CN114101888B

CN114101888B - Zirconium alloy low-temperature diffusion connection method

Info

Publication number: CN114101888B
Application number: CN202111518590.3A
Authority: CN
Inventors: 王泽明; 王晶; 肖宗林; 曾静; 侯蔼麟; 王世忠; 邱绍宇
Original assignee: Nuclear Power Institute of China
Current assignee: Nuclear Power Institute of China
Priority date: 2021-12-13
Filing date: 2021-12-13
Publication date: 2023-05-02
Anticipated expiration: 2041-12-13
Also published as: CN114101888A

Abstract

The invention discloses a zirconium alloy low-temperature diffusion connection method, which comprises the steps of processing the surface to be welded of a zirconium alloy workpiece to be welded to specified roughness and flatness; carrying out surface cleaning and oil removal on the zirconium alloy workpiece substrate after the processing treatment; modifying the surface to be welded of the zirconium alloy workpiece to be welded or adding an intermediate layer into the interface to be welded; assembling and spot-welding the zirconium alloy workpiece subjected to modification treatment or the workpiece added with the intermediate layer; diffusion connection to obtain a finished product; the diffusion connection is carried out at 760-820 ℃, the pressure value is 7-22 MPa, and the heat preservation time is 30-130 min. By means of effective surface modification treatment for the interface to be connected of the zirconium alloy or different intermediate transition layers at the connecting interface and reasonable diffusion connection process, the zirconium alloy component with good joint performance is obtained below the phase transition temperature of the zirconium alloy.

Description

Zirconium alloy low-temperature diffusion connection method

Technical Field

The invention relates to the technical field of manufacturing of nuclear fuel elements and post-treatment spent fuel transport containers, in particular to a zirconium alloy low-temperature diffusion connection method.

Background

Nuclear energy is a clean and high-efficiency energy source, and the development of nuclear energy is an energy development strategy which is not moving in China. The nuclear fuel element is a barrier core component of a nuclear reactor, has an extremely important effect on the safety and reliability of the reactor, and the cladding is the first safety barrier of the nuclear reactor. The zirconium alloy is the only fuel element cladding material adopted by the current water-cooled nuclear reactor due to low thermal neutron absorption section, good corrosion resistance and moderate mechanical property, and the research on the connection technology of the zirconium alloy directly determines the feasibility of integrated manufacturing of a fuel assembly, and whether the connection weld joint is stable and reliable directly influences the performance of the whole fuel assembly, thereby bringing hidden danger to the safe, stable and reliable operation of the nuclear reactor.

At present, research on a zirconium alloy welding technology is developed in a plurality of countries at home and abroad, a direct application object core is unfolded around a zirconium alloy rod-shaped fuel element, and particularly vacuum Electron Beam Welding (EBW), tungsten electrode gas shielded welding (TIG), pulse laser welding (LBW), pressure resistance welding (RPW) and the like are related, but few reports are provided for the diffusion connection molding aspect of the fuel element, and the diffusion connection of the fuel element for a zirconium-based cladding is more blank.

With the development of nuclear energy technology, the requirements of long service life, high fuel consumption, high safety and high reliability of the fuel element are met, and the integrated manufacturing of the novel fuel element with the multilayer dense connection structure is convenient to formally carry out. The integrated manufacturing by adopting the traditional fusion welding mode can not effectively meet the existing requirements, and mainly has the following technical difficulties: 1) The welding quantity is large, the welding deformation control difficulty is high, and the whole deformation is easy to generate out-of-tolerance; 2) The dense welding seams are small in spacing, the welding seams are overlapped and mutually influenced, the size of an internal flow channel is difficult to control, and a structure which is not completely welded is prone to long-period crevice corrosion; 3) The weld and heat affected zone temperature overshooting have an irreversible negative impact on the internal fuel core performance. On the basis, the structural size of the novel fuel element is larger, the requirements on penetration control precision are higher, the deformation control difficulty is larger, the technical problems are more remarkable, and the novel fuel element brings great challenges to the subsequent development of the novel fuel element, so that a novel connecting method and a novel process thereof are urgently required to be pursued for innovation technology substitution research.

With the development of the emerging connection technology, a vacuum diffusion connection technology of microscopic interface solid phase connection is adopted as a precise connection method, so that the method is very suitable for rapid forming and integrated manufacturing of a large number of dense welding seam multilayer overlapped components. In order to effectively reduce the adverse influence on the structure and performance of the component after being heated and simultaneously effectively reduce the difficulty in controlling the deformation size of the whole structure of the precise component, the zirconium alloy low-temperature diffusion connection technology is gradually focused and paid attention at present.

In the aspect of the prior diffusion connection technology, it has been proposed to weld by adopting a plate stitch-welded block structure which is the same as a welded workpiece in material as a structural interlayer; it has been proposed to use an outside limit and an inside stay tool to constrain thermal expansion of the part to be welded; it has also been proposed to plate the surface of the weldment with a nickel plating layer containing nickel and phosphorus. However, the diffusion connection temperature of the zirconium alloy (lower than the transformation temperature 826 ℃ of the zirconium alloy) cannot be reduced by adopting methods such as a structural middle layer, an outer limit, an inner support tool and the like, and the method is not suitable for homogeneous diffusion connection of the zirconium alloy typified by Zr-4.

