A wear-resistant and corrosion-resistant high-entropy oxide ceramic coating and its spraying process

Abstract

The invention relates to a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating and a spraying process thereof. The spraying process comprises the following steps: dissolving at least five soluble metal salts in water, heating to 75-85°C, adding a precipitant, and after the reaction is complete, taking a suspension, filtering, washing, and drying to obtain a precursor powder; dispersing the precursor powder in a solvent, performing ultrasound and emulsification to obtain a precursor suspension; and using plasma spraying technology to deposit the precursor suspension on a substrate surface through a plasma spray gun to obtain a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating. The spraying process of the invention organically combines a homogeneous coprecipitation method with a liquid-phase feed plasma spraying technology. The precursor powder prepared by the coprecipitation method can be directly prepared into a liquid-phase feed for a subsequent coating deposition process, thereby realizing the integration of micro-nanostructure construction and spraying process regulation. The invention has the advantages of a simple process flow, high deposition efficiency, high bonding strength, and high controllability of coating properties.

Description

Technical Field

[0001] The present invention belongs to the technical field of coatings, and in particular relates to a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating and a spraying process thereof. Background Art

[0002] High-entropy ceramics generally refer to solid solutions composed of five or more ceramic components. Their characteristic is that a properly designed high-entropy system can outperform the performance of any individual component, and can remain a single phase under extreme temperatures, pressures, and chemical environments. They exhibit excellent stability and are difficult for corrosive media to diffuse through. Furthermore, high-entropy ceramics offer advantages such as a vast range of component adjustments, a unique entropy effect, and controllable material properties, making them a new research hotspot for ceramic materials. These advantages give high-entropy ceramics broad application prospects in high-temperature thermal insulation, high-temperature heat protection, high-temperature corrosion and oxidation resistance, ultra-hard machining and wear-resistant coatings, and supercapacitors.

[0003] Common high-entropy oxide ceramics are made by adding powders as raw materials into a ball mill for mixing, sintering the mixed powders and quickly quenching them. The high-entropy oxide ceramics made in this way require a long reaction time, the product ratio is difficult to accurately control, and impurities are easily introduced during the preparation process, resulting in disadvantages such as poor high-temperature phase stability and insufficient thermal conductivity. Some methods use co-precipitation to pre-prepare a precursor of atomic-level mixing of raw materials, reduce the energy barrier required for synthesizing high-entropy materials, and then bake the precursor powder at a relatively low temperature to produce high-entropy oxide ceramics. This method solves the problems of impurity introduction and high-entropy phase separation, but it will make it difficult to re-sinter the product particles, making the surface morphology of the coating uncontrollable and affecting the corrosion resistance. At the same time, the ceramic coating obtained by the above method requires an additional binder to adhere to the protected metal surface. Summary of the Invention

[0004] To this end, the technical problem to be solved by the present invention is to overcome the problems in the prior art such as insufficient mixing of the main components of the ceramic coating, poor high-temperature phase stability, uncontrollable surface micromorphology, and insufficiently low thermal conductivity.

[0005] In order to solve the above technical problems, the present invention provides a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating and a spraying process thereof, combining the homogeneous co-precipitation method with the liquid-phase feeding plasma spraying technology to prepare a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating with atomic-level mixing of each metal main element and controllable surface micromorphology. The impurity-free, highly mixed precursor powder prepared by the liquid-phase feeding plasma spraying technology and the co-precipitation method is controllably sprayed onto the protected metal substrate, thereby depositing and forming a high-entropy oxide ceramic coating with a wear-resistant and corrosion-resistant micromorphology on the surface. The high-entropy metal main elements of the obtained coating are highly uniformly mixed, and because the microscale of the coating is reduced to the nanometer / submicron level, not only the pore scale in the coating is significantly reduced, but the nano effect can also enhance the comprehensive mechanical properties of the coating, thereby improving the wear resistance and corrosion resistance of the coating.

[0006] The first object of the present invention is to provide a spraying process for a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating, comprising the following steps:

[0007] S1. Dissolve at least five soluble metal salts in water, heat to 75-85°C, add a precipitant, and after the reaction is complete, filter, wash, and dry the suspension to obtain a precursor powder; the concentration of the soluble metal salt is 0.1-0.4 mol / L;

[0008] S2. Dispersing the precursor powder described in S1 in a solvent, and subjecting it to ultrasonication and emulsification to obtain a precursor suspension; the concentration of the precursor suspension is 40-80 g / L;

[0009] S3. Using plasma spraying technology, the precursor suspension described in S2 is deposited on the surface of the substrate through a plasma spray gun to obtain the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating; the power of the plasma spray gun is 28-38kW, the current is 780-860A, and the voltage is 38-42V; the spraying distance is 40-200mm; and the number of spraying cycles is 2-50 times.

