A hot corrosion kinetic method based on nickel-based superalloy coating

Abstract

A kind of hot corrosion dynamic calibration method based on nickel-based superalloy coating belongs to the technical field of coating hot corrosion evaluation. First, the same size alumina ceramic piece as alloy coating test piece is used as calibration test piece, and the alloy test piece and calibration test piece are preheated. The same thickness salt film is deposited on the surface of the preheated alloy coating test piece and calibration test piece by using salt coating method, to obtain salt film test piece and salt film calibration piece. Secondly, long period hot corrosion test is carried out above the melting point of salt film, to obtain hot corrosion data of salt film test piece and salt film calibration piece, and to draw the weight change curve per unit area of salt film test piece and salt film calibration piece in the process of hot corrosion. Finally, the volatile amount of hot salt is obtained by salt film calibration piece, and the hot corrosion kinetic curve of salt film test piece is calibrated. The present application can calibrate the kinetic difference caused by hot salt volatilization in the process of hot corrosion, and can realize the evaluation of hot corrosion damage of nickel-based superalloy coating in the environment above the melting point of hot salt.

Description

Technical Field

[0001] This invention belongs to the field of hot corrosion assessment technology for nickel-based superalloy coatings, and relates to a calibration method based on the corrosion kinetics of nickel-based superalloy coatings, particularly a calibration method for the amount of hot salt volatilization based on the hot corrosion kinetics of coatings above 900°C. Background Technology

[0002] Nickel-based superalloys, due to their excellent high-temperature strength, oxidation resistance, and corrosion resistance, have become the primary manufacturing material for turbine blades in gas turbine engines. With the rapid development of the marine industry, the performance requirements for engines are becoming increasingly stringent, leading to rising surface service temperatures. This necessitates the application of high-temperature protective coatings to the engine surface to meet the demands of the operating environment. Among these, MCrAlY coatings possess excellent ductility, toughness, fatigue resistance, and corrosion resistance, making them a primary protective coating for gas turbine blades. However, in marine applications, gas turbine blades undergo long-term operation when atmospheric NaCl salt particles react with sulfur-containing fuel gas at high temperatures, depositing a salt film (primarily Na₂SO₄ + NaCl) on the blade surface. This leads to severe hot corrosion, damaging the integrity of the surface coating and significantly limiting the blade's service life. Based on the alloy's service temperature and the state of the salt film, hot corrosion can be categorized into low-temperature hot corrosion (650℃-800℃) and high-temperature hot corrosion (850℃-950℃).

[0003] Currently, the salt coating method can uniformly deposit a mixed salt film on the alloy surface, which is not prone to blistering or peeling, and can effectively simulate the hot corrosion environment, thus becoming a universal hot corrosion testing method. Using the alloy coating after salt coating for hot corrosion testing, and simultaneously obtaining the hot corrosion kinetic curve, can, to some extent, assess the degree of coating damage. However, current conventional hot corrosion weighing methods, in their study of corrosion kinetics, assume that under the combined effects of sulfidation, oxidation, and alkaline fluxing mechanisms, molten salt elements diffuse rapidly into the matrix, and the porous nature of oxides leads to oxide shedding, resulting in overall weight loss of the alloy coating. However, in hot corrosion test environments above 900℃, the mixed salt film on the coating surface is in a molten state, and a large amount of it volatilizes; existing conventional weighing methods do not consider the mass effect of molten salt volatilization.

[0004] Therefore, when conducting hot corrosion tests in environments above the melting point of mixed salts, the volatilization of hot salts has a significant impact on the determination of hot corrosion kinetics. However, existing technologies cannot calibrate the volatilization of hot salts themselves when determining hot corrosion kinetic curves. Summary of the Invention

[0005] In view of the shortcomings of existing research, the purpose of this invention is to provide a method for calibrating thermal corrosion kinetics, taking into account the volatilization of molten salt when the coating is subjected to thermal corrosion testing at temperatures above 900°C. This method involves calibrating the thermal corrosion kinetics.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A corrosion kinetics calibration method based on a nickel-based high-temperature alloy coating is disclosed. The method involves first preheating an alumina ceramic sheet of the same size as the alloy coating test piece and the calibration test piece. A salt film of the same thickness is deposited onto the surfaces of both the preheated alloy and calibration test pieces using a salt coating method, resulting in a salt film test piece and a salt film calibration piece. Second, a long-term hot corrosion test is conducted at a temperature higher than the melting point of the salt film to obtain hot corrosion data for the salt film test piece and the salt film calibration piece. The weight change curves per unit area of ​​the salt film test piece and the salt film calibration piece during hot corrosion are then plotted. Finally, the amount of hot salt volatilization is obtained from the salt film calibration piece to calibrate the hot corrosion kinetics curve of the salt film test piece (alloy coating). The specific steps include:

[0008] Step S1: Perform a preheating test on the alloy coating test piece and the alumina ceramic sheet to obtain the alloy test piece and the calibration test piece before salt film deposition; wherein the alloy coating test piece becomes the alloy test piece and the alumina ceramic sheet becomes the calibration test piece.