Disclosure of Invention

The invention aims to solve the technical problems that the prior diffusion connection technology cannot be suitable for homogeneous diffusion connection of zirconium alloy and cannot reduce the diffusion connection temperature of zirconium alloy, and provides a low-temperature diffusion connection method for zirconium alloy to solve the problems.

The invention is realized by the following technical scheme:

a method for low temperature diffusion joining of zirconium alloys comprising:

processing the surfaces to be welded of two zirconium alloy workpieces to be welded to specified roughness and flatness;

carrying out surface cleaning and oil removal on the zirconium alloy workpiece substrate after the processing treatment;

modifying the surface to be welded of the zirconium alloy workpiece to be welded or adding an intermediate layer into the interface to be welded;

assembling and spot-welding the zirconium alloy workpiece subjected to modification treatment or the workpiece added with the intermediate layer;

diffusion connection to obtain a finished product;

the temperature for diffusion connection is 760-820 ℃, the pressure value is 7-22 MPa, and the heat preservation time is 30-130 min.

Optionally, the zirconium alloy is pure Zr or Zr-Sn or Zr-Nb or Zr-Sn-Nb system;

preferably, the zirconium alloy is Zr-0 or Zr-2 or Zr-4 or N36.

Optionally, the specified roughness is 0.8 μm or less and the specified flatness is 0.02mm or less.

Optionally, the surface cleaning and degreasing process comprises the following steps:

ultrasonically cleaning a substrate by adopting an alkaline cleaning agent, washing by deionized water, ultrasonically cleaning by absolute ethyl alcohol, and drying;

the ultrasonic cleaning time of the alkaline cleaning agent and the absolute ethyl alcohol is more than or equal to 15min.

Optionally, the surface modification treatment is performed by adopting a vacuum magnetron sputtering or vacuum ion implantation composite magnetron sputtering or vacuum cathode arc ion plating method, the modification layer is a Ti or Ni or Nb layer, and the thickness of the modification layer is 2-30 mu m.

Optionally, the coating method comprises the following steps:

the workpiece to be surface modified is put into coating equipment, a mechanical pump, a Roots pump and a molecular pump are started successively, and the system is vacuumized to be less than or equal to 1 multiplied by 10 ^-3 Pa；

Argon is introduced to enable the pressure to be less than or equal to 3Pa;

loading the bias voltage of 800-1200V, with a pulse width of 80%, and cleaning the substrate by glow discharge;

and controlling the thickness of the final film layer by controlling the size of the target current and the film coating time to obtain the surface modified workpiece.

Optionally, the intermediate layer is a Ti or Ni or Nb foil, and the foil has a thickness of 10 μm to 100 μm.

Optionally, the assembling and spot welding fixing process of the zirconium alloy workpiece to be welded after the modification treatment comprises the following steps:

assembling the zirconium alloy workpiece to be welded, wherein the misalignment amount of the upper and lower interface areas to be welded of the assembled zirconium alloy workpiece to be welded is less than 0.3mm;

and carrying out spot welding fixation on two opposite sides of the assembled workpiece.

Optionally, when the modified multi-layer zirconium alloy workpiece to be welded is assembled, corresponding positioning holes are designed and processed on each layer of the workpiece to be welded, and high-temperature alloy or high-strength hot die steel is adopted to process the workpiece to be welded into positioning pins for up-down accurate positioning, wherein the fit clearance between the positioning holes and the positioning pins is less than or equal to +/-0.01 mm, or interference fit of not more than 0.03mm is adopted.

Optionally, three stages of heating are carried out to the diffusion connection temperature value before diffusion connection, and each stage of heating is carried out at a constant speed;

the three-stage temperature rise is as follows: the first stage of heating is to raise the temperature from room temperature to 350 ℃ and preserving heat at 350 ℃;

the second stage is heated from 350 ℃ to 600 ℃ and is kept at 600 ℃;

raising the temperature from 600 ℃ to 760 ℃ to 820 ℃ in the third stage, pressurizing to 7MPa to 22MPa, and preserving heat;

and after three-stage heating, cooling to room temperature along with the furnace.

Optionally, the temperature is raised to 350 ℃ from room temperature for 50min in the first-stage heating process, and the temperature is kept at 350 ℃ for 60min;

the temperature is increased from 350 ℃ to 600 ℃ in the second-stage temperature increasing process for 60min, and the temperature is kept at 600 ℃ for 35min;

in the third stage heating process, the temperature is raised to the specified 760-820 ℃ from 600 ℃ for 70 min.

Optionally, the diffusion connection temperature and the diffusion connection pressure have the following matching relationship linearly:

and (3) heating:

the pressure value is 2-4MPa under the state of room temperature prepressing;

the temperature is from room temperature to 350 ℃ and the pressure value is 4-7MPa;

pressure value from 350 ℃ to 600 ℃): 7MPa to 22MPa;

from 600 ℃ to the specified diffusion temperature, pressure value: 7MPa to 22MPa;

and (3) a cooling process:

the pressure value is 7 MPa-22 MPa from the appointed diffusion temperature to 350 ℃;

350 ℃ and below, pressure value: 2MPa to 4MPa.

