A high-temperature-resistant mullite / yttrium silicate / zirconia composite coating and a preparation method thereof

Abstract

This invention provides a high-temperature resistant mullite / yttrium silicate / zirconia composite coating and its preparation method, belonging to the field of high-temperature coating technology. The invention involves mixing mullite, yttrium silicate, zirconia, a binder, and a dispersant, then applying the mixture to a substrate surface using brushing, spraying, or dipping processes, followed by segmented sintering to obtain the high-temperature resistant mullite / yttrium silicate / zirconia composite coating. The preparation method of this invention utilizes brushing, spraying, and dipping techniques, enabling the preparation of coatings of a certain thickness on any complex workpiece surface. It requires no specialized equipment, is simple to operate, and has high production efficiency. This invention employs a two-stage heating sintering process, simplifying the process flow. It eliminates the need for spray granulation and pre-firing feeding, completing the coating in a single sintering step. It has wide applicability, is easy to operate, and can be used for the preparation of large or irregularly shaped parts, showing broad application prospects.

Description

Technical Field

[0001] This invention relates to the field of high-temperature resistant coating technology, and in particular to a high-temperature resistant mullite / yttrium silicate / zirconia composite coating and its preparation method. Background Technology

[0002] Mullite has excellent high-temperature resistance, chemical compatibility, oxidation resistance and thermal conductivity, and is regarded as an important material for environmental barrier coatings. This coating can play a barrier role between engine component materials and harsh service environments, and has become one of the key technologies for the application of fiber reinforced ceramic matrix composites (SiCf / SiC) in hot-end components of high thrust-to-weight ratio aero engines.

[0003] However, at high temperatures, mullite loses silica through volatilization, leaving a porous alumina layer on its surface, which damages the mullite coating structure. Currently, this can be improved by coating with yttrium-stabilized zirconia (YSZ), but the coefficient of thermal expansion of YSZ differs significantly from that of mullite, resulting in insufficient cycle durability. Rare earth silicates, on the other hand, exhibit good resistance to high-temperature corrosion and excellent thermal stability, with yttrium silicate being the most commonly used; however, it still suffers from cracking during thermal cycling.

[0004] There are many methods for preparing coatings, mainly including sputtering, chemical vapor deposition (CVD), spray pyrolysis, and sol-gel methods. Currently, mullite coatings are primarily prepared using atmospheric plasma spraying (APS). This involves spray granulation and solid-state sintering to obtain a feedstock with a size of 100 μm, which is then sprayed onto the sample surface using a plasma arc. However, mullite coatings prepared using this process often contain some metastable phases, which are prone to phase transitions at high temperatures, leading to cracks due to volume changes. Furthermore, the APS production process is complex, requires high-quality raw materials and equipment, and has high production costs.

[0005] Therefore, it is very important to provide a composite coating that is resistant to high-temperature corrosion, has thermal stability, good high-temperature compatibility with other materials, is not prone to cracking, has a simple preparation process, and low production cost. Summary of the Invention

[0006] The purpose of this invention is to provide a high-temperature resistant mullite / yttrium silicate / zirconia composite coating and its preparation method, in order to solve the technical problems of poor high-temperature corrosion resistance, poor cycle durability, poor high-temperature compatibility with other materials, easy cracking, cumbersome production process and high production cost in the prior art.

[0007] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for preparing a high-temperature resistant mullite / yttrium silicate / zirconia composite coating, comprising the following steps:

[0009] (1) Mullite, yttrium silicate, zirconium oxide, binder and dispersant are mixed to obtain a pre-mixed slurry;

[0010] (2) The pre-prepared slurry is coated on the substrate surface to obtain the sample coating;

[0011] (3) The sample coating is sintered in sections to obtain a high-temperature resistant mullite / yttrium silicate / zirconia composite coating.

[0012] Furthermore, in step (1), the particle size of mullite and yttrium silicate is independently 200-500 mesh, and the particle size of zirconium oxide is 100-500 nm.

