A Zr-based alloy with enhanced deformation-induced martensitic transformation

Abstract

The present invention discloses a Zr-based alloy with enhanced deformation-induced martensitic transformation, belonging to the technical field of alloys. The Zr-based alloy described in the present invention comprises components with the following mass percentages: Zr is 54.00% - 59.00%, Co is 35.00% - 38.00%, Nb is 1.00% - 4.00%, Ta is 2.00% - 7.00%, and the rest are inevitable trace impurities; through arc melting, a relatively large volume fraction of B2 phase precipitates during the suction casting process, and during the subsequent compression process, deformation-induced martensitic transformation from B2 to B33 occurs. At the same time, by adding Nb and Ta elements, the volume fraction ratios of the B2 phase and other brittle phases such as Zr₂Co are regulated. Utilizing the above characteristics, the yield strength and ultimate compressive strength of the alloy are enhanced. At the same time, when the ultimate compressive strain reaches more than 75.00%, the alloy still does not fracture, and the work hardening ability is remarkable, significantly improving the mechanical properties of the alloy, which can meet the requirements of high-stress scenarios.

Description

Technical Field

[0001] The present invention belongs to the technical field of alloys, and particularly relates to a Zr-based alloy enhanced by deformation-induced martensitic transformation. Background Art

[0002] The core structure materials (fuel cladding, pressure tube, support, and channel tube) of water-cooled nuclear reactors work in a relatively harsh environment: Firstly, the working temperature is relatively high, and the operating temperature can still reach 360°C even under the condition of having a coolant; Secondly, the working stress is high, especially the pressure tube will bear a large stress; Thirdly, chemical actions such as oxidation and corrosion. Therefore, the core structure materials need to possess the following comprehensive properties: (1) relatively high thermal stability, that is, the corrosion resistance at high temperatures; (2) high thermal strength; (3) low thermal atomic neutron absorption cross-section and good compatibility with nuclear fuel; (4) good processability. Zr-based alloys have good corrosion resistance in high-temperature and high-pressure water vapor, moderate mechanical properties, low atomic thermal neutron absorption cross-section (zirconium is 0.18 barns), and good compatibility with nuclear fuel, and are commonly used core structure materials for water-cooled nuclear reactors. However, with the rapid development of nuclear energy technology, nuclear reactors have put forward higher requirements for safety and economy of core structure materials, including indicators such as long life, high burn-up, and zero breakage. To meet the needs of nuclear energy technology for high-performance core structure materials, scientific research workers have carried out a large number of research works. Research shows that the tensile yield strength of traditional industrial zirconium and zirconium alloys R60702 and R6075 at room temperature does not exceed 500 MPa, and the tensile plastic strain is about 50.00%. Therefore, the zirconium alloys currently on the market have low plasticity and poor strength and cannot withstand the high stress in nuclear reactors. Summary of the Invention

[0003] Aiming at the above-mentioned shortcomings of the prior art, the present invention provides a Zr-based alloy enhanced by deformation-induced martensitic transformation.

[0004] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0005] A Zr-based alloy enhanced by deformation-induced martensitic transformation, comprising the following components in mass percentage: Zr is 54.00% - 59.00%, Co is 35.00% - 38.00%, Nb is 1.00% - 4.00%, Ta is 2.00% - 7.00%, and the rest are inevitable impurities.

[0006] The preparation method of the Zr-based alloy comprises the following steps:

[0007] (1) Configure raw materials according to the mass percentage of each element;

[0008] (2) Use a mechanical pump to evacuate the vacuum in the chamber to below 30 Pa, close the mechanical pump, open the isolation valve, and wait for the vacuum to be further evacuated to below 10 Pa; open the molecular pump and evacuate the vacuum to between 2.0×10 -3 ~3.0×10 -3 Pa. Then close the isolation valve, turn off the molecular pump, and fill with argon to -0.05 MPa. Finally, repeat the operation of step (2) three times;

[0009] (3) Turn on the arc melting switch. First, melt for 15 s with a current of 180 A, then melt the raw materials with a current of 220 A, and turn over the alloy ingot with the turning rod, repeating the operation 5 - 6 times; then cut out a small piece of the alloy ingot with a current of 80 A for suction casting; finally, suction cast a round bar with a diameter of Φ2 mm and a length of 50 mm with a current of 120 A.

[0010] As a preferred embodiment of the present invention, at room temperature, the yield strength of the Zr-based alloy ≥ 629 MPa, the ultimate compressive strength ≥ 5516 MPa, and the ultimate compressive strain ≥ 75.00%.

