Ni-w-mo-cr high-temperature-resistant multi-main-element alloy for molten salt reactor and preparation method thereof
By precisely designing the composition and controlling the process of Ni-W-Mo-Cr series high-temperature resistant multi-principal alloys, the problem of balancing strength and plasticity at high temperatures for molten salt reactor materials has been solved, achieving excellent mechanical properties and microstructure stability at high temperatures, making them suitable for engineering applications in thorium-based molten salt reactors.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHANGHAI UNIV
- Filing Date
- 2026-06-23
- Publication Date
- 2026-07-24
AI Technical Summary
Existing materials for molten salt reactors have insufficient load-bearing capacity at 850°C, poor plasticity and easy brittle fracture, and are prone to precipitation of TCP-type brittle intermetallic compounds. They cannot balance high-temperature strength and plasticity, and are difficult to adapt to the harsh long-term service conditions of thorium-based molten salt reactors at 850°C.
Using a Ni-W-Mo-Cr series high-temperature resistant multi-principal alloy, a stable FCC tough matrix and BCC dispersed strengthening phase are formed through precise design of the composition ratio, thus avoiding the precipitation of TCP-type brittle intermetallic compounds. Combined with multi-pass tumbling melting, copper mold casting, high-temperature homogenization, and large deformation hot rolling processes, a synergistic match between strength and plasticity is achieved.
With a yield strength of not less than 350 MPa, a tensile strength of not less than 400 MPa, and an elongation after fracture of not less than 25% at a high temperature of 850℃, its performance is significantly better than that of existing commercial alloys. It is suitable for the long-term service requirements of molten salt reactors and has broad prospects for engineering applications.
Smart Images
Figure CN122446010A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of high-temperature resistant metal structural materials for molten salt reactors, specifically to a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors and its preparation method. Background Technology
[0002] Thorium-based molten salt reactors represent a core development direction for fourth-generation advanced nuclear energy systems. With their inherent advantages such as high safety, high fuel utilization, low nuclear waste generation, and the ability to achieve a closed-loop thorium-uranium cycle, they have become a key area in nuclear energy strategic planning. Core structural components such as reactor core support structures and heat exchange pipes must operate under extreme coupled conditions of 850°C high temperature, strong molten salt corrosion, and neutron irradiation for extended periods. This requires materials to possess stable high strength, good plasticity, and long-term structural stability at the service temperature. Their mechanical properties directly determine the reactor's operational safety, the service life of structural components, and the progress of engineering implementation.
[0003] Currently, the mainstream candidate materials for molten salt reactors are mainly commercial nickel-based alloys and refractory alloys. Among them, the most representative commercial nickel-based alloy is Hastelloy N alloy developed by Oak Ridge National Laboratory in the United States. Hastelloy N alloy exhibits good corrosion resistance in molten salt corrosion environments, but existing studies have shown that its yield strength at 850℃ is only about 250MPa, which is seriously insufficient in high-temperature load-bearing capacity. Its mechanical properties degrade significantly during long-term high-temperature service, and it cannot meet the long-term stable load-bearing requirements of the hot-end structural components of molten salt reactors.
[0004] Another category of candidate materials is refractory alloy systems, such as Mo-based alloys and W-Re alloys. Although these alloys can maintain a certain strength at high temperatures, they have extremely poor plasticity at both room temperature and high temperature, making them prone to brittle fracture. Their processing and forming capabilities and resistance to cracking during service are severely inadequate. At the same time, they are prone to microstructure coarsening during long-term high-temperature service, leading to rapid deterioration of mechanical properties, making them unsuitable for the harsh service environment of 850°C.
[0005] Existing publicly available Ni-W-Mo-Cr alloys are mostly developed for wear-resistant and welding applications. However, their composition and processing are not adapted to the long-term service requirements of molten salt reactors at 850℃, resulting in three major problems: First, the composition design does not take into account the synergy between phase stability and strong plasticity, and the precipitation of brittle TCP (topological close-packed) phases such as σ phase and μ phase during high-temperature service can easily lead to embrittlement failure. Second, the high-melting-point refractory elements W and Mo are prone to insufficient dissolution and as-cast agglomeration, resulting in uneven alloy properties and increased risk of cracking. Third, the microstructure is difficult to control, making it impossible to achieve synergistic optimization of high-temperature strength and plasticity.
[0006] In summary, there is currently no dedicated material suitable for molten salt reactors operating at 850℃ that can be engineered. Traditional commercial alloys and existing multi-element alloys cannot meet the extreme service requirements of molten salt reactors. There is an urgent need to develop a high-temperature resistant metal structural material for molten salt reactors that has strong plasticity, long-term stable microstructure, and can be engineered. Summary of the Invention
[0007] The purpose of this invention is to address the industry pain points of existing structural materials for molten salt reactors, which suffer from insufficient load-bearing capacity, poor plasticity, brittle fracture, and easy precipitation of TCP-type brittle intermetallic compounds at 850℃, and cannot simultaneously achieve high-temperature strength and plasticity, making them unsuitable for the long-term, harsh service conditions of thorium-based molten salt reactors at 850℃. This invention provides a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors and its preparation method. Through precise design of the multi-principal element alloy composition, this Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors achieves a stable FCC tough matrix and BCC dispersed strengthening phase in a two-phase solid solution structure, while avoiding the precipitation of TCP-type brittle intermetallic compounds in the alloy, achieving a high strength at 850℃. The synergistic matching of strength and plasticity under 0℃ high-temperature conditions meets the stringent long-term service requirements of molten salt reactors. In addition, the preparation method of the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for this molten salt reactor solves the core pain point of insufficient dissolution and component segregation of high-melting-point refractory elements such as W and Mo. Moreover, it does not require complex special equipment, and the raw materials are conventional high-purity Ni, W, Mo and Cr metals, which are widely available and cost-controllable. In addition, the oxygen partial pressure in the furnace is reduced by the gas absorption pretreatment of titanium ingots during the preparation process, which ensures uniform alloy composition, stable performance and high yield. It is easy to realize large-scale production and engineering promotion, and provides core material support for the engineering application of thorium-based molten salt reactors, which has broad prospects for engineering application.
