CN114101888A

CN114101888A - Zirconium alloy low-temperature diffusion bonding method

Info

Publication number: CN114101888A
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: 2022-03-01
Anticipated expiration: 2041-12-13
Also published as: CN114101888B

Abstract

The invention discloses a zirconium alloy low-temperature diffusion bonding 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; cleaning and deoiling the surface of the processed zirconium alloy workpiece substrate; 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 fixing the zirconium alloy workpiece subjected to modification treatment or the workpiece added with the intermediate layer by spot welding; diffusion bonding to obtain a finished product; the temperature for diffusion bonding is 760-820 ℃, the pressure value is 7-22 MPa, and the heat preservation time is 30-130 min. By effectively performing surface modification treatment on a zirconium alloy to-be-connected interface or adopting different intermediate transition layers at the connection interface and designing a reasonable diffusion connection process, a zirconium alloy component with good joint performance is obtained below the phase transition temperature of the zirconium alloy.

Description

Zirconium alloy low-temperature diffusion bonding method

Technical Field

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

Background

Nuclear energy is a clean and efficient energy source, and the development of nuclear energy is a strategic policy of energy development which is insistently and immovable in China at present. The nuclear fuel element is a barrier core component of the nuclear reactor, which has an extremely important influence 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 the low thermal neutron absorption cross section, good corrosion resistance and moderate mechanical property, the feasibility of the integrated manufacturing of the fuel assembly is directly determined by the research aiming at the connection technology, and the performance of the whole fuel assembly is directly influenced by whether the connection welding line is stable and reliable, so that the potential hazards are brought to the safe, stable and reliable operation of the nuclear reactor.

At present, research on zirconium alloy welding technology is systematically carried out in a plurality of countries at home and abroad, and a direct application object core is developed around a zirconium alloy rod-shaped fuel element, in particular to vacuum Electron Beam Welding (EBW), tungsten gas arc welding (TIG), pulse laser welding (LBW), pressure resistance welding (RPW) and the like.

With the development of nuclear energy technology, requirements on long service life, high fuel consumption, high safety and high reliability of fuel elements are met, and the integrated manufacturing of novel fuel elements with multilayer dense connection structures is on schedule. The traditional fusion welding method for integrated manufacturing can not effectively meet the existing requirements, and the following technical difficulties mainly exist: 1) the welding quantity is large, the welding deformation control difficulty is large, and the whole deformation is easy to be out of tolerance; 2) the interval of dense welding seams is small, the welding seams are overlapped and mutually influenced, the size of an internal flow passage is difficult to control, and the long-period seam corrosion tendency is caused by the incomplete penetration of the structure; 3) weld and its heat affected zone temperature overshoot adversely affect internal fuel core performance irreversibly. On the basis, the novel fuel element has larger structure size, higher requirement on the fusion depth control precision and larger deformation control difficulty, the technical problem is more prominent, and the development of the subsequent novel fuel element is also greatly challenged, so that a novel connecting method and a novel technology thereof are urgently needed to be researched for innovative technical substitution.

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

In the prior art, in the aspect of diffusion bonding technology, a block structure is formed by stitch welding of plates which are made of the same material as a welding workpiece and is used as a structural intermediate layer for welding; the method adopts an outer side limiting and inner supporting tool to carry out thermal expansion constraint on a part to be welded; it has also been proposed to plate a nickel plating layer containing nickel and phosphorus on the surface of the weldment. However, the diffusion bonding temperature of the zirconium alloy (lower than the phase transition temperature 826 ℃ of the zirconium alloy) cannot be reduced by adopting methods such as a structural intermediate layer, an outer side limiting method, an inner supporting tool and the like, and the method is not suitable for the homogeneous diffusion bonding of the zirconium alloy represented by Zr-4.

Disclosure of Invention

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

The invention is realized by the following technical scheme:

a low-temperature diffusion bonding method for zirconium alloy comprises the following steps:

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

cleaning and deoiling the surface of the processed zirconium alloy workpiece substrate;

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 fixing the zirconium alloy workpiece subjected to modification treatment or the workpiece added with the intermediate layer by spot welding;

diffusion bonding to obtain a finished product;

the temperature for diffusion bonding 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 oil removing process comprises:

ultrasonically cleaning a substrate by using an alkaline cleaning agent, washing by using deionized water, ultrasonically cleaning by using 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 15 min.