[0011] The present invention also claims the application of the Zr-based alloy with enhanced deformation-induced martensitic transformation in the core material of a nuclear reactor.

[0012] The present invention also claims the application of the Zr-based alloy with enhanced deformation-induced martensitic transformation in the skin material of a submarine.

[0013] Compared with the prior art, the beneficial effects of the present invention are as follows: By optimizing the alloy composition and preparation method, the present invention effectively reduces the decomposition of the B2 phase into other brittle phases such as Zr2Co, and retains the B2 phase to the greatest extent. At the same time, Nb and Ta can regulate the volume fractions of the B2 and Zr2Co phases in the alloy. The purpose of the present invention is: Adding a small amount of Nb and Ta elements to the Zr-Co alloy can improve the stability of the B2 phase, and at the same time regulate the volume fraction ratio of the B2 phase to the Zr2Co brittle phase, so as to maximize the comprehensive mechanical properties of the alloy. This alloy can withstand great stress when used in the core material structure of a nuclear reactor, and can also be used as the structural material for the skin of a submarine to resist the extrusion deformation of seawater on the submarine under deep sea conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is the XRD diffraction pattern of the Zr-Co-Nb-Ta alloy prepared in Example 1 and Example 3 of the present invention.

[0015] Figure 2 It is the Zr-Co-Nb-Ta alloy prepared in Example 1 and Example 3 of the present invention at room temperature at 5×10 -4 s -1XRD diffraction pattern after compression at a strain rate.

[0016] Figure 3 Stress-strain curves of Zr-Co, Zr-Co-Nb, Zr-Co-Ta, and Zr-Co-Nb-Ta alloys prepared in Examples 1-3, Comparative Examples 1, 4, and 6. Detailed implementation manners

[0017] To better illustrate the purpose, technical solution, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0018] Example 1

[0019] A Zr-Co-Nb-Ta alloy with enhanced deformation-induced martensitic transformation, comprising components with the following mass percentages: 59% Zr, 38.00% Co, 1.00% Nb, 2.00% Ta, and the balance being inevitable trace impurities;

[0020] The preparation method of the Zr-Co-Nb-Ta alloy comprises the following steps:

[0021] (1) Configure 20 g of raw materials according to the mass percentages of each element, and the maximum weight error of each element does not exceed 5.00%;

[0022] (2) Use a mechanical pump to evacuate the chamber to below 30 Pa, close the mechanical pump, open the isolation valve, and wait for the vacuum to be further evacuated to below 10 Pa; open the molecular pump and evacuate the vacuum to 3.0×10 -3 Pa, then close the isolation valve, close the molecular pump, fill with argon to -0.05 MPa, and finally repeat the operation of step (2) 3 times;

[0023] (3) Turn on the arc melting switch. First, melt with a current of 180 A for 15 s, then melt the raw materials with a current of 220 A, and turn over the alloy ingot with a turning rod, and repeat the operation 5 times; then cut out a small piece of the alloy ingot with a current of 80 A for suction casting; finally, suction cast a Φ2 mm×50 mm round bar with a current of 120 A. Then cut the round bar into 5 mm cylinders with a cutting machine, and finally polish the two ends of the specimen to 4 mm with sandpaper and keep the end faces flat and smooth. After sampling, perform compression mechanical property testing at a strain rate of 5×10 -4 s -1 The compression engineering stress-strain curve and mechanical properties are respectively as Figure 3 and shown in Table 1.

[0024] Example 2

[0025] A Zr-Co-Nb-Ta alloy with enhanced deformation-induced martensitic transformation, comprising the following components in mass percentage: Zr is 56%, Co is 36.00%, Nb is 2.00%, Ta is 6.00%, and the rest are inevitable trace impurities;

[0026] The preparation method of the Zr-Co-Nb-Ta alloy is the same as that in Example 1.

[0027] After sampling, the compressive mechanical properties are tested at a strain rate of 5×10 -4 s -1 at room temperature, and its compressive engineering stress-strain curve and mechanical properties are respectively as Figure 3 and shown in Table 1.

[0028] Example 3

[0029] A Zr-Co-Nb-Ta alloy with enhanced deformation-induced martensitic transformation, comprising the following components in mass percentage: Zr is 54%, Co is 35.00%, Nb is 4.00%, Ta is 7.00%, and the rest are inevitable trace impurities;

[0030] The preparation method of the Zr-Co-Nb-Ta alloy is the same as that in Example 1.