[0008] To achieve the above objectives, in a first aspect, the present invention provides a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, wherein the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors is composed of four elements: Ni, W, Mo, and Cr; wherein... Based on atomic percentage, the contents of each element in the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt stacks are Ni 55~70 at.%, W 5~10 at.%, Mo 10~17 at.%, Cr 12~20 at.%, and the total of each element is 100 at.%.
[0009] Preferably, the contents of each element in the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt stacks, by atomic percentage, are Ni 60.0~65.0 at.%, W 6.5~9.5 at.%, Mo 12.0~17.0 at.%, Cr 12.0~16.0 at.%, and the total of each element is 100 at.%.
[0010] Preferably, the microstructure of the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy used in the molten salt reactor consists of a Ni-enriched FCC matrix phase and a W / Mo-enriched BCC second-phase solid solution, without the precipitation of TCP-type brittle intermetallic compounds.
[0011] Preferably, the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy used in the molten salt reactor has a yield strength of not less than 350 MPa, a tensile strength of not less than 400 MPa, and an elongation after fracture of not less than 25% under tensile conditions at 850℃.
[0012] Secondly, the present invention provides a method for preparing a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, the preparation method comprising: 1) Under a protective atmosphere, high-purity metal raw materials of Ni, W, Mo and Cr with a purity of not less than 99.99 wt.% are melted to complete melting in a vacuum electric arc melting furnace and held at the temperature for 2 to 5 minutes to form an alloy ingot. The alloy ingot is then flipped and remelted to obtain a homogeneous alloy ingot. 2) After melting the homogeneous alloy ingot described in step 1), the as-cast alloy is obtained by copper mold casting; 3) The as-cast alloy described in step 2) is subjected to homogenization heat treatment; 4) The alloy after homogenization heat treatment in step 3) is subjected to multiple hot rolling passes; 5) The hot-rolled alloy from step 4) is subjected to solution heat treatment in a protective atmosphere to obtain the target multi-principal element alloy.
[0013] Preferably, in step 1), the protective atmosphere is an argon atmosphere and / or a helium atmosphere.
[0014] More preferably, the method for forming the protective atmosphere includes: first evacuating to a vacuum of 9 × 10⁻⁶. -4 Below Pa, a protective gas is introduced into the furnace cavity, and then high-purity titanium ingots are used for melting and gas absorption for 1-3 minutes.
[0015] Preferably, in step 1), the input ratio of the high-purity metal raw materials Ni, W, Mo and Cr by atomic percentage is Ni 55~70 at.%, W 5~10 at.%, Mo 10~17 at.%, Cr 12~20 at.%, and the total of all elements is 100 at.%.
[0016] Preferably, the input ratio of the high-purity metal raw materials Ni, W, Mo and Cr, by atomic percentage, is Ni 60.0~65.0 at.%, W 6.5~9.5 at.%, Mo 12.0~17.0 at.%, Cr 12.0~16.0 at.%, and the total of all elements is 100 at.%.
[0017] Preferably, in step 1), the conditions for the remelting include: melting the alloy ingot until it is completely melted and holding it at that temperature for 2 to 5 minutes, for a total of ≥ 8 times, preferably 8 to 12 times.
[0018] Preferably, in step 2), the melting temperature is higher than the alloy liquidus line, which is 1350~1400℃.
[0019] Preferably, in step 3), the conditions for the homogenization heat treatment include: a temperature of 1200~1300℃, a holding time of 10~24h, and rapid water quenching after the holding time.
[0020] Preferably, in step 4), the conditions for multi-pass hot rolling include: a temperature of 1100~1250℃, the alloy being held at 1200℃ for 20~30 minutes before hot rolling, and, except for the first time, being held at 1200℃ for 3~8 minutes before each rolling pass, using 3~8 rolling passes, with a deformation amount of 15~30% per pass, and a total deformation amount of not less than 70%.
[0021] Preferably, in step 5), the conditions for the solution heat treatment include: a heating rate of 8~12℃ / min, a temperature of 1150~1250℃, a holding time of 1~2h, and water quenching after the holding time.
[0022] Preferably, the preparation method further includes: pretreatment of high-purity metal raw materials of Ni, W, Mo and Cr, wherein the pretreatment includes: ultrasonic cleaning for 10-20 min with anhydrous ethanol as detergent, and drying in a vacuum drying oven at a temperature of 50-70℃ for 20-40 min.
[0023] Thirdly, the present invention provides a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors prepared by the preparation method described in the present invention.
