A high-bond-strength and strong oxygen-barrier environmental barrier coating on the surface of a silicon carbide composite material and a preparation method thereof

Abstract

The present invention discloses a high-bonding-strength and strong oxygen-barrier environmental barrier coating on the surface of a silicon carbide composite material and a preparation method thereof. The environmental barrier coating is sequentially composed of a tantalum metal bonding layer, a tantalum oxide oxygen-barrier layer, a tantalum oxide / tantalate composite transition layer, and a tantalate environmental barrier coating from bottom to top; the bonding strength between the ceramic environmental barrier coating and the silicon carbide composite material substrate is greater than 30 MPa, and the porosity is less than 5%. The preparation method is to spray a tantalum metal bonding layer on the surface of the silicon carbide composite material by atmospheric plasma spraying, and then heat it at 200 °C for 1 h to obtain a tantalum oxide barrier layer with a thickness of less than 1 micron on its surface; then, a tantalum oxide / tantalate composite transition layer and a tantalate environmental barrier coating are sequentially sprayed by atmospheric plasma spraying. The environmental barrier coating on the surface of the silicon carbide composite material prepared by the present invention has the characteristics of strong oxygen barrier and high bonding strength, and can solve the problems of low bonding strength and easy oxidation failure existing in the current silicon carbide coating materials to a certain extent.

Description

Technical Field

[0001] The present invention belongs to the technical field of ceramic coatings, and particularly relates to a high-bonding-strength and strong oxygen-blocking environmental barrier coating on the surface of a silicon carbide composite material and a preparation method thereof. Background Art

[0002] Ceramic environmental barrier coatings are widely used on the surfaces of high-temperature components in the combustion chambers of gas turbines, aero-engines, and hypersonic aircraft to provide isolation from high-temperature air and water vapor. Now, more and more high-temperature parts are made of silicon carbide composite materials. A ceramic environmental barrier coating is prepared on the surface of the silicon carbide composite material part by atmospheric plasma spraying, so as to effectively isolate the air and water vapor in the high-temperature working environment from contacting it, resulting in the oxidation failure of the silicon carbide composite material substrate. However, due to the weak bonding strength (less than 10 MPa) between the ceramic layer and the silicon carbide composite material substrate, the ceramic environmental barrier coating is prone to peeling failure during service. In the prior art, a silicon bonding layer is prepared between the ceramic layer and the substrate to improve the bonding strength between the two (reaching 20 - 30 MPa). However, with the increase in the working temperature of the combustion chamber and the rotation speed of the blades, higher requirements are put forward for the bonding strength of the ceramic coating. The bonding strength between the ceramic coating and the silicon carbide composite material substrate is directly related to its service life. Therefore, how to improve the bonding strength of the ceramic environmental barrier coating on the surface of the silicon carbide composite material is the focus of current research work. In addition, the ceramic environmental barrier coating prepared by atmospheric plasma spraying has a certain porosity (10 - 18%), and high-temperature oxygen and water vapor can contact the silicon carbide composite material through the pores, resulting in its oxidation failure. Preparing an environmental barrier coating material with high density and strong oxygen-blocking characteristics is the key to effectively protecting the silicon carbide composite material substrate. Summary of the Invention

[0003] The first object of the present invention is to provide a high-bonding-strength and strong oxygen-blocking environmental barrier coating on the surface of a silicon carbide composite material, and the second object of the present invention is to provide a preparation method for the high-bonding-strength and strong oxygen-blocking environmental barrier coating on the surface of the silicon carbide composite material.

[0004] The first object of the present invention is achieved as follows. A high-bonding-strength and strong oxygen-blocking environmental barrier coating on the surface of a silicon carbide composite material is composed of a tantalum metal bonding layer, a tantalum oxide oxygen-blocking layer, a tantalum oxide / tantalate composite transition layer, and a tantalate environmental barrier coating from bottom to top in sequence; the bonding strength between the ceramic environmental barrier coating and the silicon carbide composite material substrate is greater than 30 MPa, and the porosity is less than 5%;

[0005] The material of the metal bonding layer is tantalum, the thickness is 150 - 200 μm, and the porosity is less than 2%;

[0006] After the tantalum metal bonding layer is prepared, a tantalum oxide oxygen-blocking layer is formed on its surface by high-temperature oxidation, and the thickness of the tantalum oxide oxygen-blocking layer is less than 1 μm;

[0007] The tantalum oxide / tantalate composite transition layer is composed of Ta 2 O 5 and MTaO 4 wherein the mass fraction of Ta 2 O 5 is 21 - 35%, the coating thickness is 50 - 120 μm, and the porosity is less than 3%;

[0008] The tantalate environmental barrier coating material is MTaO 4 , with a thickness of 60 - 100 μm and a porosity less than 5%;

[0009] Among them, M in the tantalum oxide / tantalate composite transition layer and the high - environmental - barrier coating is the same element, which is one of Sc and Al.