Optionally, before the diffusion connection, assembling the zirconium alloy workpiece to be welded fixed by spot welding and the tooling plate on an assembling mechanism;

the assembly mechanism comprises a pressure head, an upper tooling plate, a graphite supporting piece, a lower tooling plate and a platform;

the assembly process is as follows:

placing the platform on a workbench of a diffusion welding machine;

coating solder resist on the surface of the upper tooling plate and the lower tooling plate;

placing the lower tooling plate on the platform;

placing the spot welded zirconium alloy workpiece between a plurality of graphite supports;

placing the upper tooling plate on the zirconium alloy workpiece;

and placing the pressure head on the upper tooling plate.

Optionally, the upper tooling plate and the lower tooling plate are graphite plates;

the graphite support piece is a graphite sheet or a graphite column;

the graphite supporting pieces are uniformly distributed between the upper tooling plate and the lower tooling plate.

Optionally, the graphite used for the upper tooling plate, the lower tooling plate and the graphite support is hot isostatic pressing graphite.

Optionally, a temperature monitoring channel is arranged in the upper tooling plate, and the temperature monitoring channel is used for arranging a temperature thermocouple.

Optionally, the graphite support height is:

in the method, in the process of the invention,

representing the height of the graphite support piece and the forming size of the zirconium alloy workpiece at 20 ℃ respectively;

representing the coefficients of thermal expansion of the HIP graphite and the zirconium alloy from room temperature to the diffusion bonding temperature, respectively.

Compared with the prior art, the invention has the following advantages and beneficial effects:

the zirconium alloy low-temperature diffusion connection method provided by the embodiment of the invention is developed based on the zirconium alloy for nuclear industry for the first time, and can be directly applied to the fields of nuclear fuel element and post-treatment spent fuel transportation container manufacturing and the like. By means of effective surface modification treatment for the interface to be connected of the zirconium alloy or different intermediate transition layers at the connecting interface and reasonable diffusion connection process, the zirconium alloy component with good joint performance is obtained below the phase transition temperature of the zirconium alloy. The detection shows that the diffusion interface is well combined, the combination rate is more than 90%, the mechanical property of the joint is superior to that of the zirconium alloy parent metal along with the furnace, and the problem that the zirconium alloy component is difficult to realize good and reliable connection at low temperature is effectively solved.

Specifically, a special diamond grinding wheel is matched with a proper cooling liquid and timely and effectively cleans residual scraps, the surface roughness of a zirconium alloy diffusion interface to be welded is processed to be not more than 0.8 mu m, and the zirconium alloy diffusion interface is cleaned through complete cleaning processes such as alkaline cleaning, deionized water, alcohol dehydration and the like, and then vacuum atmosphere protection treatment is timely carried out; and then carrying out targeted modification treatment on the surface to be welded by vacuum magnetron sputtering, vacuum ion implantation composite magnetron sputtering, vacuum cathode arc ion plating and the like, or adding a foil as an intermediate layer at the interface to be welded, and designing a proper modification layer and thickness, intermediate layer and thickness and diffusion connection process to realize the low-temperature diffusion interface combination and reliable connection of the zirconium alloy for the core, wherein the diffusion connection temperature is less than or equal to 820 ℃, the interface combination rate is more than or equal to 90%, and the interface connection strength is better than that of a furnace-associated base metal.

The diffusion connection technology has the advantages of standard and effective process flow, strong pertinence and performability, convenient realization, good repeatability and low cost.

Drawings

In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings that are needed in the examples will be briefly described below, it being understood that the following drawings only illustrate some examples of the present invention and therefore should not be considered as limiting the scope, and that other related drawings may be obtained from these drawings without inventive effort for a person skilled in the art. In the drawings:

fig. 1 is a flowchart of a low-temperature diffusion connection method for zirconium alloy according to an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of assembling a zirconium alloy workpiece and a tooling plate on an assembling mechanism in the zirconium alloy low-temperature diffusion connecting method according to the embodiment of the invention.

Fig. 3 is a schematic diagram of a position arrangement of a temperature thermocouple during diffusion connection in the low-temperature diffusion connection method of zirconium alloy according to the embodiment of the present invention.

Fig. 4 is a golden phase diagram of the interface of the finished product obtained in example 1 of the present invention.

Fig. 5 is a golden phase diagram of the interface of the finished product obtained in example 2 of the present invention.

FIG. 6 is a golden phase diagram of the interface of the finished product obtained in example 3 of the present invention.

Fig. 7 is an SEM image of the connection interface of the finished product obtained in example 4 of the present invention, where the reference points represent diffusion layers (i.e., diffusionlayers in the figure) at the diffusion connection interface.

Fig. 8 is a SEM image of the connection interface of the finished product obtained in example 5 of the present invention.

Fig. 9 is a SEM image of the connection interface of the finished product obtained in example 6 of the present invention.

Fig. 10 is a SEM image of the connection interface of the finished product obtained in example 7 of the present invention.

FIG. 11 is a SEM image of the joint interface of the finished product obtained in comparative example 1.

The reference numerals in the figures denote parts or positions: the device comprises a 1-pressure head, a 2-upper tooling plate, a 3-graphite sheet, a 4-lower tooling plate, a 5-platform, a 6-upper Zr-4 alloy plate to be welded, a 7-lower Zr-4 alloy plate to be welded, an 8-first temperature thermocouple, a 9-second temperature thermocouple, a 10-third temperature thermocouple and an 11-temperature monitoring channel.

