La and Hf co-doped yttrium titanate composite coating material and preparation method

Abstract

A lanthanum and hafnium co-doped yttrium titanate composite coating material and a preparation method thereof belong to the technical field of thermal barrier / infrared radiation composite materials. The chemical formula of the co-doped yttrium titanate composite coating material is Y (2‑X) La X Ti (2‑Y) Hf Y O7, wherein 0

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermal barrier / infrared radiation composite materials, and particularly relates to a lanthanum and hafnium co-doped yttrium titanate composite coating material and a preparation method. BACKGROUND

[0002] In recent years, with the increase of the speed of aircraft, the equipment thermal end components will produce significant infrared radiation signals in the service process, in which the 3-5 mu m wave band radiation intensity can reach 10 3 -10 4 times of the background environment, which greatly increases the risk of exposure of the aircraft and also makes the target temperature rise sharply, resulting in that the traditional infrared low emissivity coating cannot realize the infrared radiation inhibition at high temperature. Therefore, it is necessary to explore the low thermal conductivity and low emissivity coating in a high temperature environment.

[0003] Typical infrared emissivity materials are mainly metal-based thin film materials, which have low infrared radiation characteristics at room temperature, but are prone to oxidation at high temperature. The oxidation layer on the surface will significantly increase the infrared emissivity of the thin film. Low infrared emissivity ceramic coating shows excellent stability and heat resistance in a high temperature environment and can withstand high temperature conditions for a long time.

[0004] Hot pressing sintering is a sintering method for densifying and forming ceramic or composite materials by using high temperature and pressure on powder materials. With the aid of external pressure, the temperature required for sintering is lower, which can reduce the grain growth rate. Due to the action of external force, the material migration is accelerated, the densification process is accelerated, the sintering time is significantly shortened, and the production efficiency is significantly improved. Atmospheric plasma spraying occupies an important technical position in the thermal spraying process system. The technical equipment configuration is relatively simple, the equipment cost is low, and it has the characteristics of rapid preparation and high powder deposition efficiency. The commonly used ceramic powder preparation methods for atmospheric plasma spraying mainly include self-propagating high-temperature synthesis and solid phase reaction method. Although the self-propagating high-temperature synthesis method has the advantages of simple process and fast reaction, this process is mainly suitable for preparing high-temperature refractory materials. The solid phase reaction method has certain limitations in controlling the particle size and purity of the product, and it is difficult to meet the requirements of the atmospheric plasma spraying process.

[0005] Therefore, it is necessary to provide an improved technical solution to overcome the above-mentioned deficiencies of the prior art. SUMMARY

[0006] The purpose of the present application is to provide a lanthanum and hafnium co-doped yttrium titanate composite coating material and a preparation method to improve the problem of high infrared radiation intensity of the engine thermal end components in the prior art.

[0007] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0008] A lanthanum and hafnium co-doped yttrium titanate composite coating material, the chemical formula of the composite coating material is Y (2-X) La X Ti (2-Y) Hf Y O7, wherein 0

[0009] Further, the particle size of the lanthanum and hafnium co-doped yttrium titanate composite coating material is 1-50 μm, and the fluidity is 75-105 s / 50 g.

[0010] A preparation method of a lanthanum and hafnium co-doped yttrium titanate composite coating material, comprising the following steps:

[0011] (1) mixing titanium oxide, yttrium oxide, lanthanum oxide and hafnium oxide powders, and performing wet ball milling to obtain a first mixed slurry;

[0012] (2) performing solid-liquid separation on the first mixed slurry, and drying the obtained solid to obtain a solid raw powder;

[0013] (3) performing hot-pressing sintering on the solid raw powder to obtain a hot-pressing sintering product;

[0014] (4) mixing the hot-pressing sintering product, a binder and a dispersant, and performing wet ball milling to obtain a second mixed slurry;

[0015] (5) performing spray drying on the second mixed slurry to obtain granules;

[0016] (6) drying the granules to obtain the lanthanum and hafnium co-doped yttrium titanate composite coating material.

[0017] Preferably, in step (1), the titanium oxide, the yttrium oxide, the lanthanum oxide and the hafnium oxide are mixed according to a molar ratio of Y:La:Ti:Hf=(2-X):X:(2-Y):Y, wherein 0

[0018] Preferably, in step (3), the temperature of the hot-pressing sintering is 1200°C, the holding time is 6-12 h, and the vacuum degree is 10 -2 Pa.

[0019] Preferably, in step (4), the milling balls of the wet ball milling include 5 mm milling balls and 10 mm milling balls, and the mass ratio of the 5 mm milling balls to the 10 mm milling balls is (2-3):1.