[0010] The second object of the present invention is achieved as follows. The preparation method of the high - bonding - strength and strong oxygen - barrier environmental barrier coating on the surface of the silicon carbide composite material is realized according to the following steps:

[0011] 1) Spraying the tantalum metal bonding layer with the above - mentioned thickness on the surface of the silicon carbide composite material by atmospheric plasma spraying; the process parameters of atmospheric plasma spraying are: the spray gun power is 32 - 40 kW, the spray gun distance is 130 - 260 mm, the gas flow rates of argon and hydrogen are 35 / 12 and 35 / 13 slpm respectively, the feeding speed is 36 - 50 g / min, the spray gun speed is 100 - 300 mm / s, and the spraying time is 1 - 3 min;

[0012] 2) After preparing the tantalum metal bonding layer, keep it at 100 - 200 °C for 1 - 3 h to obtain a tantalum oxide oxygen - barrier layer on its surface;

[0013] 3) Spraying the tantalum oxide / tantalate composite transition layer on the surface of the tantalum oxide oxygen - barrier layer by atmospheric plasma spraying; the process parameters of atmospheric plasma spraying are: the spray gun power is 43 - 50 kW, the spray gun distance is 130 - 200 mm, the gas flow rates of argon and hydrogen are 43 / 12 and 41 / 13 slpm respectively, the feeding speed is 40 - 52 g / min, the spray gun speed is 160 - 300 mm / s, and the spraying time is 2 - 5 min;

[0014] 4) Spraying the tantalate environmental barrier coating on the surface of the tantalum oxide / tantalate composite transition layer by atmospheric plasma spraying; the process parameters of atmospheric plasma spraying are: the spray gun power is 46 - 55 kW, the spray gun distance is 100 - 230 mm, the gas flow rates of argon and hydrogen are 43 / 12 and 41 / 13 slpm respectively, the feeding speed is 45 - 52 g / min, the spray gun speed is 200 - 300 mm / s, and the spraying time is 3 - 6 min.

[0015] Tantalum metal (6.5×10 -6 K -1 ), and silicon carbide composite material (6.0×10 -6 K -1 ), have similar coefficients of thermal expansion. Therefore, there are no problems of cracking and low bonding strength caused by the difference in the coefficients of thermal expansion between the two, and it can effectively improve the bonding strength between the tantalum metal bonding layer and the silicon carbide composite material substrate; by means of high-temperature oxidation, a continuous and dense tantalum oxide oxygen barrier layer is obtained on the surface of the tantalum metal layer. First, it can improve the bonding strength, and second, it can provide excellent oxygen barrier properties;

[0016] Using a composite material composed of tantalum oxide (Ta 2 O 5 ), and MTaO 4 (M = Al, Sc) as the transition layer can obtain a coefficient of thermal expansion close to that of the tantalum oxide oxygen barrier layer, preventing insufficient bonding strength caused by the mismatch of the coefficients of thermal expansion between layers; the tantalum oxide powder used is a nano-powder, and after atmospheric plasma spraying, it can effectively fill the internal voids of the coating and reduce the porosity, further improving the bonding strength and oxidation resistance of the coating;

[0017] The tantalum oxide oxygen barrier layer, tantalum oxide (Ta 2 O 5 ) / MTaO 4 (M = Al, Sc) composite transition layer and the tantalate environmental barrier coating have similar coefficients of thermal expansion and sufficient tantalum elements. Therefore, there will be no situation of mutual diffusion between the three under high-temperature service environments, resulting in coating failure and spalling, and improving the bonding strength of the overall coating system; at the same time, the tantalum oxide oxygen barrier layer, composite transition layer, and tantalate environmental barrier coating materials prepared by the present invention are defect-free lattices, with extremely low oxygen ion transport rates and extremely low porosities, which can further enhance their oxygen barrier properties.

