Diaspore / aluminum oxide / hexagonal boron nitride, preparation method thereof and preparation method of aluminum oxide / hexagonal boron nitride coating

Abstract

The invention relates to the technical field of lubricating coatings, in particular to diaspore / aluminum oxide / hexagonal boron nitride, a preparation method thereof and a preparation method of an aluminum oxide / hexagonal boron nitride coating. The invention provides a preparation method of diaspore / aluminum oxide / hexagonal boron nitride, which comprises the following steps: mixing a diaspore aqueous solution and an acid solution, solating, and adding aluminum oxide to obtain aluminum sol containing aluminum oxide; adding hydroxylated hexagonal boron nitride slurry into the aluminum sol containing the aluminum oxide to obtain slurry; and carrying out spray drying on the slurry to obtain the diaspore / aluminum oxide / hexagonal boron nitride. The diaspore / aluminum oxide / hexagonal boron nitride prepared by the preparation method is uniform in phase distribution and strong in bonding effect, and also has the characteristics of high dispersity and high sphericity degree.

Description

Technical Field

[0001] This invention relates to the field of lubricating coating technology, and more particularly to a boehmite / alumina / hexagonal boron nitride and its preparation method, and a method for preparing an alumina / hexagonal boron nitride coating. Background Technology

[0002] Plasma-sprayed Al2O3 coatings, due to their excellent physical and chemical properties, are often deposited on metal mechanical parts to enhance their protective performance. However, their lubricity is poor, with a friction coefficient typically ranging from 0.6 to 0.8 at room temperature. To improve the tribological properties of the coating, lubricating powders, such as molybdenum disulfide (MoS2) and graphite (C), are often incorporated into the coating. However, these lubricating phases generally have low melting points and inevitably undergo oxidation and sublimation during the spraying process, leading to a loose microstructure in the coating and affecting its overall performance. This also severely limits the application of composite coatings under high-temperature conditions. In contrast, h-BN not only possesses the same lamellar structure and can provide a lubricating effect, but its high thermal conductivity and excellent thermal stability can also improve powder melting efficiency while ensuring that structural degradation or oxidation does not occur. Therefore, h-BN is considered a promising reinforcing agent in plasma-sprayed composite materials.

[0003] However, due to the inherent structural characteristics of Al2O3 particles, they cannot be modified on the crystal surface. If Al2O3 and h-BN powders are mechanically mixed through physical means, the inherent van der Waals forces of h-BN and the weak bonding between the two phases will lead to severe agglomeration, becoming a nucleation site for cracks and deteriorating the mechanical and tribological properties of the composite material. Existing studies have shown that compared to the agglomeration of h-BN in composite materials, uniform dispersion can significantly improve the flexural strength, fracture toughness, relative density, hardness, and elastic modulus of the material. Meanwhile, the structure, morphology, density, and dispersibility of the sprayed powder all have a significant impact on the friction-reducing and wear-resistant properties of the coating. Therefore, finding a suitable treatment method to strengthen the bonding between the two phases (alumina phase and lubricating phase), ensure uniform distribution, and improve dispersibility, thereby increasing the powder's density and dimensional uniformity to meet the friction-reducing and wear-resistant requirements of the sprayed coating, is crucial. Summary of the Invention

[0004] In view of this, the purpose of this invention is to provide a boehmite / alumina / hexagonal boron nitride and its preparation method, as well as a method for preparing an alumina / hexagonal boron nitride coating. The boehmite / alumina / hexagonal boron nitride phase obtained by the preparation method has a uniform phase distribution, strong bonding, and also exhibits high dispersibility and high sphericity.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0006] This invention provides a method for preparing gibbsite / alumina / hexagonal boron nitride, comprising the following steps:

[0007] Alumina-containing aluminum sol is obtained by mixing an aqueous solution of gibbsite with an acid solution and then sol-gelling it.

[0008] A hydroxylated hexagonal boron nitride slurry was added to the alumina-containing aluminum sol to obtain a slurry;

[0009] The slurry is spray-dried to obtain the diatomite / alumina / hexagonal boron nitride.

[0010] Preferably, the preparation method of the hydroxylated hexagonal boron nitride slurry includes: mixing hydroxylated hexagonal boron nitride, water and dispersant and performing high-pressure homogenization and exfoliation to obtain the hydroxylated hexagonal boron nitride slurry;

[0011] The mass ratio of the hydroxylated hexagonal boron nitride to water is 1:(7-8); the mass ratio of the dispersant to water is (2-5):100;

[0012] The dispersant includes one or more of PVP, PVA and PEG.

[0013] Preferably, the pressure of the high-pressure homogenization stripping is 300-1800 bar, the flow rate is 6-10 mL / s, and the number of revolutions is 10-80.

[0014] Preferably, the method for preparing the hydroxylated hexagonal boron nitride includes the following steps:

[0015] Hexagonal boron nitride and an alkaline grinding aid are mixed and ball-milled to obtain the hydroxylated hexagonal boron nitride;

[0016] The alkaline grinding aid includes one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide;

[0017] The mass ratio of the hexagonal boron nitride to the alkaline grinding aid is 2:(1-1.2);

[0018] The ball mill has a ball-to-material ratio of 4:(1-1.5), a rotation speed of 240-260 rpm, and a time of 5-10 h.

