Layered cathode structure based on alternating distribution of functional layer and buffer layer and its rapid trial method

Abstract

The present application relates to a layered cathode structure based on the alternative distribution of functional layers-buffer layers and its rapid trial method, belongs to the field of mechanical processing technology, and relates to a layered cathode structure comprising a functional structure surface layer and a matrix, wherein the functional structure surface layer is further composed of a plurality of sub-functional layers and buffer layers stacked and arranged alternately. In actual service, the functional layer made of thermo-chemical materials generates refractory oxide layer in situ to complete self-protection and emit electron support arc discharge; the buffer layer is made of nanocrystalline material with high plastic deformation ability, which can not only release the thermal stress of the functional layer by its own moderate deformation, but also accelerate the migration of the cathode spot to slow down the cathode burning loss when contacting the cathode arc. By utilizing the synergistic effect of the functional layer and the buffer layer, the cracking, splitting and coating peeling problems caused by plasma discharge rapid heating and rapid cooling in the application scenarios such as hole drilling by electric spark machining and arc welding of the layered cathode are solved, and the ablation uniformity is improved and the ablation rate is reduced.

Description

TECHNICAL FIELD

[0001] The present application relates to a layered cathode structure based on the alternative distribution of functional layer-buffer layer and a rapid trial method thereof, and belongs to the technical field of mechanical processing. BACKGROUND

[0002] Electrode ablation is an inevitable failure process during the service of metal electrodes. During arc discharge, arc plasma continues to burn between the cathode and the anode, and the potential difference distribution between the cathode-arc column region-anode has non-uniformity, which can be divided into a cathode potential drop region, an arc column region and an anode potential drop region. In comparison, the potential change in the near-cathode region is particularly severe, giving the positively charged particles reaching the cathode surface a larger average energy, and accordingly, the cathode arc ablation is more severe. In addition, the metal cathode is easily subjected to concentrated ablation of cathode spots during discharge, and then forms ablation pits deep into the interior, resulting in non-uniform arc ablation, and even leading to abnormal failure of cathode perforation. Cathode spots are a characteristic behavior of metal cathode discharge, and the current density at the bottom of the spot can reach 10 4 ~10 8 A / cm 2 Under the extremely high spot current density and heat flux, the cathode material is ablated in the forms of melting, oxidation and boiling spatter, etc. in turn. Cathode surface strengthening is an effective means to improve the uniformity of metal cathode discharge ablation and reduce the ablation rate. Its principle is to manufacture a strengthening layer on the surface of the original cathode substrate by surface strengthening means such as gas deposition, laser cladding, additive manufacturing, etc., so as to replace the substrate to support the arc with the strengthening layer, thereby decoupling the different performance requirements of the cathode surface and the substrate. However, under the intense heat input of the arc plasma arc root, the sudden heating and rapid cooling of the cathode surface easily induces concentrated thermal stress. When the thermal expansion properties of the strengthening layer and the metal substrate differ greatly, the strengthening layer is often deformed, cracked or even peeled off, so that the metal substrate is directly exposed to the arc root, causing the surface-strengthened cathode to fail prematurely. Therefore, it is urgent to develop a new type of layered composite cathode structure and its rapid trial technology which is resistant to cracking.

[0003] At present, hafnium and zirconium-based thermally chemical materials are suitable for the surface strengthening layer of red copper electrode. During discharge, on the one hand, the low electron work function of the material itself ensures sufficient electron emission to support the stable combustion of the arc, and on the other hand, a refractory oxide layer is generated in situ to protect the substrate. In view of the cracking problem caused by the difference in thermal expansion between the hafnium and zirconium strengthening layer and the red copper substrate, the main existing solutions are to increase the intermediate transition layer, reduce the thickness of the strengthening layer, and adjust the arc discharge parameters. Research shows that adding a certain thickness of 50% Zr+50% Cu composition gradient layer between the zirconium strengthening layer and the copper substrate can to some extent inhibit cracking, and the Zr / Cu layered electrode only appears local cracks after discharge. Further replacing the intermediate layer material with Nb, the layered electrode is intact after arc discharge. The principle of reducing the thickness of the strengthening layer to inhibit the cracking of the cathode is to use the overall deformation ability of the substrate to coordinate the deformation of the surface strengthening layer. The specific implementation of arc discharge parameter control to inhibit cracking is to reduce the arc current, set the gradient current / voltage, and prolong the arc residence time, etc., and the core is to reduce the cooling rate of the cathode surface molten pool. Taking the electric spark machining process with an arc current of 100 A as an example, compared with direct arc, after setting the gradient increasing current value of 25 A-50 A-75 A-100 A, the peeling of the strengthening layer caused by large current discharge can be alleviated.

