[0021] Specifically, sintering activity: complete densification can be achieved at ≤1800℃, which is 100-150℃ lower than the traditional process; densification effect: the resulting ceramic has a relative density ≥99.2% and an apparent porosity ≤0.15%; mechanical properties: Vickers hardness ≥17.5GPa, flexural strength ≥450MPa, and fracture toughness ≥4.5MPa·m¹ / ².

[0022] Specifically, the impurity content is controlled through the following measures: High-purity graphite crucibles (purity ≥ 99.99%) are used to avoid the introduction of metal impurities. ZrO2 grinding balls are used during the ball milling process to prevent contamination by transition metals such as Fe and Cr. Maintaining a high vacuum of 10⁻²Pa before heating to 800℃ effectively removes adsorbed water and bound water.

[0023] Specifically, the powder morphology is controlled by the following combination of process parameters: Ball milling time of 10-12 hours and rotation speed of 180-220 rpm are used to obtain the best raw material mixing uniformity. During the heating phase of 1200-1500℃, the rate was controlled at 2℃ / min to promote diffusion-controlled solid-phase reactions. Quenching should be initiated within 30 seconds after the heat preservation period ends to avoid Ostwald curing.

[0024] Through the above technical solution, this invention achieves a breakthrough improvement in the comprehensive performance of ZrB2-SiC multiphase powder. By controlling the gradient temperature (preferentially generating SiC nuclei at 1200℃ and completing ZrB2 synthesis at 1500℃), the complete reaction temperature is successfully reduced from 1600-1650℃ in the traditional process to 1500℃, reducing energy consumption by approximately 25%. The average particle size of the resulting powder is controlled within the range of 0.5-0.6μm, and the particle size distribution span [(D90-D10) / D50] < 1.0. More importantly, through a precise compensation mechanism of 20mol% excess B4C, the loss of boron source caused by the volatilization of the mesophase B2O3 is effectively avoided, reducing the oxygen content of the powder to below 0.8wt%, and eliminating the residue of impurity phases such as ZrO2 and B2O3. In terms of microstructure control, this patent achieves precise regulation of the two-phase interface and morphology. By optimizing the n(ZrO2):n(Si) ratio range of 2:1 to 4:1, the ZrB2:SiC molar ratio can be precisely controlled to be continuously adjustable between 2:1 and 4:1, with the deviation between the measured and theoretical values ​​controlled within ±2 mol%. HRTEM analysis shows that the ZrB2(101) crystal plane and the SiC(111) crystal plane form a semi-coherent interface with a lattice distortion rate ≤3%. This low-distortion interface lays the foundation for the high-temperature structural stability of the material. In addition, the "pinning points" formed by SiC particles at the ZrB2 grain boundaries effectively inhibit abnormal grain growth, making the powder exhibit a near-equiaxed morphology and avoiding the common problem of columnar and granular mixing in traditional processes. The ceramics prepared based on the self-made powder exhibit excellent comprehensive performance. The relative density of ceramic B reaches 99.24%, and the apparent porosity is only 0.12%, which is significantly improved compared with ceramic A (97.15% density) prepared from commercial powder. In terms of mechanical properties, the Vickers hardness reaches 17.93 GPa, the flexural strength is 470.00 MPa, and the fracture toughness is 4.87 MPa·m¹ / ², representing improvements of 15%, 45%, and 23% respectively compared to ceramic A. This performance optimization stems from the fine-grain strengthening effect and a unique toughening mechanism—uniformly distributed SiC particles induce crack deflection and branching, significantly extending the crack propagation path. Simultaneously, the higher sintering activity of the self-made powder transforms the densification mechanism from plastic deformation to more efficient grain boundary slip, providing a reliable guarantee for the application of ultra-high temperature ceramics in extreme environments.

[0025] Example 1: Implementation details of optimal process parameters Raw material pretreatment stage High-purity raw materials were used: ZrO2 powder (purity ≥99.99%, particle size ≤100nm, Shanghai Aladdin Biochemical Technology Co., Ltd.), B4C powder (purity ≥99.5%, particle size 500nm, Zhenhan New Materials Suzhou Co., Ltd.), Si powder (purity 99.9%, particle size 75μm, Beijing Puxitang Biotechnology Co., Ltd.), and activated carbon powder (purity ≥99%, particle size 48μm, Xi'an Carbon Plant). The ratio of n(ZrO2):n(B4C):n(Si):n(C) = 3:1.8:1:5.5 was accurately weighed. After pre-grinding in an agate mortar for 30 minutes, the mixture was transferred to a planetary ball mill and dry-milled at 200 rpm for 12 hours to ensure thorough and uniform mixing of the raw materials.

