CN109208046B - A method of molten salt in-situ electrodeposition of tungsten carbide/tungsten composite coating - Google Patents

Abstract

The invention discloses a method for in-situ electrodeposition of tungsten carbide/tungsten composite coating with molten salt. Under the protection of inert gas, a tungstate system is used as a molten salt electrolyte, and tungsten carbide or tungsten carbide-cobalt hard alloy is used as an auxiliary Electrode, the conductive plated part after grinding and polishing treatment is the working electrode, which is obtained by heating and melting, heat preservation, and in-situ electrodeposition. The invention selects the molten salt in-situ electrodeposition method to prepare the tungsten carbide/tungsten composite coating, which has the characteristics of high efficiency and short preparation process. At the same time, the tungstate system is used as the molten salt electrolyte, which has low volatility and can speed up the electrochemistry of the auxiliary electrode. The speed of dissolving is beneficial to improve its recycling rate, and it can process workpieces with complex shapes such as curved surfaces and inner holes. At the same time, the process equipment is simple, the operation is convenient, the cost is low, and the pollution is low. , the grain is complete, the bonding strength is high, the surface is smooth, the hardness is high, and the wear resistance is good, which realizes the improvement of the performance of the tungsten coating, which is of great theoretical and practical significance.

Description

A method of molten salt in-situ electrodeposition of tungsten carbide/tungsten composite coating

technical field

The invention belongs to the technical field of molten salt electroplating, relates to a preparation method of a composite coating, and in particular relates to a method for in-situ electrodeposition of tungsten carbide/tungsten composite coating by molten salt.

Background technique

Tungsten-cobalt cemented carbide has extremely high hardness and strength, and is widely used in the industry, and is known as "the tooth of the industry"; with its large-scale application in the industry, it faces a large number of scraps. It is of great significance for the development of circular economy to fully recycle and reuse the cemented carbide.

Although pure tungsten coating has certain hardness, strength and wear resistance, under complex working conditions, composite tungsten coating with tungsten carbide as reinforcement has more advantages. Compared with pure tungsten coating, composite tungsten coating has more advantages. The coating has higher hardness and strength, the wear resistance is further improved, and the application scope is wider.

Since the potential of tungsten is more negative than that of hydrogen, it can only be prepared by molten salt system, and the present invention prepares tungsten composite coating by in-situ electrodeposition of molten salt system. Compared with ex-situ electrodeposition, the in-situ electrodeposition has better contact between the coating and the substrate, and the coating has good wettability and interfacial bonding properties with the substrate, which helps to reduce the tendency of cracks during the deposition process; Moreover, the dispersion distribution of the reinforcing phase in the tungsten-based coating is beneficial to the strengthening of the coating and improves its wear resistance. Refractory metal carbides represented by tungsten carbide have many advantages such as high hardness and good wear resistance. Therefore, the in-situ electrodeposition of tungsten carbide hard phase and tungsten on the substrate is a good way to prepare tungsten reinforced coatings.

At present, from the perspective of fast deposition speed and high product quality, chemical vapor deposition (CVD) and plasma spraying (PS) methods for preparing tungsten carbide/tungsten composite coatings are close to maturity, but the prepared tungsten carbide/tungsten composite coatings There are still some deficiencies in the coating, such as weak crystallinity and matrix bonding force, high oxygen content; in the process of molten salt electroplating, the coating and the surface of the plated part are fully diffused, the binding ability is improved, and the cathode continues to undergo electro-deoxidation reaction ( reduction reaction), so the oxygen content is low, and the coating obtained by electrodeposition has good crystallinity and complete and dense grains.

So far, there are no relevant reports on the in-situ electrodeposition of tungsten carbide/tungsten composite coatings from molten salts.

SUMMARY OF THE INVENTION

Aiming at the deficiencies of the prior art, the present invention provides a method for in-situ electrodeposition of tungsten carbide/tungsten composite coating by molten salt.

