A method for direct vacuum diffusion bonding of zirconium alloys at low temperature

Abstract

The present invention belongs to the technical field of zirconium alloy connection. In order to develop a new zirconium alloy connection method and reduce the diffusion connection temperature, the present invention proposes to first subject the zirconium alloy to hydrogen treatment in high-purity hydrogen, and then conduct a new method of direct vacuum diffusion connection of the zirconium alloy. The hydrogen content of the zirconium alloy after the hydrogen treatment is between 0.05wt.% and 0.5wt.%. By adding hydrogen elements, the hydrogen elements promote the diffusion of Zr atoms during the welding process, and the direct connection of zirconium alloys can be achieved at a temperature lower than the conventional diffusion connection temperature of 100 to 150°C and a conventional diffusion pressure of 5 to 10MPa, and the joint has no pores and good strength. Compared with the prior art, the present invention greatly reduces the diffusion connection temperature of zirconium alloys, and solves the influence of temperature deviation on the requirements of long life and high reliability of new zirconium alloy fuel cladding.

Description

Technical Field

[0001] The invention belongs to the field of zirconium alloy connection, and in particular relates to a zirconium alloy low-temperature direct vacuum diffusion connection method. Background Art

[0002] As a clean energy that can be adopted on a large scale, nuclear energy is the core driving force for the growth of global energy consumption. Nuclear power is currently the only high-purity, efficient and low-carbon energy that can replace fossil fuels on a large scale. The nuclear reactor is the heart of nuclear power, and in the nuclear reactor, the fuel element cladding wraps the fuel core, which is considered to be the first safety barrier of the reactor. Zirconium alloys are widely used in nuclear reactor fuel element cladding and reactor core structural materials because of their low thermal neutron absorption cross section, strong resistance to neutron irradiation energy, excellent mechanical properties, and resistance to high temperature, high pressure and steam corrosion.

[0003] Fuel elements are mainly sealed by welding and are exposed to high temperature, high pressure, strong radiation and high coolant flow rate for a long time. Therefore, the long life and high reliability of fuel elements are crucial to the safe and stable operation of nuclear reactors, and the welding quality of zirconium alloy cladding will directly affect the performance of the entire fuel element.

[0004] In recent years, with the rapid development of the nuclear power industry and the development of new zirconium alloys, the welding of zirconium alloys has also been widely studied by scholars at home and abroad, and the most common welding methods are tungsten inert gas arc welding, electron beam welding, laser welding and other fusion welding methods. However, in view of the actual service environment of nuclear reactors, the use of traditional fusion welding methods for zirconium alloys still has the following major problems:

[0005] (1) The traditional fusion welding method has high welding heat input, which causes the welding temperature of the weld and the heat-affected zone to exceed the tolerance, causing significant changes in the zirconium alloy base material and reducing its service performance;

[0006] (2) The welds of zirconium alloy components are dense and complex, with a large number of welds. The fusion welding method easily leads to increased deformation of zirconium alloy components after welding, thus causing the overall deformation of the fuel element to exceed the tolerance;

[0007] (3) The temperature of zirconium alloy components during traditional diffusion welding is high, exceeding the phase transition temperature of the zirconium alloy, resulting in a decrease in the mechanical properties of the base material.

[0008] Therefore, based on the above problems that still exist in zirconium alloy cladding welding, it is now urgent to develop a new low-temperature connection technology for zirconium alloy components. Summary of the invention

[0009] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a method for low-temperature direct vacuum diffusion bonding of zirconium alloys. The zirconium alloy is first subjected to hydrogen treatment, and the hydrogen element is used to promote the diffusion of elements during the welding process to achieve low-temperature direct diffusion bonding of the zirconium alloy.

[0010] The object of the present invention is achieved through the following technical scheme: A method for direct vacuum diffusion bonding of zirconium alloy at low temperature, comprising the following steps:

[0011] S1, subjecting the zirconium alloy to hydrogen treatment, so that the hydrogen content in the zirconium alloy is 0.05wt.% to 0.5wt.%, preferably 0.1wt.% to 0.3wt.%; the hydrogen content in the zirconium alloy of the present invention can be precisely controlled by the equilibrium partial pressure of hydrogen;

[0012] S2. Vacuum diffusion welding the zirconium alloy after hydrogen treatment in step S1, wherein the temperature range of the vacuum diffusion welding is 600-700° C., preferably 650-680° C. The pressure range of the vacuum diffusion welding is 10-20 MPa.

