Method for electrophoretic deposition of metal boride coating on surface of special-shaped cathode in molten salt

Abstract

The invention discloses a method for electrophoretic deposition of a metal boride coating on the surface of a special-shaped cathode in molten salt, and belongs to the technical field of electrophoretic deposition preparation of surface coatings. The method comprises the following steps: mixing NaF, AlF3 and other fluorides according to a specific ratio, and dividing the mixture into molten salt powder A and molten salt powder B; heating A to form basic molten salt, mixing B with metal boride powder with the particle size of less than 10 microns, and then adding the basic molten salt to obtain suspended molten salt; the special-shaped cathode is cleaned after being subjected to surface treatment; and finally, the treated cathode is placed in suspended molten salt, and electrophoretic deposition is carried out with a graphite crucible as an anode. According to the method, nano-scale and micron-scale mixed powder is adopted, the deposition speed is high, and the effect at edges and corners is good; the graphite crucible is used as an anode to avoid the shape matching problem, and the electric field is more uniform; the bonding strength of the coating is strengthened by constructing a cathode microstructure, and the metal boride coating can be simply prepared on the surface of the special-shaped cathode in the molten salt in a high-quality mode.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electrophoretic deposition for preparing surface coating, and specifically discloses a method for electrophoretic deposition of metal boride coating on the surface of a special-shaped cathode in molten salt. BACKGROUND

[0002] Metal boride coating, as a high-performance surface protection material, has important application value in the fields of industry and science and technology. Its high hardness, excellent high-temperature resistance and chemical stability can provide effective protection for the base material in extreme environments, significantly prolonging the service life of equipment and improving the operation efficiency. In the field of aerospace, the coating can resist high-temperature gas corrosion, ensuring the reliability of key components such as turbine blades in ultra-high temperature environments; in the field of energy equipment, the boride coating provides safety protection for nuclear reactor structural materials by inhibiting hydrogen permeation and neutron irradiation damage. Its excellent wear resistance can reduce the wear rate of parts in the field of mechanical manufacturing, reducing maintenance costs. With the development of new energy and miniaturization of electronic devices, the application potential of such coatings in fuel cell bipolar plates, semiconductor heat dissipation substrates and other scenarios is continuously expanding, and their low interfacial resistance and high thermal conductivity characteristics help to optimize energy conversion efficiency.

[0003] Preparation of metal boride coating by electrophoretic deposition in molten salt has the advantages of high coating density, no cracks, and low equipment cost, and has received widespread attention in recent years. Invention patents CN112359395A, CN115094499B and CN119530914A propose adding metal boride nanoparticles to fluoride or chloride molten salt, and after applying an electric field, a dense metal boride coating can be obtained on the cathode surface by electrophoresis. Invention patents CN114045546A and CN114990634B propose first synthesizing metal boride in molten salt, and then depositing a metal boride coating by applying electricity. However, in the prior art, there is a fixed distance between the cathode and the anode. In the actual application process of metal boride coating, special-shaped samples to be deposited are more common. If the cathode to be deposited is special-shaped, the anode used usually needs to match the shape of the cathode. In addition, the more corners or bending areas of the special-shaped cathode, the larger the local current density, resulting in poor electrophoretic deposition effect. Therefore, the existing metal boride coating preparation technology inevitably has problems such as complex preparation process and poor coating quality when dealing with special-shaped cathodes.

[0004] Therefore, how to achieve simple and high-quality electrophoretic deposition of metal boride coating on the surface of a special-shaped cathode in molten salt is a technical problem that needs to be solved in the industry at present. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a method for electrophoretic deposition of metal boride coating on the surface of a special-shaped cathode in molten salt, which can realize the preparation of metal boride coating on the surface of a special-shaped cathode in molten salt, has a simple process, fast electrophoretic deposition speed, and high coating density.

[0006] In order to achieve the above technical purpose, the present application adopts the following technical solution:

[0007] A method for electrophoretic deposition of metal boride coating on the surface of a special-shaped cathode in molten salt, comprising the following steps:

[0008] S1. Mixing NaF and AlF3, and at least one fluoride selected from LiF, CaF2, and MgF2, and then dividing the mixed molten salt into molten salt powder A with a mass percentage of 50-95% and molten salt powder B with the remaining amount; the mass fraction of AlF3 in the mixed molten salt is 40-55%, and the total mass fraction of NaF and AlF3 is ≥80%;

[0009] S2. Adding molten salt powder A into a circular graphite crucible, and then heating to 900-1100℃ under inert gas protection and maintaining for 0.5-1h to form a base molten salt;