The present invention adopts following technical scheme:

A method for in-situ electrodeposition of tungsten carbide/tungsten composite coating with molten salt, under the protection of inert gas, using tungstate system as molten salt electrolyte, tungsten carbide or tungsten carbide-cobalt cemented carbide as auxiliary electrode, conductive plating The component is the working electrode, which is obtained by heating the molten salt electrolyte, keeping it warm, and in-situ electrodeposition.

In the above technical solution, the tungstate system is a mixture of tungstate and a molten salt active material with a molar ratio of 1:(0.001-0.5).

Further, in the above technical solution, the tungstate is one or more of Na ₂ WO ₄ , K ₂ WO ₄ and CaWO ₄ , preferably Na ₂ WO ₄ .

Further, in the above technical solution, the molten salt active material is one or more of NaPO ₃ , NaF, KF, WO ₃ , ZnO, and B ₂ O ₃ .

In the above technical solution, the content of cobalt in the tungsten carbide-cobalt cemented carbide is less than or equal to 6wt%.

In the above technical solution, the conductive plated part is a metal plated part whose surface roughness after grinding and polishing is not greater than Ra 1.6 and electrical conductivity is not less than 250 S·cm ⁻¹ .

Still further, in the above technical solution, the electrodeposition is in-situ electrodeposition by a constant potential step method or a constant current step method in-situ electrodeposition.

Still further, in the above technical solution, the process conditions for the in-situ electrodeposition of the potentiostatic step method are as follows: the potential is 0.2-2V, and the reference electrode is a metal platinum wire.

Still further, in the above technical solution, the process conditions for the in-situ electrodeposition of the galvanostatic step-step method are as follows: the current density is 10-150 mA/cm ² .

In the above technical solution, the inert gas is selected from one of helium, neon and argon.

In the above technical solution, the temperature of the heating, melting and heat preservation is 750-950°C.

Still further, in the above technical scheme, the method for in-situ electrodeposition of tungsten carbide/tungsten composite coating by molten salt includes the following steps:

S1, place the tungsten carbide or tungsten carbide-cobalt cemented carbide after mechanical cutting and grinding treatment in deionized water, acetone and alcohol successively for ultrasonic cleaning, and drying for use;

S2. Soak the metal plated parts after mechanical grinding and surface polishing in alkaline solution, then place them in deionized water, acetone and alcohol for ultrasonic cleaning in turn, and dry them for later use;

S3. The molten salt electrolyte after vacuum drying and dehydration at 280-350°C for 12-24h is heated to 800-900°C at a constant heating rate under an argon protective atmosphere, and the molten salt is kept for 2.5-4h to melt uniformly;

S4. Place the auxiliary electrode and the working electrode in molten salt and use the galvanostatic step method for in-situ electrodeposition, or place the auxiliary electrode, the working electrode and the reference electrode in the molten salt and use the galvanostatic step method for in-situ electrodeposition. , After cooling down, take out the metal plated parts and place them in lye solution for immersion and drying.

Compared with the prior art, the beneficial effects of the present invention are as follows:

(1) The present invention selects the molten salt in-situ electrodeposition method to prepare the tungsten carbide/tungsten composite coating, which has the characteristics of high efficiency and short preparation process. The existence of salt makes the waste cemented carbide have high electrochemical activity, accelerates the rate of electrochemical dissolution of cemented carbide, and is beneficial to improve the recycling rate of waste cemented carbide;

(2) The present invention selects the molten salt in-situ electrodeposition method to prepare the tungsten carbide/tungsten composite coating, which can process curved surfaces and workpieces with complex shapes such as inner holes, and at the same time, the process equipment is simple, the operation is convenient, and the cost is low, low pollution;

(3) The tungsten carbide/tungsten composite coating prepared by the molten salt in-situ electrodeposition method in the present invention has a compact structure, complete grains, high bonding strength, smooth surface, high hardness and good wear resistance, and realizes the tungsten coating. The performance is improved, and the waste tungsten carbide-cobalt carbide can be used as the auxiliary electrode, which can greatly reduce the pressure on the environment.

