Creep-resistant zirconium alloy and method of making same

Abstract

The application relates to an anti-creep zirconium alloy and a manufacturing method thereof, and belongs to the field of nuclear engineering materials. The manufacturing method of the anti-creep zirconium alloy comprises the following steps: providing a zirconium alloy raw material containing 0.1%-3% of an oxide forming element, and processing the zirconium alloy raw material into a zirconium alloy blank with a thickness of not more than 2 mm; heating the zirconium alloy blank to 700 DEG C-900 DEG C in an argon-oxygen mixed atmosphere with an oxygen partial pressure of 10 ‑5 MPa-10 ‑3 MPa for 4h-8h, and then continuing to heat the zirconium alloy blank in pure argon for 2h to perform homogenization annealing treatment, so as to obtain an anti-creep zirconium alloy finished product. The method can form uniformly dispersed oxide particles in the zirconium alloy structure, effectively improves the anti-creep performance of the zirconium alloy, and reduces the creep rate.

Description

Technical Field

[0001] This invention belongs to the field of nuclear engineering materials, specifically relating to a creep-resistant zirconium alloy and its manufacturing method. Background Technology

[0002] Currently, zirconium alloys are the most widely used structural materials in pressurized water reactor fuel assemblies. Zr-2, Zr-4, Zirlo, and M5 alloys exhibit excellent corrosion resistance in aqueous media at 300℃-350℃, good compatibility with uranium oxide, and a thermal neutron absorption cross-section of only 0.18 barn, approximately 1 / 20 that of stainless steel. After 70 years of commercial operation, zirconium alloy metallurgical processes are mature, the supply chain is well-established, and comprehensive irradiation data has been accumulated. Therefore, zirconium alloys are widely used in the manufacture of fuel rod cladding, fuel assembly grids, and other structures.

[0003] However, with the development of civilian nuclear power technology, the operating temperature of reactors in new nuclear power plants is getting higher and higher. In supercritical water reactors (SCWRs), the peak temperature of the fuel rod cladding can reach 600℃. Simultaneously, as industry requirements for nuclear power plant safety increase, fuel rod cladding is also required to have a longer lifespan under accident conditions. Currently, conventional zirconium alloys used in nuclear power plants exhibit significantly increased creep rates above 500℃, and significant grain growth occurs in the alloy microstructure, leading to significant changes in microstructure and overall performance, which cannot meet the design requirements of new reactors.

[0004] In the field of high-temperature materials, some technical solutions involve introducing dispersed oxide particles into alloys to improve the high-temperature mechanical properties, creep resistance, and radiation resistance of the materials through oxide dispersion strengthening (ODS) mechanisms. However, the current manufacturing process for ODS alloys is relatively complex. Preparing ODS alloys requires complex processes such as high-energy ball milling and hot extrusion, resulting in high manufacturing costs. Furthermore, oxide particles are prone to agglomeration during the forming process, causing localized embrittlement and leading to poor stability between different batches of ODS alloys. This is particularly true when processing them into thin-walled structures of approximately 1 mm, where insufficient microstructure uniformity can cause cracking. Additionally, zirconium alloy powder is chemically highly reactive and can spontaneously combust in air. These factors collectively make it difficult to directly apply the ODS process to the manufacture of zirconium alloy fuel rod cladding. Summary of the Invention

[0005] The purpose of this invention is to provide a method for manufacturing a creep-resistant zirconium alloy, thereby improving the service life of zirconium alloy structures under high-temperature conditions. This invention also provides a creep-resistant zirconium alloy.

[0006] According to one embodiment of the present invention, a method for manufacturing a creep-resistant zirconium alloy is provided, the method comprising the following steps:

[0007] Step a): Provide zirconium alloy raw material, wherein the zirconium alloy raw material contains 0.1%-3% oxide forming elements by weight, wherein the oxide forming elements include one or a combination of several of Y, Ce, and La; and melt and deform the zirconium alloy raw material to obtain plates, tubes or strips with a thickness not exceeding 2mm as zirconium alloy billets.

[0008] Step b): The zirconium alloy billet is heated to 700℃-900℃ and held for 4h-8h in a mixed atmosphere of argon and oxygen, wherein the partial pressure of oxygen in the mixed atmosphere is 10. -5 MPa-10 -3 MPa;

[0009] Step c): Continue heating in pure argon gas for 2 hours to perform homogenization annealing treatment and obtain creep-resistant zirconium alloy finished product.

[0010] This method involves adding oxide-forming elements to the zirconium alloy billet, ensuring their uniform dispersion within the billet's microstructure. Through slow oxidation heating under low-oxygen conditions, oxygen is allowed to penetrate the microstructure and combine with the oxide-forming elements, forming dispersed oxide particles, thus achieving the desired effect of pre-forming followed by ODS (Oxygen Deposition and Separation). Compared to traditional ODS alloy manufacturing processes, this method eliminates the need for complex processes such as high-energy ball milling and sintering, effectively reducing manufacturing costs, preventing material embrittlement caused by oxide particle aggregation during sintering, and improving the mechanical properties of the finished alloy.

