Method for testing porosity of a metallurgical sample of an abradable seal coating under an optical microscope

Abstract

The application discloses a method for testing porosity of a wear-resistant sealing coating metallographic sample under an optical microscope, and comprises the following steps: preparing a mixture capable of penetrating into coating pores and solidifying; preparing a metallographic sample and placing the sample in a sample preparation mold; pouring the mixture into the sample preparation mold, and immersing the metallographic sample in the mixture; placing the sample preparation mold containing the metallographic sample and the mixture into an oven for heat preservation; taking the sample preparation mold out of the oven and placing the mold at room temperature to completely solidify the mixture; taking the metallographic sample out of the sample preparation mold for grinding and polishing; placing the polished metallographic sample under an optical microscope for observation, taking a metallographic picture, and determining the porosity. The method adopts a mode of mixing liquid epoxy resin with a plasticizer, a crosslinking agent, a modifier, a diluent and a color developing agent, and then heating and penetrating into coating pores for solidification, and the specific position and area of pores can be observed under the optical microscope, the porosity is calculated, and the porosity is determined under conventional coating metallographic detection conditions.

Description

Technical Field

[0001] This invention belongs to the field of material performance testing technology, specifically relating to a method for testing the porosity of abrasive sealing coating metallographic specimens under an optical microscope. This method is applicable to testing the porosity of abrasive sealing coating metallographic specimens of aircraft engines and gas turbines. Background Technology

[0002] Abrasive sealing coatings for aircraft engines and gas turbines are typically applied using thermal spraying technology. Thermal spraying involves melting the coating material in a heat source and then using a high-speed gas stream to propel the molten particles onto the substrate surface, forming a layered structure. This process offers advantages such as rapid deposition, high production efficiency, and wide applicability. The porosity of the abrasive sealing coating directly affects its abrasive performance. However, methods for testing the porosity of metallographic samples typically involve mounting and penetrating with ordinary epoxy resin or bakelite powder, followed by testing using an optical microscope or scanning electron microscope (SEM). However, this process produces a blackish-gray substance similar to non-metallic materials (such as boron nitride and polystyrene) in the coating, making it difficult to distinguish between pores and non-pores under an optical microscope or SEM. Furthermore, SEM testing is inefficient due to its high requirements for sample quality and operation. Therefore, there is an urgent need for a method for testing the porosity of metallographic samples of abrasive sealing coatings for aircraft engines and gas turbines using an optical microscope.

[0003] The invention patent with publication number CN101256134A discloses a method for determining the porosity of the gold plating layer on a printed circuit board. The main components of the test solution are hydrochloric acid, sodium chloride and penetrant. Under certain temperature and time conditions, obvious corrosion products are generated at the discontinuities of the gold plating layer. The porosity is calculated by weighting the pore size using a graduated transparent grid material and a beveled body for auxiliary observation under a microscope. The invention patent with publication number CN109682735A discloses a method for testing the porosity of lithium-ion battery electrode coatings, including the following steps: preparing an electrode, calculating the coating volume and foil volume of the electrode; taking a certain amount of solvent, placing the solvent in a sealed, vacuum-capable container, and simultaneously placing the electrode in the container, but without the electrode contacting the solvent; evacuating the container, and when the vacuum level reaches -0.09 MPa, immersing the electrode in the solvent; after standing for 10 minutes, breaking the vacuum and then re-evacuating, with nitrogen or argon gas used for protection during vacuum breaking; immersing the electrode in the solvent and letting it stand under a protective atmosphere for 12-36 hours; reading the volume of the electrode after immersion in the solvent; and finally calculating the porosity.

[0004] In the prior art, the applicant was unable to find a method that is fully applicable to testing the porosity of metallographic specimens of wearable sealing coatings for aircraft engines and gas turbines. The two prior art references cited above are only applicable to testing the porosity of circuit board coatings and lithium battery electrode coatings, and are used here for reference only. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope, comprising the following steps in sequence:

[0006] Step 1: Prepare a color-developing mixture that can penetrate into the pores of the abrasive sealant coating and cure.

