Precise display method of laves phase in gh4169 alloy by synergistic effect of corrosion-controllable atmosphere modification and heat treatment

Abstract

The application provides a kind of corrosion-controllable atmosphere modification-heat treatment synergistic GH4169 alloy Laves phase accurate display method, comprising: sample targeted corrosion: after sample is polished, it is immersed in targeted corrosion agent and corroded, sample presents light gray, stop and blow dry when;Controllable atmosphere oxidation interface modification: sample is placed in controllable atmosphere tube furnace, high-purity argon is used as carrier gas in furnace, high-purity oxygen is doped, temperature is raised to 300-350 DEG C and then kept, temperature is reduced to room temperature after keeping, sample is taken out and washed and then blown dry;Ladder type temperature difference differential dyeing: the following processing is carried out in box furnace: temperature is raised to 340 DEG C and kept, temperature is raised to 440 DEG C and kept, temperature is raised to 480 DEG C and kept, temperature is kept, and then temperature is quickly reduced to 200 DEG C and kept, then air cooling to room temperature with furnace, then sample is washed;Microscope observation: magnification observation is carried out using optical microscope, Laves phase, matrix, NbC carbide and other alloy precipitated phase are identified.The application realizes Laves phase display with high phase distinction, strong reproducibility and full-size accurate identification.

Description

Technical Field

[0001] This invention generally relates to the field of high-temperature alloy microstructure detection technology, and more specifically, to a method for displaying the Laves phase with high phase differentiation, strong reproducibility, and accurate identification of the entire size. Background Technology

[0002] Currently, GH4169 alloy, due to its excellent low- and medium-temperature mechanical properties, corrosion resistance, and weld compatibility, has become a core material for critical equipment such as aero-engine blades and spacecraft structural components. Nitrogen (Nb) is one of the main alloying elements in this alloy, with a content of 3%–6%. During solidification, processing, and heat treatment, Nb easily segregates to form a TiNbCr2-type Laves phase. This phase is hard and brittle, significantly reducing the alloy's impact toughness, plasticity, and formability. It easily causes cracking during forging, machining, and service, seriously threatening product quality and safety. Relevant inspection standards in the aerospace industry clearly require that the size, distribution, and content of the Laves phase in key GH4169 products be strictly controlled within specified ranges. Therefore, accurate identification and analysis of the Laves phase are crucial for optimizing product process design and controlling quality throughout the entire production process.

[0003] Laves phases are easily confused with NbC carbides and other alloy precipitates in alloys, usually requiring differentiation by composition using scanning electron microscopy or electron probe microanalysis, which is time-consuming and costly. Existing methods for displaying Laves phases, which are relatively convenient and low-cost, still have limitations: single chemical etching methods, such as copper sulfate-sulfuric acid-hydrochloric acid systems and nitric acid-hydrofluoric acid systems, are efficient and have short cycles, but suffer from drawbacks such as small color differences leading to misjudgment and sample damage; single heat treatment staining methods, which differentiate Laves phases by utilizing the color differences under an optical microscope after oxidation, are simple and cause minimal sample damage, but suffer from poor process reproducibility and the tendency to miss small Laves phases; currently, there is no convenient chemical etching-heat treatment combined display method that can simultaneously achieve full-size Laves phase identification and high color difference discrimination.

[0004] Therefore, how to achieve Laves phase display with high phase differentiation, strong reproducibility, and accurate full-size identification is a technical problem that urgently needs to be solved in the field of materials process optimization and quality control in the aerospace industry. Summary of the Invention

[0005] A primary objective of this invention is to overcome at least one of the deficiencies of the prior art and to provide a method for accurately displaying the Laves phase of GH4169 alloy through a combination of corrosion-controlled atmosphere modification-heat treatment, which enables high phase differentiation, strong reproducibility, and full-size accurate identification.

