Oxidation barrier materials and processes for ceramic substrate composites

Abstract

A method of applying an environmental barrier coating and an environmental barrier coating. The method includes applying a high apparent density powder via a high temperature, high velocity (HTHV) process. The high apparent density powder includes at least one of a rare earth silicate, a mullite, or an alkali silicate.

Description

[Technical Field]

[0001] background 1. Field of Invention Materials and processes for manufacturing an airtight environmental barrier coating (EBC) to avoid fracture by thermally grown SiO2 oxide (TGO). [Background technology]

[0002] 2. Consideration of background information To protect ceramic substrate composites (CMCs) from oxidation and steam attack, environmental barrier coatings (EBCs) are applied on Si-based CMCs. Currently, existing EBC systems include a Si bond coat and a rare earth disilicate intermediate layer and / or topcoat. The rare earth disilicate has a coefficient of thermal expansion (CTE) that closely matches that of the underlying SiC substrate. In high-temperature gas turbine engine environments, steam penetrates microcracks, resulting in accelerated oxidation of the Si bond coat and causing EBC fracture when the thermally grown oxide (TGO) reaches a threshold thickness. Since this fracture of environmental barrier coatings (EBCs) induced by thermally grown SiO2 oxide (TGO) is a significant EBC failure mode, controlling the TGO growth rate is crucial to improve coating durability.

[0003] Traditionally, air plasma spraying (APS) processes are typically used to deposit rare earth silicate coatings. However, in APS processes, particle velocities are generally lower (<200 m / s), which causes significant SiO2 loss and results in the inclusion of rare earth monosilicate phases in the deposited disilicate coating. Monosilicates generally have a CTE (= 4.1 × 10⁻¹⁰) of disilicates. -6 CTE (=7.5 × 10) is much larger than / ℃. -6Because of its CTE (Cold Temperature), including a monosilicate phase with a larger CTE in the disilicate coating leads to cracking during thermal cycling. The presence of such cracks in the coating provides a transport pathway for oxidative species to the silicon bond coat, resulting in rapid TGO growth and premature failure of the coating. Therefore, controlling the phase composition in the disilicate coating is crucial to achieving highly durable EBCs. In addition, conventional APS EBCs always have porosity and microcracks, which promote the diffusion of oxidative substances through these microcracks, accelerating the oxidation of the silicon bond coat and thus reducing the durability of the EBC. [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] overview To reduce the TGO growth rate, an airtight oxidation barrier layer is required to prevent the diffusion of oxidizing substances onto the silicon bond coat surface. [Means for solving the problem]

[0005] The embodiments relate to materials and processes for producing airtight EBCs. Such deposited airtight EBCs exhibited excellent oxidation resistance in high-temperature steam environments, showing little to no TGO growth after 410 hours of exposure in a steam environment at 1316°C.

[0006] The embodiments relate to the use of exemplary high apparent density feedstock as an EBC material or raw material, where “high apparent density” is defined as greater than 1.8 g / cc according to ASTM B212. The exemplary high apparent density powder may have a solid ceramic core, which is desired to prevent SiO2 loss in the coating process. Furthermore, the exemplary EBC is deposited using a high temperature (all or average measured particle temperatures are above the melting temperature of the material composition), high speed (average measured particle velocity is 200 m / s or more) coating process (HTHV). The particle velocity in the plasma jet in this HTHV process is greater than 200 m / s, preferably 400 m / s to 800 m / s, in order to produce a high-density coating. As a non-limiting example, the exemplary high apparent density powder according to the embodiments may be a Yb2Si2O7 feedstock or powder.

[0007] According to one embodiment, an HTHV coating formed using an exemplary high apparent density powder showed almost no TGO growth after exposure to a vapor environment at 1316°C for 410 hours.

[0008] High-temperature fast (HTHV) thermal spraying processes can be used, as a non-limiting example, to deposit exemplary coatings on substrates, such as rare-earth silicate EBC deposition, preferably disilicate EBC deposition. For example, the higher particle velocities (>200 m / s) achieved by HTHV application processes are greater than those available in conventional APS processes, resulting in the deposition of high-density, microcrack-free EBCs. This high-density microstructure provides a diffusion barrier to oxidizing substances (i.e., vapor, oxygen) and thus prevents oxidation of the silicon bond coat. Furthermore, experimental results demonstrated that exemplary coatings fabricated using the high-temperature fast (HTHV) process showed little TGO growth after 410 hours of exposure at 1316°C in a vapor environment. As a non-limiting example, exemplary rare-earth silicate coatings could be Yb2Si2O7 / Si coatings.