[0010] In one embodiment of the present invention, in S1, the precursor powder is a precursor nano / submicron powder.

[0011] In one embodiment of the present invention, in S1, the soluble metal salt is a nickel salt, a cobalt salt, a copper salt, a zinc salt, an iron salt or a magnesium salt.

[0012] In one embodiment of the present invention, in S1 , the molar concentrations of the soluble metal salts are the same.

[0013] In one embodiment of the present invention, in S1 , the soluble metal salts are mixed in the same ratio of atomic number.

[0014] In one embodiment of the present invention, in S1, the precipitant is one or more of ammonia water, sodium carbonate solution and sodium hydroxide solution.

[0015] In one embodiment of the present invention, in S1, the precipitant is ammonia water, and the pH is adjusted to 6-7.

[0016] In one embodiment of the present invention, in S3, the parameter settings of the liquid phase feeding plasma spraying technology include: the main gas pressure is 0.4-0.8 MPa, the main gas flow rate is 30-70 L / min, the auxiliary gas pressure is 0.3-0.6 MPa, the auxiliary gas flow rate is 2-50 L / min; the spraying distance is 70-150 mm.

[0017] In one embodiment of the present invention, in S3, the main gas used in the liquid-phase feeding plasma spraying technology is argon and / or nitrogen; the auxiliary gas is hydrogen or helium.

[0018] In one embodiment of the present invention, in S3, the temperature of the substrate is maintained at 100-300°C during the spraying process.

[0019] In one embodiment of the present invention, in S3, the material of the substrate is alumina, stainless steel or nickel-based alloy.

[0020] In one embodiment of the present invention, in S3, the surface of the substrate is sandblasted, and the thickness of the substrate is 2-50 mm.

[0021] In one embodiment of the present invention, the method further comprises preheating the substrate, wherein the preheating temperature is 150°C-250°C.

[0022] In one embodiment of the present invention, a soluble metal salt is prepared into an equimolar concentration solution. Equal amounts of the metal salt solutions are mixed, stirred, and heated. A precipitant is added and stirred to obtain a suspension. The precipitate is collected by vacuum filtration, cleaned, and dried in an electrical box to obtain a precursor powder. The powder is added to deionized water and subjected to ultrasonic treatment and emulsification to form a uniform and stable suspension. Using liquid-phase fed plasma spraying technology, the powder rapidly heats up during the spraying process when it enters the plasma flame and rapidly cools down after being deposited on the substrate surface, resulting in a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating with a hierarchical porous surface microstructure.

[0023] The second object of the present invention is to provide a spraying process for a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating prepared by the spraying process.

[0024] In one embodiment of the present invention, the thickness of the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating is 60-150 μm.

[0025] In one embodiment of the present invention, the surface of the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating has a hierarchical porous micro-nano structure composed of nanoscale structures and micronscale structures.

[0026] The technical solution of the present invention has the following advantages over the prior art:

[0027] (1) The wear-resistant and corrosion-resistant high-entropy oxide ceramic coating of the present invention inherits the high entropy effect, slow diffusion effect, lattice distortion effect, and element mixing effect of high-entropy alloy materials, while its crystal structure is more diversified. It is no longer a simple body-centered cubic or face-centered cubic structure with local vibration, but an ordered anion and cation sublattice with more uniform element distribution. In the crystal with the intermediate sublattice, a large number of quasi-equivalent sites will increase the distribution uniformity and configuration entropy of the cations, and can have a larger material application range and performance adjustment space, so that the coating has stronger mechanical properties and lower thermal conductivity. The coating has higher strength when resisting friction and wear, and due to its excellent chemical stability, the coating can have a better service life when facing a chemical corrosion environment.

[0028] (2) The wear-resistant and corrosion-resistant high-entropy oxide ceramic coating described in the present invention has rich lattice distortion inside, which will produce a kinetic hysteresis diffusion effect when heated, and phase separation is suppressed. At the same time, since the atoms of its components are in a uniformly distributed state, the diffusion of atoms in a high-temperature environment will become coordinated and ordered, so the diffusion rate of each atom will be reduced, which will bring phase stability to the coating at high temperatures and have good thermal conductivity. When a large amount of heat is generated by friction, the coating can still maintain phase stability and prevent the occurrence of thermal damage.