[0013] Furthermore, in step (1), the adhesive comprises one or more of polyethylene glycol, ethanol, polyvinyl alcohol, and carboxymethyl cellulose;

[0014] The dispersant contains water.

[0015] Furthermore, in step (1), the mass ratio of mullite, yttrium silicate, and zirconium oxide is 60-80:10-30:5-20;

[0016] The mass of the binder is 0.1% to 1% of the total mass of mullite, yttrium silicate, and zirconium oxide;

[0017] The total mass ratio of mullite, yttrium silicate, zirconium oxide, and binder to dispersant is 1:1 to 3.

[0018] Furthermore, in step (1), the mixing is carried out under ball milling, the mixing speed is 200-300 r / min, the mixing time is 6-12 h, and the ball-to-material ratio is 1:2-5.

[0019] Furthermore, in step (2), the method of coating the pre-prepared slurry includes brushing, spraying, or dipping;

[0020] The thickness of the sample coating is 100–500 μm.

[0021] Furthermore, in step (3), the segmented sintering includes two stages: the first stage is heated to 1300-1400℃ at a heating rate of 3-5℃ / min and held for 1-2 hours; the second stage is heated to 1400-1550℃ at a heating rate of 3-5℃ / min and held for 2-3 hours.

[0022] The present invention also provides a method for preparing a high-temperature resistant mullite / yttrium silicate / zirconia composite coating.

[0023] The beneficial effects of this invention are:

[0024] (1) The preparation method of the present invention can prepare a coating of a certain thickness on the surface of any complex workpiece by pre-preparing slurry and using coating methods such as brushing, spraying or dipping. No special equipment is required, the operation is simple and the production efficiency is high.

[0025] (2) The preparation method of the present invention adopts a two-stage heating sintering process. In the first stage, mullite reacts with yttrium silicate to generate a low-temperature eutectic phase, which improves the density of the composite coating. Moreover, under the influence of yttrium silicate and the low-temperature eutectic phase, mullite grains grow into columnar crystals and form a network structure, which improves the stability of the structure. In the second stage, according to different proportions of raw materials, zirconium oxide reacts with the liquid phase in the matrix to form a high-temperature stable phase (YSZ). This not only increases the formation temperature of the eutectic phase and reduces the liquid phase, but also increases the high-temperature stable phase in the structure. Furthermore, the high-temperature stable phase formed by the reaction has a better bonding strength with the matrix grains, which significantly increases the toughness of the coating and improves its thermal shock resistance and structural stability.

[0026] (3) The preparation method of the present invention has a simple process flow, does not require spray granulation and pre-calcination feeding, and can be completed in one sintering. It has wide applicability, is easy to operate, and can be used for the preparation of large or irregular parts, and has broad application prospects. Attached Figure Description

[0027] Figure 1 Here is a cross-sectional SEM image of the composite coating prepared in Example 1;

[0028] Figure 2 The image shows the XRD pattern of the composite coating prepared in Example 2.

[0029] Figure 3 The image shows the XRD pattern of the composite coating prepared in Example 3.

[0030] Figure 4 The image shows the TEM microstructure of the composite coating prepared in Example 4.

[0031] Figure 5 SEM images of the ordinary mullite coating (a) prepared in Comparative Example 1 and the composite coating (b) prepared in Example 5. Detailed Implementation

[0032] This invention provides a method for preparing a high-temperature resistant mullite / yttrium silicate / zirconia composite coating, comprising the following steps:

[0033] (1) Mullite, yttrium silicate, zirconium oxide, binder and dispersant are mixed to obtain a pre-mixed slurry;

[0034] (2) The pre-prepared slurry is coated on the substrate surface to obtain the sample coating;

[0035] (3) The sample coating is sintered in sections to obtain a high-temperature resistant mullite / yttrium silicate / zirconia composite coating.

