A boron-doped vanadium diboride-based composite ceramic and a high-pressure high-temperature preparation method thereof

Abstract

This invention discloses a boron-doped vanadium diboride-based multiphase ceramic and its high-pressure, high-temperature preparation method. The ceramic consists of vanadium diboride and a boron-doped phase, with a boron doping amount of 15–50 vol%, preferably 50 vol%. The preparation method involves weighing VB2 powder and boron powder according to a specified ratio, ball-milling them together, pressing them into a blank, and then sintering under high pressure and high temperature (1000–2000℃) for 60–180 minutes. This invention, through the synergistic effect of controllable excess boron doping and high-pressure, high-temperature sintering, allows excess boron to form a nanoscale second phase in situ at the VB2 grain boundaries, inducing high-angle, multi-level crack deflection and promoting grain pull-out, thus significantly improving fracture toughness while maintaining high hardness. The obtained 50 vol% boron-doped multiphase ceramic exhibits a Vickers hardness of 21.27 ± 1.11 GPa and a fracture toughness of 9.41 ± 0.58 MPa·m. 1 / 2 This method achieves approximately 135% improvement in hardness and toughness compared to pure VB2 ceramics, realizing a synergistic enhancement of both. The process is simple, requires no additional sintering aids, and is suitable for preparing high-strength, high-toughness ultra-high temperature ceramic components.

Description

Technical Field

[0001] This invention relates to the field of ultra-high temperature ceramic materials technology, and in particular to a boron-doped vanadium diboride-based multiphase ceramic and its high-pressure, high-temperature preparation method. Background Technology

[0002] Transition metal diborides (MB2), such as vanadium diboride (VB2), possess high melting points, high hardness, and good thermal and electrical conductivity, making them candidate ultra-high temperature ceramic materials for applications in extreme high-temperature environments such as the nose cone of hypersonic vehicles, the leading edge of wings, and the thermal protection systems of atmospheric reentry spacecraft. However, VB2 ceramics exhibit low intrinsic fracture toughness, typically only about 3–5 MPa·m. 1 / 2 It exhibits typical brittle fracture characteristics and is prone to catastrophic fragmentation under thermal shock and mechanical loads, which severely restricts its engineering application.

[0003] Currently, the main methods to improve the toughness of MB2 ceramics include: toughening by adding second-phase particles such as SiC and ZrC, toughening by SiC whiskers or carbon fibers, constructing layered biomimetic structures, and optimizing sintering processes such as hot pressing and spark plasma sintering. However, these methods have the following limitations: (1) The improvement of a single toughening method is limited, and the fracture toughness is difficult to exceed 8 MPa·m. 1 / 2 (2) The reinforcing phase has poor compatibility with the matrix and weak interfacial bonding, which easily introduces defects and degrades hardness and high-temperature strength. (3) Carbon-based and metal-based reinforcing phases are easily oxidized or softened at high temperatures, and cannot take into account both toughness and ultra-high temperature service performance. (4) Whisker and layered structures have complex processes and high costs, making them difficult to apply in engineering. (5) Most schemes only achieve room temperature toughening, and the improvement of high-temperature toughness and thermal shock stability is insufficient.

[0004] Therefore, there is an urgent need to develop a new type of VB2-based ultra-high temperature ceramic material and its preparation method that can balance high hardness and high fracture toughness, and is relatively simple to process and suitable for engineering. Summary of the Invention

[0005] The purpose of this invention is to provide a boron-doped vanadium diboride-based multiphase ceramic and its high-pressure, high-temperature preparation method, so as to solve the problem that it is difficult to simultaneously improve the hardness and fracture toughness of existing VB2 ceramic materials.

[0006] The above-mentioned technical objective of the present invention is achieved through the following technical solution: A boron-doped vanadium diboride-based multiphase ceramic is composed of vanadium diboride and a boron-doped phase, wherein the boron doping amount is 15–50 vol.

[0007] More preferably, the boron doping amount is 50 vol%, at which point the mass percentages of each component are: vanadium diboride powder 68.6 wt%, boron powder 31.4 wt%.

[0008] Further preferably, its Vickers hardness is not less than 21.27 GPa, and its fracture toughness is not less than 9.41 MPa·m. 1 / 2 .

