Method for directly plating thick nickel on surface of tungsten alloy

Abstract

The invention relates to a method for directly plating thick nickel on the surface of tungsten alloy. The method comprises the following steps that firstly, the surface of the tungsten alloy is pretreated till fresh metal is exposed out of the surface to be plated and the welding surface roughness Ra is smaller than or equal to 0.2 micrometer; then nickel acetate electrolyte is used as main electroplating liquid, SDS is added into the nickel acetate electrolyte, the concentration of the SDS is 0.04-0.1 g / L, electroplating is started after the SDS is fully dissolved, the current density is controlled to be 0.3-1.1 A / dm < 2 > during electroplating, and the pH is controlled to be 3.5-5.5 during electroplating. In the nickel acetate electroplating solution, the initial concentration of sodium chloride is 3-14 g / L, the initial concentration of Ni < 2 + > ions is 5-10 g / L, and the initial pH is 3.5-5.5. According to the method, the number of used drugs is small, highly dangerous reagents such as hydrofluoric acid and sulfuric acid are not needed, expensive electroplating equipment such as a pulsed power supply is not needed either, the requirement for instruments is low, safety is good, production efficiency is high, a quite thick compact nickel coating can be stably obtained, and the method for electroplating the thick nickel layer on the surface of the tungsten alloy for diffusion bonding is provided. The method can be used for industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of surface treatment, in particular to a method for directly plating thick nickel on the surface of a tungsten alloy. Background Art

[0002] The preparation methods of tungsten alloy / steel composite components include diffusion welding, brazing, co-sintering, etc. In order to inhibit the generation of intermetallic compounds and relieve residual stress, a suitable intermediate layer metal must be added to the welding interface. The traditional form of intermediate layer addition is foil or powder, but the purity and thickness of the intermediate layer are difficult to control and difficult to construct. In addition, the surface cleanliness of the intermediate layer is also a major problem; although deposition methods such as PVD and CVD can deposit a certain thickness of metal covering layer on the surface of tungsten alloy, they can only deposit a very thin metal layer, which cannot meet the existing requirements for the thickness of the intermediate layer, and the construction cost is high and the efficiency is low; in contrast, the process of electrodeposition (electroplating) is mature, the equipment is highly automated, and the restrictions on the sample volume and shape are smaller. Therefore, using electroplating as a method for metal deposition on the surface of tungsten alloy, especially for the deposition of samples with more complex surfaces, is a more ideal treatment method. In addition, the nickel deposition layer can not only be used directly as a welding intermediate layer, but also improve the conductivity of the tungsten alloy itself and serve as a base for other composite coatings.

[0003] However, the conductivity of tungsten alloy itself is not good, and since diffusion bonding requires a very high thickness of the intermediate layer, at least 10-20 μm is required, which exceeds the thickness of the commonly used decorative coating or functional coating (several microns). At present, there is no thick nickel electroplating process developed for diffusion welding of tungsten alloy. In the existing literature on tungsten alloy electroplating process (CN102465325 A, CN 103173821 B and CN 105420699 B), not only the coating is very thin, but also dangerous reagents such as hydrofluoric acid and sulfuric acid need to be used in the electroplating process, which has great environmental pollution and safety hazards, is not suitable for laboratory exploration experiments, and is difficult to achieve industrial production at low cost. Therefore, a process for depositing thick nickel on the surface of tungsten alloy with simple operation process, safe and controllable, and low cost is needed. Summary of the invention

[0004] The purpose of the present invention is to provide a method for depositing a thick nickel layer on a tungsten alloy substrate using a DC power supply to address the above-mentioned defects, by adjusting the current density, the plating solution Ni 2+ A series of parameters such as ion concentration and pH are used to obtain a thicker pure nickel coating with good bonding, low porosity, fine crystals and continuously adjustable thickness to meet the welding needs of tungsten alloys; the acetate system is used instead of the traditional strong acid salt electroplating solution system such as sulfate or chloride, reducing the use of buffers (such as boric acid); acetic acid is used instead of the traditional hydrofluoric acid or concentrated sulfuric acid cleaning agent to reduce the pollution caused by strong acid and hydrofluoric acid.

[0005] The technical solution of the present invention is: a method for directly plating thick nickel on the surface of tungsten alloy, comprising the following steps: Step 1: Tungsten alloy surface pretreatment The tungsten alloy surface is mechanically processed to remove the oxide layer, and then polished until the surface to be plated exposes fresh metal and the roughness of the surface to be plated is less than Ra0.2 μm; then detergent + hot water, ethanol, and acetic acid are used to clean in sequence to obtain a cleaned sample to be plated; Step 2: Nickel plating First, add nickel acetate plating solution to the plating tank, then add sodium dodecyl sulfate (SDS) and fully dissolve it. The amount of SDS added is 0.04-0.1 g / L, preferably 0.04~0.08 g / L, and the pH of the plating tank is adjusted to 3.5-5.5, preferably 4-4.7, preferably 4.2-4.6. The anode is an electrolytic nickel plate, connected to the positive pole of the power supply, and the sample to be plated is connected to the negative pole of the power supply. Turn on the power supply and set the target current density to 0.3-1.1 A / dm 2 , preferably 0.35-0.9 A / dm 2 , further preferably 0.35-0.8A / dm 2 , start electroplating; the initial concentration of sodium chloride in the nickel acetate electroplating solution is 3-14 g / L, preferably 4-8 g / L, more preferably 5 g / L, the initial concentration of glacial acetic acid is 5-25 ml / L, the initial Ni 2+ The concentration of ions is 5-10 g / L.

[0006] When used in industry, the surface pretreatment of tungsten alloy includes: using mechanical processing methods such as sandblasting, turning, and polishing to pre-remove the significant oxide layer on the surface of the tungsten alloy, and then grinding and polishing the surface to be welded. Then use detergent + hot water, ethanol, and acetic acid for ultrasonic cleaning in sequence, and the number of cleaning times for each process is 1-2 times. Then take out the sample immediately and use running deionized water to fully clean it. The pretreatment is completed. In order to further improve the performance, the surface processing requirements of tungsten alloy to be plated are: the non-welding surface needs to expose the fresh metal surface, the welding surface needs to be finely polished, and the roughness Ra is less than or equal to 0.2 μm.

