Super-thick and strong-bonding double-ceramic-layer thermal barrier coating and preparation method thereof

Abstract

The invention relates to the technical field of thermal barrier coatings for gas turbines or aero-engines, and particularly discloses an ultra-thick and strong-bonding double-ceramic-layer thermal barrier coating and a preparation method thereof.The thermal barrier coating is composed of an MCrAlY bonding layer, a YSZ ceramic layer bottom layer and a high-entropy rare earth zirconate ceramic layer surface layer; the MCrAlY bonding layer is prepared through atmospheric plasma or hypersonic flame spraying, YSZ and high-entropy rare earth zirconate spherical powder serve as spraying raw materials, and the thermal barrier coating is prepared through an axial powder feeding high-energy plasma spraying system. The thermal barrier coating has the characteristics of super thickness (the coating thickness is 600-1200 microns), high bonding strength (gt; 19 MPa) and the like.

Description

Technical Field

[0001] This invention belongs to the technical field of thermal barrier coatings for gas turbines or aero engines, specifically relating to an ultra-thick, strongly bonded double ceramic thermal barrier coating and its preparation method. Background Technology

[0002] Advanced power equipment, represented by next-generation aero-engines and heavy-duty gas turbines, is continuously developing towards higher efficiency, higher power, and lower emissions, which inevitably requires increasing turbine inlet temperature. Taking heavy-duty gas turbines as an example, the F-class gas turbine is currently the mainstream model in service, with a gas operating temperature of approximately 1400 ℃, while the more advanced G / H-class gas turbines have reached operating temperatures of 1500 ℃. The increasing operating temperature places increasingly stringent requirements on the structure and materials of hot-end components. Under these circumstances, thermal barrier coating technology is considered an efficient and feasible means of protecting hot-end components. Research shows that increasing the thickness of the thermal barrier coating significantly improves the heat insulation effect; therefore, the preparation of ultra-thick thermal barrier coatings is better suited to the future application requirements of heavy-duty gas turbines operating at 1500 ℃.

[0003] YSZ is a widely commercially available thermal barrier coating ceramic material. However, when operating at temperatures consistently above 1200 °C, YSZ undergoes phase transformation or sintering, leading to degradation of its thermophysical and mechanical properties, reduced strain tolerance, and cracking, resulting in premature peeling and failure of the thermal barrier coating. To address this issue, researchers have created a double-ceramic-layer structure by coating a higher-performance ceramic layer on top of the YSZ layer. This alleviates the problem of poor resistance to harsh environments when only a YSZ layer is used. The presence of oxygen vacancies within the rare-earth zirconate crystal structure is beneficial for improving the coating's thermal insulation performance. The high-entropy design enhances the stability of rare-earth zirconate, ensuring that the high-entropy rare-earth zirconate coating does not undergo phase transformation in the temperature range from room temperature to high temperatures. Furthermore, by rationally controlling the high-entropy process, its coefficient of thermal expansion is close to that of YSZ. Therefore, the combination of high-entropy rare-earth zirconate and YSZ in a double-ceramic-layer thermal barrier coating structure can effectively improve the coating's lifespan. However, the dual-ceramic-layer structure design increases the likelihood of poor interlayer bonding in the thermal barrier coating, making it prone to peeling or cracking under thermal cycling and mechanical stress. Therefore, when designing a dual-ceramic-layer thermal barrier coating, emphasis should be placed on improving the interlayer bonding strength to enhance the reliability and safety of equipment operation.

[0004] Currently, the main technologies for large-scale application of thermal barrier coatings are electron beam physical vapor deposition (EB-PVD) and atmospheric plasma spraying (APS). Although both have their advantages, APS technology is more suitable for the engineering application requirements of ultra-thick coatings, especially when high porosity is required. Based on this, this invention employs axially fed high-energy APS technology. Its high powder feeding rate and single-pass powder feeding volume effectively reduce interface defects caused by deposition interruptions, which is beneficial for efficient deposition of ultra-thick coatings and improved coating adhesion. Ultimately, an ultra-thick double-ceramic thermal barrier coating applicable at 1500 °C was successfully prepared using axially fed high-energy APS technology, exhibiting excellent interlayer bonding strength and uniform coating thickness. This achievement increases the thermal barrier coating thickness to 1200 μm, potentially extending the application temperature of high-temperature alloy components to 1500 °C and above, providing coating solutions and technical support for the development of next-generation aero-engines and heavy-duty gas turbines. Summary of the Invention