[0019] Preferably, the pH value of the sol-gel is 1 to 6;

[0020] The preferred mass ratio of gibbsite to alumina in the gibbsite aqueous solution is 1:(1-3).

[0021] Preferably, the mass ratio of hydroxylated hexagonal boron nitride in the hydroxylated hexagonal boron nitride slurry to alumina in the alumina-containing alumina sol is 1:(2.5-7.5).

[0022] Preferably, the inlet temperature of the spray dryer is 80-300℃, the outlet temperature is 50-150℃, the feed rate is 10-200 rpm, and the atomizer speed is 10000-30000 r / min.

[0023] The present invention also provides a boehmite / alumina / hexagonal boron nitride prepared by the preparation method described above, wherein the boehmite / alumina / hexagonal boron nitride has a microsphere structure;

[0024] The microsphere structure includes a core and a protective layer. The core is hydroxylated hexagonal boron nitride, and the protective layer is AlO(OH). The alumina is uniformly dispersed throughout the microsphere structure.

[0025] This invention also provides a method for preparing an alumina / hexagonal boron nitride coating, comprising the following steps:

[0026] Atmospheric plasma spraying is used to spray diatomite / alumina / hexagonal boron nitride onto the substrate surface to obtain an alumina / hexagonal boron nitride coating.

[0027] The boehmite / alumina / hexagonal boron nitride mentioned above is the boehmite / alumina / hexagonal boron nitride described in the above technical solution.

[0028] Preferably, the ionized gas used in the atmospheric plasma spraying is argon, and the auxiliary gas is hydrogen;

[0029] The thickness of the alumina / hexagonal boron nitride coating is 200–500 μm.

[0030] This invention provides a method for preparing gibbsite / alumina / hexagonal boron nitride, comprising the following steps: mixing an aqueous solution of gibbsite and an acid solution, performing sol-gelation, and then adding alumina to obtain an alumina-containing aluminum sol; adding a hydroxylated hexagonal boron nitride slurry to the alumina-containing aluminum sol to obtain a slurry; and spray-drying the slurry to obtain the gibbsite / alumina / hexagonal boron nitride.

[0031] Compared with the prior art, the preparation method of the present invention has the following beneficial effects:

[0032] 1) This invention uses aluminum sol obtained by acid treatment of gibbsite aqueous solution as the aluminum source. Compared with traditional pure alumina as the aluminum source, it has higher reactivity, better dispersibility, and smaller particle size. By combining with hydroxylated hexagonal boron nitride and alumina, problems such as uneven phase distribution, poor microstructure, and poor dispersibility can be avoided. At the same time, the hydrogen bonds and strong viscosity in the alumina-containing aluminum sol prepared with gibbsite as the aluminum source allow hexagonal boron nitride to be firmly wrapped around AlO(OH) crystals, and several crystals are firmly fixed together by hydrogen bonds. The resulting composite microspheres have higher sphericity and density, and the flowability is better than that of pure alumina (the flowability can be improved by about 47% compared with pure alumina).

[0033] 2) The preparation method described is green and environmentally friendly, with a simple process, low preparation cost, and easy to mass-produce, avoiding the use of large amounts of organic solvents in existing technologies;

[0034] This invention also provides a method for preparing an alumina / hexagonal boron nitride coating, comprising the following steps: spraying a gibbsite / alumina / hexagonal boron nitride coating onto a substrate surface using atmospheric plasma spraying to obtain an alumina / hexagonal boron nitride coating; wherein the alumina / hexagonal boron nitride coating is the gibbsite / alumina / hexagonal boron nitride described in the above technical solution. The alumina / hexagonal boron nitride coating prepared by atmospheric plasma spraying using the gibbsite / alumina / hexagonal boron nitride described in this invention has higher density and a 35% reduction in porosity compared to a pure alumina coating; it also exhibits better interlayer bonding and fracture toughness, increasing by 57% and 70%, respectively; and it provides better friction reduction and wear resistance, with a maximum reduction of 38% in the coefficient of friction and 98% in the wear rate. The alumina / hexagonal boron nitride coating possesses excellent mechanical and tribological properties, providing good protection for the surfaces of worn parts under both room temperature and high temperature conditions. Attached Figure Description

[0035] Figure 1 SEM image of the AlO(OH) / Al2O3 / h-BN powder described in Example 2;

[0036] Figure 2 The image shows the EDS diagram of the AlO(OH) / Al2O3 / h-BN powder described in Example 2.

[0037] Figure 3 The image shows a surface SEM image of the Al2O3 / h-BN coating described in Example 2.

[0038] Figure 4 This is a cross-sectional SEM image of the Al2O3 / h-BN coating described in Example 2;

[0039] Figure 5The image shows a three-dimensional view of the Al2O3 / h-BN coating friction surface described in Example 2, obtained by time-of-flight secondary ion mass spectrometry.

[0040] Figure 6 The image shows the XRD patterns of the AlO(OH) / Al2O3 / h-BN powder and the Al2O3 / h-BN coating described in Example 2. Detailed Implementation

[0041] This invention provides a method for preparing gibbsite / alumina / hexagonal boron nitride, comprising the following steps:

[0042] Alumina-containing aluminum sol is obtained by mixing an aqueous solution of gibbsite with an acid solution and then sol-gelling it.