[0024] In the above technical solution, the Ni-W-Mo-Cr series high-temperature resistant multi-principal alloy for molten salt reactors of the present invention is designed specifically for the 850℃ service conditions of molten salt reactors. It consists of only four elements: Ni, W, Mo, and Cr, as well as unavoidable impurities. Through the precise ratio of the four elements, the alloy belongs to the category of multi-principal alloys. It can use the high entropy effect, hysteresis diffusion effect, and phase stabilization effect of the multi-principal alloy system to thermodynamically suppress the precipitation of σ phase, μ phase, and other TCP-type brittle intermetallic compounds.
[0025] The present invention relates to a Ni-W-Mo-Cr series high-temperature resistant multi-principal-element alloy for molten salt reactors, in which the synergistic effects of each element are clearly defined. Specifically, the Ni-enriched FCC matrix solid solution phase ensures the alloy's plasticity, formability, and crack resistance; W and Mo are the core strengthening elements, and the W / Mo-enriched BCC second-phase solid solution enhances high-temperature load-bearing capacity through both solid solution and dispersion strengthening, while also maintaining molten salt corrosion resistance; Cr regulates phase stability, inhibits the precipitation of brittle phases, ensuring the alloy is free of any TCP-type brittle intermetallic compounds, thus optimizing corrosion resistance. The continuous FCC matrix provides the alloy with excellent plasticity and crack resistance, while the uniformly dispersed BCC second phase significantly improves the alloy's high-temperature strength and long-term structural stability through dispersion strengthening and solid solution strengthening effects. Precise control of the quaternary ratio achieves a synergistic balance between matrix toughness and second-phase strengthening, solving the core problem of existing alloys' inability to simultaneously achieve high-temperature strength and plasticity.
[0026] This invention enables the Ni-W-Mo-Cr multi-principal alloy to achieve a yield strength of not less than 350 MPa, a tensile strength of not less than 400 MPa, and an elongation after fracture of not less than 25% at a high temperature of 850℃. It achieves synergistic optimization of high-temperature strength and plasticity, and its performance is significantly better than that of existing commercial molten salt reactor alloys, providing core material support for the engineering application of thorium-based molten salt reactors.
[0027] Meanwhile, the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt stacks of the present invention adopts a multi-pass tumbling melting and copper mold casting process, which effectively solves the common industry problem of insufficient melting of high-melting-point refractory elements W and Mo and component segregation, and obtains a billet with uniform composition and high density, laying the foundation for subsequent microstructure control and performance optimization.
[0028] Furthermore, this invention achieves stable and controllable dual-phase microstructure of FCC matrix solid solution phase and BCC second phase solid solution phase through the coordinated control of the entire process of high-temperature homogenization, large deformation hot rolling and precise solid solution. It refines the matrix grains and regulates the uniform dispersion distribution of BCC second phase, further enhancing the grain refinement and dispersion strengthening effects, optimizing the strength-plasticity matching and high-temperature performance stability of the alloy, effectively suppressing microstructure degradation during long-term high-temperature service, and adapting to the long-term service requirements of molten salt reactors.
[0029] Other features and advantages of the present invention will be described in detail in the following detailed description section. Attached Figure Description
[0030] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the following detailed description to explain the invention, but do not constitute a limitation thereof. In the drawings: Figure 1The images show the surface microstructure of the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloys for molten salt reactors prepared in Examples 1-2 and Comparative Examples 1-2 of this invention.
[0031] Figure 2 The images show the fracture cross-sections of the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloys for molten salt reactors prepared in Examples 1-2 and Comparative Examples 1-2 of this invention.
[0032] Figure 3 The XRD patterns are of the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloys for molten salt reactors prepared in Examples 1-2 and Comparative Examples 1-2 of this invention.
[0033] Figure 4 The data represent the high-temperature tensile properties at 850°C of the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloys for molten salt stacks prepared in Examples 1-2 and Comparative Examples 1-2 of this invention. Detailed Implementation
[0034] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.
[0035] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0036] In a first aspect, the present invention provides a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, wherein the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors is composed of four elements: Ni, W, Mo, and Cr; wherein... Based on atomic percentage, the contents of each element in the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt stacks are Ni 55~70 at.%, W 5~10 at.%, Mo 10~17 at.%, Cr 12~20 at.%, and the total of each element is 100 at.%.
[0037] In a preferred embodiment of the present invention, the contents of each element in the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt stacks, by atomic percentage, are Ni 60.0~65.0 at.%, W 6.5~9.5 at.%, Mo 12.0~17.0 at.%, Cr 12.0~16.0 at.%, and the total of each element is 100 at.%.
[0038] The present invention relates to a Ni-W-Mo-Cr series high-temperature resistant multi-principal-element alloy for molten salt reactors. Ni forms an FCC structure as the matrix, ensuring the alloy's plasticity, formability, and crack resistance. W and Mo are the core strengthening elements, enhancing high-temperature load-bearing capacity through both solid solution and dispersion strengthening, while also maintaining resistance to molten salt corrosion. Cr regulates phase stability, inhibits the precipitation of brittle phases, and optimizes the alloy's corrosion resistance. Through precise control of the quaternary ratio, a synergistic balance between matrix toughness and second-phase strengthening is achieved.