Detailed Description

The present invention will be described in further detail with reference to the following examples, for the purpose of making the objects, technical solutions and advantages of the present invention more apparent, and the description thereof is merely illustrative of the present invention and not intended to be limiting.

In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to one of ordinary skill in the art that: no such specific details are necessary to practice the invention. In other instances, well-known structures, circuits, materials, or methods have not been described in detail in order not to obscure the invention.

Throughout the specification, references to "one embodiment," "an embodiment," "one example," or "an example" mean: a particular feature, structure, or characteristic described in connection with the embodiment or example is included within at least one embodiment of the invention. Thus, the appearances of the phrases "in one embodiment," "in an example," or "in an example" in various places throughout this specification are not necessarily all referring to the same embodiment or example. Furthermore, the particular features, structures, or characteristics may be combined in any suitable combination and/or sub-combination in one or more embodiments or examples. Moreover, those of ordinary skill in the art will appreciate that the illustrations provided herein are for illustrative purposes and that the illustrations are not necessarily drawn to scale. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.

In the description of the present invention, the terms "front", "rear", "left", "right", "upper", "lower", "vertical", "horizontal", "high", "low", "inner", "outer", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, merely to facilitate description of the present invention and simplify description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the scope of the present invention.

Examples

The prior diffusion connection technology cannot be suitable for homogeneous diffusion connection of zirconium alloy and cannot reduce the diffusion connection temperature of zirconium alloy.

In order to solve the problems, the embodiment of the invention provides a zirconium alloy low-temperature diffusion connection method, which specifically adopts the following technical scheme:

a method for low temperature diffusion joining of zirconium alloys comprising:

processing the surface to be welded of the zirconium alloy workpiece to be welded to the specified roughness and flatness;

diffusion connection to obtain a finished product;

Further, the zirconium alloy is pure Zr or Zr-Sn or Zr-Nb or Zr-Sn-Nb system;

preferably, the zirconium alloy is Zr-0 or Zr-2 or Zr-4 or N36.

The selected diffusion connection temperature, pressure and heat preservation time range can keep the structure and performance of the base material stable in the diffusion connection process, and has enough energy for element diffusion.

Further, the specified roughness is 0.8 μm or less, and the specified flatness is 0.02mm or less. Preferably, the finish grinding is carried out by adopting a special diamond grinding wheel, and meanwhile, the cooling and timely cleaning of residual scraps on the grinding wheel are particularly focused in the grinding process, so that the zirconium alloy finish grinding surface is prevented from being oxidized and scratched.

Further, the surface cleaning and degreasing process comprises the following steps:

The alkaline cleaning agent is used for ultrasonic cleaning to clean the zirconium alloy substrate so as to remove oil stains, stains and oxide layers remained on the substrate.

Further, the surface modification treatment is carried out by adopting a vacuum magnetron sputtering or vacuum ion implantation composite magnetron sputtering or vacuum cathode arc ion plating method, the modified layer is a Ti or Ni or Nb layer, and the thickness of the modified layer is 2-30 mu m.

Wherein, the surface modification is to ensure the combination quality of the film quality of the modified layer and the zirconium alloy matrix, and Ti or Ni or Nb layers are plated on the surface of the zirconium alloy. And in the surface modification, a high-purity Ti target or a Ni target or a Nb target is adopted, and the thickness of the final coating is controlled by controlling the size of the target current and the coating time.

Further, the coating method comprises the following steps:

Argon is introduced to enable the pressure to be less than or equal to 3Pa;

and controlling the thickness of the final film layer by controlling the size of the target current and the film coating time to obtain the surface modified workpiece. Further, the intermediate layer is a Ti or Ni or Nb foil, and the thickness of the foil is 10-100 mu m.

The specific process of adding the intermediate layer at the interface to be welded is as follows: and (3) carrying out ultrasonic cleaning and drying on the intermediate layer foil with the size consistent with the size of the plane to be welded, and then spreading the intermediate layer foil on a lower test piece to be welded, so as to ensure that the plane to be welded is completely covered by the foil.

The thickness range of the intermediate layer selected by the invention can ensure that the intermediate layer and the base material are diffused more fully, thereby forming a diffusion connection joint with good connection quality.

Further, the process of assembling and fixing the two zirconium alloy workpieces subjected to the modification treatment comprises the following steps:

assembling two zirconium alloy workpieces, wherein the misalignment amount of the upper and lower interface areas to be welded of the two assembled zirconium alloy workpieces is less than 0.3mm;

and spot welding and fixing are carried out on two opposite edges of the assembled two workpieces, or fixing is carried out by punching positioning holes and matching with positioning pins.

