Metal material force-chemical coupling test method and device considering stress gradient

Abstract

The present application aims to reveal the influence mechanism of stress level and stress gradient on the behavior of metal material hot salt corrosion, and provides a force-chemical coupling test method and device of metal material considering stress gradient, aiming at the technical defects that mechanical load and corrosion environment are difficult to be controlled simultaneously in the existing research. First, a variable cross-section tensile deposited salt sample is designed, which can form different stress level and stress gradient distribution areas under a single loading condition. Second, the hot salt corrosion test under external stress is carried out under the condition of controlled temperature by artificially depositing the molten salt formed in the simulation of marine environment on the surface of the sample and applying external tensile load. Finally, the corrosion morphology, oxide film structure and element distribution of the sample are systematically characterized and quantitatively analyzed. The test method of the present application is simple, highly repeatable, can realize the comparative analysis of corrosion behavior under multiple stress states, and significantly improves the efficiency and accuracy of stress-corrosion synergistic effect research.

Description

Technical Field

[0001] This application relates to the field of metal corrosion performance testing technology, and in particular to a mechanical-chemical coupling test method and apparatus for metal materials that takes stress gradient into account. Background Technology

[0002] During the service of high-temperature power equipment such as gas turbines and aero engines, their key load-bearing and hot-end components are subjected to harsh environments of high temperature, thermal cycling, vibration and complex media for a long time. Therefore, it is necessary to comprehensively require the high-temperature strength, oxidation resistance and corrosion resistance of the relevant materials.

[0003] To meet the aforementioned service requirements, various metallic material systems (including but not limited to nickel-based superalloys, titanium alloys, heat-resistant stainless steel, and other heat- and corrosion-resistant alloys) are widely used in engineering to manufacture compressor blades, turbine disks, casings, and connecting / fastening components. These metallic materials typically achieve a match between microstructure and properties through alloying design and hot working / heat treatment processes, ensuring they maintain necessary strength and stability under high or medium temperature conditions. Simultaneously, an oxide film / protective layer with a certain degree of density and adhesion can form on the material surface in high-temperature environments, thereby to some extent preventing direct contact between the environmental medium and the metal substrate, enhancing its oxidation and corrosion resistance. However, when gas turbines or aero engines operate in marine or coastal environments, salt spray particles in the air can easily enter the engine's high-temperature zone with the intake air and react with sulfides produced during fuel combustion to generate sodium chloride (NaCl) and sodium sulfate (NaCl). Molten salt deposits, such as Cr oxide film, interact with the oxide film on the alloy surface at high temperatures, destroying its integrity and inducing hot salt corrosion. In the initial stage of hot corrosion, the Cr oxide film can inhibit the direct contact between the metal substrate and the molten salt to a certain extent. However, as the service time increases and the temperature rises, the molten salt will promote the pyrolysis of the oxide film and the chlorination-oxidation cycle reaction, accelerate the loss of metal elements from the alloy surface and the peeling of the film, and ultimately lead to severe corrosion damage to the material.

[0004] Existing research indicates that active hot corrosion caused by deposited salts can trigger the failure of various high-temperature alloys, including GH4169, K38G, Fe-Cr model alloys, and 1Cr-11Ni-2W-2Mo-V steel. These related studies have largely focused on the influence of environmental factors such as temperature, corrosion time, and salt concentration on hot corrosion behavior and have made some progress. However, aero-engines, during actual service, not only endure high-temperature corrosive environments but also experience complex mechanical loads. Under the synergistic effect of stress and hot corrosion, the destruction of the surface film and crack initiation are significantly accelerated, leading to premature failure of blades and disk-type components.

[0005] Currently, most studies on the mechanism of hot salt corrosion under stress, both domestically and internationally, employ experiments with uniform tensile or bending loading. These studies analyze the impact of stress on corrosion rate and film stability from both macroscopic kinetic and microscopic reaction mechanism perspectives. However, most are limited to uniform stress field conditions and have not yet systematically revealed the influence of stress gradients on hot salt corrosion behavior. In fact, significant stress gradients are commonly found in areas such as blades, hole edges, and tenons during service. The local film deformation, ion migration, and changes in reaction activation energy caused by stress gradients may play a crucial role in the hot corrosion process, but related experimental and theoretical research remains significantly insufficient.

