A high-temperature, high-strength zirconium alloy and its manufacturing method

Abstract

A high-temperature, high-strength zirconium alloy and its manufacturing method are disclosed, belonging to the field of nuclear engineering materials. The high-temperature, high-strength zirconium alloy comprises, by weight: 1%-10% Sn, 0.1%-1% O, 0.01%-3.5% Al, and 0.01%-0.5% Si and / or 0.01%-0.5% Ge, with the remainder being Zr and unavoidable impurities. In this high-temperature, high-strength zirconium alloy, Si and / or Ge can form thermodynamically stable precipitates at high temperatures, promoting grain refinement while pinning α-Zr grain boundaries at high temperatures, inhibiting solid-state phase transformation and grain growth in the zirconium alloy matrix at high temperatures, thus enabling the alloy to maintain good mechanical properties and microstructural stability at high temperatures.

Description

Technical Field

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

[0002] Zirconium alloys have a thermal neutron absorption cross-section of only 0.18 barn, approximately 1 / 20th that of stainless steel. Furthermore, zirconium alloys exhibit excellent corrosion resistance in aqueous environments below 350°C and good compatibility with uranium oxide pellets. Therefore, they are widely used in the manufacture of fuel rod cladding in water-cooled reactors. With the introduction of the fourth-generation nuclear energy system concept, the maximum operating temperature of new reactors may increase to 550°C-700°C, and existing zirconium alloys are gradually becoming insufficient to meet the design requirements of these new reactors. Therefore, providing a zirconium alloy with superior heat resistance is of positive significance for the development of the nuclear power industry. Summary of the Invention

[0003] The purpose of this invention is to provide a high-temperature, high-strength zirconium alloy, thereby increasing the service temperature of zirconium alloys. This invention also provides a method for manufacturing this high-temperature, high-strength zirconium alloy.

[0004] According to one aspect of the present invention, a high-temperature, high-strength zirconium alloy is provided, comprising, by weight: 1%-10% Sn, 0.1%-1% O, 0.01%-3.5% Al, and 0.01%-0.5% Si and / or 0.01%-0.5% Ge, with the remainder being Zr and unavoidable impurities.

[0005] Si / Ge elements preferentially precipitate during alloy solidification, acting as nucleating agents to induce other alloying elements to form a more uniform and dispersed second phase. At the same time, the Si / Ge precipitates exhibit good stability under high-temperature conditions, effectively pinning grain boundaries, refining the zirconium alloy microstructure, and improving the stability of the zirconium alloy microstructure under high-temperature service conditions, while inhibiting grain growth.

[0006] Furthermore, in some embodiments, it also includes no more than 0.3% Cr, no more than 0.3% Fe, no more than 0.1% V and no more than 0.2% Mo.

[0007] Cr, Fe, V, and Mo elements can participate in the formation of the second phase, further refining the grains and improving the strength of zirconium alloys.

[0008] Furthermore, in some embodiments, the high-temperature high-strength zirconium alloy contains, by weight, 1%-10% Sn, 0.1%-0.3% O, 0.01%-0.3% Al, and 0.1%-0.3% Si and / or 0.1%-0.3% Ge.

[0009] Furthermore, in some embodiments, the matrix of the high-temperature high-strength zirconium alloy is lath-shaped α-Zr, wherein Zr3Si and / or Zr3Ge second-phase particles are uniformly distributed.

[0010] Furthermore, in some embodiments, the average thickness of the lath-shaped α-Zr is 1 μm-5 μm, and the diameter of the second phase particles is 0.2 μm-1 μm.

[0011] Furthermore, in some embodiments, the high-temperature high-strength zirconium alloy has a yield strength of not less than 100 MPa at 600°C and a grain size increase of not more than 30% after isothermal treatment at 850°C for 1000 hours.