[0007] The process of ultrasonic cleaning of tungsten alloy parts to be plated using detergent + hot water, ethanol, and acetic acid in sequence is as follows: hot water washing uses commercially available alkaline detergent combined with hot water, the detergent addition amount is 5-15 g / L, the hot water temperature is 85-100 ℃, the detergent is fully dissolved in hot water, the sample is immersed in it and then ultrasonically cleaned, the cleaning time is 5-10 min, and the number of cleanings is 1-2 times; then the sample is fully rinsed with running cold water to remove residual detergent on the surface and then immersed in anhydrous ethanol (purity above 99.5%) for ultrasonic cleaning, the temperature of anhydrous ethanol is 20-50 ℃, the cleaning time is 5-10 min, and the number of cleanings is 1-2 times; then the sample is fully rinsed with running anhydrous ethanol and then placed in an acetic acid aqueous solution for ultrasonic cleaning, the concentration of the acetic acid aqueous solution is 40-60%vol, first dissolve the glacial acetic acid in deionized water and fully stir it before immersing the sample, the ultrasonic cleaning time is 5-10min, and the cleaning temperature is 20-50 ℃, after cleaning, quickly rinse the sample with running cold water to remove the residual acetic acid solution on the surface, and the surface treatment is completed. The running cold water can be deionized water or distilled water. When conditions are limited, tap water that meets the "Standards for Drinking Water Hygiene" can be used for rinsing. The ethanol washing solution and the acetic acid washing solution can be filtered and supplemented with ethanol and acetic acid before reuse. When the solution changes color significantly, it can be replaced.

[0008] Nickel acetate electroplating solution can be directly prepared using nickel acetate salt to ensure Ni 2+ The ion concentration and pH can be consistent with the above, and the other parameters do not need to be changed too much. However, nickel acetate has a low nickel content and the price of high-purity reagents is high. In order to save costs, improve the quality of the coating, and speed up the nickel plating process, electrolysis can also be used to prepare nickel acetate electroplating solution. The electrolytic method for preparing nickel acetate electroplating solution includes: first using sodium chloride, glacial acetic acid and water to prepare a solution, wherein the sodium chloride concentration is 3-14 g / L, and the glacial acetic acid concentration is 15-30 mL / L, and then using electrolytic nickel plates as cathodes and anodes for electrolysis until Ni in the solution 2+ The ion concentration is 5-10 g / L. In the present invention, the reason why the Ni content in the nickel acetate plating solution before electroplating is controlled is that 2+ The concentration is because Ni 2+The concentration directly determines the deposition efficiency and quality of the coating. If the concentration is too high, the coating will be cracked due to excessive stress or even overburned and nodulated. If the concentration is too low, the conductivity of the plating solution will be poor and the electroplating efficiency will be low, and a higher voltage is required to achieve electroplating. When the present invention adopts the electrolytic method to prepare nickel acetate electroplating, 3-14 g / L sodium chloride is used to reduce the polarization of the nickel anode during electrolysis and improve the dissolution efficiency of the nickel anode. 15-30 ml / L glacial acetic acid is used to adjust the pH of the electrolyte to a slightly acidic condition to avoid nickel hydroxide precipitation due to increased pH during electrolysis. The specific steps of preparing nickel acetate electroplating solution by electrolysis are as follows: first, weigh sodium chloride and dissolve it in deionized water, then measure glacial acetic acid and mix it with it and stir it evenly, and then add deionized water to the target concentration for standby use. Then pour the solution into the electroplating tank, use electrolytic nickel plates (purity of more than 99.5%) as cathodes and anodes for electrolysis, and electrolyze to a Ni ion concentration of 5-10 g / L. The reference process is as follows: first weigh 5 g of sodium chloride and dissolve it in a small amount of deionized water, then measure 25 mL of glacial acetic acid and mix it with the mixture and stir evenly, add deionized water to dilute the mixed solution to 1 L and then pour the mixed solution into the electroplating tank; use electrolytic nickel plates (purity above 99.5%) as cathode and anode to perform electrolysis at room temperature, the electrolysis current is 2 A, the electrolysis time is 325 min, after the electrolysis is completed, filter the electroplating solution and make up to 1 L for standby use. Since some nickel will be precipitated at the cathode, the nickel ion concentration in the solution is 5.611 g / L (atomic absorption spectrometry).

[0009] The present invention adopts constant current density direct current nickel plating during nickel electroplating. The method for adjusting pH by constant current density direct nickel electroplating is as follows: before plating, if the pH is too high, glacial acetic acid can be added to lower it; if the pH is too low, graphite or electrolytic nickel plate can be used as anode and cathode to electrolyze the plating solution with an appropriate current (such as 2A) to increase the pH; during the electroplating process, the pH will slowly rise, and the pH of the system can be monitored in time and glacial acetic acid can be added.

[0010] The process conditions for constant current density direct current nickel plating are: current density is 0.3-1.1 A / dm 2 , preferably 0.35-0.9A / dm 2 , further preferably 0.35-0.8A / dm 2 (This is of course 0.35-0.4A / dm 2 , also including 0.4-0.6A / dm 2 , 0.6-0.7A / dm 2 , 0.7-0.8A / dm 2These small ranges), the electroplating time can be as long as 10 hours or more according to the thickness requirements, and the coating will not crack. The plating solution temperature can be less than or equal to 30°C. The electroplating solution can be stirred by mechanical stirring, magnetic stirring, air flow stirring or directly moving the sample, but no significant bubbles can be introduced into the electroplating pool. In the present invention, too low a current density will lead to too long a deposition time, and too high a current density will lead to too fast a deposition speed, nodules or cracks, and even local overburning.

[0011] During constant current density direct current nickel plating, the temperature of the plating solution is controlled to be 10-30°C, preferably 20-30°C, further preferably 20-27°C, and further preferably 20-25°C.

[0012] In the present invention, a coating with a thickness of 24-25 μm can be obtained in 208 min; a coating with a thickness of 80 μm or more can be obtained by electroplating for 1295 min, and a coating with a thickness of 180 μm or more can be obtained by electroplating for 3000-3100 min, and the coating is well bonded to the substrate, meeting the requirements of diffusion bonding.

[0013] After the electroplating is completed, the sample is taken out of the electroplating tank, rinsed thoroughly with deionized water and dried to obtain the target plated parts. The remaining electroplating solution can be filtered and recovered, and the pH can be adjusted so that it can be reused in the preparation of nickel acetate electroplating solution by electrolysis.

[0014] The invention carries out coating quality inspection on the nickel coating, including visual inspection of coating quality and judging coating thickness and joint strength after diffusion welding with steel.

