A method for etching low-magnification flow lines of a nickel-based superalloy forging

Abstract

A method for corroding the streamlines of nickel-based superalloy forgings at low magnification includes the following steps: providing a surface-polished low-magnification sample; performing electrolytic corrosion using the low-magnification sample as the cathode and stainless steel as the anode, wherein the corrosion solution composition, by volume ratio, is HNO3:HCl:deionized water = 1:24:160, and for every 1 ml of HNO3 added, 5 g of FeCl3 is added; the electrolysis current is 1.5A-2A, and the electrolysis time is 2-4 min. This method can cause significant corrosion of the streamline structure in nickel-based superalloy forgings, making the direction and structural integrity of the streamline structure characterizable under visual or low-magnification metallographic microscopy, thereby improving the quality inspection efficiency of nickel-based superalloy forgings.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature alloys, and specifically relates to a method for etching low-magnification flow lines of nickel-based high-temperature alloy forgings. Background Technology

[0002] Nickel-based superalloy forgings are widely used in the aero-engine field to manufacture high-temperature components, such as compressor blades or bladed disks. Nickel-based superalloy forgings are typically produced by ingot casting. During the forging process, inhomogeneous structures, grain boundary impurities, and intermetallic compounds in the ingot deform or break down under pressure and deformation, rearranging themselves along the material flow direction to form a linear distribution structure, i.e., a fibrous metal structure or forging streamlines. This directional structure also leads to a significant directional distribution of mechanical properties: high tensile strength along the streamline direction and high shear strength perpendicular to the streamline direction. Therefore, when the streamline distribution matches the structure of the forged blade, it can improve the blade's mechanical performance; conversely, if the streamline distribution does not meet the mechanical performance requirements of the forged blade, or if defects such as turbulence, irregular flow, or cross-flow exist, it will adversely affect the blade's mechanical properties.

[0003] Therefore, characterizing the streamlines of nickel-based superalloy forgings is an important standard for evaluating forging quality. Due to the high alloying degree, low impurity element content, and strong corrosion resistance of nickel-based superalloys, conventional corrosion methods are insufficient to effectively represent the streamline morphology in nickel-based superalloy forgings. Using methods such as microscopic analysis would significantly increase testing costs and prolong the testing cycle, affecting the efficiency of quality evaluation for nickel-based superalloy forgings. Therefore, providing a low-magnification corrosion method for nickel-based superalloy forgings has high practical value for improving the quality inspection efficiency of nickel-based superalloy forgings. Summary of the Invention

[0004] The purpose of this invention is to provide a corrosion method for low-magnification streamlines of nickel-based superalloy forgings, thereby improving the corrosion effect of low-magnification streamline structures in nickel-based superalloy forgings.

[0005] According to an embodiment of the present invention, a method for low-magnification flowline corrosion of nickel-based superalloy forgings is provided. The method includes the following steps: providing a corrosion sample of the nickel-based superalloy forging, the corrosion sample including a target profile for low-magnification flowline analysis; grinding and polishing the corrosion sample to obtain a low-magnification sample; providing an electrolytic corrosion solution, the composition of which includes HNO3, HCl, deionized water and FeCl3, wherein, by volume ratio, HNO3:HCl:deionized water = 1:24:160, and 5g of FeCl3 is added for every 1ml of HNO3 added; using the low-magnification sample as the anode and stainless steel as the cathode, performing electrolytic corrosion treatment in the electrolytic corrosion solution, wherein the electrolytic current is 1.5A-2A and the electrolysis time is 2min-4min.

[0006] Using the above method, effective corrosion can be formed on nickel-based superalloy forgings, allowing the corrosion-induced flow lines to be directly observed with the naked eye, thus effectively improving the linear efficiency of nickel-based superalloy forgings.

[0007] Furthermore, in some embodiments, after the electrolytic corrosion treatment, a polishing step is included, wherein the polishing medium is water, and the polishing time is 2-3 seconds. Using clean water as the polishing medium for light polishing on a polishing cloth can remove some corrosion products from the surface of the low-magnification sample that interfere with observation.

[0008] Furthermore, in some embodiments, the polishing step of the corroded sample is carried out by sequentially using metallographic sandpaper of 180 mesh, 320 mesh, 800 mesh and 1200 mesh, with each polishing pass taking 1 min to 3 min.

[0009] Furthermore, in some embodiments, the polishing step of the corroded sample is performed using a diamond suspension with a particle size not exceeding 3 μm, and the polishing time is 3 min to 5 min.

[0010] Furthermore, in some embodiments, the electrolytic voltage in the electrolytic corrosion treatment is 4V-6V.