[0009] Step S2: Deposit salt film on the alloy test piece and calibration test piece after step S1 to obtain salt film test piece and salt film calibration piece. Place the salt film test piece and salt film calibration piece in corundum crucible containers of the same size and weigh the initial total mass. The parameters for salt film deposition treatment are the same for both.

[0010] Step S3: Long-cycle hot corrosion tests are conducted on the salt film test piece and the salt film calibration piece respectively. The hot corrosion data of the salt film test piece and the hot corrosion data of the salt film calibration piece are obtained by mid-course sampling method. The parameters of the long-cycle hot corrosion tests of the two are the same.

[0011] Step S4: Based on the two sets of hot corrosion data obtained in step S3, obtain the change in unit area mass of the salt film test piece and the salt film calibration piece at different hot corrosion times, and plot the unit area weight change curves of the salt film test piece and the salt film calibration piece respectively.

[0012] Step S5: Based on the weight change curve obtained in step S4, at the same hot corrosion time, the weight change of the alloy coating after the calibrated hot salt volatilization is obtained by subtracting the mass change of the salt film test piece from the mass change of the salt film calibration piece; and the hot corrosion kinetic curve of the alloy coating after the calibrated hot salt volatilization is plotted during the long-cycle hot corrosion process.

[0013] Furthermore, in step S1, the size of the calibration test piece is consistent with the size of the alloy test piece.

[0014] Further, in step S1, the preheating temperature of the alloy coating test piece is 110℃-130℃, and the preheating temperature of the alumina ceramic sheet is the same as the hot corrosion test temperature. The alloy test piece and the calibration test piece are repeatedly preheated until the weight does not change.

[0015] Further, in step S2, a mixed salt film is deposited on the surface of the alloy test piece and the calibration test piece using a salt coating method; the thickness of the mixed salt film on the surface of the salt film test piece and the salt film calibration piece is the same, and the salt film thickness is 1.0 mg / cm². 2 -3.0mg / cm 2 It is advisable;

[0016] Further, in step S2, the salt coating method is specifically a thermal spraying method: after the alloy test piece and the calibration test piece are heated on a heated nickel plate, the prepared mixed salt solution is uniformly deposited on the upper and lower surfaces of the test piece using an atomizing spray gun; the mixed salt solution is composed of NaCl and Na2SO4, wherein the weight percentage of NaCl is 0% to 25%, and the remainder is Na2SO4.

[0017] Furthermore, in step S3, the hot corrosion test temperature of the long-cycle hot corrosion test is higher than the melting point of the mixed salt film;

[0018] Furthermore, in step S3, the mid-cycle sampling method involves taking out the test piece at regular intervals, weighing the total weight of the test piece and the crucible container, and then putting it back into the muffle furnace to continue the next cycle of hot corrosion test.

[0019] The beneficial effects of this invention are as follows:

[0020] (1) The innovation of this invention is that by introducing alumina ceramic sheets as calibration test pieces, the conventional hot corrosion weighing method is improved. This method effectively calibrates the hot salt volatilization effect that is ignored in the conventional weighing process, and realizes accurate characterization of the true mass change of the alloy coating during hot corrosion.

[0021] (2) This invention can take into account the amount of hot salt volatilization during hot corrosion testing of nickel-based alloy coatings in an environment above the melting point of molten salt, thereby calibrating the hot corrosion kinetic curve, improving the reliability of hot corrosion experimental data, and providing a new research method for a deeper understanding of the hot corrosion behavior of alloy coatings. Verification has shown that this method is feasible and provides an evaluation basis for the corrosion rate of nickel-based alloy coatings under different conditions. Attached Figure Description

[0022] Figure 1This is a schematic flowchart of the nickel-based alloy coating corrosion kinetics calibration method of the present invention;

[0023] Figure 2 This is a schematic diagram showing the positional structure of the salt film test piece and salt film calibration piece during hot corrosion testing according to the present invention. In the figure: 1 Salt film test piece (alloy coating test piece); 2 Corundum crucible container; 3 Corundum crucible; 4 Salt film calibration piece;

[0024] Figure 3 The curves showing the change in weight per unit area of ​​the salt film test piece and the salt film calibration piece during hot corrosion in Examples 1 to 3 of this invention are shown.