[0007] Step 2: Prepare abrasive sealing coating samples, cut them into metallographic specimens of a certain size as required, and place them in the center of the sample preparation mold;

[0008] Step 3: Pour a certain amount of the colorimetric mixture into the sample preparation mold, so that the metallographic sample is fully immersed in the colorimetric mixture;

[0009] Step 4: Place the sample preparation mold containing the metallographic sample and colorimetric mixture into an oven for heat preservation;

[0010] Step 5: Remove the sample mold from the oven and leave it at room temperature for a certain period of time to allow the color development mixture to fully solidify;

[0011] Step 6: Remove the metallographic sample from the sample preparation mold and polish it until the cross section to be observed on the metallographic sample reaches the surface condition required by metallography.

[0012] Step 7: Place the polished metallographic sample under an optical microscope for observation and take metallographic images. Use the spectrum comparison method or image analysis software measurement method to determine the porosity of the wearable sealing coating metallographic sample.

[0013] Preferably, in step one, the colorimetric mixture includes component A and component B, and the ratio of component A to component B is 1:0.4-0.7.

[0014] In any of the above embodiments, it is preferred that component A is a mixture of bisphenol A diglycidyl ether and a plasticizer, wherein the plasticizer accounts for 5-10% of the mass percentage of component A, and the epoxy equivalent of component A is 170-280 g / mol; component B includes a crosslinking agent, a modifier, a diluent, and a color developer, wherein each substance accounts for 45-65% of the mass percentage of component B, the crosslinking agent is 5-10%, the modifier is 5-10%, the diluent is 5-10%, and the color developer is 25-35%.

[0015] In any of the above embodiments, it is preferred that the plasticizer includes at least two of dodecyl glycidyl ether, glycidyl neodecanoate, and 2-tolueneglycidyl ether. Selecting at least two of these substances as plasticizers can further reduce the viscosity of the mixture at high temperatures, increase the fluidity of the mixture, and allow the mixture to fully penetrate into the pores.

[0016] Extensive testing has demonstrated that the following combinations are more preferred for formulating plasticizers:

[0017] (1) Combination of two substances

[0018] Dodecyl glycidyl ether and neodecanoic acid glycidyl ester are mixed in a ratio of 1:8-10.

[0019] Dodecyl glycidyl ether and 2-toluene glycidyl ether are mixed in a ratio of 1:0.7-1.2.

[0020] 2-Toluene glycidyl ether and neodecanoic acid glycidyl ester are mixed in a ratio of 1:8-10.

[0021] (2) Combination of three substances

[0022] The mixture of dodecyl glycidyl ether, 2-toluene glycidyl ether, and neodecanoic acid glycidyl ester is in a ratio of 0.5-1:1-2:8-18.

[0023] Preferably, in any of the above embodiments, the crosslinking agent comprises one or more of 1,3-propanediamine, 3,3'-dichloro-4,4'-diaminodiphenylmethane, ethanolamine, diethanolamine, and triethanolamine. These substances can be used in the synthesis of epoxy resin curing agents. At high temperatures, they slow down the crosslinking process, resulting in a lower viscosity of the mixture, thereby increasing the fluidity of the mixture and promoting its full penetration into the pores. In contrast, the crosslinking agents used in the prior art accelerate the curing of the mixture at high temperatures, leading to increased viscosity, reduced fluidity, and difficulty in smoothly penetrating the pores.

