A preparation method of high-temperature anti-ablation (Hf-Zr-Nb)C ternary carbide entropy ceramics

Abstract

The application relates to the technical field of ceramic materials, and discloses a preparation method of a high-temperature ablation-resistant (Hf-Zr-Nb)C ternary carbide entropy ceramic. First, HfO2, ZrO2, Nb2O5 and C powder are mixed and then heat-treated in a high-temperature heat treatment furnace to prepare (Hf-Zr-Nb)C entropy ceramic powder by using a carbothermic reduction reaction; then the powder is pressed to obtain a ceramic block; finally, the ceramic block is sintered by using a pressureless sintering device to obtain the (Hf-Zr-Nb)C ternary carbide entropy ceramic. Compared with the existing precursor impregnation and pyrolysis and discharge plasma sintering densification technology, the pressureless sintering technology is simple in process, can greatly reduce the production cost, and can improve the yield. The entropy carbide ceramic block has good ablation resistance. The application provides technical support for the application of the high-temperature ablation-resistant entropy carbide ceramic material to the hot end components of space-aircraft.

Description

Technical Field

[0001] This invention relates to the field of ceramic materials technology, specifically to a method for preparing high-temperature ablation-resistant (Hf-Zr-Nb)C ternary carbide entropy ceramics. Background Technology

[0002] Currently, the global demand for hypersonic vehicles with extended endurance is increasingly urgent, necessitating their operation in harsh environments. Certain critical structural components, such as the nose cone, leading edge, aerodynamic control surfaces, engine combustion chamber, and nozzle, will undergo prolonged ablation tests under extremely high temperatures, pressures, and high-enthalpy chemical non-equilibrium flow. To address these demanding operating environments, it is essential to develop new material systems and explore new thermal protection theories. The performance of thermal protection materials not only determines the speed limit of hypersonic vehicles but also directly affects their service life, serving as a fundamental guarantee for the iterative development of aerospace equipment.

[0003] Ultra-high temperature ceramics, due to their high melting point, high strength, and excellent thermal shock resistance, have become the most commonly used thermal protection materials for aerospace applications. However, single-component thermal protection ceramic materials (ZrB2, HfB2, ZrC, HfC, TaC, HfN, etc.) exhibit rapid oxidation / ablation rates in high-speed, high-temperature, and strong airflow erosion environments, failing to meet current performance requirements for hot-end components of hypersonic vehicles. Therefore, developing new ultra-high temperature materials with superior performance to address the issue of highly stable thermal protection has become paramount for hypersonic vehicle development. Multi-component ultra-high temperature carbide ceramics possess higher hardness and elastic modulus, lower thermal conductivity, and superior oxidation / ablation resistance, promising to solve the problems of insufficient stability and poor oxidation / ablation resistance of traditional ultra-high temperature carbide ceramics during extreme environmental operations, making them an important candidate for thermal protection materials for hot-end components of hypersonic vehicles.

[0004] Reference 1, "Huang B, Chen L, Bai S. Bulk ultrafine binderless WC prepared by spark plasma sintering[J].Scripta Materialia,2006,54(3):441-445," describes the preparation of ultrafine WC powder with a diameter of approximately 200 nm using spark plasma sintering without adding any binder phase. Under a binder-free sintering process at 1773 K for 240 s, the WC was fully densified, exhibiting excellent mechanical properties. However, pressure-assisted sintering equipment such as spark plasma sintering is very expensive and energy-intensive, making it unsuitable for mass production and only suitable for processing small-sized and simple-shaped components.

[0005] Reference 2, "Ren J, Zhang Y, Zhang J, et al. Effects of HfC nanowire amount on the microstructure and ablation resistance of CVD-HfC coating[J]. Ceramics International, 2018, 44(10): 11340-9," describes the preparation of an HfC ceramic coating on the surface of a C / C composite material using chemical vapor deposition (CVD). The coating was applied at an oxyacetylene heat flux density of 2.4 MW / m³. 2 Failure occurred after 120 seconds of continuous ablation. This is because the HfO2 formed by the oxidation of HfC becomes porous and loose after prolonged ablation. During the ablation process, oxygen diffuses through these porous structures into the internal SiC layer and even the C / C matrix, exacerbating the damage to the C / C composite material. Furthermore, the loose framework structure of HfO2 cannot withstand the mechanical erosion during the ablation process, leading to severe cracking and detachment of the oxide layer. Therefore, HfC ceramics exhibit poor ablation resistance.