[0031] After sampling, the compressive mechanical properties are tested at a strain rate of 5×10 -4 s -1 at room temperature, and its compressive engineering stress-strain curve and mechanical properties are respectively as Figure 3 and shown in Table 1.

[0032] Comparative Example 1

[0033] A Zr-Co alloy, comprising the following components in mass percentage: Zr is 60.75%, Co is 39.25%, and the rest are inevitable trace impurities;

[0034] The preparation method of the Zr-Co alloy is the same as that in Example 1.

[0035] After sampling, the compressive mechanical properties are tested at a strain rate of 5×10 -4 s -1 at room temperature, and its compressive engineering stress-strain curve and mechanical properties are shown in Table 1.

[0036] Comparative Example 2

[0037] A Zr-Co-Nb-Ta alloy, comprising the following components in mass percentage: Zr is 59%, Co is 38.00%, Nb is 1.00%, Ta is 2.00%, and the rest are inevitable trace impurities;

[0038] The preparation method of the Zr-Co-Nb-Ta alloy comprises the following steps:

[0039] (1) Prepare a total of 20 g of raw materials according to the mass percentage content of each element, and the maximum weight error of each element does not exceed 5.00%;

[0040] (2) Put it into an arc melting crucible cleaned with alcohol, and repeatedly melt it 5 times in an arc induction melting furnace with a vacuum degree higher than 0.1 Pa; then take it out and place it in an induction melting furnace to be melted and cast into a round bar with a diameter of Φ2 mm × 50 mm. Then cut the round bar into a cylinder with a diameter of Φ2 mm × 5 mm with a cutting machine, and finally polish the two ends of the sample to 4 mm with sandpaper and keep the end face flat and smooth. After sampling, perform compression mechanical property testing at a strain rate of 5×10 -4 s -1 The compression engineering stress-strain curve and mechanical properties are shown in Table 1.

[0041] Comparative Example 3

[0042] A Zr-Co-Nb alloy strengthened by deformation-induced martensitic transformation, comprising the following components by mass percentage: Zr is 60%, Co is 38.00%, Nb is 2.00%, and the rest are inevitable trace impurities;

[0043] The preparation method of the Zr-Co-Nb alloy is the same as that of Comparative Example 2.

[0044] After sampling, perform compression mechanical property testing at a strain rate of 5×10 -4 s -1 The compression engineering stress-strain curve and mechanical properties are shown in Table 1.

[0045] Comparative Example 4

[0046] A Zr-Co-Nb alloy strengthened by deformation-induced martensitic transformation, comprising the following components by mass percentage: Zr is 60%, Co is 38.00%, Nb is 2.00%, and the rest are inevitable trace impurities;

[0047] The preparation method of the Zr-Co-Nb alloy is the same as that of Example 1.

[0048] After sampling, perform compression mechanical property testing at a strain rate of 5×10 -4 s -1 The compression engineering stress-strain curve and mechanical properties are shown in Table 1.

[0049] Comparative Example 5

[0050] A Zr-Co-Ta alloy with enhanced deformation-induced martensitic transformation, comprising components with the following mass percentages: Zr is 60%, Co is 38.00%, Ta is 2.00%, and the rest are inevitable trace impurities;

[0051] The preparation method of the Zr-Co-Ta alloy is the same as that of Comparative Example 2.

[0052] After sampling, compression mechanical property testing is carried out at room temperature at a strain rate of 5×10 -4 s -1 The compression engineering stress-strain curve and mechanical properties are shown in Table 1.

[0053] Comparative Example 6

[0054] A Zr-Co-Ta alloy with enhanced deformation-induced martensitic transformation, comprising components with the following mass percentages: Zr is 60%, Co is 38.00%, Ta is 2.00%, and the rest are inevitable trace impurities;

[0055] The preparation method of the Zr-Co-Ta alloy is the same as that of Example 1.

[0056] After sampling, compression mechanical property testing is carried out at room temperature at a strain rate of 5×10 -4 s -1 The compression engineering stress-strain curve and mechanical properties are shown in Table 1.

[0057] Table 1

[0058]

[0059] From Figure 1 it can be seen that there is a B2 phase in the Zr-Co-Nb-Ta alloy prepared by this method, indicating that the method of the present invention can effectively retain the B2 phase. From Figure 2 it can be seen that after compression, there is not only a B2 phase in the Zr-Co-Nb-Ta but also a B33 phase, which confirms that the strain does cause the B2 phase to transform into the B33 phase. By adding Nb and Ta elements to the Zr-Co alloy, the volume fractions of the B2 and Zr2Co phases in the alloy are regulated, resulting in a significant increase in the yield strength and ultimate compression strength, and at the same time, the ultimate compression strain is increased from 60.00% to over 75.00%. This alloy can withstand great stress when used in the core material structure of a nuclear reactor, and can also be used as the structural material for the skin of a submarine to resist the extrusion deformation of seawater on the submarine under deep sea conditions.