[0024] Preferably, in any of the above embodiments, the modifier comprises 4,4'-diaminodiphenyl ether and dimethylacetamide, wherein the ratio of 4,4'-diaminodiphenyl ether to dimethylacetamide is 1:0.1-0.5; or, the modifier comprises 4,4'-difluorobenzophenone and aromatic diphenol, wherein the ratio of 4,4'-difluorobenzophenone to aromatic diphenol is 1:0.7-1.2. The aromatic diphenol includes one or more of catechol, resorcinol, and hydroquinone. These substances have excellent modifying effects, especially when 4,4'-diaminodiphenyl ether is mixed with dimethylacetamide, or when 4,4'-difluorobenzophenone is mixed with aromatic diphenol, which further enhances the penetration of the colorimetric mixture into the pores of the metallographic sample.

[0025] In any of the above embodiments, it is preferred that the diluent comprises β-hydroxyethyl methacrylate and 1,6-hexanediol diacrylate, wherein the ratio of β-hydroxyethyl methacrylate to 1,6-hexanediol diacrylate is 1:0.7-1.2.

[0026] Preferably, in any of the above embodiments, the color-developing agent includes any one of 4-methoxybenzaldehyde, cerium ammonium nitrate, ninhydrin, 2,4-dinitrophenylhydrazine, nano-ferric oxide powder, and phthalocyanine blue. When the color-developing agent is added to the mixture, and the mixture fully penetrates the pores, the color of the color-developing agent can be observed at the pore locations under an optical microscope. 4-methoxybenzaldehyde, cerium ammonium nitrate, ninhydrin, 2,4-dinitrophenylhydrazine, nano-ferric oxide powder, and phthalocyanine blue exhibit yellow, orange-red, blue-violet, yellow, red, and blue colors, respectively.

[0027] In any of the above schemes, it is preferred that, in step one, a certain amount of crosslinking agent, modifier, diluent and color developer are weighed respectively, the four substances are mixed to form component B, component B is placed in a reaction vessel and heated to 60-100℃, after dissolving and stirring evenly, and after reacting for 1-5 hours, it is allowed to stand at room temperature; component A and component B are mixed evenly in a certain ratio.

[0028] In any of the above schemes, preferably, in step two, the prepared abrasive sealing coating sample is an integral sample with the coating sprayed onto the surface of the substrate material. A cut perpendicular to both the coating and the substrate material is made, and the cut surface becomes the cross-section of the metallographic specimen. The metallographic specimen is cuboid in shape, with a length not exceeding 20 mm and a width and height not exceeding 15 mm. The abrasive sealing coating applied to the substrate material surface is a metal-based material (such as NiCrAlY polystyrene), a ceramic-based material (such as ZrO2 polystyrene), or a metal-ceramic composite material (such as NiCrFeAl-BN).

[0029] In any of the above schemes, it is preferred that in step three, the coloring mixture is poured into the sample preparation mold, the coloring mixture completely covers the metallographic sample, and the height of the coloring mixture above the metallographic sample is 1.5-2.5 times the coating thickness in the metallographic sample, so as to ensure that the coloring mixture can fully penetrate into the pores during the subsequent high-temperature heating process.

[0030] In any of the above embodiments, it is preferred that, in step four, the temperature inside the oven is 100-150℃, and the temperature is maintained for 1-2 hours. Extensive testing has proven that maintaining the temperature at 100-150℃ for 1-2 hours results in a lower viscosity and greater fluidity in the colorimetric mixture, thus better promoting its penetration into the pores of the metallographic sample.

[0031] In any of the above schemes, it is preferred that, in step five, the sample preparation mold and the metallographic sample inside it are placed at room temperature for 6-24 hours.

[0032] In any of the above schemes, it is preferred that, in step seven, three methods can be used to determine the porosity:

[0033] Method 1: Observe the cross-section of the metallographic sample under a 100-400x optical microscope, visually observe the area ratio of the colored region in the coating, and then compare it with the standard porosity spectrum to determine the range of porosity.

[0034] Method 2: Take metallographic images under a 100-400x optical microscope. The colored areas are considered as pores. Then compare them with a standard porosity chart to determine the range of porosity.