[0012] According to another aspect of the present invention, a method for manufacturing a high-temperature, high-strength zirconium alloy is provided, for manufacturing the high-temperature, high-strength zirconium alloy provided in any of the foregoing embodiments, the method specifically includes the following steps:

[0013] Step a): Provide a zirconium alloy ingot that conforms to the composition of the high-temperature and high-strength zirconium alloy, and homogenize the alloy ingot by heat preservation in the β phase region;

[0014] Step b): The zirconium alloy ingot is hot-forged or hot-extruded in the β-phase region to obtain a hot-deformed blank;

[0015] Step c): The hot-deformed blank is subjected to recrystallization annealing at 600℃-950℃ to obtain an annealed blank;

[0016] Step d): The annealed billet is cold-rolled with a deformation of 10%-80%;

[0017] Step e): Repeat steps c) and d) until the dimensions of the annealed billet meet the design requirements to obtain a cold-rolled billet;

[0018] Step f): The cold-rolled billet is heated to the β phase region for isothermal treatment, and then cooled to 700°C in the furnace under the protection of an inert gas atmosphere, followed by water quenching to obtain a high-temperature and high-strength zirconium alloy finished product.

[0019] Further, in some embodiments, in step a), the zirconium alloy ingot is manufactured by: providing raw material powder, mixing the raw material powder evenly and pressing it into a green billet, the relative density of the green billet being not less than 75%; vacuum sintering the green billet at 1000°C to obtain a sintered billet; welding auxiliary electrodes onto the sintered billet, and producing the zirconium alloy ingot by a vacuum consumable melting process.

[0020] Furthermore, in some embodiments, in step c), the recrystallization annealing time is 0.5h-2.5h.

[0021] Furthermore, in some embodiments, step f) further includes sandblasting, pickling, and polishing steps after water quenching. Attached Figure Description

[0022] Figure 1 Here is a scanning electron microscope image of the microstructure of a high-temperature, high-strength zirconium alloy in one embodiment;

[0023] Figure 2 These are scanning electron microscope images of the microstructure of a Zr-4 alloy in a pair of proportions.

[0024] The purpose of the above figures 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. Detailed Implementation

[0025] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0026] 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 causing structural conflicts.

[0027] In this description, terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating relative importance or limiting the number, specific order, or primary / secondary relationship of the described technical features. In this description, "multiple" means at least two.

[0028] Zirconium alloys have a thermal neutron absorption cross-section of only 0.18 barn, approximately 1 / 20th that of stainless steel. They exhibit excellent corrosion resistance in a water environment of 300℃-350℃. Furthermore, zirconium alloys have good compatibility with uranium oxide pellets commonly used in the nuclear power industry. Therefore, since the 1950s, zirconium alloys such as Zircaloy-2, Zircaloy-4, Zirlo, and M5 have been widely used in water-cooled reactors, currently accounting for over 90% of light water reactor fuel cladding. However, with the introduction of the Generation IV (Gen IV) nuclear energy system concept, reactor design operating temperatures are continuously increasing: peak cladding temperatures in sodium-cooled fast reactors reach 550℃, in supercritical water reactors they reach 600℃, and in high-temperature gas-cooled reactors, the required cladding temperatures can even exceed 700℃. Within this temperature range, the mechanical properties of existing nuclear-grade zirconium alloys will significantly degrade, making it difficult to meet reactor design requirements.

[0029] To overcome the aforementioned shortcomings of the prior art, one embodiment of the present invention provides a high-temperature, high-strength zirconium alloy that maintains high mechanical properties above 600°C and maintains a stable microstructure during long-term service above 800°C. This high-temperature, high-strength zirconium alloy, by weight, comprises 1%-10% Sn, 0.1%-1% O, 0.01%-3.5% Al, and 0.01%-0.5% Si and / or 0.01%-0.5% Ge, with the remainder being Zr and unavoidable impurities. In a preferred embodiment, the zirconium alloy further comprises no more than 0.3% Cr, no more than 0.3% Fe, no more than 0.1% V, and no more than 0.2% Mo as second-phase forming elements. The microstructure of this zirconium alloy is lath-shaped α-Zr, wherein Zr3Si and / or Zr3Ge second-phase particles are distributed. The average thickness of the lath-shaped α-Zr is 1 μm-5 μm, and the diameter of the second-phase particles is 0.2 μm-1 μm.