[0009] To prevent significant SiO2 loss of silica-containing molten particles (such as rare earth silicates, preferably disilicates and mullite) in plasma jets, a high apparent density powder feed material, or a feed material powder prepared using a high apparent density powder as a feed material, is preferred. The high apparent density powder has a solid ceramic core, which is desired to prevent SiO2 loss in the coating process. A preferred apparent density is greater than 1.8 g / cc, preferably greater than 2.2 g / cc.

[0010] High apparent density powder, or powder prepared using high apparent density powder, has a particle size distribution of 11 μm to 125 μm, preferably 11 μm to 62 μm.

[0011] When using high apparent density powder feed materials, for example, only about 6.0 v% of the Yb2SiO5 phase is present in the HTHV-deposited Yb2Si2O7 coating, which is advantageous for matching the CTE of the coating with the CTE of the substrate.

[0012] High apparent density powders can be produced using the following process: 1. Melting / crushing; 2. Aggregation and sintering; and / or 3. Aggregation and plasma densification.

[0013] The high-temperature, high-velocity thermal spraying process may be any of the following processes and can be operated in an air or vacuum atmosphere. 1. High-temperature, high-speed atmosphere plasma spraying process; 2. High-temperature, high-speed vacuum plasma spraying process; or 3. High-temperature, high-speed oxygen fuel spraying process.

[0014] In any of the above processes, the particles in flight have an average velocity greater than 200 m / s, preferably greater than 400 m / s. Furthermore, in the high-temperature, high-velocity vacuum plasma spraying process, the vacuum is in the range of 1 mbar to 100 mbar.

[0015] The high apparent density powder feedstock according to an embodiment may have the following chemical properties: 1. Rare earth silicate, preferably disilicate, for example RE2Si2O7, wherein RE can be any one of Y, La, Ce, Sc, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu); 2. Mullite; 3. Alkaline silicate (BaO-SrO-Al2O3-SiO2); 4. Any one of the above chemical properties (1 to 3) with an additional 0.5 wt% to 10 wt% of SiO2 mixture. 5. 3.5×10 -6 / k to 6×10 -6 A material having a coefficient of thermal expansion in the range of / k. 6. Any combination of the above.

[0016] Other exemplary embodiments and advantages of the present invention can be ascertained by reviewing the present disclosure and the accompanying drawings.

[0017] Brief Description of the Drawings In the following detailed description, by way of non-limiting example of exemplary embodiments of the present invention, the invention is further described with reference to the following figures, wherein like reference numerals refer to like parts throughout the several views of the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] [Figure 1A] shows an exemplary powder produced using a melt / crush process. [Figure 1B] shows an exemplary powder produced using an agglomeration and sintering process. [Figure 2A] shows agglomerated and sintered powder produced using pre-alloyed molten / crushed powder of the exemplary powder of Figure 1A. [Figure 2B] shows agglomerated and sintered powder produced using pre-alloyed agglomerated and sintered powder of the exemplary powder of Figure 1B. [Figure 3A]This is an SEM image comparing TGO generated from a conventional APS process with TGO generated from the high-temperature, high-speed process according to the present invention. [Figure 3B] This is an SEM image comparing TGO generated from a conventional APS process with TGO generated from the high-temperature, high-speed process according to the present invention. [Figure 4] This table compares the phase composition of an exemplary coating formed using a conventional APS process with the phase composition of an exemplary coating formed using the high-temperature, high-speed process according to the present invention. [Figure 5] An example of the coating according to the present invention is shown. [Modes for carrying out the invention]

[0019] Detailed explanation The details provided herein are for illustrative purposes only, and are intended solely for illustrative purposes of embodiments of the invention, and are presented to provide what is considered to be the most useful and readily understandable explanation of the principles and conceptual aspects of the invention. In this regard, no attempt has been made to provide structural details of the invention in more detail than is necessary for a basic understanding of the invention, and this description, together with the drawings, will make it clear to those skilled in the art how some forms of the invention may actually be carried out.