[0018] The environmental barrier coating on the surface of the silicon carbide composite material prepared by the present invention has the characteristics of strong oxygen barrier and high bonding strength, and can, to a certain extent, solve the problems of low bonding strength and easy oxidation failure existing in current silicon carbide coating materials. Description of the Drawings

[0019] Figure 1 is a schematic structural diagram of the environmental barrier coating on the surface of the silicon carbide composite material of the present invention. Among them, 1 - alloy substrate, 2 - tantalum metal bonding layer, 3 - tantalum oxide oxygen barrier layer, 4 - composite transition layer, 5 - tantalate environmental barrier coating;

[0020] Figure 2 is a scanning electron microscope image of the surface morphology of the environmental barrier coatings prepared in Example 1 and Comparative Example 1. Detailed Embodiments

[0021] The present invention will be further described below, but it is not limited to the present invention in any way. Any transformation based on the present invention belongs to the protection scope of the present invention.

[0022] A high-bonding-strength and strong-oxygen-barrier environmental barrier coating on the surface of a silicon carbide composite material according to the present invention is composed of a tantalum metal bonding layer, a tantalum oxide oxygen barrier layer, a tantalum oxide / tantalate composite transition layer, and a tantalate environmental barrier coating from bottom to top; the bonding strength between the ceramic environmental barrier coating and the silicon carbide composite material substrate is greater than 30 MPa, and the porosity is less than 5%.

[0023] The material of the metal bonding layer is tantalum, with a thickness of 150 - 200 μm and a porosity less than 2%.

[0024] After the preparation of the tantalum metal bonding layer, a tantalum oxide oxygen barrier layer is formed on its surface through high-temperature oxidation, and the thickness of the tantalum oxide oxygen barrier layer is less than 1 μm.

[0025] The tantalum oxide / tantalate composite transition layer is composed of Ta 2 O 5 and MTaO 4 wherein the mass fraction of Ta 2 O 5 is 21 - 35%, the coating thickness is 50 - 120 μm, and the porosity is less than 3%.

[0026] The material of the tantalate environmental barrier coating is MTaO 4 , with a thickness of 60 - 100 μm and a porosity less than 5%.

[0027] Among them, M in the tantalum oxide / tantalate composite transition layer and the high environmental barrier coating is the same element, which is one of Sc and Al.

[0028] The Ta 2 O 5 is spherical powder with a particle size less than 10 nm.

[0029] The present invention also provides a method for preparing the high-bonding-strength and strong-oxygen-barrier environmental barrier coating on the surface of the silicon carbide composite material, which is realized according to the following steps:

[0030] 1) Spraying the tantalum metal bonding layer with the above thickness on the surface of the silicon carbide composite material by atmospheric plasma spraying; the process parameters of atmospheric plasma spraying are: the spray gun power is 32 - 40 kW, the spray gun distance is 130 - 260 mm, the gas flow rates of argon and hydrogen are 35 / 12 and 35 / 13 slpm respectively, the feeding speed is 36 - 50 g / min, the spray gun speed is 100 - 300 mm / s, and the spraying time is 1 - 3 min.

[0031] 2) After preparing the tantalum metal bonding layer, keep it at 100 - 200 °C for 1 - 3 h to obtain a tantalum oxide oxygen barrier layer on its surface;

[0032] 3) Spray a tantalum oxide / tantalate composite transition layer on the surface of the tantalum oxide oxygen barrier layer by atmospheric plasma spraying; The process parameters of atmospheric plasma spraying are: the spray gun power is 43 - 50 kW, the spray gun distance is 130 - 200 mm, the gas flow rates of argon and hydrogen are 43 / 12 and 41 / 13 slpm respectively, the feeding speed is 40 - 52 g / min, the spray gun speed is 160 - 300 mm / s, and the spraying time is 2 - 5 min;

[0033] 4) Spray a tantalate environmental barrier coating on the surface of the tantalum oxide / tantalate composite transition layer by atmospheric plasma spraying; The process parameters of atmospheric plasma spraying are: the spray gun power is 46 - 55 kW, the spray gun distance is 100 - 230 mm, the gas flow rates of argon and hydrogen are 43 / 12 and 41 / 13 slpm respectively, the feeding speed is 45 - 52 g / min, the spray gun speed is 200 - 300 mm / s, and the spraying time is 3 - 6 min.

[0034] In step 3, before spraying, mix tantalum oxide powder and tantalate spherical powder by ball milling. The ball milling speed is 200 - 600 rpm, and the ball milling duration is 3 - 8 h.