[0011] Furthermore, in some embodiments, in step a), the oxide forming element includes one or a combination of Al, Mg, and Ca.

[0012] Furthermore, in some embodiments, a step of removing the oxide layer on the surface of the zirconium alloy blank is included before step b).

[0013] Furthermore, in some embodiments, the zirconium alloy matrix obtained in step c) is α-Zr, wherein oxide particles of the oxide-forming elements are dispersedly distributed therein.

[0014] Furthermore, in some embodiments, in step c), the steady-state creep rate of the zirconium alloy product under a temperature of 385°C and a load of 108MPa does not exceed 0.0025% / h.

[0015] Furthermore, in some embodiments, steps b) and c) are performed in an atmosphere furnace.

[0016] Furthermore, in some embodiments, in step c), pure argon gas is introduced into the atmosphere furnace to remove oxygen from the atmosphere furnace.

[0017] According to another aspect of the present invention, a creep-resistant zirconium alloy is provided, which is manufactured using the manufacturing method of the creep-resistant zirconium alloy provided in any of the foregoing embodiments, wherein the microstructure of the creep-resistant zirconium alloy is α-Zr, wherein oxide particles of the oxide-forming elements are dispersedly distributed therein. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the manufacturing process of the creep-resistant zirconium alloy in one embodiment;

[0019] Figure 2 This is a transmission electron microscope image of the microstructure of a creep-resistant zirconium alloy in one embodiment.

[0020] The purpose of the above-described drawings is to provide a detailed description of the invention so that those skilled in the art can understand the technical concept of the invention, and not to limit the invention. For the sake of brevity, the above-described drawings only schematically depict the structures related to the technical features of the invention, and do not depict the complete structure and all details strictly according to actual scale. Detailed Implementation

[0021] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0022] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive, independent, or alternative embodiments. Those skilled in the art will understand that the embodiments herein can be combined with other embodiments without structural conflict. In the description herein, "a plurality of" means at least two.

[0023] To overcome the aforementioned shortcomings of the prior art, one embodiment of the present invention provides a method for manufacturing a creep-resistant zirconium alloy. This method simplifies the forming process of ODS zirconium alloys by employing a process route of first forming and then oxidizing, improves the uniformity of the microstructure, and effectively enhances the creep resistance of the zirconium alloy. Specifically, as... Figure 1 As shown, the method includes the following steps:

[0024] Step a): Provide zirconium alloy raw materials. In addition to Zr and common zirconium alloy alloying elements Sn, Nb, Fe, and Cr, the zirconium alloy raw materials also contain 0.1%-3% by weight of oxide-forming elements. These oxide-forming elements are elements with an oxide formation enthalpy lower than that of zirconium oxide, including one or more combinations of Y, Ce, and La. In some embodiments, the oxide-forming elements may also include one or more combinations of Al, Mg, and Ca. After melting the zirconium alloy raw materials into ingots, they are extruded and rolled in multiple passes to obtain plates, tubes, or strips with a thickness not exceeding 2 mm. The surface oxide layer is removed by sandblasting, pickling, and polishing, and the resulting material is used as zirconium alloy billet.

[0025] Step b): The zirconium alloy billet is placed in an atmosphere furnace and heated to 700℃-900℃ in a mixed atmosphere of argon and oxygen for 4-8 hours of low-oxidation aging treatment. Specifically, the oxygen partial pressure in the mixed atmosphere is 10. -5 MPa-10 -3 MPa. Aging treatment in a low-oxygen environment can prevent the rapid oxidation of the zirconium alloy billet surface, which forms a dense oxide film that hinders the diffusion of oxygen elements. It also induces oxygen elements to enter the zirconium alloy matrix and selectively combine with oxide-forming elements to form uniformly dispersed oxide particles.

[0026] If the oxygen content in the mixed atmosphere is too high, it will lead to the formation of a continuous and dense zirconia layer; if the oxygen content is too low, it will lead to a low oxidation rate. If the holding time is too short, the oxidation will be insufficient; if the holding time is too long, the grain size may be too large.

[0027] Step c): Pure argon gas is introduced into the atmosphere furnace to fully remove residual oxygen. The furnace is then held at a pure argon atmosphere for 2 hours for homogenization annealing to obtain the creep-resistant zirconium alloy. The microstructure of the finished zirconium alloy is α-Zr, with dispersed oxide particles of oxide-forming elements. These oxide particles exhibit good stability, acting as defect traps to effectively improve the zirconium alloy's resistance to radiation damage. Furthermore, they effectively act as pinning agents, inhibiting radiation growth and improving the radiation creep resistance of the alloy matrix.

[0028] In Example 1, the zirconium alloy raw material comprises 1.5% Sn, 0.2% Fe, 0.1% Cr, 0.3% Y and 0.13% O. The zirconium alloy raw material is melted, forged and subjected to multiple annealing and cold rolling processes to obtain a zirconium alloy plate with a thickness of about 1 mm. The surface of the zirconium alloy plate is then sandblasted, pickled and polished to obtain the zirconium alloy billet.

