A phase-stable defect Al(Ta 1-x A x )O 4-0.5x Environmental barrier coating ceramic material and method of making same

Abstract

The application relates to the technical field of high-temperature protective coating, and particularly discloses a phase-stable defect type Al(Ta 1‑x A x )O 4‑0.5x environment barrier coating ceramic material and a preparation method thereof. The application discloses a phase-stable defect type Al(Ta 1‑x A x )O 4‑0.5x environment barrier coating ceramic material and a preparation method thereof. The preparation method comprises the following steps: S1, mixing alumina, tantalum oxide Ta2O5 and IVB group element oxide; S2, ball milling, drying and sieving the raw material powder to obtain a mixed powder; S3, performing hot-press sintering on the mixed powder to obtain a ceramic block; and S4, performing annealing treatment on the ceramic block. The obtained material has a high-temperature expansion coefficient highly matched with a base body, low thermal conductivity, high hardness and excellent high-temperature phase stability, which ensures the thermal shock resistance and high-speed particle impact resistance of the coating in a large temperature range service environment, and prolongs the service life of the coating.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of high-temperature protective coating, and particularly relates to a phase-stable defect type Al(Ta 1-x A x )O 4-0.5x Environmental barrier coating ceramic material and method for preparing the same. BACKGROUND

[0002] With the development of science and technology, the research on the aero-engine is also more in-depth, and improving the thrust-to-weight ratio of the aero-engine is the current research focus, the method for improving the thrust-to-weight ratio of the aero-engine includes reducing the structural weight and improving the use temperature. Light-weight high-temperature ceramic matrix composites (CMCs) are expected to be used as high-temperature structural materials in the aerospace field to replace high-temperature nickel-based alloys due to their low density, oxidation resistance, high specific strength, and excellent high-temperature mechanical stability and chemical resistance (the density of the ceramic matrix composite is 1 / 3-1 / 4 of that of the high-temperature nickel-based alloy, the service temperature is increased by about 200 DEG C than that of the high-temperature nickel-based alloy, and the strength is also much higher than that of the nickel-based alloy). At present, the main continuous fiber reinforced ceramic matrix composites researched are carbon fiber reinforced silicon carbide (C f / SiC), silicon carbide fiber reinforced silicon carbide (SiC f / SiC) and oxide / oxide ceramic matrix composites.

[0003] However, the service environment of the aero-engine is extremely harsh, and is often accompanied by corrosion media such as water vapor and high-temperature molten salt, especially in the high-temperature water-oxygen environment, which can rapidly erode the dense thermal growth oxide (TGO) passivation layer, and generate volatile oxides mainly in the form of Si(OH)4. The high-temperature water-oxygen intolerance of the rapid decline of the high-temperature mechanical properties of the CMCs greatly shortens the service time of the CMCs, and the environmental barrier coating technology is one of the most effective ways to protect the composite matrix structure and prolong the service life of the composite.

[0004] The environmental barrier coating refers to a protective coating prepared on the hot end surface of the composite material under the complex environment in the engine, and the coating can establish an isolation barrier in the ceramic matrix composite and the high-temperature corrosion environment of the engine to improve the service time of the ceramic matrix composite.

[0005] Traditional environmental barrier coating materials have high SiO2 activity and poor chemical compatibility, so it is difficult to meet the protection requirements of active ceramic matrix composites. At present, the materials widely used in the research of environmental barrier coating for ceramic matrix composites are mullite, BSAS and rare earth silicate, etc. Mullite has low thermal conductivity and oxygen permeability, and the thermal expansion coefficient is close to that of silicon carbide, but the high-temperature water vapor erosion resistance is weak. BSAS coating is generally used in combination with mullite, and has higher reliability and longer service life than mullite, but still has the problem of rapid reduction of service life in high-temperature water vapor environment. The performance of rare earth silicate is better in terms of high-temperature stability and thermal expansion coefficient, but the environmental barrier coating made of rare earth silicate is not stable at high temperature, which causes the coating to fail prematurely.