[0005] The purpose of this invention is to provide an ultra-thick, strongly bonded double ceramic layer thermal barrier coating and its preparation method. The coating adopts a double ceramic layer structure, with the upper ceramic layer being high-entropy rare earth zirconate and the lower ceramic layer being YSZ. The ultra-thick, strongly bonded double ceramic layer thermal barrier coating is prepared by using axial powder feeding high-energy APS technology.

[0006] This invention provides an ultra-thick, strongly bonded double-ceramic thermal barrier coating, which consists of an MCrAlY adhesive layer, a YSZ ceramic underlayer, and a high-entropy rare-earth zirconate ceramic toplayer; M in the MCrAlY adhesive layer is one or more of Ni, Co, Ta, and Hf; the high-entropy rare-earth zirconate has the molecular formula (5RE). 0.2 The coating is 2Zr2O7, wherein RE is any five of the following: Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. The coating is characterized by its large thickness and high bonding strength. The total thickness of the thermal barrier coating is 600–1200 μm, wherein the MCrAlY adhesive layer is 100–300 μm thick, the YSZ ceramic underlayer is 250–450 μm thick, and the high-entropy rare-earth zirconate ceramic toplayer is 250–450 μm thick.

[0007] The present invention also provides a method for preparing the ultra-thick, strongly bonded double ceramic thermal barrier coating, the preparation method comprising the following steps: (1) using anhydrous ethanol as a medium, taking five equimolar amounts of RE2O3 powder and ZrO2 powder and mixing them uniformly according to a molar ratio of 5RE2O3:ZrO2=1:2, and placing the mixture at a high temperature of T1 for high-temperature sintering to obtain (5RE 0.2(2) Spray granulation of the prepared Zr2O7 powder, and then debinding at T2 temperature to obtain agglomerated granulated powder; (3) Prepare MCrAlY bonding layer on high temperature alloy or other metal substrate by atmospheric plasma or supersonic flame spraying (HVOF); (4) Spray YSZ ceramic layer bottom layer on the prepared MCrAlY bonding layer by axial powder feeding high energy plasma spraying equipment according to the set parameters; (5) Place the sample sprayed in step (4) under an argon protective atmosphere for heat treatment to obtain thermal barrier coating.

[0008] The method for preparing an ultra-thick, strongly bonded double ceramic thermal barrier coating provided by the present invention includes a T1 temperature of 1300~1700 ℃ and a holding time of 5~30 h in step (1); a T2 temperature of 1300~1700 ℃ and a holding time of 5~30 h; and an agglomerated granulated powder particle size distribution of 5~140 μm.

[0009] The method for preparing an ultra-thick, strongly bonded double ceramic thermal barrier coating provided by the present invention, wherein the substrate in step (2) is selected from nickel-based cast high-temperature alloys, such as MM247 or CM247.

[0010] The method for preparing an ultra-thick, strongly bonded double ceramic thermal barrier coating provided by the present invention includes the following steps (3): the axial powder feeding high-energy plasma spraying parameters are as follows: gas composition is He, Ar / H2, N2 / H2 or Ar / N2 / H2, preheating is 1 to 10 times, current is 150 to 310 A, carrier gas flow rate is 5 to 11 L / min, powder feeding rate is 6 to 10 r / min, spraying distance is 140 to 240 mm, spray gun moving speed is 0 to 1000 mm / s, and the deposition thickness per pass is 20 to 45 μm. The number of spraying passes is set according to the expected spraying thickness.