[0013] Furthermore, in step S1, the zirconium alloy is a Zr-Sn zirconium alloy. It should be noted that the main element of the zirconium alloy is Zr, and other elements have little effect on diffusion bonding. The present invention mainly improves the plasticity of Zr after hydrogenation to improve its diffusion welding performance and reduce the temperature of diffusion welding. Therefore, it can be known from principle that the present invention can be applied to other zirconium alloys.

[0014] Furthermore, in step S1, the zirconium alloy is subjected to hydrogen treatment and surface treatment and cleaning and drying are required.

[0015] Furthermore, in step S1, the surface treatment method is: using 400# to 3000# metallographic sandpaper for step-by-step grinding, specifically using 400#, 800#, 1200#, 2000# and 3000# metallographic sandpaper for step-by-step grinding.

[0016] Furthermore, in step S1, the method of hydrogen treatment is: putting the zirconium alloy after surface treatment, cleaning and drying into a hydrogen furnace, evacuating the furnace, heating it to 700-750°C, and then filling it with 99.99wt.% high-purity hydrogen. After keeping it warm for 0.3-1.5h, cool it down, and calculate the hydrogen content of each sample by weight gain.

[0017] Furthermore, in step S2, the zirconium alloy needs to be ground, polished, cleaned and dried before the vacuum diffusion welding.

[0018] Furthermore, in steps S1 and S2, the cleaning and drying method is: placing the zirconium alloy in alcohol for ultrasonic cleaning and then blowing it dry.

[0019] Furthermore, in step S2, the vacuum diffusion welding method is: using a diffusion welding fixture to place the ground, polished, cleaned and dried zirconium alloy into a diffusion welding device, and then evacuating the diffusion welding device. When the vacuum degree reaches 5×10-3 When the temperature is below 3000 °C, the temperature is raised to 600-700 °C, and then a pressure of 5-20 MPa is applied, and the temperature is kept for 20-150 min.

[0020] Furthermore, in step S2, the heating rate of the heating is 10 to 30°C / min.

[0021] The beneficial effects of the present invention are:

[0022] (1) The present invention performs hydrogen treatment on the zirconium alloy, and utilizes the hydrogen element to achieve the effect of low-temperature direct diffusion connection of the zirconium alloy.

[0023] (2) The zirconium alloy diffusion joint interface obtained by the method of the present invention has no holes or cracks, and the joint strength is good, with a shear strength of 244 MPa. At the same time, the method is simple to operate and has low requirements on diffusion welding equipment.

[0024] (3) The present invention solves the technical shortcomings of the traditional fusion welding method of zirconium alloy, such as high temperature and large deformation during welding, and realizes the low-temperature and small-deformation connection of the new fuel element, ensuring the long life, high safety and high reliability of the fuel element. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the interface diagram of the Zr-4 zirconium alloy diffusion joint obtained in Example 1 of the present invention;

[0026] Figure 2 This is the interface diagram of the Zr-4 zirconium alloy diffusion joint obtained in Example 2 of the present invention;

[0027] Figure 3 This is the interface diagram of the Zr-4 zirconium alloy diffusion joint obtained in Example 3 of the present invention;

[0028] Figure 4 This is the interface diagram of the Zr-4 zirconium alloy diffusion joint obtained in Example 4 of the present invention;

[0029] Figure 5 This is the interface diagram of the Zr-4 zirconium alloy diffusion joint obtained in Comparative Example 1 of the present invention;

[0030] Figure 6 This is the interface diagram of the Zr-4 zirconium alloy diffusion joint obtained in Comparative Example 2 of the present invention. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings, but the protection scope of the present invention is not limited to the following.

[0032] Example 1

[0033] The zirconium alloy in this embodiment is a Zr-4 zirconium alloy plate.

[0034] A method for low-temperature direct vacuum diffusion bonding of zirconium alloys, the method specifically comprising the following steps:

[0035] (1) Hydrogen treatment of Zr-4 zirconium alloy plate: Use 400#, 800#, 1200#, 2000# and 3000# metallographic sandpaper to polish step by step, then put it in alcohol for ultrasonic cleaning and blow drying to obtain a clean surface. Then put the cleaned zirconium alloy into a hydrogen furnace for hydrogen treatment, and obtain a Zr-4 zirconium alloy plate with a hydrogen content of 0.2wt.% by controlling the equilibrium partial pressure of hydrogen in the system;

[0036] (2) Assembly of hydrogenated Zr-4 zirconium alloy plate before welding: Grind the hydrogenated zirconium alloy with metallographic sandpaper and then mechanically polish it to a mirror surface. Then put the clean and bright zirconium alloy base material into the diffusion welding fixture. After assembly, put the entire fixture into the diffusion welding equipment for diffusion welding treatment;

[0037] (3) Diffusion temperature and pressure: First, the diffusion welding equipment is subjected to high vacuum extraction. When the vacuum degree in the furnace is 5×10 -3 When the temperature is below Pa, heat to 650℃ at a heating rate of 20℃ / min. After reaching the equipment temperature, apply a pressure of 15MPa to the surface of the hydrogenated zirconium alloy and keep it warm for 60min. After the insulation is completed, cool it to room temperature with the furnace.

