A method for bonding nuclear zirconium-hafnium dissimilar metals by spark plasma pressure sintering.

Abstract

This application provides a nuclear-grade zirconium-hafnium dissimilar metal and a spark plasma pressure sintering bonding method. The spark plasma pressure sintering bonding method can complete the sintering process in a shorter time, significantly improving production efficiency. Furthermore, this invention is prepared by spark plasma pressure sintering of a hafnium metal block, an intermediate layer premixed powder, and a zirconium metal block. It allows for precise adjustment of the raw material ratio of the intermediate layer premixed powder and precise control of the sintering process, thereby preparing a zirconium-hafnium dissimilar metal with a specific composition and microstructure. This results in a zirconium-hafnium dissimilar metal with high bonding strength, while retaining the intrinsic properties of both zirconium and hafnium metals. The combination of these two properties enables optimized control of the nuclear reaction process.

Description

Technical Field

[0001] This application relates to the field of nuclear materials technology, and in particular to a nuclear zirconium-hafnium dissimilar metal and a spark plasma pressure sintering bonding method. Background Technology

[0002] With the continuous development of industrial production, single metal structures are no longer sufficient to meet the needs of modern industrial production. Therefore, the use of dissimilar metal composite structures has become a new trend in industrial development. Zirconium, due to its excellent corrosion resistance, good mechanical strength and plasticity, and low thermal neutron absorption cross-section, is widely used in the nuclear and chemical industries to manufacture structural components. Hafnium, due to its large thermal neutron absorption cross-section, can absorb thermal neutrons in nuclear reactors and is used to control the reaction rate of nuclear reactors, and is often used as a control material. Therefore, by utilizing the respective properties of these two metals, combining zirconium and hafnium can achieve optimized control of the nuclear reaction process.

[0003] Currently, methods for joining dissimilar metals include welding, vacuum hot pressing, and vacuum diffusion joining. CN103862174A discloses a laser welding method for zirconium-based amorphous alloys and commercial metal alloys. However, zirconium (melting point 1852℃) and hafnium (melting point 2222℃) have significant melting point differences. When zirconium reaches its molten state, hafnium remains solid, making the weld joint difficult to complete and prone to cracking at the joint. CN101690992A discloses a method for preparing a transition joint for dissimilar metal materials, which involves machining a taper at the end of metal material A and then hot-pressing the end of metal material A together under vacuum. A joint is obtained in the inner cavity of metal material B. However, this method requires metal material A with a specific taper and metal material B with an inner cavity structure to be processed, which is not suitable for connecting planar metal materials. CN113478063A discloses a vacuum diffusion connection method for titanium-zirconium-molybdenum alloy with a refractory metal as the intermediate layer. Niobium foil or tantalum foil is used as the connection intermediate layer to realize the diffusion connection of titanium-zirconium-molybdenum alloy. However, vacuum diffusion connection requires long-term diffusion heat preservation and homogenization heat preservation, which is energy-intensive, time-consuming and difficult to improve production efficiency.

[0004] Therefore, there is an urgent need to provide a nuclear-grade zirconium-hafnium dissimilar metal bonding method using spark plasma pressure sintering, which can improve the low production efficiency. Summary of the Invention

[0005] The purpose of this application is to provide a nuclear-grade zirconium-hafnium dissimilar metal and a spark plasma pressure sintering bonding method, which can improve the low production efficiency of dissimilar metals.

[0006] In a first aspect, this application provides a zirconium-hafnium dissimilar metal, which is composed of a hafnium layer, a first diffusion layer, an intermediate layer, a second diffusion layer, and a zirconium layer in sequence. The dissimilar metal is prepared by spark plasma pressure sintering of a hafnium metal block, an intermediate layer premixed powder, and a zirconium metal block. The intermediate layer premixed powder is composed of hafnium powder and zirconium powder. Based on the total amount of the intermediate layer premixed powder, the atomic percentage of the hafnium powder is 30% to 80%, and the balance is zirconium powder.

[0007] Optionally, based on the total amount of the intermediate layer premixed powder, the atomic percentage of the hafnium powder is 40% to 80%, with the balance being zirconium powder.

[0008] Optionally, the hafnium layer has an equiaxed microstructure with a grain size of 200–800 μm, and the zirconium layer has a lamellar microstructure with a length dimension of 200–700 μm and a width dimension of 10–80 μm.

