Method for evaluating high-temperature molten salt corrosion resistance of ceramic materials

Abstract

The present application relates to the technical field of material analysis and detection, and particularly relates to a method for evaluating the high-temperature molten salt corrosion resistance of ceramic materials. The method comprises the following steps: sequentially stacking and forming different ceramic materials to obtain a stacked green body ceramic; sintering the stacked green body ceramic to obtain a stacked dense bulk ceramic; cutting the stacked dense bulk ceramic along a direction perpendicular to the surface of the stacked dense bulk ceramic to expose a cut surface; coating molten salt on the cut surface, increasing the temperature to a target temperature, and performing molten salt corrosion on the ceramic material to obtain a corroded stacked dense bulk ceramic; cutting the corroded stacked dense bulk ceramic along a direction perpendicular to the cut surface to expose a corrosion cross section; and evaluating the corrosion resistance of the ceramic material by observing the penetration depth of the molten salt. The method has the advantages of high efficiency and intuitiveness.

Description

Technical Field

[0001] This invention relates to the field of materials analysis and testing technology, and in particular to a method for evaluating the resistance of ceramic materials to high-temperature molten salt corrosion. Background Technology

[0002] The rapid development of the aviation industry has placed higher demands on the thrust-to-weight ratio of aero engines. The key to developing a high thrust-to-weight ratio lies in increasing the turbine inlet temperature and reducing structural mass. Currently, the materials for hot-end components of aero engines (such as turbine blades, guide vanes, and turbine disks) are mainly nickel-based superalloys and silicon carbide-reinforced silicon carbide ceramic composites. To improve the corrosion resistance of the matrix material and maintain its excellent mechanical properties at high temperatures, thermal barrier or environmental barrier coatings need to be applied to the surface of these components. Thermal barrier and environmental barrier coatings, as protective media for the surfaces of high-temperature structural materials used in engine operating environments, can create a barrier between the high-temperature structural materials and the engine's service environment, preventing or reducing the impact of harsh environments on the performance of high-temperature structural materials. Thermal barrier and environmental barrier coatings face serious threats from multiple corrosive media in service environments. For example, during aero engine operation, fly ash, dust, gravel, volcanic ash, and fuel impurities from the environment are absorbed into the coating, some of which deposit on the coating surface. When the temperature exceeds their melting point, these deposits adhere to the surface of the engine blades and melt to form a glassy phase substance (high-temperature molten salt). This high-temperature molten salt mainly consists of CaO, MgO, Al2O3, SiO2, and other components, and is abbreviated as CMAS. Under high-temperature service environments, CMAS melts and undergoes a chemical corrosion reaction with the coating, damaging the structure and properties of the coating and severely affecting its performance and service life.

[0003] Existing literature reports that most studies on the resistance of thermal barrier and environmental barrier coatings to CMAS molten salt corrosion involve placing CMAS on the surface of a material, reacting it at high temperatures, and then evaluating the material's resistance to CMAS corrosion. Researching the corrosion resistance of multiple materials requires extensive evaluation experiments and analytical characterization, a process that is time-consuming and inefficient. Summary of the Invention

[0004] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, this invention proposes a method for evaluating the high-temperature molten salt corrosion resistance of ceramic materials. This method can test and evaluate the resistance of multiple ceramic materials to high-temperature molten salt (CMAS) corrosion in a short time, and the evaluation method is more intuitive and efficient.

[0005] Specifically, the technical solution of the present invention is as follows:

[0006] A method for evaluating the resistance of ceramic materials to high-temperature molten salt corrosion includes the following steps:

[0007] Different ceramic materials are layered and shaped in sequence to obtain laminated ceramic bodies.

[0008] The laminated ceramic blank is sintered to obtain a laminated dense bulk ceramic.

[0009] The laminated dense bulk ceramic is cut along a direction perpendicular to the surface of the ceramic to expose the cut surface;

[0010] After coating the cut surface with molten salt, the temperature is raised to the target temperature to perform molten salt corrosion of the ceramic material, resulting in a corroded laminated dense bulk ceramic.

[0011] The corroded laminated dense bulk ceramic is cut open along a direction perpendicular to the cut surface to expose the corroded cross section. The corrosion resistance of the ceramic material is evaluated by observing the molten salt penetration depth.