[0006] Therefore, there is an urgent need to develop a thermo-salt corrosion testing device and method capable of realizing the force-chemical coupling effect. This device and method can simulate the corrosion behavior of metallic materials under different stresses and stress gradients under controlled conditions, revealing the influence mechanism of stress field distribution on the stress-corrosion synergistic effect. This research and technology will have significant engineering implications for improving service damage models of metallic materials and guiding the design optimization and life prediction of key components of aero-engines. Summary of the Invention

[0007] This invention aims to deeply reveal the influence mechanism of stress level and stress gradient on the hot salt corrosion behavior of metallic materials. Addressing the technical limitations of existing studies that struggle to simultaneously control mechanical load and corrosive environment, this invention provides a method and apparatus for hot salt corrosion testing that achieves force-chemical coupling. To achieve the above objectives: First, this invention uses GH4169 nickel-based superalloy as the research object and designs a variable cross-section tensile deposited salt specimen. This specimen can form different stress level and stress gradient distribution regions under a single loading condition. Second, this invention simulates the formation of molten salt (including...) in a marine environment by artificially depositing molten salt on the specimen surface. (such as NaCl), and apply external tensile load to carry out hot salt corrosion test under external stress under controlled temperature conditions; after the test, the present invention continues to systematically characterize and quantitatively analyze the corrosion morphology, oxide film structure and elemental distribution of the sample.

[0008] The technical solution of this invention is as follows:

[0009] A variable cross-section tensile deposited salt specimen is characterized by having a symmetrical variable cross-section structure, specifically including: a first loading section 1, a second loading section 2, and a variable cross-section working section 3 disposed between the two loading sections, which can form different stress levels and stress gradient distribution regions under a single loading condition.

[0010] The first loading segment 1 and the second loading segment 2 have clamping holes for connection with a fixture;

[0011] The cross-section of the working section 3 decreases continuously from the loading sections on both sides to the center.

[0012] Furthermore, to mitigate the stress concentration effect at the middle section, a rounded or chamfered transition is provided at the minimum section position of the working section 3.

[0013] Furthermore, the materials of the samples include, but are not limited to, GH4169, K38G, Fe–Cr model alloy and 1Cr–11Ni–2W–2Mo–V steel.

[0014] The present invention also provides a mechanical-chemical coupling test method for metallic materials considering stress gradient based on the above-mentioned specimens, characterized by comprising the following steps:

[0015] Step 1: Prepare the sample;

[0016] Step 2: Perform surface treatment on the sample and conduct initial mass measurement to obtain the reference mass of the sample;

[0017] Step 3: Prepare a corrosive medium salt solution, stir well and let it stand for later use;

[0018] Step 4: Use the corrosive medium salt solution obtained in Step 3 to uniformly deposit the corrosive medium salt on the outer surface of the working section of the sample;

[0019] Step 5: Simulate a high-temperature environment and apply different external tensile loads to multiple samples treated in steps 1-4. Conduct hot salt corrosion tests under external stress under controlled temperature conditions.

[0020] Step 6: Determine the observation position in the working section of the sample, then cut the sample along the cross section at the determined observation position, analyze the surface microstructure at the observation position of the sample, and evaluate the corrosion performance of the sample under the influence of stress and stress gradient.

[0021] Furthermore, the error of the reference mass measured in step 2 is within 0.0001 grams.

[0022] Furthermore, the corrosive medium salt solution in step 3 is selected from NaCl solution, Solution, or in the form of NaCl and The mixture is a complex salt solution prepared with solute.

[0023] Furthermore, step 4 specifically includes:

[0024] Sub-step 4.1: Based on the actual structure, set a preset value for the amount of salt deposited per unit area of ​​the working section of the sample. To control the amount of deposition and ensure a uniform distribution of the corrosive medium;

[0025] Sub-step 4.2: Calculate the surface area of ​​one side of the working section of the sample. And then according to Calculate the weight of corrosion salt that needs to be deposited on this side of the working section of the specimen; then calculate the surface area on the other side of the working section of the specimen. And then according to Calculate the weight of corrosion salt that needs to be deposited on this side of the working section of the sample;

[0026] Sub-step 4.3: Preheat the sample to 150~200℃;

[0027] Sub-step 4.4: Load the corrosive medium salt solution obtained in step 3 into the spraying device, and first perform atomized spraying on one side of the working section of the sample to form a uniform salt film deposition layer on the surface. After deposition is completed, measure the mass increase of the sample due to salt layer adhesion. Next, atomized spraying is applied to the other working section of the sample to form a uniform salt film deposition layer on the surface. After deposition is completed, the mass increase of the sample due to salt layer adhesion is measured. .

[0028] Furthermore, step 5 specifically includes:

[0029] Sub-step 5.1: Repeat steps 1-4 to obtain multiple samples with deposited corrosive medium salts. Then, install each sample onto the testing machine and apply the same constant preload. The preload is determined according to the sample material and size, and it is necessary to ensure that the sample does not generate compressive stress after heating and expansion.