[0043] A hydroxylated hexagonal boron nitride slurry was added to the alumina-containing aluminum sol to obtain a slurry;

[0044] The slurry is spray-dried to obtain the diatomite / alumina / hexagonal boron nitride.

[0045] In this invention, unless otherwise specified, all raw materials used in the preparation are commercially available products well known to those skilled in the art.

[0046] This invention involves mixing a hydrazine aqueous solution and an acid solution, sol-gelling the mixture, and then adding alumina to obtain an alumina-containing aluminum sol.

[0047] In this invention, the concentration of gibbsite (AlO(OH)) in the gibbsite aqueous solution is preferably 300-400 g / L, more preferably 300 g / L, 320 g / L, 340 g / L, 360 g / L, 380 g / L, or 400 g / L. In an embodiment of this invention, the concentration of gibbsite (AlO(OH)) in the gibbsite aqueous solution can be 357.14 g / L. In this invention, the gibbsite is preferably in the micron range.

[0048] In this invention, the concentration of the acid solution is preferably 0.1–1 mol / L, more preferably 0.1 mol / L, 0.3 mol / L, 0.6 mol / L, 0.8 mol / L, or 1 mol / L; the acid solution preferably includes hydrochloric acid and / or sulfuric acid, more preferably hydrochloric acid. In embodiments of this invention, the acid solution may be hydrochloric acid with a concentration of 1 mol / L.

[0049] The present invention does not impose any special limitation on the amount of acid solution used. Any amount known to those skilled in the art can be used, provided that the pH conditions required for sol-gelation are met.

[0050] In this invention, the pH of the sol-gelation is preferably 1 to 6, more preferably 1, 2, 3, 4, 5, or 6. In an embodiment of this invention, the pH of the sol-gelation can be 4.

[0051] In this invention, the alumina is preferably α-Al₂O₃. The α-Al₂O₃ is preferably nano-sized.

[0052] In this invention, the mass ratio of gibbsite to alumina in the gibbsite aqueous solution is preferably 1:(1-3), more preferably 1:1, 1:2, or 1:3. In embodiments of this invention, the mass ratio of gibbsite to alumina in the gibbsite aqueous solution can be 1:1, 1:2, or 1:3.

[0053] After obtaining the aluminum sol containing alumina, the present invention adds hydroxylated hexagonal boron nitride slurry to the aluminum sol containing alumina to obtain a slurry.

[0054] In this invention, the preferred method for preparing the hydroxylated hexagonal boron nitride slurry includes:

[0055] Hydroxylated hexagonal boron nitride, water, and a dispersant are mixed and subjected to high-pressure homogenization and exfoliation to obtain the hydroxylated hexagonal boron nitride slurry.

[0056] In this invention, the preferred method for preparing the hydroxylated hexagonal boron nitride includes:

[0057] Hexagonal boron nitride and an alkaline grinding aid are mixed and ball-milled to obtain the hydroxylated hexagonal boron nitride.

[0058] In this invention, the alkaline grinding aid preferably includes one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide. When the alkaline grinding aid is two or more of the above-mentioned specific selections, this invention does not impose any special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. In an embodiment of this invention, the alkaline grinding aid can be calcium hydroxide.

[0059] In this invention, the preferred mass ratio of hexagonal boron nitride to alkaline grinding aid is 2:(1-1.2), more preferably 2:1, 2:1.1, or 2:1.2. In an embodiment of this invention, the mass ratio of hexagonal boron nitride to alkaline grinding aid can be 2:1.

[0060] In this invention, the ball-to-material ratio in the ball mill is preferably 4:(1-1.5), more preferably 4:1, 4:1.1, 4:1.2, 4:1.3, 4:1.4, or 4:1.5; the ball milling speed is preferably 240-260 rpm, more preferably 240 rpm, 245 rpm, 250 rpm, 255 rpm, or 260 rpm; the ball milling time is preferably 5-10 hours, more preferably 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours. In an embodiment of this invention, the ball-to-material ratio in the ball mill can be 4:1, the speed can be 240 rpm, and the time can be 5 hours.

[0061] After the ball milling is complete, the present invention preferably includes dissolving the obtained pre-hydroxylated h-BN in deionized water, slowly adding hydrochloric acid solution for washing, and then filtering.

[0062] In this invention, the water is preferably deionized water.

[0063] In this invention, the dispersant preferably includes one or more of PVP, PVA, and PEG. When the dispersant is two or more of the above-mentioned specific selections, this invention does not impose any special limitation on the ratio of the above-mentioned specific substances, and they can be mixed in any ratio. In an embodiment of this invention, the dispersant can be PVP.

[0064] In this invention, the mass ratio of the hydroxylated hexagonal boron nitride to water is preferably 1:(7-8), more preferably 1:7, 1:7.5, or 1:8. In an embodiment of this invention, the mass ratio of the hydroxylated hexagonal boron nitride to water can be 1:7.5.

[0065] In this invention, the mass ratio of the dispersant to water is preferably (2-5):100, more preferably 2:100, 3:100, 4:100, or 5:100. In an embodiment of this invention, the mass ratio of the dispersant to water can be 2:100.