[0026] Segmented temperature control process The mixed powder was placed in a high-purity graphite crucible and then placed in a GSL-1700X tubular resistance furnace. High-purity argon gas (purity ≥99.999%) was introduced at a flow rate of 40 mL / min as a protective atmosphere. A precise temperature control program was used: first, the temperature was increased to 1200℃ at 5℃ / min and held for 30 min, during which Si and C reacted completely to form the β-SiC phase; then, the temperature was slowly increased to 1500℃ at 2℃ / min and held for 60 min, during which B4C and ZrO2 underwent a boron-carbothermic reduction reaction to form ZrB2; finally, the quenching device was activated, and the temperature was rapidly cooled to room temperature at 50℃ / min to suppress abnormal grain growth.

[0027] Product characterization results XRD analysis showed that the product contained only characteristic diffraction peaks of ZrB2 (PDF#34-0423) and β-SiC (PDF#29-1129), with no impurity phases present. SEM observation showed that the powder had a near-equiaxed morphology, an average particle size of 0.54 μm, and a uniform particle size distribution.

[0028] Raman spectroscopy revealed BB bond stretching vibration peaks at 285 cm⁻¹ and 368 cm⁻¹, and Si-C bond optical phonon vibration peaks at 600 cm⁻¹ and 800 cm⁻¹, with the absence of characteristic peaks of amorphous carbon such as D and G peaks, confirming the extremely high purity of the product. HRTEM analysis showed that the interplanar spacing of ZrB₂(101) was 0.26 nm, and that of SiC(111) was 0.25 nm, indicating a semi-coherent interface between the two phases.

[0029] Example 2: Implementation of Precise Phase Proportion Control Mix design principle Precise control of the ZrB2 to SiC phase ratio was achieved by adjusting the Si content. Three ratios were set: n(ZrO2):n(Si) = 2:1, 3:1, and 4:1, with corresponding theoretical ZrB2:SiC molar ratios of 2:1, 3:1, and 4:1. A comparative experiment was conducted by fixing n(ZrO2):n(B4C):n(C) = 3:1.8:5.5 and holding the mixture at 1500℃ for 1 hour.

[0030] Phase composition analysis results XRD patterns showed that all products contained only ZrB2 and β-SiC phases, with no raw material residue. Rietveld refined quantitative analysis showed that when n(ZrO2):n(Si)=2:1, the mass fractions of ZrB2 and SiC were 83.9wt% and 16.1wt%, respectively; when n(ZrO2):n(Si)=3:1, they were 88.2wt% and 11.8wt%, respectively; and when n(ZrO2):n(Si)=4:1, they were 90.4wt% and 9.6wt%, respectively. The deviations from the theoretical calculations were all <±2mol%, achieving precise control of the phase ratio.

[0031] Morphological Evolution Laws SEM analysis showed that as the Si content decreased, the density of SiC "pinning points" decreased, and the growth space of ZrB2 grains increased. When n(ZrO2):n(Si)=2:1, the average grain size was 0.32 μm, but agglomeration was obvious; when n(ZrO2):n(Si)=3:1, the grain size was 0.52 μm, showing a near-equiaxed morphology; when n(ZrO2):n(Si)=4:1, the grain size increased to 0.60 μm, and some grains formed agglomeration units through grain boundary migration.

[0032] Example 3: Ceramic Performance Verification Experiment Sintering process parameters The self-made ZrB2-25vol%SiC multiphase powder was wet-ball-milled in anhydrous ethanol for 6 hours, dried, and then placed into a graphite mold with an inner diameter of 30 mm for sintering in an SPS system. Process parameters: Under vacuum, the temperature was rapidly increased to 600℃ within 2 minutes, then increased to 1800℃ at a rate of 100℃ / min, held at 30 MPa for 5 minutes, and finally cooled to room temperature according to the heating rate program.

[0033] Densification Behavior Analysis Ceramic B has a relative density of 99.24% and an apparent porosity of only 0.12%, significantly better than ceramic A (97.15% density) prepared from commercial powder. According to the Bernard-Granger creep model, the self-made powder, due to its small particle size (0.5-0.54 μm) and narrow distribution, exhibits a densification mechanism primarily based on grain boundary slip during sintering; while the commercial powder, with its large particle size (1.48-1.56 μm) and wide distribution, relies mainly on plastic deformation for densification, resulting in lower efficiency.

[0034] Mechanical performance test results Three-point bending tests showed that ceramic B had a bending strength of 470.00 MPa, an improvement of 45.59% compared to ceramic A (322.83 MPa). Vickers hardness testing (load 19.6 N, held for 10 s) showed that ceramic B had a hardness of 17.93 GPa, an improvement of 14.86% compared to ceramic A (15.61 GPa). Fracture toughness testing using the single-sided notched beam method showed that ceramic B reached 4.87 MPa·m¹ / ², an improvement of 23.04% compared to ceramic A (3.96 MPa·m¹ / ²).