[0020] Preferably, in step (4), the binder is at least one of polyethyleneimine, polyethylene oxide, polyvinyl alcohol, gum arabic and cellulose, and the mass ratio of the binder to the hot-press sintering product is (1-3):100; the dispersant is ammonium citrate, and the mass ratio of the ammonium citrate to the hot-press sintering product is (0.08-0.1):100.

[0021] Preferably, in step (5), the spray drying is performed in a centrifugal spray dryer, the rotation speed of the spray dryer is 9000-16000 rpm, the air inlet temperature of the spray dryer is 230-250℃, and the air outlet temperature is 115-118℃.

[0022] The lanthanum and hafnium co-doped yttrium titanate composite coating material obtained in step (6) has a particle size of 1-50μm and a flowability of 75-105s / 50g.

[0023] The application also provides a lanthanum and hafnium co-doped yttrium titanate composite coating, which is obtained by air plasma spraying the lanthanum and hafnium co-doped yttrium titanate composite coating material prepared by the above method.

[0024] Compared with the prior art, the application has the following beneficial effects:

[0025] 1. The application adopts lanthanum and hafnium co-doped yttrium titanate to prepare a composite coating. Lanthanum and hafnium have high-temperature stability. Under high-temperature unidirectional pressure, hot-press sintering can effectively eliminate internal pores of the material, obtain a compact and dense material, greatly shorten the sintering time, avoid excessive grain growth, and form a fine-grained structure. At the same time, since the ionic radius of lanthanum is larger than that of yttrium, the introduction of lanthanum will cause lattice distortion and enhance phonon scattering, further reducing the thermal conductivity. Moreover, hafnium oxide has the characteristics of low infrared emissivity, high melting point and high stability. Hafnium doping not only improves the overall low emissivity performance of the material in the medium and far infrared wave band, but also improves the high-temperature phase stability of the material, and optimizes the thermal shock resistance of the co-doped material. Therefore, the use of lanthanum and hafnium co-doped yttrium titanate material can have low thermal conductivity and low infrared emissivity characteristics, and the lanthanum and hafnium co-doped yttrium titanate composite coating material prepared has an emissivity of less than 0.36 in the 3-5μm infrared wave band.

[0026] 2. The application provides a preparation method of a lanthanum and hafnium co-doped yttrium titanate composite ceramic material. The two ball milling processes, hot-press sintering and spray drying treatment are combined, the raw materials are directly mechanically mixed and then hot-press sintered, the steps are simple and the composite ceramic material can be mass-produced, and the prepared composite ceramic material meets the requirement of uniform particle size in the plasma spraying powder process.

[0027] 3. The composite ceramic material prepared by the method has high purity, good flowability and narrow particle size distribution. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 SEM image of the lanthanum and hafnium co-doped yttrium titanate composite coating material (powder) prepared in Embodiment 1 of the present application;

[0029] Figure 2 Particle size chart of the lanthanum and hafnium co-doped yttrium titanate composite coating material (powder) prepared in Embodiment 1 of the present application;

[0030] Figure 3 Actual image of the lanthanum and hafnium co-doped yttrium titanate composite coating prepared in Embodiment 1 of the present application;

[0031] Figure 4 Cross-sectional SEM image of the lanthanum and hafnium co-doped yttrium titanate composite coating material prepared in Embodiment 1 of the present application;

[0032] Figure 5 Thermal conductivity detection result of the lanthanum and hafnium co-doped yttrium titanate composite coating prepared in Embodiment 1 of the present application;

[0033] Figure 6 Infrared emissivity detection result of the lanthanum and hafnium co-doped yttrium titanate composite coating prepared in Embodiment 1 of the present application. DETAILED DESCRIPTION

[0034] The technical solutions in the embodiments of the present application will be described clearly and completely below. Obviously, the described embodiments are only a part 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 skilled in the art belong to the scope of protection of the present application.

[0035] The present application utilizes the characteristics of low thermal conductivity, high expansion coefficient, good high-temperature phase structure stability and adaptability to defects of yttrium titanate, and uses lanthanum oxide to dope at A site and hafnium oxide to dope at B site, which influences the crystal structure, produces defects to reduce the infrared radiation characteristics, and provides an ideal thermal barrier, low infrared emissivity ceramic coating alternative material which can serve at high temperature for a long time.