[0035] Method 3: Take metallographic images under a 100-400x optical microscope, and use image analysis software to calculate the ratio of the area of ​​the colored part to the area of ​​the coating in the field of view, which is the porosity.

[0036] The method for testing the porosity of abrasive sealing coating metallographic samples under an optical microscope according to the present invention involves directly embedding chromogenic groups into the molecular structure of a polymer resin, and then infiltrating the pores of the abrasive sealing coating with a chromogenic mixture. Heating to 100-150°C promotes infiltration. The metallographic sample is then placed at room temperature, where it polymerizes and cures under the action of an initiator and a crosslinking agent. During conventional metallographic sample preparation and observation, the pores of the coating can be filled, and the color will be displayed under an optical microscope. The chromogenic mixture of the present invention exhibits reduced viscosity and increased fluidity upon initial heating after preparation, facilitating infiltration into the pores, and curing during cooling.

[0037] This invention employs a method of mixing liquid epoxy resin with crosslinking agent, modifier, plasticizer, and color developer, followed by heating to penetrate into the pores of the coating and cure. Under an optical microscope, the specific location and area of ​​the pores can be observed, and the porosity can be calculated. This method enables the determination of porosity under conventional metallographic testing conditions for coatings, and the determination results are more accurate. Attached Figure Description

[0038] Figure 1 This is a photograph of a metallographic sample in a preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope according to the present invention.

[0039] Figure 2 for Figure 1 Metallographic images taken under an optical microscope in the illustrated embodiment.

[0040] The diagram is labeled as follows: 1-Matrix material, 2-Coating, 3-Metallic phase, 4-Non-metallic phase, 5-Porosity filled with colorimetric mixture. Detailed Implementation

[0041] To further understand the invention, the following detailed description of the invention will be provided in conjunction with specific embodiments.

[0042] Example 1:

[0043] A preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope according to the present invention includes the following steps in sequence:

[0044] Step 1: Prepare a color-developing mixture that can penetrate into the pores of the abrasive sealant coating and cure.

[0045] Step 2: Prepare abrasive sealing coating samples, cut them into metallographic specimens of a certain size as required, and place them in the center of the sample preparation mold;

[0046] Step 3: Pour a certain amount of the colorimetric mixture into the sample preparation mold, so that the metallographic sample is fully immersed in the colorimetric mixture;

[0047] Step 4: Place the sample preparation mold containing the metallographic sample and colorimetric mixture into an oven for heat preservation;

[0048] Step 5: Remove the sample mold from the oven and leave it at room temperature for a certain period of time to allow the color development mixture to fully solidify;

[0049] Step 6: Remove the metallographic sample from the sample preparation mold and polish it until the cross section to be observed on the metallographic sample reaches the surface condition required by metallography.

[0050] Step 7: Place the polished metallographic sample under an optical microscope for observation and take metallographic images. Use the spectrum comparison method or image analysis software measurement method to determine the porosity of the wearable sealing coating metallographic sample.

[0051] In step one, the colorimetric mixture comprises component A and component B, with a ratio of 1:0.5. Component A is a mixture of bisphenol A diglycidyl ether and a plasticizer, wherein the plasticizer accounts for 5% of the mass percentage of component A, and the epoxy equivalent of component A is 170 g / mol. Component B comprises a crosslinking agent, a modifier, a diluent, and a colorimetric agent, wherein the mass percentages of each substance in component B are: crosslinking agent 45%, modifier 10%, plasticizer 10%, and colorimetric agent 35%.

[0052] The plasticizer is a mixture of dodecyl glycidyl ether and neodecanoic acid glycidyl ester in a ratio of 1:8. The crosslinking agent is 1,3-propanediamine. The modifier is a mixture of 4,4'-diaminodiphenyl ether and dimethylacetamide in a ratio of 1:0.1. The diluent is a mixture of β-hydroxyethyl methacrylate and 1,6-hexanediol diacrylate in a ratio of 1:0.7. The color developer is phthalocyanine blue.