[0035] Example 1

[0036] 1. Prepare a tantalum metal bonding layer on the surface of the silicon carbide composite material by atmospheric plasma spraying. The process parameters of atmospheric plasma spraying are: the spray gun power is 40 kW, the spray gun distance is 130 mm, the gas flow rates of argon and hydrogen are 35 / 12 and 35 / 13 slpm respectively, the feeding speed is 50 g / min, the spray gun speed is 300 mm / s, and the spraying time is 1 min;

[0037] 2. Keep the tantalum metal bonding layer prepared by spraying in the atmospheric environment at 200 °C for 1 h, and a dense tantalum oxide barrier layer with a thickness of 0.05 microns can be obtained on its surface;

[0038] 3. Prepare a tantalum oxide / tantalate composite transition layer on the surface of the tantalum oxide barrier layer by atmospheric plasma spraying. When spraying by atmospheric plasma, the process parameters are: the spray gun power is 43 kW, the spray gun distance is 130 mm, the gas flow rates of argon and hydrogen are 43 / 12 and 41 / 13 slpm respectively, the feeding speed is 52 g / min, the spray gun speed is 300 mm / s, and the spraying time is 2 min;

[0039] 4. A tantalate environmental barrier coating is prepared on the surface of the tantalum oxide / tantalate composite transition layer by atmospheric plasma spraying. During atmospheric plasma spraying, the process parameters are as follows: the spray gun power is 46 kW, the spray gun distance is 130 mm, the gas flow rates of argon and hydrogen are 43 / 12 and 41 / 13 slpm respectively, the feeding speed is 52 g / min, the spray gun speed is 300 mm / s, and the spraying time is 3 min.

[0040] Examples 2 - 6, Comparative Examples 1 - 4 are different from Example 1 in terms of spraying process parameters, the thickness of the metallic tantalum bonding layer, the mass fraction of tantalum oxide spherical powder in the composite transition layer, the coating thickness, the type of M element, and the thickness of the tantalate coating. Due to the change in the preparation process, the porosity of each layer of the coating shows a certain fluctuation, but it is within the set range. The porosity of each layer of the coating is obtained according to its scanning electron microscope measurement. By scanning electron microscope testing, the area of the coating and the pores and cracks therein are measured in a certain area, and the porosity of each coating can be obtained according to the ratio of the total area to the area of pores + cracks; from the scanning electron microscope images of the surface morphology of the environmental barrier coatings prepared in Example 1 and Comparative Example 1 ( Figure 1 ), it can be seen that the coating prepared in Example 1 is dense, with very few surface pores and cracks, and a low porosity (1.1%); Comparative Example 1 has more surface pores and cracks and a high porosity (12.3%). The specific situations are shown in Tables 1 and 2.

[0041] Table 1 Coating thickness and mass fraction of tantalum oxide in the transition layer prepared in Examples 1 - 6 and Comparative Examples 1 - 4

[0042]

[0043] Table 2 Coating bonding strength, oxidation weight gain rate, and porosity of each layer of the coatings prepared in Examples 1 - 6 and Comparative Examples 1 - 4

[0044]

[0045] Detection Examples Determination of the bonding strength and oxygen barrier performance of the coatings prepared in Examples 1 - 6 and Comparative Examples 1 - 4

[0046] 1. Determination of coating bonding strength

[0047] The bonding strength of the coating is determined by the tensile method. Specifically, the silicon carbide substrate with the coating is bonded to the upper and lower ends of the tensile testing machine using strong glue, and the tensile force is continuously increased. When the entire coating is completely separated and peeled off from the substrate, the ratio of the tensile force used to the area of the silicon carbide substrate is the bonding strength of the coating;

[0048] 3. Detection of the oxygen barrier performance of the coating

[0049] The front sides of the coatings prepared in Examples 1-6 and Comparative Examples 1-4 were heated with an acetylene flame, heated to 1300 °C within 20 s, and kept warm for 1 minute. The silicon carbide substrate was oxidized and weight-reduced under the action of the acetylene flame and air. The greater the reduced weight, the worse its oxidation resistance.

[0050] The test results are shown in Table 2.

[0051] Result analysis: The difference between Comparative Example 1 and Example 1 is that nano-tantalum oxide is not added as the second phase in the transition layer, resulting in no intermediate layer for thermal expansion coefficient and bonding strength transition between the tantalum oxide oxygen barrier layer and the surface environmental barrier coating, leading to a decrease in the coating bonding strength, only 16 MPa. At the same time, there is no molten tantalum oxide to fill the internal gaps and holes of the coating, resulting in the failure of the coating oxidation resistance. The oxidation weight loss of Examples 1-6 is less than 3%, while that of Comparative Example 1 reaches 10%. In addition, the mismatch between the thermal expansion coefficients of the surface tantalate environmental barrier coating and the bonding layer causes tensile stress during high-temperature assessment, and a large number of cracks appear on the coating surface, resulting in the porosity exceeding 10%.