[0039] In this invention, the microstructure of the Ni-W-Mo-Cr series high-temperature multi-principal element alloy for molten salt reactors consists of a Ni-enriched FCC matrix phase and a W / Mo-enriched BCC second-phase solid solution, without the precipitation of TCP-type brittle intermetallic compounds. The continuous FCC matrix provides the alloy with excellent plasticity and crack resistance, while the uniformly dispersed BCC second phase significantly enhances the alloy's high-temperature strength and long-term microstructural stability through dispersion strengthening and solid solution strengthening effects.
[0040] In this invention, the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy used for molten salt reactors has a yield strength of not less than 350 MPa, a tensile strength of not less than 400 MPa, and an elongation after fracture of not less than 25% under tensile conditions at 850℃.
[0041] Secondly, the present invention provides a method for preparing a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, the preparation method comprising: 1) Under a protective atmosphere, high-purity metal raw materials of Ni, W, Mo and Cr with a purity of not less than 99.99 wt.% are melted to complete melting in a vacuum electric arc melting furnace and held at the temperature for 2 to 5 minutes to form an alloy ingot. The alloy ingot is then flipped and remelted to obtain a homogeneous alloy ingot. 2) After melting the homogeneous alloy ingot described in step 1), the as-cast alloy is obtained by copper mold casting; 3) The as-cast alloy described in step 2) is subjected to homogenization heat treatment; 4) The alloy after homogenization heat treatment in step 3) is subjected to multiple hot rolling passes; 5) The hot-rolled alloy from step 4) is subjected to solution heat treatment in a protective atmosphere to obtain the target multi-principal element alloy.
[0042] The preparation method of this invention effectively solves the problem of melting and segregation of high-melting-point elements such as W and Mo through multi-pass tumbling melting and copper mold casting; completely eliminates as-cast segregation through high-temperature homogenization treatment; achieves grain refinement and dispersed distribution of the BCC phase through large deformation hot rolling; and locks in a stable FCC and BCC dual-phase microstructure through precise solution treatment. The coordinated control of the entire process ensures stable and controllable alloy microstructure, providing a process guarantee for obtaining excellent high-temperature strength and plasticity matching.
[0043] In this invention, in step 1), in order to prevent the alloy from oxidizing during the melting process, the protective atmosphere is an argon atmosphere and / or a helium atmosphere.
[0044] In a preferred embodiment of the present invention, the method for forming the protective atmosphere includes: first evacuating to a vacuum of 9 × 10⁻⁶. - 4 Below Pa, a protective gas is introduced into the furnace cavity, and then high-purity titanium ingots are used for melting and gas absorption for 1-3 minutes.
[0045] In this invention, the input ratio of the high-purity metal raw materials Ni, W, Mo and Cr by atomic percentage is Ni 55~70 at.%, W 5~10 at.%, Mo 10~17 at.%, Cr 12~20 at.%, and the total of all elements is 100 at.%.
[0046] In this invention, the input ratio of the high-purity metal raw materials Ni, W, Mo and Cr, by atomic percentage, is Ni 60.0~65.0 at.%, W 6.5~9.5 at.%, Mo 12.0~17.0 at.%, Cr 12.0~16.0 at.%, and the total of all elements is 100 at.%.
[0047] In this invention, the conditions for the remelting process include: melting the alloy ingot to a complete melt and holding it at that temperature for 2-5 minutes, repeating this process ≥8 times, preferably 8-12 times, to ensure that the high-melting-point elements W and Mo are fully melted to form a homogeneous melt. This effectively solves the common industry problem of insufficient melting and component segregation of high-melting-point refractory elements W and Mo, resulting in a billet with uniform composition and high density.
[0048] In step 2) of this invention, the melting temperature is higher than the alloy liquidus line, which is 1350~1400℃.
[0049] In step 2) of this invention, copper molds are used for flow casting because the high thermal conductivity of copper molds leads to rapid cooling, which is key to obtaining a cast billet with uniform composition and no macroscopic segregation, thus avoiding severe agglomeration of W and Mo elements.
[0050] In this invention, in step 3), the conditions for the homogenization heat treatment include: a temperature of 1200~1300℃, which promotes element diffusion and eliminates as-cast dendrite segregation; a holding time of 10~24h, which ensures that alloying elements diffuse fully and achieve uniform distribution; and rapid water quenching after the holding time, which locks in the homogenized structure and prevents re-precipitation of segregation during the cooling process.
[0051] In this invention, step 4) includes the following conditions for multi-pass hot rolling: the temperature is 1100~1250℃, which is within the good hot working window of the alloy to avoid cracking; the alloy is held at 1200℃ for 20~30min before hot rolling to ensure sufficient preheating of the alloy, improve thermoplasticity, and reduce deformation resistance; in order to ensure the stability of the alloy temperature during rolling, except for the first rolling, the alloy is reheated at 1200℃ for 3~8min before each rolling pass, and 3~8 rolling passes are used, with a deformation of 15~30% per pass and a total deformation of not less than 70%, to ensure sufficient grain refinement effect and promote uniform dispersion of BCC phase.
[0052] In this invention, step 5) includes the following conditions for solution heat treatment: a heating rate of 8~12℃ / min to control the heating speed and prevent excessive thermal stress from causing deformation or cracking; a temperature of 1150~1250℃, which allows the BCC phase of the alloy to be fully dissolved and uniformly distributed; a holding time of 1~2h to ensure the homogenization of the microstructure and eliminate residual stress from hot rolling; and water quenching after the holding time to lock in a stable dual-phase microstructure and prevent the precipitation of brittle phases during the cooling process.