[0030] Sub-step 5.2: Start the high-temperature furnace of the testing machine, set the target temperature control value, heat each sample to the target temperature and then keep it at a constant temperature for a certain period of time to ensure that the temperature in the high-temperature furnace is uniformly distributed. During the heating and temperature control process, the sample always maintains a constant preload.

[0031] Sub-step 5.3: Pre-set different target load values ​​for each specimen, apply tensile loads to different target load values ​​at the same constant rate, and then set the isothermal corrosion test duration to complete the mechanical-chemical coupling test under the predetermined working conditions;

[0032] Sub-step 5.4: After the test reaches the predetermined duration, turn off the high-temperature furnace of the testing machine, stop loading, record and save the test data, and take out the sample for use after it has cooled to room temperature naturally.

[0033] Furthermore, step 6 specifically includes:

[0034] Sub-step 6.1: Determine the observation position to ensure that there are observation positions at the same location of the specimens under different loads, and also at the same stress point of the specimens under different loads.

[0035] Sub-step 6.2: Cut the specimens under different loads along the cross section at the determined observation position;

[0036] Sub-step 6.3: Use optical instruments to record and analyze the microstructure at different observation positions of each sample, and then use chemical analysis equipment to analyze the types of corrosion products at the observation positions.

[0037] Sub-step 6.4: Compare the test data at the same location of the specimens under different loads to analyze the influence of stress level on high-temperature corrosion of metallic materials; then compare the test data at the same stress point of the specimens under different loads to analyze the influence of stress gradient on high-temperature corrosion of metallic materials.

[0038] Furthermore, taking the left end point of the working section of the specimen as the zero point, the values ​​of each cross section of the specimen are calculated. Stress and stress gradient at the location;

[0039] Each cross section of the specimen The stress at the location follows:

[0040]

[0041] Each cross section of the specimen The stress gradient at the location follows:

[0042]

[0043] in, Indicates stress; Indicates the stress gradient; Represents the force acting on an object; The width of the working section of the sample; This refers to the length of the working section of the sample. The thickness of the working section of the sample; The cone angle of the working section of the sample.

[0044] The technical effects of this invention are as follows:

[0045] This invention proposes a mechanical-chemical coupling test method and apparatus for metallic materials considering stress gradients. It examines the mechanical-chemical coupling behavior under different stress levels and stress gradients, clarifies the influence of stress and stress gradient on stress-assisted corrosion rate, corrosion product morphology and oxide film integrity, and reveals the hot corrosion mechanism of metallic materials under mechanical-chemical coupling in a high-temperature molten salt environment. This provides a theoretical basis and experimental means for the service safety assessment and protection design of high-temperature components of aero-engines.

[0046] This invention also has the advantages of simple experimental methods, high repeatability, and the ability to compare and analyze corrosion behavior under multiple stress conditions. It can significantly improve the efficiency and accuracy of stress-corrosion synergy research and is suitable for quantitative evaluation and engineering application of the hot corrosion performance of high-temperature alloy materials. Attached Figure Description

[0047] The accompanying drawings are used to illustrate the principles and implementation methods of the present invention and do not constitute a limitation thereof. By referring to the specific embodiments in the drawings and specification, the technical solutions and beneficial effects of the present invention can be more clearly understood. The same or similar element reference numerals in the drawings represent the same or similar structural or functional features.

[0048] Figure 1 This is a flowchart of the corrosion performance testing method for metallic materials provided by the present invention;

[0049] Figure 2 This is a schematic diagram of the structure of the specimen provided in the embodiment of the present invention, wherein: 1-first loading segment; 2-second loading segment; 3-working segment;

[0050] Figure 3 The image shows the surface corrosion of the sample after the experiment in this embodiment of the invention.

[0051] Figure 4 The corrosion layer thickness (position 1) under different stress levels under the same stress gradient in the embodiments of the present invention is shown in (a) and (b) is the corrosion layer thickness at position 1 under a 6KN load.

[0052] Figure 5 The corrosion layer thickness (position 2) under different stress levels under the same stress gradient in the embodiments of the present invention is shown in (a) and (b) is the corrosion layer thickness at position 2 under a 6KN load.

[0053] Figure 6 The corrosion layer thickness (position 3) under different stress levels under the same stress gradient in the embodiments of the present invention is shown in (a) and (b) is the corrosion layer thickness at position 3 under a 6KN load.

[0054] Figure 7 The corrosion layer thickness (position 4) under different stress levels under the same stress gradient in the embodiments of the present invention is shown in (a) and (b) is the corrosion layer thickness at position 4 under a 6KN load.