[0006] To achieve the above-mentioned objectives, the present invention adopts the following technical solution:

[0007] According to one aspect of the present invention, a method for accurate display of the Laves phase in GH4169 alloy through a combination of corrosion-controlled atmosphere modification and heat treatment is provided, comprising the following steps:

[0008] Step 1, Targeted etching of the sample: The targeted etchant includes: 50-60 g of citric acid monohydrate, 8-12 g of ammonium fluoride, 15-25 ml of anhydrous ethanol, and deionized water to make up to 1000 ml; After grinding and polishing, the sample is immersed in the targeted etchant for etching until the sample surface turns a uniform light gray color, then rinsed with alcohol and dried.

[0009] Step 2, Controlled atmosphere oxidation interface modification: Place the sample in a controlled atmosphere tube furnace with high-purity argon as the carrier gas and high-purity oxygen added. Heat to 300-350℃ and hold for 8-15 minutes. After holding, cool down to room temperature in the same atmosphere. Remove the sample, clean it with alcohol by ultrasonic cleaning, and then blow it dry.

[0010] Step 3, stepped temperature-controlled differential staining: Place the sample in a box furnace and perform the following treatments: 1) Heat to 340℃ and hold for 10 min; 2) Heat to 440℃ and hold for 15 min; 3) Heat to 480℃ and hold for 20 min; After holding, rapidly cool to 200℃ and hold for 6 min, then air cool with the furnace to room temperature, and then immerse the sample in alcohol for ultrasonic cleaning for 3-5 min.

[0011] Step 4, Microscopic observation: Use an optical microscope to observe at 500-1000x magnification to identify the Laves phase, matrix, NbC carbides and other alloy precipitates.

[0012] According to one embodiment of the present invention, in step one, after the sample is ground and polished, it is immersed in a targeted etchant for 50-60 seconds.

[0013] According to one embodiment of the present invention, the pH value is adjusted down by using analytical grade citric acid monohydrate and the pH value is adjusted up by using 0.1 mol / L analytical grade ammonia solution, thereby adjusting the pH value of the targeted corrosion agent to 4.2 ± 0.5.

[0014] According to one embodiment of the present invention, in step one, the polishing liquid used in the polishing step includes a diluent of the targeted etchant, which is prepared by diluting the original targeted etchant with deionized water at a ratio of 1:15 to 1:20, and the amount added to the polishing liquid is 5-10%. The addition of the diluent does not cause significant corrosion of the sample matrix, but can directionally and slightly etch the Laves phase boundary to achieve chemical-mechanical synergistic polishing.

[0015] According to one embodiment of the present invention, in step two, the volume fraction of high-purity oxygen is 0.05%-0.1%, and the oxygen partial pressure is controlled at 50-500 Pa.

[0016] According to one embodiment of the present invention, in step two, high-purity oxygen is heated to 300-350°C at a rate of 5-8°C / min, and after the holding period, it is rapidly cooled to room temperature in the furnace at a rate of ≥20°C / min under the same atmosphere.

[0017] According to one embodiment of the present invention, in step three, the temperature is uniformly increased to 340°C at a rate of 10°C / min; uniformly increased to 440°C at a rate of 5°C / min; and uniformly increased to 480°C at a rate of 3°C / min.

[0018] According to one embodiment of the present invention, in step three, after the heat preservation is completed, the temperature is rapidly reduced to 200°C at a rate of 110°C / min.

[0019] According to one embodiment of the present invention, in step four, the Laves phase has a rounded and clear boundary, ranging from brown to black, and the matrix is ​​pale yellow; the NbC carbide has a clear boundary, shows angularity, and exhibits a bright white metallic luster, with a significant difference in morphology and color from the Laves phase.

[0020] According to one embodiment of the present invention, the sample is a cast GH4169 or a homogenized GH4169 alloy.

[0021] As can be seen from the above technical solution, the advantages and positive effects of the GH4169 alloy Laves phase accurate display method of corrosion-controlled atmosphere modification-heat treatment synergy of the present invention are as follows:

[0022] This invention enables Laves phase display with high phase differentiation, strong reproducibility, and accurate full-size identification. Attached Figure Description

[0023] Various objects, features, and advantages of the invention will become more apparent from the following detailed description of preferred embodiments of the invention, taken in conjunction with the accompanying drawings. The drawings are merely illustrative of the invention and are not necessarily drawn to scale. In the drawings, the same reference numerals always denote the same or similar parts. Wherein:

[0024] Figure 1 The metallographic structure of the as-cast GH4169 alloy treated with a single chemical etching method (500×).