[0066] In this invention, the pressure of the high-pressure homogenization stripping is preferably 300–1800 bar, more preferably 300 bar, 600 bar, 900 bar, 1200 bar, 1500 bar, or 1800 bar; the flow rate is preferably 6–10 mL / s, more preferably 6 mL / s, 7 mL / s, 8 mL / s, 9 mL / s, or 10 mL / s; and the number of rotations is preferably 10–80, more preferably 10, 20, 30, 40, 50, 60, 70, or 80 rotations. In an embodiment of this invention, the pressure of the high-pressure homogenization stripping can be 1000 bar, the flow rate can be 8 mL / s, and the number of rotations can be 20.

[0067] In this invention, the mass ratio of hydroxylated hexagonal boron nitride in the hydroxylated hexagonal boron nitride slurry to alumina in the alumina-containing aluminum sol is 1:(2.5-7.5), more preferably 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, 1:5, 1:5.5, 1:6, 1:6.5, 1:7, or 1:7.5. In embodiments of this invention, the mass ratio of the hydroxylated hexagonal boron nitride slurry to the alumina-containing aluminum sol can be 1:2.5, 1:5, or 1:7.5.

[0068] In this invention, controlling the ratio of the amounts of h-BN, AlO(OH) and Al2O3 is to maintain strong chemical bonding while leveraging the synergistic effects of h-BN and Al2O3 in lubrication and wear resistance.

[0069] The present invention does not impose any special limitations on the addition method and process of the hydroxylated hexagonal boron nitride slurry; any addition method and process known to those skilled in the art can be used.

[0070] In this invention, the inlet temperature of the spray dryer is preferably 80-300℃, more preferably 80℃, 100℃, 150℃, 200℃, 250℃ or 300℃; the outlet temperature is preferably 50-150℃, more preferably 50℃, 80℃, 90℃, 120℃ or 150℃; the feed rate is preferably 10-200 rpm, more preferably 10 rpm, 50 rpm, 100 rpm, 150 rpm or 200 rpm; the atomizer speed is preferably 10000-30000 r / min, more preferably 10000 r / min, 12000 r / min, 15000 r / min, 17000 r / min, 20000 r / min, 22000 r / min, 25000 r / min, 27000 r / min or 30000 r / min. In an embodiment of the present invention, the inlet temperature of the spray dryer can be 150°C, the outlet temperature can be 90°C, the feed rate can be 40 rpm, and the atomizer speed can be 12600 r / min.

[0071] The present invention also provides a boehmite / alumina / hexagonal boron nitride prepared by the preparation method described above, wherein the boehmite / alumina / hexagonal boron nitride has a microsphere structure;

[0072] The microsphere structure includes a core and a protective layer. The core is hexagonal boron nitride, and the protective layer is AlO(OH). The alumina is uniformly dispersed throughout the microsphere structure.

[0073] In this invention, the diatomite (AlO(OH)) in the microsphere structure preferably accounts for 22% to 42% of the total mass of the diatomite, hydroxylated hexagonal boron nitride, and alumina, more preferably 22%, 24%, 26%, 28%, 30%, 32%, 34%, 36%, 38%, 40%, or 42%. In embodiments of this invention, the diatomite (AlO(OH)) in the microsphere structure preferably accounts for 22.7%, 29.4%, or 41.7% of the total mass of the diatomite, hydroxylated hexagonal boron nitride, and alumina.

[0074] This invention also provides a method for preparing an alumina / hexagonal boron nitride coating, comprising the following steps:

[0075] Atmospheric plasma spraying is used to spray diatomite / alumina / hexagonal boron nitride onto the substrate surface to obtain an alumina / hexagonal boron nitride coating.

[0076] The boehmite / alumina / hexagonal boron nitride mentioned above is the boehmite / alumina / hexagonal boron nitride described in the above technical solution.

[0077] In this invention, the substrate is preferably a metal substrate, and more preferably a 316L stainless steel substrate.

[0078] Before performing the atmospheric plasma spraying, the present invention performs sandblasting roughening treatment. The sandblasting roughening treatment process is not particularly limited by the present invention and can be performed by a process known to those skilled in the art.

[0079] After the sandblasting roughening treatment is completed, the present invention preferably includes sequential cleaning and deposition of a metal bonding layer. The cleaning process is not particularly limited in the present invention and can be performed using a process well known to those skilled in the art. Similarly, the type and preparation process of the metal bonding layer are not particularly limited in the present invention and can be performed using a type and preparation process well known to those skilled in the art.

[0080] In this invention, the ionized gas used in the atmospheric plasma spraying is preferably argon, and the auxiliary gas is preferably hydrogen; the thickness of the alumina / hexagonal boron nitride coating is preferably 200–500 μm. In an embodiment of this invention, the thickness of the alumina / hexagonal boron nitride coating can be 350 μm.

[0081] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0082] Example 1

[0083] 200g h-BN and 100g alkaline grinding aid (Ca(OH)2) were placed in a planetary ball mill (ball-to-material ratio of 4:1, rotation speed of 240rpm, time of 5h) to pre-hydroxylate it; the pre-hydroxylated h-BN was dissolved in deionized water, hydrochloric acid solution was slowly added to the h-BN solution, excess Ca(OH)2 was washed away, and the mixture was filtered to obtain hydroxylated h-BN;

[0084] 200g of the hydroxylated h-BN was dissolved in 1500g of deionized water and 30g of PVP dispersant, and then subjected to high-pressure homogenization and exfoliation (exfoliation cycle number 20, pressure 1000 bar, flow rate 8 mL / s) to obtain hydroxylated h-BN slurry.