[0004] However, the existing anti-cracking solutions for layered composite electrodes are difficult to balance electrode service life and discharge machining quality and efficiency. The introduction of an intermediate layer, although it can inhibit brittle intermetallic compounds and release stress, needs to be combined with specific electrode material systems for intermediate layer selection, and often needs to explore the preparation process twice when preparing the strengthening layer and the intermediate layer by laser cladding, and cannot avoid the severe ablation process when the strengthening layer burns and exposes the substrate. Reducing the thickness of the surface strengthening layer of the layered electrode will result in a shorter service life of a single cathode, increasing the number of electrodes consumed during the electric processing process. Similarly, when reducing the arc current or setting the gradient current / voltage, the time required for a single electric processing is increased, and when changing the current and voltage parameters, it is easy to induce the formation of deformed and remelted layers and other deformed structures on the surface of the workpiece. Therefore, the existing anti-cracking design scheme of layered composite electrodes cannot improve the service performance of the electrode and achieve the quality and efficiency of electric processing at the same time. SUMMARY

[0005] The purpose of this invention is to provide a layered cathode structure based on alternating functional and buffer layers and its rapid prototyping method. Using this layered cathode structure, the problems of reinforcement layer cracking, splitting, and detachment during the arc discharge service of layered cathodes can be effectively solved. Specifically, the layered cathode structure includes a functional structural layer and a substrate, wherein the functional structural surface layer is further composed of several sub-functional layers and buffer layers, with layers alternately stacked and metallurgically bonded at the interface. By utilizing the synergistic effect of the sub-functional layers and buffer layers, the problems of cracking, splitting, and coating detachment caused by rapid heating and cooling during plasma discharge in applications such as EDM hole making and arc welding are solved. Simultaneously, the ablation uniformity is improved and the ablation rate is reduced, thereby achieving cathode life extension and processing efficiency improvement.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] Based on a layered cathode structure with alternating functional and buffer layers and its rapid prototyping method, several sub-functional layers and buffer layers are tightly stacked on the cathode substrate surface. During actual service, the sub-functional layers, made of thermochemical materials, discharge in situ, generating a refractory oxide layer to protect the substrate, while simultaneously emitting dense electrons to support the arc discharge. Correspondingly, the buffer layer is made of nanocrystalline material with high plastic deformation capability, which can release the thermal stress generated during the discharge process of the sub-functional layers through its own moderate deformation, and at the same time, accelerate the migration of cathode spots to reduce cathode burn-off when in contact with the cathode arc. The specific steps of the rapid prototyping technology involving the layered cathode structure are: cathode material design - substrate material deposition - surface roll-pressing grain gradient - cyclic alternating deposition - post-processing.

[0008] A layered cathode structure based on alternating functional and buffer layers and its rapid prototyping method include the following steps:

[0009] Step 1: Cathode Material and Configuration Design. Based on the environmental characteristics of the cathode during its specific service life and following the design guidelines for dedicated electrode materials, select appropriate sub-functional layer and buffer layer materials. Referencing the arc current and time of a single discharge process, design the layer thickness and number of layers in the multilayer composite structure. Based on the material type and structural characteristics, determine the fabrication method for the multilayer structure.

[0010] Step 2: Substrate Material Deposition. Metals A and B represent the sub-functional layer and buffer layer materials of the layered electrode. The first layer, A, is melt-deposited on the surface of the conductive electrode substrate using appropriate manufacturing techniques. The key control values ​​during the deposition process are layer thickness, surface and internal forming quality.

[0011] Step three: surface layer rolling grain gradient. Based on the first layer A, the surface layer is processed by unidirectional rolling to deform the near-surface layer into a nanocrystalline and submicron crystalline deformation layer. After rolling, the grain size in the deformation layer gradually increases from nanoscale to micron scale along the vertical direction, showing a gradient distribution of grain size, so as to achieve the surface grain gradient of the buffer layer material.