[0006] Reference 3, "Li B, Li H, Yao X, et al. Preparation and ablation resistance of ZrC nanowires-reinforced CVD-ZrC coating on sharp leading edge C / C composites[J]. Applied Surface Science, 2022, 584," describes the preparation of a ZrC ceramic coating on the surface of C / C composites using chemical vapor deposition at an oxyacetylene heat flux density of 2.4 MW / m³. 2 It fails after continuous ablation for 60 seconds. ZrO2 formed by the oxidation and ablation of ZrC has similar properties to HfO2. After long-term ablation, the ZrO2 oxide layer remains loose and porous, which cannot effectively inhibit oxygen diffusion. Moreover, the loose skeleton structure of ZrO2 cannot resist the mechanical erosion during the ablation process, resulting in severe cracking and detachment of the ZrO2 oxide layer. Therefore, the ablation resistance of ZrC ceramics is also poor.

[0007] In summary, the pressure-assisted sintering method for preparing ceramic bulk materials is costly and energy-intensive, hindering large-scale production. Although HfC and ZrC ceramics possess numerous advantages, such as high melting points (3890℃ and 3540℃), high thermal stability, and low vapor pressure, the ablation resistance of single-component ceramics remains limited. In high-temperature aerobic environments, a single HfC ceramic will form an HfO2 oxide layer on its surface. Due to the phase transformation of HfO2 at high temperatures, the enormous phase transformation stress causes severe damage to the oxide layer. After ablation, single ZrC materials form a loose and porous ZrO2 layer, which is difficult to withstand the erosion of high-speed heat flow. Therefore, when facing more severe ablation environments, single HfC or ZrC ceramics cannot effectively protect the internal structure of the ceramic. In conclusion, it is crucial to develop a cost-effective and simple method for preparing a novel high-performance ultra-high-temperature ceramic. Summary of the Invention

[0008] To address the insufficient ablation resistance of single-component ultra-high temperature ceramics in atmospheres with extremely high speeds and ultra-high temperatures and oxygen-containing flow, this invention proposes a high-temperature ablation-resistant (Hf-Zr-Nb)C ternary carbide medium-entropy ceramic by simplifying the sintering process and reducing preparation costs. Using HfO2 powder, ZrO2 powder, Nb2O5 powder, and C powder as raw materials, (Hf-Zr-Nb)C powder is first prepared using a carbothermal reduction method. Then, this solid solution powder is pressed into sheets and placed in a pressureless sintering furnace to obtain a uniform and dense medium-entropy carbide ceramic block. The (Hf-Zr-Nb)C ternary carbide medium-entropy ceramic exhibits excellent high-temperature stability and ablation resistance, capable of withstanding ablation by a 2200℃ oxyacetylene flame for 60 seconds with intact structure. This invention provides technical support for the application of multi-component carbide ceramics in aerospace hot-end components.

[0009] A method for preparing high-temperature ablation-resistant (Hf-Zr-Nb)C ternary carbide entropy ceramics specifically includes the following steps:

[0010] 1) Preparation of (Hf-Zr-Nb)C solid solution powder: Weigh HfO2 powder, ZrO2 powder, Nb2O5 powder and C powder, ball mill and mix them, and put them into a high-temperature heat treatment furnace with an inert atmosphere for high-temperature heat treatment. The (Hf-Zr-Nb)C solid solution powder is obtained through carbothermic reduction reaction.

[0011] 2) Molding carbide ceramic blocks: The obtained (Hf-Zr-Nb)C solid solution powder is thoroughly mixed with polyvinyl alcohol solution and poured into a mold. It is then pressed into shape using a dry press to obtain carbide ceramic blocks.

[0012] 3) Sintering of carbide ceramic blocks: The obtained carbide ceramic blocks are placed in a high-temperature heat treatment furnace for sintering to obtain dense carbide ceramic blocks.

