A high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient and a preparation method thereof

Abstract

The application relates to the technical field of electromagnetic wave absorbing materials, and provides a high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient and a preparation method thereof.The high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is composed of a ceramic matrix with a low thermal expansion coefficient and a high-temperature-resistant absorber.The high-temperature-resistant wave-absorbing coating has a low thermal expansion coefficient, can realize good thermal matching with a substrate formed by a low-expansion-coefficient material, can still effectively absorb electromagnetic waves after annealing in a high-temperature environment, and improves the wave-absorbing performance and service life of a target in a high-temperature environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of electromagnetic wave absorbing materials, in particular to a high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient and a preparation method of the high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient. BACKGROUND

[0002] In the field of aerospace, in order to improve the service life and electromagnetic wave absorbing performance of a target, a high-temperature part of the target, such as an aircraft skin, an engine, a nose cone, etc., is usually made of a traditional high-temperature alloy substrate coated with a high-temperature-resistant wave-absorbing coating. However, with the emergence of composite materials with low density, high-temperature resistance, excellent mechanical properties and other advantages, they are considered as the best candidate materials to replace traditional high-temperature alloy materials.

[0003] Compared with traditional high-temperature alloys, the thermal expansion coefficient of materials such as C / C composite materials, C / SiC composite materials, etc. is smaller. If the traditional high-temperature-resistant wave-absorbing coating is directly applied to such low-thermal-expansion-coefficient substrate materials, after undergoing multiple cold and hot alternations, the thermal expansion coefficient mismatch between the high-temperature-resistant wave-absorbing coating and the substrate will occur, resulting in deformation, cracking and even peeling off of the high-temperature-resistant wave-absorbing coating, and the wave-absorbing performance will also be affected, thereby affecting the service life and performance of the target.

[0004] Therefore, it is of great significance to develop a high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient. SUMMARY

[0005] The present application aims to provide a high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient and a preparation method of the high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient, to solve the problem of high thermal expansion coefficient of traditional high-temperature-resistant wave-absorbing materials, mismatch of thermal expansion coefficient between the traditional high-temperature-resistant wave-absorbing materials and the substrate formed by low-thermal-expansion-coefficient materials, and shortening of the service life and reduction of the wave-absorbing performance of the target.

[0006] According to a first aspect of the present application, a high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is provided: the high-temperature-resistant wave-absorbing coating is composed of a ceramic matrix with a low thermal expansion coefficient and a high-temperature-resistant absorber.

[0007] In some embodiments of the present application, based on the foregoing scheme, the ceramic matrix with a low thermal expansion coefficient is a combination of one or more of cordierite, mullite, BSAS, mono-silicate, pyrosilicate, ZrW2O8, ZrV2O7, Al2TiO5, Al2O 12 W3;

[0008] The high-temperature-resistant absorber is a combination of one or more of a metal silicide, a metal boride, a metal carbide, a metal nitride or a metal oxide with electrical conductivity.

[0009] In some embodiments of the present application, based on the foregoing scheme, the molecular formula of the monosilicate is ReSiO5, and the molecular formula of the pyrosilicate is Re2Si2O7, wherein Re is La, Ce, Pr, Nd, Sm, Eu, Tb, Yb, Y, Ho, or Gd.

[0010] In some embodiments of the present application, based on the foregoing scheme, the particle size of the ceramic matrix with low thermal expansion coefficient and the particle size of the high-temperature-resistant absorber are both greater than zero and less than or equal to 80 μm, and the thickness of the high-temperature-resistant wave-absorbing coating is greater than zero and less than or equal to 2 mm.

[0011] According to a second aspect of the present application, a method for preparing a high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient is provided: ceramic matrix materials with low thermal expansion coefficient and high-temperature-resistant absorbers are weighed according to a predetermined mass ratio, and a composite powder is prepared by using a conventional spray drying method; and the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient as described in the above embodiments is prepared on a pretreated substrate using the composite powder as raw material.

[0012] In some embodiments of the present application, based on the foregoing scheme, the composite powder is prepared by using a conventional spray drying method, which includes: ball milling the ceramic matrix materials and the high-temperature-resistant absorbers to obtain a mixed slurry; and granulating the mixed slurry to obtain the composite powder.

[0013] In some embodiments of the present application, based on the foregoing scheme, the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient as described in the above embodiments is prepared on a pretreated substrate, which includes: forming the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient on the substrate by using a plasma spraying method, a flame spraying method, or a laser cladding method.

[0014] The high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient of the present application has the following advantages compared with the prior art:

[0015] 1. The high-temperature-resistant wave-absorbing coating in the present application has low thermal expansion coefficient, and can achieve good thermal matching with a substrate formed of a low-thermal-expansion-coefficient material.

[0016] 2. The high-temperature-resistant wave-absorbing coating in the present application can stably work in a high-temperature environment of 800℃ or higher, thereby improving the service life and wave-absorbing performance of a target in a high-temperature environment.

[0017] 3. The high-temperature-resistant wave-absorbing coating in the present application can be prepared by using a plasma spraying method, a flame spraying method, a laser cladding method, or the like, and has the advantages of simple preparation process, low equipment requirement, and high repeatability.

[0018] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the application, as claimed. BRIEF DESCRIPTION OF DRAWINGS

[0019] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments consistent with the application and serve to explain the principles of the application. It is readily apparent to one skilled in the art that the following figures are merely illustrative of some embodiments of the application and that other figures can be obtained from these figures without paying creative labor.

[0020] Figure 1 The flow chart schematically shows the method for preparing the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient in the application.