[0009] This invention also provides a high-pressure, high-temperature preparation method for boron-doped vanadium diboride-based multiphase ceramics, comprising the following steps: S1. Weigh vanadium diboride powder and boron powder according to the ratio, and ball mill them together evenly to obtain composite powder; S2. Press the composite powder under pressure to obtain a pressed blank; S3. The pressed blank is subjected to high-pressure and high-temperature sintering at a pressure of 5 GPa and a temperature of 1000-2000℃, and the temperature and pressure are maintained for 60-180 minutes. After cooling and depressurization, the boron-doped vanadium diboride-based multiphase ceramic is obtained.

[0010] More preferably, the sintering temperature in step S3 is 1900℃, and the holding and pressure holding time is 120 minutes.

[0011] More preferably, the ball-to-material ratio in the ball milling process in step S1 is 5:1, the rotation speed is 250-350 rpm, and the mixing time is 20-40 minutes.

[0012] More preferably, the pressing pressure in step S2 is 10-20 MPa.

[0013] In summary, the present invention has the following beneficial effects: Firstly, this invention creatively utilizes boron as a single dopant element, without introducing other heterogeneous phases. Through the synergistic design of controllable excess boron doping and high-pressure, high-temperature sintering, excess boron forms an in-situ nanoscale second phase at the grain boundaries of the VB2 matrix. This nanoscale second phase exhibits good compatibility with the matrix and can effectively induce high-angle (>45°) multi-level deflection and grain pull-out of indentation cracks, significantly extending the crack propagation path and dissipating fracture energy. Thus, while maintaining the material's high hardness (approximately 21.27 GPa), the fracture toughness is significantly improved to 9.41 MPa·m. 1 / 2 The above achieves a synergistic enhancement of hardness and toughness.

[0014] Secondly, the method of this invention employs a high-pressure condition of 5 GPa, which effectively suppresses grain coarsening during the high-temperature sintering process, resulting in fine grains and a uniform microstructure, further ensuring mechanical properties. The entire preparation process requires no additional sintering aids, is simple and controllable, and is expected to provide a new approach for the preparation of highly reliable ultra-high temperature ceramic components. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the high-pressure high-temperature sintering experimental component and a schematic diagram of the experimental temperature and pressure loading procedure in an embodiment of the present invention, wherein a is a schematic diagram of the experimental component assembly and b is a schematic diagram of the experimental temperature and pressure loading procedure. Figure 2 This is a SEM image of the fracture morphology of a 50 vol% boron-doped vanadium diboride-based multiphase ceramic prepared according to an embodiment of the present invention. Figure 3 This is a SEM image of the indentation crack propagation path of a 50 vol% boron-doped vanadium diboride-based multiphase ceramic prepared according to an embodiment of the present invention. Figure 4 This is a comparison chart of the hardness-fracture toughness properties of the multiphase ceramic prepared in the embodiments of the present invention and that of typical existing ultra-high temperature ceramics. Detailed Implementation

[0016] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0017] Example: A boron-doped vanadium diboride-based multiphase ceramic and its high-pressure, high-temperature preparation method.

[0018] (1) Raw materials and proportions: Main ingredient: Vanadium diboride (VB2) powder, purity ≥99.99%; Dopant: Boron (B) powder, purity ≥99.99%.

[0019] Based on a boron doping content of 50 vol%, 68.6 wt% of VB2 powder and 31.4 wt% of boron powder were weighed.

[0020] (2) Powder mixing: The weighed powders were placed together in a ball mill jar, and anhydrous ethanol was used as the dispersion medium. Using cemented carbide balls, the mixture was ball-milled for 30 minutes at a ball-to-powder ratio of 5:1 and a rotation speed of 300 rpm. After mixing, the slurry was removed, dried, ground, and sieved to obtain a uniform composite powder.

[0021] (3) Blank pressing: The composite powder is poured into a mold and pressed into a cylindrical blank with a diameter of 4 mm on a uniaxial press at a pressure of 10 MPa.