[0012] Step four: cyclic alternating deposition. Based on the layer A after rolling, the surface sub-functional layer B is deposited again by adjusting the parameter combination, and the layer thickness and surface / interior forming quality are also controlled. Then, according to the number of layers contained in the specific electrode structure, the steps two to four are iterated multiple times to deposit the layer A and layer B alternately. Finally, after several cycles, the functional layer-substrate layered composite electrode blank is prepared, and the functional layer contains the preset stacked distribution of sub-functional layer-buffer layer.

[0013] Step five, post-processing. For the layered composite electrode blank prepared by steps one to four, the outer wall and the upper surface are processed by numerical control machining to remove burrs, spheroidized particles and other surface defects, and to ensure that the surface to be discharged is smooth and flat.

[0014] Further, the electrode material design criteria involved in the cathode material design stage are specifically around the sub-functional layer material and the buffer layer material. The sub-functional layer should have the following basic physical and chemical properties: 1) thermal chemical discharge properties, the self-ionization energy is lower than 4.2eV, and the surface can form a conductive refractory oxide layer after discharge in air, and the oxide layer has stable performance and the melting point is higher than that of pure metal; 2) the melting point is higher than that of the substrate material; 3) has a certain plastic deformation ability. The buffer layer should have the following basic physical and chemical properties: 1) the plastic deformation ability is higher than that of the sub-functional layer material; 2) the self-ionization energy is not higher than 4.6eV; 3) when the linear expansion coefficient of the substrate is X, the thermal expansion coefficient of the buffer layer is between 0.8X and 1.2X.

[0015] Further, the functional layer of the layered cathode involves several layers of sub-functional layers and buffer layers, showing a multi-layer stacked structure, the thickness of a single layer should be between 1-3mm, and the overall thickness of the functional layer should not exceed 20mm. In this way, the concentrated thermal stress of the functional layer during arc discharge is released layer by layer, and the deformation mismatch caused by the mismatch of the thermal expansion properties of the functional layer and the substrate is relieved.

[0016] Further, in the deposition process of the substrate material, in order to ensure the interface bonding performance between the buffer layer and the substrate, laser wire deposition, high-speed laser cladding and other strong interface metallurgical bonding metal melting deposition technologies should be preferred. At the same time, in order to meet the design requirements of single layer thickness and micron level grain size in the structure design stage, high scanning speed and high laser power parameter combination should be adopted in the deposition process to improve the pool cooling rate and promote grain refinement.

[0017] Further, the buffer layer surface roller pressing grain gradient processing, its implementation is conducive to the unidirectional roller processing on the buffer layer surface to form the gradient change of nanocrystalline-micron crystal grain size. The upper surface of the processed buffer layer is nanocrystalline, and the grain size gradually increases from the surface to the inside to the micron scale.

[0018] Further, the cyclic deposition of the sub-functional layer and the buffer layer has the characteristics of rapidness and large design domain. Taking high-speed laser cladding deposition as an example, when two or more metal powder feeding modules are adopted, by placing A powder and B powder in feeding modules 1 and 2 respectively, when two kinds of materials are deposited alternately in the present application, the rapid and flexible preparation of heterogeneous materials can be realized through module switching.

[0019] Further, the layered cathode structure of the functional layer-buffer layer alternately distributed, the anti-cracking characteristic is realized through the multi-metal layer stacking structure design. The sub-functional layer directly faces the arc root, and it is difficult to avoid the generation of thermal stress during service. At this time, the buffer layer at the back will support the deformation of the sub-functional layer with strong plastic deformation ability, so as to partially release the stress. After the composition of multiple sub-functional layers-buffer layers, the thermal stress of the discharge ablation can be released to the maximum extent, the deformation is relieved, and the interlayer cracking is inhibited.

[0020] Further, the functional layer-buffer layer layered cathode structure has high uniformity and ablation resistance in the discharge ablation process. When the arc discharge continues, the sub-functional layer generates a refractory oxide layer in situ, which protects the substrate to reduce the ablation rate, and at the same time promotes the formation of a type 1 cathode spot to improve the ablation uniformity. When a single functional layer is ablated, the buffer layer directly faces the arc root, and the nanocrystalline on the surface can accelerate the migration of the cathode spot, reduce the residence time of the spot, and reduce the heat flux density on the cathode surface. Based on the system mechanism of the sub-functional layer and the buffer layer, the anti-cracking characteristic and the ablation-resistant long-life characteristic of the cathode are simultaneously promoted.