[0036] Embodiment 1

[0037] The preparation method of the lanthanum and hafnium co-doped yttrium titanate composite ceramic material of the present embodiment comprises the following steps:

[0038] (1) mixing four raw material powders of titanium oxide, yttrium oxide, lanthanum oxide and hafnium oxide according to a molar ratio of Y:La:Ti:Hf = 1.8:0.2:1.8:0.2 to perform wet ball milling treatment to obtain a first mixed slurry; wherein, during the wet ball milling treatment, deionized water (as a solution medium), the raw material powders (the sum of the amounts of titanium oxide, yttrium oxide, lanthanum oxide and hafnium oxide) and zirconium oxide grinding balls are mixed according to a mass ratio of 1:1:5, 5mm and 10mm zirconium oxide balls are mixed according to a mass ratio of 1:1; the rotating speed of the ball mill is 300r / min, and the ball milling time is 6h;

[0039] (2) performing solid-liquid separation on the first mixed slurry, and drying the obtained solid to obtain a solid raw powder;

[0040] (3) placing the solid raw powder into a hot pressing tank to perform hot pressing sintering to obtain a hot pressing sintering product; wherein, the hot pressing sintering temperature is 1200℃, the holding time is 12h, and the vacuum degree is 10 -2 Pa;

[0041] (4) uniformly mixing the hot pressing sintering product with a binder, a dispersing agent, a solution medium (deionized water) and grinding balls (zirconium oxide grinding balls, including 5mm zirconium oxide grinding balls and 10mm zirconium oxide grinding balls) to obtain a second mixed slurry; wherein, the binder is polyethyleneimine, and the mass ratio of the polyethyleneimine to the hot pressing sintering product is 1:100; the dispersing agent is ammonium citrate, and the mass ratio of the ammonium citrate to the hot pressing sintering product is 0.08:100; in the second mixed slurry, the mass ratio of the deionized water, the zirconium oxide grinding balls and the hot pressing sintering product is 2:5:1, and the mass ratio of the 5mm zirconium oxide grinding balls to the 10mm zirconium oxide grinding balls is 2:1; the ball milling is performed in a planetary ball mill, the rotating speed is 325r / min, and the time is 20h;

[0042] (5) performing spray drying treatment on the second mixed slurry to obtain granules; wherein, the main process of the spray drying treatment is as follows: a high-speed centrifugal spray dryer is used, the rotating speed of an atomizer is 9000rpm, the inlet air temperature of spray granulation is 230℃, and the outlet air temperature is 115℃;

[0043] (6) drying the granules to obtain the lanthanum and hafnium co-doped yttrium titanate composite ceramic material of the present embodiment; wherein, the drying is performed by placing the granules obtained by the above spray drying treatment in an oven at 100℃ to remove excess deionized water to obtain a dried powder, and then performing screening treatment (the screen mesh aperture is 100μm) to obtain the co-doped yttrium titanate composite ceramic material of the present embodiment (in the form of powder, which can be used for atmospheric plasma spraying).

[0044] The particle size of the co-doped yttrium titanate composite ceramic material of the embodiment is 1-50 μm (the particle size of most yttrium titanate ceramic materials is distributed in 1-50 μm), and the fluidity is 85 s / 50 g.

[0045] Figure 1 The SEM diagram of the lanthanum and hafnium co-doped yttrium titanate composite coating material (powder) prepared for the embodiment 1 of the application is shown in the figure. Figure 1 It can be seen that the powder prepared in the embodiment has a good spherical shape, no internal cavity, and uniform size. Figure 2 The particle size diagram of the lanthanum and hafnium co-doped yttrium titanate composite coating material (powder) prepared for the embodiment 1 of the application is shown in the figure. It can be seen that the powder particle size distribution is narrow, in 1-41.5 μm, which meets the requirements of the plasma spraying process. The particle size distribution of the prepared powder is measured by the laser particle size analyzer in the embodiment of the application, and the particle size distribution (D10, D50, D90) is obtained. Since the median particle size D50 can be used to reflect the general level of the overall powder particle size, the particle size concentration trend of the particles can be more obviously shown, so the D50 value is selected in the embodiment of the application.

[0046] The preparation method of the lanthanum and hafnium co-doped yttrium titanate composite coating of the embodiment comprises the following steps:

[0047] I. Embed the alloy substrate covered with a bonding layer (for example, a nickel-chromium-aluminum-yttrium bonding layer) into a clamp, and install it on the workbench in the center of the vacuum chamber. Adjust the spraying distance and height. Check all instruments, gas cylinder gas volume, and ensure that the gas pipeline, powder feeding pipeline and cooling circulating water are working normally;

[0048] II. Use the powder feeder to send the co-doped yttrium titanate composite ceramic material powder and heat the powder to 80℃. Close the vacuum chamber and form a vacuum sealed environment by vacuumizing. Set the gas argon 220 scfh, gas nitrogen 100 scfh, and gas hydrogen 40 scfh in the vacuum chamber by remote control workbench. Set the spraying power 55 kW, working current 275 A, and working voltage 130 V;

[0049] III. Open the powder feeder, adjust the powder feeder speed to 2.0 (i.e. the powder feeding rate is 15 g / min), and spray 30 times to prepare the co-doped yttrium titanate composite ceramic coating of the embodiment (as shown in the figure). Figure 3

[0050] Figure 3 The real object diagram of the lanthanum and hafnium co-doped yttrium titanate composite coating prepared for the embodiment 1 of the application is shown in the figure. The surface is white with a certain roughness, and no peeling and cracking phenomenon occurs.