[0011] The method for preparing an ultra-thick, strongly bonded double ceramic thermal barrier coating provided by the present invention includes the following steps (4): the axial powder feeding high-energy plasma spraying parameters are as follows: gas composition is He, Ar / H2, N2 / H2 or Ar / N2 / H2, preheating is 1 to 10 times, current is 120 to 280 A, carrier gas flow rate is 5 to 11 L / min, powder feeding rate is 5 to 13 r / min, spraying distance is 100 to 290 mm, spray gun moving speed is 0 to 1000 mm / s, and the deposition thickness per pass is 20 to 50 μm. The number of spraying passes is set according to the expected spraying thickness.

[0012] The advantages and beneficial effects of this invention are: (1) The high-entropy rare earth zirconate material prepared by the present invention has a uniform element distribution and is a single pyrochlore phase, which does not undergo phase transformation at 1500 ℃; its thermal expansion coefficient is close to that of YSZ, and it matches well with the YSZ layer when preparing the double ceramic layer; the ultra-thick coating characteristics can enhance the heat insulation effect and can be applied to working conditions at 1500 ℃; in addition, the coating bonding strength exceeds 19 MPa, which helps to extend the service life of the coating.

[0013] (2) The axial powder feeding high-energy APS technology used in this invention has high preparation efficiency and can realize the rapid preparation of ultra-thick coatings; at the same time, through the high powder feeding rate and single-pass powder feeding amount, the interface interruption problem in the deposition process is effectively reduced, and the interlayer bonding state is significantly improved. Compared with existing spraying equipment, it has the advantages of low cost, high production efficiency, wide range of coating thickness, and suitability for large-scale production.

[0014] Therefore, the method for preparing an ultra-thick, strongly bonded double ceramic thermal barrier coating provided by this invention effectively improves the coating thickness and enhances the coating bonding strength, providing reliable technical support for the large-scale preparation of ultra-thick, strongly bonded double ceramic thermal barrier coatings. Attached Figure Description

[0015] Figure 1 The image shows the XRD pattern of the high-entropy rare-earth zirconate in Example 1. Figure 2 Thermogravimetric-differential thermal analysis (TGA) diagram of the high-entropy rare earth zirconate in Example 1; Figure 3 The thermal expansion coefficient diagram of the high-entropy rare earth zirconate in Example 1; Figure 4 The microstructure of a portion of the heat-treated coated sample obtained in Example 1 is shown. Figure 5 The microstructure of a portion of the heat-treated coated sample obtained in Example 2 is shown. Figure 6 The macroscopic morphology of the surface of the prepared coating sample obtained in Example 1; Figure 7 The macroscopic morphology of the prepared coating sample obtained in Comparative Example 1; Figure 8 The microstructure of the cross-section of the prepared coating sample obtained in Example 1; Figure 9 The cross-sectional microstructure of the prepared coated sample obtained in Comparative Example 1; Figure 10 The microstructure of the cross-section of the heat-treated coated sample obtained in Example 2; Figure 11 The image shows the cross-sectional microstructure of the heat-treated coated sample obtained in Comparative Example 2. Detailed Implementation

[0016] The present invention will be further described below with reference to specific drawings and embodiments, but the implementation of the present invention is not limited thereto.

[0017] The performance test information in the examples is as follows: 1. Phase identification: The crystal structure of high-entropy rare-earth zirconates was analyzed using an X-ray diffractometer (Bruker, D8 Advance, Germany). 2. Performance Analysis: The thermal expansion coefficient of high entropy rare earth zirconates was tested using a high-temperature thermal expansion coefficient tester (Linseis, L75HD1600C, Germany). The bonding strength of the coating was tested using a hydraulic universal testing machine (Lisheng Scientific Instrument Co., Ltd., LD26.105, China); 3. Morphological observation: The coating cross-section was characterized using field emission scanning electron microscopy (Tescan, Clara, Czech Republic).

