Nickel-based alloy blade overheating structure evaluation method

Abstract

The invention discloses a nickel-based alloy blade overheating structure evaluation method. The method comprises the following steps: taking a sample for metallographic analysis from a blade; inlaying the sample by adopting a resin material to obtain an insert; polishing the insert, and corroding the insert by adopting a corrosion mode capable of displaying a gamma'phase; carrying out magnification observation on the insert, and comparing with the front edge, the middle chord and the rear edge in the tissue of the cross section sample by taking the tissue of the tenon part in the longitudinal section sample as a standard; if any one of five conditions of cracks in the area outside the blade tip, grain boundary creep cavities in the direction perpendicular to the main shaft of the blade, gamma'phase redissolution with the volume fraction smaller than 45%, gamma 'phase redissolution with the gamma' phase rafts and matrix initial dissolution exists, it is judged that the blade cannot continue to be used. Whether the overtemperature blade can continue to serve or not can be rapidly judged.

Description

Technical Field

[0001] The invention belongs to the technical field of blade microstructure assessment, and in particular relates to a method for assessing the overheated structure of a nickel-based alloy blade. Background Art

[0002] Nickel-based superalloys are nickel-based alloys with a certain amount of chromium added, as well as solid solution strengthening, precipitation strengthening, and grain boundary strengthening elements for full strengthening. They are primarily used in industries such as aviation, aerospace, shipbuilding, and power generation. They are the most widely used, with the most brands, the largest usage volume, and the most important position. Within the entire superalloy field, nickel-based superalloys hold a particularly important position. Compared to iron- and cobalt-based alloys, nickel-based alloys offer superior high-temperature performance and excellent oxidation and corrosion resistance. It can be said that the development of nickel-based superalloys has laid the foundation for the development of aviation turbine engines and has also determined the development of the aviation industry.

[0003] In aircraft engines, nickel-based superalloys are primarily used to manufacture hot-end components such as turbine blades, guide vanes, turbine disks, and combustion chambers. As the most critical and crucial engine component, turbine blades are also subject to the harshest service environments. Operating under high temperatures, high pressures, and thermal corrosion, turbine blades are primarily subject to fatigue, overheating, creep, foreign object damage, and thermal corrosion. Overheating accounts for 6.87% of failures. Generally speaking, overheating can occur during engine operation due to factors such as surge, inlet distortion, poor fuel regulation, poor nozzle atomization, and operational errors. Overheating can severely damage turbine blades, leading to premature failure and even major accidents.

[0004] Nickel-based cast superalloys use a γ phase as the matrix, strengthened by adding aluminum, titanium, niobium, tantalum, and other additives to form a γ′ phase. The γ′ phase is present in significant quantities, sometimes exceeding 60%. To achieve optimal strengthening, the γ′ phase should have a regular morphology, uniform distribution, and size. Overheating can cause changes in the morphology, quantity, and size of the γ′ strengthening phase, weakening the strengthening effect.

[0005] How to quickly determine whether an overheated blade can continue to serve is something worth studying, and there is currently no public report on how to evaluate the overheating structure of high-temperature alloys. Summary of the Invention

[0006] The present invention provides a method for evaluating the overheated structure of a nickel-based alloy blade, which can quickly determine whether an overheated blade can continue to serve.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] The present invention discloses a method for evaluating the overheated structure of a nickel-based alloy blade, comprising the following steps:

[0009] Take samples for metallographic analysis from the blades. For solid blades, the samples include a longitudinal section sample and a high-temperature zone cross-sectional sample, and the longitudinal section sample of a blade with a shroud must include the shroud portion. For hollow blades, the samples include three cross-sectional samples including the high-temperature zone and the high-stress zone, and one longitudinal section sample.

[0010] Inlaying the sample with a resin material to obtain an inlaid piece;

[0011] polishing the inlay and etching the inlay using an etching method that can reveal a γ′ phase;

[0012] The inlay is magnified and observed, and the microstructure of the tenon part in the longitudinal section sample is used as the standard for comparison with the microstructure of the leading edge, mid-chord, and trailing edge in the cross-sectional sample. If any of the following five conditions exist: cracks in the area outside the blade tip, grain boundary creep voids perpendicular to the main axis of the blade, γ' phase re-dissolution with a volume fraction less than 45%, γ' phase re-dissolution and γ' phase rafting, and matrix initial dissolution, the blade is judged to be unusable.