[0015] The diffusion bonding and test conditions are as follows: first, the coating on the surface to be welded and the butted steel block are polished to Ra less than 0.2 μm, and then, after being fully cleaned, hot pressing or hot isostatic pressing diffusion bonding is used, the diffusion bonding temperature is 900-1000 °C, the welding pressure is 10-40 MPa (hot pressing diffusion) and 50-200 MPa (hot isostatic pressing diffusion), and the joint evaluation method is tensile strength. This test method is also the first of its kind in the present invention.

[0016] The beneficial effects of the present invention are as follows: compared with the existing technology, the rust removal and electroplating of the tungsten alloy surface are completed by using an acetic acid system cleaning agent and an electroplating solution, thereby avoiding the use of highly or highly polluting chemicals such as hydrofluoric acid or sulfuric acid, and being safe and environmentally friendly; electroplating can be completed by using a direct current power supply and a few types of chemicals, the process is simple, and the requirements of laboratory electroplating are met; a lower current density range is used, which can match the poor electrical conductivity of the tungsten alloy, realize the deposition of a thick coating, obtain a nickel coating that meets the needs and whose thickness can be adjusted within a wide range, and meet the needs of welding tungsten alloy and steel.

[0017] Principles and advantages The present invention discloses a green and environmentally friendly method for direct thick nickel plating on the surface of a constant current density tungsten alloy for diffusion connection. The difficulty lies in the treatment of the surface of the tungsten alloy and obtaining a dense thick nickel layer. The present invention proposes an electroplating process of a nickel acetate system, and by coordinating processes such as surface pretreatment, a dense nickel layer with continuously adjustable plating thickness is prepared to meet the needs of tungsten alloy diffusion connection.

[0018] The specific principle is: first prepare the nickel acetate electroplating solution, which can be prepared by electrolysis or nickel acetate salt preparation. The electrolysis method is preferred because the solution obtained has higher purity and lower cost, saving a lot of nickel acetate storage and preparation problems. The sodium chloride in the electroplating solution can improve the conductivity of the solution and prevent the nickel anode from passivation, thereby improving the efficiency of anode dissolution; acetic acid can provide acetate on the one hand, and on the other hand adjust the pH to avoid the formation of too much hydroxide to make Ni 2+ The nickel hydroxide is precipitated, and it can also form an acetic acid-acetate buffer system with the generated nickel acetate. No additional buffer such as boric acid is required, thus avoiding the introduction of impurities caused by the additional buffer. Then the sample is pre-treated by mechanical polishing and ultrasonic cleaning of detergent + hot water, ethanol, and acetic acid in sequence. Mechanical processing and polishing are mainly to expose the fresh surface and reduce the difficulty of subsequent cleaning. For unimportant surfaces, it is sufficient to expose the fresh metal surface, while for important welding surfaces, it is necessary to polish to the required surface roughness. Hot water ultrasound uses an alkaline detergent containing a surfactant, which can fully remove various oil stains including mineral oil on the sample surface on the one hand, and can fully remove possible tungsten oxides on the surface with the help of high-temperature alkaline solutions on the other hand. Anhydrous ethanol cleaning is to further remove residual organic matter and detergents. Acetic acid cleaning is to further remove tungsten oxides and nickel-iron oxides on the surface of tungsten alloy, expose the fresh activated surface, improve the bonding strength of the coating, and wash away the possible residual ethanol in the previous step to prevent the sample from being brought into the plating tank and causing contamination to the plating solution.

[0019] The cleaned tungsten alloy is then plated. Due to the poor conductivity of tungsten alloy, it cannot be plated with a higher current density and a higher cation concentration like steel. This will lead to stress concentration in the coating or severe overburning in some parts, resulting in coating failure, making it difficult to obtain a thick coating. The more appropriate current density is 0.3-1.1 A / dm 2 , a more suitable Ni 2+The ion concentration is 5-10 g / L, and the concentration can be quickly identified by colorimetry. If it exceeds the tolerance, it can be diluted with deionized water. Since acetic acid and nickel acetate can form a buffer system, the pH will only increase slowly during the electroplating process. When it exceeds the range, glacial acetic acid can be added in time to adjust the pH to the target range. Before electroplating, an appropriate amount of SDS is added as an anti-pinhole agent to reduce the surface tension of hydrogen bubbles and overflow from the surface of the plated part in time to prevent the pores from being wrapped in the coating, resulting in low density of the coating and even pinholes and nodules.

[0020] Compared with the existing methods, the advantages of the present invention are: 1. The electroplating process is simple and the chemicals are low in toxicity. It is not only suitable for laboratory-level small-batch sample electroplating, but can also be expanded to industrial production. When using the acetic acid system electroplating solution, the only reagents required are sodium chloride, nickel acetate (this reagent can be omitted when preparing the solution by electrolysis), glacial acetic acid, electrolytic nickel plate, and sodium dodecyl sulfate (SDS). The auxiliary reagents only require alkaline detergents (dishwashing liquid, washing powder, etc.) and ethanol. Since acetic acid and acetate can form a buffer system by themselves, there is no need to add additional pH buffers (boric acid, etc.) to maintain the pH stability of the plating solution; electroplating can be carried out stably at room temperature (25°C) without the need for additional constant temperature equipment; using an ordinary DC power supply can achieve better results without the need for expensive pulse power supplies.

[0021] 2. The coating has good bonding quality, high density, and continuously controllable thickness. It matches the conductivity of tungsten alloy and uses a lower current density to obtain a fairly thick nickel coating (greater than 20 μm), which is enough to meet the needs of different samples for different thicknesses of the intermediate layer, and can cover the tortuous surface with a coating without cracking.

[0022] 3. A higher interface bonding strength can be obtained by actual diffusion welding of the electroplated sample with steel. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a short-time electroplating (0.76 A / dm 2 , 6h) surface effect (a) and the process is suitable for long-term electroplating (0.76 A / dm 2 , 18 h) surface effect (b). The surface of the electroplated layer is flat and dense, and even after long-term electroplating, there are only a few pits, no pinholes and nodules, and a slight polishing is sufficient to meet welding requirements.

[0024] Figure 2The following are the interface side views of Examples 1, 2, 3, 4, 5, 6, and 7, and some of the pictures were taken after the sample was broken. (a): Example 1; (b): Example 2; (c): Example 3; (d): Example 4; (e): Example 5; (f): Example 6; (g): Example 7. The thickness of the Ni layer after welding is measured to be 24 μm, 43 μm, 80 μm, 17 μm, 184 μm, 45 μm, and 17 μm, respectively. After welding, the coating is dense and has no holes, and no significant cracks are found, indicating that the present invention can provide a dense Ni coating in a wide thickness range.