[0055] Figure 8 This is a graph showing the variation of corrosion layer thickness with location in an embodiment of the present invention;

[0056] Figure 9The corrosion layer thicknesses under different stress gradients at the same stress level in the embodiments of the present invention are shown in (a) and (b) respectively. (a) is the corrosion layer thickness at position 2 under a 6KN load and (b) is the corrosion layer thickness at position 1 under an 8kN load. Detailed Implementation

[0057] To make the objectives, technical solutions, and beneficial effects of this invention more intuitive and clear, the embodiments of this invention will be further described in detail below with reference to the accompanying drawings. The same or similar reference numerals in the drawings indicate components having the same or similar functions. It should be understood that the embodiments described below are only used to illustrate the principles and implementation of this invention, and are not intended to limit the scope of protection of this invention. Equivalent substitutions or improvements made by those skilled in the art without departing from the spirit of this invention should be included within the scope of protection of this invention.

[0058] In this specification, it should be noted that when terms such as "above," "below," "left," "right," "inner," "outer," "vertical," and "horizontal" are used to describe orientation or spatial position, their meanings are based on the positional relationships shown in the accompanying drawings or the product's posture in normal use. These terms are used only to help the reader understand the structure of the invention and do not limit the relevant components to strictly maintaining this orientation in actual application. Therefore, such orientation expressions should not be considered as a substantial limitation of the invention. Similarly, designations such as "first" and "second" are only used to distinguish different elements or steps and do not indicate priority or importance.

[0059] Furthermore, the terms "horizontal" and "vertical" appearing in this invention do not require the components to be in a completely horizontal or absolutely vertical position, but rather allow for a certain range of deviation. For example, "horizontal" usually indicates an attitude that is more horizontal than the vertical direction, but does not exclude slight tilting.

[0060] Furthermore, the terms "set," "install," "connect," and "link" in this specification should be interpreted broadly, and may include fixed connections, detachable connections, integral molding connections, as well as mechanical, electrical, or indirect connections achieved through intermediate components, and may even indicate internal connectivity between components. Those skilled in the art can reasonably interpret these terms based on the specific structure and context.

[0061] In a first aspect, the present invention provides a variable cross-section tensile deposited salt sample, such as... Figure 2 As shown, the specimen includes: a first loading section 1, a second loading section 2, and a variable cross-section working section 3 located between the two loading sections, which can form different stress levels and stress gradient distribution regions under a single loading condition;

[0062] The cross-section of the working section 3 decreases continuously from the loading sections on both sides to the center.

[0063] Furthermore, to mitigate the stress concentration effect at the middle section, a rounded or chamfered transition is provided at the minimum section location.

[0064] Secondly, the present invention also provides a mechanical-chemical coupling test method for metallic materials that considers stress gradients, such as... Figure 1 As shown, it includes the following steps:

[0065] Step 1: Prepare the sample;

[0066] The sample has loading sections at both ends, with clamping holes for connection to fixtures; a continuously variable cross-section working section is provided in the middle of the sample, the length of which is denoted as . The thickness is recorded as Its cross-section gradually decreases from the loading section towards the center, and the width at both ends is denoted as . The width in the middle is denoted as Its cone angle is denoted as Furthermore, to mitigate the stress concentration effect at the middle section, rounded or chamfered transitions are provided at the minimum section position; the specimen as a whole has a symmetrical variable cross-section structure;

[0067] Furthermore, the materials used to prepare the samples include, but are not limited to, GH4169, K38G, Fe–Cr model alloy and 1Cr–11Ni–2W–2Mo–V steel;

[0068] Step 2: First, the sample surface is degreased, cleaned, and dried sequentially. Then, an initial mass determination is performed to obtain the reference mass of the sample, denoted as . During the measurement, the error of the reference mass must be within 0.0001 grams;

[0069] Step 3: Prepare a corrosive medium salt solution, stir well and let it stand for later use;

[0070] Furthermore, the corrosive medium salt solution is selected from NaCl solution, Solution, or in the form of NaCl and The mixture is a composite salt solution prepared with solute; the concentration of the corrosive medium salt solution can be adjusted according to the test conditions and corrosion intensity requirements by mixing NaCl and... Adjust the proportions accordingly;

[0071] Step 4: Using the corrosive medium solution obtained in Step 3, uniformly deposit corrosive medium salt on the outer surface of the working section of the sample using an atomization method. While depositing the corrosive medium salt, control the deposition amount to ensure that the amount of salt deposited per unit area of ​​the working section reaches the preset value. To ensure a uniform distribution of the corrosive medium, specifically:

[0072] Sub-step 4.1: Based on the actual structure, set a preset value for the amount of salt deposited per unit area of ​​the working section of the sample. To control the amount of deposition and ensure a uniform distribution of the corrosive medium;