[0030] In this alloy, Si and / or Ge elements exhibit high precipitation temperatures in the Zr matrix; for example, according to thermodynamic phase diagram analysis, Zr3Si begins to precipitate below 1540℃. During the solidification and cooling process of the zirconium alloy matrix, the preferential precipitation of Si and / or Ge-containing phases acts as a nucleating agent, inducing other alloying elements to further form uniformly dispersed precipitates. Simultaneously, Zr3Si and / or Zr3Ge effectively pin grain boundaries, refining the Zr matrix grains. Under high-temperature conditions, Zr3Si and / or Zr3Ge maintain morphological stability, effectively suppressing grain boundary migration in the Zr matrix under high-temperature conditions and inhibiting grain growth in the zirconium alloy. This high-temperature, high-strength zirconium alloy exhibits a yield strength of not less than 100 MPa at 600℃, and after isothermal treatment at 850℃ for 1000 hours, the grain size growth does not exceed 30%.

[0031] The high-temperature, high-strength zirconium alloy provided in the above embodiments can be manufactured by a method for manufacturing high-temperature, high-strength zirconium alloy provided in another aspect of the present invention, the method specifically including the following steps:

[0032] Step a): Provide a zirconium alloy ingot conforming to the zirconium alloy composition, and heat it to the β phase region for homogenization treatment, the homogenization treatment time being at least 1 hour. In a preferred embodiment, the zirconium alloy ingot can be prepared by vacuum arc remelting or vacuum induction melting processes.

[0033] In a preferred embodiment, the specific steps for preparing zirconium alloy ingots via vacuum arc remelting are as follows: First, using sponge zirconium, zirconium oxide, pure Sn, pure Al, and Al-Si alloy and / or Al / Ge alloy powders as raw material powders, the raw material powders are mixed uniformly using a mixer and pressed into green billets with a relative density of not less than 75%. The green billets are then vacuum sintered at 1000°C to obtain sintered billets. Subsequently, auxiliary electrodes are welded onto the sintered billets, and zirconium alloy ingots are produced via vacuum arc remelting.

[0034] Step b): The zirconium alloy ingot is hot-forged or hot-extruded in the β-phase region to obtain a hot-deformed blank. Depending on the design requirements, the hot-deformed blank can be a plate, tube, bar, or other structural profile.

[0035] Step c): The hot-deformed blank is subjected to recrystallization annealing at 600℃-950℃ to obtain an annealed blank. The holding time for recrystallization annealing is 0.5h-2.5h.

[0036] Step d): The annealed blank is cold rolled, and the deformation during cold rolling is 10%-80%.

[0037] Step e): Repeat steps c) and d) until the dimensions of the annealed blank meet the design requirements, and obtain the cold-rolled blank.

[0038] Step f): The cold-rolled billet is heated to the β phase region for isothermal treatment and held for at least 0.5 hours. Then, inert gas is introduced into the heating furnace for protection. When the cold-rolled billet is cooled to 700°C in the furnace, it is taken out and water-quenched. Then, it is sandblasted, pickled and polished to remove the surface oxide film and obtain the high-temperature high-strength zirconium alloy finished product.

[0039] In a first preferred embodiment, a high-temperature, high-strength zirconium alloy containing 5% Sn, 3% Al, 0.3% O, and 0.3% Si by weight, with the remainder being Zr, is prepared through the following process:

[0040] Using sponge zirconium, pure Sn, pure Al, Al-Si alloy, and zirconium oxide powder as raw materials, a V-type mixer was used to mix the powder at 30 rpm for 30 min under argon protection. The mixed powder was then loaded into a mold and pressed at 280 MPa for 15 s to produce a green billet with a relative density of 82%.