[0036] In this invention, in step (1), the particle size of mullite and yttrium silicate is independently 200-500 mesh, preferably 200-400 mesh, and more preferably 200-300 mesh; the particle size of zirconium oxide is 100-500 nm, preferably 100-400 nm, and more preferably 100-300 nm.

[0037] In this invention, in step (1), the mass ratio of mullite, yttrium silicate and zirconium oxide is 60-80:10-30:5-20, preferably 65-78:15-25:8-15, and more preferably 70-75:18-20:10-12.

[0038] In this invention, in step (1), the adhesive comprises one or more of polyethylene glycol, ethanol, polyvinyl alcohol and carboxymethyl cellulose, preferably one or more of polyethylene glycol, polyvinyl alcohol and carboxymethyl cellulose, and more preferably polyvinyl alcohol and / or carboxymethyl cellulose.

[0039] The binder comprises 0.1-1% of the total mass of mullite, yttrium silicate, and zirconium oxide, preferably 0.3-0.9%, and more preferably 0.5-0.8%.

[0040] In this invention, the dispersant is preferably water.

[0041] The total mass ratio of mullite, yttrium silicate, zirconium oxide, and binder to dispersant is 1:1 to 3, preferably 1:1.5 to 2.5, and more preferably 1:2.

[0042] In this invention, in step (1), the mixing is carried out under ball milling, the mixing speed is 200-300 r / min, preferably 210-280 r / min, more preferably 230-360 r / min; the mixing time is 6-12 h, preferably 8-11 h, more preferably 9-10 h; the ball-to-material ratio of the ball mill is 1:2-5, preferably 1:2.5-4, more preferably 1:3-3.5.

[0043] In this invention, the method of coating the pre-made slurry in step (2) includes brushing, spraying or dipping, preferably brushing or spraying, and more preferably spraying.

[0044] In this invention, the coating methods of brushing, spraying, or dipping are simple and the thickness is controllable.

[0045] In this invention, the thickness of the sample coating is 100-500 μm, preferably 150-400 μm, and more preferably 200-300 μm.

[0046] In this invention, step (3) includes two stages of segmented sintering: the first stage is heated to 1300-1400°C at a heating rate of 3-5°C / min and held for 1-2 hours; the second stage is heated to 1400-1550°C at a heating rate of 3-5°C / min and held for 2-3 hours.

[0047] Preferably, in the first stage, the temperature is increased to 1320–1390°C at a heating rate of 3.4–4.5°C / min and held for 1.2–1.8 h; in the second stage, the temperature is increased to 1420–1500°C at a heating rate of 3.4–4.5°C / min and held for 2.2–2.8 h.

[0048] More preferably, in the first stage, the temperature is increased to 1350-1380℃ at a heating rate of 4℃ / min and held for 1.5h; in the second stage, the temperature is increased to 1450-1480℃ at a heating rate of 4℃ / min and held for 2.5h.

[0049] In this invention, the segmented sintering is preferably carried out at atmospheric pressure, and the atmosphere for segmented sintering is preferably an oxidizing atmosphere or an air atmosphere.

[0050] The present invention also provides a method for preparing a high-temperature resistant mullite / yttrium silicate / zirconia composite coating.

[0051] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0052] Example 1

[0053] (1) 75g of mullite with a particle size of 200 mesh, 20g of yttrium silicate with a particle size of 200 mesh, 5g of zirconium oxide with a particle size of 500nm, 0.5g of polyvinyl alcohol and 200g of water were ball-milled at a speed of 300r / min. The ball-to-material ratio of the ball milling was 1:3. After 10h, a pre-made slurry was obtained.

[0054] (2) The pre-made slurry was coated on the surface of the SiC ceramic substrate to obtain a sample coating with a thickness of 100 μm;

[0055] (3) The sample coating was heated from room temperature to 1300℃ at a rate of 3℃ / min in an air atmosphere muffle furnace and held for 1h. Then the temperature was increased to the sintering temperature of 1450℃ at a rate of 3℃ / min and held for 2h. Finally, it was naturally cooled to room temperature to obtain a high temperature resistant mullite / yttrium silicate / zirconia composite coating.

