A low-hydrogen embrittlement and high-toughness sponge zirconium-based composite material and its preparation method

Abstract

The present invention relates to the field of zirconium-based composite materials, and provides a low hydrogen embrittlement and high toughness sponge zirconium-based composite material and a preparation method thereof. The low hydrogen embrittlement and high toughness sponge zirconium-based composite material is composed of nano-ZrC and a Zr matrix. The volume fraction of nano-ZrC is 4.5-8.0%, and the average particle size is 10-60 nm, which is in-situ generated from sponge zircon powder and nano carbon black at high temperature. The material has a gradient microstructure, including a surface layer (35-70 μm), a transition zone (50-150 μm) and a core. The grain boundary ratios of each region are optimized to improve toughness and hydrogen embrittlement resistance. The preparation method includes: (1) mechanically alloying sponge zircon powder and carbon black to prepare Zr-C composite powder; (2) hot isostatic pressing densification and in-situ synthesis of nano-ZrC reinforcement phase; (3) ultrasonic impact surface grinding to form a nanocrystalline layer; (4) multi-stage warm rolling to regulate gradient grain boundaries; (5) zone annealing to stabilize the microstructure. This material has excellent toughness and hydrogen embrittlement resistance, and is suitable for the nuclear industry and high corrosion-resistant environments.

Description

Technical Field

[0001] The present invention relates to the field of zirconium-based composite materials, and particularly to a low hydrogen embrittlement and high toughness sponge zirconium-based composite material and a preparation method thereof. Background Art

[0002] Sponge zirconium-based composite materials have extensive applications in the nuclear industry, high-end aerospace, and corrosion-resistant fields. Especially in nuclear fuel cladding, nuclear reactor structural components, and high-temperature corrosion-resistant alloys, sponge zirconium has become a key material due to its low thermal neutron absorption cross-section, excellent corrosion resistance, and high-temperature stability. However, with the rapid development of the nuclear industry and aerospace technology, the service environment of materials has become increasingly harsh, such as long-term exposure to high temperature, high pressure, strong irradiation, and hydrogenation environments, resulting in a significant increase in the risk of hydrogen embrittlement of materials. At the same time, higher requirements are put forward for the mechanical properties, toughness, and microstructural stability of materials. In the nuclear reactor environment, hydrogen atoms are prone to diffuse and accumulate inside zirconium-based materials, leading to interphase debonding, embrittlement, and a decrease in strength, seriously affecting the reliability and service life of materials. Therefore, while ensuring the excellent corrosion resistance of materials, improving their hydrogen embrittlement resistance and optimizing the microstructural organization to enhance toughness have become important research directions in the current field of materials science and engineering. To meet this demand, strategies such as nano-reinforcement mechanisms, grain boundary structure optimization, and gradient microstructure regulation have become key means to improve the comprehensive properties of zirconium-based composite materials, which can effectively alleviate hydrogen-induced cracking, improve the toughness and service stability of materials, thereby promoting the application expansion of such materials in complex environments and enhancing the safety and sustainability of nuclear energy and aerospace technologies.

[0003] Although a large number of studies have been devoted to improving the hydrogen embrittlement problem of zirconium-based materials, there are still significant technical bottlenecks. For example, Chinese Patent No. CN113201666A discloses a zirconium alloy for fuel assemblies, its manufacturing method, and the cladding tube of the fuel assembly, which improves the hydrogen resistance performance through microalloying means, but still faces the problem of high hydrogen embrittlement sensitivity and is difficult to serve in extreme environments for a long time. In addition, some researchers have introduced nano-particles to improve strength and corrosion resistance, but due to the limited interfacial bonding force between the ceramic phase and the metal matrix, the toughness of the material is reduced, and it is difficult to balance high strength and high toughness. Existing technologies often have the side effect of a decrease in toughness while improving the hydrogen embrittlement resistance performance. The main reason is that traditional methods mostly rely on solid solution strengthening, precipitation strengthening, or surface coating methods, and fail to achieve grain boundary optimization and gradient regulation at the microstructural level, thus unable to effectively inhibit the propagation of hydrogen-induced cracks. In addition, the distribution uniformity of nano-reinforcing phases, the interfacial bonding force between phases, and the processing adaptability of materials are also key problems restricting their practical applications at present. Therefore, there is an urgent need to develop a sponge zirconium-based composite material with both low hydrogen embrittlement and high toughness, and through nano-structure design, gradient grain boundary regulation, and optimized preparation processes, to achieve the stable service of materials in extreme environments. Summary of the Invention

[0004] (1) Technical problems to be solved

[0005] The object of the present invention is to provide a low hydrogen embrittlement and high toughness sponge zirconium-based composite material and a preparation method thereof, so as to solve the problems of insufficient low hydrogen embrittlement and high toughness performance of the current sponge zirconium-based composite material.

[0006] (2) Technical solutions

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] A preparation method of a low hydrogen embrittlement and high toughness sponge zirconium-based composite material, comprising the following steps:

[0009] S1. Pretreatment of raw materials and mechanical alloying: Using sponge zirconium powder and nano carbon black as raw materials, mixing them and then performing mechanical alloying to obtain Zr-C composite powder;

[0010] S2. Hot isostatic pressing densification and in-situ synthesis: Subjecting the Zr-C composite powder obtained in step S1 to hot isostatic pressing densification to in-situ synthesize a nano ZrC dispersion-strengthened zirconium-based composite material blank;

[0011] S3. Surface mechanical grinding treatment: Subjecting the blank obtained in step S2 to surface mechanical grinding treatment to form a surface nano-crystalline structure;

[0012] S4. Multi-stage warm rolling and grain boundary gradient regulation, subjecting the blank treated in step S3 to primary rolling and core rolling in sequence to obtain a gradient structure blank;

[0013] S5. Partition annealing to stabilize the gradient grain boundary: Subjecting the blank treated in step S4 to surface annealing and core annealing in sequence to finally obtain a low hydrogen embrittlement and high toughness sponge zirconium-based composite material.