[0021] Figure 2 The scanning electron microscope image of the composite powder formed by 35wt% TiB2+65wt% ytterbium monosilicate in the application is shown.

[0022] Figure 3 The particle size distribution histogram of the composite powder formed by 35wt% TiB2+65wt% ytterbium monosilicate in the application is shown.

[0023] Figure 4 The reflection loss curve of the high-temperature-resistant wave-absorbing coating in the application after annealing treatment at room temperature and 900°C is shown.

[0024] Figure 5 The thermal expansion coefficient curve of different high-temperature-resistant wave-absorbing coatings in the application is shown. DETAILED DESCRIPTION

[0025] Example implementations will now be described more fully with reference to the accompanying drawings. Example implementations may, however, be implemented in many different forms and should not be construed as limited to the examples set forth herein; rather, these implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of example implementations to those skilled in the art.

[0026] Moreover, the described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of embodiments of the application. One skilled in the relevant art will recognize, however, that the

[0027] Unless otherwise indicated, various materials, reagents, and equipment used in the present application are commercially available or can be prepared by known methods.

[0028] Electromagnetic wave absorption is to absorb electromagnetic radiation generated by electronic devices, and currently electromagnetic wave absorption is mainly to absorb X-band (8.2GHz-12.4GHz) microwaves. In the field of aerospace, the temperature of the outer surface of the fuselage and the nose cone of the target such as fighter aircraft and hypersonic missile can reach hundreds or even thousands of degrees Celsius when flying at high speed. In order to improve the service life and wave absorption performance of the target, the high-temperature parts of the target are usually made of metal alloy materials coated with high-temperature wave absorption coating in the related art.

[0029] With the rapid development of new materials, some materials with low density, high temperature resistance, excellent mechanical properties and many other advantages are considered as the best candidate materials to replace traditional high-temperature alloy materials. However, the thermal expansion coefficient of these materials is smaller than that of high-temperature alloy materials, so the traditional high-temperature wave absorption coating cannot be directly applied to the substrate formed by such materials, for example, C / C composite material, C / SiC composite material, etc. have the advantages of low density, high temperature resistance, good mechanical properties, etc., but the thermal expansion coefficient is small, which cannot be combined with traditional high-temperature wave absorption coating and used for a long time in high-temperature environment.

[0030] In view of the above problems, the present application provides a high-temperature wave absorption coating with low thermal expansion coefficient and a preparation method. Next, the high-temperature wave absorption coating with low thermal expansion coefficient and the preparation method thereof in the embodiments of the present application will be described in detail.

[0031] The present application first provides a high-temperature wave absorption coating with low thermal expansion coefficient, which is composed of a ceramic matrix with low thermal expansion coefficient and a high-temperature absorbing agent.

[0032] In an embodiment of the present application, the ceramic matrix with low thermal expansion coefficient can be cordierite, mullite, BSAS, monosilicate, pyrosilicate, ZrW2O8, ZrV2O7, Al2TiO5, Al2O 12 W3, or a combination thereof, wherein BASA is a shorthand for (1-x)BaO-xSrO-Al2O3-2SiO2 (0≤x≤1).

[0033] In an embodiment of the present application, the molecular formula of the monosilicate is ReSiO5, wherein Re is La, Ce, Pr, Nd, Sm, Eu, Tb, Yb, Y, Ho or Gd; the molecular formula of the pyrosilicate is Re2Si2O7, wherein Re is La, Ce, Pr, Nd, Sm, Eu, Tb, Yb, Y, Ho or Gd.

[0034] In an embodiment of the present application, the high-temperature-resistant absorber is formed of a high-temperature-resistant conductive material, specifically, the high-temperature-resistant absorber can be one or a combination of a conductive metal silicide, a conductive metal boride, a conductive metal carbide, a conductive metal nitride, or a conductive metal oxide, for example, the conductive metal silicide can be MoSi2, etc., the conductive metal boride can be TiB2, ZrB2, etc., the conductive metal carbide can be TiC, WC, Mo2C, ZrC, etc., the conductive metal nitride can be TiN, TaN, etc., and the conductive metal oxide can be ZnO, SnO2, etc.

[0035] It is worth noting that in a high-temperature use scenario, the magnetic property of the material will disappear, and therefore, in order to improve the wave-absorbing performance of the coating, a high-temperature-resistant conductive material is preferably used as the high-temperature-resistant absorber in the embodiments of the present application.

[0036] The high-temperature-resistant absorber in the present application not only has high electrical conductivity at high temperatures, but also has certain oxidation resistance, which improves the stability and service life of the high-temperature-resistant absorber. Further, since the ceramic matrix has a low thermal expansion coefficient, and the proportion of the ceramic matrix in the high-temperature-resistant wave-absorbing coating is higher than that of the high-temperature-resistant absorber, the high-temperature-resistant wave-absorbing coating prepared by mixing the ceramic matrix and the high-temperature-resistant absorber also has a low thermal expansion coefficient, that is, the high-temperature-resistant wave-absorbing coating composed of the ceramic matrix and the high-temperature-resistant absorber with a low thermal expansion coefficient can have both low thermal expansion coefficient and high-temperature wave-absorbing performance.