[0011] Furthermore, in some embodiments, a cleaning step is included after the electrolytic corrosion treatment, in which the low-magnification sample is rinsed 1-2 times with water or anhydrous ethanol.

[0012] Furthermore, in some embodiments, the nickel-based superalloy is configured as a Ni-Cr-Fe alloy or a Ni-Cr-Co alloy.

[0013] Furthermore, in some embodiments, the nickel-based superalloy is configured as IN718 alloy or GH4169D alloy.

[0014] Furthermore, in some embodiments, the nickel-based superalloy forging is configured as an aero-engine forged blade or an aero-engine forged bladed disk. Attached Figure Description

[0015] Figure 1 This is a streamline photograph of a nickel-based superalloy blade forging in an upsetting state after corrosion, as shown in one embodiment.

[0016] Figure 2 This is a streamline photograph of a nickel-based superalloy blade forging in its final forging state after corrosion, as shown in one embodiment.

[0017] Figure 3 Photographs of a pair of upset nickel-based superalloy blade forgings after corrosion.

[0018] Figure 4 This is a photograph of a pair of medium-sized nickel-based superalloy blade forgings after corrosion.

[0019] The purpose of the above figures is to provide a detailed description of the present invention so that those skilled in the art can understand the technical concept of the invention, and not to limit the invention. Detailed Implementation

[0020] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0021] The term "embodiment" as used herein means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment herein. The phrase appearing in various places in the specification does not necessarily refer to the same embodiment, nor is it limited to mutually exclusive, independent, or alternative embodiments. Those skilled in the art will understand that the embodiments herein can be combined with other embodiments without structural conflict. In the description herein, "a plurality of" means at least two.

[0022] Forging can break down inhomogeneous structures such as dendrites formed during casting, eliminate defects such as pinholes during solidification, and promote the rearrangement of second-phase particles, thereby improving the alloy's microstructure and properties. Therefore, nickel-based superalloy forgings are widely used in aero-engines; for example, compressor blades are often forged from nickel-based superalloys. Due to the directional flow of material during forging, the forged microstructure typically exhibits significant anisotropy, with noticeable differences in mechanical properties in different directions. Therefore, in the quality inspection of nickel-based superalloy forgings, etching the forging sample and then characterizing it with low-magnification streamlines using the naked eye or a low-magnification metallographic microscope is a crucial aspect of evaluating the quality of forged blades. On one hand, the morphology of the streamlines can determine whether the distribution characteristics of the material microstructure during forging conform to the part design requirements; on the other hand, the presence of defects such as turbulent flow, irregular flow, or through-flow in the forging streamlines indicates the existence of forging defects in the material microstructure. Therefore, low-magnification streamline characterization allows for effective quality inspection of nickel-based superalloy forgings through visual observation, without the need for complex and expensive tools such as electron microscopes or X-ray diffraction equipment. However, because nickel-based superalloys have a high degree of alloying and low content of impurity elements, and the alloys used in the manufacture of aero-engines have good corrosion resistance, conventional chemical corrosion methods are difficult to be effective.

[0023] For example, when using a mixed solution of copper sulfate, sulfuric acid, and hydrochloric acid, or a mixed solution of hydrochloric acid, phosphoric acid, and ferric chloride, commonly used in the metallographic etching of nickel-based alloys, chemical etching of IN718 and GH4169D nickel-based superalloys at room temperature after grinding and polishing, it is impossible to observe the streamline structure on the polished surface. This seriously restricts the efficiency and accuracy of quality inspection of nickel-based superalloy forgings.

[0024] To address the above problems, embodiments of the present invention provide a method for etching low-magnification streamlines of nickel-based superalloy forgings, the method comprising the following steps:

[0025] First, a corrosion sample of a nickel-based superalloy forging is provided. This sample is cut from the forging using methods such as abrasive wheel cutting, laser cutting, or wire cutting. The cross-section is taken from the surface requiring low-magnification streamline characterization. In a preferred embodiment, the cross-section is cut along the ideal streamline extension direction. The cross-section is then ground and polished to obtain a low-magnification sample. In a preferred embodiment, the grinding step involves four passes using 180-grit, 320-grit, 800-grit, and 1200-grit metallographic abrasive paper, with each pass lasting 1-3 minutes. The polishing step uses a 3μm diamond suspension as the polishing medium and is performed on the polishing cloth of a polishing machine.

[0026] Next, the electrolytic etching solution is prepared. The electrolytic etching solution consists of HNO3, HCl, deionized water, and FeCl3, wherein, by volume ratio, HNO3... 3: The ratio of HCl to deionized water is 1:24:160, and for every 1 ml of HNO3 added, 5 g of FeCl3 is added.