[0014] Furthermore, the detailed process of step S1 is as follows: Mixing sponge zirconium powder and carbon black according to a mass ratio of (97.0~98.0):(2.0~3.0), placing the mixed powder in a high-energy planetary ball mill, and performing mechanical alloying under argon protection. The ball-to-powder ratio is set as (10.0~12.0):1, the rotation speed is 300~350 rpm, and the ball milling time is 25~30 h to obtain Zr-C composite powder.

[0015] The purpose of adopting S1 in the present invention is to achieve sufficient interfacial interaction between zirconium sponge powder and nano carbon black on the basis of uniform mixing through raw material pretreatment and mechanical alloying process, so as to obtain Zr-C composite powder with uniform distribution, providing an excellent precursor for subsequent densification and in-situ synthesis. Mechanical alloying can not only promote the diffusion and reaction between zirconium sponge powder and nano carbon black, but also introduce a high density of lattice defects through the high-energy ball milling process, improving the solid solubility of carbon atoms and providing sufficient reaction activity for the in-situ generation of nano-ZrC under subsequent hot isostatic pressing conditions. By using a high-energy planetary ball mill to carry out mechanical alloying on zirconium sponge powder and carbon black under argon protection, it can not only effectively prevent powder oxidation and maintain the chemical purity of the material, but also control the microstructure of the powder through appropriate ball-to-powder ratio, rotation speed and ball milling time, ensuring the acquisition of Zr-C composite powder with uniform particle size and good dispersibility.

[0016] Furthermore, the detailed process of step S2 is as follows: The Zr-C composite powder obtained in step S1 is filled into a soft steel jacket, evacuated to ≤5×10⁻³ Pa, and then sealed by electron beam welding. The sealed powder jacket is placed in a hot isostatic pressing furnace, heated to 1200~1250 °C at a heating rate of 10~15 °C / min, a pressure of 120~150 MPa is applied, and heat preservation and pressure holding are carried out for 180~240 min. After the reaction is completed, it is cooled to room temperature at a cooling rate of 6.0~12.0 °C / min.

[0017] The hot isostatic pressing densification and in-situ synthesis process of S2 in the present invention depends on the uniformity and activity of the composite powder obtained in S1, promoting the dispersed distribution of nano-ZrC inside the zirconium matrix under high temperature and high pressure conditions, thereby effectively enhancing the strengthening effect of the material and enabling it to have good plasticity and toughness while maintaining high strength.

[0018] Furthermore, the detailed process of step S3 is as follows: The green body obtained in step S2 is placed in an ultrasonic surface mechanical grinding device, WC-Co grinding balls are used, the vibration frequency is set to 20~25 kHz, the amplitude is 50~60 μm, the treatment time is 50~60 min, argon jet cooling is adopted during the treatment process, and after the treatment is completed, argon jet cooling is used, and the cooling rate is 40~50 °C / s.

[0019] The purpose of adopting S3 in the present invention is to introduce a high density of grain boundaries and nanoscale grains into the material surface layer through surface mechanical grinding treatment to form a nanocrystalline structure, thereby optimizing the microstructure of the material and improving its hydrogen embrittlement resistance and mechanical properties. Although the nanocrystalline ZrC dispersion-strengthened zirconium-based composite billet obtained in S2 already has relatively high strength, plasticity and toughness, there may still be relatively large grain sizes on its surface layer, which is not conducive to the hydrogen resistance and crack propagation resistance of the material in complex service environments. Therefore, in S3, through ultrasonic surface mechanical grinding means, the surface layer material undergoes severe plastic deformation. Under the action of high-frequency impact and shear, the grains are refined, and a nanocrystalline structure is formed on the surface layer. Using WC-Co grinding balls and treating under appropriate vibration frequencies and amplitudes helps to increase the deformation energy storage per unit volume, enabling dynamic recrystallization to occur on the material surface layer, while introducing a high density of low-angle grain boundaries and dislocation twin structures, thereby effectively improving the toughness of the material. In addition, the formation of the nanocrystalline structure can also enhance the surface hardness of the material, improve its wear resistance and crack initiation resistance, and lay a foundation for subsequent grain boundary gradient regulation. During the whole process, adopting argon jet cooling not only helps to suppress surface overheating and maintain a uniform tissue state, but also avoids the adverse effects of high-temperature oxidation on the material properties. The mechanical grinding treatment in S3 provides an optimized initial structure for the subsequent multi-stage warm rolling in S4, making the construction of the gradient structure more precise, and finally realizing the stabilization of grain boundaries during the partition annealing process in S5, ensuring the service stability of the material in complex environments. Through the synergistic effect of S3 and the front and back processes in the present invention, while ensuring the overall strength of the material, the surface layer structure is highly optimized, thereby endowing the material with excellent comprehensive properties and meeting the application requirements of low hydrogen embrittlement and high toughness.

[0020] Further, the detailed process of the primary rolling in the step S4 is as follows: The surface of the billet after being treated in S3 is induction heated to 650 - 700 °C, rolled with a rolling force of 780 - 800 kN, the reduction per pass is 15 - 20%, and it is rolled in 4 - 6 passes.

[0021] Further, the detailed process of the core rolling in the step S4 is as follows: The billet after the primary rolling is heated as a whole to 600 - 650 °C, rolled with a rolling force of 250 - 300 kN, the reduction per pass is 5.0 - 8.0%, and it is rolled in 4 - 6 passes.