[0085] Add 1 mol / L hydrochloric acid to 1400 mL of an AlO(OH) aqueous solution with a concentration of 357.14 g / L (containing 500 g of AlO(OH)) until the pH value is 4. After sol-gelling, add 500 g of nano-sized α-Al2O3 to obtain an aluminum sol containing aluminum oxide.

[0086] The hydroxylated h-BN was added to the alumina-containing alumina sol (the mass ratio of hydroxylated hexagonal boron nitride in the hydroxylated hexagonal boron nitride slurry to alumina in the alumina-containing alumina sol was 1:2.5), and spray drying was performed (inlet temperature 150℃, outlet temperature 90℃, feed rate 40 rpm, atomization speed 12600 r / min) to obtain gibbsite / alumina / hexagonal boron nitride powder (AlO(OH) / Al2O3 / h-BN powder);

[0087] Using 20mm*12mm*12mm 316L stainless steel as the substrate, the substrate was first sandblasted using a GS-943 sandblasting machine (Beijing Changkong Sandblasting Equipment Co., Ltd.). The sandblasted substrate was then ultrasonically cleaned in acetone to remove impurities from its surface. Before preparing the coating, a Ni-24.5Cr-6Al-0.4Y metal bonding layer with a thickness of approximately 100μm was deposited on the sandblasted 316L metal substrate. The plasma thermal spraying process parameters for the bonding coating were: voltage 72V, current 600A, argon flow rate 57L / h, hydrogen flow rate 8L / h, delivery energy 42.5kW, and spraying angle 90°.

[0088] The AlO(OH) / Al2O3 / h-BN powder prepared in this embodiment was sprayed onto a substrate containing a Ni-24.5Cr-6Al-0.4Y metal binder layer using a plasma thermal spraying process (voltage 70V, current 600A, argon flow rate 50L / h, hydrogen flow rate 9L / h, delivery energy 42.5kW, spraying angle 90°), resulting in an Al2O3 / h-BN coating with a thickness of 350μm. (The Al2O3 / h-BN coating has an interlayer bonding strength of 50.21MPa, a porosity of 7.6%, a hardness of 6.8GPa, and a fracture toughness of 2.13MPa·m.) 1 / 2 (At a high temperature of 1000℃, the coefficient of friction is 0.16); at room temperature, the coefficient of friction and wear rate of the Al2O3 / h-BN coating under different loads and different friction pairs are shown in Table 1:

[0089] Table 1 shows the coefficients of friction and wear rates of the alumina / hexagonal boron nitride coatings under different loads and friction pairs.

[0090]

[0091] Example 2

[0092] 200g h-BN and 100g alkaline grinding aid (Ca(OH)2) were placed in a planetary ball mill (ball-to-material ratio of 4:1, rotation speed of 240rpm, time of 5h) to pre-hydroxylate it; the pre-hydroxylated h-BN was dissolved in deionized water, hydrochloric acid solution was slowly added to the h-BN solution, excess Ca(OH)2 was washed away, and the mixture was filtered to obtain hydroxylated h-BN;

[0093] 200g of the hydroxylated h-BN was dissolved in 1500g of deionized water and 30g of PVP dispersant, and then subjected to high-pressure homogenization and exfoliation (exfoliation cycle number 20, pressure 1000 bar, flow rate 8 mL / s) to obtain hydroxylated h-BN slurry.

[0094] A 1 mol / L hydrochloric acid solution was added to 1400 mL of an AlO(OH) aqueous solution with a concentration of 357.14 g / L (containing 500 g of AlO(OH)) until the pH value reached 4. After sol-gelling, 1000 g of nano-sized α-Al2O3 was added to obtain an aluminum sol containing aluminum oxide.

[0095] The hydroxylated h-BN slurry was added to the alumina-containing alumina sol (the mass ratio of hydroxylated hexagonal boron nitride in the hydroxylated hexagonal boron nitride slurry to alumina in the alumina-containing alumina sol was 1:5), and spray drying was performed (inlet temperature 150℃, outlet temperature 90℃, feed rate 40 rpm, atomization speed 12600 r / min) to obtain gibbsite / alumina / hexagonal boron nitride powder (AlO(OH) / Al2O3 / h-BN powder);

[0096] Figure 1 The image shows a SEM image of the AlO(OH) / Al2O3 / h-BN powder. Figure 1 It can be seen that the AlO(OH) / Al2O3 / h-BN powder has good sphericity and its surface is completely passivated, forming a coating layer;

[0097] Figure 2 The EDS diagram of the AlO(OH) / Al2O3 / h-BN powder is shown below. Figure 2 It can be seen that the phase distribution in the AlO(OH) / Al2O3 / h-BN powder is uniform;

[0098] Using 20mm*12mm*12mm 316L stainless steel as the substrate, the substrate was first sandblasted using a GS-943 sandblasting machine (Beijing Changkong Sandblasting Equipment Co., Ltd.). The sandblasted substrate was then ultrasonically cleaned in acetone to remove impurities from its surface. Before preparing the coating, a Ni-24.5Cr-6Al-0.4Y metal bonding layer with a thickness of approximately 100μm was deposited on the sandblasted 316L metal substrate. The plasma thermal spraying process parameters for the bonding coating were: voltage 72V, current 600A, argon flow rate 57L / h, hydrogen flow rate 8L / h, delivery energy 42.5kW, and spraying angle 90°.