[0013] Compared with the prior art, the present invention has at least the following advantages and beneficial effects:

[0014] The present invention takes samples of the overheated blade and embeds them for magnified observation, and uses the tissue at the tenon as a reference to judge the degradation of the leading edge, mid-chord and trailing edge tissues, so as to quickly determine whether the blade can continue to serve. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 This is the microstructure diagram of the cross-section sample of the high-temperature zone of the nickel-based alloy blade of a certain engine in Example 1 after magnification 5000 times;

[0017] Figure 2 This is the microstructure diagram of the cross-section sample of the high-temperature zone of the nickel-based alloy blade of a certain engine in Example 1 after magnification 1000 times;

[0018] Figure 3 This is the microstructure diagram of the cross-section sample of the high stress area of ​​the nickel-based alloy blade of a certain engine in Example 1 after magnification 5000 times;

[0019] Figure 4This is the microstructure diagram of the cross-section sample of the high stress area of ​​the nickel-based alloy blade of a certain engine in Example 1 after magnification 1000 times;

[0020] Figure 5 This is the microstructure diagram of the tenon part of the longitudinal section of the nickel-based alloy blade of a certain engine in Example 1 after magnification 5000 times;

[0021] Figure 6 This is the microstructure diagram of the tenon of the longitudinal section specimen of a nickel-based alloy blade of a certain engine in Example 1 after magnification 1000 times;

[0022] Figure 7 This is the microstructure diagram of the cross-section sample of the high-temperature zone of the nickel-based alloy blade of a certain engine in Example 2 after magnification 5000 times;

[0023] Figure 8 This is the microstructure diagram of the cross-section sample of the high-temperature zone of the nickel-based alloy blade of a certain engine in Example 2 after magnification 1000 times;

[0024] Figure 9 This is the microstructure diagram of the cross-section sample of the high stress area of ​​the nickel-based alloy blade of a certain engine in Example 2 after magnification 5000 times;

[0025] Figure 10 This is the microstructure diagram of the cross-section sample of the high stress area of ​​the nickel-based alloy blade of a certain engine in Example 2 after being magnified 1000 times;

[0026] Figure 11 This is the microstructure diagram of the tenon of the longitudinal section specimen of a nickel-based alloy blade of an engine in Example 2 after magnification 5000 times;

[0027] Figure 12 This is the microstructure diagram of the tenon part of the longitudinal section of the nickel-based alloy blade of a certain engine in Example 2 after magnification 1000 times;

[0028] Figure 13 This is a schematic diagram of the sampling position of solid leaf specimens without crowns;

[0029] Figure 14 This is a schematic diagram of the sampling position of the crowned solid leaf specimen;

[0030] Figure 15 This is a schematic diagram of the sampling position of the hollow blade sample;

[0031] Figure 16 Schematic diagram of the sample and the inlay mold, wherein the sample is a hollow blade sample;

[0032] Figure 17 Schematic diagram of the specimen and the inlay mold, where the specimens are two groups of solid leaves with crowns. DETAILED DESCRIPTION

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention more clear, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations.

[0034] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention as claimed, but rather merely represents selected embodiments of the present invention. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are also within the scope of protection of the present invention.

[0035] It should be noted that, in the absence of conflict, the embodiments and features of the embodiments of the present invention can be combined with each other.

[0036] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined or explained in subsequent drawings.

[0037] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is typically placed when in use, or are the orientations or positional relationships commonly understood by those skilled in the art. These terms are intended only to facilitate the description of the present invention and to simplify the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, be constructed, or operate in a specific orientation. Therefore, they should not be construed as limiting the present invention. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0038] The present invention discloses a method for evaluating overheated structure of a nickel-based alloy blade, which comprises steps S01 to S04.

[0039] Step S01: Take samples for metallographic analysis from the blade. For a solid blade, the samples include a longitudinal section sample and a high-temperature zone cross-sectional sample 41, and the longitudinal section sample 42 of a shrouded blade must include a shroud portion 421. For a hollow blade, the samples include three cross-sectional samples including a high-temperature zone and a high-stress zone, and one longitudinal section sample.