[0022] The purpose of S4 of the present invention is to introduce a gradient grain structure into the material through a multi-stage warm rolling process, gradually optimize the microstructure of the surface layer, transition zone, and core, so as to improve the mechanical properties and hydrogen embrittlement resistance of the material. The surface mechanical grinding in S3 has formed a nanocrystalline structure on the material surface layer, but the overall structure still needs further regulation to ensure a reasonable grain distribution in different regions, so as to balance high strength, high toughness, and excellent hydrogen resistance. Therefore, in S4, first through primary rolling, the surface of the billet is deformed and strengthened at a temperature of 650-700°C, so that the surface layer structure is further refined. At the same time, the grain boundary evolution in the transition zone is promoted, the dislocation density is increased, and the overall uniformity of the material is enhanced. By using an appropriate rolling force and multi-pass rolling method, the degree of deformation can be effectively controlled to ensure a reasonable grain boundary structure in the surface layer and transition zone. Subsequently, the core rolling is carried out under relatively low temperature conditions, so that the overall structure remains uniform under a small amount of deformation, while reducing the internal residual stress and preventing the material from cracking or excessive tissue distortion. Through this gradient deformation mechanism, the surface layer of the material obtains an ultrafine grain structure, the transition zone forms a fine grain structure, and the core maintains a moderate equiaxed grain distribution, thus optimizing the mechanical properties as a whole. The multi-stage warm rolling in S4 not only lays an organizational foundation for the zoning annealing in S5, but also ensures the comprehensive performance of the final composite material, enabling it to have excellent service stability and hydrogen damage resistance in complex environments.

[0023] Further, the detailed process of the surface annealing in step S5 is as follows: Selective laser heating is used, the heating power density is 4.0-5.0 W / mm², the spot diameter is 2.0-4.0 mm, the surface area is heated to 650-660°C, after holding for 30-45 min, argon gas jet cooling is used, and the cooling rate is 40-50°C / s.

[0024] Further, the detailed process of the core annealing in step S5 is as follows: The billet is placed in an electric resistance furnace and heated to 480-490°C at a heating rate of 5.0-8.0°C / min, after holding for 90-120 min, it is cooled to room temperature at a cooling rate of 2.0-5.0°C / min.

[0025] The purpose of step S5 of the present invention is to further stabilize the gradient microstructure of the material, optimize the grain boundary distribution, reduce the residual stress, and improve the comprehensive mechanical properties and hydrogen embrittlement resistance of the material. During the multi-stage warm rolling process in S4, a gradient grain structure has been formed in the surface layer, transition zone, and core of the material. However, due to the introduction of a high dislocation density and residual stress during the rolling process, it is necessary to regulate through a reasonable heat treatment process to ensure the microstructure stability and service performance of the material. Therefore, the present invention adopts a combination of surface annealing and core annealing to achieve precise heat treatment of different regions. The surface annealing adopts a selective laser heating method, performs short-time heat preservation in the temperature range of 650-660 °C, and uses argon gas jet cooling to ensure the stabilization of the surface structure, while avoiding abnormal grain growth, so that the surface layer still maintains a fine grain structure and improves its hydrogen embrittlement resistance. At the same time, the core annealing adopts an overall heating method at a lower temperature, performs long-time heat preservation at 480-490 °C, effectively releases the residual stress in the core, and promotes dislocation rearrangement and grain boundary migration, thereby optimizing the internal structure and improving the toughness and plasticity of the material. By precisely controlling the annealing temperature and cooling rate of different regions, the tissue uniformity of the surface layer, transition zone, and core and the stability of the gradient structure are ensured, so that the material has excellent toughness and hydrogen damage resistance while maintaining high strength. The zoning annealing process in S5 not only improves the gradient structure constructed by the aforementioned surface mechanical grinding in S3 and multi-stage warm rolling in S4, but also ensures the long-term stability of the material in a complex service environment, providing important support for the engineering application of low-hydrogen embrittlement and high-toughness sponge zirconium-based composites.

[0026] The present invention also discloses a low-hydrogen embrittlement and high-toughness sponge zirconium-based composite material, which is obtained by the above preparation method;

[0027] The sponge zirconium-based composite material is composed of nano-ZrC and a Zr matrix;

[0028] The volume ratio of the nano-ZrC to the Zr matrix is (4.5-8.0):(92.0-95.5);

[0029] The average diameter of the nano-ZrC is 10.0-60.0 nm;

[0030] The nano-ZrC is in-situ generated from sponge zirconium powder and nano-carbon black at high temperature;

[0031] The sponge zirconium-based composite material sequentially includes a surface layer region, a transition region, and a core region from the outside to the inside;

[0032] The thickness of the surface layer region is 35 - 70 μm; the proportion of small-angle grain boundaries in the surface layer region is 82.3 - 88.7%; the proportion of large-angle grain boundaries is 11.7 - 15.9%; the proportion of twin boundaries is 0.4% - 1.0%;

[0033] The thickness of the transition region is 50 - 150 μm; the proportion of small-angle grain boundaries in the transition region is 25.7 - 34.7%; the proportion of large-angle grain boundaries is 59.7 - 67.3%; the proportion of twin boundaries is 5.1 - 7.5%;

[0034] The proportion of small-angle grain boundaries in the core is 6.5 - 10.5%, the proportion of large-angle grain boundaries is 71.8 - 78.8%; the proportion of twin boundaries is 13.4 - 19.0%.

[0035] The design of using nano-ZrC to reinforce the Zr matrix in the present invention is mainly used to enhance the hydrogen embrittlement resistance and toughness of the zirconium sponge matrix composite. Through the dispersion strengthening effect of nano-ZrC and the optimization of the gradient grain boundary structure, high strength, high toughness and good service stability of the material are achieved. The volume fraction of nano-ZrC is controlled within a reasonable range and is formed by in-situ reaction of zirconium sponge powder and nano-carbon black at high temperature, so that the reinforcing phase is uniformly distributed in the matrix, effectively improving the strengthening effect of the material and avoiding the problem of insufficient interfacial bonding force that may be brought by traditional externally added reinforcing phases. The microstructure of the material gradually changes from the surface layer region, the transition region to the core region, forming a gradient grain boundary distribution, enabling the material to have both high strength and good toughness in different regions, thereby enhancing the overall hydrogen embrittlement resistance. Due to experiencing strong plastic deformation and dynamic recrystallization during the preparation process, the grains in the surface layer region are further refined, forming a high density of small-angle grain boundaries, which helps to inhibit the diffusion and aggregation of hydrogen, reduce the hydrogen embrittlement sensitivity, and improve the wear resistance and surface hardness of the material. The grain boundary structure in the transition region forms a reasonable distribution among small-angle grain boundaries, large-angle grain boundaries and twin boundaries, ensuring the balance between the strength and toughness of the material, deflecting cracks during the propagation process, and thus improving the fracture toughness. The core region is mainly composed of large-angle grain boundaries and a relatively high proportion of twin boundaries. The existence of twin boundaries can effectively absorb deformation energy, improve the plastic toughness of the material, and reduce the risk of hydrogen-induced cracking. Through the synergistic effect of nano-ZrC reinforcement and gradient grain boundary regulation, the material has excellent toughness and hydrogen embrittlement resistance while maintaining high strength, meeting the service requirements in harsh environments and enhancing its application value in the nuclear industry and high corrosion resistance fields.