[0010] S3. Mixing molten salt powder B and metal boride powder with a particle size of less than 10μm by oscillation, ball milling or rod milling for 0.5-6h, adding into the base molten salt for dispersion and maintaining for 1-2h to obtain a metal boride suspension molten salt;

[0011] S4. Surface treating the special-shaped cathode by one or more of polishing, wire drawing, and chemical etching, and then surface cleaning with ethanol to obtain a deposition cathode;

[0012] S5. Placing the deposition cathode in the metal boride suspension molten salt and positioning on the central axis of the graphite crucible, taking the graphite crucible as an anode, and applying an electric field between the anode and the cathode for electrophoretic deposition to obtain a special-shaped cathode with a metal boride coating.

[0013] Further, the metal boride in step S3 is one or more of titanium diboride, zirconium diboride, hafnium diboride, or lanthanum hexaboride.

[0014] Further, the concentration of the metal boride in the metal boride suspension molten salt in step S3 is 20-80g / L.

[0015] Further, the mass percentage of the 1-10μm particle size fraction in the metal boride powder in step S3 is 5-20%, the mass percentage of the 0.1-1μm particle size fraction is 40-80%, and the remaining powder has a particle size of less than 0.1μm.

[0016] Further, the special-shaped cathode in the step S4 is graphite, stainless steel, titanium, molybdenum or alloy thereof.

[0017] Further, the special-shaped cathode in the step S4 is arc line type or broken line type.

[0018] Further, the arithmetic average roughness Ra of the special-shaped cathode after surface treatment in the step S4 is 0.05-5 μm.

[0019] Further, the ratio of the inner diameter R of the graphite crucible to the maximum length L of the vertical projection of the special-shaped cathode in the step S5 is 2:1 to 5:1, and the ratio of the distance H of the special-shaped cathode from the bottom of the graphite crucible to the nearest distance D of the special-shaped cathode from the inner wall of the graphite crucible is 2:1 to 5:1.

[0020] Further, the ratio of the voltage U applied to the two ends of the anode and the cathode to the nearest distance D of the special-shaped cathode from the inner wall of the crucible in the step S5 is 0.1-0.5 V / cm, and the electrophoretic deposition time is 0.5-2 h.

[0021] The present application has the following beneficial effects: the present application proposes a method for electrophoretic deposition of metal boride coating on the surface of special-shaped cathode in molten salt, which realizes the simple and high-quality electrophoretic deposition of metal boride coating on the surface of special-shaped cathode in molten salt by improving the molten salt system, adjusting the anode structure and optimizing the surface morphology of the cathode. Compared with the prior art, the present application uses mixed powder of nano and micro metal boride instead of nano powder of narrow particle size, which has a faster deposition speed in the electrophoretic deposition process, and the electrophoretic deposition effect is better at the corners. In addition, the present application uses graphite crucible as anode, which avoids the problem that the anode needs to match the shape of the cathode when the electrodes are arranged relatively in the prior art. By adjusting the inner diameter of the graphite crucible, the uniformity of the electric field intensity is realized, thereby realizing efficient electrophoretic deposition. Finally, by constructing a microstructure on the surface of the cathode, the bonding strength of the metal boride coating and the surface of the special-shaped cathode is strengthened. BRIEF DESCRIPTION OF DRAWINGS

[0022] In order to facilitate the understanding of those skilled in the art, the present application will be further described below with reference to the accompanying drawings.

[0023] Figure 1 It is a front view of the electrophoretic deposition device used in the present application embodiment 1. In the figure, 1 is an anode guide rod, 2 is a cathode guide rod, 3 is a cathode to be deposited, 4 is a molten salt, and 5 is a graphite crucible.

[0024] Figure 2 It is a top view of the electrophoretic deposition device used in the present application embodiment 1.

[0025] Figure 3 It is an SEM image of the cross section of the metal titanium special-shaped cathode after electrophoretic deposition in the present application embodiment 1.

[0026] Figure 4 Figure 2 is a metallographic microscope image of a cross section of a graphite special-shaped cathode after electrophoretic deposition in Example 2 of the present application. DETAILED DESCRIPTION

[0027] The technical solutions in the present application will be clearly and completely described below in combination with the embodiments in the present application. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort belong to the scope of the present application.