[0060] Comparing Example 3 with Comparative Examples 2, 3, and 5, the yield strength, ultimate compressive strength, and ultimate compressive strain of the Zr-Co-Nb-Ta alloy prepared by the preparation method of the present invention are significantly improved. The cooling rate of the preparation method of the present invention is faster than that of the method in Comparative Example 2. During the preparation process, the B2 phase can be retained, and the B2 phase is retained to the greatest extent, inhibiting the formation of the Zr2Co phase. Therefore, there is enough B2 phase to undergo martensitic transformation during compression.

[0061] Comparing Examples 1-3 with Comparative Examples 1, 4, and 6, it is found that adding only Nb or Ta elements improves one or two of the compressive yield strength, ultimate compressive strain, and ultimate compressive strength of the Zr-Co alloy, while the improvement of the other performance indexes is not much. The reason is that the action mechanisms of Nb and Ta on the alloy are different. The Nb element is more sensitive to the B2 phase, while the Ta element is more sensitive to the Zr2Co brittle phase. Adding only the Nb element significantly improves the ultimate compressive strain, while adding only the Ta element significantly improves the strength. Therefore, the present invention makes full use of the advantages of both. By adding Nb and Ta elements simultaneously, the B2 phase in the alloy is stabilized, and the volume fraction of the B2 phase is increased compared with that of the Zr-Co alloy, Zr-Co-Nb alloy, and Zr-Co-Ta alloy. At the same time, the Zr2Co increases the strength, ensuring that the alloy has a sufficiently high strength. Through the synergistic effect of Nb and Ta elements, the volume fractions of the B2 and Zr2Co phases in the alloy are fully regulated, resulting in a significant improvement in the yield strength, ultimate compressive strength, and ultimate compressive strain.

[0062] Comparing Example 3 with Comparative Examples 3-4, and Example 3 with Comparative Examples 5-6, the comprehensive mechanical properties of the Zr-Co-Nb-Ta alloy are significantly improved compared with those of the Zr-Co-Nb and Zr-Co-Ta alloys. The optimization of the alloy composition and the preparation method synergistically achieve the improvement of the yield strength, ultimate compressive strength, and ultimate compressive strain properties.

[0063] The above examples are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A Zr-based alloy enhanced by deformation-induced martensitic transformation, characterized in that: The composition comprises the following components in percentage by mass: Zr is 54.00% to 59.00%, Co is 35.00% to 38.00%, Nb is 1.00% to 4.00%, Ta is 2.00% to 7.00%, and the rest are unavoidable trace impurities; The method for preparing the deformation-induced martensitic transformation-enhanced Zr-Co-Nb-Ta alloy comprises the following steps: (1) Prepare the raw materials according to the mass percentage of each element; (2) Use a mechanical pump to pump the vacuum in the chamber to below 30 Pa, turn off the mechanical pump, open the isolation valve, and wait for the vacuum to be further pumped to below 10 Pa; turn on the molecular pump and pump the vacuum to 2.0×10 -3 ~3.0×10 -3 Pa, then close the isolation valve, turn off the molecular pump, fill with argon to -0.05MPa, and finally repeat step (2) 3 times; (3) Turn on the arc melting switch, first use a current of 180A to melt for 15s, then use a current of 220A to melt the raw materials, and use a turning rod to turn the alloy ingot over, repeating the operation 5 to 6 times; then use a current of 80A to cut a small piece of the alloy ingot for suction casting; finally use a current of 120A to suction cast a Φ2mm×50mm round bar.

2. The Zr-based alloy with deformation-induced martensitic transformation enhancement according to claim 1, characterized in that: At room temperature, the Zr-Co-Nb-Ta alloy has a yield strength of ≥629 MPa, an ultimate compressive strength of ≥5516 MPa, and an ultimate compressive strain of ≥75.00%.

3. Use of the Zr-based alloy with deformation-induced martensitic transformation enhancement according to claim 1 in a core material of a nuclear reactor.

4. Use of the Zr-based alloy enhanced by deformation-induced martensitic transformation according to claim 1 in submarine skin materials.

Images