[0073] Sub-step 4.2: Calculate the surface area of ​​one side of the working section of the sample. And then according to Calculate the weight of corrosion salt that needs to be deposited on this side of the working section of the specimen; then calculate the surface area on the other side of the working section of the specimen. And then according to Calculate the weight of corrosion salt that needs to be deposited on the test specimen;

[0074] Sub-step 4.3: Place the sample in a heating furnace for preheating treatment to 150~200℃;

[0075] Sub-step 4.4: Load the corrosive medium salt solution obtained in step 3 into a spraying device (atomizer). First, perform atomized spraying on one side of the working section of the sample to form a uniform salt film deposition layer on the surface. After deposition is complete, measure the mass increase of the sample due to salt layer adhesion. Next, atomized spraying is applied to the other working section of the sample to form a uniform salt film deposition layer on the surface. After deposition is completed, the mass increase of the sample due to salt layer adhesion is measured. ;

[0076] Step 5: Simulate a high-temperature environment by applying different external tensile loads to multiple samples treated in steps 1-4, and conducting hot salt corrosion tests under controlled temperature conditions. Specifically:

[0077] Sub-step 5.1: Repeat steps 1-4 to obtain multiple samples with deposited corrosive medium salts. Then, install each sample onto the testing machine and apply the same constant preload. The preload is determined according to the sample material and size, and it is necessary to ensure that the sample does not generate compressive stress after heating and expansion.

[0078] Sub-step 5.2: Start the high-temperature furnace of the testing machine, set the target temperature control value, heat each sample to the target temperature and then keep it at a constant temperature for a certain period of time to ensure that the temperature in the high-temperature furnace is uniformly distributed. During the heating and temperature control process, the sample always maintains a constant preload.

[0079] Sub-step 5.3: Pre-set different target load values ​​for each specimen, apply tensile loads to different target load values ​​at the same constant rate, and then set the isothermal corrosion test duration to complete the mechanical-chemical coupling test under the predetermined working conditions;

[0080] Sub-step 5.4: After the test reaches the predetermined duration, turn off the high-temperature furnace of the testing machine, stop loading, record and save the test data, and take out the sample for use after it has cooled to room temperature naturally.

[0081] Step 6: Determine the observation position on the working section of the sample. Then, cut the sample along the cross-section at the determined observation position, analyze the surface microstructure at the observation position, and evaluate the corrosion performance of the sample under the influence of stress and stress gradient. Specifically:

[0082] Sub-step 6.1: Determine the observation position to ensure that there are observation positions at the same location of the specimens under different loads, and also at the same stress point of the specimens under different loads.

[0083] According to the stress calculation formula:

[0084]

[0085] in, Indicates stress, This represents the force acting on an object. Represents the area on which the force acts;

[0086] Under this load level, with the left end of the working section as the zero point, the cross-section of the specimen can be obtained. The stress at the location follows:

[0087]

[0088] in, It is the cone angle;

[0089] Stress gradient follows:

[0090]

[0091] Sub-step 6.2: Cut the specimens under different loads along the cross section at the determined observation position;

[0092] Sub-step 6.3: Use optical instruments to record and analyze the microstructure at different observation positions of each sample, and then use chemical analysis equipment to analyze the types of corrosion products at the observation positions.

[0093] Sub-step 6.4: Compare the test data at the same location of the specimens under different loads to analyze the influence of stress level on high-temperature corrosion of metallic materials; then compare the test data at the same stress point of the specimens under different loads to analyze the influence of stress gradient on high-temperature corrosion of metallic materials.

[0094] In the above method, since the specimen is set with a continuously variable cross-section working section, after the target load is applied to the specimen, the stress of each cross-section increases continuously from both sides to the middle, and the stress gradient increases continuously from both sides to the middle. By analyzing the high-temperature corrosion morphology of the cross-section at the same observation position of the test piece under different loads, the high-temperature corrosion kinetic data of the metal material under multiple stress levels can be obtained. By analyzing the high-temperature corrosion morphology of the cross-section at the same stress observation position under different loads, the influence of different stress gradients on the high-temperature corrosion of the metal material can be obtained.

[0095] The following description, using an optional embodiment, illustrates the content involved in the above embodiments.

[0096] Step 1: Prepare the sample;

[0097] like Figure 2 As shown, this embodiment of the invention describes the working conditions of two identical specimens under two stress levels. GH4169 nickel-based high-temperature alloy plate is selected as the test material, with a width of 25 mm and a thickness of 2 mm. The two ends of the GH4169 alloy plate are machined into loading sections with a length of 30 mm each, and clamping holes are provided for connection with the fixture. A working section with a length of 100 mm is machined along the long side between the two loading sections. The cross-section gradually decreases from the loading section to the center, forming a symmetrical variable cross-section structure with a cone angle of approximately 11°. To reduce the stress concentration effect at the middle section, a rounded or chamfered transition is provided at the minimum cross-section position, with a chamfer radius of 5 mm.