[0040] For leaves with different structures, the sampling positions are also different. The specific sampling positions are as follows: Figures 13 to 15 As shown, the sampling position of the longitudinal section sample is shown in Figures 13 to 15 The AA position in the figure, the sampling position of the cross-section specimen is as follows: Figures 13 to 15 When sampling, the distance between the longitudinal section sample and the exhaust edge 1 is 3.2mm to 6.4mm, leaving enough thickness for metallographic sample preparation.

[0041] When sampling, use an automatic, manual, or wire-cutting machine. The blade clamp should be designed to prevent deformation and cracking of the surface coating. Aluminum or diamond blades can be used. During cutting, use commercial coolant, control the feed rate to 0.02mm / s to 0.04mm / s, and the rotation speed to 2000rpm to 2500rpm to ensure that the cut surface is free of damage and overheating, thereby improving the accuracy of overheated structure assessment.

[0042] Step S02: Inlaying the sample with a resin material to obtain an inlaid part.

[0043] During the inlaying process, the sample is inlaid using an inlaying machine. Specifically, the inlaying machine can be a hot pressure inlaying machine or a cold vacuum inlaying machine. The resin material is phenolic resin, transparent synthetic resin or epoxy resin.

[0044] The mounting parameters of the mounting machine are pressure 140 bar to 180 bar, temperature 150° C. to 180° C., and time 5 min to 8 min to prevent gaps between the sample and the mounting material and to prevent cracks in the coating.

[0045] The distance between the specimen and the edge of the inlay mold 3 is greater than 1.27 mm to prevent the inlay material from cracking. Figure 16 、 17 shown.

[0046] Step S03: polishing the inlay and etching the inlay in a manner that can reveal the γ′ phase.

[0047] This step polishes the inlay to an acceptable mirror finish. Specifically, manual polishing or automated polishing equipment can be used to remove at least 0.25 mm of material from the cut surface to achieve an acceptable mirror finish and improve the accuracy of subsequent overheated structure assessments. Polishing parameters include a pressure of 12 to 16 N, a rotation speed of 350 to 450 rpm, and a time of 2 to 4 minutes. The polishing agent is typically a suspension of water-based diamond and a cooling lubricant to prevent coating cracking, specimen rounding, overheating, over-polishing, and separation of the specimen from the inlay.

[0048] After polishing, the inlay should be etched as soon as possible until the sample surface exhibits a golden yellow color. Etching can be performed using a variety of existing etching methods that can reveal the γ′ phase, with copper sulfate wiping being preferred. This method is relatively simple and convenient, and the etchant contains the following components in a volume ratio of CuSO₄:HCl:H₂O = 1:5:5. Dip cotton in the etchant and wipe it over the polished surface of the inlay three to five times, until the sample surface exhibits noticeable discoloration, until it exhibits a golden yellow color.

[0049] Scratches, stains, insufficient corrosion and excessive corrosion are not allowed on the surface of the inlay.

[0050] Step S04: Magnify and observe the inlay, and compare the microstructure of the tenon portion of the longitudinal section sample with the microstructure of the leading edge, mid-chord, and trailing edge of the cross-sectional sample. If any of the following conditions exists: cracks in areas outside the blade tip, grain boundary creep cavities perpendicular to the main axis of the blade, γ' phase re-dissolution with a volume fraction less than 45%, γ' phase re-dissolution and γ' phase rafting, or matrix incipient dissolution, the blade is determined to be unusable.

[0051] During observation, use an optical microscope or scanning electron microscope that can magnify 1000 to 5000 times. The observation area should avoid the coating and the coating diffusion area, and the observation point should be about 0.25 mm away from the coating diffusion area.

[0052] During observation, the microstructure at the tenon of the longitudinal cross-section specimen is used as the standard. This is because the blade tenon experiences relatively low temperatures during engine operation, and its cross-sectional microstructure typically exhibits minimal degradation. The tenon microstructure serves as a benchmark for evaluating the microstructure of the blade's high-temperature region, assessing its degradation.