[0028] Example 1

[0029] S1. NaF, AlF3, LiF, CaF2 and MgF2 are mixed according to mass fractions of 45%, 45%, 2%, 3% and 5%, and then the mixed molten salt is divided into 50% molten salt powder A and 50% molten salt powder B;

[0030] S2. The molten salt powder A is added into a circular graphite crucible, and then heated to 900℃ under inert gas protection for 1h to form a base molten salt;

[0031] S3. The molten salt powder B and titanium diboride powder with a particle size less than 10μm are mechanically mixed by oscillation method for 0.5-6h, and then added into the base molten salt for dispersion and heat preservation for 1-2h to obtain 20g / L titanium diboride suspension molten salt, wherein the mass fraction of the 1-10μm particle size level in the titanium diboride powder is 20%, and the mass fraction of the 0.1-1μm particle size level is 70%;

[0032] S4. The arc-shaped metal titanium special-shaped cathode is surface treated by a wire drawing method, and the average roughness of the treated surface is 2.5μm, and then the surface is cleaned by ethanol to obtain a to-be-deposited metal titanium cathode;

[0033] S5. The to-be-deposited metal titanium cathode is placed into the titanium diboride suspension molten salt and located at the central axis of the graphite crucible, and the graphite crucible serves as an anode; wherein the maximum length L of the vertical projection of the special-shaped cathode is 2cm, and the inner diameter R of the graphite crucible is 10cm (R:L=5:1); the closest distance D between the special-shaped cathode and the inner wall of the graphite crucible is 2cm, and the distance H between the special-shaped cathode and the bottom of the graphite crucible is 10cm (H:D=5:1); a voltage U of 0.4V (U / D=0.2V / cm) is applied between the anode and the cathode, and the electrophoretic deposition time is 1h to obtain a metal titanium special-shaped cathode with a titanium diboride coating.

[0034] It is detected that the titanium diboride coating on the surface of the metal titanium special-shaped cathode is uniformly distributed. The SEM image of the cross section of the metal titanium special-shaped cathode after electrophoretic deposition is shown in Figure 2. Figure 3, the average thickness of the titanium diboride coating is 42 μm.

[0035] Example 2

[0036] S1. NaF, AlF3, LiF and CaF2 are mixed according to mass fractions of 50%, 40%, 5% and 5%, and then the mixed molten salt is divided into molten salt powder A with a mass percentage of 95% and molten salt powder B with a mass percentage of 5%;

[0037] S2. The molten salt powder A is added to a circular graphite crucible, and then heated to 1100℃ under inert gas protection for 0.5h to form a base molten salt;

[0038] S3. The molten salt powder B is mixed with the zirconium diboride powder with a particle size less than 10 μm by ball milling for 4h, and then added to the base molten salt for dispersion and heat preservation for 2h to obtain 60g / L zirconium diboride suspension molten salt, wherein the mass percentage of the 1-10 μm particle size fraction in the zirconium diboride powder is 5%, and the mass percentage of the 0.1-1 μm particle size fraction is 80%;

[0039] S4. The surface of the fold line type graphite special-shaped cathode is treated by polishing, and the arithmetic average roughness Ra of the treated surface is 0.05 μm, and then the surface is cleaned with ethanol to obtain a graphite cathode to be deposited;

[0040] S5. The graphite cathode to be deposited is placed in the zirconium diboride suspension molten salt and placed at the central axis of the graphite crucible, and the graphite crucible serves as the anode; wherein the maximum length L of the vertical projection of the special-shaped cathode is 5 cm, the inner diameter R of the graphite crucible is 10 cm (R:L=2:1), the closest distance D between the special-shaped cathode and the inner wall of the graphite crucible is 5 cm, and the distance H between the special-shaped cathode and the bottom of the graphite crucible is 10 cm (H:D=2:1). A voltage U of 0.5V (U / D=0.1V / cm) is applied between the anode and the cathode, and the electrophoretic deposition time is 0.5h to obtain a graphite special-shaped cathode with a zirconium diboride coating.

[0041] It is detected that the zirconium diboride coating on the surface of the graphite special-shaped cathode is uniformly distributed. The metallographic microscope results of the cross section of the graphite special-shaped cathode after electrophoretic deposition are shown in Figure 4 , the average thickness of the zirconium diboride coating is 36 μm.