[0098] Step 2: Perform surface treatment on the sample and conduct initial mass measurement to obtain the reference mass of the sample;

[0099] The sample surface was degreased and cleaned sequentially with water and anhydrous ethanol using ultrasonic waves. After drying with a hair dryer, the initial mass of the sample was measured using an electronic balance with an error within 0.0001 grams, and recorded as _____. .

[0100] Step 3: Prepare a corrosive medium salt solution, stir well and let it stand for later use;

[0101] This embodiment uses a mixed salt solute to prepare a corrosive medium salt solution. Specifically: first, NaCl with a mass ratio of 5:95 is taken and... Then add deionized water to prepare a compound salt solution, and finally stir thoroughly to completely dissolve the solute before letting it stand for later use.

[0102] Step 4: Use the corrosive medium salt solution obtained in Step 3 to uniformly deposit the corrosive medium salt on the outer surface of the working section of the sample;

[0103] Sub-step 4.1: Set the preset value for the amount of salt deposited per unit area of ​​the working section. To control the amount of deposition and ensure a uniform distribution of the corrosive medium;

[0104] Sub-step 4.2: Calculate the surface area of ​​one side of the working section of the sample. And then according to Calculate the weight of corrosion salt that needs to be deposited on this side of the working section of the specimen; then calculate the surface area on the other side of the working section of the specimen. And then according to Calculate the weight of corrosion salt that needs to be deposited on the test specimen;

[0105] Sub-step 4.3: Place the sample in a heating furnace and heat it to approximately 150°C;

[0106] Sub-step 4.4: Load the corrosive medium salt solution obtained in step 3 into the atomizer, and first perform atomization spraying on one side of the working section of the sample to form a uniform salt film deposition layer on the surface. After the deposition is completed, measure the mass increase of the sample due to the salt layer adhesion. Next, atomized spraying is applied to the other working section of the sample to form a uniform salt film deposition layer on the surface. After deposition is completed, the mass increase of the sample due to salt layer adhesion is measured. .

[0107] Step 5: Repeat steps 1-4 to obtain two samples. Simulate a high-temperature environment and apply external tensile loads to the two samples. Conduct hot salt corrosion tests under external stress under controlled temperature conditions.

[0108] Sub-step 5.1: Fix the two specimens treated according to steps 1-4 onto the RD-100 electronic creep testing machine and apply a constant pre-tensile load of 200N to both specimens.

[0109] Sub-step 5.2: Start the high-temperature furnace, set the temperature control to the target value of 650℃, heat each sample to 650℃ and then keep it at a constant temperature for 30 minutes to ensure uniform temperature distribution in the high-temperature furnace. During the heating and holding process, the sample is always kept under a tensile load of 200N.

[0110] Sub-step 5.3: After holding at a constant temperature for 30 minutes, apply a tensile load at a constant rate of 100 N / s to make the two specimens reach the preset target load values ​​respectively. The target load of one specimen is 6000 N and the target load of the other specimen is 8000 N. Then set the constant temperature corrosion test duration to 50 hours to complete the force-chemical coupling test.

[0111] Sub-step 5.4: After the test reaches the predetermined duration, turn off the high-temperature furnace of the testing machine, stop loading, record and save the test data, and take out the sample for use after it has cooled to room temperature naturally.

[0112] Step 6: Determine the observation position in the working section of the sample, then cut the sample along the cross section at the determined observation position, analyze the corrosion layer thickness at the observation position, and evaluate the corrosion performance of the sample under the influence of stress and stress gradient.

[0113] Sub-step 6.1: Taking the left end point of the working section as the zero point, the stress and stress gradient of each cross section of the specimen can be calculated:

[0114]

[0115]

[0116] In this embodiment, taking the left end point of the working section as the origin, a point is taken at 20 mm, and then points are taken every 10 mm to the right. A total of 4 observation positions are determined for each specimen. The calculated stress of the specimen at different cross-sections is shown in Table 1 below:

[0117] Table 1. Stress at different cross-sections of the specimen

[0118]

[0119] Based on the calculation data in the table above, the calculated stresses at position 2 under a 6kN load and position 1 under an 8kN load are approximately equal. Therefore, these two positions are taken as the observation positions at the same stress points of the specimens under different loads.