[0029] (3) The wear-resistant and corrosion-resistant high-entropy oxide ceramic coating described in the present invention is prepared by a homogeneous co-precipitation method combined with liquid-phase feeding plasma spraying technology, and has the advantages of high deposition efficiency and fine coating structure. The precursor powder is gradually deposited on the substrate by plasma spraying, rather than being combined by calcination to form a coating. The coating size and thickness can be precisely controlled while the hierarchical porous structure of the coating surface can be retained to the greatest extent, thereby avoiding the destruction of the micro-nano structure of the coating surface during the calcination process.

[0030] (4) The spraying process described in the present invention uses a precipitant and produces a precipitation reaction at high temperature when preparing the precursor powder. The surface of the precursor powder is porous and rough, and the overall appearance is a cauliflower-like agglomerated structure with a size of 5-10 μm composed of particles with a diameter of 60-90 nm, that is, a hierarchical porous structure. This structure can provide a high specific surface area for the coating surface, thereby making the coating have a certain hydrophobicity, which is beneficial to improving the coating's resistance to thermal corrosion.

[0031] (5) The spraying process described in the present invention uses the precursor suspension as the liquid material in the liquid phase feed plasma spraying process. Due to the high energy density and large temperature gradient of the plasma flame, the powder rapidly heats up during the flight process after entering the plasma flame and is deposited on the substrate. After leaving the plasma flame, it rapidly cools down. The short thermal change prevents its microstructure from being destroyed, and it is finally deposited as a coating with a surface microstructure.

[0032] (6) The spraying process described in the present invention uses a precursor suspension prepared from a precursor powder as the liquid feed in the liquid-phase plasma spraying process, which can achieve uniform and stable delivery of the precursor powder, ensuring uniform deposition of the powder during the spraying process, thereby achieving controllable construction of the surface micromorphology, avoiding powder agglomeration and uneven coating caused by sintering, and achieving precise control of the spraying process. This means that the coating has better stability at high temperatures and can protect the hierarchical porous structure of the precursor powder from being destroyed during the coating preparation process.

[0033] (7) The spraying process described in the present invention organically combines the homogeneous co-precipitation method with the liquid-phase feed plasma spraying technology. The precursor powder prepared by the co-precipitation method can be directly prepared into the liquid-phase feed for the subsequent coating deposition process. By controlling the concentration of the precursor suspension, the liquid flow rate and the spraying power, the deposition efficiency and specific surface area of ​​the coating can be controlled, realizing the integration of micro-nano structure construction and spraying process regulation. It has the advantages of simple process flow, high deposition efficiency, high bonding strength, and high controllability of coating characteristics. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0035] Figure 1 This is a schematic diagram of the process flow for preparing the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating of the present invention.

[0036] Figure 2 Schematic diagram of the solid phase sintering process flow.

[0037] Figure 3 This is a graph showing the friction and wear performance of the ceramic coating in Test Example 1 of the present invention.

[0038] Figure 4 This is a graph showing the friction, wear and electrochemical corrosion performance of the ceramic coating in Test Example 2 of the present invention. DETAILED DESCRIPTION

[0039] The present invention will be further described below with reference to the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it. However, the embodiments are not intended to limit the present invention.

[0040] Example 1

[0041] Reference Figure 1 As shown, a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating and its spraying process specifically include the following steps:

[0042] (1) Preparation of precursor powder: magnesium nitrate, nickel nitrate, cobalt nitrate, copper nitrate, zinc nitrate, and ferric nitrate were dissolved in deionized water to a concentration of 0.1 mol / L for each metal ion, and heated to 80°C. Ammonia water was added to the solution to adjust the pH value to 6-7, and then stirred steadily for 1 hour to obtain a turbid suspension and a precipitate. The suspension was placed in a vacuum filtration pump for filtration, and the product obtained after filtration was washed and dried to obtain a pure precursor powder.

[0043] (2) Preparation of precursor suspension: 500 mL of deionized water was added with 25 g of precursor powder and ultrasonically treated for 2 h. The mixture was then placed in an emulsifier for 20 min to obtain a uniform precursor suspension.

[0044] (3) Substrate: The surface of the stainless steel substrate was sandblasted and the thickness was set to 2 mm. It was preheated to 200 °C before coating deposition to ensure the deposition efficiency of the first coating during the spraying process.