[0037] In an embodiment of the present application, the thermal expansion coefficient of the high-temperature-resistant wave-absorbing coating is between the thermal expansion coefficient of the ceramic matrix and the thermal expansion coefficient of the high-temperature-resistant absorber, and in the embodiments of the present application, the thermal expansion coefficient of the high-temperature-resistant wave-absorbing coating is less than or equal to 8x10 -6 K -1 Compared with the thermal expansion coefficient of the traditional high-temperature-resistant wave-absorbing coating, the thermal expansion coefficient of the high-temperature-resistant wave-absorbing coating composed of the ceramic matrix and the high-temperature-resistant absorber with a low thermal expansion coefficient is lower, and accordingly, the high-temperature-resistant wave-absorbing coating in the present application can be substantially thermally matched with the substrate formed of a low-thermal-expansion-coefficient material, improving the wave-absorbing performance and service life of the target.

[0038] In an embodiment of the present application, the particle size of the ceramic matrix with low thermal expansion coefficient and the particle size of the high-temperature-resistant absorbent can be set according to actual needs, preferably, the particle size of the ceramic matrix and the particle size of the high-temperature-resistant absorbent can be set to be greater than zero and less than or equal to 80 pm, further, the particle size of the ceramic matrix and the particle size of the high-temperature-resistant absorbent can be the same or different, which is not specifically limited in the embodiment of the present application.

[0039] In an embodiment of the present application, the thickness of the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient can also be set according to actual needs, preferably, the coating thickness can be set to be greater than zero and less than or equal to 2 mm, of course, other thickness values can also be set, which is not specifically limited in the embodiment of the present application.

[0040] The high-temperature-resistant wave-absorbing coating in the present application is composed of a ceramic matrix with low thermal expansion coefficient and a high-temperature-resistant absorbent, so that the high-temperature-resistant wave-absorbing coating in the present application can have good wave-absorbing performance and low thermal expansion coefficient in a high-temperature environment, further, can realize good thermal matching with a substrate formed by a low-thermal-expansion-coefficient material, and further improve the service life and wave-absorbing performance of the target in a high-temperature environment.

[0041] The present application also provides a preparation method of a high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient, Figure 1 The preparation method of the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient is schematically shown in a flowchart, as shown in the figure, the preparation method comprises: Figure 1 The preparation method of the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient is schematically shown in a flowchart, as shown in the figure, the preparation method comprises:

[0042] Step S110: The ceramic matrix material with low thermal expansion coefficient and the high-temperature-resistant absorbent are weighed according to a preset mass ratio, and a composite powder is prepared by using a conventional spray drying method.

[0043] Step S120: The high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient is prepared on the pretreated substrate by using the composite powder as raw material.

[0044] Next, the preparation method and performance of the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient in the present application are described in detail.

[0045] In step S110, the ceramic matrix material with low thermal expansion coefficient and the high-temperature-resistant absorbent are weighed according to a preset mass ratio, and a composite powder is prepared by using a conventional spray drying method.

[0046] In an embodiment of the present application, first, the ceramic matrix and the high-temperature-resistant absorber with low thermal expansion coefficient are weighed according to a preset mass ratio, and then the composite powder is prepared by using the ceramic matrix and the high-temperature-resistant absorber as raw materials by means of a conventional spray drying method, and the composite powder is used to prepare the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient. In the process of preparing the composite powder by means of the conventional spray drying method, first, the ceramic matrix and the high-temperature-resistant absorber are ball milled to obtain a mixed slurry, and then the mixed slurry is granulated to obtain the composite powder.

[0047] In an embodiment of the present application, when ball milling, not only the ceramic matrix and the high-temperature-resistant absorber need to be added into the ball mill, but also a liquid grinding aid needs to be added. In the embodiment of the present application, when the ceramic matrix and the high-temperature-resistant absorber with low thermal expansion coefficient are weighed according to a preset mass ratio, first, the ceramic matrix and the high-temperature-resistant absorber are weighed according to a first mass ratio, and then the liquid grinding aid is weighed according to a second mass ratio and the mass of the solid state substance corresponding to the ceramic matrix and the high-temperature-resistant absorber. In the first mass ratio, the mass percentage of the ceramic matrix is greater than that of the high-temperature-resistant absorber, and in the second mass ratio, the mass percentage of the liquid grinding aid is greater than or equal to the mass percentage of the solid state substance corresponding to the ceramic matrix and the high-temperature-resistant absorber. Preferably, the ratio of the mass of the liquid grinding aid to the mass of the solid state substance is 1:1 to 2:1. Of course, other ratios can also be set according to actual needs, which are not limited in the embodiment of the present application.

[0048] In an embodiment of the present application, after the ceramic matrix, the high-temperature-resistant absorber and the liquid grinding aid are weighed, the ceramic matrix, the high-temperature-resistant absorber and the liquid grinding aid can be placed in the ball mill for ball milling to obtain a mixed slurry. The ball milling parameters of the ball mill can be set as follows: the rotation speed is 40-80 r / min, and the ball milling time is 8-24 hours.

[0049] After the mixed slurry is obtained, the mixed slurry can be used as raw material to perform granulation by using a spray granulator to obtain a composite powder. The specific granulation process is as follows: first, 2wt%-5wt% polyvinyl alcohol or carboxymethyl cellulose sodium aqueous solution is added into the mixed slurry, 1-5 drops of defoaming agent is dropped, and then the mixture is stirred uniformly; then, the uniformly stirred mixed slurry is introduced into the spray granulator configured with granulation parameters to obtain a powder; wherein the granulation parameters can be set as follows: the inlet air temperature is 280-380℃, the outlet air temperature is 70-140℃, and the rotation speed of the peristaltic pump is 18-25 r / min; finally, the powder is sieved by using a 100-200 mesh screen, and the sieved powder is dried in an environment at 60-150℃ for 2-5 hours to obtain a mixed powder, which is the mixed powder formed by the ceramic matrix and the high-temperature-resistant absorber.