[0025] Figure 3 The following is a comparison of the electroplating effects of a 2 mm pitch threaded sample. The left side shows the electroplated sample (0.76 A / dm 2 , 3h), the right side is before electroplating, it can be seen that the coating is dense without blistering or cracking, and the color is uniform.

[0026] Figure 4 Schematic diagram of the test sample size for the tensile strength of the sample joint (a) and the tensile strength of the joint of the corresponding embodiment (b).

[0027] Figure 5 These are actual pictures of coating failures of various comparison examples that deviate from the optimal parameter range, (a) is comparison example 1, (b) is comparison example 2, (c) is comparison example 3, and (d) is comparison example 4. DETAILED DESCRIPTION

[0028] The present invention is described in detail below through specific embodiments. Example

[0029] (1) Preparation of nickel acetate electroplating solution by electrolysis: First, weigh 5 g of sodium chloride and dissolve it in a small amount of deionized water. Then, weigh 25 mL of glacial acetic acid and mix them together and stir evenly. Add deionized water to dilute the mixed solution to 1 L and pour the mixed solution into the electroplating tank. Use electrolytic nickel plates (purity above 99.5%) as anode and cathode to perform electrolysis at room temperature. The electrolysis current is 2 A and the electrolysis time is 325 min. After the electrolysis is completed, filter to obtain a nickel acetate solution for electroplating (at this time, Ni 2+ The concentration is 5.611 g / L, and the analysis method is atomic absorption spectrometry).

[0030] (2) Surface pretreatment of tungsten alloy: A 93W-4.9Ni-2.1Fe tungsten alloy specimen with a diameter of 30 mm and a height of 13 mm was selected. The entire cylindrical surface and one end face were turned to expose the fresh surface, and the other end face was polished to Ra less than 0.2 μm. Then the sample was placed on a hanger and first cleaned with hot water at a temperature of 96 °C and a detergent content of 10 g / L. The hot water was completely immersed in the sample during ultrasonic cleaning. After ultrasonic cleaning for 5 min, the residual detergent on the surface was fully rinsed with running cold water. The sample was then immersed in anhydrous ethanol (purity 99.5%) for ultrasonic cleaning at a temperature of 30 °C for 5 min. After cleaning, the sample was fully rinsed with clean anhydrous ethanol and then immersed in an acetic acid aqueous solution for ultrasonic cleaning. The concentration of the acetic acid aqueous solution was 50% vol. The immersed sample was cleaned with an ultrasonic machine at 30 °C for 5 min. The acetic acid aqueous solution was prepared by first measuring 200 mL of glacial acetic acid and then adding deionized water to 400 mL. mL and mix well. After cleaning, quickly rinse the sample with running cold water to remove the residual acetic acid solution on the surface. The surface treatment is completed.

[0031] (3) Direct nickel electroplating at constant current density: First, add 1 L of the nickel acetate solution prepared in step (1) to a 1 L electrolytic cell, then add 0.05 g of SDS and stir thoroughly to dissolve, adjust the pH of the electroplating cell to 4.42, then place the anode plate in the cell and connect it to the anode, then connect the plated part to the cathode of the power supply, and adjust the output current to 0.2 A (theoretical current density 0.76 A / dm 2 , 100% cathode efficiency) and then turn on the DC power switch, and immerse the sample completely in the electroplating bath under power-on. The electroplating time is 208 min. During the electroplating period, a magnetic stirrer is used to slowly rotate the plating solution in the stirring bath. The speed is based on the absence of bubbles. The solution temperature in the electroplating bath is kept stable at 25 °C, and the pH in the electroplating bath is kept less than 5.

[0032] (4) After step (3) is completed, remove the sample from the electroplating tank, rinse it thoroughly with deionized water, and then dry it to obtain the target plated part. The remaining electroplating solution can be filtered and recovered, and the pH value can be adjusted to 4.42 for later use. (5) Conduct a coating quality inspection on the nickel coating produced in step (3), including visual inspection of the coating quality and determination of the coating thickness and joint strength after diffusion welding with steel. Visually inspect whether there are significant cracks or peeling or warping. If there are no significant problems after visual inspection, polish the coating on the surface to be welded and the butted steel block to Ra less than 0.2 μm, then thoroughly clean them and use hot pressing diffusion connection. The diffusion welding process is: heat from room temperature to 1000 °C at a rate of 10 °C / min, then keep warm for 1 hour, apply 28 MPa pressure at the same time and keep the pressure for 1 hour, then remove the pressure and cool to 550 °C at a rate of 5 °C / min, then keep warm for 1 hour, and finally cool in the furnace, take a dog-bone shaped specimen, and measure the tensile strength of the joint by butt joint. The interface morphology of the sample after welding is as follows: Figure 2 As shown in (a), the coating is dense and uniform without significant holes. The average thickness is about 24 μm. The mechanical properties of the joint at room temperature are as follows: Figure 4 As shown, the tensile strength of the joint is about 381 MPa. Example

[0033] The other conditions were the same as those in Example 1, except that the process conditions for direct nickel electroplating at constant current density were: SDS addition amount was 0.07 g / L, pH of the electroplating bath was adjusted to 4.6 before electroplating, electroplating time was 840 min, current was 0.1 A (theoretical current density 0.38 A / dm 2 , 100% cathode efficiency), the sample is completely immersed in the electroplating bath under power-on state, and a magnetic stirrer is used to rotate slowly during electroplating, so as not to cause bubbles to appear, and the solution temperature in the electroplating bath is kept stable at 25 °C. The interface morphology of the sample after welding is as follows Figure 2 As shown in (b), the coating is dense and uniform without significant holes. The average thickness is about 43 μm. The room temperature mechanical properties are as follows: Figure 4 As shown, the tensile strength of the joint is about 541 MPa. Example

[0034] The other conditions were the same as those in Example 1, except that the process conditions for direct nickel electroplating at constant current density were: SDS addition amount was 0.05 g / L, pH of the electroplating bath was adjusted to 4.42 before electroplating, electroplating time was 1295 min, current was 0.2 A (theoretical current density 0.76 A / dm 2 , 100% cathode efficiency), the sample was completely immersed in the electroplating bath under power-on condition, and a magnetic stirrer was used to rotate slowly during electroplating, and bubbles were not generated, and the solution temperature in the electroplating bath was kept stable at 27 °C. The morphology of the steel side of the fractured sample after welding is as follows: Figure 2 As shown in (c), the coating is dense and uniform without significant holes. The average thickness is about 80 μm. The room temperature mechanical properties are as follows: Figure 4As shown, the tensile strength of the joint is about 444 MPa. Example