Optionally, the surface modification treatment is performed by 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 μm to 30 μm.

Optionally, the coating method comprises the following steps:

loading the workpiece to be surface modified into coating equipment, successively starting mechanical pump, Roots pump and molecular pump, and vacuumizing the system to less than or equal to 1 × 10^-3Pa；

Introducing argon to make the pressure less than or equal to 3 Pa;

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

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

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

Optionally, the process of assembling and fixing the modified zirconium alloy workpiece to be welded by spot welding is as follows:

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

and performing spot welding and fixing on two opposite sides of the assembled workpiece.

Optionally, when the modified multiple layers of to-be-welded zirconium alloy workpieces are assembled, corresponding positioning holes are designed and processed on each layer of to-be-welded test piece, and a high-temperature alloy or high-strength hot die steel is processed into positioning pins for accurate vertical positioning, wherein a 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.

Optionally, heating to a diffusion bonding temperature value in three stages before diffusion bonding, wherein each stage of heating is constant-speed heating;

the third-stage temperature rise is as follows: the first-stage heating is carried out from room temperature to 350 ℃, and the temperature is kept at 350 ℃;

the second-stage temperature rise is from 350 ℃ to 600 ℃, and the temperature is kept at 600 ℃;

the third stage of temperature rise is from 600 ℃ to 760 ℃ to 820 ℃, and the pressure is increased to 7MPa to 22MPa, and the temperature is kept;

and (5) carrying out third-stage temperature rise and then cooling to room temperature along with the furnace.

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

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

and in the third-stage heating process, the temperature is increased to 760-820 ℃ from 600 ℃ within 70 min.

Optionally, the diffusion bonding temperature and diffusion bonding pressure have the following linear matching relationship:

and (3) heating process:

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

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

from 350 ℃ to 600 ℃, pressure values: 7MPa to 22 MPa;

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

and (3) cooling:

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

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

Optionally, before the diffusion bonding, assembling the to-be-welded zirconium alloy workpiece 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 support piece, a lower tooling plate and a platform;

the assembling process comprises the following steps:

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

coating solder resists on the surfaces 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 supporting piece is a graphite sheet or a graphite column;

and 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 provided in the upper tooling plate, and a temperature thermocouple is arranged in the temperature monitoring channel.

Optionally, the graphite support height is:

in the formula (I), the compound is shown in the specification,

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

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

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

the zirconium alloy low-temperature diffusion bonding method provided by the embodiment of the invention is developed based on the nuclear industry zirconium alloy low-temperature diffusion bonding technology for the first time, and the technology can be directly applied to the fields of nuclear fuel elements, post-processing spent fuel transport container manufacturing and the like. By effectively performing surface modification treatment on a zirconium alloy to-be-connected interface or adopting different intermediate transition layers at the connection interface and designing a reasonable diffusion connection process, a 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 has good combination, the combination rate reaches more than 90 percent, the mechanical property of the joint is superior to that of the zirconium alloy base 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 effective residual debris cleaning frequency, the surface roughness of a diffusion interface of the zirconium alloy to be welded is processed to be not more than 0.8 mu m, cleaning is carried out through complete cleaning processes of alkali cleaning, deionized water, alcohol dehydration and the like, and then vacuum atmosphere protection treatment is carried out in time; and performing 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, thickness, intermediate layer and diffusion connection process, so that the low-temperature diffusion interface bonding and reliable connection of the nuclear zirconium alloy are realized, the diffusion connection temperature is less than or equal to 820 ℃, the interface bonding rate is more than or equal to 90%, and the interface connection strength is superior to that of a furnace-following parent metal.

The diffusion bonding 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 required to be used in the embodiments will be briefly described below, it should be understood that the following drawings only illustrate some embodiments of the present invention and therefore should not be considered as limiting the scope, and that for those skilled in the art, other related drawings can be obtained from these drawings without inventive effort. In the drawings:

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

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

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

FIG. 4 is a schematic diagram of the gold phase of the connection interface of the final product obtained in example 1 of the present invention.

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

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

Fig. 7 is an SEM image of the bonding interface of the finished product obtained in example 4 of the present invention, where the marked places represent the diffusion layers (i.e., diffusionlayer in the figure) at the diffusion bonding interface.