The method comprises the steps of selecting and limiting the misalignment amount of the upper and lower interface areas to be welded of two zirconium alloy workpieces after assembly to be smaller than 0.3mm, wherein the purpose of ensuring the uniformity and stability of the applied pressure in the diffusion connection process is to ensure that when the misalignment amount of the upper and lower plates of the two zirconium alloy workpieces is larger than 0.3mm, the edge is pressed unevenly, the connection effect of the edge of the connecting surface is obviously lower than the center position of the connecting surface, and meanwhile, the forming of an internal flow channel and the dimensional accuracy guarantee are directly influenced after the misalignment amount of the interface to be welded is too large. When the to-be-welded alloy workpiece is assembled, fixing the two opposite edges by adopting a TIG spot welding mode, or fixing the two opposite edges by punching positioning holes and matching positioning pins (designing and processing the positioning holes on each layer of to-be-diffused workpiece, processing the positioning pins into positioning pins by adopting high-temperature alloy or high-strength hot die steel for carrying out up-down accurate positioning, wherein the matching clearance between the positioning holes and the positioning pins is less than or equal to +/-0.01 mm, or interference fit of not more than 0.03mm is adopted), so as to prevent the occurrence of relative displacement in the subsequent steps and cause the offset.

Further, when the modified multi-layer zirconium alloy workpiece to be welded is assembled, corresponding positioning holes are designed and processed on each layer of zirconium alloy workpiece to be welded, high-temperature alloy or high-strength hot die steel is adopted to process the zirconium alloy workpiece to be welded into positioning pins for up-down accurate positioning, wherein the fit clearance between the positioning holes and the positioning pins is less than or equal to +/-0.01 mm, or interference fit of less than or equal to 0.03mm is adopted.

Further, three stages of heating are carried out to the diffusion connection temperature value before diffusion connection, and each stage of heating is carried out at a constant speed;

the second stage is heated from 350 ℃ to 600 ℃ and is kept at 600 ℃;

Further, in the first-stage heating process, the temperature is raised to 350 ℃ from room temperature for 50min, and the temperature is kept at 350 ℃ for 60min;

Wherein, because the zirconium alloy has strong activity, the surface is easy to oxidize to generate compact ZrO ₂ At the same time extremely easily adsorb O ₂ 、N ₂ And S, and other impurities, a three-stage heating mode is designed, the temperature is kept at 350 ℃ for 1h and is mainly used for degassing so as to effectively remove residual gas in a base material, on the basis, the temperature is gradually raised to 600 ℃ for heat preservation, the temperature uniformity of a workpiece is ensured, secondary degassing is carried out, and then the temperature is raised to the corresponding diffusion connection temperature, so that the diffusion connection process is completed.

Further, because the zirconium alloy has good plasticity and low strength and hardness, in the diffusion connection process, measures such as slow pressure application, gradual pressure application, stable pressure maintaining, temperature reduction and pressure application and the like are adopted in sequence to ensure the reliable connection of interfaces of the zirconium alloy components at low temperature. The temperature rising process is matched with a pressure curve, and the pressure value is 2-4MPa in a pre-pressing state at room temperature; room temperature to 350 ℃ and pressure value of 4-7MPa;350 ℃ to 600 ℃, pressure value: 7MPa to 22MPa;600 ℃ to a specified diffusion temperature, pressure value: 7MPa to 22MPa;

in the cooling process, the diffusion temperature is designated to 350 ℃ and the pressure value is 7MPa to 22MPa;350 ℃ and below, pressure value: 2-4Mpa;

further, before the diffusion connection, assembling the two zirconium alloy workpieces fixed by spot welding and the tooling plate on an assembling mechanism;

the assembling mechanism comprises a pressure head, an upper tooling plate, a graphite supporting piece, a lower tooling plate and a platform, wherein the pressure head is arranged on one side of the tooling plate, the platform is arranged on one side of the lower tooling plate, and the graphite supporting piece is arranged between the upper tooling plate and the lower tooling plate;

the assembling process of the zirconium alloy workpiece to be welded and the tooling plate on the assembling mechanism comprises the following steps:

placing the platform on a workbench of a diffusion welding machine;

placing the lower tooling plate on the platform;

placing the two zirconium alloy workpieces fixed by spot welding between a plurality of graphite supporting pieces;

placing the upper tooling plate on the zirconium alloy workpiece;

and placing the pressure head on the upper tooling plate.

the graphite support piece is a graphite sheet or a graphite column;

The pressure head and the platform play a role in transmitting and applying pressure; the upper tooling plate and the lower tooling plate play a role in adjusting the effective working height; the graphite flake or the graphite column plays a supporting and limiting role, so that the zirconium alloy workpiece to be welded is prevented from being unevenly pressed, and meanwhile, the compression amount of a diffusion interface and the size precision control of a runner can be effectively realized through the displacement stroke control of the pressure head. By adopting the assembly mode, on one hand, uniformity and verticality can be ensured when diffusion connection pressure is applied, and on the other hand, the compression amount of a diffusion interface can be accurately controlled through the limit of a graphite sheet or a graphite column, so that the diffusion degree of the diffusion interface, the internal flow passage forming and the size deformation amount can be effectively controlled, excessive pressure is prevented, and the diffusion connection effect is ensured.

Wherein the solder resist comprises boron nitride and Al ₂ O ₃ Any one of the above materials is mixed with water, alcohol, etc. in a certain proportion for use.