[0050] In an embodiment of the present application, the composite powder is in the form of granules, rather than in the form of ceramic matrix particles or high-temperature-resistant absorbent particles, Figure 2 A scanning electron microscope image of the composite powder formed by 35wt% TiB2+65wt% ytterbium monosilicate is shown in FIG. 3. Figure 2 As shown, the mixed slurry is granulated by a spray granulator to form granules containing the ceramic matrix and the high-temperature-resistant absorbent, and the diameter of the granules is greater than 20 μm.

[0051] Further, Figure 3 A particle size distribution histogram of the composite powder formed by 35wt% TiB2+65wt% ytterbium monosilicate is shown in FIG. 4. Figure 3 As shown, the particle size distribution of the granules obtained by granulation is between 20 μm and 110 μm, wherein the proportion of the granules with a particle size of 50 μm to 60 μm in the composite powder is the largest, reaching 28%, and the proportion of the granules with a particle size of 20 μm to 30 μm and 90 μm to 100 μm in the composite powder is the smallest, less than 1%, and the average value of the particle size of the composite powder is 56.9 μm.

[0052] It is worth noting that the particle size distribution of the composite powder with different components will be different, and therefore the particle size of the composite powder is not limited to 20 μm to 110 μm, but can also be other numerical ranges, which are not limited in the embodiments of the present application.

[0053] In step S120, a high-temperature-resistant wave-absorbing coating layer with a low thermal expansion coefficient is prepared on the pretreated substrate using the composite powder as a raw material.

[0054] In an embodiment of the present application, after obtaining the composite powder, a high-temperature-resistant wave-absorbing coating layer with a low thermal expansion coefficient can be prepared on the substrate using the composite powder as a raw material. It should be noted that before preparing the high-temperature-resistant wave-absorbing coating layer, the substrate needs to be pretreated. Specifically, the substrate can be sandblasted and cleaned to remove impurities on the surface of the substrate and to increase the roughness of the surface of the substrate, thereby improving the bonding force between the high-temperature-resistant coating layer and the substrate.

[0055] In an embodiment of the present application, any method can be used to prepare the high-temperature-resistant wave-absorbing coating layer formed by the composite powder on the pretreated substrate. For example, a spraying method such as plasma spraying or flame spraying can be used to form the high-temperature-resistant wave-absorbing coating layer on the pretreated substrate, a laser cladding method can be used to form the high-temperature-resistant wave-absorbing coating layer on the pretreated substrate, a screen printing method can be used to form the high-temperature-resistant wave-absorbing coating layer on the pretreated substrate, and the like, which are not limited in the embodiments of the present application.

[0056] For example, in the case of forming the high-temperature-resistant wave-absorbing coating on the pretreated substrate by the plasma spraying method, the plasma spraying parameters can be set as follows: argon gas pressure 40-50 psi, 10% hydrogen / argon mixed gas pressure 40-60 psi, powder feeding flow rate 10-15 g / min, spraying voltage 25-37 V, spraying current 600-900 A, spraying angle 90°, and spraying distance 80-100 mm. Meanwhile, the coating thickness can also be set, which can be greater than zero and less than or equal to 2 mm, or can be set to other values, which are not limited in the embodiments of the present application.

[0057] Next, the preparation method of the high-temperature-resistant wave-absorbing coating in the embodiments of the present application is described through thirteen examples.

[0058] First example:

[0059] S1: The solid-state raw materials were weighed according to the mass ratio of MoSi2:cordierite of 1:4, and the liquid grinding aid was weighed according to the mass ratio of solid-state raw materials:liquid grinding aid of 1:1. Then, the solid-state raw materials and the liquid grinding aid were placed in a ball mill jar and ball-milled at a ball-milling speed of 80 r / min for 8 h to obtain a mixed slurry.

[0060] S2: The mixed slurry was added to a spray granulator for granulation to obtain a composite powder. The spray granulation parameters of the spray granulator were as follows: inlet temperature 280±10℃, outlet temperature 70±5℃, peristaltic pump speed 18 r / min, powder drying temperature 60±5℃, and powder drying time 5 h.

[0061] S3: The composite powder obtained in S2 was used as raw material to prepare a high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient on a pretreated substrate by the plasma spraying method. The plasma spraying parameters were as follows: argon gas pressure 40 psi, 10% hydrogen / argon mixed gas pressure 40 psi, powder feeding flow rate 15 g / min, spraying voltage 25 V, spraying current 600 A, spraying angle 90°, spraying distance 90 mm, and coating thickness 1.5 mm.

[0062] Second example:

[0063] S1: The solid-state raw materials were weighed according to the mass ratio of MoSi2:cordierite of 1:3, and the liquid grinding aid was weighed according to the mass ratio of solid-state raw materials:liquid grinding aid of 1:1. Then, the solid-state raw materials and the liquid grinding aid were placed in a ball mill jar and ball-milled at a ball-milling speed of 80 r / min for 8 h to obtain a mixed slurry.

[0064] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: air inlet temperature 280±10℃, air outlet temperature 70±5℃, peristaltic pump speed 18r / min, powder drying temperature 60±5℃, and powder drying time 5h;

[0065] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate by using the composite powder obtained in S2 as a raw material and adopting a plasma spraying method; the plasma spraying parameters are: argon gas pressure 40psi, 10% hydrogen / argon mixed gas pressure 45psi, powder feeding flow rate 15g / min, spraying voltage 25V, spraying current 600A, spraying angle 90°, spraying distance 90mm, and coating thickness 1.4mm.