[0035] Except that the electrolyte is prepared directly from nickel acetate, the other parameters are exactly the same as those in Example 1. The preparation method of the electrolyte is as follows: weigh 24 g of nickel acetate tetrahydrate (in this case Ni 2+ The concentration is about 5.6 g / L), 5 g sodium chloride, and 0.05 g SDS are placed in a beaker, and appropriate amount of deionized water is added to fully dissolve, then 8 ml of acetic acid is added and water is added to make up to 1 L, stirred thoroughly, and the pH is adjusted to 4.42 with glacial acetic acid before pouring into a 1 L electrolytic cell. The side morphology of the sample after welding is as follows Figure 2 As shown in (d), the coating is dense and uniform without significant holes. The average thickness is about 17 μm. The room temperature mechanical properties are as follows: Figure 4 As shown, the tensile strength of the joint is about 332 MPa, which is basically close to that of Example 1 but still has room for improvement, and the process parameters may need to be adjusted accordingly. Example

[0036] The other conditions were the same as those in Example 1, except that the process conditions for direct nickel electroplating at constant current density were: the amount of SDS added was 0.05 g / L, the pH of the electroplating bath was adjusted to 4.56 before electroplating, the electroplating time was 3096 min, the current was 0.2 A (theoretical current density 0.76 A / dm 2 , 100% cathode efficiency), the sample was completely immersed in the electroplating bath under power-on condition, and a magnetic stirrer was used to rotate slowly during electroplating, so as not to cause bubbles to appear, and the solution temperature in the electroplating bath was kept stable at 24 °C. The interface microstructure of the sample after welding is shown in Figure 2 As shown in (e), the coating is dense and uniform without significant holes. The average thickness is about 184 μm. The room temperature mechanical properties are as follows: Figure 4 As shown, the tensile strength of the joint is about 675 MPa. Example

[0037] The other conditions were the same as those in Example 1, except that the electrolyte was naturally evaporated after preparation to concentrate it. The Ni content in the electrolyte was measured. 2+ The concentration is 7.905 g / L (atomic absorption spectrometry). The process conditions for constant current density direct nickel electroplating are: SDS addition amount is 0.05 g / L, the pH of the electroplating bath is adjusted to 4.44 before electroplating, the electroplating time is 647 min, the current is 0.2 A (theoretical current density 0.76 A / dm 2 , 100% cathode efficiency), the sample is completely immersed in the electroplating bath under power-on state, and a magnetic stirrer is used to rotate slowly during electroplating, so as not to cause bubbles to appear, and the solution temperature in the electroplating bath is kept stable at 25 °C. The interface morphology of the sample after welding is as follows Figure 2As shown in (f), the coating is dense and uniform without significant holes. The average thickness is about 45 μm. The room temperature mechanical properties are as follows: Figure 4 As shown, the tensile strength of the joint is about 560 MPa. Example

[0038] The other conditions were the same as those in Example 1, except that: the electrolyte was naturally evaporated after preparation to make it concentrated, and the Ni content in the electrolyte was determined by visual colorimetry. 2+ The concentration is between 8-10g / L, close to 10g / L (directly prepare nickel acetate to prepare the standard colorimetric series, with 2g / L as the graduation, from 2g / L to 16g / L). The process conditions for constant current density direct nickel electroplating are: SDS addition amount is 0.08 g / L, the pH of the electroplating bath is adjusted to 4.5 before electroplating, the electroplating time is 215 min, and the current is 0.2 A (theoretical current density 0.76 A / dm 2 , 100% cathode efficiency), the sample is completely immersed in the electroplating bath under power-on state, and a magnetic stirrer is used to rotate slowly during electroplating, so as not to cause bubbles to appear, and the solution temperature in the electroplating bath is kept stable at 25 °C. The interface morphology of the sample after welding is as follows Figure 2 As shown in (g), the coating is dense and uniform without significant holes. The average thickness is about 17 μm. The room temperature mechanical properties are as follows: Figure 4 As shown, the tensile strength of the joint is about 524 MPa. Example

[0039] In this case, the sample is a sample with a hole and external thread. The inner hole of the sample is 10 mm, the outer diameter is 30 mm, the height is 13 mm, the external thread is a 55° triangular thread, the pitch is 2 mm, and the depth is 2 mm. The process conditions for constant current density direct nickel electroplating are: SDS addition amount is 0.05 g / L, the pH of the electroplating bath is adjusted to 4.2 before electroplating, the electroplating time is 180 min, and the current is 0.2 A (theoretical current density 0.76 A / dm 2 , 100% cathode efficiency), the sample was completely immersed in the electroplating bath under power-on condition, and a magnetic stirrer was used to rotate slowly during electroplating, so as not to cause bubbles to appear, and the solution temperature in the electroplating bath was kept stable at 25°C. The other steps were the same as those in Example 1. The appearance of the sample is as follows Figure 3 As shown, the left side is the sample after electroplating, and the right side is the sample before electroplating. It can be seen that the coating is dense and uniform, without significant holes or nodules. This example is only to illustrate that this process can be well deposited on the tortuous surface of tungsten alloy, and no further welding test is performed to test its strength.

[0040] (1) Prepare nickel acetate electroplating solution by electrolysis: first weigh 5 g of sodium chloride and dissolve it in a small amount of deionized water, then measure 25 mL of glacial acetic acid and mix it with the solution and stir evenly. Dilute the mixed solution to 1 L and pour the mixed solution into the electroplating tank. Use electrolytic nickel plates (purity above 99.5%) as anode and cathode to perform electrolysis at room temperature with an electrolysis current of 2 A and an electrolysis time of 325 min. After the electrolysis is completed, filter the electroplating solution and set it aside.

[0041] (2) Surface pretreatment of tungsten alloy: A 93W-4.9Ni-2.1Fe tungsten alloy specimen with a diameter of 30 mm and a height of 13 mm was selected. The entire cylindrical surface and one end face were turned to expose the fresh surface, and the other end was ground to Ra0.8 μm using a grinder. Then the sample was placed on a hanger and immersed in anhydrous ethanol (purity 99.5%) for ultrasonic cleaning. The temperature of anhydrous ethanol was 30°C and the ultrasonic cleaning time was 5 min. After cleaning, the sample was fully rinsed with clean anhydrous ethanol and then immersed in acetic acid aqueous solution for ultrasonic cleaning. The concentration of acetic acid aqueous solution was 50% vol. First, 200 mL of glacial acetic acid was measured, and then deionized water was added to make up to 400 mL and mixed evenly. Then the sample was immersed in an ultrasonic machine for cleaning at 30°C for 5 min. After cleaning, the sample was quickly rinsed with running cold water to remove the residual acetic acid solution on the surface. The surface treatment was completed.