Description of drawings

Fig. 1 is the XRD spectrum of the tungsten carbide/tungsten composite coating obtained by the molten salt in-situ electrodeposition method in the embodiment of the present invention 1;

2 is a low-magnification SEM photo of the tungsten carbide/tungsten composite coating obtained by the molten salt in-situ electrodeposition method in Example 1 of the present invention;

3 is a high magnification SEM photograph of the tungsten carbide/tungsten composite coating prepared by the molten salt in-situ electrodeposition method in Example 1 of the present invention.

Detailed ways

In order to facilitate the understanding of the present invention, the method for in-situ electrodeposition of tungsten carbide/tungsten composite coating by molten salt of the present invention is further described in a more comprehensive and detailed manner below with reference to the accompanying drawings and examples.

Preferred embodiments of the present invention are shown in the accompanying drawings; however, the present invention may be embodied in many different forms and is not limited to the embodiments described herein; rather, these embodiments are provided for the purpose of This is to make the understanding of the disclosure of the present invention more thorough and complete.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terms used herein in the description of the present invention are for the purpose of describing specific embodiments only, and are not intended to limit the present invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

The raw materials and related experimental equipment used in the examples and comparative examples of the present invention are all commercially available products.

Example 1

The embodiment of the present invention provides a method for in-situ electrodeposition of tungsten carbide/tungsten composite coating by molten salt, using waste tungsten carbide as an auxiliary electrode, using a molybdenum plate as a working electrode, and adopting a constant current step method in-situ electrodeposition process preparation.

Specifically, it includes the following steps:

S1. The waste tungsten carbide is simply mechanically cut to obtain a suitable size, and after mechanical grinding, it is soaked in alkali solution for 20 minutes, then cleaned with deionized water, ultrasonically cleaned in acetone and alcohol, and dried for use;

S2. The molybdenum plate is mechanically ground and polished to a smooth surface, soaked in lye solution for 20 minutes, then cleaned with deionized water, ultrasonically cleaned in acetone and alcohol, and dried for later use;

S3. The Na ₂ WO ₄ was pre-dried in a 300°C vacuum drying oven for 12 hours, and subjected to dehydration treatment. A certain amount of Na ₂ WO ₄ molten salt was weighed, put into an electrolytic cell, and raised to 900° C. at a stable heating rate. , keep the temperature for 3 hours to make the molten salt melt evenly;

S4, place the auxiliary electrode and the working electrode in molten salt, connect the electrochemical workstation, adopt the in-situ electrodeposition process of the galvanostatic step method, set the cathode current density to 50mA/cm ² , carry out electrodeposition for 5 hours, and then, Take out the working electrode, soak it in lye solution, and wash the salt in the coating.

1 is the XRD spectrum of the tungsten carbide/tungsten composite coating prepared by the molten salt in-situ electrodeposition method in Example 1 of the present invention. As can be seen from the figure, the prepared composite coating mainly includes 3 Species include both the matrix tungsten phase and the two enhanced phases, tungsten carbide and ditungsten carbide. The crystal form of the tungsten phase is body-centered cubic, and the diffraction angles are 40.26°, 58.27°, 73.19°, and 87.02°, respectively. In the crystal plane indices (110), (200), (211) and (220), the tungsten carbide and ditungsten carbide phases are all hexagonal.

2 is a low-magnification SEM photo of the tungsten carbide/tungsten composite coating obtained by the molten salt in-situ electrodeposition method in Example 1 of the present invention. It can be seen from the figure that the obtained composite coating has a clear outline, The surface is flat, without obvious bumps and pits, the porosity is very low, and the surface is clean and smooth.

3 is a high-magnification SEM photo of the tungsten carbide/tungsten composite coating obtained by the molten salt in-situ electrodeposition method in Example 1 of the present invention. It can be seen from the figure that the obtained composite coating has obvious crystal grains , complete, irregular shape, close arrangement between grains, few voids, high microscopic density.