[0013] As a preferred embodiment, the purity of the HfO2 powder, ZrO2 powder, Nb2O5 powder, and C powder is all >99.9%, and the particle size is 1-3μm.

[0014] As a preferred embodiment, the molar ratio of HfO2 powder, ZrO2 powder, Nb2O5 powder and C powder in step 1) is 1-3:1-3:0.5-2:10-30.

[0015] As a preferred embodiment, the ball milling described in step 1) is carried out in a polytetrafluoroethylene ball milling jar, the grinding balls are made of ZrO2, the ball-to-material ratio is 3:1, and the mixture is ball-milled at a speed of 200-400 r / min for 6-12 hours.

[0016] As a preferred embodiment, the heating rate of the high-temperature heat treatment in step 1) is 3-7℃ / min to 1900-2200℃.

[0017] As a preferred embodiment, the holding time for the high-temperature heat treatment in step 1) is 1.5-2.5 hours.

[0018] As a preferred option, in step 1), the high-temperature heat treatment is followed by furnace cooling.

[0019] As a preferred embodiment, the concentration of the polyvinyl alcohol solution in step 2) is 0.008-0.028 g / L.

[0020] As a preferred option, in step 2), the dry press load pressure is 20-40 MPa, the loading rate is 20-35 MPa / min, and the pressure holding time is 1-5 min.

[0021] As a preferred embodiment, the sintering heating rate in step 3) is 3-7℃ / min to 1900-2200℃ and held for 1.5-2.5h, followed by furnace cooling after sintering.

[0022] The advantages of this invention compared to the prior art are:

[0023] 1. This invention patent combines carbothermal reduction and pressureless sintering to prepare (Hf-Zr-Nb)C ternary carbide medium-entropy ceramics. Oxyacetylene ablation test proves that it has superior ablation resistance, solving the problems of non-dense microstructure, cracking and spalling after ablation of binary carbide ceramics.

[0024] 2. The (Hf-Zr-Nb)C ternary carbide medium-entropy ceramic prepared by this invention exhibits excellent ablation resistance after oxyacetylene ablation, with a dense surface, low ablation temperature, and good synergistic effect among elements. This lays a theoretical foundation for subsequent research on the ablation resistance of medium / high-entropy carbide ceramics. Attached Figure Description

[0025] Figure 1 This is the XRD pattern of the (Hf-Zr-Nb)C ceramic block before ablation in Example 1.

[0026] Figure 2 This is the XRD pattern of the (Hf-Zr)C ceramic block before ablation in Comparative Example 1.

[0027] Figure 3 This is the XRD pattern of the (Hf-Zr-Nb)C ceramic block of Example 1 after ablation for 60 s.

[0028] Figure 4 This is the XRD pattern of the (Hf-Zr)C ceramic block of Comparative Example 1 after ablation for 60 s.

[0029] Figure 5 The image shows the microstructure and EDS analysis of the (Hf-Zr-Nb)C ceramic after ablation for 60 s in Example 1.

[0030] Figure 6 The image shows the microstructure and EDS analysis of the (Hf-Zr)C ceramic in Comparative Example 1 after ablation for 60 s.

[0031] Figure 7 Example 1 (Hf-Zr-Nb)C at 2.4MW / m 2 Morphological images before and after ablation under 30s ablation conditions.

[0032] Figure 8 Example 1 (Hf-Zr-Nb)C at 2.4MW / m 2 Morphological images before and after ablation under 60s ablation conditions.

[0033] Figure 9 The comparison ratio 1 (Hf-Zr)C at 2.4MW / m 2 Morphological images before and after ablation under 30s ablation conditions.