[0021] Compared with the existing layered cathode, the present application has the following advantages:

[0022] 1) The cathode structure and size type are widely applicable. The anti-cracking is realized by using the functional layer-buffer layer stacking design, and the thermal stress in the service process is fully released on the material level and the structure level. This multi-layer electrode structure is suitable for thin-walled cylindrical arc heater cathodes and rod-shaped electric spark machining hole electrodes, and can be flexibly transferred to various structures and sizes.

[0023] 2) The ablation resistance performance of the cathode is excellent in the whole life cycle. During the discharge service of the layered cathode, the functional layer generates a refractory oxide layer in situ to protect the substrate and reduce the ablation rate, and at the same time promotes the formation of a type 1 spot with slight ablation. When the sub-functional layer is ablated, the nanocrystalline surface of the buffer layer accelerates the migration of the cathode spot to reduce the input heat flux density. Both the functional layer and the buffer layer can improve the ablation resistance performance of the cathode and ensure the service performance in the whole life cycle.

[0024] 3) High cathode design life achievement rate. Most existing layered cathodes have excellent ablation performance under short-time, low-current discharge conditions, but are prone to cracking and premature failure after long-term service heat accumulation. The layered cathode involved in the present application relies on the multi-layer structure of soft-hard alternating stacking, effectively improving the achievement rate of cathode design life, and avoiding abnormal failure before reaching the theoretical life. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1(a) is a schematic diagram of a layered cathode structure with alternating distribution of functional layers and buffer layers;

[0026] Figure 1(b) is a schematic diagram of the working process of a layered electrode;

[0027] Figure 1(c) is a schematic diagram of the buffer layer becoming the carrier of the arc root;

[0028] Figure 2 Figure 2 is a preparation process diagram for a layered cathode with alternating distribution of functional layers and buffer layers;

[0029] Figure 3(a) is a schematic diagram of a functional layer and buffer layer thickness uniform structure;

[0030] Figure 3(b) is a schematic diagram of increasing the thickness of the sub-functional layer;

[0031] Figure 3(c) is a schematic diagram of increasing the thickness of the buffer layer;

[0032] Figure 4 Figure 4 is a schematic diagram of the anti-cracking mechanism of the cross-section of a layered cathode arc discharge;

[0033] Figure 5 Figure 5 is a scanning electron micrograph of the burned surface of a layered cathode;

[0034] Figure 6(a) is the morphology structure of a layered cathode prepared only by adopting a regulation process;

[0035] Figure 6(b) is the cross-sectional morphology structure of a layered cathode prepared only by adopting a regulation process.

[0036] In the figure: 1-functional structure layer, 2-substrate, 3-sub-functional layer, 4-buffer layer, 5-arc plasma, 6-anode, 7-layered cathode, 8-refractory oxide layer, 9-cathode spot, 10-raw material feeding module, 11-rolling mill. DETAILED DESCRIPTION

[0037] Figure 1 is a schematic diagram of the structure and discharge of a new layered cathode, Figure 2 Figure 2 is a preparation process diagram for a layered cathode with alternating distribution of functional layers and buffer layers, and Figure 3 is a variety of layered cathode structure design schemes, Figure 4 Figure 4 is a schematic diagram of the anti-cracking mechanism of the cross-section of a layered cathode arc discharge, Figure 5Figure 6 is a scanning electron micrograph of a burned surface of a layered cathode, and Figure 7 is a scanning electron micrograph of a cross-sectional structure of a layered cathode prepared only by a regulation process.

[0038] The present application relates to a layered cathode structure with alternating functional layers and buffer layers, as shown in Figure 1a which specifically comprises a functional structure layer (1) and a substrate (2), wherein the functional structure layer is further composed of several sub-functional layers (3) and buffer layers (4), which are alternately stacked and metallurgically combined at the interfaces. In actual service, the layered cathode can significantly solve the problems of cracking and functional layer separation of conventional layered cathodes, and has the advantages of 1) wide application of cathode structure and size type; 2) excellent ablation resistance throughout the life cycle; and 3) high design life achievement rate.