[0025] Figure 4 The above are the thermal corrosion kinetic curves of the alloy coating test pieces in Examples 1 to 3 of this invention after calibration of hot salt volatilization.

[0026] Figure 5 The curves showing the change in weight per unit area of ​​the salt film test piece and the salt film calibration piece during hot corrosion in Example 4 of this invention are shown.

[0027] Figure 6 The image shows the thermal corrosion kinetics curve of the alloy coating test piece in Example 4 of this invention after calibration of the hot salt volatilization amount. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be understood that the described embodiments are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0029] like Figure 1 As shown, a method for calibrating the thermal corrosion kinetics of a nickel-based superalloy coating includes the following steps:

[0030] Step S1: Preheating test is performed on alloy coating test piece and alumina ceramic sheet to obtain alloy test piece and calibration test piece before salt film deposition; wherein the alloy coating test piece becomes alloy test piece, and the alumina ceramic sheet becomes calibration test piece.

[0031] In one or more embodiments of the present invention, in step S1, the preheating temperature of the alloy test piece is 110℃-130℃, the preheating temperature of the calibration test piece and the corundum crucible container is the same as the hot corrosion test temperature, and the preheating is repeated until the weight of the alloy coating test piece and the alumina ceramic sheet does not change, and the calibration test piece and the alloy test piece are the same size.

[0032] Specifically, in one or more embodiments of the present invention, the calibration test piece and the alloy test piece are 8mm × 8mm × 2mm in size.

[0033] Step S2: Deposit a salt film on the alloy test piece and calibration test piece processed in step S1 to obtain a salt film test piece and a salt film calibration piece. Place the salt film test piece and the salt film calibration piece in corundum crucibles of the same size and weigh their initial total mass.

[0034] In one or more embodiments of the present invention, in step S2, a mixed salt film is deposited on the upper and lower surfaces of the alloy test piece and the calibration test piece using the salt coating method, and the salt film deposition treatment parameters are the same for both.

[0035] Specifically, in one or more embodiments of the present invention, the salt coating method refers to placing the alloy test piece and the calibration test piece on a nickel plate at 80°C, and using an atomizing spray gun to uniformly deposit a prepared mixed salt solution onto the upper and lower surfaces of the alloy test piece and the calibration test piece in multiple applications, ensuring that a salt film of the same thickness is formed on the surfaces of the salt film test piece and the salt film calibration piece. The salt film thickness is 1.0 mg / cm². 2 -3.0mg / cm 2 It is advisable to use a mixed salt solution consisting of NaCl and Na₂SO₄, where the weight percentage of NaCl is 0% to 25%, and the remainder is Na₂SO₄. Place the salt film test piece and the salt film calibration piece separately into corundum crucible containers and transfer them to a constant temperature drying oven to dry until the total weight does not change. Then, weigh the initial total weight of the salt film test piece and the corundum crucible container, as well as the initial total weight of the salt film calibration piece and the corundum crucible container.

[0036] Step S3: Long-cycle hot corrosion tests are conducted on the salt film test piece and the salt film calibration piece, and hot corrosion data are obtained by mid-course sampling method; the parameters of the long-cycle hot corrosion tests for the two are the same.

[0037] In one or more embodiments of the present invention, in step S3, the hot corrosion test temperature is higher than the melting point of the salt film, and the intermediate sampling method is to take out the test piece at regular intervals, weigh the total weight of the test piece and the corundum crucible container, and then put it back into the muffle furnace to continue the next cycle of hot corrosion test.

[0038] Specifically, in one or more embodiments of the present invention, the hot corrosion test temperature is 950°C and 900°C, and the sampling time is 0.5h, 2h, 5h, 10h, 15h, 25h, 50h, 75h, 100h, 150h, and 200h.

[0039] Step S4: Based on the two sets of hot corrosion data obtained in step S3, plot the weight change curves of the unit area weight change of the salt film test piece and the salt film calibration piece as a function of hot corrosion time.

[0040] S5. Based on the weight change curve obtained in step S4, at the same hot corrosion time, the weight change of the alloy coating after the calibrated hot salt volatilization amount is obtained by subtracting the unit area mass change of the salt film test piece from the unit area mass change of the salt film calibration piece; and the hot corrosion kinetic curve of the alloy coating after the calibrated hot salt volatilization amount is plotted during the long-cycle hot corrosion process.