[0053] In this invention, the preparation method further includes: pretreatment of high-purity Ni, W, Mo and Cr metal raw materials, wherein the pretreatment includes: ultrasonic cleaning for 10-20 min with anhydrous ethanol as detergent to remove oil and oxide layer on the surface of the metal raw materials to ensure smelting quality; and drying in a vacuum drying oven at 50-70℃ for 20-40 min to remove residual moisture and prevent the introduction of harmful elements such as hydrogen and oxygen during the smelting process.
[0054] In this invention, to reduce the oxygen partial pressure inside the furnace and prevent oxidation, a vacuum of 9 × 10⁻⁶ is first applied before smelting. -4 Below Pa; in order to further reduce the oxygen partial pressure in the furnace and purify the atmosphere, high-purity titanium ingots are used for smelting and gas absorption for 1-3 minutes.
[0055] Thirdly, the present invention provides a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors prepared by the preparation method described in the present invention.
[0056] In this invention, the room temperature is 15~30℃.
[0057] The present invention will be described in detail below through examples. In the following examples, the pharmaceuticals and agents are all conventional commercially available products.
[0058] Example 1 The target alloy (a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors) was designed with the following composition: Ni 64 at.%, W 9 at.%, Mo 15 at.%, and Cr 12 at.%, by atomic percentage. The specific preparation steps are as follows: (1) According to the chemical composition of the target alloy, weigh high-purity Ni, W, Mo and Cr respectively, put them into anhydrous ethanol, ultrasonically clean for 15 min to remove surface oil and oxide layer, take them out and place them in a vacuum drying oven, dry at 60℃ for 30 min, and set aside for later use.
[0059] (2) Place the dried raw material from step (1) into a vacuum arc melting furnace. First, evacuate the furnace cavity until the vacuum level inside the furnace reaches 9×10⁻⁶. -4 After the pressure drops below Pa, high-purity argon gas is introduced into the furnace cavity to form an inert protective atmosphere. The high-purity titanium ingot is then melted and the gas is absorbed for 1 minute to further reduce the oxygen partial pressure in the furnace. The raw materials are then subjected to electric arc melting. After the raw materials are completely melted, they are held at the temperature for 3 minutes to form an alloy ingot. The alloy ingot is flipped and the melting operation is repeated. The ingot is flipped and remelted a total of 8 times to ensure that the high melting point elements are fully melted and the alloy composition is uniform throughout. After the melting is completed, the ingot is cooled with the furnace to obtain a homogeneous alloy ingot.
[0060] (3) The alloy ingot obtained in step (2) is reheated to complete melting, and the melt temperature is controlled to be higher than the alloy liquidus line (1350~1400℃). A plate-shaped cast alloy billet with a thickness of 5mm is formed by copper mold casting.
[0061] (4) Place the plate-shaped cast alloy billet obtained in step (3) into a box-type heat treatment furnace and heat it to 1250°C at a heating rate of 10°C / min. Hold it for 12 hours. After the holding period, take out the billet quickly and quench it in water to room temperature (15~30°C) to completely eliminate the dendrite segregation in the cast state and achieve uniform distribution of alloy elements.
[0062] (5) Place the homogenized alloy billet from step (4) into a box furnace, heat it to 1200℃ and hold it for 25 minutes; then quickly take it out and perform multi-pass hot rolling. Use 5 passes for hot rolling, control the deformation amount of each pass to 15~20%, and the total deformation amount to 80%, and finally roll it into an alloy sheet with a thickness of 1mm; return it to the furnace for 5 minutes before each rolling to ensure that the alloy temperature is stable during the rolling process.
[0063] (6) Place the alloy sheet obtained in step (5) into a box-type heat treatment furnace and heat it to 1200℃ at a heating rate of 10℃ / min. Hold it for 1 hour. After the holding period, take it out quickly and immediately quench it with water to obtain the target alloy, namely the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt stacks, denoted as B1.
[0064] Example 2 The method described in Example 1 was implemented, except that "the chemical composition of the target alloy by atomic percentage is Ni 64 at.%, W 9 at.%, Mo 15 at.% and Cr 12 at.%" was replaced with "the chemical composition of the target alloy by atomic percentage is Ni 63 at.%, W 8 at.%, Mo 15 at.% and Cr 14 at.%", while keeping other conditions unchanged. The target alloy, namely the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, was obtained and denoted as B2.
[0065] Example 3 The method described in Example 1 was implemented, except that "the chemical composition of the target alloy, by atomic percentage, is Ni 64 at.%, W 9 at.%, Mo 15 at.%, and Cr 12 at.%" was replaced with "the chemical composition of the target alloy, by atomic percentage, is Ni 65 at.%, W 7 at.%, Mo 13 at.%, and Cr 15 at.%", while keeping other conditions unchanged. The target alloy, namely the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, was obtained and denoted as B3.
[0066] Example 4 The method described in Example 1 was implemented, except that "the chemical composition of the target alloy by atomic percentage is Ni 64 at.%, W 9 at.%, Mo 15 at.%, and Cr 12 at.%" was replaced with "the chemical composition of the target alloy by atomic percentage is Ni 55 at.%, W 10 at.%, Mo 15 at.%, and Cr 20 at.%", while keeping other conditions unchanged. The target alloy, namely the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, was obtained and denoted as B4.