[0009] Optionally, the intermediate layer has a sheet-like structure with a length dimension of 60–500 μm, a width dimension of 3–64 μm, and an aspect ratio of 5–35.

[0010] Optionally, the length dimension of the sheet-like tissue is 60-500 μm, the width dimension is 3-30 μm, and the aspect ratio is 9-35.

[0011] Optionally, based on the total amount of the intermediate layer premixed powder, the atomic percentage of the hafnium powder is 40% to 60%, with the balance being zirconium powder. The microstructure of the intermediate layer is a lamellar structure, with the lamellar structure having a length dimension of 60 to 500 μm, a width dimension of 5 to 30 μm, and an aspect ratio of 9 to 33.

[0012] Optionally, the thickness of the first diffusion layer is 200-400 μm, the thickness of the second diffusion layer is 200-500 μm, and the ratio of the total thickness of the first diffusion layer and the second diffusion layer to the total thickness of the first diffusion layer, the second diffusion layer and the intermediate layer is 0.41-0.60.

[0013] Secondly, the present invention provides a zirconium-hafnium dissimilar metal spark plasma pressure sintering bonding method, comprising the following steps:

[0014] S1. Provide hafnium metal blocks, intermediate layer premixed powder and zirconium metal blocks, wherein the intermediate layer premixed powder is composed of hafnium powder and zirconium powder, and the atomic percentage of hafnium powder is 30% to 80% based on the total amount of intermediate layer premixed powder, with the remainder being zirconium powder;

[0015] S2. The hafnium metal block, the intermediate layer premixed powder, and the zirconium metal block are stacked in a mold, with the intermediate layer premixed powder located between the hafnium metal block and the zirconium metal block;

[0016] S3. The mold is placed in a spark plasma sintering system and subjected to pressure sintering to prepare zirconium-hafnium dissimilar metal.

[0017] Optionally, the hafnium metal block and zirconium metal block in step S1 are prepared by spark plasma pressure sintering, with the sintering temperature of the hafnium metal block being 1600-1700℃, the sintering pressure being 20-40MPa, and the sintering time being 5-15min, and the sintering temperature of the zirconium metal block being 1450-1550℃, the sintering pressure being 20-40MPa, and the sintering time being 5-15min.

[0018] Optionally, in step S3, the sintering temperature is 1450–1550℃, the sintering pressure is 20–40MPa, and the sintering time is 5–15min.

[0019] In summary, this application has at least one of the following beneficial effects:

[0020] 1. This invention provides a zirconium-hafnium dissimilar metal, which employs a spark plasma pressure sintering bonding method. This method enables the sintering process to be completed in a short time, significantly improving production efficiency. Furthermore, this invention is prepared by spark plasma pressure sintering of a hafnium metal block, an intermediate layer premixed powder, and a zirconium metal block. It allows for precise adjustment of the raw material ratio of the intermediate layer premixed powder and precise control of the sintering process, thereby preparing a zirconium-hafnium dissimilar metal with a specific composition and microstructure. This results in a zirconium-hafnium dissimilar metal with high bonding strength. In subsequent embodiments, the shear strength of the zirconium-hafnium dissimilar metal was measured to be above 422 MPa, and in a preferred embodiment, it reached above 522 MPa, with an optimal value of 555 MPa. Simultaneously, it retains the intrinsic properties of zirconium and hafnium metals, and the combination of the two enables optimized control of the nuclear reaction process.

[0021] 2. The present invention provides a zirconium-hafnium dissimilar metal, which is composed of a hafnium layer, a first diffusion layer, an intermediate layer, a second diffusion layer, and a zirconium layer. The hafnium layer has an equiaxed structure, the zirconium layer has a lamellar structure, and the intermediate layer has a lamellar structure. The first and second diffusion layers have specific thicknesses and structures, which enable the intermediate layer and the hafnium and zirconium layers at both ends to form a metallurgical bond, thereby improving the bond strength. At the same time, the lamellar structure of the intermediate layer has specific length, width, and aspect ratio, which enables the intermediate layer itself to have high strength. Under the combined effect of multiple factors, the overall shear strength of the zirconium-hafnium dissimilar metal is improved.