[0018] Example 1: (1) Using anhydrous ethanol as a medium, RE2O3 powder (RE = Nd, Sm, Eu, Gd, Yb) and ZrO2 powder were mixed evenly according to the molar ratio of Nd2O3:Sm2O3:Eu2O3:Gd2O3:Yb2O3:ZrO2 = 1:1:1:1:10. The mixture was then kept at 1550 °C for 20 h to obtain (Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 Yb 0.2 )2Zr2O7 powder; the prepared powder was spray granulated, and then kept at 1500 ℃ for 20 h to obtain agglomerated granulated powder with a particle size of 5~120 μm; (2) An (Ni, Co)CrAlY bonding layer was prepared on a directional nickel-based superalloy CM247 using the APS method. The parameters used for the APS method were: gas composition of 70% Ar, 10% N2 and 20% H2, preheating twice, current of 230 A, carrier gas flow rate of 6 L / min, powder feeding rate of 4 r / min, spraying distance of 200 mm, spray gun moving speed of 500 mm / s, 6 spraying passes, and the final bonding layer thickness of 280~300 μm. (3) On the sample with the prepared adhesive layer, YSZ was used as the spraying material and sprayed by axial powder feeding high-energy plasma spraying equipment according to the set parameters. The set parameters were: gas composition of 75% N2 and 25% H2, preheating twice, current of 210A, carrier gas flow rate of 7 L / min, powder feeding rate of 7 r / min, spraying distance of 200 mm, spray gun moving speed of 600 mm / s, 10 spraying passes, and spraying thickness of 400~450 μm. (4) On the basis of the good ceramic layer base layer, continue to use high entropy rare earth zirconate as material, and spray it according to the set parameters through the axial powder feeding high energy plasma spraying equipment. The set parameters are: gas composition of 75% N2 and 25% H2, preheating twice, current of 190 A, carrier gas flow rate of 8 L / min, powder feeding rate of 8 r / min, spraying distance of 200 mm, spray gun moving speed of 400 mm / s, spraying 9 times, and spraying thickness of 400~450 μm.

[0019] (5) The prepared sample was placed under an argon protective atmosphere for heat treatment. The heat treatment parameters were 1080 °C for 4 h and then 850 °C for 20 h.

[0020] The prepared high-entropy rare-earth zirconate powder was analyzed: Figure 1 The X-ray diffraction pattern of the high-entropy rare-earth zirconate used in Example 1 proves that single-phase pyrochlore powder has been successfully prepared; its thermal stability at 1500 °C was tested ( Figure 2 It can be seen that this material does not undergo a phase change at 1500 ℃, which meets the application requirements of G / H class heavy-duty gas turbines; in addition, such as Figure 3 As shown, the coefficient of thermal expansion of this material is 10.82 × 10⁻⁶. -6 / K (1500 ℃), and the thermal expansion coefficient of YSZ (10~11×10) -6 The K value is close to that of YSZ, making it suitable for use in the preparation of thermal barrier coatings with a double ceramic layer structure.

[0021] The bonding strength of the coating in Example 1 was tested using a hydraulic universal testing machine. The experimental results for the three groups of samples were 19.3 ± 0.4 MPa. The cross-section of the coating prepared in Example 1 was observed using a scanning electron microscope (e.g., ...). Figure 4 As shown in the figure, the results show that the coating thickness meets the design requirements and the bonding between the layers is good, proving that an ultra-thick, strongly bonded double ceramic thermal barrier coating has been successfully prepared.