[0012] Compared to existing technologies, this invention stacks different ceramic materials in layers, distributing all materials in the same sample. After CMAS etching under the same experimental conditions, it can test the reaction of multiple ceramic materials with high-temperature molten salt CMAS within a certain time. It can more intuitively compare the products, distribution, and morphological characteristics of different ceramic materials after reacting with high-temperature molten salt CMAS. By comparing the cross-section of the stacked sample after etching, the corrosion depth of different ceramic materials under the same environment and time can be directly compared. The evaluation method is more intuitive and efficient.

[0013] In some embodiments of the present invention, the ceramic material is a thermal barrier or environmental barrier ceramic, including at least one of rare earth silicates and rare earth tantalates.

[0014] In some embodiments of the present invention, the rare earth silicate includes at least one of RE2SiO5 and RE2Si2O7, wherein RE = La to Lu, Y, Sc.

[0015] In some embodiments of the present invention, at least one of the rare earth tantalates RETaO4, RE3TaO7, and RETa3O9 is used.

[0016] In some embodiments of the present invention, the different ceramic materials include different rare earth silicates or different rare earth tantalates.

[0017] In some embodiments of the present invention, the stacking sequence can be designed according to actual research needs. For example, when studying the resistance to high-temperature molten salt corrosion of different rare earth silicates or different rare earth tantalates, the layers can be stacked according to the ionic radius of the rare earth elements or other sequences to obtain the stacked ceramic body. Generally, the resistance to CMAS corrosion of rare earth ceramic materials is related to the rare earth ionic radius. By stacking in this order, the resistance to high-temperature molten salt corrosion of different rare earth silicates can be directly observed.

[0018] In some embodiments of the present invention, during the stacking process, the raw material powders of two adjacent ceramic materials are weighed in a ratio of 1:(0.8 to 1.2) with a theoretical density, preferably 1:1.

[0019] In some embodiments of the present invention, the ceramic material can be ball-milled before lamination to form a uniformly sized powder for lamination. As an example, the ball milling process uses anhydrous ethanol as the medium, the milling jar and milling balls are made of zirconium oxide or agate, the rotation speed is 180-250 r / min, the time is 10-20 h, and after ball milling, the material is passed through a 60-120 mesh sieve.

[0020] In some embodiments of the present invention, the step of sequentially stacking different ceramic materials is specifically as follows: the first type of ceramic material is placed into a cold press mold, a press head is inserted, and the pressure is maintained at 0.2-1 MPa for 10-30 seconds before the press head is removed; the second type of ceramic material is placed into a cold press mold, a press head is inserted, and the pressure is maintained at 0.2-1 MPa for 10-30 seconds before the press head is removed, and this step is repeated until all ceramic materials are sequentially pressed into the cold press mold.

[0021] In some embodiments of the present invention, the molding method sequentially includes cold pressing and cold isostatic pressing steps.

[0022] In some embodiments of the present invention, the pressure of the cold pressing is 1 to 5 MPa, preferably 2 to 3 MPa; and the holding time is 60 to 120 s.

[0023] In some embodiments of the present invention, the pressure of the cold isostatic pressing is 100-500 MPa, preferably 150-200 MPa; the holding time is 5-30 min, preferably 10-20 min.

[0024] In some embodiments of the present invention, the temperature for sintering the laminated blank is 1000–2000°C, preferably 1500–1700°C; and the sintering time is 5–30 h, preferably 10–20 h.

[0025] In some embodiments of the present invention, the different ceramic materials include different rare earth silicates, and the sintering temperature of the laminated green body is 1500-1600°C, and the sintering time is 5-15 hours.

[0026] In some embodiments of the present invention, the different ceramic materials include different rare earth tantalates, and the sintering temperature of the laminated green body is 1600-1700°C, and the sintering time is 15-25 hours.

[0027] In some embodiments of the present invention, the main components of the molten salt include CaO, MgO, Al2O3, and SiO2.

[0028] In some embodiments of the present invention, the coating amount of the molten salt is 10–50 mg / cm³. 2 Preferred concentration: 30–40 mg / cm³ 2 More preferably 35mg / cm 2 .

[0029] In some embodiments of the present invention, the target temperature can be selected according to evaluation needs. As an example, the target temperature can be set to 1000–1700°C, preferably 1200–1500°C.

[0030] In some embodiments of the present invention, the heating rate during the process of raising the temperature to the target temperature is 2 to 10 °C / min, preferably 4 to 6 °C / min.

[0031] In some embodiments of the present invention, after reaching the target temperature, the heat preservation time is 1 to 50 hours, preferably 10 to 30 hours.