[0020] To prevent significant SiO2 loss of silica-containing molten particles (such as rare earth silicates, preferably disilicates, and mullite) in plasma jets, a high apparent density powder feed material, or a feed material powder prepared using a high apparent density powder as a feed material, is preferred. The high apparent density powder has a solid ceramic core, which is desired to prevent SiO2 loss in the coating process. A preferred apparent density is greater than 1.8 g / cc, preferably greater than 2.2 g / cc.

[0021] High apparent density powders can be produced using the following process: 1. Melting / crushing; 2. Aggregation and sintering; and / or 3. Aggregation and plasma densification.

[0022] Furthermore, the powders produced according to these processes have a phase purity of over 95%.

[0023] Figures 1A and 1B show high apparent density and high phase purity powders. As shown in Figure 1A, exemplary high apparent density powders, such as rare earth silicates like Yb2Si2O7 powder, can be prepared using a melting / grinding method. Such melting / grinding exemplary Yb2Si2O7 powder has an apparent density greater than 2.2 g / cc. Figure 1B shows a high apparent density powder, such as rare earth silicates like Yb2Si2O7 powder, which can be prepared using an agglomeration and sintering method. Such agglomerated and sintered exemplary Yb2Si2O7 powder has an apparent density greater than 2.4 g / cc. The powders in Figures 1A and 1B have a phase purity greater than 95 v%.

[0024] Figures 2A and 2B show exemplary powders prepared using the above-described high apparent density and high-purity powders (i.e., pre-alloyed powders) as raw materials. Therefore, in addition to directly using the above-described high apparent density and high-phase purity powders as feedstock for thermal spray EBCs, these high apparent density and high-phase purity pre-alloyed powders can also be used as raw materials for the production of relatively lower apparent density powders. In these embodiments, the high apparent density and high-phase purity powders shown in Figures 1A and 1B are ground to a size of less than 10 μm, preferably less than 3 μm, and these finer powders can then be agglomerated and sintered to a desired particle size distribution in the range of 11 μm to 105 μm, preferably 11 μm to 62 μm. Figure 2A shows an exemplary agglomerated and sintered powder prepared using the pre-alloyed molten / ground powder of Figure 1A, for example, a rare earth silicate such as Yb2Si2O7 powder. This agglomerated and sintered exemplary Yb2Si2O7 powder has an apparent density greater than 1.4 g / cc. Figure 2B shows exemplary aggregated and sintered powders, such as rare earth silicates like Yb2Si2O7 coatings, prepared using the pre-alloyed aggregated and sintered powders of Figure 1B. Such exemplary aggregated and sintered Yb2Si2O7 powders have an apparent density greater than 1.6 g / cc. The advantage in these embodiments is that these low apparent density powders, prepared using pre-alloyed, higher apparent density powders as raw materials, can prevent the loss of SiO2 from the particles during the high-temperature thermal spraying process, and can result in high-purity coatings, allowing high-density coatings to be prepared using these low apparent density powders through the HTHV process.

[0025] Furthermore, exemplary high apparent density powders or pre-alloyed exemplary high apparent density powder feedstocks are not limited to the rare earth silicates specified above, but may have the following chemical properties: 1. A rare earth silicate, preferably a disilicate, such as RE2Si2O7, where RE can be any of Y, La, Ce, Sc, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu. 2. Mullite; 3. Alkali silicates (BaO-SrO-Al2O3-SiO2); 4. Any of the above chemical properties (1-3) with an additional 0.5% to 10% by weight of SiO2 mixture. 5.3.5×10 -6 / k~6×10 -6 A material having a thermal expansion coefficient in the range of / k. 6. Any combination of the above.

[0026] The high apparent density powder according to the embodiment can be deposited using a high-temperature, high-velocity (HTHV) thermal spraying process to form an EBC. This HTHV process generates higher particle velocities (>200 m / s) than can be achieved through conventional APS processes, and has been found to deposit high-density EBCs with, for example, <5% porosity and no microcracks. This high-density microstructure provides a diffusion barrier to oxidizing substances (i.e., vapor, oxygen) and thus prevents oxidation of the silicon bond coat. Preferably, the HTHV process generates particle velocities greater than 400 m / s.