[0036] (3) Beneficial technical effects

[0037] Through the synergistic effects of in-situ generation of nano-ZrC, mechanical alloying, high-temperature densification, multi-stage warm rolling, and zoning annealing, the present invention achieves low hydrogen embrittlement and high toughness of the sponge zirconium-based composite material. Compared with the prior art, the present invention optimizes the distribution of nano-ZrC, improves the interfacial bonding force, avoids the non-uniformity problem caused by traditional externally added reinforcing phases, and at the same time improves the overall toughness through gradient grain boundary regulation, overcoming the defect that conventional zirconium alloys are prone to embrittlement in high-temperature and high-hydrogen environments. The present invention can be widely applied to high-end fields such as the nuclear industry and aerospace to meet the long-term service requirements. Brief Description of the Drawings

[0038] Figure 1 It is a microstructural interface morphology diagram of the sponge zirconium-based composite material prepared in Example 1 of the present invention.

[0039] Figure 2 It is an electron backscatter diffraction pattern of the surface layer region prepared in Example 1 of the present invention. Detailed Description of the Embodiments

[0040] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention.

[0041] Example 1

[0042] A preparation method of a low-hydrogen embrittlement and high-toughness sponge zirconium-based composite material includes the following steps:

[0043] S1. Raw material pretreatment and mechanical alloying: Using sponge zirconium powder and nano carbon black as raw materials, they are mixed and then subjected to mechanical alloying to obtain Zr-C composite powder; the detailed process is as follows: Mix sponge zirconium powder and carbon black according to a mass ratio of 97.0:3.0, place the mixed powder in a high-energy planetary ball mill, and carry out mechanical alloying under argon protection. The ball milling parameters are set as follows: the ball-to-material ratio is 10.0:1, the rotation speed is 300 rpm, and the ball milling time is 25 h to obtain Zr-C composite powder.

[0044] S2. Hot isostatic pressing densification and in-situ synthesis: Subject the Zr-C composite powder obtained in step S1 to hot isostatic pressing densification to in-situ synthesize a nano-ZrC dispersion-reinforced zirconium-based composite material blank; the detailed process is as follows: Put the Zr-C composite powder obtained in step S1 into a soft steel jacket, evacuate to ≤5×10⁻³ Pa, and then seal it by electron beam welding. Place the sealed powder jacket in a hot isostatic pressing furnace, heat it to 1200 °C at a heating rate of 10 °C / min, apply a pressure of 120 MPa, keep the temperature and pressure for 180 min. After the reaction is completed, cool it to room temperature at a cooling rate of 6.0 °C / min.

[0045] S3. Surface mechanical grinding treatment: The green body obtained in step S2 is subjected to surface mechanical grinding treatment to form a surface nanocrystalline structure. The detailed process is as follows: The green body obtained in step S2 is placed in an ultrasonic surface mechanical grinding equipment, WC-Co grinding balls are used, the vibration frequency is set to 20 kHz, the amplitude is 50 μm, the treatment time is 50 min, argon gas jet cooling is adopted during the treatment process, and after the treatment is completed, argon gas jet cooling is used, and the cooling rate is 40 °C / s.

[0046] S4. Multi-stage warm rolling and grain boundary gradient regulation: The green body treated in step S3 is successively subjected to primary rolling and core rolling to obtain a gradient structure green body. The detailed process of primary rolling is as follows: The surface of the green body treated in step S3 is induction heated to 650 °C, and rolling is carried out with a rolling force of 780 kN, the reduction per pass is 15%, and it is rolled in 4 passes; The detailed process of core rolling is as follows: The whole green body after primary rolling is heated to 600 °C, and rolling is carried out with a rolling force of 250 kN, the reduction per pass is 5.0%, and it is rolled in 4 passes. S5. Zone annealing to stabilize the gradient grain boundary: The green body treated in step S4 is successively subjected to surface annealing and core annealing to finally obtain a low hydrogen embrittlement and high toughness sponge zirconium-based composite material. The detailed process of surface annealing is as follows: Selective laser heating is adopted, the heating power density is 4.0 W / mm², the spot diameter is 2.0 mm, the surface area is heated to 650 °C, after holding for 30 min, argon gas jet cooling is used, and the cooling rate is 40 °C / s. The detailed process of core annealing is as follows: The green body is placed in an electric resistance furnace, heated to 480 °C at a heating rate of 5.0 °C / min, after holding for 90 min, it is cooled to room temperature at a cooling rate of 2.0 °C / min.

[0047] A low hydrogen embrittlement and high toughness sponge zirconium-based composite material according to this embodiment, the sponge zirconium-based composite material is composed of nano-ZrC and Zr matrix; the volume ratio of nano-ZrC and Zr matrix is 8.0:92.0; the average diameter of nano-ZrC is 60 nm; nano-ZrC is in-situ generated from sponge zirconium powder and nano carbon black at high temperature; the sponge zirconium-based composite material from the outside to the inside is successively a surface region, a transition region, and a core region; the thickness of the surface region is 35 μm; the proportion of small angle grain boundaries in the surface region is 82.3%; the proportion of large angle grain boundaries is 14.2%; the proportion of twin boundaries is 0.5%; the thickness of the transition region is 51 μm; the proportion of small angle grain boundaries in the transition region is 25.7%; the proportion of large angle grain boundaries is 59.7%; the proportion of twin boundaries is 6.0%; the proportion of small angle grain boundaries in the core is 6.5%, the proportion of large angle grain boundaries is 71.8%; the proportion of twin boundaries is 13.4%.