Wherein, the multilayer zirconium alloy workpiece carries out layered dimension design according to the forming dimension of the workpiece and the single-layer compression amount of the diffusion connection of the zirconium alloy, and the specific mode is as follows: carrying out single-layer interface diffusion connection on zirconium alloy workpieces with the same structure under the condition of no graphite support piece, and recording single-layer compression s ₀ The thickness dimensions of the layers of the zirconium alloy before diffusion bonding are as follows:

S ₁ ＝S+s ₀ (2)

formula 1 is suitable for upper and lower layers, formula 2 is suitable for core interlayer, S is the forming size of each layer of zirconium alloy workpiece, S ₁ Is the processing size of each layer of zirconium alloy workpiece before diffusion connection. Through the reasonable design of the processing size of each layer of zirconium alloy workpiece, the uniform compression of each layer can be realized, and the dimensional accuracy of the internal structure after each layer is formed can be effectively controlled.

The calculation formula of the height of the graphite support piece is as follows:

in the method, in the process of the invention,

the height of the graphite support piece and the forming size of the zirconium alloy workpiece at 20 ℃ respectively;

the coefficients of thermal expansion of the isostatic graphite and the zirconium alloy are respectively from room temperature to the diffusion bonding temperature. The relative thermal expansion coefficients of the graphite support and the zirconium alloy used in this example at the diffusion bonding temperature were 5.6X10, respectively ^-6 Per DEG C and 6.0X10 ^-6 and/C. According to the design method of the graphite support piece, the heights of the graphite support piece for the zirconium alloy diffusion connection with different specifications and sizes can be calculated by acquiring the physical properties of graphite and zirconium alloy.

Through the design and the control of the graphite support piece and the sizes of the zirconium alloy workpieces of each layer in the above mode, the uniform compression of the zirconium alloy workpieces of each layer can be realized, and the diffusion connection effect is better.

Further, the graphite used for the upper tooling plate, the lower tooling plate and the graphite support piece is hot isostatic pressing graphite.

In addition, a temperature monitoring channel for reserving a center point of a workpiece to be diffused is processed in the upper tooling plate and is used for arranging a temperature thermocouple at the center position.

According to the zirconium alloy low-temperature diffusion connection method provided by the embodiment of the invention, by aiming at effective surface modification treatment of a zirconium alloy interface to be connected or adding an intermediate transition layer into the interface to be connected, and designing a reasonable diffusion connection process, a zirconium alloy component with good joint performance is obtained below the phase transition conversion temperature (lower than 826 ℃), the diffusion interface is well combined, the combination rate is more than 90%, the mechanical property of the joint is superior to that of a zirconium alloy parent metal along with a furnace, and the problem that the zirconium alloy component is difficult to realize good and reliable connection at low temperature is effectively solved.

Example 1

As shown in fig. 1, a method for low-temperature diffusion bonding of zirconium alloy comprises the following steps in sequence:

(1) Processing diffusion connection surfaces of two Zr-4 alloy plates to be welded:

the special diamond-impregnated grinding wheel is adopted for fine grinding, meanwhile, the cooling is particularly focused and the residual scraps on the grinding wheel are cleaned in time in the grinding process, the oxidation and scratch of the fine grinding surface of the Zr-4 alloy are avoided, the diffusion connection surface of the Zr-4 alloy plate to be welded is processed to be not more than 0.8 mu m, and the flatness is not more than 0.02mm.

(2) Cleaning and degreasing the surface of the Zr-4 alloy plate to be welded:

firstly, ultrasonically cleaning a Zr-4 substrate by adopting an alkaline cleaning agent for more than or equal to 15min, removing oil stains and oxide layers remained on the substrate, then washing by adopting deionized water, finally ultrasonically cleaning by adopting absolute ethyl alcohol for more than or equal to 15min, and then drying by adopting dry air.

(3) Carrying out surface modification on the surfaces to be welded of the two Zr-4 alloy plates to be welded:

after the sample is put into the coating equipment, the mechanical pump, the Roots pump and the molecular pump are successively started, and the system is vacuumized to be less than or equal to 1 multiplied by 10 ^-3 Pa; argon is introduced to enable the pressure to reach a target pressure value of 3Pa; then loading bias voltage of 1000V, pulse width of 80%, and glow discharge cleaning the substrate to further remove oxide film and impurities on the surface of the substrate, so that the substrate is exposed to a fresh surface. By controlling the magnitude of the target currentAnd controlling the final coating thickness by coating time to realize the surface modification deposition of the metal Ti layer 15 mu m on the Zr-4 alloy plate.

(4) Accurately assembling and spot-welding and fixing the two Zr-4 alloy plates to be welded after modification treatment:

and precisely assembling the two Zr-4 alloy plates to be welded, wherein the two Zr-4 alloy plates to be welded are identical in size and shape, and the misalignment of the upper plate and the lower plate after the two plates are assembled is smaller than 0.3mm.

After the two plates are accurately assembled, the two opposite sides are fixed by adopting a TIG spot welding mode.

(5) Assembling the two Zr-4 alloy plates to be welded, which are obtained in the step (4) and are fixed through spot welding, with a tooling plate

And (3) coating solder resist on the surfaces of the upper tooling plate and the lower tooling plate, and assembling the Zr-4 alloy plate to be welded with the pressure head, the upper tooling plate, the graphite sheet, the lower tooling plate and the platform.