[0099] The AlO(OH) / Al2O3 / h-BN powder prepared in this embodiment was sprayed onto a substrate containing a Ni-24.5Cr-6Al-0.4Y metal binder layer using a plasma thermal spraying process (voltage 70V, current 600A, argon flow rate 50L / h, hydrogen flow rate 9L / h, power supply 42.5kW, spraying angle 90°) to obtain an Al2O3 / h-BN coating with a thickness of 350μm. (The Al2O3 / h-BN coating has an interlayer bonding strength of 55.75MPa, a porosity of 4.6%, a hardness of 8.4GPa, and a fracture toughness of 2.35MPa·m.) 1 / 2 (At a high temperature of 1000℃, the coefficient of friction is 0.17); at room temperature, the coefficient of friction and wear rate of the Al2O3 / h-BN coating under different loads and different friction pairs are shown in Table 2:

[0100] Table 2 shows the coefficients of friction and wear rates of the alumina / hexagonal boron nitride coatings under different loads and friction pairs.

[0101]

[0102] Figure 3 Here is a surface SEM image of the Al2O3 / h-BN coating. Figure 4 Here is a cross-sectional SEM image of the Al2O3 / h-BN coating, from... Figure 3 and Figure 4 It can be seen that the surface of the Al2O3 / h-BN coating is in good melting state, presenting a pancake shape. The coating is relatively dense, with a thickness of about 350 μm, and it is very tightly bonded to the metal substrate interface. This indicates that the high thermal conductivity of h-BN increases the degree of melting of the coating.

[0103] Figure 5 The three-dimensional image of the Al2O3 / h-BN coating friction surface described in Example 2 by time-of-flight secondary ion mass spectrometry confirms that the phase distribution in the coating is uniform, and after friction, a large area of ​​h-BN lubricating film is formed on the coating surface, which enhances the friction reduction performance of the coating.

[0104] Figure 6 The XRD patterns of the AlO(OH) / Al2O3 / h-BN powder and the Al2O3 / h-BN coating described in Example 2 show that the AlO(OH) phase in the AlO(OH) / Al2O3 / h-BN powder was completely transformed into the Al2O3 phase in the plasma high-temperature flame. Furthermore, due to its excellent thermal stability, h-BN did not undergo a phase transformation, and the hard α-Al2O3 phase was also well preserved.

[0105] Example 3

[0106] 200g h-BN and 100g alkaline grinding aid (Ca(OH)2) were placed in a planetary ball mill (ball-to-material ratio of 4:1, rotation speed of 240rpm, time of 5h) to pre-hydroxylate it; the pre-hydroxylated h-BN was dissolved in deionized water, hydrochloric acid solution was slowly added to the h-BN solution, excess Ca(OH)2 was washed away, and the mixture was filtered to obtain hydroxylated h-BN;

[0107] 200g of the hydroxylated h-BN was dissolved in 1500g of deionized water and 30g of PVP dispersant, and then subjected to high-pressure homogenization and exfoliation (exfoliation cycle number 20, pressure 1000 bar, flow rate 8 mL / s) to obtain hydroxylated h-BN slurry.

[0108] A 1 mol / L hydrochloric acid solution was added to 1400 mL of an AlO(OH) aqueous solution with a concentration of 357.14 g / L (containing 500 g of AlO(OH)) until the pH value reached 4. After sol-gelling, 1500 g of nano-sized α-Al2O3 was added to obtain an aluminum sol containing aluminum oxide.

[0109] The hydroxylated h-BN slurry was added to the alumina-containing alumina sol (the mass ratio of hydroxylated hexagonal boron nitride in the hydroxylated hexagonal boron nitride slurry to alumina in the alumina-containing alumina sol was 1:7.5), and spray drying was performed (inlet temperature 150℃, outlet temperature 90℃, feed rate 40 rpm, atomization speed 12600 r / min) to obtain gibbsite / alumina / hexagonal boron nitride powder (AlO(OH) / Al2O3 / h-BN powder);

[0110] Using 20mm*12mm*12mm 316L stainless steel as the substrate, the substrate was first sandblasted using a GS-943 sandblasting machine (Beijing Changkong Sandblasting Equipment Co., Ltd.). The sandblasted substrate was then ultrasonically cleaned in acetone to remove impurities from its surface. Before preparing the coating, a Ni-24.5Cr-6Al-0.4Y metal bonding layer with a thickness of approximately 100μm was deposited on the sandblasted 316L metal substrate. The plasma thermal spraying process parameters for the bonding coating were: voltage 72V, current 600A, argon flow rate 57L / h, hydrogen flow rate 8L / h, delivery energy 42.5kW, and spraying angle 90°.