[0042] Example 3

[0043] S1. NaF, AlF3 and MgF2 are mixed according to mass fractions of 30%, 55% and 15%, and then the mixed molten salt is divided into molten salt powder A with a mass percentage of 70% and molten salt powder B with a mass percentage of 30%;

[0044] S2. The molten salt powder A is added to a circular graphite crucible, and then heated to 1000℃ under inert gas protection for 0.8h to form a base molten salt;

[0045] S3. The molten salt powder B is mixed with the lanthanum hexaboride powder with a particle size of less than 10 μm by a rod milling method for 3 h, then added to the base molten salt for dispersion and heat preservation for 1.5 h, to obtain 80 g / L lanthanum hexaboride suspension molten salt, wherein the mass percentage of the 1-10 μm particle size fraction of the lanthanum hexaboride powder is 10%, and the mass percentage of the 0.1-1 μm particle size fraction is 50%;

[0046] S4. The arc-shaped stainless steel special-shaped cathode is surface treated by a chemical etching method, and the arithmetic average roughness Ra of the treated surface is 5 μm, then the surface is cleaned with ethanol to obtain a graphite cathode to be deposited;

[0047] S5. The stainless steel cathode to be deposited is placed in the lanthanum hexaboride suspension molten salt and located at the axial position of the graphite crucible; wherein the maximum length L of the vertical projection of the special-shaped cathode is 4 cm, the inner diameter R of the graphite crucible is 12 cm (R:L = 3:1), the closest distance D of the special-shaped cathode to the inner wall of the crucible is 3 cm, and the distance H from the bottom is 9 cm (H:D = 3:1). A voltage of 0.9 V is applied to the anode and the cathode (voltage / D = 0.3 V / cm), the electrophoretic deposition time is 1.5 h, and the coating thickness reaches 38 μm.

[0048] It is detected that the lanthanum hexaboride coating on the surface of the stainless steel special-shaped cathode is uniformly distributed, and the average thickness of the coating is 64 μm.

[0049] Example 4:

[0050] S1. NaF, AlF3 and LiF are mixed according to the mass fraction of 45%, 45% and 10%, then the mixed molten salt is divided into 80% molten salt powder A and 20% molten salt powder B;

[0051] S2. The molten salt powder A is added to a circular graphite crucible, then heated to 1050℃ under inert gas protection, and heat preserved for 0.6 h to form a base molten salt;

[0052] S3. The molten salt powder B is mixed with the hafnium diboride and lanthanum hexaboride mixed powder (mass ratio 1:1) with a particle size of less than 10 μm by a shaking method for 2 h, then added to the base molten salt for dispersion and heat preservation for 1.2 h, to obtain 40 g / L metal boride suspension molten salt, wherein the mass percentage of the 1-10 μm particle size fraction of the hafnium diboride and lanthanum hexaboride powder is 15%, and the mass percentage of the 0.1-1 μm particle size fraction is 60%;

[0053] S4. The fold line type molybdenum alloy special-shaped cathode is surface treated by a combination of wire drawing and chemical etching, and the arithmetic average roughness Ra of the treated surface is 0.1 μm, then the surface is cleaned with ethanol to obtain a cathode to be deposited;

[0054] S5. The cathode to be deposited is placed in the metal boride suspension molten salt and positioned on the central axis of the graphite crucible, and the graphite crucible is used as the anode; wherein the inner diameter R of the graphite crucible is 8 cm, the maximum length L of the vertical projection of the special-shaped cathode is 2 cm (R:L = 4:1), the closest distance D between the special-shaped cathode and the inner wall of the graphite crucible is 1 cm, and the distance H from the bottom of the graphite crucible is 4 cm (H:D = 4:1). A voltage of 0.5V is applied between the anode and the cathode (voltage / D = 0.5V / cm), and the electrophoretic deposition time is 2h, thereby obtaining a special-shaped cathode with a metal boride coating.

[0055] It is detected that the surface coating of the molybdenum alloy special-shaped cathode is dense and uniform, and the average thickness is 50μm.

[0056] Example 5:

[0057] S1. NaF, AlF3 and CaF2 are mixed according to the mass fraction of 35%, 55% and 10% (AlF3 mass fraction 55%), and then the mixed molten salt is divided into 60% molten salt powder A and 40% molten salt powder B;

[0058] S2. The molten salt powder A is added to a circular graphite crucible, and then heated to 950℃ under argon protection for 0.7h to form a base molten salt;

[0059] S3. The mixed powder of titanium diboride and zirconium diboride with a particle size of less than 10μm (mass ratio 1:9) is mixed by ball milling for 5h, then added to the base molten salt for dispersion and heat preservation for 1.8h, to obtain 40g / L metal boride suspension molten salt, wherein the mass fraction of the 1-10μm particle size fraction in the mixed powder is 18%, and the mass fraction of the 0.1-1μm particle size fraction is 65%;

[0060] S4. The arc-shaped titanium alloy special-shaped cathode is surface treated by polishing, and the arithmetic average roughness Ra of the treated surface is 3μm, and then the surface is cleaned with ethanol to obtain a cathode to be deposited;

[0061] S5. The cathode to be deposited is placed in the metal boride suspension molten salt and positioned on the central axis of the graphite crucible, and the graphite crucible is used as the anode; wherein the inner diameter R of the graphite crucible is 9 cm, the maximum length L of the vertical projection of the special-shaped cathode is 3 cm (R:L = 3:1), the closest distance D between the special-shaped cathode and the inner wall of the graphite crucible is 1.5 cm, and the distance H from the bottom of the graphite crucible is 6 cm (H:D = 4:1). A voltage of 0.75V is applied between the anode and the cathode (voltage / D = 0.5V / cm), and the electrophoretic deposition time is 1.2h, thereby obtaining a special-shaped cathode with a metal boride coating.