(6) Performing diffusion connection on two Zr-4 alloy plates to be welded to obtain a finished product

Before diffusion connection, three stages of temperature rise are carried out until the specified temperature value is reached, and each stage of temperature rise is uniform temperature rise. The first-stage heating is carried out after 50min from room temperature to 350 ℃, and the temperature is kept at 350 ℃ for 60min; the temperature rise of the second stage is increased from 350 ℃ to 600 ℃ through 60min, and the temperature is kept at 600 ℃ for 35min; the temperature rise in the third stage is from 600 ℃ to 820 ℃ through 70min, the pressure is increased to 9MPa when the temperature rises to the specified temperature, the temperature is kept for 120min at 820 ℃ and 9MPa, and then the temperature is cooled to the room temperature along with the furnace.

The assembly mechanism used in the step (5) is shown in fig. 2, and comprises a pressing head 1, an upper tooling plate 2, a plurality of graphite sheets 3, a lower tooling plate 4 and a platform 5. The assembly process is as follows:

the method comprises the steps of placing a platform 5 on a workbench of a diffusion welding machine, placing a lower tooling plate 4 coated with a solder resist on the platform 5, placing two upper Zr-4 alloy plates 6 to be welded and fixed by spot welding, placing a lower Zr-4 alloy plate 7 to be welded on the lower tooling plate 4, uniformly distributing a plurality of graphite sheets 3 on the periphery of the Zr-4 alloy plates 6 and the Zr-4 alloy plates 7 and on the lower tooling plate 4, placing an upper tooling plate 2 coated with the solder resist on the upper Zr-4 alloy plate 6 to be welded and on the lower tooling plate 4, and finally placing a pressure head 1 on the upper tooling plate 2.

In addition, a temperature monitoring channel 11 for reserving a center point of a workpiece to be diffused can be machined in the upper tooling plate, and is used for arranging a temperature thermocouple at a center position, and a first temperature thermocouple 8 is arranged in the temperature monitoring channel as shown in fig. 3. Meanwhile, two temperature thermocouples, namely a second temperature thermocouple 9 and a third temperature thermocouple 10, can be arranged on the periphery of the workpiece to be welded.

The quality of the diffusion connection interface obtained in the embodiment is detected by adopting ultrasonic waves, and no echo wave with any defect is found through detection, so that the diffusion connection interface is well combined.

Metallographic analysis was performed on the diffusion-bonded interface obtained in this example, and the result was shown in fig. 4. As can be seen from fig. 4, no uncombination was observed in the metallographic photograph of the diffusion-bonded interface of example 1.

And (3) carrying out a shearing test on the diffusion connection interface obtained in the embodiment, wherein a sample in the shearing test is broken at the position of the base material, so that the connection strength of the diffusion connection interface is superior to that of the base material along with the furnace.

Example 2:

this embodiment differs from embodiment 1 in that: in this example, when diffusion bonding was performed, the diffusion bonding temperature was 800℃and the diffusion bonding pressure was 12MPa.

The quality of the diffusion joint interface of example 2 was examined by ultrasonic waves, and no echo wave with any defect was found by the examination, and the diffusion joint interface was well bonded.

As can be seen from the golden phase diagram in fig. 5, no uncombination was observed in the metallographic image of the connection interface in example 2.

And the sample is broken at the base material position in the shearing test, which shows that the connection strength of the surface diffusion connection interface is superior to that of the base material along with the furnace.

Example 3:

this embodiment differs from embodiment 1 in that: in this example, the diffusion temperature was 780℃and the diffusion bonding pressure was 16MPa when the diffusion bonding was performed.

The quality of the diffusion joint interface of example 3 was examined by ultrasonic waves, and no echo wave with any defect was found by the examination, and the diffusion joint interface was well bonded.

As can be seen from the golden phase diagram in fig. 6, no uncombination was observed in the metallographic image of the connection interface in example 3.

The sample breaks at the base material position in the shear test.

Example 4:

this embodiment differs from embodiment 1 in that: in the embodiment, the surfaces to be welded of two Zr-4 alloy plates to be welded are not subjected to surface modification, but 50 mu mNb foil is adopted as an intermediate layer; and the diffusion temperature is 820 ℃ and the diffusion connection pressure is 7MPa when diffusion connection is carried out, and the heat preservation time is 30min.

Specifically, the process of adding an intermediate layer between the surfaces to be welded of two Zr-4 alloy plates to be welded is as follows: and (3) carrying out ultrasonic cleaning and drying on the intermediate layer foil with the size consistent with the size of the plane to be welded, and then spreading the intermediate layer foil on a lower test piece to be welded, so as to ensure that the plane to be welded is completely covered by the foil. .

As shown in fig. 7, the SEM image of the connection interface obtained in example 4 showed no uncombined portion, and the interface bonding rate was about 98%.

The sample breaks at the base material position in the shear test.

Example 5:

this embodiment differs from embodiment 4 in that: the diffusion temperature in this example was 800 ℃ when diffusion bonding was performed.

The quality of the diffusion connection interface in the embodiment is detected by adopting ultrasonic waves, and no echo wave with any defect is found through detection, so that the diffusion connection interface is well combined.

As shown in FIG. 8, no uncombined portion was observed in the SEM image of the joined interface, and the interfacial bonding ratio was about 97%.

The sample breaks at the base material position in the shear test.

Example 6:

this embodiment differs from embodiment 5 in that: the diffusion temperature in this example was 780 ℃ when diffusion bonding was performed.

As shown in fig. 9, no unbonded portion was observed in the SEM image of the bonded interface, and the interfacial bonding ratio was about 95%.