[0022] 3. The present invention provides a zirconium-hafnium dissimilar metal discharge plasma pressure sintering bonding method, which has the characteristics of rapid heating, short sintering time, external pressure, and high density of the resulting material. It can also precisely control the temperature and accurately regulate the microstructure and properties of the zirconium-hafnium dissimilar metal. Attached Figure Description

[0023] Figure 1 This is a SEM image of the hafnium metal block obtained in Embodiment 1 of the present invention;

[0024] Figure 2 This is a SEM image of the zirconium metal block obtained in Example 1 of the present invention;

[0025] Figure 3 This is a SEM image of the zirconium-hafnium dissimilar metal obtained in Example 1 of this invention;

[0026] Figure 4 This is a SEM image of the zirconium-hafnium dissimilar metal obtained in Example 2 of this invention;

[0027] Figure 5 This is a SEM image of the zirconium-hafnium dissimilar metal obtained in Example 3 of this invention;

[0028] Figure 6 This is a SEM image of the zirconium-hafnium dissimilar metal obtained in Example 4 of this invention;

[0029] Figure 7 This is a SEM image of the zirconium-hafnium dissimilar metal obtained in Example 5 of this invention;

[0030] Figure 8 This is a SEM image of the zirconium-hafnium dissimilar metal prepared in Comparative Example 3 of this invention.

[0031] Figure 9 This is a schematic diagram of the shear strength test of the present invention. Detailed Implementation

[0032] This application provides a zirconium-hafnium dissimilar metal bonding method and a spark plasma pressure sintering method. To make the objectives, technical solutions, and effects of this application clearer and more explicit, the following provides a more detailed description. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0033] Zirconium metal possesses excellent corrosion resistance, good mechanical strength and plasticity, and a low thermal neutron absorption cross-section, making it widely used in the nuclear and chemical industries for manufacturing structural components. Hafnium metal, due to its large thermal neutron absorption cross-section, can absorb thermal neutrons in nuclear reactors and is used to control the reaction rate, often serving as a control material. Therefore, combining zirconium and hafnium, leveraging their respective properties, can achieve optimized control of nuclear reaction processes. Current conventional methods for joining dissimilar metals include welding, hot pressing, and vacuum diffusion. However, the significant difference in melting points between zirconium (melting point 1852℃) and hafnium (melting point 2222℃), the need for planar metal joining, and the requirement for high production efficiency make these methods unsuitable for preparing zirconium-hafnium dissimilar metals. After a long period of research, the inventors discovered that a zirconium-hafnium dissimilar metal can be prepared by using a hafnium metal block, an intermediate layer of premixed powder, and a zirconium metal block in a discharge plasma pressure sintering bonding method. By precisely adjusting the sintering process and raw material ratio, zirconium-hafnium dissimilar metals with specific microstructures can be obtained. While retaining the intrinsic properties of zirconium and hafnium, the dissimilar metals have high bonding strength, meeting the requirements for nuclear-grade zirconium-hafnium dissimilar metals and significantly improving production efficiency.

[0034] In an embodiment of the present invention, a zirconium-hafnium dissimilar metal is provided. The dissimilar metal is composed of a hafnium layer, a first diffusion layer, an intermediate layer, a second diffusion layer, and a zirconium layer in sequence. The dissimilar metal is prepared by spark plasma pressure sintering of a hafnium metal block, an intermediate layer premixed powder, and a zirconium metal block. The intermediate layer premixed powder is composed of hafnium powder and zirconium powder. Based on the total amount of the intermediate layer premixed powder, the atomic percentage of hafnium powder is 30% to 80%, with the balance being zirconium powder. Preferably, the atomic percentage of hafnium powder is 40% to 80%, more preferably, 40% to 60%, even more preferably, 45% to 55%, and even more preferably, 48% to 52%.

[0035] In embodiments of the present invention, the hafnium layer has an equiaxed microstructure with a grain size of 200–800 μm, preferably 400–600 μm, and the zirconium layer has a lamellar microstructure with a length dimension of 200–700 μm and a width dimension of 10–80 μm, preferably 200–500 μm and 20–40 μm.

[0036] In embodiments of the present invention, the intermediate layer has a sheet-like structure with a length dimension of 60–500 μm, a width dimension of 3–64 μm, and an aspect ratio of 5–35; preferably, the sheet-like structure has a length dimension of 60–500 μm, a width dimension of 3–30 μm, and an aspect ratio of 9–35; more preferably, the intermediate layer has a sheet-like structure with a length dimension of 60–500 μm, a width dimension of 5–30 μm, and an aspect ratio of 9–33.