Example 2

The embodiment of the present invention provides a method for in-situ electrodeposition of tungsten carbide/tungsten composite coating by molten salt, using waste WC-6Co cemented carbide (tungsten carbide-cobalt cemented carbide with a cobalt content of 6wt%) as an auxiliary The electrode, with copper plate as working electrode and platinum wire as reference electrode, was prepared by in-situ electrodeposition process of potentiostatic step method.

Specifically, it includes the following steps:

S1. Carry out simple mechanical cutting of waste WC-6Co cemented carbide to obtain the appropriate size, and after mechanical grinding, put it into lye solution for 20 minutes, then clean it with deionized water, ultrasonically clean it in acetone and alcohol, and dry it. spare;

S2. The copper plate is mechanically ground and polished to a smooth surface, soaked in alkali solution for 20 minutes, then cleaned with deionized water, ultrasonically cleaned in acetone and alcohol, and dried for use. After cleaning, dry for use;

S3. Pre-dry Na ₂ WO ₄ and NaPO ₃ in a vacuum drying oven at 300° C. for 12 hours, perform dehydration treatment, and weigh Na ₂ WO ₄ and NaPO respectively according to the mole percentage as Na ₂ WO ₄ : NaPO ₃ =1:0.15 _3. Put the mixed molten salt into the electrolytic cell, raise it to 850°C at a stable heating rate, and keep it for 3 hours to make the molten salt melt evenly;

S4. Place the auxiliary electrode, the working electrode and the reference electrode in the molten salt, connect to the electrochemical workstation, use the potentiostatic step method in-situ electrodeposition process, set the voltage to 1.5V, and carry out electrodeposition for 10 hours, then, Take out the working electrode, soak it in lye solution, and wash the salt in the coating.

Example 3

The embodiment of the present invention provides a method for in-situ electrodeposition of tungsten carbide/tungsten composite coating by molten salt, using waste tungsten carbide as an auxiliary electrode, using a stainless steel plate as a working electrode, and adopting a constant current step method in-situ electrodeposition process preparation.

Specifically, it includes the following steps:

S1. The waste tungsten carbide is simply mechanically cut to obtain a suitable size, and after mechanical grinding, it is soaked in alkali solution for 20 minutes, then cleaned with deionized water, ultrasonically cleaned in acetone and alcohol, and dried for use;

S2. The stainless steel plate is mechanically ground and polished to a smooth surface, soaked in lye solution for 20 minutes, then cleaned with deionized water, ultrasonically cleaned in acetone and alcohol, and dried for later use;

S3. Dry K ₂ WO ₄ and KF in a vacuum drying oven at 300° C. for 24 hours in advance, and perform dehydration treatment. According to the mole percentage, K ₂ WO ₄ : KF=1:0.2 are weighed to K ₂ WO ₄ and KF respectively, Put the mixed molten salt into the electrolytic cell, raise it to 850°C at a stable heating rate, and keep it for 3 hours to make the molten salt melt evenly;

S4, place the auxiliary electrode and the working electrode in molten salt, connect to an electrochemical workstation, adopt a constant current step method in-situ electrodeposition process, set the cathode current density to 80mA/cm ² , and perform electrodeposition for 15 hours, then, Take out the working electrode, soak it in lye solution, and wash the salt in the coating.

Comparative Example 1

The comparative example of the present invention provides a method for in-situ electrodeposition of tungsten carbide/tungsten composite coating by molten salt, using waste WC-9.5Co cemented carbide (tungsten carbide-cobalt cemented carbide with a cobalt content of 9.5wt%) As the auxiliary electrode, the stainless steel plate is used as the working electrode, and it is prepared by the in-situ electrodeposition process of the constant current step method.