[0048] consisting of Figure 1It can be seen that the zirconium sponge-based composite material prepared in Example 1 of the present invention has an obvious gradient structure. Its microstructure is successively divided into a surface layer region, a transition region, and a core region from the outside to the inside. A large number of fine grains are presented in the surface layer region, which proves that the present invention has successfully constructed a surface fine grain structure through a specific process. In addition, Figure 2 The electron backscatter diffraction (EBSD) analysis results of

[0049] Example 2

[0050] A preparation method of a low-hydrogen embrittlement and high-toughness zirconium sponge-based composite material includes the following steps:

[0051] S1. Raw material pretreatment and mechanical alloying: Using zirconium sponge powder and nano carbon black as raw materials, they are mixed and then mechanically alloyed to obtain Zr-C composite powder. The detailed process is as follows: Mix zirconium sponge powder and carbon black according to a mass ratio of 97.3:2.7. Place the mixed powder in a high-energy planetary ball mill and carry out mechanical alloying under argon protection. The ball milling parameters are set as follows: the ball-to-material ratio is 10.6:1, the rotation speed is 315 rpm, and the ball milling time is 27 h to obtain Zr-C composite powder.

[0052] S2. Hot isostatic pressing densification and in-situ synthesis: The Zr-C composite powder obtained in step S1 is subjected to hot isostatic pressing densification to in-situ synthesize a nano-ZrC dispersion-strengthened zirconium-based composite material blank. The detailed process is as follows: Load the Zr-C composite powder obtained in step S1 into a soft steel jacket, evacuate to ≤5×10⁻³ Pa, and then seal it by electron beam welding. Place the sealed powder jacket in a hot isostatic pressing furnace, heat it to 1215 °C at a heating rate of 12 °C / min, apply a pressure of 129 MPa, hold the temperature and pressure for 198 min. After the reaction is completed, cool it to room temperature at a cooling rate of 7.8 °C / min.

[0053] S3. Surface mechanical grinding treatment: The blank obtained in step S2 is subjected to surface mechanical grinding treatment to form a surface nano-crystalline structure. The detailed process is as follows: Place the blank obtained in step S2 in an ultrasonic surface mechanical grinding device, use WC-Co grinding balls, set the vibration frequency to 22 kHz, the amplitude to 53 μm, and the treatment time to 53 min. During the treatment process, argon jet cooling is adopted. After the treatment is completed, argon jet cooling is used, and the cooling rate is 43 °C / s.

[0054] S4. Multi-stage warm rolling and grain boundary gradient regulation. The billet after being processed in step S3 is successively subjected to primary rolling and core rolling to obtain a gradient structure billet. The detailed process of primary rolling is as follows: The surface of the billet after being processed in step S3 is induction heated to 665 °C, and rolling is carried out with a rolling force of 786 kN, the reduction per pass is 17%, and it is rolled in 5 passes. The detailed process of core rolling is as follows: The billet after primary rolling is heated as a whole to 615 °C, and rolling is carried out with a rolling force of 265 kN, the reduction per pass is 5.9%, and it is rolled in 5 passes.

[0055] S5. Zone annealing to stabilize the gradient grain boundary: The billet after being processed in step S4 is successively subjected to surface annealing and core annealing to finally obtain a low hydrogen embrittlement and high toughness sponge zirconium-based composite material. The detailed process of surface annealing is as follows: Selective laser heating is adopted, the heating power density is 4.3 W / mm², the spot diameter is 2.6 mm, the surface area is heated to 653 °C, after holding for 35 min, argon gas jet cooling is adopted, and the cooling rate is 43 °C / s. The detailed process of core annealing is as follows: The billet is placed in an electric resistance furnace and heated to 483 °C at a heating rate of 5.9 °C / min, after holding for 99 min, it is cooled to room temperature at a cooling rate of 2.9 °C / min.

[0056] A low hydrogen embrittlement and high toughness sponge zirconium-based composite material of this embodiment. The sponge zirconium-based composite material is composed of nano-ZrC and Zr matrix; the volume ratio of nano-ZrC and Zr matrix is 7.3:92.7; the average diameter of nano-ZrC is 46.0 nm; nano-ZrC is in-situ generated from sponge zirconium powder and nano-carbon black at high temperature; the sponge zirconium-based composite material is successively the surface area, the transition area, and the core area from the outside to the inside; the thickness of the surface area is 45 μm; the proportion of small angle grain boundaries in the surface area is 84.5%; the proportion of large angle grain boundaries is 12.0%; the proportion of twin boundaries is 0.8%; the thickness of the transition area is 85 μm; the proportion of small angle grain boundaries in the transition area is 28.0%; the proportion of large angle grain boundaries is 60.0%; the proportion of twin boundaries is 6.5%; the proportion of small angle grain boundaries in the core is 7.5%, the proportion of large angle grain boundaries is 74.0%; the proportion of twin boundaries is 15.5%.

[0057] Example 3

[0058] A preparation method of a low hydrogen embrittlement and high toughness sponge zirconium-based composite material, comprising the following steps:

[0059] S1. Pretreatment of raw materials and mechanical alloying: Using sponge zirconium powder and nano carbon black as raw materials, they are mixed and then subjected to mechanical alloying to obtain Zr-C composite powder. The detailed process is as follows: Mix sponge zirconium powder and carbon black in a mass ratio of 97.6:2.4. Place the mixed powder in a high-energy planetary ball mill and carry out mechanical alloying under argon protection. The ball milling parameters are set as follows: the ball-to-powder ratio is 11.2:1, the rotation speed is 330 rpm, and the ball milling time is 28 h to obtain Zr-C composite powder.