[0053] Weigh out the corresponding amounts of crosslinking agent, modifier, diluent and color developer, mix the four substances to form component B, put component B into a reaction vessel and heat to 100°C, stir evenly after dissolving, react for 3 hours and then let stand to room temperature; mix component A and component B evenly in proportion.

[0054] In step two, the prepared abrasive sealing coating sample is an integral sample with the coating sprayed onto the surface of the substrate material. A cut perpendicular to both the coating and the substrate material is made, and the cut surface becomes the cross-section of the metallographic specimen. The metallographic specimen is rectangular in shape, with a length not exceeding 20 mm and a width and height not exceeding 15 mm. Figure 1 As shown, the wearable sealing coating 2 coated on the surface of the substrate material 1 is a composite material of metal and ceramic, specifically NiCrFeAl-BN.

[0055] In step three, the color development mixture is poured into the sample preparation mold. The color development mixture should completely cover the metallographic sample, and the height of the color development mixture above the metallographic sample should be 2.5 times the thickness of the coating in the metallographic sample. This is to ensure that the color development mixture can fully penetrate into the pores during the subsequent high-temperature heating process.

[0056] In step four, the temperature inside the oven is 150℃, and the temperature is maintained for 2 hours.

[0057] In step five, the sample preparation mold and the metallographic sample inside it are placed at room temperature for 24 hours.

[0058] In step seven, metallographic images are taken under a 100-400x optical microscope. The colored areas are considered as pores, and then compared with a standard porosity chart to determine the range of porosity. Figure 2 As shown, under an optical microscope, the coating was observed to contain a bright white metallic phase 3, a black non-metallic phase 4, and pores 5 filled with a coloring mixture. The pores appeared blue, and the location, shape, and size of the pores could be clearly identified.

[0059] This embodiment describes a method for testing the porosity of abrasive sealing coating metallographic samples under an optical microscope. The method involves directly embedding chromogenic groups into the molecular structure of a polymer resin, and then infiltrating the pores of the abrasive sealing coating with a chromogenic mixture. Heating to 150°C promotes infiltration. The metallographic sample is then placed at room temperature, where it polymerizes and solidifies under the action of an initiator and crosslinking agent. This method fills the coating pores and displays color under an optical microscope, enabling the determination of porosity under conventional coating metallographic testing conditions with greater accuracy. In this embodiment, the chromogenic mixture exhibits reduced viscosity and increased fluidity upon initial heating after preparation, facilitating infiltration into the pores, and solidifies during cooling.

[0060] Example 2:

[0061] Another preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic specimens under an optical microscope according to the present invention has the same testing steps, instruments used, principles, and beneficial effects as in Embodiment 1, except that:

[0062] In step one, the ratio of component A to component B in the colorimetric mixture is 1:0.7. Component A is a mixture of bisphenol A diglycidyl ether and a plasticizer, wherein the plasticizer accounts for 10% of the mass percentage of component A, and the epoxy equivalent of component A is 230 g / mol. Component B includes a crosslinking agent, a modifier, a plasticizer, and a colorimetric agent, wherein the mass percentage of each substance in component B is 65% crosslinking agent, 5% modifier, 5% diluent, and 25% colorimetric agent.

[0063] The plasticizer is a mixture of dodecyl glycidyl ether and 2-tolueneglycidyl ether in a 1:1 ratio. The crosslinking agent is 3,3'-dichloro-4,4'-diaminodiphenylmethane. The modifier is a mixture of 4,4'-diaminodiphenyl ether and dimethylacetamide in a 1:0.5 ratio. The diluent is a mixture of β-hydroxyethyl methacrylate and 1,6-hexanediol diacrylate in a 1:1 ratio. The color developer is nano-ferric oxide powder.