[0041] The green billet was subjected to vacuum sintering at 1000℃ for 4 hours, followed by vacuum arc remelting to obtain zirconium alloy ingots.

[0042] Based on phase diagram analysis, the α / β phase transformation temperature of the zirconium alloy with this composition is 930℃. The zirconium alloy ingot was homogenized at 1180℃ for 2 hours and then air-cooled to room temperature.

[0043] Subsequently, the zirconium alloy ingot was forged into a slab of about 10 cm at 1050 degrees Celsius.

[0044] Next, recrystallization annealing is carried out at 700℃ for 1 hour, followed by cold rolling with a deformation of 30%-80%. The annealing-cold rolling process is repeated 3-4 times until a sheet with the designed dimensions is obtained.

[0045] Next, the plate is placed in a heating furnace and vacuum heated to 1050℃ and held for 1 hour. Then, an inert gas is introduced for protection. After cooling to 700℃ in the furnace, it is taken out and water-quenched. After sandblasting, pickling and polishing to remove the surface oxide layer, the high-temperature high-strength zirconium alloy plate is obtained.

[0046] The microstructure of the zirconium alloy plate is as follows: Figure 1 As shown, a lath-shaped α-Zr quenched structure (Widmanstätten) matrix 1 with a thickness of 1 μm has a thickness of 1 μm-5 μm. The matrix structure is uniform in composition without segregation, and Zr3Si precipitates 2 with a diameter of 0.2 μm-1 μm are uniformly distributed in the matrix structure.

[0047] The zirconium alloy plate has a yield strength (RP0.2) of 200 MPa at 600℃, and after isothermal treatment at 850℃ for 1000 h, the grain size increases by no more than 30%, and no β phase precipitation occurs.

[0048] In a second preferred embodiment, a high-temperature, high-strength zirconium alloy containing 1% Sn, 0.01% Al, 0.1% O, and 0.1% Si by weight, with the remainder being Zr, is prepared through the following process:

[0049] Using sponge zirconium, pure Sn, pure Al, Al-Si alloy, and zirconium oxide powder as raw materials, a V-type mixer was used to mix the powder at 30 rpm for 30 min under argon protection. The mixed powder was then loaded into a mold and pressed at 280 MPa for 15 s to produce a green billet with a relative density of 82%.

[0050] The green billet was subjected to vacuum sintering at 1000℃ for 4 hours, followed by vacuum arc remelting to obtain zirconium alloy ingots.

[0051] Based on phase diagram analysis, the α / β phase transformation temperature of the zirconium alloy with this composition is 880℃. The zirconium alloy ingot was homogenized at 1180℃ for 2 hours and then air-cooled to room temperature.

[0052] Subsequently, the zirconium alloy ingot was forged into a slab of about 10 cm at 1050 degrees Celsius.

[0053] Next, recrystallization annealing is carried out at 700℃ for 1 hour, followed by cold rolling with a deformation of 30%-80%. The annealing-cold rolling process is repeated 3-4 times until a sheet with the designed dimensions is obtained.

[0054] Next, the plate is placed in a heating furnace and vacuum heated to 1050℃ and held for 1 hour. Then, an inert gas is introduced for protection. After cooling to 700℃ in the furnace, it is taken out and water-quenched. After sandblasting, pickling and polishing to remove the surface oxide layer, the high-temperature high-strength zirconium alloy plate is obtained.

[0055] The zirconium alloy plate has a lath-shaped α-Zr quenched structure (Widmanstätten) matrix with a thickness of 1 μm. The lath structure of the matrix has a thickness of 1 μm-5 μm. The matrix has a uniform composition without segregation and Zr3Si precipitates with a diameter of 0.2 μm-1 μm are uniformly distributed in the matrix.