[0042] (3) Direct nickel electroplating at constant current density: First, add 1 L of the nickel acetate solution prepared in step (1) to a 1 L electrolytic cell, then add 0.05 g of SDS and stir thoroughly to dissolve, adjust the pH of the electroplating cell to 4.42, then place the anode plate in the cell and connect it to the anode, then connect the plated part to the cathode of the power supply, and adjust the output current to 0.2 A (theoretical current density 0.76 A / dm 2 , 100% cathode efficiency) and then turn on the DC power switch, and immerse the sample completely in the electroplating bath while it is powered on. The electroplating time is 208 min. During the electroplating period, a magnetic stirrer is used to rotate slowly without bubbles. The solution temperature in the electroplating bath is kept stable at 25 °C, and the pH in the electroplating bath is kept less than 5.

[0043] (4) After step (3) is completed, the sample is removed from the electroplating bath, and then rinsed with deionized water and dried to obtain the target plated part. The remaining electroplating solution can be filtered and recovered, and the pH value is adjusted to 4.42 for later use; (5) Perform coating quality inspection on the nickel coating obtained in step (3), including visual inspection of coating quality and determination of coating thickness and joint strength after diffusion welding with steel. Visually inspect whether there are significant cracks or peeling and warping. If there are no significant problems after visual inspection, polish the coating on the surface to be welded and the butted steel block to Ra less than 0.2 μm, then thoroughly clean and use hot pressing diffusion connection. The diffusion welding process is: heat from room temperature to 1000 ℃ at a rate of 10 ℃ / min, then keep warm for 1 hour, apply 28 MPa pressure and keep pressure for 1 hour, then remove pressure, and cool to 550 ℃ at a rate of 5 ℃ / min, then keep warm for 1 hour, and finally cool in the furnace. Take a dog-bone shaped specimen and measure the tensile strength of the joint by butt joint. The visual inspection results are as follows: Figure 4 As shown in (a), due to the poor surface machining quality, there are still scratches on the surface, which reduces the bonding ability between the coating and the substrate. In addition, the tungsten alloy has not been cleaned with a hot detergent solution, so it is difficult to fully remove the oil and thin oxide on the surface of the tungsten alloy, causing the electroplating to fail.

[0044] (1) Prepare nickel acetate electroplating solution by electrolysis: first weigh 5 g of sodium chloride and dissolve it in a small amount of deionized water. Then, weigh 25 mL of glacial acetic acid and mix it with the solution and stir evenly. Add deionized water to dilute the mixed solution to 1 L and then pour the mixed solution into the electroplating tank. Use electrolytic nickel plates (purity above 99.5%) as anode and cathode to perform electrolysis at room temperature. The electrolysis current is 2 A and the electrolysis time is 325 min. After the electrolysis is completed, filter the electrolyte and set it aside.

[0045] (2) Surface pretreatment of tungsten alloy: A 93W-4.9Ni-2.1Fe tungsten alloy specimen with a diameter of 30 mm and a height of 13 mm was selected. The entire cylindrical surface and one end face were turned to expose the fresh surface, and the other end face was polished to Ra less than 0.2 μm. Then the sample was mounted on a hanger and first cleaned with hot water at 90 °C and 10 g / L of detergent. The hot water completely immersed the sample. After ultrasonic cleaning for 5 min, the residual detergent on the surface was fully rinsed with running cold water. The sample was then immersed in anhydrous ethanol (purity 99.5%) for ultrasonic cleaning at 30 °C for 5 min. After cleaning, the sample was fully rinsed with clean anhydrous ethanol and then immersed in an acetic acid aqueous solution for ultrasonic cleaning. The concentration of the acetic acid aqueous solution was 50% vol. First, 200 mL of glacial acetic acid was measured, and then deionized water was added to make up to 400 mL. Then the sample was immersed in an ultrasonic machine for cleaning at 30 °C for 5 min. min. After cleaning, quickly rinse the sample with running cold water to remove the residual acetic acid solution on the surface. The surface treatment is complete.

[0046] (3) Direct nickel electroplating at constant current density: First, add 1 L of the nickel acetate solution prepared in step (1) to a 1 L electrolytic cell, then add 0.07 g of SDS and stir thoroughly to dissolve, adjust the pH of the electroplating cell to 4.40, then place the anode plate in the electrolytic cell and connect it to the anode, then connect the plated part to the cathode of the power supply, and adjust the output current to 0.35 A (theoretical current density 1.32 A / dm 2 , 100% cathode efficiency) and then turn on the DC power switch, and immerse the sample completely in the electroplating bath while it is powered on. The electroplating time is 217 min. During the electroplating period, a magnetic stirrer is used to rotate slowly without bubbles. The solution temperature in the electroplating bath is kept stable at 27 °C, and the pH in the electroplating bath is kept less than 5.

[0047] (4) After step (3) is completed, the sample is removed from the electroplating bath, and then rinsed with deionized water and dried to obtain the target plated part. The remaining electroplating solution can be filtered and recovered, and the pH value is adjusted to 4.42 for later use; (5) Conduct a coating quality inspection on the nickel coating produced in step (3), including visual inspection of the coating quality and determination of the coating thickness and joint strength after diffusion welding with steel. Visually inspect whether there are significant cracks or peeling or warping. If there are no significant problems after visual inspection, polish the coating on the surface to be welded and the butted steel block to Ra less than 0.2 μm, then thoroughly clean them and use hot pressing diffusion connection. The diffusion welding process is: heat from room temperature to 1000 °C at a rate of 10 °C / min, then keep warm for 1 hour, apply 28 MPa pressure at the same time and keep the pressure for 1 hour, then remove the pressure and cool to 550 °C at a rate of 5 °C / min, then keep warm for 1 hour, and finally cool in the furnace, take a dog-bone shaped specimen, and measure the tensile strength of the joint by butt joint. The visual inspection results are as follows: Figure 4 As shown in (b), due to the high current density and the poor conductivity of tungsten alloy itself, the coating thickens significantly at the edge, causing severe stress concentration, resulting in cracking of the coating and failure of electroplating.

[0048] (1) Prepare nickel acetate electroplating solution by electrolysis: first weigh 5 g of sodium chloride and dissolve it in a small amount of deionized water. Then, weigh 25 mL of glacial acetic acid and mix it with the solution and stir evenly. Add deionized water to dilute the mixed solution to 1 L and then pour the mixed solution into the electroplating tank. Use electrolytic nickel plates (purity above 99.5%) as anode and cathode to perform electrolysis at room temperature. The electrolysis current is 2 A and the electrolysis time is 325 min. After the electrolysis is completed, filter the electrolyte and set it aside.