[0060] S2. Hot isostatic pressing densification and in-situ synthesis: The Zr-C composite powder obtained in step S1 is subjected to hot isostatic pressing densification to in-situ synthesize a nano-ZrC dispersion-reinforced zirconium matrix composite billet. The detailed process is as follows: Load the Zr-C composite powder obtained in step S1 into a soft steel jacket, evacuate to ≤5×10⁻³ Pa, and then seal it by electron beam welding. Place the sealed powder jacket in a hot isostatic pressing furnace, heat it to 1230 °C at a heating rate of 13 °C / min, apply a pressure of 138 MPa, hold for 216 min. After the reaction is completed, cool it to room temperature at a cooling rate of 9.6 °C / min.

[0061] S3. Surface mechanical grinding treatment: The billet obtained in step S2 is subjected to surface mechanical grinding treatment to form a surface nanocrystalline structure. The detailed process is as follows: Place the billet obtained in step S2 in an ultrasonic surface mechanical grinding device, use WC-Co grinding balls, set the vibration frequency to 23 kHz, the amplitude to 56 μm, and the treatment time to 56 min. During the treatment, argon jet cooling is adopted. After the treatment is completed, argon jet cooling is used, and the cooling rate is 46 °C / s.

[0062] S4. Multi-stage warm rolling and grain boundary gradient regulation: The billet treated in step S3 is successively subjected to primary rolling and core rolling to obtain a gradient structure billet. The detailed process of primary rolling is as follows: Inductively heat the surface of the billet treated in step S3 to 680 °C, roll it with a rolling force of 792 kN, the pass reduction is 18%, and it is rolled in 5 passes. The detailed process of core rolling is as follows: Heat the whole billet after primary rolling to 630 °C, roll it with a rolling force of 280 kN, the pass reduction is 6.8%, and it is rolled in 5 passes.

[0063] S5. Partition annealing to stabilize the gradient grain boundary: The billet after the treatment in step S4 is subjected to surface annealing and core annealing in sequence, and finally a low hydrogen embrittlement and high toughness sponge zirconium-based composite material is obtained. The detailed process of surface annealing is as follows: Selective laser heating is adopted, the heating power density is 4.6 W / mm², the spot diameter is 3.2 mm, the surface area is heated to 656 °C, after holding for 39 min, argon jet cooling is adopted, and the cooling rate is 46 °C / s. The detailed process of core annealing is as follows: The billet is placed in an electric resistance furnace and heated to 486 °C at a heating rate of 6.8 °C / min, after holding for 108 min, it is cooled to room temperature at a cooling rate of 3.8 °C / min.

[0064] A low hydrogen embrittlement and high toughness sponge zirconium-based composite material in this embodiment, the sponge zirconium-based composite material is composed of nano-ZrC and Zr matrix; the volume ratio of nano-ZrC and Zr matrix is 6.5:93.5; the average diameter of nano-ZrC is 27.5 nm; nano-ZrC is in-situ generated from sponge zirconium powder and nano-carbon black at high temperature; the sponge zirconium-based composite material from the outside to the inside is successively a surface layer region, a transition region, and a core region; the thickness of the surface layer region is 55 μm; the proportion of small angle grain boundaries in the surface layer region is 86.0%; the proportion of large angle grain boundaries is 11.5%; the proportion of twin boundaries is 0.5%; the thickness of the transition region is 110 μm; the proportion of small angle grain boundaries in the transition region is 30.0%; the proportion of large angle grain boundaries is 62.0%; the proportion of twin boundaries is 6.5%; the proportion of small angle grain boundaries in the core is 9.7%, the proportion of large angle grain boundaries is 77.5%; the proportion of twin boundaries is 12.8%.

[0065] Example 4

[0066] A preparation method of a low hydrogen embrittlement and high toughness sponge zirconium-based composite material, comprising the following steps:

[0067] S1. Raw material pretreatment and mechanical alloying: Using sponge zirconium powder and nano-carbon black as raw materials, after mixing, mechanical alloying is carried out to obtain Zr-C composite powder; the detailed process is as follows: Mix sponge zirconium powder and carbon black according to a mass ratio of 98.0:2.0, place the mixed powder in a high-energy planetary ball mill, and carry out mechanical alloying under argon protection. The ball milling parameters are set as follows: the ball-to-material ratio is 12.0:1, the rotation speed is 350 rpm, and the ball milling time is 30 h to obtain Zr-C composite powder.

[0068] S2. Hot Isostatic Pressing Densification and In-situ Synthesis: The Zr-C composite powder obtained in step S1 is subjected to hot isostatic pressing densification to in-situ synthesize a nanocrystalline ZrC dispersion-strengthened zirconium-based composite material blank; the detailed process is as follows: The Zr-C composite powder obtained in step S1 is loaded into a soft steel jacket, evacuated to ≤5×10⁻³ Pa, and then sealed by electron beam welding. The sealed powder jacket is placed in a hot isostatic pressing furnace, heated to 1250 °C at a heating rate of 15 °C / min, a pressure of 150 MPa is applied, and it is kept at temperature and pressure for 240 min. After the reaction is completed, it is cooled to room temperature at a cooling rate of 12.0 °C / min.

[0069] S3. Surface Mechanical Grinding Treatment: The blank obtained in step S2 is subjected to surface mechanical grinding treatment to form a surface nanocrystalline structure; the detailed process is as follows: The blank obtained in step S2 is placed in an ultrasonic surface mechanical grinding device, WC-Co grinding balls are used, the vibration frequency is set to 25 kHz, the amplitude is 60 μm, the treatment time is 60 min, and argon jet cooling is adopted during the treatment. After the treatment is completed, argon jet cooling is used, and the cooling rate is 50 °C / s.

[0070] S4. Multi-stage Warm Rolling and Grain Boundary Gradient Regulation: The blank treated in step S3 is subjected to primary rolling and core rolling in sequence to obtain a gradient structure blank; the detailed process of primary rolling is as follows: The surface of the blank treated in step S3 is induction heated to 700 °C, and rolling is carried out with a rolling force of 800 kN, the reduction per pass is 20%, and it is rolled in 6 passes; the detailed process of core rolling is as follows: The blank after primary rolling is heated to 650 °C as a whole, and rolling is carried out with a rolling force of 300 kN, the reduction per pass is 8.0%, and it is rolled in 6 passes.