[0037] In an embodiment of the present invention, the thickness of the first diffusion layer is 200-400 μm, the thickness of the second diffusion layer is 200-500 μm, and the ratio of the total thickness of the first diffusion layer and the second diffusion layer to the total thickness of the first diffusion layer, the second diffusion layer and the intermediate layer is 0.41-0.60.

[0038] In an embodiment of the present invention, a zirconium-hafnium dissimilar metal discharge plasma pressure sintering bonding method includes the following steps:

[0039] S1. Provide hafnium metal blocks, intermediate layer premixed powder and zirconium metal blocks, wherein the intermediate layer premixed powder is composed of hafnium powder and zirconium powder, and the atomic percentage of hafnium powder is 30% to 80% based on the total amount of intermediate layer premixed powder, with the remainder being zirconium powder;

[0040] S2. The hafnium metal block, the intermediate layer premixed powder, and the zirconium metal block are stacked in a mold, with the intermediate layer premixed powder located between the hafnium metal block and the zirconium metal block;

[0041] S3. The mold is placed in a spark plasma sintering system and subjected to pressure sintering to prepare zirconium-hafnium dissimilar metal.

[0042] In an embodiment of the present invention, the hafnium metal block and the zirconium metal block in step S1 are prepared by electrostatic plasma pressure sintering. The sintering temperature of the hafnium metal block is 1600-1700℃, the sintering pressure is 20-40MPa, and the sintering time is 5-15min. The sintering temperature of the zirconium metal block is 1450-1550℃, the sintering pressure is 20-40MPa, and the sintering time is 5-15min.

[0043] In the embodiments of the present invention, in step S3, the sintering temperature is 1450-1550℃, the sintering pressure is 20-40MPa, and the sintering time is 5-15min.

[0044] The embodiments and comparative examples of this application will be described in further detail below.

[0045] Example 1

[0046] S1-1. Preparation of hafnium metal blocks: Place raw hafnium powder (irregular granular powder, particle size less than 100μm, purity 99.9%) in a graphite mold, then place it in the vacuum chamber of a spark plasma sintering furnace, close the chamber door, evacuate to below 30Pa, and perform pressure sintering. The heating rate is 100℃ / min, the sintering temperature is 1650℃, the sintering pressure is 30MPa, and the temperature and pressure are held for 10min to obtain hafnium metal blocks.

[0047] SEM image of hafnium metal block as shown Figure 1 As shown, the microstructure of the hafnium metal block is equiaxed, with a grain size of 50–250 μm.

[0048] S1-2. Preparation of zirconium metal blocks: Place the raw zirconium powder (spherical powder, particle size 30-50 μm, purity 99.9%) in a graphite mold, then place it in the vacuum chamber of a spark plasma sintering furnace, close the chamber door, evacuate to below 30 Pa, and perform pressure sintering. The heating rate is 100 °C / min, the sintering temperature is 1500 °C, the sintering pressure is 30 MPa, and the temperature and pressure are held for 10 min to obtain zirconium metal blocks.

[0049] SEM image of zirconium metal block as shown Figure 2 As shown, the microstructure of the zirconium metal block is lamellar, with a length dimension of 200–450 μm and a width dimension of 20–60 μm.

[0050] S1-3. Cut the hafnium metal block from step S1-1 and the zirconium metal block from step S1-2 to the target size. Then, use a manual surface grinder to grind the surfaces to be joined until they are smooth and shiny. After that, use 1500# and 2000# metallographic sandpaper to grind the surfaces until there are no obvious scratches. Place the treated zirconium and hafnium metal blocks in anhydrous ethanol for ultrasonic cleaning for 10 minutes and then dry them for later use.

[0051] S1-4. Prepare the intermediate layer premixed powder. Weigh the raw materials hafnium powder (irregular granular powder, particle size less than 100μm, purity 99.9%) and zirconium powder (spherical powder, particle size 30-50μm, purity 99.9%) at an atomic ratio of 8:2. The atomic percentage of hafnium powder is 80% based on the total amount of the intermediate layer premixed powder, with the remainder being zirconium powder. Then, put the weighed raw materials hafnium powder and zirconium powder into a mixing tank and mix them in a 3D mixing system. After mixing evenly, set aside for later use.