Specifically, it includes the following steps:

S1. Carry out simple mechanical cutting of waste WC-9.5Co cemented carbide to obtain the appropriate size, and after mechanical grinding, put it into lye solution for 20 minutes, then clean it with deionized water, ultrasonically clean it in acetone and alcohol, and bake it. dry spare;

S2. The stainless steel plate is mechanically ground and polished to a smooth surface, soaked in lye solution for 20 minutes, then cleaned with deionized water, ultrasonically cleaned in acetone and alcohol, and dried for later use;

S3. K ₂ WO ₄ and ZnO are pre-dried in a vacuum drying oven at 300° C. for 24 hours, and subjected to dehydration treatment, and K ₂ WO ₄ and ZnO are weighed respectively according to the mole percentage as K ₂ WO ₄ : ZnO=1:0.12, Put the mixed molten salt into the electrolytic cell, raise it to 850°C at a stable heating rate, and keep it for 3 hours to make the molten salt melt evenly;

S4, place the auxiliary electrode and the working electrode in molten salt, connect the electrochemical workstation, adopt the in-situ electrodeposition process of the galvanostatic step method, set the cathode current density to 65mA/cm ² , carry out electrodeposition for 9 hours, and then, Take out the working electrode, soak it in lye solution, and wash the salt in the coating.

The coating prepared in Comparative Example 1 has complex phases, including not only the matrix tungsten phase, the tungsten carbide reinforced phase and the ditungsten carbide reinforced phase, but also the cobalt phase, and the comprehensive mechanical properties of the prepared coating are poor.

Comparative Example 2

The comparative example of the present invention provides a method for in-situ electrodeposition of tungsten carbide/tungsten composite coating by molten salt, using waste tungsten carbide as auxiliary electrode, molybdenum plate as working electrode, Ag/AgCl as reference electrode, using constant Prepared by the potential step method in situ electrodeposition process.

Specifically, it includes the following steps:

S1. The waste tungsten carbide is simply mechanically cut to obtain a suitable size, and after mechanical grinding, it is soaked in alkali solution for 20 minutes, then cleaned with deionized water, ultrasonically cleaned in acetone and alcohol, and dried for use;

S2. The molybdenum plate is mechanically ground and polished to a smooth surface, soaked in alkali solution for 20 minutes, then cleaned with deionized water, ultrasonically cleaned in acetone and alcohol, dried for use, and at the same time, the silver wire is polished with sandpaper, After cleaning with alcohol, dry it for later use;

S3. Pre-dry Na ₂ WO ₄ and NaPO ₃ in a vacuum drying oven at 300° C. for 12 hours, perform dehydration treatment, and weigh Na ₂ WO ₄ and NaPO respectively according to the mole percentage as Na ₂ WO ₄ : NaPO ₃ =1:0.09 _3. Put the mixed molten salt into the electrolytic cell, raise it to 850°C at a stable heating rate, and keep it for 3 hours to make the molten salt melt evenly;

S4. Place the auxiliary electrode, the working electrode and the reference electrode in molten salt, connect the electrochemical workstation, adopt the potentiostatic step method in-situ electrodeposition process, set the voltage to 3.2V, and conduct electrodeposition for 10 hours, then, Take out the working electrode, soak it in lye solution, and wash the salt in the coating.

In Comparative Example 2, a coating with a dense structure and a smooth surface could not be obtained, a large number of nodules and a little powder deposits appeared on the surface of the coating, and its comprehensive performance was poor.

The coatings prepared by each embodiment of the present invention and the comparative example were tested, and their adhesion was tested by grid method; the wear resistance at room temperature was tested by an abrasion tester (CS-10 grinding wheel, 500g load force, 500 cycles) , and its wear resistance is characterized by its mass loss; its hardness is tested by a Vickers hardness tester, and the specific results are shown in Table 1 below.