[0035] Toughening Mechanism Analysis Fracture surface SEM revealed that ceramic B has a uniform fine-grained structure, and the crack propagation exhibits obvious deflection and branching phenomena. This is because the difference in thermal expansion coefficients between ZrB2 and SiC leads to residual stress at the interface, causing the crack to propagate around the SiC particles (crack deflection). At the same time, under the action of stress, the main crack branches to generate secondary cracks (crack branching), which together consume fracture energy and achieve a toughening effect.

[0036] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method, characterized in that: Includes the following steps: The raw material ratio adopts a molar ratio of n(ZrO2):n(B4C):n(Si):n(C) = 3:(1.8-2.0):1:(5.5-6.0), in which B4C is in excess at 20-30 mol% to compensate for the volatilization loss of the mesophase B2O3 above 450℃. Segmented temperature control: First, the temperature is increased to 1200℃ at 5℃ / min and held for 30min to preferentially complete the Si+C→SiC reaction to generate β-SiC crystal nuclei; then, the temperature is slowly increased to 1500℃ at 2℃ / min and held for 60min to complete the main reaction via B4C+ZrO2+C→ZrB2+CO. Rapid cooling process: A quenching device is used to rapidly cool to room temperature at a rate of >50℃ / min to suppress abnormal grain growth and phase separation.

2. The nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method according to claim 1, characterized in that: The B4C powder meets the following technical specifications: Purity ≥ 99.5%, particle size distribution D50 ≤ 500 nm, specific surface area ≥ 3.5 m² / g Oxygen content ≤ 0.5 wt%, free carbon content ≤ 0.3 wt%. The crystal structure is rhombohedral, space group R3m, and there is no surface oxide layer.

3. The nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method according to claim 1, characterized in that: During the 1500℃ holding stage, an argon-containing atmosphere of 5-10 vol% CH4 is introduced, and an amorphous carbon film with a thickness of 2-5 nm is formed on the powder surface by chemical vapor deposition. This carbon film can: Inhibit surface oxidation of powders during storage and transportation It acts as an internal lubricant to promote densification during subsequent sintering. Adjusting the interfacial energy between ZrB2 and SiC promotes the formation of a semi-coherent interface.

4. The nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method according to claim 1, characterized in that: It possesses the following microstructural characteristics: Crystallographic characteristics: ZrB2 is hexagonal (space group P6 / mmm), and SiC is cubic β phase (space group F43m). Interface structure: The ZrB2(101) plane and the SiC(111) plane form a semi-coherent interface with a lattice mismatch of <5% and an interface distortion rate of ≤3%. Particle size distribution: Average particle size 0.5-0.6 μm, D100 < 0.71 μm, particle size distribution span [(D90-D10) / D50] < 1.0 Chemical purity: Oxygen content ≤0.8wt%, free of impurities such as ZrO2, B2O3, and free carbon.

5. The nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method according to claim 4, characterized in that: By adjusting the n(ZrO2):n(Si) ratio in the raw materials to within the range of 2:1 to 4:1, the ZrB2:SiC molar ratio can be precisely controlled. When n(ZrO2):n(Si) = 2:1, the ZrB2:SiC mass ratio is 83.9wt%:16.1wt%. When n(ZrO2):n(Si) = 3:1, the ZrB2:SiC mass ratio is 88.2wt%:11.8wt%. When n(ZrO2):n(Si) = 4:1, the ZrB2:SiC mass ratio is 90.4wt%:9.6wt%. The deviation between the measured value and the theoretical value is controlled within ±2 mol%.

6. The nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method according to claim 4, characterized in that: Sintering activity: Complete densification can be achieved at ≤1800℃, which is 100-150℃ lower than the traditional process; Densification effect: The resulting ceramic has a relative density of ≥99.2% and an apparent porosity of ≤0.15%; Mechanical properties: Vickers hardness ≥17.5GPa, flexural strength ≥450MPa, and fracture toughness ≥4.5MPa·m¹ / ².

7. The nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method according to claim 1, characterized in that: The impurity content is controlled through the following measures: High-purity graphite crucibles (purity ≥ 99.99%) are used to avoid the introduction of metal impurities. ZrO2 grinding balls are used during the ball milling process to prevent contamination by transition metals such as Fe and Cr. Maintaining a high vacuum of 10⁻²Pa before heating to 800℃ effectively removes adsorbed water and bound water.

8. The nano-ZrB2-SiC multiphase ceramic powder based on gradient ratio control and its low-temperature preparation method according to claim 1, characterized in that: The powder morphology can be controlled by the following combination of process parameters: Ball milling time of 10-12 hours and rotation speed of 180-220 rpm are used to obtain the best raw material mixing uniformity. During the heating phase of 1200-1500℃, the rate was controlled at 2℃ / min to promote diffusion-controlled solid-phase reactions. Quenching should be initiated within 30 seconds after the heat preservation period ends to avoid Ostwald curing.