[0052] S2. Stack the hafnium metal block from step S1-3, the intermediate layer premixed powder from step S1-4, and the zirconium metal block from step S1-3 in a graphite mold, such that the intermediate layer premixed powder from step S1-4 is located between the hafnium metal block and the zirconium metal block.

[0053] S3. Place the graphite mold in the vacuum chamber of the spark plasma sintering furnace, close the chamber door, evacuate to below 30 Pa, and perform pressure sintering. The heating rate is 100℃ / min, the sintering temperature is 1500℃, the sintering pressure is 30MPa, and the temperature and pressure are held for 10 min to prepare zirconium-hafnium dissimilar metal.

[0054] SEM images of the zirconium-hafnium dissimilar metals prepared in Example 1 are shown below. Figure 3 As shown, from Figure 3 It can be seen that the zirconium-hafnium dissimilar metal is composed of 1. hafnium layer, 2. first diffusion layer, 3. intermediate layer, 4. second diffusion layer and 5. zirconium layer. The interface achieves good connection and there are no defects such as microcracks, diffusion pores and incomplete welding. The intermediate layer has mutual diffusion with metallic hafnium and metallic zirconium, forming a continuous diffusion layer of a certain thickness. The microstructure of the hafnium layer was measured to be equiaxed with a grain size of 400–600 μm; the microstructure of the zirconium layer was measured to be lamellar with a length dimension of 200–500 μm and a width dimension of 20–40 μm; the microstructure of the intermediate layer was measured to be lamellar with a length dimension of 300–430 μm and a width dimension of 3–12 μm, with an aspect ratio of 10–35; the thickness of the first diffusion layer was measured to be 200 μm; the thickness of the second diffusion layer was measured to be 500 μm; and the ratio of the total thickness of the first and second diffusion layers to the total thickness of the first, second, and intermediate layers was 0.44.

[0055] The zirconium-hafnium dissimilar metal prepared in Example 1 was cut to a size of 15mm × 10mm × 2mm and then installed into a shearing die. A shearing test was performed using a universal testing machine at a speed of 0.2mm / min. The shearing test results are shown in the figure. Figure 9 As shown, the zirconium-hafnium dissimilar metal sample was clamped using a fixture, and a pressure test head was applied to the interface. The shear strength of the zirconium-hafnium dissimilar metal prepared in Example 1 was measured to be 522.7 MPa.

[0056] Example 2

[0057] The difference between Example 2 and Example 1 is that in step S1-4 of Example 2, in the preparation of the intermediate layer premixed powder, the raw material hafnium powder and raw material zirconium powder are weighed at an atomic ratio of 6:4. Based on the total amount of the intermediate layer premixed powder, the atomic percentage of hafnium powder is 60%, and the remainder is zirconium powder. The remaining preparation steps are the same as in Example 1, and a zirconium-hafnium dissimilar metal is prepared.

[0058] SEM image of the zirconium-hafnium dissimilar metal interlayer prepared in Example 2 is shown below. Figure 4 As shown, from Figure 4It can be seen that the zirconium-hafnium dissimilar metal is composed of 1. a hafnium layer, 2. a first diffusion layer, 3. an intermediate layer, 4. a second diffusion layer, and 5. a zirconium layer. The interface achieves good bonding, without microcracks, diffusion voids, or incomplete bonding defects. The intermediate layer undergoes mutual diffusion with both metallic hafnium and metallic zirconium, forming a continuous diffusion layer of a certain thickness. The microstructure and dimensions of the hafnium and zirconium layers in Example 2 are the same as in Example 1. The microstructure of the intermediate layer in Example 2 is measured to be lamellar, with a length dimension of 60–420 μm and a width dimension of 5–30 μm, resulting in an aspect ratio of 12–14. The thickness of the first diffusion layer is measured to be 260 μm, and the thickness of the second diffusion layer is 400 μm. The ratio of the total thickness of the first and second diffusion layers to the total thickness of the first, second, and intermediate layers is 0.51.

[0059] Using the same testing method as in Example 1, the shear strength of the zirconium-hafnium dissimilar metal prepared in Example 2 was tested to be 524.7 MPa.