[0025] Figure 2 The metallographic structure of the as-cast GH4169 alloy treated with a single hot dyeing method (500×).

[0026] Figure 3The metallographic structure (500×) of the as-cast GH4169 alloy processed using the method of this invention.

[0027] Figure 4 The metallographic structure of the homogenized GH4169 alloy treated with a single chemical etching method (1000×).

[0028] Figure 5 The metallographic structure of the homogenized GH4169 alloy treated with a single hot dyeing method (1000×).

[0029] Figure 6 The metallographic structure (1000×) of the homogenized GH4169 alloy processed by the method of the present invention. Detailed Implementation

[0030] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that the invention will be thorough and complete, and the concept of the exemplary embodiments will be fully conveyed to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore their detailed description will be omitted.

[0031] In the following description of various examples of the invention, reference is made to the accompanying drawings, which form part of the invention, and in which different exemplary structures, systems, and steps that can implement various aspects of the invention are shown by way of example. It should be understood that other specific embodiments of the components, structures, exemplary devices, systems, and steps may be used, and structural and functional modifications may be made without departing from the scope of the invention. Furthermore, while the terms “top,” “bottom,” “front,” “rear,” “side,” etc., may be used in this specification to describe various exemplary features and elements of the invention, these terms are used herein only for convenience, such as the orientation according to the examples shown in the drawings. Nothing in this specification should be construed as requiring a specific three-dimensional orientation of the structure to fall within the scope of the invention.

[0032] According to one aspect of the present invention, a method for accurate display of the Laves phase in GH4169 alloy through a combination of corrosion-controlled atmosphere modification and heat treatment is provided, comprising the following steps:

[0033] Step 1, Targeted etching of the sample: The targeted etchant includes: 50-60 g of citric acid monohydrate, 8-12 g of ammonium fluoride, 15-25 ml of anhydrous ethanol, and deionized water to make up to 1000 ml; After grinding and polishing, the sample is immersed in the targeted etchant for etching until the sample surface turns a uniform light gray color, then rinsed with alcohol and dried.

[0034] Step 2, Controlled atmosphere oxidation interface modification: Place the sample in a controlled atmosphere tube furnace with high-purity argon as the carrier gas and high-purity oxygen added. Heat to 300-350℃ and hold for 8-15 minutes. After holding, cool down to room temperature in the same atmosphere. Remove the sample, clean it with alcohol by ultrasonic cleaning, and then blow it dry.

[0035] Step 3, stepped temperature-controlled differential staining: Place the sample in a box furnace and perform the following treatments: 1) Heat to 340℃ and hold for 10 min; 2) Heat to 440℃ and hold for 15 min; 3) Heat to 480℃ and hold for 20 min; After holding, rapidly cool to 200℃ and hold for 6 min, then air cool with the furnace to room temperature, and then immerse the sample in alcohol for ultrasonic cleaning for 3-5 min.

[0036] Step 4, Microscopic observation: Use an optical microscope to observe at 500-1000x magnification to identify the Laves phase, matrix, NbC carbides and other alloy precipitates.

[0037] According to one embodiment of the present invention, in step one, after the sample is ground and polished, it is immersed in a targeted etchant for 50-60 seconds.

[0038] According to one embodiment of the present invention, the pH value is adjusted down by using analytical grade citric acid monohydrate and the pH value is adjusted up by using 0.1 mol / L analytical grade ammonia solution, thereby adjusting the pH value of the targeted corrosion agent to 4.2 ± 0.5.

[0039] According to one embodiment of the present invention, in step one, the polishing liquid used in the polishing step includes a diluent of the targeted etchant, which is prepared by diluting the original targeted etchant with deionized water at a ratio of 1:15 to 1:20, and the amount added to the polishing liquid is 5-10%. The addition of the diluent does not cause significant corrosion of the sample matrix, but can directionally and slightly etch the Laves phase boundary to achieve chemical-mechanical synergistic polishing.

[0040] According to one embodiment of the present invention, in step two, the volume fraction of high-purity oxygen is 0.05%-0.1%, and the oxygen partial pressure is controlled at 50-500 Pa.