[0071] S5. Zoning Annealing to Stabilize the Gradient Grain Boundary: The blank treated in step S4 is subjected to surface annealing and core annealing in sequence to finally obtain a low hydrogen embrittlement and high toughness sponge zirconium-based composite material. The detailed process of surface annealing is as follows: Selective laser heating is used, the heating power density is 5.0 W / mm², the spot diameter is 4.0 mm, the surface area is heated to 660 °C, after holding for 45 min, argon jet cooling is adopted, and the cooling rate is 50 °C / s. The detailed process of core annealing is as follows: The blank is placed in an electric resistance furnace, heated to 490 °C at a heating rate of 8.0 °C / min, held for 120 min, and then cooled to room temperature at a cooling rate of 5.0 °C / min.

[0072] A low-hydrogen embrittlement and high-toughness sponge zirconium-based composite material of this embodiment, the sponge zirconium-based composite material is composed of nano-ZrC and a Zr matrix; the volume ratio of nano-ZrC to the Zr matrix is 4.5:95.5; the average diameter of nano-ZrC is 10.0 nm; the nano-ZrC is in-situ generated from sponge zirconium powder and nano-carbon black at high temperature; the sponge zirconium-based composite material from the outside to the inside is successively a surface layer region, a transition region, and a core region; the thickness of the surface layer region is 68 μm; the proportion of small-angle grain boundaries in the surface layer region is 83.0%; the proportion of large-angle grain boundaries is 11.7%; the proportion of twin boundaries is 0.5%; the thickness of the transition region is 145 μm; the proportion of small-angle grain boundaries in the transition region is 32.5%; the proportion of large-angle grain boundaries is 63.0%; the proportion of twin boundaries is 7.0%; the proportion of small-angle grain boundaries in the core is 10.5%, the proportion of large-angle grain boundaries is 78.8%; the proportion of twin boundaries is 18.7%.

[0073] Comparative Example 1

[0074] It is basically the same as Example 1, except that the sponge zirconium powder and nano-carbon black are mixed according to a mass ratio of 96.5:3.5.

[0075] Comparative Example 2

[0076] It is basically the same as Example 1, except that the ball milling time is set to 20 h.

[0077] Comparative Example 3

[0078] It is basically the same as Example 1, except that the ball milling time is set to 35 h.

[0079] Comparative Example 4

[0080] It is basically the same as Example 1, except that the hot isostatic pressing temperature is set to 1180 °C.

[0081] Comparative Example 5

[0082] It is basically the same as Example 1, except that the surface mechanical grinding vibration frequency is set to 18 kHz.

[0083] Comparative Example 6

[0084] It is basically the same as Example 1, except that the initial rolling temperature is set to 620 °C.

[0085] Comparative Example 7

[0086] It is basically the same as Example 1, except that the cooling rate after surface annealing is set to 30 °C / s.

[0087] Comparative Example 8

[0088] It is basically the same as Example 1, except that the core annealing temperature is set to 500 °C.

[0089] Performance test:

[0090] Tensile property test: The tensile experiment was carried out on the composite material using an electronic universal testing machine to test its yield strength, tensile strength and elongation. The samples were prepared according to ASTM E8 standard, and the test temperature was set at room temperature and 400 °C to simulate the mechanical properties under different service environments. The strength and plasticity of the composite material were evaluated through the stress-strain curve, and the crack propagation mechanism was observed by combining the fracture analysis.

[0091] Impact toughness test: The impact toughness test of the composite material was carried out using a Charpy impact testing machine, and the test temperatures included room temperature and low temperature (-196 °C, liquid nitrogen environment). The impact specimens were prepared according to ASTM E23 standard, and the brittle fracture characteristics of the material were evaluated through the fracture morphology analysis. This experiment can be used to evaluate the influence of nano-ZrC reinforcement on toughness.

[0092] Hydrogen embrittlement sensitivity test: This test scheme was carried out according to ASTM G142-98 standard for hydrogen embrittlement evaluation of metallic materials. The test was carried out in a high-pressure hydrogen environment (0.1 MPa, 1 MPa, 5 MPa), and the test temperature was ensured to be constant (such as 300 °C, 600 °C). The slow strain rate tensile (SSRT) method was used for the test, and the strain rate was set at 10⁻ 6 ~10⁻ 5 s⁻¹, which meets the recommended range of the standard. After the tensile test, the yield strength, tensile strength and elongation after fracture were measured, and the mechanical properties were compared with those of the non-hydrogen-charged specimens. After the test was completed, a scanning electron microscope (SEM) was used to observe the fracture morphology and analyze the hydrogen embrittlement fracture characteristics, such as intergranular fracture and quasi-cleavage fracture, to evaluate the hydrogen embrittlement sensitivity of the material.

[0093] Hydrogen permeation test: The Sievert method was used to measure the hydrogen permeability of the material, and the test temperature range was 200~600 °C to simulate the nuclear industry application environment. By measuring the hydrogen permeation rate at different temperatures, the influence of the surface nanocrystalline structure on the hydrogen diffusion behavior was analyzed, and the hydrogen barrier ability of the material was verified.

[0094] The performances of the sponge zirconium-based composite materials of Examples 1~4 and Comparative Examples 1~7 were summarized in Table 1.