[0053] The typical characteristics of the microstructure of nickel-based alloys are as follows:

[0054] 1. There are a large number of γ' precipitates in the γ matrix. Most alloys usually have cubic γ' precipitates, and some other alloys have non-cubic γ' precipitates.

[0055] 2. Some alloys contain a small amount of island-shaped γ eutectics and massive MC-type carbides, which are mainly located at grain boundaries and interdendritic regions.

[0056] 3. Borides, nitrides and other types of carbides can exist in the form of chains along the grain boundaries. Other types of carbides such as M6C and M 23 C6.

[0057] The effect of high temperature on microstructure is mainly the change of morphology, content, size and distribution of γ' precipitated phase in the matrix caused by high temperature, which is manifested in the following aspects:

[0058] 1. γ' phase coarsening

[0059] Among them, the manifestation of γ' phase coarsening is:

[0060] a. The size of the γ′ phase is larger than that of the original microstructure, but the volume fraction is similar.

[0061] b. The shape of the γ' phase is slightly spherical.

[0062] c. Eutectics, carbides, borides and nitrides are not affected.

[0063] 2. γ' phase dissolution

[0064] Among them, the manifestation of γ' phase dissolution is:

[0065] a.The size and volume fraction of γ' phase are reduced.

[0066] b. The shape of the γ' phase is obviously more irregular.

[0067] 3. γ' phase rafting

[0068] Among them, the manifestation of γ' phase rafting is:

[0069] a. The shape of the γ' phase is mainly elongated in one direction.

[0070] b. The volume fraction of γ' phase is similar to that of the original microstructure.

[0071] c. The elongation of the γ' phase is always perpendicular to the direction of local stress.

[0072] Blades in service may have a mixed structure of γ' phase coarsening + rafting or γ' phase dissolution + rafting. Creep voids may also exist in blades in long-term service, mainly near grain boundaries and phase boundaries. Grain boundary voids related to creep preferentially extend in the direction perpendicular to the main axis of the blade body.

[0073] In this regard, when judging whether the blade can continue to be used, if it meets any of the following five conditions, it cannot be used; otherwise, it can be used.

[0074] The following five situations may cause you to stop using the device:

[0075] 1. There are cracks in the area outside the blade tip;

[0076] 2. Grain boundary creep cavities perpendicular to the main axis of the blade;

[0077] 3. The γ' phase dissolves back and the volume fraction is less than 45%;

[0078] 4. γ' phase dissolves back and γ' phase rafts

[0079] 5. Initial dissolution of the matrix.

[0080] Example 1: Take a nickel-based alloy blade of a certain type of engine as an example. The engine experienced a transient overtemperature of 2°C for 2 seconds. The above method was used to analyze the gas turbine blade sample. The microstructure of the high temperature area, high stress area and tenon part is as follows: Figures 1 to 6 As shown in the figure. Among them, the magnified image of the cross-section sample in the high temperature zone after magnification 5000 times is shown in the figure. Figure 1 As shown, the enlarged image of the cross-section sample in the high temperature zone after magnification 1000 times is as follows Figure 2 As shown; the cross-sectional sample structure of the high stress area is magnified 5000 times as shown in Figure 3 As shown in the figure, the cross-section of the high stress area is magnified 1000 times as shown in the figure. Figure 4 As shown in the figure, the enlarged image of the tenon part of the longitudinal section sample after magnification 5000 times is as follows Figure 5 As shown in the figure, the enlarged image of the tenon part of the longitudinal section sample after 1000 times magnification is as follows Figure 6 Observation comparison Figures 1 to 6 It can be judged that the blade body tissue has degraded, but no overheating tissue characteristics have appeared. The blade can continue to serve. The blade has been used for 900 hours.