[0032] In some embodiments of the present invention, after cutting the corroded, stacked, dense block, the process further includes grinding and polishing the corroded cross-section. Grinding and polishing improve the surface smoothness of the corroded cross-section, reduce the influence of surface roughness on corrosion, and facilitate observation.

[0033] In some embodiments of the present invention, the observation method includes at least one of X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), and X-ray energy dispersive spectroscopy (EDS).

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] This invention stacks different ceramic materials to test the interaction between multiple ceramic materials and CMAS in a short time, enabling faster and more efficient CMAS corrosion resistance testing of different ceramic materials. Simultaneously, the stacked samples allow for a more direct comparison of the morphology and arrangement of corrosion products from different ceramic materials and CMAS. Furthermore, by comparing the corrosion depth differences in the barrier coating ceramic materials from different environments after the stacked ceramic materials react with CMAS in the same environment and at the same time, the corrosion cross-sections clearly demonstrate the differences in corrosion depth.

[0036] Therefore, the evaluation method of the present invention has the advantages of being efficient and intuitive. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of a stacked structure;

[0038] Figure 2 The image shows the XRD pattern of the rare earth silicate laminated sample in Example 1.

[0039] Figure 3 The image shows the surface XRD pattern of Example 1 after CMAS etching.

[0040] Figure 4 The images shown are SEM images and EDS surface scan results after CMAS etching in Example 1, where a represents adjacent Tb2SiO5 and Dy2SiO5, b represents adjacent Dy2SiO5, Y2SiO5 and Er2SiO5, c represents adjacent Er2SiO5, Tm2SiO5 and Yb2SiO5, and d represents adjacent Yb2SiO5 and Lu2SiO5.

[0041] Figure 5 The images shown are SEM images and EDS surface scan results after CMAS etching in Example 2, where a represents adjacent Er2TaO5 and HoTaO4, b represents adjacent HoTaO4 and DyTaO4, c represents adjacent DyTaO4 and GdTaO4, d represents adjacent GdTaO4 and EuTaO4, e represents adjacent EuTaO4 and SmTaO4, and f represents adjacent SmTaO4 and YTaO4. Detailed Implementation

[0042] The technical solution of the present invention will be further illustrated below with reference to specific embodiments. Unless otherwise specified, the raw materials used in the following embodiments can be obtained from conventional commercial channels; unless otherwise specified, the processes employed are conventional processes in the art.

[0043] Example 1

[0044] This embodiment forms a layered structure by stacking different rare earth silicates, such as... Figure 1 As shown, the resistance of different rare earth silicates to CMAS corrosion was evaluated. These rare earth silicates included Tb₂SiO₅, Dy₂SiO₅, Y₂SiO₅, Er₂SiO₅, Tm₂SiO₅, Yb₂SiO₅, and Lu₂SiO₅. The specific steps are as follows:

[0045] (1) Synthesize pure phase rare earth silicate RE2SiO5 (RE: rare earth elements, RE = Tb, Dy, Y, Er, Tm, Yb, Lu) powder;

[0046] (2) Use a ball mill to wet ball mill each powder separately, using anhydrous ethanol as the medium, with the ball milling jar and grinding balls made of zirconium oxide or agate, the rotation speed is 200 r / min, the time is 8 h, after mixing, dry and pass through a 60 mesh sieve to obtain each raw material powder;

[0047] (3) Weigh each rare earth silicate raw material powder according to the theoretical density of 1:1:1:1:1:1:1;

[0048] (4) According to the size of the rare earth ion radius, the first type of rare earth silicate raw material powder is placed into the cold pressing mold, the press head is inserted, and the pressure is maintained at 0.5 MPa for 20 seconds. Then the press head is removed. Then the second type of rare earth silicate raw material powder is placed into the cold pressing mold, the press head is inserted, and the pressure is maintained at 0.5 MPa for 20 seconds. Then the press head is removed. This step is repeated until all the rare earth silicate raw material powders are pressed into the cold pressing mold in sequence, and then cold pressing is performed. The pressure of cold pressing is 2 MPa, and the holding time is 2 min. Then cold isostatic pressing is performed. The pressure of cold isostatic pressing is 200 MPa, and the holding time is 15 min, to obtain a rare earth silicate laminated preform.

[0049] (5) The obtained rare earth silicate laminated preform was placed in a high-temperature muffle furnace and sintered in an air atmosphere at a temperature of 1550℃ and a holding time of 10h to obtain a rare earth silicate laminated dense block.

