Preparation method of metallographic sample of large component coated with thermal barrier coating

Abstract

The invention belongs to the field of metallographic sample preparation, and particularly relates to a metallographic sample preparation method of a large component coated with a thermal barrier coating, which comprises the following steps: step 1, selecting a to-be-observed area with a crack and coating falling position on the surface of the component, scribing by extending a certain distance towards the periphery by taking the to-be-observed area as the center, and cutting along the scribing to obtain a sample; 2, the sample is subjected to cold inlaying and curing through a cold inlaying agent, and damage to cracks and a coating in the further machining process of the sample is avoided; 3, the sample is cut in the direction perpendicular to the surface crack of the sample so that the size of the sample can be matched with a scanning electron microscope sample chamber, and grinding and polishing are conducted; and 4, cleaning and blow-drying the sample, spraying metal, placing the sample on a sample table, pasting a conductive adhesive tape, and carrying out scanning electron microscope microstructure observation.

Description

Technical Field

[0001] The present application belongs to the field of metallographic sample preparation, and in particular relates to a method for preparing a metallographic sample of a large component coated with a thermal barrier coating. Background Art

[0002] The invention relates to the field of metallographic sample preparation, in particular to the preparation of metallographic samples of components coated with thermal barrier coatings, brittle materials with ceramic properties and cracks, and belongs to the field of microstructure observation and detection technology.

[0003] Hot end components are the most important components in aircraft engines and gas turbines. They are subjected to the high-temperature airflow at the outlet of the combustion chamber during service, so the hot end component materials are required to have good high-temperature performance. At present, the common hot end component materials are high-temperature alloys. With the increase of the outlet temperature of the combustion chamber, taking turbine blades as an example, the blade material preparation process has also evolved from traditional forging to the current single crystal high-temperature alloy, but the gas temperature still exceeds the allowable temperature of the metal material. Therefore, a high-temperature resistant, corrosion-resistant, and highly heat-insulating thermal barrier coating is coated on the surface of the component to reduce the temperature of the metal substrate. During use, cracks or other damage may occur in the thermal barrier coating, metal substrate, and the interface between the coating and the substrate, which will have a great impact on the service performance of the entire component. In order to study the initiation, expansion, and evolution of cracks, it is necessary to prepare metallographic samples of cracked components for microstructural observation for analysis and research.

[0004] In terms of the publicly available prior art, domestic research institutes mainly prepare metallographic samples and conduct research on small specimens, but have not considered the sample preparation of real large components.

[0005] Existing technical solutions and shortcomings of the existing technology:

[0006] 1) Small specimens can be directly placed in the sample chamber for microstructure observation due to their small size and regular shape. However, large real components cannot be placed due to limited space in the sample chamber. At the same time, some components have irregular shapes and cannot be placed stably, posing a safety hazard of tipping over.

[0007] 2) Although ceramic brittle components can be cut using a diamond cutting machine, cracks may occur during cutting, so it is impossible to accurately determine whether the cracks are originally in the component or caused during cutting. If it is known that the component already has cracks, the coating may fall off as a whole during cutting, and the coating detachment position cannot be accurately restored, making it impossible to obtain the crack propagation path. Summary of the invention

[0008] In order to solve the above problems, the present application provides a method for preparing metallographic samples of large components coated with thermal barrier coatings, comprising:

[0009] Step 1: Select an area to be observed with cracks and coating shedding positions on the surface of the component, draw a line with a certain distance extending around the area to be observed, and cut along the line to obtain a sample;

[0010] Step 2: cold mounting the sample using a cold mounting agent and curing the sample to avoid damage to the cracks and coating during further processing;

[0011] Step 3: Cut the sample perpendicular to the crack direction on the sample surface to make it fit the sample chamber of the scanning electron microscope, and grind and polish it;

[0012] Step 4: Clean the sample, blow dry it, and then spray gold. Then place the sample on the sample stage and stick conductive tape on it for scanning electron microscope microstructure observation.

[0013] Preferably, in step 1, a diamond cutting machine is used to cut the component at a rotation speed of 50 to 300 RPM.

[0014] Preferably, in step 4, when the sample is too large to fit into the sample chamber of the scanning electron microscope, it is first observed using an optical microscope after being cleaned and dried with anhydrous ethanol, and then step 3 is repeated until the sample can fit into the sample chamber of the scanning electron microscope.

[0015] Preferably, in step 1, when the thickness of the metal substrate of the component is greater than a preset value, the component surface coating is cut first, and then the metal substrate is cut using the electric spark wire cutting technology.

[0016] Preferably, the cold mounting agent is prepared by mixing epoxy resin and curing agent in a ratio of 1:1 to 2:1.

[0017] Preferably, the specific method of cold mounting the sample using a cold mounting agent in step 2 comprises:

[0018] Make a mold that fits the sample, place the sample in the center of the mold, and use the cold mounting process to pour the cold mounting agent along the sample or the edge of the mold until the area to be observed is completely immersed in the cold mounting agent, and place it at room temperature for 24 to 48 hours to solidify.