[0034] Figure 10 The comparison ratio 1 (Hf-Zr)C at 2.4MW / m 2 Morphological images before and after ablation under 60s ablation conditions. Detailed Implementation

[0035] The technical solution of the present invention is not limited to the specific embodiments listed below, but also includes any reasonable combination of the specific embodiments. Detailed Implementation

[0037] Example 1

[0038] Step 1: Weigh HfO2 powder, ZrO2 powder, Nb2O5 powder and C powder in a molar ratio of 2:2:1:19. Pour the weighed powder into a polytetrafluoroethylene ball mill jar with a ball-to-powder ratio of 3:1. Add industrial alcohol and wet mill for 8 hours. Then dry in a constant temperature drying oven at 70°C for 10 hours. This step will yield a uniform oxide mixed powder. The oxide mixture powder was poured into a graphite crucible with graphite paper lining the inner wall, and then placed in a high-temperature heat treatment furnace protected by Ar gas. The heating rate was 5℃ / min, and the temperature was raised to 2100℃ and held for 2 hours, followed by natural cooling with the furnace. The (Hf-Zr-Nb)C solid solution block was obtained by carbothermal reduction reaction, placed in a polytetrafluoroethylene ball mill jar with a ball-to-material ratio of 3:1, wet-milled with industrial alcohol for 8 hours, and then dried in a constant temperature drying oven at 70℃ for 10 hours. After this step, (Hf-Zr-Nb)C medium-entropy ceramic powder can be obtained.

[0039] Step 2: Take 5g of the (Hf-Zr-Nb)C medium-entropy ceramic powder obtained in Step 1 and place it in an agate mortar. Add 3 drops of PVA solution using a dropper, grind for 10 minutes, and then pour in a Cr-based mortar. 12 In the MoV mold, the mold is placed under the pressure head of a dry press, the load pressure is set to 30MPa, and the pressure is held for 1.5 minutes before unloading. After this step, a preliminary (Hf-Zr-Nb)C medium-entropy ceramic preform can be obtained.

[0040] Step 3: Wrap the (Hf-Zr-Nb)C medium-entropy ceramic blank obtained in Step 2 with graphite paper, place it in a graphite crucible with graphite paper lining the inner wall, and then place it in a high-temperature heat treatment furnace protected by Ar gas. The heating rate is 5℃ / min. After heating to 2100℃, hold for 2 hours, and then let it cool naturally in the furnace. This step yields a sintered and dense (Hf-Zr-Nb)C medium-entropy ceramic block.

[0041] Figure 1 This is the XRD pattern of the (Hf-Zr-Nb)C ceramic bulk before ablation, from... Figure 1 It can be seen that (Hf-Zr-Nb)C medium-entropy ceramics are prepared by carbothermic reduction reaction.

[0042] The prepared (Hf-Zr-Nb)C medium-entropy ceramic bulk was subjected to oxyacetylene ablation tests. The oxyacetylene flame heat flux density was 2.4 MW / m³. 2 The acetylene gas flow rate was 0.18 L / s, the oxygen gas flow rate was 0.24 L / s, the acetylene pressure was 0.095 MPa, and the oxygen pressure was 0.4 MPa. The ablation times were 30 s and 60 s, respectively. After 30 s of ablation, only a few small cracks appeared on the surface of the ceramic block. After 60 s of ablation, there was still no obvious peeling on the surface of the ceramic block. Figure 3This is the XRD pattern of a (Hf-Zr-Nb)C ceramic bulk after ablation for 60 s. The figure shows that the ablated oxide layer mainly consists of the high-melting-point oxide (Hf,Zr)O2 and the low-melting-point oxide Zr6Nb2O. 17 composition. Figure 5 These are the surface morphology and EDS analysis images of (Hf-Zr-Nb)C ceramic after ablation for 60 s. It can be seen that the low-melting-point oxide Zr6Nb2O... 17 It can effectively fill the voids and cracks around high-melting-point oxides, providing good bonding and inhibiting large-scale peeling of the oxide layer. Meanwhile, the low-melting-point oxide Zr6Nb2O... 17 During melting and volatilization, more heat is carried away, lowering the ablation temperature of the ceramic and thus reducing thermal stress concentration. In addition, the dense oxide layer can prevent oxygen-containing gases from further penetrating into the ceramic interior, thus resisting further erosion by oxidizing gases.