[0095] Table 1 Summary of the performances of the sponge zirconium-based composite materials of Examples 1~4 and Comparative Examples 1~7

[0096]

[0097] The mechanical properties and hydrogen embrittlement resistance of the material are significantly affected by multiple process parameters. First of all, the raw material ratio directly determines the uniformity of the distribution of the nano-reinforcing phase. If the carbon content is too high, it may lead to an increase in particle size, reducing the ductility and impact toughness of the material. The mechanical alloying process is also a key factor. If the ball milling time is too short, the powder mixing will be uneven, affecting the density of subsequent sintering. If the ball milling time is too long, powder agglomeration may occur, weakening the overall mechanical properties of the material. The hot isostatic pressing temperature affects the in-situ synthesis degree of ZrC. A relatively low temperature may lead to an increase in porosity, reducing the strength and toughness of the material. Surface mechanical grinding improves the surface strengthening effect of the material by refining the surface grains. If the vibration frequency is too low, the nano-crystalline structure may not be refined enough, reducing the strengthening degree of the material. The warm rolling process affects the stability of the gradient grain boundary. A relatively low rolling temperature may lead to uneven deformation, further affecting the comprehensive mechanical properties of the material. Annealing treatment is also an important link in determining the final properties. If the cooling rate is too low, the nano-grains will grow, reducing the surface strengthening effect. Appropriately increasing the core annealing temperature can optimize the stress state of the material, thereby improving some mechanical properties. Generally speaking, factors such as the raw material ratio, ball milling time, hot isostatic pressing temperature, and surface treatment parameters have an important impact on the hydrogen embrittlement sensitivity of the material. Reasonably optimizing each process parameter can improve its hydrogen embrittlement resistance while ensuring excellent mechanical properties of the material, achieving the best comprehensive performance.

[0098] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that any equivalent structural transformation made under the concept of the present invention by using the content of the specification and drawings of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a low hydrogen embrittlement and high toughness sponge zirconium-based composite material, characterized in that: The following steps are involved: S1. Raw material pretreatment and mechanical alloying: Sponge zirconium powder and nano carbon black are used as raw materials, and mixed in a mass ratio of (97.0-98.0): (2.0-3.0) to obtain a mixed powder, and the mixed powder is placed in a high-energy planetary ball mill for mechanical alloying under argon protection. The ball milling parameters are set as follows: ball-to-material ratio is (10.0-12.0):1, the rotation speed is 300-350rpm, and the ball milling time is 25-30h to obtain Zr-C composite powder; S2. Hot isostatic pressing densification and in-situ synthesis: The Zr-C composite powder obtained in step S1 is heated to 1200~1250°C and a pressure of 120~150MPa is applied for hot isostatic pressing densification, and a nano ZrC dispersion-reinforced zirconium-based composite body is synthesized in situ; S3 surface mechanical grinding treatment: The body obtained in step S2 is placed in an ultrasonic surface mechanical grinding device, using WC-Co grinding balls, setting the vibration frequency to 20 ~ 25kHz, forming a surface nanocrystalline structure; S4. Multi-stage warm rolling and grain boundary gradient control: The blank treated in step S3 is subjected to primary rolling and core rolling in sequence to obtain a gradient structure blank; The detailed process of the primary rolling is as follows: the surface of the billet treated in step S3 is induction heated to 650-700°C, and the billet is rolled at a rolling force of 780-800 kN, with a pass reduction of 15-20%, and the billet is rolled in 4-6 passes; the detailed process of the core rolling is as follows: the billet after the primary rolling is heated as a whole to 600-650°C, and the billet is rolled at a rolling force of 250-300 kN, with a pass reduction of 5.0-8.0%, and the billet is rolled in 4-6 passes; S5. Partition annealing to stabilize gradient grain boundaries: The blank treated in step S4 is subjected to surface annealing and core annealing in sequence. The detailed process of surface annealing is as follows: laser selective heating is adopted with a heating power density of 4.0~5.0W / mm² and a spot diameter of 2.0~4.0mm to heat the surface area to 650~660℃, and after keeping the temperature for 30~45min, argon gas jet cooling is adopted with a cooling rate of 40~50℃ / s; the detailed process of core annealing is as follows: the blank is placed in a resistance furnace, heated to 480~490℃ at a heating rate of 5.0~8.0℃ / min, and after keeping the temperature for 90~120min, it is cooled to room temperature at a cooling rate of 2.0~5.0℃ / min; finally, a sponge zirconium-based composite material with low hydrogen embrittlement and high toughness is obtained.

2. The method for preparing a low hydrogen embrittlement and high toughness sponge zirconium-based composite material according to claim 1, characterized in that: The detailed process of step S2 is as follows: the Zr-C composite powder obtained in step S1 is placed in a soft steel bag, and the vacuum is evacuated to ≤5×10 - 3 After Pa, electron beam sealing welding is used for sealing. The sealed powder package is placed in a hot isostatic pressing furnace, heated to 1200~1250℃ at a heating rate of 10~15℃ / min, a pressure of 120~150MPa is applied, and the temperature and pressure are maintained for 180~240min. After the reaction is completed, the powder package is cooled to room temperature at a cooling rate of 6.0~12.0℃ / min.

3. The method for preparing a low hydrogen embrittlement and high toughness sponge zirconium-based composite material according to claim 1, characterized in that: In step S3, the amplitude is 50-60 μm, the treatment time is 50-60 min, argon gas jet cooling is adopted during the treatment process, and after the treatment is completed, argon gas jet cooling is adopted, and the cooling rate is 40-50° C. / s.

4. A low hydrogen embrittlement and high toughness sponge zirconium-based composite material, characterized in that: The zirconium sponge-based composite material is prepared by the preparation method according to any one of claims 1 to 3; The sponge zirconium-based composite material is composed of nano ZrC and a Zr matrix; The volume ratio of the nano ZrC and the Zr matrix is ​​(4.5~8.0): (92.0~95.5); The average diameter of the nano ZrC is 10.0-60.0 nm; The nano ZrC is in-situ self-generated from sponge zirconium powder and nano carbon black at high temperature.

5. A low hydrogen embrittlement and high toughness sponge zirconium-based composite material as claimed in claim 4, characterized in that: The sponge zirconium-based composite material is composed of a surface region, a transition region, and a core region from the outside to the inside; The thickness of the surface region is 35-70 μm; the small-angle grain boundaries in the surface region account for 82.3-86.0%; the large-angle grain boundaries account for 11.7-15.9%; and the twin boundaries account for 0.4%-1.0%; The thickness of the transition region is 50-150 μm; the small-angle grain boundaries in the transition region account for 25.7-34.7%; the large-angle grain boundaries account for 59.7-67.3%; and the twin boundaries account for 5.1-7.5%; The small-angle grain boundaries in the core account for 6.5-10.5%, the large-angle grain boundaries account for 71.8-78.8%; and the twin boundaries account for 13.4-19.0%.

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