[0056] The composite coating prepared in Example 1 was tested. Figure 1 This is a cross-sectional SEM image of the composite coating prepared in Example 1. Figure 1 It can be seen that the composite coating and SiC ceramic have good interfacial bonding, with no obvious gaps or voids at the interface. The composite coating has a dense structure, consisting of a gray mullite matrix phase and a white reinforcing phase, with a hardness of 8.25 GPa.

[0057] Example 2

[0058] (1) 75g of mullite with a particle size of 200 mesh, 15g of yttrium silicate with a particle size of 200 mesh, 10g of zirconium oxide with a particle size of 500nm, 0.5g of polyvinyl alcohol and 200g of water were ball-milled at a speed of 300r / min. The ball-to-material ratio of the ball milling was 1:3. After 10h, a pre-made slurry was obtained.

[0059] (2) The pre-made slurry was coated on the surface of the SiC ceramic substrate to obtain a sample coating with a thickness of 200 μm;

[0060] (3) The sample coating was heated from room temperature to 1350°C at a rate of 3°C / min in an air atmosphere muffle furnace and held for 1 hour. Then the temperature was increased to the sintering temperature of 1450°C at a rate of 3°C / min and held for 2 hours. Finally, it was naturally cooled to room temperature to obtain a high-temperature resistant mullite / yttrium silicate / zirconia composite coating.

[0061] The composite coating prepared in Example 2 was tested. Figure 2 The image shows the XRD pattern of the composite coating prepared in Example 2. Figure 2 It can be seen that the composite coating not only contains mullite, yttrium silicate and zirconium oxide phases, but also forms a high-temperature stable phase Y. 0.19 Zr 0.18 O 1.91 (YSZ) can significantly improve the high-temperature stability of the composite coating, with a hardness of 9.07 GPa.

[0062] Example 3

[0063] (1) 70g of mullite with a particle size of 200 mesh, 15g of yttrium silicate with a particle size of 200 mesh, 15g of zirconium oxide with a particle size of 500nm, 0.5g of polyvinyl alcohol and 200g of water were ball-milled at a speed of 300r / min. The ball-to-material ratio of the ball milling was 1:3. After 10h, a pre-made slurry was obtained.

[0064] (2) The pre-made slurry was coated on the surface of the SiC ceramic substrate to obtain a sample coating with a thickness of 200 μm;

[0065] (3) The sample coating was heated from room temperature to 1350°C at a rate of 3°C / min in an air atmosphere muffle furnace and held for 1 hour. Then the temperature was increased to the sintering temperature of 1450°C at a rate of 3°C / min and held for 2 hours. Finally, it was naturally cooled to room temperature to obtain a high-temperature resistant mullite / yttrium silicate / zirconia composite coating.

[0066] The composite coating prepared in Example 3 was tested. Figure 3 The image shows the XRD pattern of the composite coating prepared in Example 3. Figure 3 It can be seen that with the increase of zirconium oxide content, a new zirconium silicate phase is formed in the coating, and the hardness of the composite coating is 9.38 GPa.

[0067] Example 4

[0068] (1) 75g of mullite with a particle size of 200 mesh, 15g of yttrium silicate with a particle size of 200 mesh, 10g of zirconium oxide with a particle size of 500nm, 0.5g of polyvinyl alcohol and 200g of water were ball-milled at a speed of 300r / min. The ball-to-material ratio of the ball milling was 1:3. After 10h, a pre-made slurry was obtained.

[0069] (2) The pre-made slurry was coated on the surface of the SiC ceramic substrate to obtain a sample coating with a thickness of 200 μm;

[0070] (3) The sample coating was heated from room temperature to 1350°C at a rate of 3°C / min in an air atmosphere muffle furnace and held for 1 hour. Then the temperature was increased to the sintering temperature of 1500°C at a rate of 3°C / min and held for 2 hours. Finally, it was naturally cooled to room temperature to obtain a high-temperature resistant mullite / yttrium silicate / zirconia composite coating.