[0038] The microstructure of the diffusion bonding interface obtained by the implementation was analyzed, and the following results were obtained: Figure 1 As shown. Figure 1 The results show that no unwelded areas are observed at the interface and the shear strength can reach 244 MPa.

[0039] Example 2

[0040] The difference between this embodiment and embodiment 1 is that the welding temperature in this embodiment is 680° C.

[0041] The microstructure of the diffusion bonding interface obtained by the implementation was analyzed, and the following results were obtained: Figure 2 As shown. Figure 2 As a result, no unwelded area was observed at the interface.

[0042] Example 3

[0043] The difference between this embodiment and embodiment 1 is that during welding in this embodiment, the diffusion bonding pressure is 20 MPa.

[0044] The microstructure of the diffusion bonding interface obtained by the implementation was analyzed, and the following results were obtained: Figure 3 As shown. Figure 3 As a result, no unwelded area was observed at the interface.

[0045] Example 4

[0046] The difference between this embodiment and embodiment 1 is that in this embodiment, the heat preservation time during welding is 90 minutes.

[0047] The microstructure of the diffusion bonding interface obtained by the implementation was analyzed, and the following results were obtained: Figure 4 As shown. Figure 4 As a result, no unwelded area was observed at the interface.

[0048] Comparative Example 1

[0049] The difference between Comparative Example 1 and Example 1 is that the Zr-4 zirconium alloy is not subjected to hydrogen treatment, and the welding temperature is 700° C. and the pressure is 20 MPa.

[0050] The microstructure of the diffusion bonding interface obtained by the implementation was analyzed, and the following results were obtained: Figure 5 As shown. Figure 5 The results show that the Zr-4 zirconium alloy that has not been hydrogenated cannot be welded under this process, and its shear strength is 55 MPa, which is significantly lower than the joint strength in Example 1 with lower welding temperature and welding pressure.

[0051] Comparative Example 2

[0052] The difference between Comparative Example 2 and Example 1 is that the Zr-4 zirconium alloy is not subjected to hydrogen treatment, and the welding temperature is 780° C. and the pressure is 15 MPa.

[0053] The microstructure of the diffusion bonding interface obtained by the implementation was analyzed, and the following results were obtained: Figure 6 As shown. Figure 6 The results show that no unwelded area is observed at the interface, and the shear strength is 251 MPa, which is similar to the strength in Example 1.

[0054] The data of the above embodiments and comparative examples are summarized in Table 1 below:

[0055] Table 1 Shear strength of joints with different welding parameters

[0056]

[0057] The above is only a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the form disclosed herein, and should not be regarded as excluding other embodiments, but can be used in various other combinations, modifications and environments, and can be modified within the scope of the concept described herein through the above teachings or the technology or knowledge of the relevant field. The changes and modifications made by those skilled in the art shall not deviate from the spirit and scope of the present invention, and shall be within the scope of protection of the claims attached to the present invention.

Claims

1. A method for direct vacuum diffusion bonding of zirconium alloy at low temperature, characterized in that: It consists of the following steps: S1, performing surface treatment on the zirconium alloy, cleaning and drying the zirconium alloy, and then subjecting the zirconium alloy to hydrogen treatment to make the hydrogen content in the zirconium alloy be 0.1wt.%~0.3wt.%; Wherein, the surface treatment method is: using 400#~3000# metallographic sandpaper for step-by-step grinding; The hydrogenation treatment method is as follows: placing the zirconium alloy after surface treatment, cleaning and drying into a hydrogenation furnace, evacuating the furnace, heating it to 700-750° C., and then filling it with 99.99wt.% high-purity hydrogen, and keeping the temperature for 0.3-1.5h; The zirconium alloy is a Zr-Sn series zirconium alloy; S2, grinding, polishing, cleaning and drying the zirconium alloy after the hydrogen treatment in step S1, and then vacuum diffusion welding; The vacuum diffusion welding method comprises: placing the ground, polished, cleaned and dried zirconium alloy into a diffusion welding device, and then evacuating the diffusion welding device. When the vacuum degree reaches 5×10 -3 When the pressure is below 0.05 Pa, heat to 650-680℃ at a rate of 10-30℃ / min, then apply a pressure of 10-20MPa and keep warm for 20-150min. After the heat preservation, cool to room temperature with the furnace.

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