[0060] Example 3

[0061] The difference between Example 3 and Example 1 is that in step S1-4 of Example 3, in the preparation of the intermediate layer premixed powder, the raw material hafnium powder and raw material zirconium powder are weighed at an atomic ratio of 5:5. Based on the total amount of the intermediate layer premixed powder, the atomic percentage of hafnium powder is 50%, and the remainder is zirconium powder. The remaining preparation steps are the same as in Example 1, and a zirconium-hafnium dissimilar metal is prepared.

[0062] SEM image of the zirconium-hafnium dissimilar metal interlayer prepared in Example 3 is shown below. Figure 5 As shown, from Figure 5 It can be seen that the zirconium-hafnium dissimilar metal is composed of 1. a hafnium layer, 2. a first diffusion layer, 3. an intermediate layer, 4. a second diffusion layer, and 5. a zirconium layer. The interface achieves good bonding, without microcracks, diffusion voids, or incomplete bonding defects. The intermediate layer undergoes mutual diffusion with both metallic hafnium and metallic zirconium, forming a continuous diffusion layer of a certain thickness. The microstructure and dimensions of the hafnium and zirconium layers in Example 3 are the same as in Example 1. The microstructure of the intermediate layer in Example 3 is measured to be lamellar, with a length dimension of 200–233 μm and a width dimension of 15–25 μm, resulting in an aspect ratio of 9–13. The thickness of the first diffusion layer is measured to be 200 μm, and the thickness of the second diffusion layer is 400 μm. The ratio of the total thickness of the first and second diffusion layers to the total thickness of the first, second, and intermediate layers is 0.41.

[0063] Using the same testing method as in Example 1, the shear strength of the zirconium-hafnium dissimilar metal prepared in Example 3 was tested to be 555 MPa.

[0064] Example 4

[0065] The difference between Example 4 and Example 1 is that in step S1-4 of Example 4, in the preparation of the intermediate layer premixed powder, the raw material hafnium powder and raw material zirconium powder are weighed at an atomic ratio of 4:6. Based on the total amount of the intermediate layer premixed powder, the atomic percentage of hafnium powder is 40%, and the remainder is zirconium powder. The remaining preparation steps are the same as in Example 1, and a zirconium-hafnium dissimilar metal is prepared.

[0066] SEM image of the zirconium-hafnium dissimilar metal interlayer prepared in Example 4 is shown below. Figure 6 As shown, from Figure 6 It can be seen that the zirconium-hafnium dissimilar metal is composed of 1. a hafnium layer, 2. a first diffusion layer, 3. an intermediate layer, 4. a second diffusion layer, and 5. a zirconium layer. The interface achieves good bonding, without microcracks, diffusion voids, or incomplete bonding defects. The intermediate layer undergoes mutual diffusion with both metallic hafnium and metallic zirconium, forming a continuous diffusion layer of a certain thickness. The microstructure and dimensions of the hafnium and zirconium layers in Example 4 are the same as in Example 1. The microstructure of the intermediate layer in Example 4 is measured to be lamellar, with a length dimension of 100–500 μm, a width dimension of 5–15 μm, and an aspect ratio of 20–33. The thickness of the first diffusion layer is measured to be 400 μm, and the thickness of the second diffusion layer is 250 μm. The ratio of the total thickness of the first and second diffusion layers to the total thickness of the first, second, and intermediate layers is 0.60.

[0067] Using the same testing method as in Example 1, the shear strength of the zirconium-hafnium dissimilar metal prepared in Example 4 was tested to be 533 MPa.

[0068] Example 5

[0069] The difference between Example 5 and Example 1 is that in step S1-4 of Example 5, in the preparation of the intermediate layer premixed powder, the raw material hafnium powder and raw material zirconium powder are weighed at an atomic ratio of 3:7. Based on the total amount of the intermediate layer premixed powder, the atomic percentage of hafnium powder is 30%, and the remainder is zirconium powder. The remaining preparation steps are the same as in Example 1, and a zirconium-hafnium dissimilar metal is prepared.