Table 1 Comparison table of mechanical properties of the coatings prepared by each experimental example and comparative example of the present invention

It can be seen from analyzing the results in Table 1 that in the embodiment of the present invention, the molten salt in-situ electrodeposition method is used to prepare the tungsten carbide/tungsten composite coating, which has the characteristics of high efficiency and short preparation process. At the same time, the tungstate system is used as the molten salt electrolyte. With low volatility, the existence of tungstate makes the waste cemented carbide have high electrochemical activity, which accelerates the electrochemical dissolution rate of cemented carbide, which is beneficial to improve the recycling rate of waste cemented carbide. At the same time, this method can The curved surface and workpieces with complex shapes such as inner holes are processed, and at the same time, the process equipment is simple, the operation is convenient, the cost is low, and the pollution is low; The coating structure is dense, the grain is complete, the bonding strength is high, the surface is smooth, the hardness is high, and the wear resistance is good, which realizes the improvement of the performance of the tungsten coating. Reduce pressure on the environment.

Finally, the above are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims (5)

1. a method for molten salt in-situ electrodeposition of tungsten carbide/tungsten composite coating, is characterized in that, under inert gas protection, with tungstate system as molten salt electrolyte, tungsten carbide or tungsten carbide-cobalt cemented carbide It is an auxiliary electrode, and the conductive plating piece is a working electrode. After heating and melting the molten salt electrolyte, it is kept warm, and the in-situ electrodeposition is obtained; Wherein, the tungstate system is a mixture of tungstate and molten salt active material with a molar ratio of 1:(0.001-0.5), and the tungstate is among Na ₂ WO ₄ , K ₂ WO ₄ , and CaWO ₄ One or more of the molten salt active material is one or more of NaPO ₃ , NaF, KF, WO ₃ , ZnO and B ₂ O ₃ ; the content of cobalt in the tungsten carbide-cobalt cemented carbide Less than or equal to 6 wt%; the electrodeposition is in-situ electrodeposition by the potentiostatic step method or the in-situ electrodeposition by the potentiostatic step method, and the process condition of the in-situ electrodeposition by the potentiostatic step method is: the potential is 0.2 -2 V, the reference electrode is a metal platinum wire, and the process conditions of the in-situ electrodeposition by the galvanostatic step method are: the current density is 10-150 mA/cm ² ; the temperature of the heating, melting and heat preservation is 750- 950°C. 2 . The method for in-situ electrodeposition of tungsten carbide/tungsten composite coating by molten salt according to claim 1 , wherein the tungstate is preferably Na ₂ WO ₄ . 3 . 3. the method for molten salt in-situ electrodeposition of tungsten carbide/tungsten composite coating according to claim 1, is characterized in that, described conductive plating part is that the surface roughness after grinding and polishing is not greater than Ra 1.6 and electric conductivity Metal plating with a rate of not less than 250 S·cm ^-1 . 4 . The method for in-situ electrodeposition of tungsten carbide/tungsten composite coating from molten salt according to claim 1 , wherein the inert gas is selected from the group consisting of helium, neon and argon. 5 . 5. the method for molten salt in-situ electrodeposition of tungsten carbide/tungsten composite coating according to any one of claims 1-4, is characterized in that, comprises the following steps: S1, place the tungsten carbide or tungsten carbide-cobalt cemented carbide after mechanical cutting and grinding treatment in deionized water, acetone and alcohol successively for ultrasonic cleaning, and drying for use; S2. Soak the metal plated parts after mechanical grinding and surface polishing in alkaline solution, then place them in deionized water, acetone and alcohol for ultrasonic cleaning in turn, and dry them for later use; S3. The molten salt electrolyte after vacuum drying and dehydration at 280-350 °C for 12-24 h is heated to 800-900 °C at a constant heating rate under an argon protective atmosphere, and the molten salt is melted uniformly for 2.5-4 h. ; S4. Place the auxiliary electrode and the working electrode in molten salt and use the galvanostatic step method for in-situ electrodeposition, or place the auxiliary electrode, the working electrode and the reference electrode in the molten salt and use the galvanostatic step method for in-situ electrodeposition. , After cooling down, take out the metal plated parts and place them in lye solution for immersion and drying.

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