[0071] The composite coating prepared in Example 4 was tested. Figure 4 The image shows the TEM microstructure of the composite coating prepared in Example 4. Figure 4 It can be seen that ZrO2 grains can achieve microscopic bonding with mullite and yttrium silicate grains. From Figure 4 (a) It can be seen that there are many dislocations and defects between mullite and yttrium silicate grains, which is related to the large difference in lattice spacing between the two crystals. Therefore, lattice distortion is easily caused at the grain boundaries. However, ZrO2 can form a good coherent interface with both crystals, with fewer defects at the interface. ZrO2 can play a role in improving the strength of the microstructure. Figure 4(b) The corresponding line scan energy dispersive spectroscopy (EDS) provides a more intuitive view of the changes in elemental content. In the mullite phase, only O, Si, and Al elements are present. At the interface between mullite and yttrium silicate grains, the elements show a slow transition, indicating the formation of a eutectic phase at the interface and good interfacial bonding. However, within the yttrium silicate crystals, Al is almost absent, and the ratio of Y to Si is almost 1:1, which is the standard yttrium silicate (Y₂O₃·2SiO₂) phase. However, from the yttrium silicate grains to the ZrO₂ grains, the Si element decreases sharply until it disappears, while the Y element decreases slightly. This indicates that the stable phase formed by Zr and Y is mainly oxide, possibly the YSZ phase, which can improve the high-temperature stability of the coating. The hardness of this composite coating is 9.83 GPa.

[0072] Example 5

[0073] (1) 75g of mullite with a particle size of 200 mesh, 15g of yttrium silicate with a particle size of 200 mesh, 10g of zirconium oxide with a particle size of 500nm, 0.5g of polyvinyl alcohol and 200g of water were ball-milled at a speed of 300r / min. The ball-to-material ratio of the ball milling was 1:3. After 10h, a pre-made slurry was obtained.

[0074] (2) The pre-made slurry was coated on the surface of the SiC ceramic substrate to obtain a sample coating with a thickness of 200 μm;

[0075] (3) The sample coating was heated from room temperature to 1400℃ at a rate of 3℃ / min in an air atmosphere muffle furnace and held for 1h. Then the temperature was increased to the sintering temperature of 1450℃ at a rate of 3℃ / min and held for 2h. Finally, it was naturally cooled to room temperature to obtain a high temperature resistant mullite / yttrium silicate / zirconia composite coating.

[0076] Example 6

[0077] (1) 75g of mullite with a particle size of 200 mesh, 15g of yttrium silicate with a particle size of 200 mesh, 10g of zirconium oxide with a particle size of 500nm, 0.5g of polyvinyl alcohol and 201g of water were ball-milled at a speed of 300r / min. The ball-to-material ratio of the ball milling was 1:3. After 10h, a pre-made slurry was obtained.

[0078] (2) The pre-made slurry was coated on the surface of the SiC ceramic substrate to obtain a sample coating with a thickness of 200 μm;

[0079] (3) The sample coating was heated from room temperature to 1350°C at a rate of 3°C / min in an air atmosphere muffle furnace and held for 1 hour. Then the temperature was increased to the sintering temperature of 1550°C at a rate of 3°C / min and held for 2 hours. Finally, it was naturally cooled to room temperature to obtain a high-temperature resistant mullite / yttrium silicate / zirconia composite coating.

[0080] The composite coating prepared in Example 6 was tested, and the hardness of the composite coating was 10.26 GPa.

[0081] Comparative Example 1

[0082] 100g of mullite with a particle size of 200 mesh, 0.5g of polyvinyl alcohol and 200g of water were ball-milled at a speed of 300 r / min with a ball-to-material ratio of 1:3. After 10 hours, a pre-mixed slurry was obtained.