[0081] Example 2: Take the nickel-based alloy blade of a certain type of engine as an example. The engine overheated to 300℃. The above method was used to analyze the structure of the turbine blade. The high temperature area, high stress area and tenon part structure are as follows: Figures 7 to 12 As shown in the figure. Among them, the magnified image of the cross-section sample in the high temperature zone after magnification 5000 times is shown in the figure. Figure 7 As shown, the enlarged image of the cross-section sample in the high temperature zone after magnification 1000 times is as follows Figure 8 As shown; the cross-sectional sample structure of the high stress area is magnified 5000 times as shown in Figure 9 As shown in the figure, the cross-section of the high stress area is magnified 1000 times as shown in the figure. Figure 10 As shown in the figure, the enlarged picture of the tenon part of the longitudinal section specimen after 5000 times magnification is as follows Figure 11 As shown in the figure, the enlarged picture of the tenon part of the longitudinal section specimen after 1000 times magnification is as follows Figure 12 Observation comparison Figures 7 to 12 It can be judged that the tissue in the high-temperature area of ​​the blade has completely dissolved, and the tissue in the high-stress area has shown dissolution and rafting characteristics, showing typical overheating tissue characteristics. The blade cannot continue to be used.

[0082] The above method only requires metallographic sample preparation materials and equipment and an optical microscope or scanning electron microscope. It can quickly and easily perform overheating tissue analysis and tissue degradation judgment on nickel-based alloy blades, provide support for judging whether the blades can continue to be used or extend their life, and can save a large number of turbine blades and achieve the reuse of blades that have reached the end of their service life.

[0083] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for evaluating the overheated structure of a nickel-based alloy blade, characterized in that: The following steps are involved: Take samples for metallographic analysis from the blades. For solid blades, the samples include a longitudinal section sample and a high-temperature zone cross-sectional sample, and the longitudinal section sample of a blade with a shroud must include the shroud portion. For hollow blades, the samples include three cross-sectional samples including the high-temperature zone and the high-stress zone, and one longitudinal section sample. Inlaying the sample with a resin material to obtain an inlaid part; polishing the inlay and etching the inlay using an etching method that can reveal a γ′ phase; The inlay is magnified and observed, and the microstructure of the tenon part in the longitudinal section sample is used as the standard for comparison with the microstructure of the leading edge, mid-chord, and trailing edge in the cross-sectional sample. If any of the following five conditions exist: cracks in the area outside the blade tip, grain boundary creep voids perpendicular to the main axis of the blade, γ' phase re-dissolution with a volume fraction less than 45%, γ' phase re-dissolution and γ' phase rafting, and matrix initial dissolution, the blade is judged to be unusable.

2. The method for evaluating the overheated structure of a nickel-based alloy blade according to claim 1, wherein: When taking samples from the blade for metallographic analysis, the distance between the longitudinal section sample and the exhaust edge is 3.2 mm to 6.4 mm.

3. The method for evaluating the overheated structure of a nickel-based alloy blade according to claim 1, wherein: When taking samples for metallographic analysis on the blade, a cutting machine is used for cutting while cooling with coolant, and the feed rate of the cutting machine is controlled to be 0.02 mm / s to 0.04 mm / s and the rotation speed is controlled to be 2000 rpm to 2500 rpm.

4. The method for evaluating the overheated structure of a nickel-based alloy blade according to claim 1, wherein: The adopting resin material to embed the sample comprises: The sample is inlaid using an inlay machine, wherein the resin material is phenolic resin, transparent synthetic resin or epoxy resin, and the distance between the sample and the edge of the inlay mold is greater than 1.27 mm.

5. The method for evaluating the overheated structure of a nickel-based alloy blade according to claim 1, wherein: When the sample is inlaid with a resin material, an inlay machine is used to inlay the sample. The inlay parameters of the inlay machine are pressure 140 bar to 180 bar, temperature 150° C. to 180° C., and time 5 min to 8 min.

6. The method for evaluating the overheated structure of a nickel-based alloy blade according to claim 1, wherein: When the inlay is polished, the removal amount is greater than or equal to 0.25 mm.

7. The method for evaluating the overheated structure of a nickel-based alloy blade according to claim 1, wherein: The inlay is polished by a polishing machine with polishing parameters of 12N-16N pressure, 350rpm-450rpm speed and 2min-4min time. The polishing agent of the polishing machine is a suspension composed of water-based diamond and cooling lubricant.

8. The method for evaluating the overheated structure of a nickel-based alloy blade according to claim 1, wherein: When the inlay is corroded by the etching method that can reveal the γ′ phase, cotton is corroded in the corrosive agent and wiped on the polished surface of the inlay 3 to 5 times, wherein the volume ratio of the components in the corrosive agent and their volume ratio is CuSO4:HCl:H2O=1:5:5.

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