[0111] The AlO(OH) / Al2O3 / h-BN powder prepared in this embodiment was sprayed onto a substrate containing a Ni-24.5Cr-6Al-0.4Y metal binder layer using a plasma thermal spraying process (voltage 70V, current 600A, argon flow rate 50L / h, hydrogen flow rate 9L / h, delivery energy 42.5kW, spraying angle 90°), resulting in an Al2O3 / h-BN coating with a thickness of 350μm. (The Al2O3 / h-BN coating has an interlayer bonding strength of 51.33MPa, a porosity of 6.8%, a hardness of 8.5GPa, and a fracture toughness of 2.04MPa·m.) 1 / 2 (At a high temperature of 1000℃, the coefficient of friction is 0.19); at room temperature, the coefficient of friction and wear rate of the Al2O3 / h-BN coating under different loads and different friction pairs are shown in Table 3:

[0112] Table 3 shows the friction coefficients and wear rates of the alumina / hexagonal boron nitride coatings under different loads and friction pairs.

[0113]

[0114] Comparative Example 1

[0115] Using 20mm*12mm*12mm 316L stainless steel as the substrate, the substrate was first sandblasted using a GS-943 sandblasting machine (Beijing Changkong Sandblasting Equipment Co., Ltd.) to ensure better adhesion between the coating and the substrate. The sandblasted substrate was then ultrasonically cleaned in acetone to remove impurities from the surface. Before preparing the coating, a Ni-24.5Cr-6Al-0.4Y metal bonding layer with a thickness of approximately 100μm was deposited on the sandblasted 316L metal substrate (plasma thermal spraying process parameters: voltage 72V, current 600A, argon flow rate 57L / h, hydrogen flow rate 8L / h, delivery energy 42.5kw, spraying angle 90°).

[0116] Al2O3 powder was sprayed onto a substrate containing a Ni-24.5Cr-6Al-0.4Y metal binder layer using a plasma thermal spraying process (voltage 70V, current 600A, argon flow rate 50L / h, hydrogen flow rate 9L / h, delivery energy 42.5kw, spraying angle 90°) to obtain an Al2O3 coating with a thickness of 350μm.

[0117] The coefficient of friction and wear rate of the Al2O3 coating under different loads and different friction pairs at room temperature are shown in Table 4:

[0118] Table 4 shows the friction coefficients and wear rates of the Al2O3 coating under different loads and friction pairs.

[0119]

[0120] Comparative Example 2

[0121] 200g of hexagonal boron nitride powder and 1000g of alumina powder were selected as raw materials and mixed evenly in a mechanical mixer to obtain a mechanically mixed alumina / hexagonal boron nitride spraying powder. Using 20mm*12mm*12mm 316L stainless steel as the substrate, the substrate was first sandblasted using a GS-943 sandblasting machine (Beijing Changkong Sandblasting Equipment Co., Ltd.) to ensure better adhesion between the coating and the substrate. The sandblasted substrate was then ultrasonically cleaned in acetone to remove impurities from the substrate surface. Before preparing the coating, a Ni-24.5Cr-6Al-0.4Y metal bonding layer with a thickness of approximately 100μm was deposited on the sandblasted 316L metal substrate (plasma thermal spraying process parameters: voltage 72V, current 600A, argon flow rate 57L / h, hydrogen flow rate 8L / h, delivery energy 42.5kw, spraying angle 90°).

[0122] A mechanically mixed alumina / hexagonal boron nitride powder was sprayed onto a substrate with a Ni-24.5Cr-6Al-0.4Y metal binder layer using a plasma thermal spraying process (voltage 70V, current 600A, argon flow rate 50L / h, hydrogen flow rate 9L / h, delivery energy 42.5kw, spraying angle 90°) to obtain an Al2O3 / h-BN coating with a thickness of 350μm.

[0123] Table 5 shows the friction coefficient and wear rate of the Al2O3 / h-BN coating under different loads and different friction pairs at room temperature.

[0124] Table 5 shows the friction coefficients and wear rates of the Al2O3 / h-BN coating under different loads and friction pairs.

[0125]

[0126] The porosity (calculated using Image Pro software based on the longitudinal section morphology) and interlayer adhesion of the Al2O3 / h-BN coatings described in Examples 1, 2, and 3, and the Al2O3 coatings and Al2O3 / h-BN coatings described in Comparative Examples 1 and 2 were measured. The testing process involved depositing a NiCrAlY metal bonding layer with a thickness of approximately 50 μm on a sandblasted 316L metal substrate to avoid excessive residual stress between the coating and the substrate. Then, the Al2O3 / h-BN coatings described in Examples 1-3 or the Al2O3 coatings described in Comparative Examples 1-2 were prepared. E-7 type epoxy resin high-temperature structural adhesive was then uniformly applied to the coating surface. A weight (5 kg / piece) was placed on top and the coating was placed in a muffle furnace, and the temperature was raised to 120°C (3°C / min). After holding at that temperature for 3 hours, the mixture was cooled to room temperature and compared using a microcomputer-controlled electronic universal testing machine (LE3504-H500, China). The porosity of the Al2O3 / h-BN coating in Example 2 was 4.6%, significantly lower than the porosities of the Al2O3 coating in Comparative Example 1 and the Al2O3 / h-BN coating in Comparative Example 2 (7.1%, 8.6%). The interlayer bonding strength and fracture toughness of the Al2O3 / h-BN coating in Example 2 were 55.75 MPa and 2.35 MPa·m, respectively. 1 / 2 Compared to the Al2O3 coating described in Comparative Example 1 and the Al2O3 / h-BN coating described in Comparative Example 2 (35.62 MPa, 1.38 MPa·m), 1 / 2 27.12 MPa, 1.65 MPa·m 1 / 2 (It has increased significantly.)