[0039] During the operation of the layered electrode, arc plasma (5) burns between the anode (6) and the layered cathode (7), and the sub-functional layers made of thermochemical materials generate refractory oxide layers (8) in situ to resist arc root ablation, as shown in Figure 1b which protects the substrate and prolongs the life of the cathode, and the non-metallic oxide layer promotes the migration of the cathode spot at high speed, making the cathode surface present uniform ablation. Correspondingly, when the electrode continues to discharge until the surface sub-functional layer is burned out, the buffer layer becomes the carrier of the arc root, as shown in Figure 1c which is made of nanocrystalline materials with high plastic deformation ability, which can not only release the thermal stress generated during the discharge of the sub-functional layer, but also accelerate the migration of the cathode spot when the cathode arc is contacted to slow down the ablation of the cathode. The numerous cathode spots (9) on the surface of the cathode migrate at high speed in the discharge area, dispersing the arc root of the cathode.

[0040] The preparation process of the layered cathode structure with alternating functional layers and buffer layers is shown in Figure 2 which mainly includes the following series of steps: 1) cathode material and configuration design; 2) substrate material deposition; 3) surface layer rolling grain grading; 4) cyclic alternating deposition; and 5) post-processing.

[0041] Cathode material and configuration design. As shown in Figure 2As shown in FIG. a, the layered electrode structure is stacked alternately by sub-functional layers A and buffer layers B. In the cathode material and structure design stage, the material types (A1, A2, B1, B2…) and structure characteristics (thickness a, number of layers β) need to be designed. The sub-functional layer should have the following physical and chemical properties: 1) thermal chemical discharge properties, the self work function is lower than 4.2eV, and the oxidation layer is difficult to fuse, stable in performance and the melting point is higher than that of pure metal; 2) the melting point is higher than the melting point of the substrate material; 3) has a certain plastic deformation ability. The buffer layer should have the following physical and chemical properties: 1) the plastic deformation ability is higher than that of the sub-functional layer material; 2) the self work function is not higher than 4.6eV; 3) when the base line expansion coefficient is X, the thermal expansion coefficient of the buffer layer is between 0.8X and 1.2X. Referring to the single discharge processing arc current and time, the layer thickness and the number of layers of the multi-layer composite structure are designed, among which the single layer thickness should be between 1-3mm, and the overall functional layer thickness should be less than 20mm.

[0042] Deposition of base material. On the surface of the conductive substrate, the first layer A is deposited based on reasonable manufacturing technology, and the key control values of the deposition process are layer thickness, surface and internal forming quality. Taking high-speed laser cladding deposition as an example, as shown in FIG. Figure 2 b, the manufacturing process adopts a parameter combination of high scanning speed and high laser power to improve the cooling rate of the molten pool and promote grain refinement. In order to facilitate the subsequent alternating cladding process efficiently, a deposition equipment containing two raw material feeding modules (10) is adopted, and the raw materials A and B of the sub-functional layer and the buffer layer are loaded into the two feeding modules respectively, and the rapid and flexible preparation of heterogeneous materials is realized by relying on module switching.

[0043] Surface rolling grain gradient. Based on the first layer A, the surface is processed by unidirectional rolling to make the near-surface layer deform into a nanocrystalline and sub-micron crystalline deformation layer, as shown in FIG. Figure 2 c. After rolling processing (11), the grain size in the deformation layer gradually increases from nanometer to micrometer along the vertical direction, showing a grain size gradient distribution, so as to achieve the surface grain gradient of the buffer layer material. The nanocrystalline surface can promote the migration of the cathode spot to reduce the single-point residence time, so as to improve the arc ablation resistance of the buffer layer.

[0044] Cyclic alternating deposition. Based on the layer A after rolling processing, the second deposition of the surface sub-functional layer B is carried out by adjusting the parameter combination, as shown in FIG. Figure 2 d, and the same key control layer thickness and surface / interior forming quality. Then according to the number of layers contained in the specific electrode structure, the steps 2-4 are iterated multiple times to alternately deposit layers A and B. After several cycles, a functional layer-substrate layered composite electrode blank is prepared, which contains a preset stack of sub-functional layer-buffer layer.

[0045] Post-processing. For the layered composite electrode blanks prepared by steps 1-4, the outer peripheral wall and the upper surface are finished by numerical control machining or the like to remove burrs, spheroidized particles and other surface defects, and to ensure that the surface to be discharged is smooth and flat.