[0052] The difference between Comparative Example 2 and Example 1 is that the thickness of the transition layer is larger, reducing the bonding strength of the coating system. The bonding strengths of Examples 1-6 all exceed 40 MPa, while that of Comparative Example 2 is only 22 MPa; the difference between Comparative Example 3 and Example 1 is that the bonding layer is too thin, resulting in a decrease in the coating bonding strength, only 20 MPa; the difference between Comparative Example 4 and Example 1 is that the porosity of the transition layer is larger, resulting in insufficient oxidation resistance, so the oxidation weight loss reaches 10.2%.

[0053] In summary, the coating prepared by the present invention has the characteristics of strong oxygen barrier and high bonding strength, and can solve the problems of low bonding strength and easy oxidation failure existing in the current silicon carbide coating materials to a certain extent.

Claims

1. A high-bonding-strength and strong-oxygen-barrier environmental barrier coating on the surface of a silicon carbide composite material, characterized in that, it is composed of a tantalum metal bonding layer (2), a tantalum oxide oxygen barrier layer (3), a tantalum oxide / tantalate composite transition layer (4), and a tantalate environmental barrier coating (5) from bottom to top on the surface of the silicon carbide composite material substrate; the preparation method is realized according to the following steps: 1) Spraying a tantalum metal bonding layer (2) on the surface of the silicon carbide composite material substrate by atmospheric plasma spraying; the process parameters of atmospheric plasma spraying are: the spray gun power is 32 - 40 kW, the spray gun distance is 130 - 260 mm, the gas flow rates of argon and hydrogen are 35 / 12 and 35 / 13 slpm respectively, the feeding speed is 36 - 50 g / min, the spray gun speed is 100 - 300 mm / s, and the spraying time is 1 - 3 min; the material for preparing the tantalum metal bonding layer (2) is tantalum, the coating thickness is 150 - 200 μm, and the porosity is less than 2%; 2) After keeping the prepared tantalum metal bonding layer (2) at 100 - 200 °C for 1 - 3 h, a tantalum oxide oxygen barrier layer (3) is obtained on its surface, and the thickness of the tantalum oxide oxygen barrier layer (3) is less than 1 μm; 3) A tantalum oxide / tantalate composite transition layer (4) is sprayed on the surface of the tantalum oxide oxygen barrier layer (3) by atmospheric plasma spraying; the process parameters of atmospheric plasma spraying are as follows: the spray gun power is 43 - 50 kW, the spray gun distance is 130 - 200 mm, the gas flow rates of argon and hydrogen are 43 / 12 and 41 / 13 slpm respectively, the feeding speed is 40 - 52 g / min, the spray gun speed is 160 - 300 mm / s, and the spraying time is 2 - 5 min; the materials for preparing the tantalum oxide / tantalate composite transition layer (4) are Ta 2 O 5 and MTaO 4 wherein the mass fraction of Ta 2 O 5 is 21 - 35%, Ta 2 O 5 is spherical powder with a particle size less than 10 nm, the coating thickness is 50 - 120 μm, and the porosity is less than 3%; 4) A tantalate environmental barrier coating (5) is sprayed on the surface of the tantalum oxide / tantalate composite transition layer (4) by atmospheric plasma spraying; the process parameters of atmospheric plasma spraying are as follows: the spray gun power is 46 - 55 kW, the spray gun distance is 100 - 230 mm, the gas flow rates of argon and hydrogen are 43 / 12 and 41 / 13 slpm respectively, the feeding speed is 45 - 52 g / min, the spray gun speed is 200 - 300 mm / s, and the spraying time is 3 - 6 min; the material for preparing the tantalate environmental barrier coating (5) is MTaO 4 , the coating thickness is 60 - 100 μm, and the porosity is less than 5%; the M in the tantalum oxide / tantalate composite transition layer (4) and the MTaO 4 in the tantalate environmental barrier coating (5) is the same element, which is one of Sc and Al; the bonding strength between the high bonding strength and strong oxygen barrier environmental barrier coating and the silicon carbide composite material substrate is greater than 40 MPa, and the oxidation weight loss is less than 3%.

2. The high-bonding-strength and strong-oxygen-barrier environmental barrier coating on the surface of a silicon carbide composite material according to claim 1, characterized in that, in step 3), before spraying, the tantalum oxide powder and the tantalate spherical powder are ball-milled and mixed, the ball-milling speed is 200 - 600 rpm, and the ball-milling duration is 3 - 8 h.

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