[0056] The zirconium alloy plate has a yield strength (RP0.2) of 130 MPa at 600℃, and after isothermal treatment at 850℃ for 1000 h, the grain size increases by no more than 30%, and no β phase precipitation occurs.

[0057] In the third preferred embodiment, a high-temperature, high-strength zirconium alloy containing 10% Sn, 0.01% Al, 0.1% O, and 0.1% Si by weight, with the remainder being Zr, is prepared through the following process:

[0058] Using sponge zirconium, pure Sn, pure Al, Al-Si alloy, and zirconium oxide powder as raw materials, a V-type mixer was used to mix the powder at 30 rpm for 30 min under argon protection. The mixed powder was then loaded into a mold and pressed at 280 MPa for 15 s to produce a green billet with a relative density of 82%.

[0059] The green billet was subjected to vacuum sintering at 1000℃ for 4 hours, followed by vacuum arc remelting to obtain zirconium alloy ingots.

[0060] Based on phase diagram analysis, the α / β phase transformation temperature of the zirconium alloy with this composition is 970℃. The zirconium alloy ingot was homogenized at 1180℃ for 2 hours and then air-cooled to room temperature.

[0061] Subsequently, the zirconium alloy ingot was forged into a slab of about 10 cm at 1050 degrees Celsius.

[0062] Next, recrystallization annealing is carried out at 940℃ for 1 hour, followed by cold rolling with a deformation of 30%-80%. The annealing-cold rolling process is repeated 3-4 times until a sheet with the designed dimensions is obtained.

[0063] Next, the plate is placed in a heating furnace and vacuum heated to 1050℃ and held for 1 hour. Then, an inert gas is introduced for protection. After cooling to 700℃ in the furnace, it is taken out and water-quenched. After sandblasting, pickling and polishing to remove the surface oxide layer, the high-temperature high-strength zirconium alloy plate is obtained.

[0064] The zirconium alloy plate has a lath-shaped α-Zr quenched structure (Widmanstätten) matrix with a thickness of 1 μm. The lath structure of the matrix has a thickness of 1 μm-5 μm. The matrix has a uniform composition without segregation and Zr3Si precipitates with a diameter of 0.2 μm-1 μm are uniformly distributed in the matrix.

[0065] The zirconium alloy plate has a yield strength (RP0.2) of 250 MPa at 600℃; after isothermal treatment at 850℃ for 1000 h, the grain size increases by no more than 30%; after isothermal treatment, Zr4Sn precipitates in the microstructure, but no β phase precipitates.

[0066] In the first comparative example, a commercial Zr-4 alloy with a composition of 1.5% Sn, 0.2% Fe, 0.1% Cr, 0.1% O, and the remainder Zr was used as raw material. The finished sheet was obtained through forging, multiple cold rolling deformation processes, and annealing at 580℃ for 3 hours. Its microstructure is as follows: Figure 2 As shown. The comparative zirconium alloy sheet has a matrix microstructure of α-Zr equiaxed crystals with a grain size of approximately 10 μm and exhibits a distinct texture (α-close-packed hexagonal grains). <c>(Axis points to the normal direction of the plate). No obvious compositional segregation is observed in the matrix, but Zr-Fe-Cr precipitates are present. Testing showed that the yield strength of this zirconium alloy plate at 600℃ was 50 MPa; after isothermal treatment at 850℃ for 1000 h, significant β-phase precipitation occurred, and α-phase grains grew considerably. The high-temperature mechanical properties and microstructural stability of this comparative zirconium alloy plate are significantly insufficient.

[0067] In the second comparative example, a commercial Zr-4 alloy with a composition of 1.5% Sn, 0.2% Fe, 0.1% Cr, 0.1% O, and the remainder Zr was used as raw material. The finished sheet was obtained after forging, multiple cold rolling deformation processes, annealing at 1150℃ for 1 hour, and water quenching. The matrix structure of this comparative example zirconium alloy sheet was a banded α-Zr quenched structure (Widmanstätten), with a grain size of approximately 1μm-5μm. The matrix structure was isotropic, with no obvious compositional segregation. Testing showed that the yield strength of this zirconium alloy sheet at 600℃ was 60MPa; after isothermal treatment at 850℃ for 1000 hours, the Widmanstätten structure significantly grew and transformed from banded to equiaxed crystals, with obvious β-phase precipitation. The high-temperature mechanical properties and microstructural stability of this comparative example zirconium alloy sheet were significantly insufficient.