[0045] (4) Preparation of wear-resistant and corrosion-resistant high-entropy oxide ceramic coating: setting spraying process parameters, using plasma spraying technology to deposit the precursor on the substrate surface through a plasma spray gun to obtain a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating; by combining a robotic arm to control the movement of the plasma spray gun, the robotic arm movement speed is set to 400 mm / s, the spraying distance is set to 100 mm, the number of spraying cycles is set to 25 times, and the liquid flow rate is set to 30 mL / min; the plasma spray gun power is set to 32 kW, of which the current is set to 800 A, the voltage is set to 40 V, the main gas pressure is 0.7 MPa, the main gas flow rate is set to 38 L / min, the auxiliary gas pressure is 0.4 MPa, and the auxiliary gas flow rate is set to 38 L / min; the thickness of the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating is set to 62 μm, and the surface micromorphology presents a cauliflower-like structure composed of flaky particles with a size of 7-9 μm; the gases used in the spraying technology are helium and argon. During the spraying process, the substrate temperature was maintained at 200°C by cooling.

[0046] Example 2

[0047] A wear-resistant and corrosion-resistant high-entropy oxide ceramic coating and a spraying process thereof, specifically comprising the following steps:

[0048] The process is basically the same as Example 1, except that the mass of the precursor powder added to the precursor suspension is 30 g, the thickness of the obtained coating is 69 μm, and the microscopic morphology of the coating surface presents a cauliflower-like structure composed of particles.

[0049] Example 3

[0050] A wear-resistant and corrosion-resistant high-entropy oxide ceramic coating and a spraying process thereof, specifically comprising the following steps:

[0051] The method is basically the same as Example 1, except that the mass of the powder added to the precursor suspension is 35 g, the thickness of the obtained coating is 73 μm, and the microscopic morphology of the coating surface presents a cauliflower-like structure composed of particles.

[0052] Example 4

[0053] A wear-resistant and corrosion-resistant high-entropy oxide ceramic coating and a spraying process thereof, specifically comprising the following steps:

[0054] The method is basically the same as Example 1, except that the number of spraying cycles is set to 15 times, the obtained coating thickness is 66 μm, and the microscopic morphology of the coating surface presents a cauliflower-like structure composed of flaky particles.

[0055] Example 5

[0056] A wear-resistant and corrosion-resistant high-entropy oxide ceramic coating and a spraying process thereof, specifically comprising the following steps:

[0057] The method is basically the same as Example 1, except that: during the spraying process, the power is set to 36 kW, the current is set to 860 A, the voltage is set to 42 V, the thickness of the obtained coating is 77 μm, and the microscopic morphology of the coating surface presents a cauliflower-like structure composed of particles. Compared with Example 1, the density of its flaky particles is lower.

[0058] Comparative Example 1

[0059] The method is basically the same as Example 1, except that: during the spraying process, the power is set to 40 kW, the current is set to 860 A, the voltage is set to 47 V, the thickness of the obtained coating is 74 μm, the microscopic morphology of the coating surface is a continuous plane with protruding particles, and the surface of the particles is relatively smooth.

[0060] Comparative Example 2

[0061] Reference Figure 2 As shown, the coating is formed by baking and sintering instead of the liquid phase feeding plasma spraying step. The precursor powder is placed in a sintering furnace and the sintering temperature is set to 1200°C. The temperature is slowly increased and maintained at the sintering temperature for 2 hours before cooling to room temperature to obtain a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating. The obtained coating has a thickness of 86 μm. Particles are visible on the surface of the coating, but no hierarchical microstructure is observed.

[0062] Comparative analysis:

[0063] By comparing the results of Example 1 with Example 4, it can be seen that the deposition number of extremely high coatings within a certain range can effectively increase the thickness of the coating; by comparing the results of Example 1 with Example 2 and Example 3, it can be seen that increasing the concentration of the precursor suspension can improve the deposition efficiency of the coating within a certain range, but since increasing the concentration of the precursor powder will lead to the generation of precipitation, the improvement effect is limited; by comparing Example 1 with Example 5, it can be seen that if the hierarchical porous structure of the coating surface is to be retained, the spraying power needs to be controlled within an appropriate range; Comparative Example 1 shows that excessive power will destroy the hierarchical porous structure of the precursor powder; Comparative Example 2 proves that the liquid-phase feeding plasma spraying technology has better control over the microstructure of the coating surface than the solid-phase sintering method, and indirectly proves that the coating prepared by the liquid-phase feeding plasma spraying technology avoids the occurrence of insufficient sintering or burn-out in the baking and sintering process during the deposition process, so that the coating has better phase stability and lower thermal conductivity in a high-temperature environment.