[0064] Component B, formed by mixing the four substances, is placed in a reaction vessel and heated to 60°C. After dissolving, the mixture is stirred until homogeneous and reacted for 5 hours. Then, it is allowed to stand at room temperature. Component A and Component B are mixed evenly in the specified proportions.

[0065] In step four, the temperature inside the oven is 100℃, and the temperature is maintained for 1.5 hours.

[0066] In step five, the sample preparation mold and the metallographic sample inside it are placed at room temperature for 18 hours.

[0067] In step seven, metallographic images are taken under an optical microscope at 100-400x magnification. Image analysis software is used to calculate the ratio of the area of ​​the colored region to the area of ​​the coating in the field of view, which is the porosity.

[0068] Example 3:

[0069] Another preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic specimens under an optical microscope according to the present invention has the same testing steps, instruments used, principles, and beneficial effects as in Embodiment 1, except that:

[0070] In step one, the ratio of component A to component B in the colorimetric mixture is 1:0.4. Component A is a mixture of bisphenol A diglycidyl ether and a plasticizer, wherein the plasticizer accounts for 8% of the mass percentage of component A, and the epoxy equivalent of component A is 280 g / mol. Component B includes a crosslinking agent, a modifier, a plasticizer, and a colorimetric agent, wherein the mass percentage of each substance in component B is 55% crosslinking agent, 8% modifier, 7% diluent, and 30% colorimetric agent.

[0071] The plasticizer is a mixture of 2-toluene glycidyl ether and neodecanoic acid glycidyl ester in a ratio of 1:9. The crosslinking agent is diethanolamine. The modifier is a mixture of 4,4'-diaminodiphenyl ether and dimethylacetamide in a ratio of 1:0.3. The diluent is a mixture of β-hydroxyethyl methacrylate and 1,6-hexanediol diacrylate in a ratio of 1:1.2. The color developer is ninhydrin.

[0072] Component B, formed by mixing the four substances, is placed in a reaction vessel and heated to 80°C. After dissolving, the mixture is stirred until homogeneous and reacted for 1 hour, then allowed to stand at room temperature. Component A and component B are then mixed evenly in the specified proportions.

[0073] In step four, the temperature inside the oven is 125℃, and the temperature is maintained for 1 hour.

[0074] In step five, the sample preparation mold and the metallographic sample inside it are placed at room temperature for 6 hours.

[0075] Example 4:

[0076] Another preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope according to the present invention has the same testing steps, instruments used, principles, and beneficial effects as any of the embodiments one to three, except that:

[0077] In step one, the plasticizer is a mixture of dodecyl glycidyl ether and neodecanoic acid glycidyl ester in a ratio of 1:10. The modifier is a mixture of 4,4'-difluorobenzophenone and catechol in a ratio of 1:0.7.

[0078] Example 5:

[0079] Another preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope according to the present invention has the same testing steps, instruments used, principles, and beneficial effects as any of the embodiments one to three, except that:

[0080] In step one, the plasticizer is a mixture of dodecyl glycidyl ether and 2-toluene glycidyl ether in a ratio of 1:0.7. The modifier is a mixture of 4,4'-difluorobenzophenone and catechol in a ratio of 1:1.2.

[0081] Example 6:

[0082] Another preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope according to the present invention has the same testing steps, instruments used, principles, and beneficial effects as any of the embodiments one to three, except that:

[0083] In step one, the plasticizer is a mixture of dodecyl glycidyl ether and 2-toluene glycidyl ether in a ratio of 1:1.2. The modifier is a mixture of 4,4'-difluorobenzophenone and catechol in a ratio of 1:1.

[0084] Example 7:

[0085] Another preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope according to the present invention has the same testing steps, instruments used, principles, and beneficial effects as any of the embodiments one to three, except that:

[0086] In step one, the plasticizer is a mixture of 2-toluene glycidyl ether and neodecanoic acid glycidyl ester in a ratio of 1:8. The modifier is a mixture of 4,4'-diaminodiphenyl ether and dimethylacetamide in a ratio of 1:0.4.