[0043] Comparative Example 1

[0044] Step 1: Weigh HfO2 powder, ZrO2 powder, and C powder in a molar ratio of 1:1:6. Pour the weighed powder into a polytetrafluoroethylene ball mill jar with a ball-to-powder ratio of 3:1. Add industrial alcohol and wet mill for 8 hours. Dry in a constant temperature drying oven at 70℃ for 10 hours. This step yields a uniform oxide mixture powder. Pour the oxide mixture powder into a graphite crucible with the inner wall lined with graphite paper. Then place it in a high-temperature heat treatment furnace under Ar gas protection. The heating rate is 5℃ / min. After heating to 2100℃, hold for 2 hours, and then allow it to cool naturally in the furnace. Prepare (Hf-Zr)C solid solution blocks through carbothermal reduction reaction. Place them in a polytetrafluoroethylene ball mill jar with a ball-to-powder ratio of 3:1. Add industrial alcohol and wet mill for 8 hours. Dry in a constant temperature drying oven at 70℃ for 10 hours. This step yields (Hf-Zr)C medium-entropy ceramic powder.

[0045] Step 2: Take 5g of the (Hf-Zr)C medium-entropy ceramic powder obtained in Step 1 and place it in an agate mortar. Add 3 drops of PVA solution using a dropper, grind for 10 minutes, and then pour in Cr... 12 In the MoV mold, the mold is placed under the pressure head of a dry press, the load pressure is set to 30MPa, and the pressure is held for 1.5 minutes before unloading. After this step, a preliminary (Hf-Zr)C medium-entropy ceramic preform can be obtained.

[0046] Step 3: Wrap the (Hf-Zr)C medium-entropy ceramic blank obtained in Step 2 with graphite paper, place it in a graphite crucible with graphite paper lining the inner wall, and then place it in a high-temperature heat treatment furnace protected by Ar gas. The heating rate is 5℃ / min. After heating to 2100℃, hold for 2 hours, and then let it cool naturally in the furnace. This step yields a sintered and dense (Hf-Zr)C medium-entropy ceramic block.

[0047] Figure 2 This is the XRD pattern of the (Hf-Zr)C ceramic bulk before ablation, from... Figure 2 It can be seen that (Hf-Zr-Nb)C medium-entropy ceramics are prepared by carbothermic reduction reaction.

[0048] Oxyacetylene ablation tests were performed on the prepared (Hf-Zr)C medium-entropy ceramic bulk. The oxyacetylene heat flux density was 2.4 MW / m³. 2 The acetylene gas flow rate was 0.18 L / s, the oxygen gas flow rate was 0.24 L / s, the acetylene pressure was 0.095 MPa, and the oxygen pressure was 0.4 MPa. The ablation times were 30 s and 60 s, respectively. (Hf-Zr)C ceramic blocks prepared by combining carbothermal reduction and pressureless sintering showed several penetrating cracks on the macroscopic surface of the ceramic block after 30 s of ablation. These cracks interconnected, forming larger cracks, and the oxide layer partially peeled off. After 60 s of ablation, the oxide layer on the upper surface of the ceramic block had completely peeled off, leaving only a small amount of ceramic oxide residue on the surface. Figure 4 The image shows the XRD pattern of (Hf-Zr)C ceramic bulk after ablation for 60 s. As can be seen from the image, the oxide layer after ablation is mainly a high-melting-point (Hf,Zr)O2 solid solution. Figure 6 The images show the microstructure and EDS analysis of (Hf-Zr)C ceramics after ablation for 60 s. It can be seen that the oxides of (Hf-Zr)C ceramics after ablation are rich in Hf and Zr elements, have high melting points, and are loose and porous. During the ablation process, the oxide layer cracks and peels off due to mechanical erosion.

[0049] Table 1

[0050]

[0051] Comparison of ablation resistance performance between Example 1 and Comparative Example 1

[0052] Existing sintering processes commonly use spark plasma sintering or hot pressing equipment, which are very expensive and energy-intensive, making them unsuitable for mass production and only suitable for processing small-sized and simple-shaped components. This solution uses pressureless sintering, which allows ceramic blanks of different shapes to be placed in a heat treatment furnace for batch sintering, resulting in high yield, simple operation, and low cost.