[0067] Example 5 The method described in Example 1 was implemented, except that "the chemical composition of the target alloy by atomic percentage is Ni 64 at.%, W 9 at.%, Mo 15 at.% and Cr 12 at.%" was replaced with "the chemical composition of the target alloy by atomic percentage is Ni 70 at.%, W 8 at.%, Mo 10 at.%, Cr 12 at.%", while keeping other conditions unchanged. The target alloy, namely the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, was obtained and denoted as B5.
[0068] Comparative Example 1 The method described in Example 1 was implemented, except that "the chemical composition of the target alloy by atomic percentage is Ni 64 at.%, W 9 at.%, Mo 15 at.% and Cr 12 at.%" was replaced with "the chemical composition of the target alloy by atomic percentage is Ni 62 at.%, W 8 at.%, Mo 18 at.% and Cr 12 at.%", while keeping other conditions unchanged. The target alloy, namely the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, was obtained and denoted as D1.
[0069] Comparative Example 2 The method described in Example 1 was implemented, except that the following was changed in step (5): "Place the homogenized alloy billet from step (4) into a box furnace, heat it to 1200°C and hold it for 25 minutes; then quickly take it out and perform multi-pass hot rolling, using 5 passes, with the deformation amount controlled at 15%~20% per pass, and the total deformation amount being 80%, and finally roll it into an alloy sheet with a thickness of 1 mm; return it to the furnace for 5 minutes before each rolling to ensure the alloy temperature is stable during the rolling process" was changed to "Perform multi-pass cold rolling of the homogenized alloy billet from step (4) at room temperature, with a total deformation amount of 80%, and finally roll it into an alloy sheet with a thickness of 1 mm". Other conditions remained unchanged, and the target alloy, namely the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, was obtained, denoted as D2.
[0070] Comparative Example 3 The method described in Example 1 was implemented, except that "the chemical composition of the target alloy by atomic percentage is Ni 64 at.%, W 9 at.%, Mo 15 at.% and Cr 12 at.%" was replaced with "the chemical composition of the target alloy by atomic percentage is Ni 76 at.%, W 4 at.%, Mo 10 at.% and Cr 10 at.%", while other conditions remained unchanged, and the target alloy, namely the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, was obtained, denoted as D3.
[0071] Comparative Example 4 The method described in Example 1 was implemented, except that the following was changed in step (5): "Place the homogenized alloy billet from step (4) into a box furnace, heat it to 1200°C and hold it for 25 minutes; then quickly take it out and perform multi-pass hot rolling, using 5 passes, with the deformation amount controlled at 15~20% per pass, and the total deformation amount at 80%, and finally roll it into an alloy sheet with a thickness of 1 mm; return it to the furnace for 5 minutes before each rolling to ensure the alloy temperature is stable during the rolling process" was changed to "Perform multi-pass hot rolling of the homogenized alloy billet from step (4) at room temperature, using 3 passes, with the deformation amount controlled at 15~20% per pass, and the total deformation amount at 50%, and finally roll it into an alloy sheet with a thickness of 2.5 mm". Other conditions remained unchanged, and the target alloy, namely the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, was obtained, denoted as D4.
[0072] Detection Example 1 The microstructure of the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloys for molten salt reactors prepared in Examples 1-2 and Comparative Examples 1-2 was characterized by scanning electron microscopy and X-ray diffraction (XRD), respectively, and their phase composition was analyzed. The results are as follows: Figure 1-3 As shown.
[0073] Depend on Figure 1 As shown in the surface microstructure diagrams of the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloys for molten salt reactors prepared in Examples 1-2 and Comparative Examples 1-2, the surface microstructure of the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloys for molten salt reactors in Examples 1 and 2 exhibits a uniform two-phase structure, consisting of a continuous light gray Ni-enriched FCC matrix phase and a uniformly dispersed dark gray W / Mo-enriched BCC second phase. The second phase has a size of approximately 0.5~2 μm and exhibits no obvious segregation, coarse precipitates, or TCP-type brittle intermetallic compounds, demonstrating excellent overall microstructure uniformity. In Comparative Example 1, the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloy for molten salt reactors has a Ni-enriched FCC matrix phase in its alloy microstructure, with no BCC reinforcing phase formation. In Comparative Example 2, the W-rich BCC phase exhibits local aggregation in its alloy microstructure, forming coarse compositional segregation regions.
[0074] Depend on Figure 2The fracture cross-section diagrams of the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloys for molten salt reactors prepared in Examples 1-2 and Comparative Examples 1-2 show that the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloys for molten salt reactors in Examples 1-2 have uniform fracture surfaces covered with uniform and fine equiaxed dimples, accompanied by a large number of tearing edges, without obvious cleavage planes or intergranular fracture characteristics, which belongs to typical ductile fracture; the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloys for molten salt reactors in Comparative Examples 1-2 exhibit typical intergranular brittle fracture characteristics, proving that the alloy of the present invention has a better match between plasticity and toughness.