[0041] According to one embodiment of the present invention, in step two, high-purity oxygen is heated to 300-350°C at a rate of 5-8°C / min, and after the holding period, it is rapidly cooled to room temperature in the furnace at a rate of ≥20°C / min under the same atmosphere.

[0042] According to one embodiment of the present invention, in step three, the temperature is uniformly increased to 340°C at a rate of 10°C / min; uniformly increased to 440°C at a rate of 5°C / min; and uniformly increased to 480°C at a rate of 3°C / min.

[0043] According to one embodiment of the present invention, in step three, after the heat preservation is completed, the temperature is rapidly reduced to 200°C at a rate of 110°C / min.

[0044] According to one embodiment of the present invention, in step four, the Laves phase has a rounded and clear boundary, ranging from brown to black, and the matrix is ​​pale yellow; the NbC carbide has a clear boundary, shows angularity, and exhibits a bright white metallic luster, with a significant difference in morphology and color from the Laves phase.

[0045] According to one embodiment of the present invention, the sample is a cast GH4169 or a homogenized GH4169 alloy.

[0046] As can be seen from the above technical solution, the advantages and positive effects of the GH4169 alloy Laves phase accurate display method of corrosion-controlled atmosphere modification-heat treatment synergy of the present invention are as follows:

[0047] 1. Compared to existing methods that suffer from small color differences and are prone to misjudgment, this invention utilizes a synergistic mechanism of targeted corrosion to reveal the phase boundary, controlled atmosphere interface modification, and multi-stage heat treatment to amplify the color difference. Initially, a citric acid monohydrate-ammonium fluoride (CA-NH4F) targeted corrosion system is used to avoid the over-corrosion problem of conventional corrosion systems and accurately locate the phase boundary. Then, a controlled atmosphere oxidation process is used to receive the fresh interface after corrosion, simultaneously achieving matrix passivation and targeted activation of the Laves phase. Finally, multi-stage temperature-controlled heat treatment amplifies the difference between the Laves phase and the matrix, resulting in a significant color difference between the Laves phase, the matrix, and NbC carbides under incident light under an optical microscope. This effectively solves the problem of misjudgment caused by color confusion and reliance on subjective shape judgment. It also facilitates the rapid acquisition of high-quality metallographic images for analysis using image analysis software and reduces human error.

[0048] 2. Compared to existing methods where fine Laves phases (<3μm) are often obscured and easily missed, this invention addresses these shortcomings by pre-polishing to locate fine phase boundaries, using a gentle CA-NH4F corrosion system during the targeted corrosion process to fully preserve the reaction interface of the fine phases. A controlled atmosphere oxidation process further ensures 100% activation of the fine Laves phase boundaries after corrosion, providing uniform nucleation sites for subsequent heat treatment and color development. Stepped temperature-controlled heat treatment achieves differentiated color development, increasing the identification rate of fine Laves phases to over 90%, covering all sizes of Laves phases that have a potential impact on the mechanical properties of the alloy, eliminating missed detections, and providing accurate data for material quality control and process optimization.

[0049] 3. Compared with the shortcomings of existing methods in terms of poor process reproducibility, this invention reduces parameter dependence through multiple mechanisms: the intensity of the targeted etchant is precisely matched with the corrosion sensitivity of the material; a controlled atmosphere oxidation process is added to completely avoid human interference with the interface state through clear atmosphere and temperature control; the multi-stage temperature-controlled heat treatment ensures that the parameters are precise and the cooling process is orderly, thus ensuring the stability and controllability of the entire heat treatment process. The consistency of results between different batches and different operators is significantly improved, the data reproducibility is greatly enhanced, and the statistical reliability of the test data is improved, meeting the dual requirements of analytical accuracy and efficiency.

[0050] 4. This invention only requires a metallographic microscope and conventional heat treatment and etching equipment, without the need for expensive instruments such as scanning electron microscopes and electron probes. Moreover, the etchant is low in cost, the process parameters are simple and easy to execute, and the test results are intuitive and accurate.