[0019] Advantages of this application include:

[0020] 1) A method for selecting and cutting characteristic parts of large real components coated with thermal barrier coatings was proposed, which enabled the microstructure observation of typical parts of large components;

[0021] 2) A method for protecting the characteristics of components with damage such as cracks and chipped pieces is proposed. It does not generate new damage but protects existing damage, so as to truly and accurately obtain the damage characteristics and provide a basis for the study of damage evolution and expansion laws. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a flow chart of a method for preparing metallographic samples of large components coated with thermal barrier coatings according to a preferred embodiment of the present application. DETAILED DESCRIPTION

[0023] In order to make the technical solution and advantages of the present application clearer, the technical solution of the present application will be further described in detail in detail and in detail in conjunction with the accompanying drawings. It can be understood that the specific embodiments described here are only partial embodiments of the present application, which are only used to explain the present application, not to limit the present application. It should be noted that, for the convenience of description, only the parts related to the present application are shown in the accompanying drawings, and other related parts can refer to the general design. In the absence of conflict, the embodiments in the present application and the technical features in the embodiments can be combined with each other to obtain new embodiments.

[0024] In addition, it should be noted that, unless otherwise clearly specified and limited, the words "installed", "connected", "connected" and similar terms used in the description of this application should be understood in a broad sense. For example, the connection can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, an indirect connection through an intermediate medium, or the internal connection of two components. Technical personnel in the field can understand their specific meanings in this application according to the specific circumstances.

[0025] Step 1: Selection and segmentation of typical feature parts of components

[0026] Select the area to be observed on the surface of the component, such as cracks, coating shedding, etc., and draw a line around the area with a radius of (3-5) cm. Use a diamond cutter at a speed of (50-300) RPM to cut the component at the drawn line. If the metal substrate of the component is thick, the metal substrate can be cut by wire EDM technology after the surface coating is cut. In this way, the characteristic parts of the component are obtained.

[0027] Step 2: Inlaying the characteristic parts of components

[0028] Based on step 1, select a sample inlay mold of appropriate size. You can also make a suitable mold according to the size of the sample, apply a mold release agent inside the mold, put the characteristic part cut in step 1 into the center of the mold, use a cold inlay process, use an epoxy resin and a curing agent in a ratio of 1:1 to 2:1, and immediately pour along the edge of the component or mold after mixing the cold inlay agent. When the characteristic part is completely immersed in the cold inlay agent, place it at room temperature for (24 to 48 hours) to cure;

[0029] Step 3: Cutting the damaged area of ​​the component

[0030] Based on step 2, the mounted sample is cut with a diamond cutting machine perpendicular to the crack direction or the coating shedding position, and the cutting speed is the same as that in step 1;

[0031] Step 4: Grinding and polishing of metallographic samples

[0032] Based on the sample cut in step 3, the prototype of the metallographic sample is basically determined, and grinding and polishing are completed according to the preparation process of the metallographic sample;

[0033] Step 5: Spraying and observation of metallographic samples

[0034] Based on the sample prepared in step 4, clean it with anhydrous ethanol before observation, blow dry it and immediately spray gold, then place the sample on the sample stage and stick conductive tape on it for scanning electron microscope microstructure observation; if the sample is still too large to fit into the scanning electron microscope sample chamber at this time, clean it with anhydrous ethanol and blow dry it, then first observe it with an optical microscope, and then repeat steps 3 and 4 until the sample can fit into the scanning electron microscope sample chamber.

[0035] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application shall be based on the protection scope of the claims.

Claims

1. A method for preparing metallographic samples of large components coated with thermal barrier coatings, characterized in that: include: Step 1: Select an area to be observed with cracks and coating shedding positions on the surface of the component, draw a line with a certain distance extending around the area to be observed as the center, and cut along the line to obtain a sample; Step 2: cold mounting the sample using a cold mounting agent and curing the sample to avoid damage to the cracks and coating during further processing; Step 3: Cut the sample perpendicular to the crack direction on the sample surface to make it fit the sample chamber of the scanning electron microscope, and grind and polish it; Step 4: Clean the sample, blow dry it, and then spray gold. Then place the sample on the sample stage and stick conductive tape on it for scanning electron microscope microstructure observation.

2. The method for preparing metallographic samples of large components coated with thermal barrier coatings according to claim 1, characterized in that: In step 1, a diamond cutting machine is used to cut the component at a rotation speed of 50 to 300 RPM.

3. The method for preparing metallographic samples of large components coated with thermal barrier coatings according to claim 1, characterized in that: In step 4, when the sample is too large to fit into the sample chamber of the scanning electron microscope, it is first observed using an optical microscope after being cleaned and blown dry with anhydrous ethanol, and then step 3 is repeated until the sample can fit into the sample chamber of the scanning electron microscope.

4. The method for preparing metallographic samples of large components coated with thermal barrier coatings according to claim 2, characterized in that: In step 1, when the thickness of the metal substrate of the component is greater than a preset value, the surface coating of the component is cut first, and then the metal substrate is cut using the electric spark wire cutting technology.

5. The method for preparing metallographic samples of large components coated with thermal barrier coatings according to claim 1, characterized in that: The cold mounting agent is made of epoxy resin and curing agent in a ratio of 1:1 to 2:

1.

6. The method for preparing metallographic samples of large components coated with thermal barrier coatings according to claim 1, characterized in that: The specific method of cold mounting the sample using a cold mounting agent in step 2 includes: Make a mold that fits the sample, place the sample in the center of the mold, and use the cold mounting process to pour the cold mounting agent along the sample or the edge of the mold until the area to be observed is completely immersed in the cold mounting agent, and place it at room temperature for 24 to 48 hours to solidify.

Images