[0075] Depend on Figure 3 The XRD patterns of the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloys for molten salt reactors prepared in Examples 1-2 and Comparative Examples 1-2 show that Examples 1 and 2 only exhibit characteristic peaks of Ni-enriched FCC phase and W / Mo-enriched BCC phase, without impurity peaks of TCP-type brittle phases such as σ phase and μ phase, indicating a pure phase composition. However, the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloy for molten salt reactors in Comparative Example 1, except for the FCC phase, does not show obvious characteristic peaks of the BCC reinforcing phase. The peak intensity ratio of the FCC and BCC phases in the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloy for molten salt reactors in Comparative Example 2 is significantly different from that in Examples 1-2, with a significantly reduced BCC phase peak intensity, insufficient precipitation, and poor dispersion strengthening effect. These results indicate that the Ni-W-Mo-Cr high-temperature resistant multi-principal element alloys for molten salt reactors of this invention have a pure alloy phase composition and stable microstructure, meeting the phase design objectives of this invention.
[0076] Detection Example 2 The Ni-W-Mo-Cr high-temperature resistant multi-principal element alloys for molten salt reactors prepared in Examples 1-5 and Comparative Examples 1-4 were subjected to high-temperature tensile tests at 850°C. The test methods were carried out in accordance with GB / T 228.2-2015 "Metallic materials, tensile testing—Part 2: High-temperature testing methods". The test results are shown in [Figure number missing]. Figure 4 See Table 1.
[0077] Table 1 Depend on Figure 4 As shown in Table 1, the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloys for molten salt reactors in Examples 1-5 of this invention exhibit yield strengths above 380 MPa at 850℃, with a maximum of 429.58 MPa; tensile strengths above 420 MPa, with a maximum of 447.29 MPa; and elongation after fracture of up to 55.38%. This indicates that the alloys of this invention achieve both high strength and good plasticity at 850℃, demonstrating an excellent balance between strength and plasticity.
[0078] The Ni-W-Mo-Cr high-temperature multi-principal element alloy for molten salt reactors in Comparative Example 1 has a Mo content of 18 at.%, exceeding the 10-17 at.% range of the present invention. Its yield strength is only 260.11 MPa, tensile strength is 291.33 MPa, and elongation after fracture is only 6.94%, all significantly lower than those in Examples 1-5 of the present invention. Microstructural analysis reveals that the performance degradation is due to the precipitation of brittle σ phase in the alloy, while uneven distribution of the BCC phase leads to stress concentration and premature fracture. This demonstrates that the defined composition range of the present invention is crucial for achieving superior performance.
[0079] In Comparative Example 2, the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, which underwent cold rolling instead of hot rolling, exhibited a yield strength of only 186.61 MPa, a tensile strength of 190.03 MPa, and an elongation after fracture of only 5.28%, significantly lower than those in Examples 1-5 of this invention. Microstructural analysis revealed that the performance degradation was caused by the generation of numerous dislocations and microcracks within the alloy during cold rolling, which were difficult to completely eliminate even after solution treatment, resulting in insufficient high-temperature strength and decreased plasticity. This demonstrates that the hot rolling process of this invention is a necessary technical feature for obtaining superior performance.
[0080] The Ni-W-Mo-Cr high-temperature multi-principal element alloy for molten salt reactors in Comparative Example 3 has a Cr content of 10 at.%, which is outside the Cr range of 12~20 at.% specified in this invention. Its yield strength is only 149.91 MPa, tensile strength is 252.63 MPa, and elongation after fracture is only 26.66%. Compared with Examples 1-5 of this invention, both yield strength and tensile strength are significantly reduced, indicating that the decrease in Cr content has a significant negative impact on the high-temperature strength of the alloy. Insufficient Cr content weakens the solid solution strengthening effect and reduces the driving force for BCC phase precipitation, preventing the dispersion strengthening effect of W and Mo from being fully utilized. The elongation after fracture in Comparative Example 3 is comparable to that in Example 4, indicating that the low Cr content does not impair the alloy's plasticity, but the strength is significantly reduced. This further proves that the Cr content range specified in this invention is key to obtaining high strength without sacrificing plasticity.
[0081] Comparative Example 4, using a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, reduced the number of hot rolling cycles and decreased deformation. Its yield strength was only 297.96 MPa, tensile strength was 342.83 MPa, and elongation after fracture was only 11.65%. Compared to Examples 1-5, both strength and plasticity decreased. This was due to insufficient hot rolling deformation leading to inadequate dynamic recrystallization, resulting in coarse and uneven grains in the FCC matrix. Simultaneously, the insufficient driving force for BCC phase precipitation caused it to tend to agglomerate at the original grain boundaries, forming a discontinuous network distribution rather than uniformly dispersed particles. This microstructure reduced the dispersion strengthening effect and, due to the coarsening of the BCC phase at the grain boundaries, caused stress concentration during high-temperature tensile testing, inducing early intergranular fracture and resulting in simultaneous deterioration of strength and plasticity. This demonstrates that limiting the total deformation to no less than 70% is a necessary condition for obtaining excellent mechanical properties.
[0082] The data and results above demonstrate that, through precise composition design and synergistic control of the entire preparation process, the Ni-W-Mo-Cr high-temperature resistant multi-principal-element alloy for molten salt reactors obtained in this invention forms a stable two-phase structure consisting of an FCC matrix phase and a BCC second-phase solid solution, without the precipitation of TCP-type brittle intermetallic compounds. This alloy exhibits a yield strength of 429.58 MPa, a tensile strength of 447.29 MPa, and an elongation after fracture of 55.38% at 850℃, demonstrating significantly superior overall performance compared to the comparative example. This solves the technical challenge of existing structural materials for molten salt reactors failing to balance high-temperature strength and ductility under 850℃ service conditions.