[0066] Third embodiment:

[0067] S1: Solid raw materials are weighed according to a mass ratio of TiB2:cordierite of 1:4, and liquid grinding aids are weighed according to a mass ratio of solid raw materials:liquid grinding aids of 1:1.3, then the solid raw materials and the liquid grinding aids are placed in a ball mill jar for ball milling at a ball milling speed of 60r / min for 12h to obtain a mixed slurry;

[0068] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: air inlet temperature 320±10℃, air outlet temperature 100±5℃, peristaltic pump speed 22r / min, powder drying temperature 80±5℃, and powder drying time 4h;

[0069] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate by using the composite powder obtained in S2 as a raw material and adopting a plasma spraying method; the plasma spraying parameters are: argon gas pressure 40psi, 10% hydrogen / argon mixed gas pressure 45psi, powder feeding flow rate 15g / min, spraying voltage 30V, spraying current 800A, spraying angle 90°, spraying distance 100mm, and coating thickness 1.5mm.

[0070] Fourth embodiment:

[0071] S1: Solid raw materials are weighed according to a mass ratio of TiB2:cordierite of 3:7, and liquid grinding aids are weighed according to a mass ratio of solid raw materials:liquid grinding aids of 1:1.3, then the solid raw materials and the liquid grinding aids are placed in a ball mill jar for ball milling at a ball milling speed of 60r / min for 12h to obtain a mixed slurry;

[0072] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: air inlet temperature 320±10℃, air outlet temperature 100±5℃, peristaltic pump speed 22r / min, powder drying temperature 80±5℃, and powder drying time 4h;

[0073] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate by using the composite powder obtained in S2 as a raw material and adopting a plasma spraying method; the plasma spraying parameters are: argon gas pressure 40psi, 10% hydrogen / argon mixed gas pressure 50psi, powder feeding flow rate 15g / min, spraying voltage 30V, spraying current 800A, spraying angle 90°, spraying distance 100mm, and coating thickness 1.2mm.

[0074] Fifth embodiment:

[0075] S1: Solid raw materials are weighed according to a mass ratio of TiB2: ytterbium monosilicate of 3:7, and liquid grinding aids are weighed according to a mass ratio of solid raw materials: liquid grinding aids of 1:1.5, then the solid raw materials and the liquid grinding aids are placed in a ball mill jar for ball milling at a ball milling speed of 60r / min for 12h to obtain a mixed slurry;

[0076] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: air inlet temperature 350±10℃, air outlet temperature 120±5℃, peristaltic pump speed 25r / min, powder drying temperature 130±5℃, and powder drying time 2.5h;

[0077] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate by using the composite powder obtained in S2 as a raw material and adopting a plasma spraying method; the plasma spraying parameters are: argon gas pressure 40psi, 10% hydrogen / argon mixed gas pressure 50psi, powder feeding flow rate 13g / min, spraying voltage 32V, spraying current 800A, spraying angle 90°, spraying distance 90mm, and coating thickness 1.4mm.

[0078] Sixth embodiment:

[0079] S1: Solid raw materials are weighed according to a mass ratio of TiB2: ytterbium monosilicate of 7:13, and liquid grinding aids are weighed according to a mass ratio of solid raw materials: liquid grinding aids of 1:1.5, then the solid raw materials and the liquid grinding aids are placed in a ball mill jar for ball milling at a ball milling speed of 60r / min for 12h to obtain a mixed slurry;

[0080] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: air inlet temperature 350±10℃, air outlet temperature 120±5℃, peristaltic pump speed 25r / min, powder drying temperature 130±5℃, and powder drying time 2.5h;

[0081] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate by using the composite powder obtained in S2 as a raw material and adopting a plasma spraying method; the plasma spraying parameters are: argon gas pressure 45psi, 10% hydrogen / argon mixed gas pressure 55psi, powder feeding flow rate 13g / min, spraying voltage 32V, spraying current 800A, spraying angle 90°, spraying distance 90mm, and coating thickness 1.3mm.

[0082] Seventh embodiment:

[0083] S1: Solid raw materials are weighed according to a mass ratio of ZrB2: ytterbium disilicate of 1:3, and liquid grinding aids are weighed according to a mass ratio of solid raw materials: liquid grinding aids of 1:1.2, then the solid raw materials and the liquid grinding aids are placed in a ball mill jar for ball milling at a ball milling speed of 60r / min for 12h to obtain a mixed slurry;

[0084] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: air inlet temperature 300±10℃, air outlet temperature 90±5℃, peristaltic pump speed 20r / min, powder drying temperature 100±5℃, and powder drying time 4h;

[0085] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate by using the composite powder obtained in S2 as a raw material and adopting a plasma spraying method; the plasma spraying parameters are: argon gas pressure 40psi, 10% hydrogen / argon mixed gas pressure 45psi, powder feeding flow rate 15g / min, spraying voltage 32V, spraying current 800A, spraying angle 90°, spraying distance 90mm, and coating thickness 1.5mm.

[0086] Eighth embodiment:

[0087] S1: Solid raw materials are weighed according to a mass ratio of ZrB2: ytterbium disilicate of 3:7, and liquid grinding aids are weighed according to a mass ratio of solid raw materials: liquid grinding aids of 1:1.2, then the solid raw materials and the liquid grinding aids are placed in a ball mill jar for ball milling at a ball milling speed of 60r / min for 12h to obtain a mixed slurry;

[0088] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: air inlet temperature 300±10℃, air outlet temperature 90±5℃, peristaltic pump speed 20r / min, powder drying temperature 100±5℃, and powder drying time 4h;

[0089] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate by using the composite powder obtained in S2 as a raw material and adopting a plasma spraying method; the plasma spraying parameters are: argon gas pressure 45psi, 10% hydrogen / argon mixed gas pressure 50psi, powder feeding flow rate 13g / min, spraying voltage 32V, spraying current 800A, spraying angle 90°, spraying distance 90mm, and coating thickness 1.4mm.