[0006] Although the environmental barrier coating products that have been developed and put on the market still have problems such as service life and instability at high temperature, compared with diffusivity coating, cladding coating and thermal barrier coating, some of their performances have unique advantages, and they are still one of the important development directions of high-temperature protective coating in the future. With the continuous expansion of China's aerospace industry, the demand for high-temperature protective coating will continue to grow, and the importance of environmental barrier coating research and production is increasingly prominent, and it is urgent to find an environmental thermal barrier coating material with good performance. SUMMARY

[0007] The present application aims to provide a phase-stable defect type Al(Ta 1-x A x )O 4-0.5x environmental barrier coating ceramic material and a preparation method thereof, which has a thermal expansion coefficient highly adapted to ceramic matrix composites, low thermal conductivity, high hardness and excellent high-temperature phase stability, ensuring the thermal shock resistance and high-speed particle impact performance of the coating in a large temperature range service environment, and prolonging the service life of the coating.

[0008] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is as follows:

[0009] A phase-stable defect type Al(Ta 1-x A x )O 4-0.5x environmental barrier coating ceramic material, comprising mixing alumina, tantalum oxide and Group IVB element oxide into raw material powder according to a molar ratio of 1:1-x:2x, wherein x ranges from 0.01 to 0.2; and then sintering the prepared powder into a phase-stable defect type Al(Ta 1-x A x )O 4-0.5x environmental barrier coating ceramic material by a solid phase sintering method.

[0010] The principle and advantages of the present application are as follows:

[0011] The scheme of the present application adopts the above raw materials and the ratio, first, the stable phase defect type Al(Ta 1-x A x )O 4-0.5x The environmental barrier coating material has a lower thermal expansion coefficient (5.3-6.1*10 -6 K -1 ) and a higher hardness (12.4 GPa) compared with the rare earth silicate Yb2SiO5 (thermal expansion coefficient 7.1-7.4*10 -6 K -1 ) and Lu2SiO5 (thermal expansion coefficient 6.7*10 -6 K -1 ) of the prior art, which makes the material have obvious advantages in the application of the environmental barrier coating, ensures the thermal shock resistance and high-speed particle impact performance of the coating in a large temperature range service environment, and greatly prolongs the service life of the coating under the simultaneous improvement of the comprehensive performance of the environmental barrier coating of the present scheme.

[0012] In addition, with the increase of the oxygen vacancy concentration of the material, the pinning effect exists in the system, which reduces the diffusion coefficient of oxygen ions in the material and greatly inhibits the growth rate of the internal TGO layer; secondly, according to the DSC test, it can also be found that the material has excellent high-temperature phase stability under the combination of the A element (i.e. the IVB group element) and the specific x value, so that the Al(Ta 1-x A x )O 4-0.5x The environmental barrier coating ceramic material maintains the initial bonding strength and high-temperature thermodynamic performance with the ceramic matrix composite, thereby further prolonging the service life of the environmental barrier coating in a complex environment.

[0013] Preferably, as an improvement, the purity of the IVB group element oxide is greater than or equal to 99.99%.

[0014] The present application also provides a preparation method of the stable phase defect type Al(Ta 1-x A x )O 4-0.5x environmental barrier coating ceramic material, comprising the following steps:

[0015] S1, aluminum oxide, tantalum oxide Ta2O5 and IVB group element oxide are weighed according to a molar ratio of 1:1-x:2x, and the three are mixed into raw material powder;

[0016] S2, the raw material powder of S1 is ball milled, then dried, and then sieved to obtain a mixed powder;

[0017] S3, the mixed powder of S2 is subjected to hot-pressing sintering to obtain a ceramic block;

[0018] S4, annealing the ceramic block obtained in S3.