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

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

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

FIG. 11 is an SEM image of the bonding interface of the final product obtained in comparative example 1 of the present invention.

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

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail below with reference to examples, and the exemplary embodiments and descriptions thereof are only used for explaining the present invention and are not used as limitations of the present invention.

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: it is not necessary to employ these specific details to practice the present invention. In other instances, well-known structures, circuits, materials, or methods have not been described in detail so as not to obscure the present invention.

Throughout the specification, reference to "one embodiment," "an embodiment," "one example," or "an example" means: the particular features, structures, or characteristics described in connection with the embodiment or example are included in at least one embodiment of the invention. Thus, the appearances of the phrases "one embodiment," "an embodiment," "one example" or "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. Further, those of ordinary skill in the art will appreciate that the illustrations provided herein are for illustrative purposes and are not necessarily drawn to scale. As used herein, the term "and/or" 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", "upper", "lower", "inner", "outer", etc. indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and therefore, should not be construed as limiting the scope of the present invention.

Examples

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

In order to solve the above problems, an embodiment of the present invention provides a zirconium alloy low-temperature diffusion bonding method, specifically adopting the following technical scheme:

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

diffusion bonding to obtain a finished product;

Further, the zirconium alloy is a 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 bonding temperature, pressure and heat preservation time range can keep the structure and performance of the base material stable in the diffusion bonding process, and has enough energy to carry out element diffusion.

Further, the specified roughness is 0.8 μm or less, and the specified flatness is 0.02mm or less. Preferably, a special diamond grinding wheel is adopted for finish grinding, and meanwhile, particularly, the cooling and timely cleaning of residual scraps on the grinding wheel are emphasized in the grinding process, so that the oxidation and scratching of the finish grinding surface of the zirconium alloy are avoided.

Further, the surface cleaning and oil removing process comprises the following steps:

The ultrasonic cleaning with alkaline detergent is to clean zirconium alloy substrate to eliminate residual oil stain, dirt and oxide layer 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 modification layer is a Ti or Ni or Nb layer, and the thickness of the modification layer is 2-30 μm.

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 layer is selected to be plated on the surface of the zirconium alloy. And during surface modification, a high-purity Ti target or Ni target or Nb target is adopted, and the thickness of the final coating is controlled by controlling the magnitude of the target current and the coating time.

Further, the coating method comprises the following steps:

Introducing argon to make the pressure less than or equal to 3 Pa;

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

The specific process of adding the middle layer to the interface to be welded is as follows: and (3) ultrasonically cleaning and drying the middle foil with the size consistent with the plane to be welded by alcohol, and then flatly paving the middle foil on the lower test piece to be welded 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 can realize more sufficient diffusion, thereby forming a diffusion connection joint with good connection quality.

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

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

and spot welding and fixing two opposite sides of the assembled two workpieces, or fixing the workpieces by punching positioning holes and matching positioning pins.

Wherein, treat welding interface region unfitness of butt joint volume of mistake less than 0.3mm about selecting two zirconium alloy work pieces of injecing after the equipment, be in order to guarantee the even and stable of diffusion bonding in-process applied pressure, the upper and lower slab unfitness of butt joint of two zirconium alloy work pieces is greater than 0.3mm, can cause the edge to be pressed unevenly, and then lead to connecting the joining effect at face edge obviously to be less than and connect the face central point to put, simultaneously, treat that welding interface unfitness of butt joint is too big after, direct influence inside flow path takes shape and size precision guarantees. After the alloy workpieces to be welded are assembled, the two opposite sides are fixed in a TIG spot welding mode, or are fixed by matching positioning holes with positioning pins (the positioning holes are designed and processed on each layer of test piece to be diffused, high-temperature alloy or high-strength hot die steel is adopted to be processed into the positioning pins to be accurately positioned up and down, the fit clearance between the positioning holes and the positioning pins is less than or equal to +/-0.01 mm, or the interference fit of the positioning holes and the positioning pins is not more than 0.03 mm), and the misalignment caused by relative displacement in the subsequent steps is prevented.