[0090] Ninth embodiment:

[0091] S1: Solid raw materials are weighed according to a WC: ytterbium disilicate mass ratio of 7:13, and liquid grinding aids are weighed according to a solid raw material: liquid grinding aid mass ratio of 1:1.2, then the solid raw materials and the liquid grinding aids are placed in a ball mill jar for ball milling at a ball milling speed of 40r / min for 24h to obtain a mixed slurry;

[0092] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: air inlet temperature 300±10℃, air outlet temperature 90±5℃, peristaltic pump speed 20r / min, powder drying temperature 100±5℃, and powder drying time 4h;

[0093] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate by using the composite powder obtained in S2 as a raw material and adopting a plasma spraying method; the plasma spraying parameters are: argon gas pressure 45psi, 10% hydrogen / argon mixed gas pressure 50psi, powder feeding flow rate 13g / min, spraying voltage 32V, spraying current 800A, spraying angle 90°, spraying distance 90mm, and coating thickness 1.4mm.

[0094] Tenth embodiment:

[0095] S1: Solid raw materials are weighed according to a WC: mullite mass ratio of 2:3, and liquid grinding aids are weighed according to a solid raw material: liquid grinding aid mass ratio of 1:2, then the solid raw materials and the liquid grinding aids are placed in a ball mill jar for ball milling at a ball milling speed of 80r / min for 18h to obtain a mixed slurry;

[0096] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: inlet temperature 380±10℃, outlet temperature 140±5℃, peristaltic pump speed 20r / min, powder drying temperature 150±5℃, and powder drying time 2h;

[0097] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate by using the composite powder obtained in S2 as a raw material and adopting a plasma spraying method; the plasma spraying parameters are: argon gas pressure 50psi, 10% hydrogen / argon mixed gas pressure 60psi, powder feeding flow rate 10g / min, spraying voltage 37V, spraying current 900A, spraying angle 90°, spraying distance 80mm, and coating thickness 1.4mm.

[0098] Eleventh embodiment:

[0099] S1: Solid raw materials are weighed according to a mass ratio of MoSi2: ZrB2: cordierite of 4:3:13, and liquid grinding aids are weighed according to a mass ratio of solid raw materials: liquid grinding aids of 1:1.3, then the solid raw materials and the liquid grinding aids are placed in a ball mill tank for ball milling at a ball milling speed of 80r / min for 8h to obtain a mixed slurry;

[0100] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: inlet temperature 320±10℃, outlet temperature 100±5℃, peristaltic pump speed 22r / min, powder drying temperature 80±5℃, and powder drying time 4h;

[0101] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate by using the composite powder obtained in S2 as a raw material and adopting a plasma spraying method; the plasma spraying parameters are: argon gas pressure 40psi, 10% hydrogen / argon mixed gas pressure 50psi, powder feeding flow rate 12g / min, spraying voltage 32V, spraying current 700A, spraying angle 90°, spraying distance 90mm, and coating thickness 1.4mm.

[0102] Twelfth embodiment:

[0103] S1: Solid raw materials are weighed according to a mass ratio of MoSi2: cordierite: ytterbium disilicate of 1:2:1, and liquid grinding aids are weighed according to a mass ratio of solid raw materials: liquid grinding aids of 1:1.3, then the solid raw materials and the liquid grinding aids are placed in a ball mill tank for ball milling at a ball milling speed of 80r / min for 12h to obtain a mixed slurry;

[0104] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: inlet temperature 320±10℃, outlet temperature 100±5℃, peristaltic pump speed 22r / min, powder drying temperature 80±5℃, powder drying time 4h;

[0105] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate using the composite powder obtained in S2 as a raw material by a plasma spraying method; the plasma spraying parameters are: argon gas pressure 40psi, 10% hydrogen / argon mixed gas pressure 45psi, powder feeding flow rate 13g / min, spraying voltage 32V, spraying current 600A, spraying angle 90°, spraying distance 90mm, coating thickness 1.5mm.

[0106] Thirteenth embodiment:

[0107] S1: Solid raw materials are weighed according to a mass ratio of MoSi2:ZrB2:cordierite:Yb2Si2O7 of 2:1:4:3, and liquid grinding aids are weighed according to a mass ratio of solid raw materials:liquid grinding aids of 1:1.3, then the solid raw materials and the liquid grinding aids are placed in a ball mill jar for ball milling at a ball milling speed of 80r / min for 12h to obtain a mixed slurry;

[0108] S2: The mixed slurry is added into a spray granulator for granulation to obtain a composite powder; the spray granulation parameters of the spray granulator are: inlet temperature 320±10℃, outlet temperature 100±5℃, peristaltic pump speed 22r / min, powder drying temperature 80±5℃, powder drying time 4h;

[0109] S3: A high-temperature-resistant wave-absorbing coating with a low thermal expansion coefficient is prepared on a pretreated substrate using the composite powder obtained in S2 as a raw material by a plasma spraying method; the plasma spraying parameters are: argon gas pressure 40psi, 10% hydrogen / argon mixed gas pressure 45psi, powder feeding flow rate 13g / min, spraying voltage 32V, spraying current 600A, spraying angle 90°, spraying distance 90mm, coating thickness 1.5mm.