[0027] The aforementioned electrolyte is added to an electrolytic cell, with stainless steel as the cathode and a low-magnification sample as the anode, for electrolytic corrosion. Electrolytic corrosion parameters are controlled: electrolytic current of 1.5A-2A and electrolysis time of 2-4 minutes. In a preferred embodiment, the electrolytic current is adjusted by controlling the electrolytic voltage between 4V and 6V.

[0028] After electrolysis, rinse the low-magnification sample 1-2 times with clean water or anhydrous ethanol. Optionally, use water as a polishing medium and place the low-magnification sample on the polishing cloth of the polishing machine for 2-3 seconds of light polishing to remove corrosion products that are not conducive to flowline observation formed on the sample surface during electrolysis.

[0029] After cleaning, the samples are placed in an oven to dry, and then characterized by visual inspection or under a low-magnification metallographic microscope. These nickel-based superalloy forgings can be forged blades for aero-engines or forged bladed disks.

[0030] In a preferred embodiment, the low-magnification streamline corrosion method for nickel-based superalloy forged blades is as follows:

[0031] Longitudinal corrosion samples of nickel-based superalloy blades in the upset state were obtained by wire cutting, such as... Figure 1 As shown, the sample was made of IN718 alloy, with the following composition by mass: 50.0–55.0% Ni, 17.0–21.0% Cr, 2.80–3.30% Mo, 4.75–5.50% Nb, 15.0–21.0% Fe, 0.75–1.15% Ti, 0.3–0.7% Al, ≤1.0% Co, ≤0.3% Cu, ≤0.35% Si, and ≤0.35% Mn. The sample profile was sequentially polished using 180-grit, 320-grit, 800-grit, and 1200-grit sandpaper. Each polishing pass was performed with consistent grinding marks, resulting in a smooth surface free of scratches from the previous pass. Each polishing pass lasted 1–3 minutes. Subsequently, the sample was polished using a diamond suspension with 3 μm particles on a polishing machine for 3–5 minutes. Polishing completes the process, yielding a low-magnification sample.

[0032] Next, prepare the etching solution, which consists of 5 ml of analytical grade HNO3, 120 ml of analytical grade HCl, 25 g of FeCl3, and 800 ml of deionized water.

[0033] The above-mentioned electrolyte was added to the electrolytic cell, with stainless steel as the anode and a low-magnification sample as the cathode, for electrolytic corrosion treatment. During the electrolytic corrosion process, the electrolysis voltage was controlled at 4V-6V, the electrolysis current at 1.5A-2A, and the electrolysis time at 2min-4min.

[0034] After electrolysis, the low-magnification sample was placed on a polishing machine and lightly polished for 2-3 seconds with water as the polishing medium to remove corrosion products that would affect flowline observation.

[0035] Rinse the low-magnification sample 1-2 times with water or anhydrous ethanol, dry it in an oven at 80℃-90℃ until the surface is dry, and then it can be used for low-magnification streamline characterization.

[0036] like Figure 1 As shown, the low-magnification sample surface after etching exhibits obvious streamline structure. In the blade tenon region 1, streamline 4 expands along the direction of the edge plate 2, and the extension direction of streamline 4 is generally consistent with the length direction of the blade body 3.

[0037] In another preferred embodiment, a longitudinal corrosion sample of the nickel-based superalloy blade in its final forging state is obtained by wire cutting, such as... Figure 2 As shown, the sample was made of IN718 alloy. The sample profile was sequentially polished using 180-grit, 320-grit, 800-grit, and 1200-grit sandpaper. Each polishing pass aimed to ensure consistent grinding marks, a smooth surface free of scratches from the previous pass, and a polishing time of 1-3 minutes per pass. Subsequently, the sample was polished using a diamond suspension with 3μm particle size on a polishing machine for 3-5 minutes. The polished sample was then obtained at low magnification.

[0038] Next, prepare the etching solution, which consists of 5 ml of analytical grade HNO3, 120 ml of analytical grade HCl, 25 g of FeCl3, and 800 ml of deionized water.

[0039] The above-mentioned electrolyte was added to the electrolytic cell, with stainless steel as the anode and a low-magnification sample as the cathode, for electrolytic corrosion treatment. During the electrolytic corrosion process, the electrolysis voltage was controlled at 4V-6V, the electrolysis current at 1.5A-2A, and the electrolysis time at 2min-4min.

[0040] After electrolysis, the low-magnification sample was placed on a polishing machine and lightly polished for 2-3 seconds with water as the polishing medium to remove corrosion products that would affect flowline observation.

[0041] Rinse the low-magnification sample 1-2 times with water or anhydrous ethanol, dry it in an oven at 80℃-90℃ until the surface is dry, and then it can be used for low-magnification streamline characterization.