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

Further, heating to a diffusion bonding temperature value in three stages before diffusion bonding, wherein the heating at each stage is constant-speed heating;

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

Wherein, because of the strong activity of the zirconium alloy, the surface is easy to be oxidized to generate compact ZrO₂And at the same time is very easy to adsorb O₂、N₂And S and other impurities, and therefore a three-level heating mode is designed, the temperature is kept at 350 ℃ for 1h and mainly used for degassing to effectively remove residual gas in the parent metal, on the basis, the temperature is gradually raised to 600 ℃ for heat preservation to ensure that the temperature of a workpiece is uniform, secondary degassing is carried out, and then the temperature is raised to the corresponding diffusion connection temperature to complete the diffusion connection process.

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

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

further, before the diffusion connection, assembling two zirconium alloy workpieces fixed by spot welding and a 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 process of assembling the zirconium alloy workpiece to be welded and the tooling plate on the assembling mechanism is as follows:

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 through 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 supporting piece is a graphite sheet or a graphite column;

Wherein, the pressure head and the platform play a role in transferring and applying pressure; the upper tooling plate and the lower tooling plate have the function of adjusting the effective working height; the graphite flake or graphite post play and support limiting displacement, prevent to treat the zirconium alloy work piece uneven under pressure of welding, can effectively realize diffusion interface's compressive capacity and runner size precision control through pressure head displacement stroke control simultaneously. Adopt even and perpendicular when this package assembly mode can guarantee diffusion bonding pressure to exert on the one hand, but on the other hand passes through spacing accurate control diffusion interface compression volume of graphite flake or graphite post, and then effective control diffusion interface diffusion degree, inside runner shaping and size deflection to prevent to exert pressure excessively, guarantee the diffusion bonding effect.

Wherein the solder resist comprises boron nitride and Al₂O₃Any of them, and is used after being mixed with water, alcohol and the like in a certain proportion.

The multilayer zirconium alloy workpiece is subjected to layered size design according to the workpiece forming size and the zirconium alloy diffusion connection single-layer compression amount, 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 the single-layer compression amount s₀Then, the thickness dimensions of each layer of the zirconium alloy before diffusion bonding are as follows:

S₁＝S+s₀ (2)

formula 1 applies to the upper and lower layers, formula 2 applies to the core sandwich layer, S is the forming size of each layer of the zirconium alloy workpiece, S₁The processing size of each layer of zirconium alloy workpiece before diffusion bonding. Through the reasonable design of the machining size of each layer of zirconium alloy workpiece, the uniform compression of each layer can be realized, and the size precision of the internal structure after each layer is formed is effectively controlled.

Wherein, the height calculation formula of the graphite support is as follows:

in the formula (I), the compound is shown in the specification,

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, respectively, from room temperature to the diffusion bonding temperature. The graphite support and the zirconium alloy used in this example had relative thermal expansion coefficients of 5.6X 10 at the diffusion bonding temperature, respectively^-6/° C and 6.0X 10^-6V. C. According to the graphite support piece design method, the graphite support piece height for zirconium alloy diffusion bonding of different specifications and sizes can be calculated by obtaining the physical properties of graphite and zirconium alloy.

By designing and controlling the sizes of the graphite support piece and each layer of zirconium alloy workpiece in the above mode, the zirconium alloy workpieces at all layers can be uniformly pressed, and the diffusion connection effect is better.

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

In addition, a temperature monitoring channel of the central point of the workpiece to be diffused is reserved in the upper tooling plate in a processing mode and is used for arranging a temperature thermocouple in the central position.

According to the zirconium alloy low-temperature diffusion connection method provided by the embodiment of the invention, a zirconium alloy component with good joint performance is obtained below the phase transition conversion temperature (lower than 826 ℃) of a zirconium alloy through effective surface modification treatment on a to-be-connected interface of the zirconium alloy or adding an intermediate transition layer on the to-be-connected interface and designing a reasonable diffusion connection process, the diffusion interface is good in combination, the combination rate is more than 90%, the mechanical property of the joint is superior to that of a furnace-associated zirconium alloy base material, 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 the diffusion bonding surfaces of two to-be-welded Zr-4 alloy plates:

and (3) carrying out fine grinding by adopting a special diamond grinding wheel, particularly paying attention to cooling and timely cleaning residual scraps on the grinding wheel in the grinding process, avoiding the oxidation and scratch of the fine grinding surface of the Zr-4 alloy, and processing the diffusion bonding surface of the Zr-4 alloy plate to be welded to be not more than 0.8 mu m and not more than 0.02mm in flatness.