[0083] In summary, the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors and its preparation method provided by this invention, through precise composition design and coordinated control of the entire preparation process, yields an alloy material that possesses both high strength and good plasticity at a high temperature of 850℃, while also exhibiting long-term structural stability. This material can meet the stringent service requirements of thorium-based molten salt reactor hot-end structural components and has significant engineering application value.
[0084] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details of the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.
[0085] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.
[0086] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.
Claims
1. A Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, characterized in that, The Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy used in the molten salt reactor is composed of four elements: Ni, W, Mo, and Cr; among which... Based on atomic percentage, the contents of each element in the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt stacks are Ni 55~70 at.%, W 5~10 at.%, Mo 10~17 at.%, Cr 12~20 at.%, and the total of each element is 100 at.%.
2. The Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors according to claim 1, characterized in that, Based on atomic percentage, the contents of each element in the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors are Ni 60.0~65.0 at.%, W 6.5~9.5 at.%, Mo 12.0~17.0 at.%, Cr 12.0~16.0 at.%, and the total of each element is 100 at.%.
3. The Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors according to claim 1 or 2, characterized in that, The microstructure of the Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy used in the molten salt reactor consists of a Ni-enriched FCC matrix phase and a W / Mo-enriched BCC second-phase solid solution, without the precipitation of TCP-type brittle intermetallic compounds.
4. The Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors according to any one of claims 1-3, characterized in that, The Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy used in the molten salt reactor has a yield strength of not less than 350 MPa, a tensile strength of not less than 400 MPa, and an elongation after fracture of not less than 25% under tensile conditions at 850℃.
5. A method for preparing a Ni-W-Mo-Cr series high-temperature resistant multi-principal element alloy for molten salt reactors, characterized in that, The preparation method includes: 1) Under a protective atmosphere, high-purity metal raw materials of Ni, W, Mo and Cr with a purity of not less than 99.99 wt.% are melted to complete melting in a vacuum electric arc melting furnace and held at the temperature for 2 to 5 minutes to form an alloy ingot. The alloy ingot is then flipped and remelted to obtain a homogeneous alloy ingot. 2) After melting the homogeneous alloy ingot described in step 1), the as-cast alloy is obtained by copper mold casting; 3) The as-cast alloy described in step 2) is subjected to homogenization heat treatment; 4) The alloy after homogenization heat treatment in step 3) is subjected to multiple hot rolling passes; 5) The hot-rolled alloy from step 4) is subjected to solution heat treatment in a protective atmosphere to obtain the target multi-principal element alloy.
6. The preparation method according to claim 5, characterized in that, In step 1), the protective atmosphere is an argon atmosphere and / or a helium atmosphere; Preferably, the method for forming the protective atmosphere includes: first evacuating to a vacuum of 9 × 10⁻⁶. -4 Below Pa, a protective gas is introduced into the furnace cavity, and then high-purity titanium ingots are used for melting and gas absorption for 1-3 minutes; The protective gas is argon and / or helium; Based on atomic percentage, the input ratio of the high-purity Ni, W, Mo, and Cr high-purity metal raw materials is Ni 55~70 at.%, W 5~10 at.%, Mo 10~17 at.%, Cr 12~20 at.%, with the total of all elements being 100 at.%. Preferably, the input ratio of the high-purity Ni, W, Mo, and Cr high-purity metal raw materials, by atomic percentage, is Ni 60.0~65.0 at.%, W 6.5~9.5 at.%, Mo 12.0~17.0 at.%, Cr 12.0~16.0 at.%, with the total of all elements being 100 at.%. The conditions for the remelting process include: melting the alloy ingot until it is completely melted and holding it at that temperature for 2 to 5 minutes, repeating the process ≥ 8 times, preferably 8 to 12 times.
7. The preparation method according to claim 5 or 6, characterized in that, In step 2), the melting temperature is higher than the alloy liquidus line, which is 1350~1400℃; In step 3), the conditions for the homogenization heat treatment include: a temperature of 1200~1300℃, a holding time of 10~24h, and rapid water quenching after the holding time.
8. The preparation method according to any one of claims 5-7, characterized in that, In step 4), the conditions for multi-pass hot rolling include: a temperature of 1100~1250℃, holding the alloy at 1200℃ for 20~30 minutes before hot rolling, and, except for the first pass, reheating at 1200℃ for 3~8 minutes before each pass, using 3~8 passes, with a deformation of 15~30% per pass, and a total deformation of not less than 70%. In step 5), the conditions for the solution heat treatment include: a heating rate of 8~12℃ / min, a temperature of 1150~1250℃, a holding time of 1~2h, and water quenching after the holding time.
9. The preparation method according to any one of claims 5-8, characterized in that, The preparation method further includes: pretreatment of high-purity metal raw materials of Ni, W, Mo and Cr, wherein the pretreatment includes: ultrasonic cleaning for 10-20 min with anhydrous ethanol as detergent, and drying in a vacuum drying oven at a temperature of 50-70℃ for 20-40 min.
10. A Ni-W-Mo-Cr high-temperature resistant multi-principal element alloy for molten salt reactors prepared by the preparation method according to any one of claims 5-9.