[0120] Sub-step 6.2: Cut the specimens under the two loads along the cross section at the determined observation position;

[0121] Sub-step 6.3: Use optical instruments to record and analyze the microstructure of the two samples at different observation positions, and then use chemical analysis equipment to analyze the types of corrosion products at the observation positions.

[0122] Sub-step 6.4: Compare the test data at the same observation location under the two loads to analyze the influence of stress level on high-temperature corrosion of metallic materials; then compare the test data at location 2 under 6kN load and location 1 under 8kN load to analyze the influence of stress gradient on high-temperature corrosion of metallic materials.

[0123] from Figures 3-8 It can be seen that under the coupled force-thermal-chemical action, corrosion pits and microcracks were generated on the surface of the test piece. Furthermore, the higher the stress level, the larger the corrosion pit size and the lower the surface density of the alloy. Therefore, the stress level promotes corrosion. Figure 3 The surface corrosion of the sample after the test; Figure 4The corrosion layer thickness (position 1) is under the same stress gradient but different stress levels, where (a) is the corrosion layer thickness at position 1 under a 6 kN load and (b) is the corrosion layer thickness at position 1 under an 8 kN load. Figure 5 The corrosion layer thickness (position 2) is given under the same stress gradient but different stress levels, where (a) is the corrosion layer thickness at position 2 under a 6 kN load and (b) is the corrosion layer thickness at position 2 under an 8 kN load. Figure 6 The corrosion layer thickness (position 3) is given under the same stress gradient but different stress levels, where (a) is the corrosion layer thickness at position 3 under a 6 kN load and (b) is the corrosion layer thickness at position 3 under an 8 kN load. Figure 7 The corrosion layer thickness (position 4) is given under the same stress gradient but different stress levels, where (a) is the corrosion layer thickness at position 4 under a 6 kN load and (b) is the corrosion layer thickness at position 4 under an 8 kN load. Figure 8 This is a graph showing the trend of corrosion layer thickness as a function of location.

[0124] Figure 9 The figures represent the corrosion layer thicknesses under different stress gradients at the same stress level, where (a) is the corrosion layer thickness at position 2 under a 6 kN load, and (b) is the corrosion layer thickness at position 1 under an 8 kN load. Figure 9 It can be seen that the stress gradient has little effect on corrosion.

[0125] In the above embodiment, a working section with a continuously changing cross section is set between the two loading sections. By applying different loads to the two test pieces respectively, different stress levels and stress gradients are achieved. This method has the advantages of being simple to test, highly repeatable, and capable of comparative analysis of corrosion behavior under multiple stress states. It can significantly improve the efficiency and accuracy of stress-corrosion synergy research and is suitable for quantitative evaluation and engineering application of the hot corrosion performance of high-temperature alloy materials.

[0126] The above description is merely a few specific embodiments of the present invention, and the scope of protection of the present invention is not limited thereto. Those skilled in the art can make various equivalent modifications, improvements, or substitutions within the scope of the technical solutions disclosed in the present invention, and these equivalent solutions should also be included within the scope of protection of the present invention.

[0127] It should be noted that the technical features mentioned in the above embodiments can be combined and applied in any way according to specific needs, provided that they do not conflict with or are compatible with each other. To avoid repetition, this specification does not elaborate on all possible combinations.

[0128] Furthermore, different embodiments of the present invention can also be combined with each other. As long as they do not deviate from the core concept and technical idea of ​​the present invention, such combinations should also be considered to fall within the protection scope of the present invention.

Claims

1. A variable cross-section tensile deposited salt sample, characterized in that, The overall structure is a symmetrical variable cross section, specifically including: a first loading section (1), a second loading section (2) and a variable cross section working section (3) set between the two loading sections, which can form different stress levels and stress gradient distribution areas under a single loading condition; The first loading segment (1) and the second loading segment (2) have clamping holes for connecting with a clamp; The cross-section of the working section (3) decreases continuously from the loading sections on both sides to the center.

2. The variable cross-section tensile deposited salt sample as described in claim 1, characterized in that: To mitigate the stress concentration effect at the middle section, a rounded or chamfered transition is provided at the minimum section position of the working section (3).

3. The variable cross-section tensile deposited salt sample as described in claim 2, characterized in that: The materials of the samples include, but are not limited to, GH4169, K38G, Fe–Cr model alloy and 1Cr–11Ni–2W–2Mo–V steel.