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

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

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

after the sample is loaded into the film 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 × 10^-3Pa; introducing argon to make the pressure reach a target pressure value of 3 Pa; then, a bias voltage of 1000V is loaded, the pulse width is 80%, and the base material is cleaned by glow discharge so as to further remove the oxide film and impurities on the surface of the base material and expose a fresh surface of the base material. The final coating thickness is controlled by controlling the target current and the coating time, so that the surface of the Zr-4 alloy plate is modified and deposited with a metal Ti layer of 15 mu m.

(4) Accurately assembling and fixing the two modified Zr-4 alloy plates to be welded by spot welding:

and accurately assembling the two Zr-4 alloy plates to be welded, wherein the two Zr-4 alloy plates to be welded have the same size and shape, and the misalignment amount of the upper plate and the lower plate after the two plates are assembled is less than 0.3 mm.

After the two sheets 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 fixed by spot welding obtained in the step (4) with a tooling plate

And coating solder resists 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 flake, the lower tooling plate and the platform.

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

And heating to a specified temperature value in three stages before diffusion connection, wherein the temperature rise of each stage is constant. The first stage of temperature rise is from room temperature to 350 ℃ after 50min, and the temperature is kept at 350 ℃ for 60 min; the second-stage temperature rise is from 350 ℃ to 600 ℃ after 60min, and the temperature is kept at 600 ℃ for 35 min; and the third-stage heating is carried out for 70min from 600 ℃ to 820 ℃, the pressure is increased to 9MPa when the temperature is increased 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 step (5) is shown in fig. 2, and includes 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 in sequence:

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 an upper Zr-4 alloy plate 6 to be welded and a lower Zr-4 alloy plate 7 to be welded which are accurately assembled and fixed in a spot welding mode on the lower tooling plate 4, uniformly distributing a plurality of graphite flakes 3 on the peripheries of the Zr-4 alloy plate 6 and the Zr-4 alloy plate 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 aligned with 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 the central point of the workpiece to be diffused can be processed in the upper tooling plate and is used for arranging a temperature thermocouple at the central position, and as shown in fig. 3, a first temperature thermocouple 8 is arranged in the temperature monitoring channel. Meanwhile, two temperature thermocouples can be arranged on the periphery of the workpiece to be welded, namely a second temperature thermocouple 9 and a third temperature thermocouple 10.

The quality of the diffusion bonding interface obtained in the embodiment is detected by ultrasonic waves, and the diffusion bonding interface is well combined after detection without finding echo waves with any defects.

The metallographic structure analysis of the diffusion bonded interface obtained in this example was carried out, and the result was shown in fig. 4. As can be seen from fig. 4, no unbonded portion was observed in the metallographic photograph of the diffusion bonded interface of example 1.

The diffusion bonding interface obtained in the example was subjected to a shear test, and the sample in the shear test was broken at the base material position, indicating that the bonding strength of the diffusion bonding interface was superior to that of the furnace base material.

Example 2:

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

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

As can be seen from the metallographic image in fig. 5, no unbonded portion was observed in the metallographic image of the connection interface in example 2.

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

Example 3:

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

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

As can be seen from the metallographic image of fig. 6, no unbonded portion was observed in the metallographic image of the connection interface in example 3.

And the sample breaks at the position of the parent metal in the shear test.

Example 4:

this example differs from example 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 a 50 mu mNb foil is adopted as an intermediate layer; and the diffusion temperature is 820 ℃, the diffusion bonding pressure is 7MPa, and the heat preservation time is 30min when the diffusion bonding is carried out.

Specifically, the process of adding the middle layer between the surfaces to be welded of the two Zr-4 alloy plates to be welded is as follows: and (3) ultrasonically cleaning and drying the middle foil with the size consistent with the plane to be welded by alcohol, and then flatly paving the middle foil on the lower test piece to be welded to ensure that the plane to be welded is completely covered by the foil. .

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

And the sample breaks at the position of the parent metal in the shear test.

Example 5:

this example differs from example 4 in that: in this example, the diffusion temperature was 800 ℃ at the time of diffusion bonding.

The quality of the diffusion bonding interface of the embodiment is detected by ultrasonic waves, and the diffusion bonding interface is well combined without finding echo waves with any defects through detection.