[0070] SEM image of the zirconium-hafnium dissimilar metal interlayer prepared in Example 5 is shown below. Figure 7 As shown, from Figure 7It can be seen that the zirconium-hafnium dissimilar metal is composed of 1. a hafnium layer, 2. a first diffusion layer, 3. an intermediate layer, 4. a second diffusion layer, and 5. a zirconium layer. The interface achieves good bonding, without microcracks, diffusion voids, or incomplete bonding defects. The intermediate layer undergoes mutual diffusion with both metallic hafnium and metallic zirconium, forming a continuous diffusion layer of a certain thickness. The microstructure and dimensions of the hafnium and zirconium layers in Example 5 are the same as in Example 1. The microstructure of the intermediate layer in Example 5 is measured to be lamellar, with a length dimension of 218–345 μm and a width dimension of 27–64 μm, resulting in an aspect ratio of 5–8. The thickness of the first diffusion layer is measured to be 400 μm, and the thickness of the second diffusion layer is 300 μm. The ratio of the total thickness of the first and second diffusion layers to the total thickness of the first, second, and intermediate layers is 0.44.

[0071] Using the same testing method as in Example 1, the shear strength of the zirconium-hafnium dissimilar metal prepared in Example 5 was tested to be 422 MPa.

[0072] As can be seen from Examples 1-5, the zirconium-hafnium dissimilar metals prepared in Examples 1-4 are significantly superior to those in Example 5. The main reason for this is presumably that the lamellar structure in the intermediate layer of the zirconium-hafnium dissimilar metal in Example 5 is coarsened in the width direction, resulting in a decreased aspect ratio and failing to fully utilize the properties of the lamellar structure, leading to a reduction in shear strength. Examples 2-4 are even better, mainly because the zirconium-hafnium dissimilar metals in Examples 2-4 have relatively fine lamellar structures with better aspect ratios. Example 3 is particularly superior, as the zirconium-hafnium dissimilar metal in Example 3 has fine lamellar structures with a suitable aspect ratio.

[0073] Comparative Example 1

[0074] The difference between Comparative Example 1 and Example 3 is that in step S3, the sintering temperature is 1400℃ and the holding and pressure time is 5min. The remaining preparation steps are the same as in Example 3, and zirconium-hafnium dissimilar metal is prepared.

[0075] The microstructure of the zirconium-hafnium dissimilar metal interlayer prepared in Comparative Example 1 was measured to be lamellar, with a length dimension of 40–125 μm, a width dimension of 10–18 μm, and an aspect ratio of 4–7. Using the same method as in Example 3, the shear strength of the zirconium-hafnium dissimilar metal prepared in Comparative Example 1 was measured to be 238 MPa. Combining Examples 3 and 1, it can be seen that the lamellar structure of the zirconium-hafnium dissimilar metal interlayer in Comparative Example 1 is fine; however, the aspect ratio of the lamellar structure is small, failing to fully utilize its lamellar properties, resulting in a decrease in shear strength.

[0076] Comparative Example 2

[0077] The difference between Comparative Example 2 and Example 3 is that in step S3, the sintering temperature is 1600℃ and the holding time is 15min. The remaining preparation steps are the same as in Example 3, and zirconium-hafnium dissimilar metal is prepared.

[0078] The microstructure of the zirconium-hafnium dissimilar metal interlayer prepared in Comparative Example 2 was measured to be lamellar, with dimensions of 340-950 μm in the length direction and 17-25 μm in the width direction, resulting in an aspect ratio of 20-38. Using the same method as in Example 3, the shear strength of the zirconium-hafnium dissimilar metal prepared in Comparative Example 2 was measured to be 356 MPa. Combining Examples 3 and 2, it can be seen that the lamellar structure of the zirconium-hafnium dissimilar metal interlayer in Comparative Example 2 has a large aspect ratio; however, the grains in the length direction of the lamellar structure are coarse, which also leads to a decrease in shear strength.

[0079] Comparative Example 3

[0080] The difference between Comparative Example 3 and Example 1 is that no intermediate layer premixed powder is added to the zirconium-hafnium interface in Comparative Example 3, steps S1-4 are omitted, and in step S2, the hafnium metal block and zirconium metal block from steps S1-3 are stacked in a graphite mold and subjected to spark plasma pressure sintering. The remaining preparation steps are the same as in Example 1.