The sample breaks at the base material position in the shear test.

Example 7:

this embodiment differs from embodiment 6 in that: the diffusion temperature in this example was 760 ℃ when diffusion bonding was performed.

As shown in fig. 10, no unconjugated portion was observed in the SEM image of the connecting interface, and the interface binding rate was about 93%.

The sample breaks at the base material position in the shear test.

Comparative example 1:

the difference between this comparative example and example 7 is that: no intermediate layer was added in this example.

As shown in fig. 11, SEM images of the diffusion-bonded interfaces showed that there were significant un-bonded interfaces, with an interfacial bonding rate of about 43%. The test specimen breaks at the interface of the connection during the shear test.

The processes, process methods, test methods and equipment not mentioned in the embodiments of the present invention are all known techniques. Not described in detail herein.

The foregoing detailed description of the invention has been presented for purposes of illustration and description, and it should be understood that the invention is not limited to the particular embodiments disclosed, but is intended to cover all modifications, equivalents, alternatives, and improvements within the spirit and principles of the invention.

Claims

1. A method for low-temperature diffusion bonding of zirconium alloy, comprising the steps of:

diffusion connection to obtain a finished product;

the temperature of the diffusion connection is 760-820 ℃, the pressure value is 7-22 MPa, and the heat preservation time is 30-130 min;

the zirconium alloy is pure Zr or Zr-Sn or Zr-Nb or Zr-Sn-Nb system;

the intermediate layer is Ti or Nb foil;

the surface modification treatment is carried out by adopting a vacuum magnetron sputtering or vacuum ion implantation composite magnetron sputtering or vacuum cathode arc ion plating method, the modification layer is a Ti or Ni or Nb layer, and the thickness of the modification layer is 2-30 mu m;

the coating method comprises the following steps:

Argon is introduced to enable the pressure to be less than or equal to 3Pa;

2. The method of claim 1, wherein the zirconium alloy is Zr-0 or Zr-2 or Zr-4 or N36.

3. The method for low-temperature diffusion bonding of zirconium alloy according to claim 1, wherein the specified roughness is 0.8 μm or less and the specified flatness is 0.02mm or less.

4. The method for low-temperature diffusion bonding of zirconium alloy according to claim 1, wherein the surface cleaning and degreasing process comprises:

5. The method of low temperature diffusion bonding of zirconium alloy according to claim 1, wherein the foil has a thickness of 10 μm to 100 μm.

6. The method for low-temperature diffusion bonding of zirconium alloy according to claim 1, wherein the assembling and spot welding fixing process of the zirconium alloy workpiece to be welded after modification treatment is as follows:

7. The method for connecting zirconium alloy by low-temperature diffusion according to claim 1, wherein when the modified multi-layer zirconium alloy workpiece to be welded is assembled, corresponding positioning holes are designed and processed on each layer of zirconium alloy workpiece to be welded, high-temperature alloy or high-strength hot die steel is adopted to process positioning pins for up-down accurate positioning, and a fit clearance between the positioning holes and the positioning pins is less than or equal to +/-0.01 mm or interference fit of not more than 0.03mm is adopted.

8. A low-temperature diffusion bonding method of zirconium alloy according to claim 1, wherein,

before diffusion connection, three stages of heating are carried out to the diffusion connection temperature value, and each stage of heating is carried out at a constant speed;

the second stage is heated from 350 ℃ to 600 ℃ and is kept at 600 ℃;

9. The method for low-temperature diffusion bonding of zirconium alloy according to claim 8, wherein the temperature is raised from room temperature to 350 ℃ for 50min and maintained at 350 ℃ for 60min during the first-stage heating;

10. The method for low-temperature diffusion bonding of zirconium alloy according to claim 8, wherein the diffusion bonding temperature and the diffusion bonding pressure have the following matching relationship:

and (3) heating:

the pressure value is 2-4MPa under the state of room temperature prepressing;

pressure value from 350 ℃ to 600 ℃): 7MPa to 22MPa;

and (3) a cooling process:

350 ℃ and below, pressure value: 2MPa to 4MPa.

11. The method for low-temperature diffusion bonding of zirconium alloy according to claim 1, further comprising assembling the zirconium alloy workpiece to be welded, which is fixed by spot welding, with a tooling plate on an assembly mechanism before the diffusion bonding is performed;

the assembly process is as follows:

placing the platform on a workbench of a diffusion welding machine;

placing the lower tooling plate on the platform;

placing the upper tooling plate on the zirconium alloy workpiece;

and placing the pressure head on the upper tooling plate.

12. The method for low-temperature diffusion bonding of zirconium alloy according to claim 11, wherein the upper and lower tooling plates are graphite plates;

the graphite support piece is a graphite sheet or a graphite column;

13. The method of claim 11, wherein the graphite used for the upper and lower tooling plates and the graphite support is hot isostatic pressing graphite.

14. The method for low-temperature diffusion connection of zirconium alloy according to claim 12, wherein a temperature monitoring channel is arranged in the upper tooling plate, and a temperature thermocouple is arranged in the temperature monitoring channel.

15. The method of claim 11, wherein the graphite support has a height of:

in the method, in the process of the invention,

representing the coefficients of thermal expansion of the HIP graphite and the zirconium alloy from room temperature to the diffusion bonding temperature, respectively. />