[0049] (2) Surface pretreatment of tungsten alloy: A 93W-4.9Ni-2.1Fe tungsten alloy specimen with a diameter of 30 mm and a height of 13 mm was selected. The entire cylindrical surface and one end face were turned to expose the fresh surface, and the other end face was polished to Ra less than 0.2 μm. Then the sample was mounted on a hanger and immersed in anhydrous ethanol (purity 99.5%) for ultrasonic cleaning. The temperature of anhydrous ethanol was 30°C and the ultrasonic cleaning time was 5 min. After cleaning, the sample was fully rinsed with clean anhydrous ethanol and then immersed in an acetic acid aqueous solution for ultrasonic cleaning. The concentration of the acetic acid aqueous solution was 50% vol. First, 200 mL of glacial acetic acid was measured, and then deionized water was added to make up to 400 mL. Then the sample was immersed in an ultrasonic machine for ultrasonic cleaning at 30°C for 5 min. After cleaning, the sample was quickly rinsed with running cold water to remove the residual acetic acid solution on the surface. The surface treatment was completed.

[0050] (3) Direct nickel electroplating at constant current density: First, add 1 L of the nickel acetate solution prepared in step (1) to a 1 L electrolytic cell, adjust the pH of the electroplating cell to 4.0, then place the anode plate in the cell and connect it to the anode, then connect the plated part to the cathode of the power supply, and adjust the output current to a constant 0.2 A (theoretical current density 0.76 A / dm 2 , 100% cathode efficiency) and then turn on the DC power switch, and immerse the sample completely in the electroplating bath while it is powered on. The electroplating time is 236 min. During the electroplating period, a magnetic stirrer is used to rotate slowly without bubbles. The solution temperature in the electroplating bath is kept stable at 22 °C, and the pH value in the electroplating bath is kept less than 5.

[0051] (4) After step (3) is completed, the sample is removed from the electroplating bath, and then rinsed with deionized water and dried to obtain the target plated part. The remaining electroplating solution can be filtered and recovered, and the pH value is adjusted to 4.42 for later use; (5) The nickel coating prepared in step (3) is subjected to coating quality inspection, including visual inspection of coating quality and determination of coating thickness and joint strength after diffusion welding with steel. Visual inspection is performed to see if there are significant cracks or peeling and warping. If there are no significant problems after visual inspection, the coating on the surface to be welded and the butted steel block are polished to Ra less than 0.2 μm, and then thoroughly cleaned and diffused by hot pressing. The diffusion welding process is: heating from room temperature to 1000°C at a rate of 10°C / min, then keeping the temperature for 1 hour, while applying 28 MPa pressure and keeping the pressure for 1 hour, then removing the pressure, and cooling to 550°C at a rate of 5°C / min, then keeping the temperature for 1 hour, and finally furnace cooling, taking a dog-bone-shaped specimen, and measuring the tensile strength of the joint by butt joint. Due to insufficient preliminary cleaning of the samples, the initial pH of the electroplating was too low, and SDS was not added as an anti-pinhole agent, resulting in a large amount of hydrogen precipitation on the surface during electroplating, leaving a large number of pits and shallow grooves on the coating. The overall coating also showed an orange peel pattern and was uneven. The coating quality was too poor and did not meet the requirements of diffusion welding.

[0052] (1) Prepare nickel acetate electroplating solution using nickel acetate tetrahydrate: First, weigh 5 g of sodium chloride and 64 g of nickel acetate (tetrahydrate) and dissolve them in a small amount of deionized water. Add deionized water to dilute the mixed solution to 1 L, then use glacial acetic acid to adjust the pH to 4.5, and then keep the mixed solution for later use. At this time, the Ni content in the solution is 2+ The concentration is about 15 g / L (2) Surface pretreatment of tungsten alloy: A 93W-4.9Ni-2.1Fe tungsten alloy specimen with a diameter of 30 mm and a height of 13 mm was selected. The entire cylindrical surface and one end face were turned to expose the fresh surface, and the other end face was polished to Ra less than 0.2 μm. Then the sample was mounted on a hanger and immersed in anhydrous ethanol (purity 99.5%) for ultrasonic cleaning. The temperature of anhydrous ethanol was 30°C and the ultrasonic cleaning time was 5 min. After cleaning, the sample was fully rinsed with clean anhydrous ethanol and then immersed in an acetic acid aqueous solution for ultrasonic cleaning. The concentration of the acetic acid aqueous solution was 50% vol. First, 200 mL of glacial acetic acid was measured, and then deionized water was added to make up to 400 mL. Then the sample was immersed in an ultrasonic machine for cleaning at 30°C for 5 min. After cleaning, the sample was quickly rinsed with running cold water to remove the residual acetic acid solution on the surface. The surface treatment was completed.

[0053] (3) Direct nickel electroplating at constant current density: First, add 1 L of the nickel acetate solution prepared in step (1) to a 1 L electrolytic cell, then add 0.05 g of SDS and stir thoroughly to dissolve, adjust the pH of the electroplating cell to 4.50, then place the anode plate in the cell and connect it to the anode, then connect the plated part to the cathode of the power supply, and adjust the output current to 0.2 A (theoretical current density 0.76 A / dm 2, 100% cathode efficiency) and then turn on the DC power switch, and immerse the sample completely in the electroplating bath while it is powered on. The electroplating time is 540 min. During the electroplating period, a magnetic stirrer is used to rotate slowly without bubbles. The solution temperature in the electroplating bath is kept stable at 27 °C, and the pH in the electroplating bath is kept less than 5.

[0054] (4) After step (3) is completed, the sample is removed from the electroplating bath, and then rinsed with deionized water and dried to obtain the target plated part. The remaining electroplating solution can be filtered and recovered, and the pH value is adjusted to 4.42 for later use; (5) Conduct a coating quality inspection on the nickel coating produced in step (3), including visual inspection of the coating quality and determination of the coating thickness and joint strength after diffusion welding with steel. Visually inspect whether there are significant cracks or peeling and warping. If there are no significant problems after visual inspection, polish the coating on the surface to be welded and the butted steel block to Ra less than 0.2 μm, then thoroughly clean them and use hot pressing diffusion connection. The diffusion welding process is: heat from room temperature to 1000 °C at a rate of 10 °C / min, then keep warm for 1 hour, apply 28 MPa pressure and keep the pressure for 1 hour, then remove the pressure and cool to 550 °C at a rate of 5 °C / min, then keep warm for 1 hour, finally cool in the furnace, take a dog-bone shaped specimen, and measure the tensile strength of the joint by butt joint. Due to the solution Ni 2+ The concentration is too high and the conductivity is too good, which makes the coating deposition speed too fast and produces a significant current density concentration at the edge of the tungsten alloy sample, resulting in excessive stress on the coating, making it difficult to adhere to the substrate surface and falling off as a whole, causing electroplating failure.