As shown in fig. 8, no unbonded portion was observed in the SEM image of the connection interface, and the interface bonding rate was about 97%.

And the sample breaks at the position of the parent metal in the shear test.

Example 6:

this example differs from example 5 in that: the diffusion temperature in this example was 780 ℃ at the time of diffusion bonding.

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

And the sample breaks at the position of the parent metal in the shear test.

Example 7:

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

As shown in fig. 10, no unbonded portion was observed in the SEM image of the connection interface, and the interface bonding rate was about 93%.

And the sample breaks at the position of the parent metal in the shear test.

Comparative example 1:

this comparative example differs from example 7 in that: no intermediate layer was added in this example.

As shown in fig. 11, SEM image of the diffusion bonded interface shows that there is a significant unconnected portion in the interface, and the interface bonding rate is about 43%. The test specimen breaks at the joint interface in the shear test.

The processes, process methods, test methods and equipment which are not mentioned in the embodiments of the present invention are all known technologies. And will not be described in detail herein.

The above embodiments are provided to further explain the objects, technical solutions and advantages of the present invention in detail, it should be understood that the above embodiments are merely exemplary embodiments of the present invention and are not intended to limit the scope of the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims

1. A zirconium alloy low-temperature diffusion bonding method is characterized by comprising the following steps:

diffusion bonding to obtain a finished product;

2. The method of claim 1, wherein 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.

3. The method 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 zirconium alloy low-temperature diffusion bonding method according to claim 1, wherein the surface cleaning and oil removing process comprises the following steps:

5. The method of claim 1, wherein the surface modification treatment is performed by vacuum magnetron sputtering or vacuum ion implantation composite magnetron sputtering or vacuum cathode arc ion plating, the modification layer is a Ti or Ni or Nb layer, and the thickness of the modification layer is 2 μm to 30 μm.

6. The method of claim 5, wherein the coating method comprises the following steps:

Introducing argon to make the pressure less than or equal to 3 Pa;

7. The method of claim 1, wherein the intermediate layer is a Ti or Ni or Nb foil, and the thickness of the foil is 10 μm to 100 μm.

8. The zirconium alloy low-temperature diffusion bonding method of claim 1, wherein the processes of assembling and fixing the modified zirconium alloy workpiece to be welded by spot welding are as follows:

9. The method for low-temperature diffusion bonding of zirconium alloy according to claim 1, wherein when the modified multi-layer to-be-welded zirconium alloy workpiece is assembled, a corresponding positioning hole is designed and processed on each layer of to-be-welded test piece, and a positioning pin is processed by using high-temperature alloy or high-strength hot-working die steel to perform precise positioning up and down, wherein a fit clearance between the positioning hole and the positioning pin is less than or equal to +/-0.01 mm, or an interference fit of not more than 0.03mm is adopted.

10. The low-temperature diffusion bonding method for zirconium alloys according to claim 1,

heating to a diffusion bonding temperature value in three stages before diffusion bonding, wherein each stage of heating is constant-speed heating;

11. The method for low-temperature diffusion bonding of zirconium alloy according to claim 10, wherein the first-stage temperature rise is carried out at a temperature of from room temperature to 350 ℃ over 50min and is carried out at 350 ℃ for 60 min;

12. The method of claim 10, wherein the diffusion bonding temperature and diffusion bonding pressure have a linear matching relationship:

and (3) heating process:

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

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

from 350 ℃ to 600 ℃, pressure values: 7MPa to 22 MPa;

and (3) cooling:

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

13. The method for low-temperature diffusion bonding of zirconium alloy according to claim 1, further comprising assembling the to-be-welded zirconium alloy workpiece fixed by spot welding and the tooling plate on an assembling mechanism before the diffusion bonding;

the assembling process 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 upper tooling plate on the zirconium alloy workpiece;

and placing the pressure head on the upper tooling plate.

14. The method according to claim 13, wherein the upper tool plate and the lower tool plate are graphite plates;

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

15. The method of claim 13, wherein the graphite used for the upper tooling plate, the lower tooling plate and the graphite support is hot isostatic pressed graphite.

16. The method of claim 14, wherein a temperature monitoring channel is provided in the upper tooling plate for arranging a temperature thermocouple in the temperature monitoring channel.

17. The method of claim 13, wherein the graphite support has a height of:

in the formula (I), the compound is shown in the specification,