[0051] Comparative Example 1

[0052] After grinding and polishing, the as-cast GH4169 sample was immersed in a conventional copper sulfate-sulfuric acid-hydrochloric acid etching system for high-temperature alloys for 30 seconds. The sample surface was then rinsed with alcohol and dried. Observation under an optical microscope revealed the following microstructure: Figure 1 As shown in the figure, the Laves phase and NbC carbides are white / light gray, with little color difference (<40%), making them easily confused.

[0053] Comparative Example 2

[0054] After grinding and polishing, exposing the polished surface, the as-cast GH4169 sample was placed in a 500℃ resistance furnace for 60 minutes and then air-cooled. After cooling, the sample was observed under an optical microscope; the microstructure was as follows: Figure 2 As shown in the figure, the oxidation degree of the sample surface is uneven, the color of the Laves phase varies, and the color difference of some fine Laves phases is not obvious, the boundary with the matrix is ​​blurred, and they are difficult to identify, resulting in a low identification rate of fine Laves phases (<60%).

[0055] Example 1

[0056] According to the above-described method of the present invention, the as-cast GH4169 sample, after grinding and polishing, is treated with the method of the present invention, and the microstructure is as follows: Figure 3 As shown in the figure, the Laves phase is brown to black with rounded and clear boundaries, the NbC carbides are angular and have a bright white metallic luster, and the matrix is ​​pale yellow. The color difference between the three is significant (>60%). The small Laves phases are clearly displayed, and the recognition rate is improved (>90%).

[0057] Comparative Example 3

[0058] The sample was a homogenized GH4169 alloy, and the treatment steps were exactly the same as those in Comparative Example 1. The microstructure was as follows: Figure 4As shown in the figure, the Laves phase and NbC carbides are white / light gray, with little color difference (<40%), making them easily confused.

[0059] Comparative Example 4

[0060] The sample was a homogenized GH4169 alloy, which was placed in a 500℃ resistance furnace and held for 20 minutes. The remaining treatment steps were exactly the same as those in Comparative Example 2. The microstructure was as follows: Figure 5 As shown in the figure, the Laves phase and NbC carbides are black / gray, with little color difference (<40%), making them easily confused. Some fine Laves phases are difficult to identify, resulting in a low identification rate (<60%).

[0061] Example 2

[0062] The sample was a homogenized GH4169 alloy, treated using the method of this invention, and its microstructure was as follows. Figure 6 As shown in the figure, the Laves phase is brown to black with rounded and clear boundaries, the NbC carbides are angular and have a metallic luster, and the matrix is ​​pale yellow. The color difference between the three is significant (>60%). The small Laves phases are clearly displayed, and the recognition rate is improved (>90%).

[0063] In summary, this invention addresses the shortcomings of existing Laves phase display methods, such as small color difference leading to misjudgment, easy omission of small phases, and poor process reproducibility, through multiple mechanisms including chemical-mechanical synergistic polishing and selective etching phase boundary pre-positioning, controlled atmosphere oxidation directional exposure, and graded temperature-controlled heat treatment for high-contrast color development. It can achieve accurate display of full-size Laves phases, providing a convenient and reliable detection method for material process optimization and quality control in the aerospace field.

[0064] The above descriptions are several embodiments of the present invention, and are merely illustrative and not intended to limit the implementation of the present invention. The scope of protection of the present invention is determined by the claims.

[0065] Those skilled in the art should understand that the specific structures and processes shown in the above detailed embodiments are merely exemplary and not restrictive. Furthermore, those skilled in the art can combine the various technical features described above in various possible ways to form new technical solutions or make other modifications, all of which fall within the scope of this invention.