[0046] In the design of cathode materials and configurations, the structural design scheme of the sub-functional layer and the buffer layer is shown in FIG. 3. When the cathode arc discharge processing condition is relatively conventional, the structure with uniform thickness of the sub-functional layer and the buffer layer is preferred, as shown in Figure 3a When the single discharge processing time is relatively long, the thickness of the sub-functional layer can be appropriately increased to ensure the stability of the processing, as shown in Figure 3b Correspondingly, when the single discharge processing time is short and the current is large, the thickness of the buffer layer should be appropriately increased to fully release the concentrated stress caused by the large current, as shown in Figure 3c

[0047] The mechanism of uniform discharge ablation and anti-cracking of the layered electrode with alternating distribution of the sub-functional layer and the buffer layer is shown in Figure 4 a. The refractory oxide layer is formed in situ on the surface of the sub-functional layer, which protects the substrate and promotes the high-speed moving cathode spot. The temperature of the cathode discharge site is high, while the temperature of the surrounding non-discharge site is low. The thermal stress is formed under the influence of the temperature gradient, which further causes the cathode to bend and deform towards the center, as shown by the arrow in Figure 4 a. Benefiting from the "soft-hard" composite of the multi-layer sub-functional layer and the buffer layer, the deformation is released layer by layer, thereby reducing the cracking tendency of the cathode. However, the layered cathode with surface coating strengthening alone is prone to cracking under concentrated stress, as shown in Figure 4 b. Under the influence of bending stress, the surface strengthening layer and the substrate are pulled apart and peeled off at the edge, and the internal part is also longitudinally cracked.

[0048] In this embodiment, the electrode is applied to the preparation of diamond-shaped hole structure by electric spark machining. The original layered electrode is a copper-chromium alloy electrode, the rod-shaped electrode has a length of 20 cm and a diamond-shaped cross section with opposite diagonal lines of 4 mm and 2 mm in length. During use, the electrode is severely ablated by discharge, which even leads to the formation of connected holes in adjacent diamond-shaped holes. In order to improve the service life of the electrode, a functional layer is designed on the surface of the original copper-chromium substrate. The functional layer is internally composed of continuously and alternately distributed zirconium-based sub-functional layers and copper-chromium buffer layers in the vertical direction. In the design of cathode materials and configurations, the air ablation resistance and uniform discharge performance of the cathode need to be strengthened considering that the electric spark machining for hole making occurs in an oxygen-containing atmosphere. Therefore, a thermally-chemically zirconium-based alloy is adopted as the material of the sub-functional layer. In order to alleviate the cracking and peeling of the functional layer caused by the high brittleness of zirconium oxide, a copper-chromium alloy with balanced high plasticity is adopted as the buffer layer, which is supplemented by surface rolling processing for surface grain nanocrystallization. In terms of configuration design, the overall thickness of the functional layer is set to 30 mm, the single layer thickness is 1.5 mm, and the thickness of a single zirconium-based alloy / copper-chromium alloy structure is 3 mm. Therefore, the overall functional layer contains 10 layers of zirconium-based alloy / copper-chromium alloy.​

[0049] Copper-chromium base material deposition. A high-speed laser cladding system equipped with a double-powder cartridge raw material feeding module was used to prepare the copper-chromium base layer. During deposition, the laser power was 3000 W, the working distance was 15.5 mm, the scanning speed was 6 mm / s, the cladding head moved back and forth according to the preset trajectory, and the closed area formed was a rhombus with diagonal lengths of 8 mm and 4 mm, thereby ensuring the consistency of the thickness of the deposited layer on the surface edge and the inside of the rod-shaped electrode.

[0050] Copper-chromium surface layer rolling grain gradientization. Based on the deposited copper-chromium base, a unidirectional rolling process was used for surface layer rolling with a reduction of 0.5 mm, so that the copper-chromium surface was deformed into nanocrystalline.

[0051] Zirconium-based alloy and copper-chromium alloy alternate cladding deposition. Zirconium-based alloy powder and copper-chromium alloy powder were loaded into two raw material feeding modules respectively. During the deposition of the zirconium-based alloy, the laser power was 3500 W, the working distance was 16.5 mm, the scanning speed was 8 mm / s, and the cladding head also moved back and forth within the rhombus area with diagonal lengths of 8 mm and 4 mm according to the preset trajectory. Then, the alternate deposition of the copper-chromium buffer layer and the zirconium-based alloy functional layer was carried out, and the two raw material feeding modules were activated respectively when switching the raw materials. Argon gas was used as the powder carrying gas to be delivered to the forming surface until the deposition and manufacturing of 10 layers of zirconium-based alloy / copper-chromium alloy on the surface of the copper-chromium base were completed.