[0027] Furthermore, the HTHV thermal spraying process may be any of the following processes and can be operated in an air atmosphere or a vacuum atmosphere. 1. High-temperature, high-speed atmosphere plasma spraying process; 2. High-temperature, high-speed vacuum plasma spraying process; or 3. High-temperature, high-speed oxygen fuel spraying process.

[0028] In any of the above processes, the particles in flight have an average velocity greater than 200 m / s, preferably greater than 400 m / s. Furthermore, in the high-temperature high-speed vacuum plasma spraying process, the vacuum is in the range of 1 mbar to 100 mbar.

[0029] Figures 3A and 3B show SEM images comparing TGO growth after exposure of exemplary EBC systems, such as the Yb2Si2O7 / Si EBC system, to a 90%H2O-10%O2 environment at 1316°C for 410 hours. The SEM image in Figure 3A, showing a Yb2Si2O7 / Si EBC system fabricated using a conventional low-speed APS process, shows approximately 11 μm of TGO thickness between the Si bond coat and the applied Yb2Si2O7 layer. In contrast, the SEM image in Figure 3B, showing a Yb2Si2O7 / Si EBC system fabricated using a high-temperature high-speed (HTHV) process, shows almost no discernible TGO growth between the Si bond coat and the Yb2Si2O7 layer.

[0030] Figure 4 provides a table comparing the phase composition of exemplary coatings fabricated by conventional slow processes, such as rare earth silicate coatings like Yb2Si2O7, with that of exemplary coatings fabricated by high-speed HTHV processes. This table shows that the phase composition of the slow-speed APS-deposited Yb2Si2O7 (disilicate) coating contains approximately 38.0 v% Yb2SiO5 (monosilicate) phase, while the HTHV-deposited Yb2Si2O7 (disilicate) coating contains only approximately 6.0 v% Yb2SiO5 (monosilicate) phase. This monosilicate Yb2SiO5 has a CTE (= 4.1 × 10⁻¹⁰) of disilicate Yb2Si2O7. -6 CTE (=7.5 × 10) is much larger than / ℃. -6 Because of its CTE (CtE) value, the volume reduction of the CTE-monosilicate phase in disilicate coatings deposited by the HTHV process results in high-density, microcrack-free EBCs compared to coatings deposited by the APS process, which induce cracks during thermal cycling to form transport pathways for oxidative species to the silicon bond coat. Therefore, controlling the phase composition in disilicate coatings according to the disclosed embodiments is advantageous for achieving highly durable EBCs. However, it can be understood that some rare earth monosilicates with low CTEs may be advantageously utilized as EBCs via the high-speed HTHV process described above.

[0031] According to the embodiment, Figure 5 shows an example of coating according to the embodiment. The exemplary coating is formed on a substrate such as SiC or Si3N4 having a thickness of more than 40 mils. The exemplary coating may include a deposited bond coat layer on the substrate having a thickness of 2 μm to 500 μm, preferably 25 μm to 200 μm. This bond coat layer may be applied by a thermal spraying process such as APS, HTHV or vacuum plasma spraying, or by a physical vapor deposition process or a chemical vapor deposition process, so as to have a porosity of less than 10%, preferably less than 5%. Furthermore, the bond coat layer may have the following chemical properties: 1. Si; 2. Si oxides, for example, Al2O3, B2O3, HfO2, TiO2, TaO2, BaO, SrO; 3. Silicides, e.g., RESi, HfSi2, TaSi2, Ti2Si2; 4.RE2Si2O7-Si; 5. RE2Si2O7-Silicide; 6. Mullite-Si 7. Mullite-silicides 8. The above combinations. Furthermore, RE can be any of Y, La, Ce, Sc, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu.