[0081] SEM image of the zirconium-hafnium dissimilar metal interlayer prepared in Comparative Example 3 is shown below. Figure 8 As shown, from Figure 8 As can be seen, the zirconium-hafnium dissimilar metal consists of 1. a hafnium layer, 2. a diffusion layer, and 3. a zirconium layer, in sequence. Metallic hafnium and metallic zirconium undergo interdiffusion, forming a continuous diffusion layer of a certain thickness. Using the same testing method as in Example 1, the shear strength of the zirconium-hafnium dissimilar metal prepared in Comparative Example 3 was measured to be 195 MPa. Combining Example 1 and Comparative Example 3, it can be seen that the intermediate layer can significantly improve the bonding strength of the zirconium-hafnium dissimilar metal.

[0082] It should be understood that the application of this application is not limited to the examples above. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the scope of the appended claims.

Claims

1. A zirconium-hafnium dissimilar metal, characterized in that, The dissimilar metal is composed of a hafnium layer, a first diffusion layer, an intermediate layer, a second diffusion layer, and a zirconium layer. The dissimilar metal is prepared by spark plasma pressure sintering of a hafnium metal block, an intermediate layer premixed powder, and a zirconium metal block. The intermediate layer premixed powder is composed of hafnium powder and zirconium powder. Based on the total amount of the intermediate layer premixed powder, the atomic percentage of the hafnium powder is 30% to 80%, and the balance is zirconium powder. The hafnium layer has an equiaxed microstructure with a grain size of 200-800 μm, and the zirconium layer has a lamellar microstructure with a length dimension of 200-700 μm and a width dimension of 10-80 μm. The intermediate layer has a sheet-like structure with a length dimension of 60-500 μm, a width dimension of 3-64 μm, and an aspect ratio of 5-35.

2. The zirconium-hafnium dissimilar metal according to claim 1, characterized in that, Based on the total amount of the intermediate layer premixed powder, the atomic percentage of the hafnium powder is 40% to 80%, with the remainder being zirconium powder.

3. The zirconium-hafnium dissimilar metal according to claim 1, characterized in that, The sheet-like tissue of the intermediate layer has a length dimension of 60~500μm, a width dimension of 3~30μm, and an aspect ratio of 9~35.

4. The zirconium-hafnium dissimilar metal according to claim 1, characterized in that, Based on the total amount of the intermediate layer premixed powder, the atomic percentage of the hafnium powder is 40% to 60%, with the remainder being zirconium powder. The microstructure of the intermediate layer is lamellar, with the lamellar structure having a length dimension of 60 to 500 μm, a width dimension of 5 to 30 μm, and an aspect ratio of 9 to 33.

5. The zirconium-hafnium dissimilar metal according to claim 1, characterized in that, The thickness of the first diffusion layer is 200~400μm, the thickness of the second diffusion layer is 200~500μm, and the ratio of the total thickness of the first diffusion layer and the second diffusion layer to the total thickness of the first diffusion layer, the second diffusion layer and the intermediate layer is 0.41-0.

60.

6. A zirconium-hafnium dissimilar metal spark plasma pressure sintering bonding method according to claim 1, comprising the following steps: S1. Provide hafnium metal blocks, intermediate layer premixed powder and zirconium metal blocks, wherein the intermediate layer premixed powder is composed of hafnium powder and zirconium powder, and the atomic percentage of hafnium powder is 30%~80% based on the total amount of intermediate layer premixed powder, with the remainder being zirconium powder; S2. The hafnium metal block, the intermediate layer premixed powder, and the zirconium metal block are stacked in a mold, with the intermediate layer premixed powder located between the hafnium metal block and the zirconium metal block; S3. The mold is placed in a spark plasma sintering system and pressure sintered to prepare zirconium-hafnium dissimilar metal.

7. The zirconium-hafnium dissimilar metal discharge plasma pressure sintering bonding method according to claim 6, characterized in that, The hafnium metal block and zirconium metal block in step S1 are prepared by spark plasma pressure sintering. The sintering temperature of the hafnium metal block is 1600~1700℃, the sintering pressure is 20~40MPa, and the sintering time is 5~15min. The sintering temperature of the zirconium metal block is 1450~1550℃, the sintering pressure is 20~40MPa, and the sintering time is 5~15min.

8. The zirconium-hafnium dissimilar metal discharge plasma pressure sintering bonding method according to claim 6, characterized in that, In step S3, the sintering temperature is 1450~1550℃, the sintering pressure is 20~40MPa, and the sintering time is 5~15min.

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