[0051] Figure 4 ​The cross-section SEM image of the lanthanum and hafnium co-doped yttrium titanate composite coating material prepared in Example 1 of the present application is shown in Figure 1. Figure 4 It can be seen that the coating prepared in the present example has a layered structure, the inside of the coating is compact and tight, and is accompanied by pores and cracks.

[0052] Figure 5 The thermal conductivity detection result of the lanthanum and hafnium co-doped yttrium titanate composite coating prepared in Example 1 of the present application shows that the thermal conductivity of the prepared composite coating at room temperature is about 1.3 W / mK.

[0053] Figure 6 The infrared emissivity detection result of the lanthanum and hafnium co-doped yttrium titanate composite coating prepared in Example 1 of the present application shows that the infrared emissivity (3-5 μm) is about 0.36.

Claims

1. A lanthanum, hafnium co-doped yttrium titanate composite coating material, characterized in that, The chemical formula of the composite coating material is Y (2-X) La X Ti (2-Y) Hf Y O7, wherein 0 < X < 2, 0 < Y < 2. 2.The lanthanum and hafnium co-doped yttrium titanate composite coating material according to claim 1, characterized in that, The lanthanum and hafnium co-doped yttrium titanate composite coating material has a particle size of 1-50 μm and a fluidity of 75-105 s / 50 g.

3. A method for preparing a lanthanum, hafnium co-doped yttrium titanate composite coating material, characterized in that, The method comprises the following steps: (1) mixing titanium oxide, yttrium oxide, lanthanum oxide and hafnium oxide raw material powders, and performing wet ball milling to obtain a first mixed slurry; (2) performing solid-liquid separation on the first mixed slurry, and drying to obtain a solid green powder; (3) performing hot-pressing sintering on the solid green powder to obtain a hot-pressing sintering product; (4) mixing the hot-pressing sintering product, a binder and a dispersant, and performing wet ball milling to obtain a second mixed slurry; (5) performing spray drying on the second mixed slurry to obtain granules; (6) drying the granules to obtain the lanthanum and hafnium co-doped yttrium titanate composite coating material.

4. The method for preparing the lanthanum and hafnium co-doped yttrium titanate composite coating material according to claim 3, characterized in that, In step (1), the titanium oxide, yttrium oxide, lanthanum oxide and hafnium oxide are mixed according to a molar ratio of Y:La:Ti:Hf=(2-X):X:(2-Y):Y, wherein 0X<2 and 0Y<2.

5. The method for preparing the lanthanum and hafnium co-doped yttrium titanate composite coating material according to claim 3, characterized in that, In step (3), the temperature of the hot-press sintering is 1200℃, the holding time is 6-12h, and the vacuum degree is 10 -2 Pa.

6. The method for preparing the lanthanum and hafnium co-doped yttrium titanate composite coating material according to claim 3, characterized in that, In step (4), the wet ball milling uses grinding balls including 5 mm grinding balls and 10 mm grinding balls, and the mass ratio of the 5 mm grinding balls to the 10 mm grinding balls is (2-3):

1.

7. The method for preparing the lanthanum and hafnium co-doped yttrium titanate composite coating material according to claim 3, characterized in that, In step (4), the binder is at least one of polyethyleneimine, polyethylene oxide, polyvinyl alcohol, gum arabic and cellulose, and the mass ratio of the binder to the hot-pressing sintering product is (1-3):100; the dispersant is ammonium citrate, and the mass ratio of the ammonium citrate to the hot-pressing sintering product is (0.08-0.1):

100.

8. The method for preparing the lanthanum and hafnium co-doped yttrium titanate composite coating material according to claim 3, characterized in that, In step (5), the spray drying is performed in a centrifugal spray dryer, the rotation speed of the spray dryer is 9000-16000 rpm, the air inlet temperature of the spray dryer is 230-250 ℃, and the air outlet temperature is 115-118 ℃.

9. A lanthanum and hafnium co-doped yttrium titanate composite coating, which is obtained by performing atmospheric plasma spraying on the lanthanum and hafnium co-doped yttrium titanate composite coating material prepared by the method according to any one of claims 3 to 8.

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