[0019] The above preparation method has the following beneficial effects:

[0020] 1. The oxide of the IVB group element such as titanium oxide TiO2 is used as the dopant, and the structure and performance are stable. In the above preparation method, the oxide dopant is mixed into the raw material powder before wet ball milling. In the high-temperature solid-phase sintering process, the 4-valence IVB group element doping ion is solid-solved into the Ta element position to carry a negative charge, thereby introducing corresponding positive charge oxygen vacancies. The oxygen vacancy clusters are formed in the system, and the oxygen ion conductivity gradually decreases with the decrease of the carrier concentration. The slow diffusion speed in the system provides a low-oxygen environment for the internal matrix. The formation equation of the oxygen vacancy is:

[0021]

[0022] Because the ion radius of the IVB group element in the dopant is smaller than the radius of the host element aluminum, and the atomic mass difference is large, the atomic spacing is small, the atomic interaction force is increased, the thermal expansion coefficient is reduced, the lattice distortion is increased, the phonon scattering is enhanced, the thermal conductivity is reduced, and the solid solution strengthening further improves the hardness of the material. The obtained environmental barrier coating material has more excellent effects on the thermal expansion coefficient and the thermal conductivity.

[0023] 2. The environmental barrier coating ceramic material prepared in the application has a more dense structure than ordinary sintering under hot-pressing sintering. The density of the obtained material is not less than 97%, and the sintered ceramic block can eliminate the internal stress formed in the cooling process after annealing treatment.

[0024] Preferably, as an improvement, S4 is specifically: removing the carbon paper on the surface of the ceramic block obtained in S3, and then annealing at 1050-1200 DEG C to form a phase-stable defect type Al(Ta 1-x A x )O 4-0.5xx environmental barrier coating ceramic material.

[0025] Preferably, as an improvement, when the surface carbon paper is removed, a plurality of sandpapers with gradually decreasing grits are used to polish the surface of the ceramic block in turn. The polishing is performed in a horizontal and vertical alternating polishing manner until the surface of the ceramic block is smooth and defect-free.

[0026] Beneficial effects: this scheme can completely remove the carbon paper coated on the surface of the ceramic block in the high-temperature and high-pressure sintering process, eliminate the influence of surface element interdiffusion, ensure the phase stability of the ceramic material at high temperature, and at the same time process the material performance test in the later stage, improve the detection accuracy and reduce the error.

[0027] Preferably, as an improvement, in the S3, the hot-pressing sintering condition is 2-2.5h of solid-phase sintering at 1600-1750℃, a pressure of 40-70MPa, and a temperature rising rate of 3-5℃ / min.

[0028] Preferably, as an improvement, the S2 is specifically: wet ball milling with anhydrous ethanol as the medium, a ball-to-material volume ratio of (7-9):1, drying after ball milling, and sieving after drying to obtain a mixed powder with a particle size of ≤40μm.

[0029] Preferably, as an improvement, the ball-to-material volume ratio is (7-8.5):1, the ball milling time is 12h-48h, and the ball mill rotation speed is 300-500r / min, so that the raw material powder can be distributed more uniformly and the subsequent reaction can be more sufficient.

[0030] Preferably, as an improvement, the raw material powder synthesized in the S1 has a particle size distribution D50=23-27μm.

[0031] Preferably, as an improvement, the alumina, the tantalum oxide and the Group IVB element oxide in the S1 all need to be dehumidified before being weighed.

[0032] Beneficial effects: The requirements on the particle size and dehumidification of the raw material powder in the present scheme make the raw material powder more easily homogenized during the mixing process, ensure the consistency between the actual powder ratio and the scheme design, and thus realize the accurate control of the oxygen vacancy concentration. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 is the XRD pattern of the present embodiment 1-4 and the comparative example 1.

[0034] Figure 2 is the DSC-TG result of the present embodiment 1-4.

[0035] Figure 3 is the electrical conductivity result of the present embodiment 1-4 and the comparative examples 1-2.