Claims

1. A method for accurate display of the Laves phase in GH4169 alloy through a combination of corrosion-controlled atmosphere modification and heat treatment, characterized in that: Includes the following steps: Step 1, Targeted etching of the sample: The targeted etchant includes: 50-60 g of citric acid monohydrate, 8-12 g of ammonium fluoride, 15-25 ml of anhydrous ethanol, and deionized water to make up to 1000 ml; After grinding and polishing, the sample is immersed in the targeted etchant for etching until the sample surface turns a uniform light gray color, then rinsed with alcohol and dried. Step 2, Controlled atmosphere oxidation interface modification: Place the sample in a controlled atmosphere tube furnace with high-purity argon as the carrier gas and high-purity oxygen added. Heat to 300-350℃ and hold for 8-15 minutes. After holding, cool down to room temperature in the same atmosphere. Remove the sample, clean it with alcohol by ultrasonic cleaning, and then blow it dry. Step 3, stepped temperature-controlled differential staining: Place the sample in a box furnace and perform the following treatments: 1) Heat to 340℃ and hold for 10 min; 2) Heat to 440℃ and hold for 15 min; 3) Heat to 480℃ and hold for 20 min; After holding, rapidly cool to 200℃ and hold for 6 min, then air cool with the furnace to room temperature, and then immerse the sample in alcohol for ultrasonic cleaning for 3-5 min. Step 4, Microscopic observation: Use an optical microscope to observe at 500-1000x magnification to identify the Laves phase, matrix, NbC carbides and other alloy precipitates.

2. The method for accurate display of the Laves phase in GH4169 alloy through corrosion-controlled atmosphere modification-heat treatment synergy as described in claim 1, characterized in that: In step one, after the sample is ground and polished, it is immersed in the targeted etchant for 50-60 seconds.

3. The method for accurate display of the Laves phase in GH4169 alloy through corrosion-controlled atmosphere modification-heat treatment synergy as described in claim 1 or 2, characterized in that: The pH value was adjusted down using analytical grade monohydrate citric acid and up using 0.1 mol / L analytical grade ammonia solution, thus controlling the pH value of the targeted corrosion agent to 4.2 ± 0.

5.

4. The method for accurate display of the Laves phase in GH4169 alloy through corrosion-controlled atmosphere modification-heat treatment synergy as described in claim 3, characterized in that: In step one, the polishing liquid used in the polishing step includes a diluent of the targeted etchant. The diluent is prepared by diluting the original targeted etchant with deionized water at a ratio of 1:15 to 1:20, and the amount added to the polishing liquid is 5-10%. The addition of the diluent does not cause significant corrosion of the sample matrix, but it can directionally and slightly etch the Laves phase boundary to achieve chemical-mechanical synergistic polishing.

5. The method for accurate display of the Laves phase in GH4169 alloy through corrosion-controlled atmosphere modification-heat treatment synergy as described in claim 1, characterized in that: In step two, the volume fraction of high-purity oxygen is 0.05%-0.1%, and the oxygen partial pressure is controlled at 50-500 Pa.

6. The method for accurate display of the Laves phase in GH4169 alloy through corrosion-controlled atmosphere modification-heat treatment synergy as described in claim 5, characterized in that: In step two, high-purity oxygen is heated to 300-350°C at a rate of 5-8°C / min, and after holding at that temperature, it is rapidly cooled to room temperature in the furnace at a rate of ≥20°C / min under the same atmosphere.

7. The method for accurate display of the Laves phase in GH4169 alloy through corrosion-controlled atmosphere modification-heat treatment synergy as described in claim 1, characterized in that: In step three, the temperature is increased uniformly to 340°C at a rate of 10°C / min; then to 440°C at a rate of 5°C / min; and finally to 480°C at a rate of 3°C / min.

8. The method for accurate display of the Laves phase in GH4169 alloy through corrosion-controlled atmosphere modification-heat treatment synergy as described in claim 7, characterized in that: In step three, after the heat preservation is completed, the temperature is rapidly reduced to 200℃ at a rate of 110℃ / min.

9. The method for accurate Laves phase display of GH4169 alloy through corrosion-controlled atmosphere modification-heat treatment synergy as described in claim 1, characterized in that: In step four, the Laves phase has a rounded and clear boundary, ranging from brown to black, while the matrix is ​​pale yellow; the NbC carbide has a clear boundary, is angular, and exhibits a bright white metallic luster, showing a significant difference in morphology and color from the Laves phase.

10. The method for accurate display of the Laves phase in GH4169 alloy through corrosion-controlled atmosphere modification-heat treatment synergy as described in claim 1, characterized in that: The sample was either as-cast GH4169 or homogenized GH4169 alloy.

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