[0022] Example 2 (1) Using anhydrous ethanol as a medium, RE2O3 powder (RE = Nd, Sm, Eu, Gd, Yb) and ZrO2 powder were mixed evenly according to the molar ratio of Nd2O3:Sm2O3:Eu2O3:Gd2O3:Yb2O3:ZrO2 = 1:1:1:1:10. The mixture was then kept at 1550 °C for 20 h to obtain (Nd 0.2 Sm 0.2 Eu 0.2 Gd 0.2 Yb 0.2 )2Zr2O7 powder; the prepared powder was spray granulated, and then kept at 1500 ℃ for 20 h to obtain agglomerated granulated powder with a particle size of 5~120 μm; (2) A (Ni, Co)CrAlY bonding layer was prepared on equiaxed nickel-based superalloy MM247 using the HVOF method. The parameters used for HVOF were: 3 preheating passes, O2 flow rate 850 L / min, kerosene flow rate 22 L / h, powder feeding rate 40 g / min, N2 carrier gas flow rate 5 L / min, spraying distance 320 mm, spray gun moving speed 550 mm / s, 11 spraying passes, and the final bonding layer thickness was 280~300 μm. (3) On the sample with the prepared adhesive layer, YSZ was used as the spraying material and sprayed by an axial powder feeding high-energy plasma spraying equipment according to the set parameters. The set parameters were: gas composition of 75% N2 and 25% H2, preheating 4 times, current of 230A, carrier gas flow rate of 8 L / min, powder feeding rate of 6 r / min, spraying distance of 210 mm, spray gun moving speed of 500 mm / s, 10 spraying passes, and spraying thickness of 400~450 μm. (4) On the basis of the good ceramic layer base layer, continue to use high entropy rare earth zirconate as material, and spray it with axial powder feeding high energy plasma spraying equipment according to the set parameters. The set parameters are: gas composition of 75% N2 and 25% H2, preheating 4 times, current of 220 A, carrier gas flow rate of 8 L / min, powder feeding rate of 9 r / min, spraying distance of 180 mm, spray gun moving speed of 500 mm / s, spraying 9 times, and spraying thickness of 400~450 μm.

[0023] (5) The prepared sample was placed under an argon protective atmosphere for heat treatment. The heat treatment parameters were 1080 °C for 4 h and then 850 °C for 20 h.

[0024] The bonding strength of the coating in Example 2 was tested using a hydraulic universal testing machine. The experimental results for the three groups of samples were 19.8 ± 0.3 MPa. The cross-section of the coating prepared in Example 2 was observed using a scanning electron microscope (e.g., ...). Figure 5 As shown in the figure, the results show that even with adjustments to the process parameters, the thickness of the prepared coating still meets the design requirements when spraying within the preferred process range, and the bonding between the layers is good, proving that an ultra-thick, strongly bonded double ceramic thermal barrier coating has been successfully prepared.

[0025] Comparative Example 1 Comparative Example 1 and Example 1 have basically the same process, except that: In step (4), the spraying distance used for spraying the ceramic surface layer is 80 mm, which is not within the preferred process range.

[0026] The sample in Comparative Example 1 cracked immediately after spraying, therefore no further heat treatment was performed. To investigate the effect of spraying distance on coating morphology, the surface and cross-sectional morphology of the prepared samples of Example 1 and Comparative Example 1 were systematically characterized. Observing the macroscopic surface morphology, the coating surface of the sample in Example 1 was intact (…). Figure 6 The sample in Comparative Example 1 showed no obvious defects, while the coating of the sample in Comparative Example 1 showed obvious cracking. Figure 7 ). The cross-sectional morphology was observed under a scanning electron microscope, and the coating layer bonding of the sample in Example 1 was relatively good. Figure 8 The thickness distribution is uniform, while the sample in Comparative Example 1 shows cracking at the ceramic layer. Figure 9 The results show that when the spraying distance is within the range defined in the claims, the prepared coating has a good morphology. However, when the spraying distance exceeds this range, the coating is prone to cracking. This is because when the spraying distance is too close, the temperature of the spraying area is too high, and the degree of powder melting is significantly increased. When the molten powder is deposited on the sample surface, it will generate large thermal stress during the rapid cooling process, which in turn leads to coating cracking.

[0027] Comparative Example 2 Comparative Example 2 and Example 2 have basically the same process, except that: In step (4), the current used for spraying the ceramic layer is 300 A, which is not within the preferred process range.

[0028] Observe the cross-sectional morphology of Example 2 and Comparative Example 2 in the annealed state, and compare the effect of current on the coating morphology. The sample of Example 2 has better interlayer bonding. Figure 10 In Comparative Example 2, cracks occurred at the edge between the bottom ceramic layer and the adhesive layer of the sample. Figure 11 Furthermore, vertical cracks appeared on the ceramic surface layer. It was demonstrated that coatings prepared using current within the scope of the claims maintained their morphology intact after heat treatment. However, coatings prepared outside this scope were prone to cracking after heat treatment. This is because increased current during spraying affects the coefficient of thermal expansion of the surface layer, potentially increasing interlayer and intralayer stress after heat treatment, leading to coating cracking.