[0087] Example 8:

[0088] Another preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope according to the present invention has the same testing steps, instruments used, principles, and beneficial effects as any of the embodiments one to three, except that:

[0089] In step one, the plasticizer is a mixture of 2-toluene glycidyl ether and neodecanoic acid glycidyl ester, with a ratio of 1:10. The modifier is a mixture of 4,4'-difluorobenzophenone and catechol, with a ratio of 1:0.8.

[0090] Example 9:

[0091] Another preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope according to the present invention has the same testing steps, instruments used, principles, and beneficial effects as any of the embodiments in Examples 1 to 8, except that:

[0092] In step one, the plasticizer is a mixture of dodecyl glycidyl ether, 2-toluene glycidyl ether, and neodecanoic acid glycidyl ester, with a ratio of 0.5:1:8.

[0093] Example 10:

[0094] Another preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope according to the present invention has the same testing steps, instruments used, principles, and beneficial effects as any of the embodiments in Examples 1 to 8, except that:

[0095] In step one, the plasticizer is a mixture of dodecyl glycidyl ether, 2-toluene glycidyl ether, and neodecanoic acid glycidyl ester, with a ratio of 1:2:18.

[0096] Example 11:

[0097] Another preferred embodiment of the method for testing the porosity of a wearable sealing coating metallographic sample under an optical microscope according to the present invention has the same testing steps, instruments used, principles, and beneficial effects as any of the embodiments in Examples 1 to 8, except that:

[0098] In step one, the plasticizer is a mixture of dodecyl glycidyl ether, 2-toluene glycidyl ether, and neodecanoic acid glycidyl ester, with a ratio of 0.8:1.5:12.

[0099] Special Note: The technical solutions of this invention involve numerous parameters, and the synergistic effects between these parameters must be comprehensively considered to achieve the beneficial effects and significant progress of this invention. Furthermore, the value ranges of each parameter in the technical solutions were obtained through extensive experimentation. For each parameter and its combinations, the inventors recorded a large amount of experimental data; however, due to space limitations, the specific experimental data is not disclosed here. All substances used in the embodiments of this invention were purchased from Aladdin Chemical Reagents website.