[0127] Dry friction experiments were conducted on the Al2O3 / h-BN coatings described in Examples 1, 2, and 3, and the Al2O3 coatings and Al2O3 / h-BN coatings described in Comparative Examples 1 and 2, using a reciprocating friction mode on a CSM friction testing machine. The specific friction conditions were: room temperature, relative humidity of 20±5%, linear velocity of 10cm / s, amplitude of 2.5mm, loads of 3N, 5N, and 8N, respectively, total sliding distance of 150m, and friction pairs of 316L stainless steel ball, Si3N4 ball, and WC ball (all with a diameter of 6mm). Before the friction test, the Al2O3 / h-BN coatings described in Examples 1, 2, and 3, and the Al2O3 and Al2O3 / h-BN coatings described in Comparative Examples 1 and 2 were mechanically ground and polished until their surface roughness was Ra≈0.2μm. Under the same friction conditions, the friction coefficient of the Al2O3 / h-BN coating described in Example 2 was significantly lower than that of the Al2O3 coating described in Comparative Example 1 (the friction coefficient of the Al2O3 coating is shown in Table 4). This is because the transverse shear stress during sliding breaks the interlayer van der Waals bonds of the h-BN particles, and the h-BN forms a lubricating film on the contact surface, preventing direct contact between the coating and the friction pair. Furthermore, the wear rate of the Al2O3 / h-BN coating described in Example 2 was generally better than that of the Al2O3 coating described in Comparative Example 1. This is attributed to the coating's excellent mechanical properties and dense microstructure. The high thermal stability and thermal conductivity of h-BN help reduce surface damage caused by frictional heat, alleviate material softening due to the accumulation of frictional heat, and enhance the tribological properties of the coating. Compared to the Al2O3 / h-BN coating described in Comparative Example 2, the reduction in wear rate of the Al2O3 / h-BN coating described in Example 2 is also attributed to the uniform dispersion of h-BN in the composite material.

[0128] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing gibbsite / alumina / hexagonal boron nitride, characterized in that, Includes the following steps: Alumina-containing aluminum sol is obtained by mixing an aqueous solution of gibbsite with an acid solution and then sol-gelling it. A hydroxylated hexagonal boron nitride slurry was added to the alumina-containing aluminum sol to obtain a slurry; The slurry is spray-dried to obtain the diatomite / alumina / hexagonal boron nitride.

2. The preparation method according to claim 1, characterized in that, The preparation method of the hydroxylated hexagonal boron nitride slurry includes: mixing hydroxylated hexagonal boron nitride, water and dispersant and performing high-pressure homogenization exfoliation to obtain the hydroxylated hexagonal boron nitride slurry; The mass ratio of the hydroxylated hexagonal boron nitride to water is 1:(7-8); the mass ratio of the dispersant to water is (2-5):100; The dispersant includes one or more of PVP, PVA and PEG.

3. The preparation method according to claim 2, characterized in that, The high-pressure homogenization stripping pressure is 300–1800 bar, the flow rate is 6–10 mL / s, and the number of revolutions is 10–80.

4. The preparation method according to claim 2 or 3, characterized in that, The method for preparing the hydroxylated hexagonal boron nitride includes the following steps: Hexagonal boron nitride and an alkaline grinding aid are mixed and ball-milled to obtain the hydroxylated hexagonal boron nitride; The alkaline grinding aid includes one or more of sodium hydroxide, potassium hydroxide, and calcium hydroxide; The mass ratio of the hexagonal boron nitride to the alkaline grinding aid is 2:(1-1.2); The ball mill has a ball-to-material ratio of 4:(1-1.5), a rotation speed of 240-260 rpm, and a time of 5-10 h.

5. The preparation method according to claim 1, characterized in that, The pH value of the sol-gel is 1-6; The preferred mass ratio of gibbsite to alumina in the gibbsite aqueous solution is 1:(1-3).

6. The preparation method according to claim 1, characterized in that, The mass ratio of hydroxylated hexagonal boron nitride in the hydroxylated hexagonal boron nitride slurry to alumina in the alumina-containing alumina sol is 1:(2.5-7.5).

7. The preparation method according to claim 1, characterized in that, The spray dryer has an inlet temperature of 80–300°C, an outlet temperature of 50–150°C, a feed rate of 10–200 rpm, and an atomizer speed of 10,000–30,000 rpm.

8. The boehmite / alumina / hexagonal boron nitride prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The diatomite / alumina / hexagonal boron nitride has a microsphere structure; The microsphere structure includes a core and a protective layer. The core is hydroxylated hexagonal boron nitride, and the protective layer is AlO(OH). The alumina is uniformly dispersed throughout the microsphere structure.

9. A method for preparing an alumina / hexagonal boron nitride coating, characterized in that, Includes the following steps: Atmospheric plasma spraying is used to spray diatomite / alumina / hexagonal boron nitride onto the substrate surface to obtain an alumina / hexagonal boron nitride coating. The gibbsite / alumina / hexagonal boron nitride is the gibbsite / alumina / hexagonal boron nitride described in claim 8.

10. The preparation method according to claim 9, characterized in that, The atmospheric plasma spraying uses argon as the ionized gas and hydrogen as the auxiliary gas. The thickness of the alumina / hexagonal boron nitride coating is 200–500 μm.

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