Claims

1. A method for directly plating thick nickel on the surface of tungsten alloy, characterized in that: The steps include: Step 1: Tungsten alloy surface pretreatment The tungsten alloy surface is mechanically processed to remove the oxide layer, and then polished until the surface to be plated exposes fresh metal, and the roughness of the surface to be plated is less than Ra0.2μm; then detergent + hot water, ethanol, and acetic acid are used to clean in sequence; the sample to be plated is obtained after cleaning; Step 2: Nickel plating First, add nickel acetate plating solution to the plating tank, then add sodium dodecyl sulfate and fully dissolve it. The amount of sodium dodecyl sulfate added is 0.04-0.1g / L, and the pH of the plating tank is adjusted to between 3.5-5.

5. The anode is an electrolytic nickel plate, connected to the positive pole of the power supply, and the sample to be plated is connected to the negative pole of the power supply. Turn on the power supply and set the target current density to 0.3-1.1A / dm 2 , start electroplating; the initial concentration of sodium chloride in the nickel acetate electroplating solution is 3-14g / L, preferably 4-8g / L, and more preferably 5g / L, and the initial concentration of glacial acetic acid is 5-25ml / L, and the pH of the electroplating pool is adjusted to between 3.5-5.5, preferably 4.2-4.6, and the initial Ni 2+ The concentration of ions is 5-10g / L.

2. A method for directly plating thick nickel on a tungsten alloy surface according to claim 1, characterized in that: The surface pretreatment of tungsten alloy includes: using sandblasting, turning, polishing and other mechanical processing methods to pre-remove the significant oxide layer on the surface of tungsten alloy, and then polishing the surface to be welded. Then use detergent + hot water, ethanol, and acetic acid to ultrasonically clean in sequence, and the number of cleaning times for each process is 1-2 times. Then immediately take out the sample and use running water to fully clean it. The pretreatment is completed.

3. A method for directly plating thick nickel on a tungsten alloy surface according to claim 2, characterized in that: The process of ultrasonic cleaning of tungsten alloy to be plated parts using detergent + hot water, ethanol, and acetic acid in sequence is as follows: hot water washing is carried out using commercially available alkaline detergent combined with hot water, the detergent addition amount is 5-15g / L, the hot water temperature is 85-100°C, the detergent is first fully dissolved in hot water and then the sample is immersed in it and then ultrasonically cleaned, the cleaning time is 5-10min, and the number of cleanings is 1-2 times; then the sample is fully rinsed with running cold water to remove residual detergent on the surface and then immersed in anhydrous ethanol with a purity of more than 99.5% for ultrasonic cleaning, the temperature of anhydrous ethanol is 20-50°C, the cleaning time is 5-10min, and the number of cleanings is 1-2 times; then the sample is fully rinsed with running anhydrous ethanol and then placed in an acetic acid aqueous solution for ultrasonic cleaning, the concentration of the acetic acid aqueous solution is 40-60%vol, first the glacial acetic acid is dissolved in deionized water and then fully stirred and then the sample is immersed, the ultrasonic cleaning time is 5-10min, and the cleaning temperature is 20-50°C, after the cleaning is completed, the sample is quickly rinsed with running cold water to remove residual acetic acid solution on the surface, and the surface treatment is completed.

4. The method for directly plating thick nickel on a tungsten alloy surface according to claim 1, wherein: The nickel acetate electroplating solution is prepared by using chemically pure nickel acetate or by using electrolysis method; The electrolytic method for preparing nickel acetate electroplating solution includes: first preparing a solution using sodium chloride, glacial acetic acid and water, wherein the sodium chloride concentration is 3-14 g / L and the glacial acetic acid concentration is 15-30 mL / L, and then using electrolytic nickel plates as anodes and cathodes for electrolysis until the Ni ion concentration in the solution is 5-10 g / L.

5. The method for directly plating thick nickel on a tungsten alloy surface according to claim 1, wherein: When electroplating nickel, constant current density direct current electroplating nickel is used; the method for adjusting pH by constant current density direct electroplating nickel is: before plating, if the pH is too high, add glacial acetic acid to lower it; If the pH is too low, use graphite or electrolytic nickel plates as electrodes and apply power to increase the pH of the system. Monitor the pH as it rises. When the pH exceeds the specified range, add glacial acetic acid until the pH returns to the specified range.

6. The method for directly plating thick nickel on a tungsten alloy surface according to claim 1, characterized in that: The process conditions for constant current density direct current nickel plating are: current density is 0.3-1.1A / dm 2 , preferably 0.4-0.9A / dm 2 , further preferably 0.57-0.76A / dm 2 The electroplating time can be as long as 10 hours or more depending on the thickness requirements. The plating solution temperature is less than or equal to 30 degrees Celsius. The plating solution is stirred by mechanical stirring, magnetic stirring, air flow stirring or directly moving the sample.

7. The method for directly plating thick nickel on a tungsten alloy surface according to claim 1, characterized in that: After the electroplating is completed, the sample is taken out of the electroplating tank, rinsed thoroughly with water and dried to obtain the target plated parts. The remaining electroplating solution can be filtered and recovered, and the pH can be adjusted so that it can be reused in the electrolytic method to prepare nickel acetate electroplating solution.

8. The method for directly plating thick nickel on a tungsten alloy surface according to claim 1, characterized in that: Electroplating for 208 minutes can obtain a coating with a thickness of 24-25 μm; electroplating for 1295 minutes can obtain a coating with a thickness greater than or equal to 80 μm.

9. The method for directly plating thick nickel on a tungsten alloy surface according to claim 1, characterized in that: Conduct coating quality inspection on nickel coating, including visual inspection of coating quality and judging coating thickness and joint strength after diffusion welding with steel; Diffusion bonding and test conditions are as follows: first polish the coating on the surface to be welded and the butted steel block to Ra less than 0.2μm, then use hot pressing or hot isostatic pressing for diffusion bonding after thorough cleaning, the diffusion bonding temperature is 900-1000℃, the welding pressure is 10-40MPa and 50-200MPa, and the joint evaluation method is tensile strength.

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