[0062] It is detected that the surface coating of the titanium alloy special-shaped cathode is defect-free, and the average thickness is 48μm.

Claims

1. A method for electrophoretic deposition of a metal boride coating on a shaped cathode surface in a molten salt, characterized in that: The steps include: S1. NaF and AlF3, and at least one fluoride selected from LiF, CaF2, MgF2 are mixed, and the mixed molten salt is then divided into 50-95% by mass of molten salt powder A and the remainder of molten salt powder B; the mass fraction of AlF3 in the mixed molten salt is 40-55%, and the total mass fraction of NaF and AlF3 is ≥80%; S2. The molten salt powder A in step S1 is added to a circular graphite crucible, and then heated to 900-1100°C under inert gas protection and kept warm for 0.5-1h to form a base molten salt; S3. The molten salt powder B of step S1 and the metal boride powder with a particle size of less than 10 μm are mixed by oscillation, ball milling or rod milling for 0.5-6 hours, and then added to the base molten salt of step S2 and dispersed and kept warm for 1-2 hours to obtain a metal boride suspended molten salt; S4. Surface treatment of the shaped cathode is performed by one or more methods including grinding, wire drawing, and chemical etching, followed by surface cleaning with ethanol to obtain a cathode to be deposited; S5. Place the cathode to be deposited described in step S4 in a metal boride suspended molten salt and position it on the central axis of the graphite crucible. Use the graphite crucible as the anode and apply an electric field at both ends of the anode and cathode for electrophoretic deposition to obtain a special-shaped cathode with a metal boride coating.

2. The method for electrophoretic deposition of a metal boride coating on a special-shaped cathode surface in a molten salt according to claim 1, characterized in that: In step S3, the metal boride is one or more of titanium diboride, zirconium diboride, hafnium diboride or lanthanum hexaboride.

3. The method for electrophoretic deposition of a metal boride coating on a special-shaped cathode surface in a molten salt according to claim 1, characterized in that: The concentration of the metal boride in the metal boride suspension molten salt in step S3 is 20-80 g / L.

4. The method for electrophoretic deposition of a metal boride coating on a special-shaped cathode surface in a molten salt according to claim 1, characterized in that: In the step S3, the mass of the metal boride powder having a particle size of 1-10 μm accounts for 5-20%, the mass of the particle size of 0.1-1 μm accounts for 40-80%, and the particle size of the remaining powder is less than 0.1 μm.

5. The method for electrophoretic deposition of a metal boride coating on a special-shaped cathode surface in a molten salt according to claim 1, characterized in that: In step S4, the special-shaped cathode is made of graphite, stainless steel, titanium, molybdenum or alloys thereof.

6. The method for electrophoretic deposition of a metal boride coating on a special-shaped cathode surface in a molten salt according to claim 1, characterized in that: In step S4, the special-shaped cathode is arc-shaped or broken-line-shaped.

7. The method for electrophoretic deposition of a metal boride coating on a special-shaped cathode surface in a molten salt according to claim 1, characterized in that: The arithmetic average roughness Ra of the special-shaped cathode after surface treatment in step S4 is 0.05-5 μm.

8. The method for electrophoretic deposition of a metal boride coating on a special-shaped cathode surface in a molten salt according to claim 1, characterized in that: In step S5, the ratio of the inner diameter R of the graphite crucible to the maximum length L of the vertical projection of the special-shaped cathode is 2:1 to 5:1, and the ratio of the distance H between the special-shaped cathode and the bottom of the graphite crucible and the closest distance D between the special-shaped cathode and the inner wall of the graphite crucible is 2:1 to 5:

1.

9. The method for electrophoretic deposition of a metal boride coating on a special-shaped cathode surface in a molten salt according to claim 1, characterized in that: In step S5, the ratio of the voltage U applied across the anode and cathode to the closest distance D between the special-shaped cathode and the inner wall of the crucible is 0.1-0.5 V / cm, and the electrophoretic deposition time is 0.5-2 h.

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