[0029] Next, the zirconium alloy plate is placed into the atmosphere furnace, and heated at an oxygen partial pressure of 10. -3A aging treatment is performed by heating the zirconium alloy plate to 800℃ in a mixed atmosphere of argon and oxygen at a pressure of MPa and holding for 6 hours. During the holding process, oxygen enters the microstructure of the zirconium alloy plate. Because the enthalpy of formation of Y₂O₃ is lower than that of zirconium oxide, the oxidation reaction rate decreases under low oxygen partial pressure, preventing the formation of a dense oxide film on the surface of the zirconium alloy plate. This allows the oxygen entering the microstructure to preferentially combine with Y to form Y₂O₃ particles. Since Y is uniformly distributed within the zirconium alloy plate microstructure during melting, the formed Y₂O₃ particles are also uniformly dispersed. Subsequently, pure argon is introduced into the furnace to completely remove the remaining oxygen, and the temperature is maintained for another 2 hours for homogenization, resulting in the finished creep-resistant zirconium alloy plate. Figure 2 As shown, the microstructure of the creep-resistant zirconium alloy plate is α-Zr, with Y2O3 particles dispersed within it. A creep test was conducted at 385℃ with a load of 108 MPa, and the steady-state creep rate was measured to be 0.00207% / h.

[0030] In the comparative example, a zirconium alloy (commercial Zr-4 alloy) containing 1.5% Sn, 0.2% Fe, 0.1% Cr, and 0.1% O was used as the raw material. After forging and multiple cold rolling, it was annealed at 580°C for 3 hours to obtain a comparative zirconium alloy plate with a thickness of approximately 1 mm. Since no oxide-forming elements were added to the Zr-4 alloy, and Zr itself has a strong affinity for oxygen, an oxide layer formed on the alloy surface during processing, but no effective oxide dispersion strengthening was formed inside the alloy. A creep test was conducted on the comparative zirconium alloy plate at 385°C under a load of 108 MPa, and its steady-state creep rate reached 0.00417% / h, twice that of Example 1.

[0031] By comparing the above embodiments and comparative examples, it can be seen that the manufacturing method of the creep-resistant zirconium alloy provided by the embodiments of the present invention can form uniformly dispersed oxide particles in the zirconium alloy structure, without the need for complex powder metallurgy methods, effectively reducing the manufacturing cost of ODS zirconium alloy and facilitating the mass production of thin-walled ODS zirconium alloy parts. By introducing uniformly dispersed oxide particles into the zirconium alloy structure, the high-temperature mechanical properties and creep resistance of the zirconium alloy are effectively improved. Compared with commercial Zr-4 alloy, its creep rate is significantly reduced. Using this zirconium alloy to manufacture fuel rod cladding, grids, strips, and other structures in fuel assemblies can effectively improve the reliability and service life of pressurized water reactor fuel assemblies.

[0032] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent substitution of the method steps involved, as well as combination of implementation methods in different embodiments without causing structural and principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a creep-resistant zirconium alloy, characterized in that, Includes the following steps: Step a): Provide zirconium alloy raw material, wherein the zirconium alloy raw material contains 0.1%-3% oxide forming elements by weight, wherein the oxide forming elements include one or a combination of several of Y, Ce, and La; and melt and deform the zirconium alloy raw material to obtain plates, tubes or strips with a thickness not exceeding 2mm as zirconium alloy billets. Step b): The zirconium alloy billet is heated to 700℃-900℃ and held for 4h-8h in a mixed atmosphere of argon and oxygen, wherein the partial pressure of oxygen in the mixed atmosphere is 10. -5 MPa-10 -3 MPa; Step c): Continue to hold in pure argon for 2 hours for homogenization annealing to obtain creep-resistant zirconium alloy finished product. The matrix of the zirconium alloy finished product is α-Zr, in which oxide particles of the oxide forming element are dispersed. The steady-state creep rate of the zirconium alloy finished product under a temperature of 385℃ and a load of 108MPa does not exceed 0.0025% / h.

2. The method for manufacturing the creep-resistant zirconium alloy according to claim 1, characterized in that, In step a), the oxide forming elements also include one or more of Al, Mg, and Ca.

3. The method for manufacturing the creep-resistant zirconium alloy according to claim 1 or 2, characterized in that, The process includes a step of removing the oxide layer from the surface of the zirconium alloy billet before step b).

4. The method for manufacturing the creep-resistant zirconium alloy according to claim 1 or 2, characterized in that, Steps b) and c) are performed in an atmosphere furnace.

5. The method for manufacturing the creep-resistant zirconium alloy according to claim 4, characterized in that, In step c), pure argon gas is introduced into the atmosphere furnace to remove the oxygen inside the atmosphere furnace.

6. A creep-resistant zirconium alloy, characterized in that, The creep-resistant zirconium alloy is manufactured using the manufacturing method described in any one of claims 1 to 5, wherein the microstructure of the creep-resistant zirconium alloy is α-Zr, wherein oxide particles of the oxide forming urea are dispersedly distributed therein.

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