[0029] Obviously, the above embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

Claims

1. A super-thick, strongly bonded double-ceramic thermal barrier coating, characterized in that, The thermal barrier coating consists of an MCrAlY bonding layer, a YSZ ceramic layer bottom layer, and a high-entropy rare earth zirconate ceramic layer top layer. In the MCrAlY adhesive layer, M is one or more of Ni, Co, Ta, and Hf; The molecular formula of high-entropy rare earth zirconate is (5RE) 0.2 )2Zr2O7, where RE is any 5 of Y, Sc, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

2. The ultra-thick, strongly bonded double-ceramic thermal barrier coating according to claim 1, characterized in that, The total thickness of the thermal barrier coating is 600~1200 μm, of which the thickness of the MCrAlY adhesive layer is 100~300 μm, the thickness of the YSZ ceramic layer bottom layer is 250~450 μm, and the thickness of the high-entropy rare earth zirconate ceramic layer top layer is 250~450 μm.

3. A method for preparing the ultra-thick, strongly bonded double-ceramic thermal barrier coating as described in claim 1, characterized in that, The preparation method involves the following steps: (1) Using anhydrous ethanol as a medium, five equimolar amounts of RE2O3 powder and ZrO2 powder were mixed uniformly at a molar ratio of 5RE2O3:ZrO2 = 1:

2. The mixture was then subjected to high-temperature sintering at temperature T1 to obtain (5RE2O3:ZrO2 = 1:2). 0.2 )2Zr2O7 powder, and then debinding at temperature T2 to obtain agglomerated granulated powder; (2) Prepare an MCrAlY bonding layer on the substrate; (3) On the prepared MCrAlY bonding layer, the YSZ ceramic layer underlayer is sprayed according to the set parameters using an axial powder feeding high-energy plasma spraying equipment; (4) On the prepared YSZ ceramic layer, the high-entropy rare earth zirconate ceramic layer is sprayed with the powder prepared in step (1) according to the set parameters using an axial powder feeding high-energy plasma spraying equipment. (5) The sample coated in step (4) is placed under an argon protective atmosphere for heat treatment to obtain a thermal barrier coating.

4. The method for preparing an ultra-thick, strongly bonded double-ceramic thermal barrier coating according to claim 3, characterized in that, In step (1), the temperature of T1 is 1300~1700 ℃ and the holding time is 5~30 h; the temperature of T2 is 1300~1700 ℃ and the holding time is 5~30 h; the particle size distribution of the agglomerated granulated powder is 5~140 μm.

5. The method for preparing an ultra-thick, strongly bonded double-ceramic thermal barrier coating according to claim 3, characterized in that, In step (2), the matrix can be selected from nickel-based cast high-temperature alloys.

6. The method for preparing an ultra-thick, strongly bonded double-ceramic thermal barrier coating according to claim 3, characterized in that, In step (3), the parameters for axial powder feeding high-energy plasma spraying are as follows: gas composition is He, Ar / H2, N2 / H2 or Ar / N2 / H2, preheating 1 to 10 times, current is 150 to 310 A, carrier gas flow rate is 5 to 11 L / min, powder feeding rate is 6 to 10 r / min, spraying distance is 140 to 240 mm, spray gun moving speed is 0 to 1000 mm / s, and the deposition thickness per pass is 20 to 45 μm. The number of spraying passes is set according to the expected spraying thickness.

7. The method for preparing an ultra-thick, strongly bonded double-ceramic thermal barrier coating according to claim 3, characterized in that, In step (4), the parameters for axial powder feeding high-energy plasma spraying are as follows: gas composition is He, Ar / H2, N2 / H2 or Ar / N2 / H2, preheating 1 to 10 times, current is 120 to 280 A, carrier gas flow rate is 5 to 11 L / min, powder feeding rate is 5 to 13 r / min, spraying distance is 100 to 290 mm, spray gun moving speed is 0 to 1000 mm / s, and the deposition thickness per pass is 20 to 50 μm. The number of spraying passes is set according to the expected spraying thickness.

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