[0050] (6) Cut the rare earth silicate laminated dense block along the diameter, mix CMAS powder with alcohol, and coat the longitudinal section. Place the CMAS-coated sample (CaO, MgO, Al2O3, SiO2 molar ratio of 33:9:7.5:45) in an oven and keep it at 80℃ for 6 hours. Repeat the coating and drying process until the surface CMAS reaches 35 mg / cm³. 2 ;

[0051] (7) Place the rare earth silicate laminated dense block coated with CMAS into a muffle furnace and heat it to 1300℃ at a heating rate of 5℃ / min, and hold it for 20h.

[0052] (8) Cut the dense block of rare earth silicate stack after reacting with CMAS perpendicular to the layer interface to expose the corrosion section; after grinding and polishing, compare the different structures of different rare earth silicates after CMAS corrosion by XRD, SEM and EDS analysis.

[0053] Figure 2 The XRD results of the longitudinal section of the dense rare earth silicate stack after cutting in step (6) (before coating with CMAS) are consistent with the XRD results of pure phase rare earth silicates (the crystal structures of different rare earth silicates are very similar, so the diffraction peaks are also very similar). Figure 2The Y2SiO5 standard card diagram in the image is used to indicate that the material on the longitudinal section is a rare earth silicate, and no new phase is formed. Therefore, the method of evaluating the CMAS corrosion resistance by stacking multiple rare earth silicates is feasible, and there is no problem of multiple rare earth silicates reacting during the stacking process, leading to the formation of new phases and inaccurate evaluation results.

[0054] Figure 3 The XRD pattern of the etched cross section after CMAS etching shows that all rare earth silicates and CMAS etching products are apatite phase Ca2RE8(SiO4)6O2.

[0055] Figure 4 The images show the SEM and corresponding EDS surface scan results of the corroded cross-section after CMAS etching. Different rare earth elements are represented by different colors in the EDS surface scan results. As can be seen from the images, the corroded cross-section is divided into three parts: the uppermost black part is the residual molten salt, the lower, brighter part is the rare earth silicate matrix, and there is a corrosion reaction zone between the residual molten salt and the matrix. The red line indicates the lowermost part of the reaction zone, which is also the deepest part of the corrosion, while the yellow line indicates the boundary between the molten salt and the reaction zone. The cross-section shows that the corrosion depth and the thickness of the reaction zone vary for different rare earth silicate layers. Combining SEM and EDS surface scan results, the boundary between the molten salt and the reaction zone corresponds to the uppermost colored area in the rare earth element distribution map. The boundary between the reaction zone and the matrix corresponds to the lighter and darker colored positions in the rare earth element distribution. Changes in corrosion depth and reaction zone thickness can be observed at different rare earth silicate boundaries. Among them, the corrosion depth and reaction zone thickness change significantly from Tb2SiO5, Dy2SiO5, Y2SiO5 to Er2SiO5, while the corrosion depth and reaction zone thickness change less from Tm2SiO5, Yb2SiO5 to Lu2SiO5. Furthermore, as the rare earth ion radius decreases from large to small (Tb-Dy-Y-Er-Tm-Yb-Lu), the corrosion depth and reaction zone thickness decrease.

[0056] Based on the relationship between the radii of rare earth ions in different rare earth silicates, at 1300℃, rare earth silicates with smaller ionic radii have better resistance to CMAS molten salt corrosion than rare earth silicates with larger ionic radii.

[0057] Example 2

[0058] This embodiment evaluates the CMAS corrosion resistance of different rare earth tantalates, including YTaO4, SmTaO4, EuTaO4, GdTaO4, DyTaO4, HoTaO4, and Er2TaO4. The specific steps are as follows:

[0059] (1) Synthesize pure phase rare earth tantalate RETaO4 (RE = Y, Sm, Eu, Gd, Dy, Ho, Er) powder;

[0060] (2) Use a ball mill to wet ball mill each powder separately, using anhydrous ethanol as the medium, with the ball milling jar and grinding balls made of zirconium oxide or agate, the rotation speed is 200 r / min, the time is 8 h, after mixing, dry and pass through a 60 mesh sieve to obtain each raw material powder;

[0061] (3) Weigh each rare earth tantalate raw material powder according to the theoretical density of 1:1:1:1:1:1:1;

[0062] (4) The raw material powders were pressed into the cold press mold in the order of YTaO4, SmTaO4, EuTaO4, GdTaO4, DyTaO4, HoTaO4 and Er2TaO5. The pressure of cold pressing was 2MPa and the pressure was held for 2min. Then, cold isostatic pressing was performed. The pressure of cold isostatic pressing was 200MPa and the pressure was held for 15min to obtain rare earth tantalate laminated preforms.