[0036] Figure 4 is the material hardness test result of the present embodiment 1-4 and the comparative examples 1-2. DETAILED DESCRIPTION

[0037] The following will be further described in detail through specific embodiments:

[0038] EMBODIMENT

[0039] A phase-stable defect-type Al(Ta 1-x A x )O 4-0.5xAn environmental barrier coating ceramic material, a raw material powder comprising alumina Al2O3, tantalum oxide Ta2O5 and a dopant, the dopant being an oxide of a Group IVB element, the Al2O3, Ta2O5 and dopant being mixed in a molar ratio of 1:1-x:2x, wherein the dopant has a purity of ≥99.99% and a particle size in the range of 10-40 μm, the raw material powder being processed by dehumidification, ball milling, drying, sieving, hot-press sintering, polishing and heat treatment to obtain a phase-structured stable defective Al(Ta 1-x Tix)O 4-0.5x An environmental barrier coating ceramic material.

[0040] In Example 1, x=0.08 and the dopant is titanium oxide TiO2.

[0041] The above phase-structured stable defective Al(Ta 0.92 Ti 0.08 )O 3.96 A method for preparing an environmental barrier coating ceramic material, comprising the following steps:

[0042] S1. Using aluminum foil, alumina Al2O3, tantalum oxide Ta2O5 and a dopant powder titanium oxide TiO2 are weighed in a molar ratio of 1:0.92:0.16, a total of 500 g, with a particle size distribution D50=23-27 μm, and the overall characteristics of normal distribution, and all the powders are dehumidified at 900°C before weighing.

[0043] S2. Wet ball milling is performed by preferentially injecting 500-1000 ml of anhydrous ethanol, with a raw material ratio of 2-3:1, a ball milling time of 24 h, a ball milling machine speed of 350 r / min, a ball-to-material ratio of 7:1, and a mixed material drying time of 90°C for 24 h. The dehumidified powder is sieved through a 400 mesh sieve, and the obtained mixed powder has a particle size of ≤38 μm.

[0044] S3. Hot-press sintering is performed at 1600°C for 2 h, with a pressure of 40 MPa and a heating rate of 3°C / min, and the furnace is cooled to room temperature, and the sample is taken after pressure relief, to obtain a dense ceramic block;

[0045] S4. The carbon paper on the surface of the dense ceramic block is peeled off, and the surface is polished by alternately using 280, 1000 and 1500 mesh sandpaper, and the surface is smooth and defect-free. The annealing process is performed for 3 h, with a heating rate of 2°C / min to 1100°C, and then a cooling rate of 10°C / min, to finally form a phase-structured stable defective Al(Ta 0.92 Ti 0.08 )O 3.96 An environmental barrier coating ceramic block material.

[0046] The annealed Al(Ta 0.92 Ti 0.08 )O 3.96The environmental barrier coating ceramic bulk material is cut and polished, such as Figure 1 The composition and phase structure of the environmental barrier coating ceramic material prepared in the embodiment are analyzed according to the XRD diffraction pattern shown in Table 1 and Figure 2 It can be seen from the results of the thermal mechanical analyzer and DSC tests that the material prepared in the embodiment has a thermal expansion coefficient suitable for ceramic matrix composite materials and excellent phase stability at high temperatures, and the impedance value of the sample at 600-900 ℃ is tested by an alternating current impedance tester, and the conductivity is calculated, and the results are shown in Table 1 or the accompanying drawings. Figure 3 The hardness test results of the sample are shown in Table 1 or the accompanying drawings. Figure 4

[0047] Example 2

[0048] The difference from Example 1 is that the molar ratio x of the dopant is 0.12, the ball milling time is 30 h, the ball mill speed is 500 r / min, and the phase-stable defect type Al(Ta 0.88 Ti 0.12 )O 3.94 The environmental barrier coating ceramic bulk material, the XRD, TMA, DSC and conductivity results are shown in Table 1 or the accompanying drawings.

[0049] Example 3

[0050] The difference from Example 1 is that the dopant is zirconium oxide HfO2, the molar ratio x is 0.04, the ball milling time is 12 h, the ball mill speed is 400 r / min, the hot-pressing sintering temperature is 1700 ℃, and the pressure is 60 MPa, and the phase-stable defect type

[0051] Al(Ta 0.96 Hf 0.04 )O 3.98 The environmental barrier coating ceramic bulk material, the XRD, TMA, DSC and conductivity results are shown in Table 1 or the accompanying drawings.