[0052] Post-processing. The layered composite cathode was prepared by using a high-speed milling method to moderately process the discharge surface and the peripheral contour of the layered composite cathode.

[0053] Using the layered composite cathode with stacked functional layers / buffer layers, 40 rhombic holes were manufactured by electric spark machining. After about 15 minutes of overall discharge, the surface of the layered composite cathode was slightly blackened, and the strengthening layer structure was intact without obvious peeling or cracking. As shown in FIG. 8, the zirconium-based alloy center was recessed, and the burnout area presented a nearly circular contour. The cathode electric arc discharge and ablation were uniform, thereby confirming that the layered cathode based on the alternate distribution of functional layers / buffer layers has good anti-cracking and arc ablation resistance performance. Figure 5

[0054] Comparative Example 1

[0055] In this comparative example, the service scenario of the electrode was consistent with that of the embodiment. The specific difference was that only the zirconium-based alloy / copper-chromium alloy layered cathode was prepared by adjusting the process parameters. The specific process adjustment method was to gradually increase the arc current to the preset value with 20 A as the gradient value, thereby relieving the cracking of the strengthening layer caused by the sudden increase of the current value.

[0056] ​The deposition of zirconium-based alloy on the surface of copper-chromium alloy was also carried out by high-speed laser cladding equipment. The laser power was 3000 W, the working distance was 15.5 mm, the scanning speed was 6 mm / s, and the cladding head moved back and forth according to the preset trajectory.

[0057] The electrical discharge machining test of the layered cathode was carried out in the way of increasing the arc current by gradient. After the electrical discharge machining of 40 diamond-shaped holes was completed in about 15 minutes, the surface of the layered cathode was obviously blackened, cracks across the surface of the strengthening layer appeared in the middle, and the cathode was seriously burned. Further, the surface morphology of the burned area was observed, as shown in FIG. 8, horizontal cracks were formed in the burned area, and the strengthening layer was obviously peeled off. After the cracks were formed, the arc root was easily induced to adhere and concentrate the discharge ablation, which aggravated the failure of the cathode. It can be seen that the cracking problem of the layered cathode cannot be effectively inhibited by simply relying on process control means. Figure 6a Figure 6b ) After the cracks were formed, the arc root was easily induced to adhere and concentrate the discharge ablation, which aggravated the failure of the cathode. It can be seen that the cracking problem of the layered cathode cannot be effectively inhibited by simply relying on process control means.​

Claims

1. A layered cathode structure based on the alternative distribution of functional layers - buffer layers and a rapid method for its trial production, characterized in that, The method comprises the following steps: Step 1: Cathode material and configuration design; according to the environmental characteristics of the cathode in the specific service process, the sub-function layer and buffer layer materials are selected according to the special electrode material design criteria; the layer thickness and the number of layers of the multi-layer composite structure are designed by referring to the single discharge processing arc current and time; based on the material type and structure characteristics, the multi-layer structure preparation method is determined; Step 2: Deposition of base material; Metal A and B are used as the sub-function layer and buffer layer materials of the layered electrode; on the surface of the conductive electrode base, the first layer A is deposited by melting based on reasonable manufacturing technology, and the key control values of the deposition process are layer thickness, surface and internal forming quality; Step 3: Surface rolling grain gradient; based on the first layer A, the surface layer is processed by one-way rolling to deform the near-surface layer into a nanocrystalline and sub-micron crystalline deformation layer; after rolling processing, the grain size in the deformation layer gradually increases from nanometer to micrometer along the vertical direction, showing a grain size gradient distribution, so as to achieve the surface grain gradient of the buffer layer material; Step 4: Cyclic alternating deposition; based on the layer A after rolling processing, the second deposition of the surface sub-function layer B is carried out by adjusting the parameter combination, and the layer thickness and surface / interior forming quality are also controlled; then according to the number of layers contained in the specific electrode structure, the alternating deposition of layer A and layer B is carried out by multiple iterations of steps 2-4, and finally after several cycles, the functional layer-base layered composite electrode blank is prepared, and the functional layer contains the preset stacked distribution of sub-function layer-buffer layer; Step 5, post-processing; for the layered composite electrode blank prepared in steps 1-4, the outer wall and upper surface are precisely processed by numerical control processing to remove burrs and spheroidized particle surface defects, and to ensure that the discharge surface is smooth and smooth.