[0100] Those skilled in the art will readily understand that the method for testing the porosity of abrasive sealing coating metallographic samples under an optical microscope according to the present invention includes any combination of the inventive description and specific embodiments described in the above specification and the various parts shown in the accompanying drawings. Due to space limitations and for the sake of brevity, not all of these combinations have been described in detail. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method of testing the porosity of a metallurgical specimen of an abradable seal coating under an optical microscope, characterized in that, The method is suitable for testing the porosity of the metallographic sample of the abradable seal coating of the aircraft engine and the gas turbine, the abradable seal coating is a composite material of metal and ceramic, namely NiCrFeAl-BN; the method comprises the following steps in sequence: Step one: preparing a color developing mixture which can penetrate into the pores of the abradable seal coating and solidify; Step two: preparing the abradable seal coating sample, which is an integral sample with the coating sprayed on the surface of the base material, cutting vertically to the coating and the base material, the cutting surface is the cross section of the metallographic sample, the metallographic sample is a cuboid, the length is not more than 20mm, and the width and height are both not more than 15mm, and the metallographic sample is placed in the center of the sample preparation mold; Step three: pouring a certain amount of color developing mixture into the sample preparation mold, the color developing mixture completely covers the metallographic sample, and the height of the color developing mixture above the metallographic sample is 1.5-2.5 times the thickness of the coating in the metallographic sample, so as to ensure that the color developing mixture can fully penetrate into the pores during the later high temperature heating process; Step four: placing the sample preparation mold containing the metallographic sample and the color developing mixture into an oven at 100-150℃ and keeping warm for 1-2h; Step five: taking out the sample preparation mold from the oven and placing it at room temperature for 6-24h to make the color developing mixture fully solidify; Step six: taking out the metallographic sample from the sample preparation mold and polishing it until the cross section to be observed on the metallographic sample reaches the surface state required by the metallography; Step seven: placing the polished metallographic sample under an optical microscope for observation and taking a metallographic picture, and determining the porosity of the abradable seal coating metallographic sample by using the atlas comparison method or the image analysis software measurement method; In step one, the color developing mixture comprises A component and B component, and the ratio of the A component to the B component is 1:0.4-0.7; The A component is a mixture of bisphenol A diglycidyl ether and a plasticizer, wherein the mass percentage of the plasticizer in the A component is 5-10%, and the epoxy equivalent weight of the A component is 170-280g / mol; the plasticizer comprises at least two of dodecyl glycidyl ether, neodecanoyl glycidyl ester and 2-toluene glycidyl ether; If two substances are selected for combination: dodecyl glycidyl ether and neodecanoyl glycidyl ester are mixed, and the ratio of the two is 1:8-10; or dodecyl glycidyl ether and 2-toluene glycidyl ether are mixed, and the ratio of the two is 1:0.7-1.2; or 2-toluene glycidyl ether and neodecanoyl glycidyl ester are mixed, and the ratio of the two is 1:8-10; If three substances are selected for combination: dodecyl glycidyl ether, 2-toluene glycidyl ether and neodecanoyl glycidyl ester are mixed, and the ratio of the three is 0.5-1:1-2:8-18; The B component comprises a crosslinking agent, a modifier, a diluent and a color developing agent, wherein the mass percentage of each substance in the B component is 45-65% for the crosslinking agent, 5-10% for the modifier, 5-10% for the diluent and 25-35% for the color developing agent. The cross-linking agent comprises one or more of 1,3-propanediamine, 3,3'-dichloro-4,4'-diaminodiphenyl methane, ethanolamine, diethanolamine, and triethanolamine; The modifier comprises 4,4'-diamino diphenyl ether and dimethylacetamide, the ratio of the 4,4'-diamino diphenyl ether to the dimethylacetamide being 1:0.1-0.5; or the modifier comprises 4,4'-difluorobenzophenone and aromatic dihydric phenol, the ratio of the 4,4'-difluorobenzophenone to the aromatic dihydric phenol being 1:0.7-1.2, the aromatic dihydric phenol comprising one or more of o-dihydroxybenzene, m-dihydroxybenzene, and p-dihydroxybenzene; The diluent comprises methacrylic acid-beta-hydroxyethyl ester and 1,6-hexanediol diacrylate, the ratio of the methacrylic acid-beta-hydroxyethyl ester to the 1,6-hexanediol diacrylate being 1:0.7-1.2; The color developing agent comprises any one of 4-methoxybenzaldehyde, cerium ammonium nitrate, indantrione, 2,4-dinitrophenylhydrazine, nano iron oxide powder, and phthalocyanine blue; A certain amount of the cross-linking agent, the modifier, the diluent, and the color developing agent are weighed respectively, the four substances are mixed to form the B component, the B component is placed in a reaction kettle and heated to 60-100 DEG C, dissolved and stirred uniformly, and then left to stand at room temperature after reaction for 1-5 hours; the A component and the B component are mixed uniformly at a certain ratio; In step seven, the porosity is determined by using the following three methods: The cross-coloring area in the coating is observed under a 100-400 times optical microscope, and the area ratio in the coating is observed by naked eyes, and then compared with a standard porosity atlas to determine the porosity range; The cross-coloring area in the coating is observed under a 100-400 times optical microscope, and the area ratio in the coating is observed by naked eyes, and then compared with a standard porosity atlas to determine the porosity range; The cross-coloring area in the coating is observed under a 100-400 times optical microscope, and the area ratio in the coating is observed by naked eyes, and then compared with a standard porosity atlas to determine the porosity range.

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