[0052] Example 4

[0053] The difference from Example 1 is that the dopant is zirconium oxide ZrO2, the molar ratio x is 0.18, the ball milling time is 30 h, the ball mill speed is 500 r / min, the hot-pressing sintering temperature is 1750 ℃, and the pressure is 70 MPa, and the phase-stable defect type

[0054] Al(Ta 0.82 Zr 0.18 )O 3.91 The environmental barrier coating ceramic bulk material, the XRD, TMA, DSC and conductivity results are shown in Table 1 or the accompanying drawings.

[0055] Comparative Example 1 ​

[0056] The difference from Example 1 is that there is no dopant, and finally a defect-free tantalate ceramic bulk material is formed, and the XRD, TMA and conductivity results are shown in Table 1 or the figure.

[0057] Comparative Example 2

[0058] The common environmental barrier coating material Yb2SiO5 is used as a control group, and the thermal expansion coefficient is shown in Table 1, and the XRD, TMA and conductivity results are shown in Table 1 or the figure.

[0059] Comparative Example 3

[0060] YSZ is used as a control group, and the thermal expansion coefficient is shown in Table 1.

[0061] Table 1 Thermal expansion coefficient table of ceramic matrix composite material, example and comparative example

[0062]

[0063] In combination with Table 1, compared with Comparative Examples 1-2, the material of the present application has a thermal expansion coefficient more suitable for the ceramic matrix composite material, so that it has a more excellent thermal shock resistance as an environmental barrier coating

[0064] In combination with Figure 1 The defect-free tantalate ceramic bulk material of Example 1-4 and Comparative Example 1 without dopant obtained by the present application is completely consistent with the standard card, which shows that the dopant of the Group IVB element oxide used in the present application can completely enter the host crystal lattice, and there is no impurity, which shows that the environmental barrier coating ceramic material formed by the synthetic material and the preparation method of the present application has a single phase structure belonging to the monoclinic system, and no second phase is generated; through in-depth research and analysis, it is found that the polycrystalline state of the existing rare earth silicate is an unfavorable factor for it as an environmental barrier coating, and the conversion between different crystal states of the rare earth silicate at high temperature will cause volume difference, thereby generating internal stress and further causing crack propagation. The synthetic material of the present application is monoclinic, has a single phase structure, and is therefore very stable at high temperature, can meet the thermal shock resistance and high-speed particle impact performance of the coating, so that the service life of the environmental barrier coating material prepared by the present application is high in a large temperature range.

[0065] According to Figure 2 the DSC-TG results, it can be found that the defect-free environmental barrier coating material prepared by the present application has no obvious mass change and phase change at 25-1400℃, and has a very stable phase structure in the temperature range of 25-1400℃, compared with the polycrystalline state of the rare earth silicate and the phase change of YSZ at 1200℃, the present application provides a good material basis for the stable service of the environmental barrier coating at high temperature environment.

[0066] In combination with Figure 3From the embodiment 1 and the embodiment 2, it can be known that under the same dopant, with the increase of the dopant content, the oxygen vacancy concentration is improved, but the change rate of the oxygen vacancy conductivity is negatively increased, because with the increase of the oxygen vacancy concentration, defect association occurs in the system, and the association between the vacancies causes part of the oxygen vacancies to be unable to serve as the oxygen ion transmission path, and further reduces the conductivity of the material. And compared with the control group, the environmental barrier coating ceramic material of the application can effectively reduce the conductivity of the material.

[0067] In addition, the material preparation method of the embodiment adopts one-time sintering forming through the pre-calculated molar ratio, so that the obtained material has a high expansion coefficient, high hardness and excellent high-temperature phase stability, which realizes all-round optimization of the environmental barrier coating material in physical performance, guarantees the thermal shock resistance and high-speed particle impact performance of the coating in a large temperature service environment, and prolongs the service life of the coating. In addition, the entire preparation process of the application is very simple, and the cost of the dopant is lower than that of rare earth silicate, which is easy to industrialize.