[0022] (4) High-pressure, high-temperature sintering: The pressed blank is loaded into a BN ceramic tube, and then the graphite heating tube, pyrophyllite pressure transmission medium, and other components are assembled externally in sequence, such as... Figure 1 As shown in Figure a. All components were baked in a 100℃ oven for 12 hours before use. The assembled sample was placed in a domestic GY560 large-cavity cubic press, and the pressure was increased to 5 GPa within 10 minutes, followed by a temperature increase to 1900℃ within 10 minutes, and held at that temperature and pressure for 120 minutes. After sintering, the heating power was turned off, and the sample was allowed to cool to room temperature with the furnace before being depressurized and removed. The sintering temperature and pressure program is as follows: Figure 1 As shown in b.

[0023] Performance Characterization The hardness of the material was tested using a Vickers hardness tester under a load of 4.9 N, and the fracture toughness was calculated using the indentation method. Performance data show that the Vickers hardness of the 50 vol% boron-doped VB2 multiphase ceramic prepared in this embodiment is 21.27 ± 1.11 GPa, and the fracture toughness is 9.41 ± 0.58 MPa·m. 1 / 2 Compared to pure VB2 ceramics (hardness approximately 22 GPa, toughness approximately 4 MPa·m) 1 / 2 Compared to the previous method, under conditions where the hardness is basically the same, the fracture toughness is significantly improved by about 135%.

[0024] Microstructure analysis like Figure 2 As shown, the sample fracture surface is rough, with numerous pits and protrusions formed by grain pull-out, exhibiting fracture characteristics dominated by intergranular fracture. Grain pull-out is an effective toughening mechanism. Figure 3 The results show that the indentation crack encountered the grain boundary nanoscale second phase during propagation, undergoing multiple high-angle deflections (>45°), making the crack propagation path extremely tortuous and significantly consuming fracture energy. This is direct evidence of a substantial improvement in toughness. Grain size statistics show that the average grain size after sintering is only 1.05–1.42 μm, confirming the effective suppression of grain growth by high pressure.

[0025] Comparative analysis Appendix Figure 4 This figure compares the hardness-fracture toughness properties of the material prepared in this embodiment with those of typical reported binary transition metal borides and multiphase ceramics. As shown in the figure, the material of this invention falls within the upper right region of "high hardness-high toughness," significantly breaking through the traditional trade-off between hardness and toughness, and achieving synergistic strengthening.

[0026] Finally, it should be noted that the above description is merely a preferred embodiment of the present invention and does not limit the scope of the patent. Any equivalent structural or procedural modifications made based on the description and drawings of this invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of this invention.

Claims

1. A boron-doped vanadium diboride-based multiphase ceramic, characterized in that: It consists of vanadium diboride and a boron-doped phase, wherein the boron doping amount is 15–50 vol.

2. The boron-doped vanadium diboride-based multiphase ceramic according to claim 1, characterized in that: The boron doping amount is 50 vol%, at which point the mass percentages of each component are: vanadium diboride powder 68.6 wt%, boron powder 31.4 wt%.

3. The boron-doped vanadium diboride-based multiphase ceramic according to claim 2, characterized in that: Its Vickers hardness is not less than 21.27 GPa, and its fracture toughness is not less than 9.41 MPa·m. 1 / 2 .

4. A high-pressure, high-temperature preparation method for boron-doped vanadium diboride-based multiphase ceramics according to any one of claims 1 or 2, characterized in that, Includes the following steps: S1. Weigh vanadium diboride powder and boron powder according to the ratio, and ball mill them together evenly to obtain composite powder; S2. Press the composite powder under pressure to obtain a pressed blank; S3. The pressed blank is subjected to high-pressure and high-temperature sintering at a pressure of 5 GPa and a temperature of 1000-2000℃, and the temperature and pressure are maintained for 60-180 minutes. After cooling and depressurization, the boron-doped vanadium diboride-based multiphase ceramic is obtained.

5. The high-pressure, high-temperature preparation method of boron-doped vanadium diboride-based multiphase ceramics according to claim 4, characterized in that: The sintering temperature in step S3 is 1900℃, and the holding time is 120 minutes.

6. The high-pressure, high-temperature preparation method for boron-doped vanadium diboride-based multiphase ceramics according to claim 4, characterized in that: In step S1, the ball-to-material ratio for ball milling is 5:1, the rotation speed is 250-350 rpm, and the mixing time is 20-40 minutes.

7. The high-pressure, high-temperature preparation method of boron-doped vanadium diboride-based multiphase ceramics according to claim 4, characterized in that: The pressing pressure in step S2 is 10-20 MPa.

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