[0042] like Figure 2As shown, the low-magnification sample surface after etching exhibits obvious streamline structure. The streamlines 4 at the end of the blade tenon region 1 are distributed along the length of the blade body 3. In the region near the edge plate 2, the streamlines 4 expand laterally and converge to the location of the blade body 3.

[0043] In a comparative example, the same upset-head nickel-based superalloy etching sample as in the aforementioned examples was used, and a low-magnification sample was prepared after grinding and polishing. An etching solution was prepared using 5 ml of analytical grade HNO3, 120 ml of analytical grade HCl, 25 g of FeCl3, and 50 ml of deionized water. The etching solution was applied to the surface of the low-magnification sample with degreased cotton and wiped for 10 seconds. After the surface of the low-magnification sample turned gray, it was cleaned and dried. The resulting sample is shown below. Figure 3 As shown.

[0044] In another comparative example, the same forged nickel-based superalloy corrosion sample as in the previous examples was used, and a low-magnification sample was prepared by grinding and polishing. A corrosion solution was prepared using 5 ml of analytical grade HNO3, 120 ml of analytical grade HCl, 25 g of FeCl3, and 50 ml of deionized water. The corrosion solution was applied to the surface of the low-magnification sample with degreased cotton and wiped for 10 seconds. After the surface of the low-magnification sample turned gray, it was cleaned and dried. The resulting sample is shown below. Figure 4 As shown.

[0045] Depend on Figure 3 and Figure 4 It can be seen that when using conventional chemical etching solutions and following the general metallographic etching methods for nickel-based alloys, the sample surface exhibits a uniform silver color. It is impossible to form a streamlined corrosion structure visible to the naked eye or a low-magnification metallographic microscope on the target cross-section of the low-magnification sample, which does not meet the requirements for low-magnification streamlined structure characterization of nickel-based high-temperature alloy forgings.

[0046] In other embodiments, the above method can also be used to etch GH4169D alloy forging samples for low-magnification streamline characterization.

[0047] The purpose of the above embodiments is to provide a further detailed description of the present invention in conjunction with the accompanying drawings, so that those skilled in the art can understand the technical concept of the present invention. Within the scope of the present invention, optimization or equivalent substitution of the method steps involved, as well as combination of implementation methods in different embodiments without causing structural and principle conflicts, all fall within the protection scope of the present invention.

Claims

1. A method of etching low magnification flow lines of a nickel-based superalloy forging, characterized by, The nickel-based superalloy is configured as a Ni-Cr-Fe alloy or a Ni-Cr-Co alloy, and includes the following steps: A corrosion sample of a nickel-based superalloy forging is provided, the corrosion sample including a target profile for low-magnification streamline analysis, and the corrosion sample is ground and polished to obtain a low-magnification specimen; An electrolytic etching solution is provided, the components of which include HNO3, HCl, deionized water and FeCl3, wherein the volume ratio of HNO3:HCl:deionized water is 1:24:160, and 5g of FeCl3 is added for every 1ml of HNO3 added. Using the low-magnification sample as the anode and stainless steel as the cathode, electrolytic corrosion treatment was carried out in the electrolytic corrosion solution. The electrolytic current was 1.5A-2A, the electrolytic voltage was 4V-6V, and the electrolytic time was 2min-4min.

2. The corrosion method for low-magnification streamlines of nickel-based superalloy forgings according to claim 1, characterized in that, After the electrolytic corrosion treatment, the process further includes a polishing step on the low-magnification sample, wherein the polishing medium is water and the polishing time is 2-3 seconds.

3. The corrosion method for low-magnification streamlines of nickel-based superalloy forgings according to claim 1 or 2, characterized in that, In the step of polishing the corroded sample, metallographic sandpaper of 180 mesh, 320 mesh, 800 mesh and 1200 mesh is used in sequence for polishing, and the polishing time for each pass is 1min-3min.

4. The corrosion method for low-magnification streamlines of nickel-based superalloy forgings according to claim 1 or 2, characterized in that, In the polishing step of the corroded sample, a diamond suspension with a particle size not exceeding 3μm is used for polishing, and the polishing time is 3min-5min.

5. The corrosion method for low-magnification streamlines of nickel-based superalloy forgings according to claim 1 or 2, characterized in that, The electrolytic corrosion treatment is followed by a cleaning step, in which the low-magnification sample is rinsed 1-2 times with water or anhydrous ethanol.

6. The corrosion method for low-magnification streamlines of nickel-based superalloy forgings according to claim 1, characterized in that, The nickel-based superalloy is configured as IN718 alloy or GH4169D alloy.

7. The corrosion method for low-magnification streamlines of nickel-based superalloy forgings according to claim 1 or 2, characterized in that, The nickel-based superalloy forgings are configured as forged blades or forged disks for aero-engines.

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