[0068] The above is only an embodiment of the application, and the specific technical solutions and / or common knowledge of the scheme are not described in detail. It should be noted that for those skilled in the art, without departing from the technical solutions of the application, a number of modifications and improvements can be made, which should also be considered as the protection scope of the application, which will not affect the effect and practicality of the application. The protection scope of the present application should be subject to the content of its claims, and the specific implementation mode and the like in the specification can be used to explain the content of the claims.

Claims

1. A phase-stable, defect Al(Ta 1-x A x )O 4-0.5x environmentally barrier coated ceramic material, characterized by: The application relates to a method for preparing a stable defect type Al(Ta 1-x A x )O 4-0.5x environmental barrier coating ceramic material The Group IVB element oxide is one of TiO2, ZrO2 and HfO2, and the environmental barrier coating ceramic material has no phase transition at 25-1400℃.

2. A phase-stable faulted Al(Ta 1-x A x )O 4-0.5x environmental barrier coating ceramic material, characterized in that, The purity of the Group IVB element oxide is ≥99.99%.

3. A phase-stable, defect Al(Ta 1-x A x )O 4-0.5x environmental barrier coating ceramic material, characterized in that, The method comprises the following steps: S1, taking alumina, tantalum oxide Ta2O5 and Group IVB element oxide according to a molar ratio of 1:1-x:2x, and mixing the three to form raw material powder; the Group IVB element oxide is one of TiO2, ZrO2 and HfO2; S2, ball milling the raw material powder of S1, then drying, and then sieving to obtain mixed powder; S3, hot-press sintering the mixed powder of S2 to obtain a ceramic block; the hot-press sintering is performed at 1600-1750℃ for 2-2.5h under a pressure of 40-70Mpa; S4, annealing the ceramic block obtained in S3.

4. A phase-stable faulted Al(Ta 1-x A x )O 4-0.5x Method for producing an environmental barrier coating ceramic material, characterized in that, The S4 is specifically: removing the carbon paper on the surface of the ceramic block obtained in S3, and then performing annealing treatment at 1050-1200°C to form a phase-stable defective Al(Ta 1-x A x )O 4-0.5xx environmental barrier coating ceramic material.

5. A phase-stable faulted Al(Ta 1-x A x )O 4-0.5x Method for producing an environmental barrier coating ceramic material, characterized in that, When removing the surface carbon paper, a plurality of sandpapers with gradually decreasing grits are used to polish the surface of the ceramic block in turn, and a horizontal and vertical polishing method is adopted during polishing until the surface of the ceramic block is smooth and defect-free.

6. A phase-stable faulted Al(Ta 1-x A x )O 4-0.5xx Method for producing an environmental barrier coating ceramic material, characterized in that, In S3, the heating rate in the hot-press sintering is 3-5℃ / min.

7. A phase-stable faulted Al(Ta 1-x A x )O 4-0.5x Method for producing an environmental barrier coating ceramic material, characterized in that, In S2, wet ball milling is performed with anhydrous ethanol as medium, and the ball-to-material volume ratio is (7-9):1; after ball milling, drying is performed, and then sieving is performed to obtain mixed powder with a particle size ≤40μm.

8. A phase-stable faulted Al(Ta 1-x A x )O 4-0.5x Method for producing an environmental barrier coating ceramic material, characterized in that, The ball-to-material volume ratio is (7-8.5):1, the ball milling time is 12h-48h, and the ball mill rotation speed is 300-500r / min.

9. A phase-stable faulted Al(Ta 1-x A x )O 4-0.5x Method for producing an environmental barrier coating ceramic material, characterized in that, The raw material powder synthesized in S1 has a particle size distribution D50=23-27μm.

10. A phase-stable faulted Al(Ta 1-x A x )O 4-0.5x Method for producing an environmental barrier coating ceramic material, characterized in that, In S1, the alumina, tantalum oxide and Group IVB element oxide all need to be dehumidified before being taken.

Images