[0083] (2) The pre-made slurry was coated on the surface of the SiC ceramic substrate to obtain a sample coating with a thickness of 200 μm;

[0084] (3) The sample coating was heated from room temperature to 1400℃ at a rate of 3℃ / min in an air atmosphere muffle furnace and held for 1h. Then the temperature was increased to the sintering temperature of 1450℃ at a rate of 3℃ / min and held for 2h. Finally, it was naturally cooled to room temperature to obtain a high temperature resistant mullite coating.

[0085] The composite coatings prepared in Example 5 and Comparative Example 1 were tested. Figure 5 SEM images of the ordinary mullite coating (a) prepared in Comparative Example 1 and the composite coating (b) prepared in Example 5. Figure 5 It is known that ordinary mullite coatings (a) decompose at high temperatures, forming a porous structure. The composite coating (b) prepared by this invention exhibits significantly enhanced resistance to high-temperature decomposition and vaporization under high-temperature vacuum conditions. After treatment at 1200℃ and 10Pa for 48 hours, it still maintains the integrity of the coating structure, and the coating hardness is 9.51 GPa.

[0086] As shown in the above embodiments, this invention provides a high-temperature resistant mullite / yttrium silicate / zirconia composite coating and its preparation method. Mullite, yttrium silicate, zirconia, binder, and dispersant are mixed and coated onto the substrate surface using brushing, spraying, or dipping processes. Then, segmented sintering is performed to obtain the high-temperature resistant mullite / yttrium silicate / zirconia composite coating. This invention, through pre-prepared slurry, can prepare coatings of a certain thickness on the surface of any complex workpiece using brushing, spraying, or dipping methods. No specialized equipment is required, the operation is simple, and production efficiency is high. The two-stage heating sintering not only improves the density and structural stability of the composite coating but also increases the formation temperature of the eutectic phase, increases the high-temperature stable phase in the structure, and improves the bonding strength between the reacted high-temperature stable phase and the substrate grains, significantly increasing the coating's toughness, thermal shock resistance, and structural stability. The composite coating prepared by this invention can achieve a hardness of 10.26 GPa.

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a high-temperature resistant mullite / yttrium silicate / zirconia composite coating, characterized in that, Includes the following steps: (1) Mullite, yttrium silicate, zirconium oxide, binder and dispersant are mixed to obtain a pre-made slurry; In step (1), the particle size of mullite and yttrium silicate is 200-500 mesh, and the particle size of zirconium oxide is 100-500 nm. In step (1), the mass ratio of mullite, yttrium silicate, and zirconium oxide is 60-80:10-30:5-20; the mass of the binder is 0.1-1% of the total mass of mullite, yttrium silicate, and zirconium oxide. The total mass ratio of the mullite, yttrium silicate, zirconium oxide, and binder to the dispersant is 1:1~3. (2) The pre-prepared slurry is coated on the surface of the substrate to obtain the sample coating; (3) The sample coating was sintered in sections to obtain a high-temperature resistant mullite / yttrium silicate / zirconia composite coating; In step (3), the segmented sintering includes two stages: the first stage is heated to 1300-1400℃ at a heating rate of 3-5℃ / min and held for 1-2 hours; the second stage is heated to 1400-1550℃ at a heating rate of 3-5℃ / min and held for 2-3 hours.

2. The preparation method according to claim 1, characterized in that, In step (1), the adhesive comprises one or more of polyethylene glycol, ethanol, polyvinyl alcohol and carboxymethyl cellulose; The dispersant contains water.

3. The preparation method according to claim 1 or 2, characterized in that, In step (1), the mixing is carried out under ball milling, the mixing speed is 200~300r / min, the mixing time is 6~12h, and the ball-to-material ratio is 1:2~5.

4. The preparation method according to claim 3, characterized in that, In step (2), the method of coating the pre-made slurry includes brushing, spraying or dipping; The thickness of the sample coating is 100~500μm.

5. The high-temperature resistant mullite / yttrium silicate / zirconia composite coating prepared by the preparation method according to any one of claims 1 to 4.

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