[0032] Exemplary coatings may also include an oxide barrier layer formed on the bond coat layer to block oxygen and vapor diffusion. The thickness of the oxide barrier layer deposited on the bond coat layer can be 10 μm to 1000 μm, preferably 50 μm to 250 μm. This oxide barrier layer is applied by an HTHV process to have a porosity of less than 10%, preferably less than 5%, according to the embodiment. Furthermore, the oxide barrier layer may have the following chemical properties: 1. Rare earth silicates, preferably disilicates, such as RE2Si2O7, where RE can be any of Y, La, Ce, Sc, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu; 2. Mullite 3. Alkaline silicate (BaO, SrO, Al₂O₃ or SiO₂); 4. The chemical properties of items 1 to 3, further comprising an additional 0.5 wt% to 10 wt% of SiO₂ mixture; 5. 3.5×10 -6 / k to 6×10 -6 / k, a material having a coefficient of thermal expansion within said range; 6. Any combination of the above.

[0033] It should be noted that the foregoing examples are provided for illustrative purposes only, and shall in no way be construed as limiting the present invention. Although the present invention has been described with reference to exemplary embodiments, it should be understood that the terms used herein are descriptive and illustrative words, rather than words of limitation. Changes may be made, without departing from the scope and spirit of the present invention in its aspects, within the scope of the claims, as presently stated and as amended. While the present invention has been described herein with reference to particular means, materials and embodiments, the present invention is not intended to be limited to the details disclosed herein, but rather the present invention extends to all functionally equivalent structures, methods and uses that fall within the scope of the claims.

Claims

1. A method for applying an environmental barrier coating, This includes applying a high apparent density powder as a raw material via a high-temperature high-speed (HTHV) process, A method for applying an environmental barrier coating, wherein the high apparent density powder has an apparent density greater than 1.8 g / cc and contains at least one rare earth silicate or alkali silicate, or is mullite.

2. The aforementioned alkali silicate is BaO-SrO-Al ２ O ３ -SiO ２ The method according to claim 1, including the method described in claim 1.

3. The aforementioned high apparent density powder contains 0.5% to 10% by weight of SiO ２ The method according to claim 1, further comprising a mixture.

4. The material of the aforementioned high apparent density powder is 3.5 × 10 －６ / k ~ 6 x 10 －６ The method according to claim 1, having a thermal expansion coefficient in the range of / k.

5. The method according to claim 1, wherein the HTHV process generates a particle velocity greater than 200 m / s.

6. The method according to claim 5, wherein the HTHV process generates a particle velocity greater than 400 m / s.

7. The method according to claim 1, wherein the HTHV process comprises one of a high-temperature high-speed atmosphere plasma spraying process, a high-temperature high-speed vacuum plasma spraying process, or a high-temperature high-speed oxygen fuel spraying process.

8. The method according to claim 1, wherein the rare earth silicate includes a disilicate.

9. The disilicate is RE ２ Si ２ O ７ The method according to claim 8, wherein RE can be any one of Y, La, Ce, Sc, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb or Lu.

10. A method for manufacturing an environmental barrier coating, A process for preparing a high apparent density powder, The process includes manufacturing an environmental barrier coating on a Si-containing bond coat layer by a high-temperature, high-speed (HTHV) process using the aforementioned high apparent density powder as a raw material. The aforementioned high apparent density powder has an apparent density greater than 1.8 g / cc. A method for producing an environmental barrier coating comprising at least one of rare earth silicates or alkali silicates, or mullite.

11. The aforementioned alkali silicate is BaO-SrO-Al ２ O ３ -SiO ２ A method for producing an environmental barrier coating according to claim 10, including the method described in claim 10.

12. The aforementioned high apparent density powder contains 0.5% to 10% by weight of SiO ２ A method for producing an environmental barrier coating according to claim 10, further comprising a mixture.

13. The material of the aforementioned high apparent density powder is 3.5 × 10 －６ / k ~ 6 x 10 －６ A method for manufacturing an environmental barrier coating according to claim 10, having a thermal expansion coefficient in the range of / k.

14. The method for producing an environmental barrier coating according to claim 10, wherein the rare earth silicate includes a disilicate.

15. The aforementioned disilicate is RE ２ Si ２ O ７ A method for producing an environmental barrier coating according to claim 14, comprising, wherein RE may be any of Y, La, Ce, Sc, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, or Lu.

16. The method according to claim 1, wherein the apparent density is greater than 2.2 g / cc.

17. The method according to claim 1, wherein the powder of the high apparent density powder has a particle size distribution of 15 μm to 125 μm.

18. The method according to claim 17, wherein the powder of the high apparent density powder has a particle size distribution of 15 μm to 62 μm.

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