4. A mechanical-chemical coupling test method for metallic materials considering stress gradients based on the variable cross-section tensile deposited salt specimens described in claims 1-3, characterized in that, Includes the following steps: Step 1: Prepare the sample; Step 2: Perform surface treatment on the sample and conduct initial mass measurement to obtain the reference mass of the sample; Step 3: Prepare a corrosive medium salt solution, stir well and let it stand for later use; Step 4: Use the corrosive medium salt solution obtained in Step 3 to uniformly deposit the corrosive medium salt on the outer surface of the working section of the sample; Step 5: Simulate a high-temperature environment and apply different external tensile loads to multiple samples treated in steps 1-4. Conduct hot salt corrosion tests under external stress under controlled temperature conditions. Step 6: Determine the observation position in the working section of the sample, then cut the sample along the cross section at the determined observation position, analyze the surface microstructure at the observation position of the sample, and evaluate the corrosion performance of the sample under the influence of stress and stress gradient.

5. The mechanical-chemical coupling test method for metallic materials as described in claim 4, characterized in that, The error of the reference mass measured in step 2 is within 0.0001 grams.

6. The mechanical-chemical coupling test method for metallic materials as described in claim 4, characterized in that, The corrosive medium salt solution in step 3 is selected from NaCl solution. Solution, or in the form of NaCl and The mixture is a complex salt solution prepared with solute.

7. The mechanical-chemical coupling test method for metallic materials as described in claim 4, characterized in that, Step 4 specifically includes: Sub-step 4.1: Based on the actual structure, set a preset value for the amount of salt deposited per unit area of ​​the working section of the sample. To control the amount of deposition and ensure a uniform distribution of the corrosive medium; Sub-step 4.2: Calculate the surface area of ​​one side of the working section of the sample. And then according to Calculate the weight of corrosion salt that needs to be deposited on this side of the working section of the specimen; then calculate the surface area on the other side of the working section of the specimen. And then according to Calculate the weight of corrosion salt that needs to be deposited on this side of the working section of the sample; Sub-step 4.3: Preheat the sample to 150~200℃; Sub-step 4.4: Load the corrosive medium salt solution obtained in step 3 into the spraying device, and first perform atomized spraying on one side of the working section of the sample to form a uniform salt film deposition layer on the surface. After deposition is completed, measure the mass increase of the sample due to salt layer adhesion. Next, atomized spraying is applied to the other working section of the sample to form a uniform salt film deposition layer on the surface. After deposition is completed, the mass increase of the sample due to salt layer adhesion is measured. .

8. The mechanical-chemical coupling test method for metallic materials as described in claim 4, characterized in that, Step 5 specifically includes: Sub-step 5.1: Repeat steps 1-4 to obtain multiple samples with deposited corrosive medium salts. Then, install each sample onto the testing machine and apply the same constant preload. The preload is determined according to the sample material and size, and it is necessary to ensure that the sample does not generate compressive stress after heating and expansion. Sub-step 5.2: Start the high-temperature furnace of the testing machine, set the target temperature control value, heat each sample to the target temperature and then keep it at a constant temperature for a certain period of time to ensure that the temperature in the high-temperature furnace is uniformly distributed. During the heating and temperature control process, the sample always maintains a constant preload. Sub-step 5.3: Pre-set different target load values ​​for each specimen, apply tensile loads to different target load values ​​at the same constant rate, and then set the isothermal corrosion test duration to complete the mechanical-chemical coupling test under the predetermined working conditions; Sub-step 5.4: After the test reaches the predetermined duration, turn off the high-temperature furnace of the testing machine, stop loading, record and save the test data, and take out the sample for use after it has cooled to room temperature naturally.

9. The mechanical-chemical coupling test method for metallic materials as described in claim 4, characterized in that, Step 6 specifically includes: Sub-step 6.1: Determine the observation position to ensure that there are observation positions at the same location of the specimens under different loads, and also at the same stress point of the specimens under different loads. Sub-step 6.2: Cut the specimens under different loads along the cross section at the determined observation position; Sub-step 6.3: Use optical instruments to record and analyze the microstructure at different observation positions of each sample, and then use chemical analysis equipment to analyze the types of corrosion products at the observation positions. Sub-step 6.4: Compare the test data at the same location of the specimens under different loads to analyze the influence of stress level on high-temperature corrosion of metallic materials; then compare the test data at the same stress point of the specimens under different loads to analyze the influence of stress gradient on high-temperature corrosion of metallic materials.

10. The mechanical-chemical coupling test method for metallic materials as described in claim 9, characterized in that, Taking the left end point of the working section of the specimen as the 0 point, the calculations for each cross section of the specimen are obtained. Stress and stress gradient at the location; Each cross section of the specimen The stress at the location follows: Each cross section of the specimen The stress gradient at the location follows: in, Indicates stress; Indicates the stress gradient; Represents the force acting on an object; The width of the working section of the sample; This refers to the length of the working section of the sample. The thickness of the working section of the sample; The cone angle of the working section of the sample.

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