[0064] Test Example 1

[0065] The coating in Example 1 was subjected to friction and wear tests. The coating obtained in Example 1 was placed on a friction and wear tester and rubbed at a speed of 0.5 m / s to test the mass loss rate. After a 100 m length friction factor test, the test results are as follows: Figure 3 As shown in the figure, after a sliding distance of 40m, the friction coefficient stabilizes at about 0.51, and the mass loss rate corresponding to each sliding of 100m is 0.23%. This is because the crystal structure of the high-entropy ceramic has ordered anion and cation sublattices, the difference between each cation lattice site is very small, and the combination of large atomic mismatch and components of different crystal structures is conducive to the formation of a single-phase solid solution with high mechanical properties and corrosion resistance, which proves that the coating of the present invention has good friction stability and wear resistance.

[0066] Test Example 2

[0067] The coating in Example 1 was subjected to an electrochemical corrosion test. The coating obtained in Example 1 was connected to the electrode of the electrochemical workstation and immersed in the corrosion solution to test the change in current density of the coating at different voltages. The test results are shown in Figure 2. Figure 4As shown, potassium hydroxide solution and methanol solution were used as corrosion solutions. The current density in 1 mol / L potassium hydroxide solution and a mixed solution of 1 mol / L potassium hydroxide and 0.5 mol / L formaldehyde were 5.3 A / g and 79.9 A / g at 10 mV / s, respectively. This is because the high-entropy ceramic coating was prepared using a precursor powder with high surface energy, which made the ceramic easier to densify during the forming process. The dense ceramic coating itself has good chemical stability and prevents further electrochemical reactions from occurring inside the coating, proving that the coating has good corrosion resistance.

[0068] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of the present invention.

Claims

1. A spraying process for a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating, characterized in that: The following steps are included: S1. Dissolve at least five soluble metal salts in water, heat to 75-85° C., add a precipitant, and after the reaction is complete, filter the suspension, wash, and dry to obtain a precursor powder; the concentration of the soluble metal salt is 0.1-0.4 mol / L; the soluble metal salt is a nickel salt, a cobalt salt, a copper salt, a zinc salt, an iron salt, or a magnesium salt; and the precipitant is one or more of ammonia water, sodium carbonate solution, and sodium hydroxide solution; S2. Dispersing the precursor powder described in S1 in a solvent, and subjecting it to ultrasonication and emulsification to obtain a precursor suspension; the concentration of the precursor suspension is 40-80 g / L; S3. Use plasma spraying technology to deposit the precursor suspension described in S2 on the surface of the substrate through a plasma spray gun to obtain the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating; the power of the plasma spray gun is 28-38kW, the current is 780-860A, and the voltage is 38-42V; the spraying distance is 40-200mm; the number of spraying cycles is 2-50 times; and the liquid flow rate is 5-50mL / min.

2. The spraying process of the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating according to claim 1 is characterized in that: In S3, the parameter settings of the plasma spraying technology include: main gas pressure of 0.4-0.8 MPa, main gas flow of 30-70 L / min, auxiliary gas pressure of 0.3-0.6 MPa, auxiliary gas flow of 2-50 L / min; spraying distance of 70-150 mm.

3. The spraying process of the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating according to claim 1 is characterized in that: In S3, the main gas used in the plasma spraying technology is argon and / or nitrogen; the auxiliary gas is hydrogen or helium.

4. The spraying process of the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating according to claim 1 is characterized in that: In S3, the temperature of the substrate is maintained at 100-300°C during the spraying process.

5. The spraying process of the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating according to claim 1 is characterized in that: In S3, the material of the substrate is alumina, stainless steel or nickel-based alloy.

6. The spraying process of the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating according to claim 1 is characterized in that: The method further comprises preheating the substrate, wherein the preheating temperature is 150° C.-250° C.

7. A spraying process for preparing a wear-resistant and corrosion-resistant high-entropy oxide ceramic coating by the spraying process according to any one of claims 1 to 6.

8. The wear-resistant and corrosion-resistant high-entropy oxide ceramic coating according to claim 7, characterized in that: The thickness of the wear-resistant and corrosion-resistant high-entropy oxide ceramic coating is 60-150 μm.

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