2. The layered cathode structure based on the alternative distribution of functional layer-buffer layer and its rapid prototyping method according to claim 1, characterized in that, The electrode material design criteria involved in the cathode material design stage are specifically around the sub-function layer material and the buffer layer material; the sub-function layer should have the following basic physical and chemical properties: 1) thermal chemical discharge attribute, the self-ionization potential is lower than 4.2eV, and the surface can form a conductive refractory oxide layer after air discharge, and the oxide layer has stable performance and a melting point higher than that of pure metal; 2) the melting point is higher than that of the base material; 3) has a certain plastic deformation ability; the buffer layer should have the following basic physical and chemical properties: 1) the plastic deformation ability is higher than that of the sub-function layer material; 2) the self-ionization potential is not higher than 4.6eV; 3) when the base material linear expansion coefficient is X, the buffer layer thermal expansion coefficient is between 0.8X and 1.2X.

3. The layered cathode structure based on the alternative distribution of functional layer - buffer layer and the rapid production method thereof according to claim 1 or 2, characterized in that, The functional layer of the layered cathode contains several sub-function layers and buffer layers, showing a multi-layer stacked structure, and the thickness of a single layer should be between 1-3mm, and the overall functional layer thickness should not exceed 20mm; in this way, the concentrated thermal stress of the functional layer during arc discharge is released layer by layer, and the deformation mismatch caused by the mismatch of the thermal expansion performance of the functional layer and the base material is relieved.

4. The layered cathode structure based on the alternative distribution of functional layer-buffer layer and the rapid manufacturing method thereof according to claim 1 or 2, characterized in that, In the base material deposition process, laser wire deposition, high-speed laser cladding strong interface metallurgical bonding metal melting deposition technology is used, and during the deposition manufacturing process, high scanning speed and high laser power parameter combination should be adopted to improve the pool cooling rate and promote grain refinement.

5. The layered cathode structure based on the alternative distribution of functional layer - buffer layer and its rapid prototyping method according to claim 3, characterized in that, The base material deposition process uses laser wire deposition, high-speed laser cladding strong interface metallurgical bonding metal melting deposition technology, and high scanning speed and high laser power parameter combination should be adopted in the deposition manufacturing process to improve the molten pool cooling rate and promote grain refinement.

6. The layered cathode structure based on the alternative distribution of functional layer - buffer layer and its rapid prototyping method according to claim 1 or 2 or 5, characterized in that, The buffer layer surface rolling grain gradient processing realizes the formation of nanocrystalline-micrometer crystal grain size gradient on the upper surface of the buffer layer by one-way rolling processing; and the upper surface of the processed buffer layer is nanocrystalline, and the grain size gradually increases from the surface to the inside to the micrometer scale.

7. The layered cathode structure based on the alternative distribution of functional layer-buffer layer and the fast manufacturing method thereof according to claim 1 or 2 or 5, characterized in that, The functional layer-buffer layer alternating distribution layered cathode structure has the anti-cracking characteristics, which is realized by the multi-metal layer stacking structure design; the sub-functional layer directly faces the arc root, and it is difficult to avoid the generation of thermal stress during service, at this time, the buffer layer at the back will support the deformation of the sub-functional layer with strong plastic deformation ability, so as to partially release the stress; After the composite of multiple sub-functional layers-buffer layers, the thermal stress of discharge ablation can be released to the maximum extent, the deformation is relieved, and the interlayer cracking is inhibited.

8. The layered cathode structure based on the alternative distribution of functional layer-buffer layer and the rapid manufacturing method thereof according to claim 1 or 2 or 5, characterized in that, The functional layer-buffer layer layered cathode structure has high uniformity and ablation resistance in the discharge ablation process; when the arc discharge continues, the sub-functional layer generates a refractory oxide layer in situ, which protects the substrate to reduce the ablation rate, and at the same time promotes the formation of a type of cathode spot to improve the ablation uniformity; when the single functional layer is ablated, the buffer layer directly faces the arc root, and the surface nanocrystalline can accelerate the migration of the cathode spot, reduce the residence time of the spot, and reduce the heat flux density of the cathode surface.

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