[0063] (5) The obtained rare earth tantalate laminated preform was placed in a high-temperature muffle furnace and sintered in an air atmosphere at a temperature of 1650℃ and a holding time of 20h to obtain a rare earth tantalate laminated dense bulk.

[0064] (6) Cut the rare earth tantalate laminated dense block along the diameter, mix CMAS powder with alcohol, and coat the longitudinal section. Place the CMAS-coated sample (composition the same as in Example 1) in an oven and keep it at 80°C for 6 hours. Repeat coating and drying until the surface CMAS reaches 35 mg / cm³. 2 ;

[0065] (7) Place the rare earth tantalate laminated dense block coated with CMAS into a muffle furnace and heat it to 1300℃ at a heating rate of 5℃ / min, and hold it for 20h.

[0066] (8) Cut the dense block of rare earth tantalate stack after reacting with CMAS perpendicular to the layer interface to expose the corrosion section; after grinding and polishing, compare the relative corrosion depth and reaction layer thickness of different rare earth tantalates after CMAS corrosion by XRD, SEM and EDS analysis.

[0067] Figure 5This image shows the SEM and corresponding EDS surface scan results of the corroded cross-section after CMAS etching. The corroded cross-section is divided into three parts: the uppermost black part is the residual molten salt, the lower, brighter part is the rare earth tantalate matrix, and there is a corrosion reaction zone between the residual molten salt and the matrix. The red line indicates the lowermost end of the reaction zone, which is also the deepest part of the corrosion, and the yellow line indicates the boundary between the molten salt and the reaction zone. The cross-section shows that the corrosion depth and reaction zone thickness vary among different rare earth tantalate layers. Combining the SEM and EDS surface scan results, the boundary between the molten salt and the reaction zone corresponds to the uppermost colored area in the rare earth element distribution map, and the boundary between the reaction zone and the matrix corresponds to the lighter and darker colored positions in the rare earth element distribution. Variations in corrosion depth and reaction zone thickness can be observed at different rare earth tantalate boundaries. 3+ Ho 3+ Dy 3 + Gd 3+ Eu 3+ 、Sm 3+ The radius of rare earth ions increases sequentially, and the corrosion depth decreases as the radius of rare earth ions increases. 3+ Although the radius of rare ions is smaller than Er 3+ However, it is clearly visible at the cross-sectional boundary between YTaO4 and SmTaO4 that the corrosion depth on the YTaO4 side is significantly less than that on the SmTaO4 side. The cross-section also shows that the reaction zone of the rare earth tantalates with deeper corrosion depth is actually thicker.

[0068] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for evaluating the resistance of ceramic materials to high-temperature molten salt corrosion, characterized in that: Includes the following steps: Different ceramic materials are layered and shaped in sequence to obtain laminated ceramic bodies. The laminated ceramic blank is sintered to obtain a laminated dense bulk ceramic. The laminated dense bulk ceramic is cut along a direction perpendicular to the surface of the ceramic to expose the cut surface; After coating the cut surface with molten salt, the temperature is raised to the target temperature to perform molten salt corrosion of the ceramic material, resulting in a corroded laminated dense bulk ceramic. The corroded laminated dense bulk ceramic was cut open along a direction perpendicular to the cut surface to expose the corroded cross section. The corrosion resistance of the ceramic material was evaluated by observing the molten salt penetration depth. During the stacking process, the raw material powders of the two adjacent ceramic materials are weighed according to a theoretical density ratio of 1:(0.8~1.2); The ceramic material is a thermal barrier ceramic, selected from at least one of rare earth silicates and rare earth tantalates; The rare earth silicate is selected from at least one of RE2SiO5 and RE2Si2O7, wherein RE = La~Lu, Y, Sc; The rare earth tantalate is selected from at least one of RETaO4, RE3TaO7, and RETa3O9, wherein RE = La~Lu, Y, and Sc.

2. The evaluation method according to claim 1, characterized in that: The sintering temperature for the laminated ceramic body is 1000~2000℃.

3. The evaluation method according to claim 1, characterized in that: The main components of the molten salt include CaO, MgO, Al2O3, and SiO2.

4. The evaluation method according to claim 3, characterized in that: The coating amount of the molten salt is 10~50 mg / cm³. 2 .

5. The evaluation method according to claim 1, characterized in that: The target temperature is 1000~1700℃.

6. The evaluation method according to claim 1, characterized in that: The observation methods include scanning electron microscopy analysis.

Images