[0110] Through high-temperature wave-absorbing performance testing and thermal expansion coefficient testing of the high-temperature-resistant wave-absorbing coatings prepared in the above thirteen groups of embodiments, the X-band absorption bandwidth of each embodiment corresponding to a reflectance loss ≤-10dB after heat treatment at different temperature-resistant temperatures and the thermal expansion coefficient of each group of high-temperature-resistant wave-absorbing coatings in the range of room temperature to temperature-resistant temperature can be obtained, as shown in Table 1:

[0111] Table 1: Coating components, temperature-resistant temperature and performance corresponding to each embodiment

[0112]

[0113] As can be seen from Table 1, the thermal expansion coefficient of the high-temperature-resistant wave-absorbing coating in the embodiments of the present application is ≤8x10 -6 K -1 , which indicates that the high-temperature-resistant wave-absorbing coating in the embodiments of the present application has a low thermal expansion coefficient, and meanwhile, the X-band absorption bandwidth of the wave-absorbing coating after heat treatment at the temperature-resistant temperature is ≥1.5GHz when the corresponding reflection loss is ≤-10dB. Since the temperature-resistant temperature in each embodiment is a high temperature, the high-temperature-resistant wave-absorbing coating in the embodiments of the present application still has an absorption bandwidth of ≥1.5GHz after being treated at the temperature-resistant temperature, which indicates that the high-temperature-resistant wave-absorbing coating in the embodiments of the present application has excellent microwave absorption performance in a high-temperature environment of 800℃ or above.

[0114] Figure 4 The reflection loss curves of the high-temperature-resistant wave-absorbing coating after annealing at room temperature and 900℃ are shown in FIG. 2, wherein curve A is the reflection loss curve of the high-temperature-resistant wave-absorbing coating in Example 2 at room temperature, and curve B is the reflection loss curve of the high-temperature-resistant wave-absorbing coating in Example 2 after being annealed in air at 900℃ for two hours. Figure 4 As can be seen from curve A, the effective absorption bandwidth of the high-temperature-resistant wave-absorbing coating is 2GHz (10GHz-12GHz) at room temperature when the reflection loss is -10dB, and as can be seen from curve B

[0115] , the effective absorption bandwidth of the high-temperature-resistant wave-absorbing coating is 1.9GHz (10.4GHz-12.3GHz) after being annealed in air at 900℃ for two hours when the reflection loss is -10dB. As can be seen from curves A and B, Figure 4 , the high-temperature-resistant wave-absorbing coating has an effective absorption bandwidth of ≥1.9GHz whether it is at room temperature or after being annealed in air at 900℃ for two hours, which further indicates that the high-temperature-resistant wave-absorbing coating in the embodiments of the present application has excellent wave-absorbing performance in a high-temperature environment.

[0116] In one embodiment of the present application, the thermal expansion coefficients of the high-temperature-resistant wave-absorbing coatings under different temperature conditions can be measured to obtain the thermal expansion coefficients in Table 1. Specifically, the thermal expansion coefficients of the high-temperature-resistant wave-absorbing coatings in each embodiment at room temperature can be measured first, and then the high-temperature-resistant wave-absorbing coatings are heated at a heating rate of 5℃ / min and the thermal expansion coefficients are measured until the temperature is raised to the temperature-resistant temperature, so as to obtain the thermal expansion coefficient range of each high-temperature-resistant wave-absorbing coating.

[0117] Figure 5 The thermal expansion coefficient curves of different high-temperature-resistant wave-absorbing coatings are shown in FIG. 3, wherein curve A is the thermal expansion coefficient curve of the high-temperature-resistant wave-absorbing coating in Example 1, curve B is the thermal expansion coefficient curve of the high-temperature-resistant wave-absorbing coating in Example 2, and curve C is the thermal expansion coefficient curve of the high-temperature-resistant wave-absorbing coating in Example 3. Figure 5As shown, curve T1 is the thermal expansion coefficient curve corresponding to the high-temperature-resistant wave-absorbing coating of Example 1, curve T2 is the thermal expansion coefficient curve corresponding to the high-temperature-resistant wave-absorbing coating of Example 4, and curve T3 is the thermal expansion coefficient curve corresponding to the high-temperature-resistant wave-absorbing coating of Example 8, wherein curve T1 and curve T2 overlap in the range of 0-200℃. According to curves T1, T2 and T3, the thermal expansion coefficients of the high-temperature-resistant wave-absorbing coatings of Examples 1, 4 and 8 all show a trend of decrease-increase-decrease-increase-decrease-increase as the temperature increases from 0℃ to 1000℃, and the maximum values of the thermal expansion coefficients of the three groups of high-temperature-resistant wave-absorbing coatings are 5.1×10 -6 K -1 , 5.3×10 -6 K -1 and 5×10 -6 K -1 respectively, indicating that the high-temperature-resistant wave-absorbing coatings in the examples have low thermal expansion coefficients in the range of room temperature to 1000℃.

[0118] It should be noted that, Figure 5 the thermal expansion coefficient of curve T1 in Example 1 suddenly drops to -1.2×10 -6 K -1 in the range of 900-1000℃, which is not expected, and therefore the temperature resistance of Example 1 can be set to 900±50℃ to ensure that the high-temperature-resistant wave-absorbing material has both low thermal expansion coefficient and high-temperature wave-absorbing performance.

[0119] The ceramic matrix with low thermal expansion coefficient and the high-temperature-resistant wave-absorbing agent in the present application can be prepared into a composite powder by using a conventional spray drying method, and the wave-absorbing coating prepared from the composite powder not only has high-temperature resistance and good wave-absorbing performance, but also has a low thermal expansion coefficient, which can be well thermally matched with a substrate formed by using a material with low thermal expansion coefficient, and can work stably in a high-temperature environment and effectively absorb electromagnetic waves.