[0053] Traditional HfC and ZrC ceramics have high melting points (3890℃ and 3890℃), and their oxides also have high melting points (2810℃ and 2677℃), meaning they can act as a good framework when facing high-temperature flame streams. However, conversely, under high thermal stress, once cracks occur, oxygen rapidly diffuses inward. If the molten phase is not used to fill the cracks and pores, the oxygen erosion on the ceramic surface will be further intensified. The resulting ceramic oxides cannot withstand the erosive effect of high-speed oxyacetylene flame streams, leading to spalling and triggering a chain reaction that further promotes the diffusion of oxygen-containing streams, thus creating a vicious cycle. Compared to HfC and ZrC ceramics, NbC ceramics have a melting point of 3000℃, while its oxides have a melting point of only 1520℃, lower than the oxide melting points of high-melting-point ceramics such as HfC, ZrC, TaC, and TiC, and also lower than the actual test temperature for oxyacetylene. Therefore, this scheme employs a carbothermal reduction method to prepare a high-temperature ablation-resistant (Hf-Zr-Nb)C ternary carbide medium-entropy ceramic. Ablation tests were conducted on the ceramic using an oxyacetylene ablation apparatus for 30 s and 60 s, respectively. Phase analysis of the oxide layer after ablation was performed using XRD data. The results show that a Nb-rich, low-melting-point oxide, Zr6Nb2O, was generated during the ablation process. 17 (Melting point is 2040℃), and high-melting-point oxides (Hf,Zr)O2 (melting point is 2715℃). During the ablation process, the high-melting-point oxides act as the framework phase, while the low-melting-point oxides fill the pores and cracks. The above components work synergistically to make the oxide layer dense and stable during the ablation process, preventing further oxygen penetration and significantly improving the ablation resistance of the ceramic.

[0054] The present invention and its embodiments have been described above. This description is not restrictive, and the accompanying drawings are only one embodiment of the present invention; the actual structure is not limited thereto. In conclusion, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for preparing a high-temperature ablation-resistant (Hf-Zr-Nb)C ternary carbide entropy ceramic, characterized in that, Specifically, the following steps are included: 1) Preparation of (Hf-Zr-Nb)C solid solution powder: Weigh HfO2 powder, ZrO2 powder, Nb2O5 powder, and C powder in a molar ratio of 2:2:1:

19. Pour the weighed powder into a polytetrafluoroethylene ball mill jar with a ball-to-powder ratio of 3:

1. Add industrial alcohol and wet mill for 8 hours. Dry in a constant temperature drying oven at 70℃ for 10 hours. Pour the oxide mixture into a graphite crucible with graphite paper covering the inner wall, and then place it in a circulating water system. In a high-temperature heat treatment furnace protected by Ar gas, the heating rate was 5℃ / min, and the temperature was raised to 2100℃ and held for 2 hours, followed by natural cooling with the furnace. The (Hf-Zr-Nb)C solid solution block was prepared by carbothermal reduction reaction, placed in a polytetrafluoroethylene ball mill jar with a ball-to-material ratio of 3:1, wet-milled with industrial alcohol for 8 hours, and then dried in a constant temperature drying oven at 70℃ for 10 hours to obtain (Hf-Zr-Nb)C medium-entropy ceramic powder. 2) Molding carbide ceramic blocks: (Hf-Zr-Nb)C medium-entropy ceramic powder is placed in an agate mortar, PVA solution is added, and it is ground for 10 minutes. It is then poured into a mold and pressed into shape using a dry press. The load pressure is set to 30 MPa, and the pressure is held for 1.5 minutes before unloading to obtain a preliminary (Hf-Zr-Nb)C medium-entropy ceramic blank. 3) Sintered carbide ceramic bulk: The (Hf-Zr-Nb)C medium-entropy ceramic blank is wrapped with graphite paper, placed in a graphite crucible with graphite paper on the inner wall, and then placed in a high-temperature heat treatment furnace with Ar gas protection. The heating rate is 5℃ / min. After heating to 2100℃, it is held for 2h and then cooled naturally with the furnace to obtain the (Hf-Zr-Nb)C medium-entropy ceramic bulk.

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