[0068] 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, optimizations or equivalent substitutions of the technical features involved in the present invention, as well as combinations of implementation methods in different embodiments without causing a conflict of principles, all fall within the protection scope of the present invention.< / c>

Claims

1. A high-temperature, high-strength zirconium alloy, characterized in that, The high-temperature, high-strength zirconium alloy comprises, by weight: 1%-10% Sn, 0.1%-1% O, 0.01%-3.5% Al, and 0.01%-0.5% Si and / or 0.01%-0.5% Ge, with the remainder being Zr and unavoidable impurities; the matrix of the high-temperature, high-strength zirconium alloy is lath-shaped α-Zr, wherein Zr3Si and / or Zr3Ge second-phase particles are uniformly distributed; the average thickness of the lath-shaped α-Zr is 1μm-5μm, and the diameter of the second-phase particles is 0.2μm-1μm; the high-temperature, high-strength zirconium alloy has a yield strength of not less than 100MPa at 600℃, and a grain size increase of not more than 30% after isothermal treatment at 850℃ for 1000h.

2. The high-temperature, high-strength zirconium alloy according to claim 1, characterized in that, It also includes no more than 0.3% Cr, no more than 0.3% Fe, no more than 0.1% V and no more than 0.2% Mo.

3. The high-temperature, high-strength zirconium alloy according to claim 1, characterized in that, The high-temperature, high-strength zirconium alloy contains, by weight, 1%-10% Sn, 0.1%-0.3% O, 0.01%-0.3% Al, and 0.1%-0.3% Si and / or 0.1%-0.3% Ge.

4. A method for manufacturing a high-temperature, high-strength zirconium alloy, characterized in that, For manufacturing high-temperature, high-strength zirconium alloys as described in any one of claims 1 to 3, the method comprises the following steps: Step a): Provide a zirconium alloy ingot that conforms to the composition of the high-temperature and high-strength zirconium alloy, and homogenize the alloy ingot by heat preservation in the β phase region; Step b): The zirconium alloy ingot is hot-forged or hot-extruded in the β-phase region to obtain a hot-deformed blank; Step c): The hot-deformed blank is subjected to recrystallization annealing at 600℃-950℃ to obtain an annealed blank; Step d): The annealed billet is cold-rolled with a deformation of 10%-80%; Step e): Repeat steps c) and d) until the dimensions of the annealed billet meet the design requirements to obtain a cold-rolled billet; Step f): The cold-rolled billet is heated to the β phase region for isothermal treatment, and then cooled to 700°C in the furnace under the protection of an inert gas atmosphere, followed by water quenching to obtain a high-temperature and high-strength zirconium alloy finished product.

5. The method for manufacturing high-temperature, high-strength zirconium alloy according to claim 4, characterized in that, In step a), the zirconium alloy ingot is manufactured by the following method: providing raw material powder, mixing the raw material powder evenly and pressing it into a green billet, the relative density of the green billet being not less than 75%; vacuum sintering the green billet at 1000°C to obtain a sintered billet; welding auxiliary electrodes onto the sintered billet, and producing the zirconium alloy ingot by vacuum consumable melting process.

6. The method for manufacturing high-temperature, high-strength zirconium alloy according to claim 4 or 5, characterized in that, In step c), the recrystallization annealing time is 0.5h-2.5h.

7. The method for manufacturing high-temperature, high-strength zirconium alloy according to claim 4 or 5, characterized in that, In step f), after water quenching, the process also includes sandblasting, pickling, and polishing.

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