[0120] Next, the performance of the high-temperature-resistant wave-absorbing coating in the examples of the present application is described by two comparative examples.

[0121] Comparative Example 1

[0122] A wave-absorbing coating with a thickness of 1.4mm is formed by using 20wt% BC4 and 80wt% Al2O3, which can work in an environment not exceeding 500℃, and if the temperature exceeds 500℃, the wave-absorbing performance of the coating will disappear. In an environment of 450±50℃, the X-band absorption bandwidth of the wave-absorbing coating is 1.7GHz, and the thermal expansion coefficient is 10.4×10 -6 K -1 -13.2×10 -6 K-1 It can be known that the wave-absorbing coating in Comparative Example 1 cannot work stably in a high-temperature environment of 800℃ or above, and has a high thermal expansion coefficient, which cannot realize good thermal matching with a substrate formed by a material with a low thermal expansion coefficient, and thus cannot improve the stability and service life of the target.

[0123] Comparative Example 2

[0124] A wave-absorbing coating with a thickness of 1.3mm is formed by 15wt% MWCNTs and 85wt% Al2O3, and the wave-absorbing coating can work in an environment of not more than 450℃, and if more than 450℃, the wave-absorbing performance of the wave-absorbing coating disappears. In an environment of 400±50℃, the X-band absorption bandwidth of the wave-absorbing coating is 1.9GHz, and the thermal expansion coefficient is 9.1×10 -6 K -1 ~11.3×10 -6 K -1 The wave-absorbing coating in Comparative Example 1 cannot work stably in a high-temperature environment of 800℃ or above, and has a high thermal expansion coefficient, which cannot realize good thermal matching with a substrate formed by a material with a low thermal expansion coefficient, and thus cannot improve the stability and service life of the target.

[0125] In the present application, the ceramic with a low thermal expansion coefficient is used as a substrate, and a high-temperature resistant absorber is added to the substrate to form a wave-absorbing coating, and the wave-absorbing coating has both a low thermal expansion coefficient and a high-temperature wave-absorbing performance. The high-temperature resistant wave-absorbing coating with a low thermal expansion coefficient in the present application can realize good thermal matching with a substrate formed by a material with a low thermal expansion coefficient, for example, can realize good thermal matching with a substrate formed by C / C composite material and C / SiC composite material, so that the prepared coating is not easy to fall off and crack, and has a longer service life. In addition, since the high-temperature resistant wave-absorbing coating in the present application can be used in a high-temperature environment of 800℃ or above, the high-temperature resistant wave-absorbing coating with a low thermal expansion coefficient in the present application has a wide application range, for example, can be applied to fighter planes, hypersonic missiles and other targets, specifically, the high-temperature resistant wave-absorbing coating in the present application can be prepared on a substrate formed by a material with a low thermal expansion coefficient, low density, high-temperature resistance, good mechanical properties and other advantages, such as C / C composite material, C / SiC composite material, to realize radar stealth of the target.

[0126] It should be understood that the present application is not limited to the precise construction which has been described above and illustrated in the accompanying drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the application is limited only by the claims that follow.

[0127] The above merely provides preferred embodiments of the present application and not to limit the patent range of the present application. The present application can have various changes and modifications for those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the patent protection range of the present application.

Claims

1.A high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient, characterized in that: the high-temperature-resistant wave-absorbing coating is composed of a ceramic matrix with low thermal expansion coefficient and a high-temperature-resistant absorber; the ceramic matrix with low thermal expansion coefficient is a combination of one or more of cordierite, mono-silicate and pyrosilicate; the high-temperature-resistant absorber is a combination of one or more of metal silicides, metal borides or metal carbides with electrical conductivity; and the thickness of the high-temperature-resistant wave-absorbing coating is greater than or equal to 1.2 mm and less than or equal to 2 mm. 2.The high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient according to claim 1, characterized in that: the mono-silicate has a molecular formula of ReSiO 5, and the pyrosilicate has a molecular formula of Re 2 Si 2 O 7, wherein Re is La, Ce, Pr, Nd, Sm, Eu, Tb, Yb, Y, Ho or Gd. 3.The high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient according to claim 1 or 2, characterized in that: the particle size of the ceramic matrix with low thermal expansion coefficient and the particle size of the high-temperature-resistant absorber are both greater than zero and less than or equal to 80 μm. The preparation method comprises: weighing the ceramic matrix with low thermal expansion coefficient and the high-temperature-resistant absorber according to a preset mass ratio, preparing a composite powder by using a conventional spray drying method; and preparing the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient according to any one of claims 1-3 on a pretreated substrate using the composite powder as raw material. The preparation of the composite powder by using the conventional spray drying method comprises: ball milling the ceramic matrix and the high-temperature-resistant absorber to obtain a mixed slurry; and granulating the mixed slurry to obtain the composite powder. The preparation of the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient according to any one of claims 1-3 on the pretreated substrate comprises: forming the high-temperature-resistant wave-absorbing coating with low thermal expansion coefficient on the substrate by using a plasma spraying method, a flame spraying method or a laser cladding method. ​ ​ ​ 4. A method for preparing a high-temperature resistant wave-absorbing coating with low thermal expansion coefficient, characterized in that, ​ ​ ​ 5. The method of claim 4, wherein the method further comprises the step of: ​ ​ ​ ​ 6. The method of claim 4, wherein the method is characterized by: ​ ​

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