[0041] The specific solution is detailed in the following embodiments:

[0042] Example 1

[0043] The mixed salt composition was selected as 75 wt.% Na₂SO₄ + 25 wt.% NaCl. The alloy coating test piece was a DZ411 nickel-based superalloy with an MCrAlY coating. Alumina ceramic sheets were used as calibration test pieces, and numerous small round corundum crucibles and large square corundum crucibles were prepared.

[0044] The first step involves preheating the alloy-coated test piece in a constant-temperature drying oven at 130℃ until its mass remains unchanged. Then, the alumina ceramic test piece and all used crucibles are preheated in a muffle furnace at 950℃ for a sufficient time to ensure no change in mass and to remove any residual moisture. The ceramic calibration piece should have the same dimensions as the alloy-coated test piece; in all implementation cases, its dimensions were 8mm × 8mm × 2mm. Both the preheated alloy and calibration test pieces are weighed separately, five times each time, and the average value is taken as the initial mass of both.

[0045] The second step involves preparing a mixed salt solution of 75 wt.% Na₂SO₄ and 25 wt.% NaCl. The alloy test piece and calibration test piece are placed on a heated nickel plate at 80°C. Using an atomizing spray gun, the prepared mixed salt solution is deposited evenly onto the upper and lower surfaces of the test and calibration test pieces in multiple applications, ensuring that the salt film thickness on the surfaces of the salt film test and calibration test pieces is 3.0 ± 0.2 mg / cm². 2 .

[0046] The third step involves placing the salt film test piece and the salt film calibration piece into separate circular corundum crucibles and transferring them to a constant-temperature drying oven to dry to constant weight. The total weight of the salt film test piece and its container, along with the total weight of the salt film calibration piece and its container, are then recorded as the initial mass m0 of the salt film test piece and calibration piece, respectively. All the circular crucibles containing the test pieces are then placed together in a large square crucible (as shown in the attached image). Figure 2The samples were then transferred to a muffle furnace for a long-term hot corrosion test at 950℃. During the hot corrosion test, the sample pieces and crucible were removed at predetermined time intervals t (0.5h, 2h, 5h, 10h, 15h, 25h, 50h, 75h, 100h, 150h, 200h), cooled to room temperature, and their total weight m was measured. t When weighing, the average of five weighing results is taken as the final recorded value.

[0047] The fourth step involves using the thermal corrosion data obtained in the third step, combined with the surface area A (cm²) of the test piece and calibration piece. 2 ), calculate the change in mass per unit area W = (m²) of the salt film test piece and the salt film calibration piece at each hot corrosion moment. t -m0) / A, unit: mg / cm³ 2 Plot the weight per unit area variation curves for the salt film test piece and the salt film calibration piece. (See attached diagram) Figure 3 When the salt film composition is 75 wt.% Na₂SO₄ + 25 wt.% NaCl, both the salt film test piece and the salt film calibration piece exhibit mass loss characteristics during hot corrosion.

[0048] Fifth, based on the weight change curve obtained in step four, subtract the weight change per unit area of ​​the salt film test piece from the weight change per unit area of ​​the salt film calibration piece at the same hot corrosion time to obtain the weight change per unit area of ​​the alloy coating test piece after the calibrated hot salt volatilization amount at that hot corrosion time. Finally, plot the hot corrosion kinetic curve of the alloy coating after the calibrated hot salt volatilization amount during long-term hot corrosion; as shown below. Figure 4 After calibration by hot salt volatilization, the thermal corrosion kinetic curves of the alloy coating test piece in a 75 wt.% Na2SO4 + 25 wt.% NaCl salt film environment are shown. Figure 4 The data shows a continuous increasing trend in mass per unit area, indicating that the alloy coating actually experienced a significant mass gain during the hot corrosion process.

[0049] Example 2

[0050] The mixed salt solution composition in step 2 of Example 1 was changed to 95 wt.% Na₂SO₄ + 5 wt.% NaCl, with all other components remaining unchanged. (See attached...) Figure 3 Analysis of the mass change curves per unit area shows that when the salt film composition is 95 wt.% Na₂SO₄ + 5 wt.% NaCl, both the salt film test piece and the salt film calibration piece exhibit mass loss characteristics during hot corrosion. After calibration by hot salt volatilization, the hot corrosion kinetic curve of the alloy coating test piece in a 95 wt.% Na₂SO₄ + 5 wt.% NaCl salt film environment is shown in the figure. Figure 4 The data shows a continuous increasing trend in mass per unit area, indicating that the alloy coating actually underwent a weight gain process during hot corrosion.

[0051] Example 3

[0052] The mixed salt solution composition in step 2 of Example 1 was changed to 100 wt.% Na2SO4, with all other components remaining unchanged. (See attached...) Figure 3 Analysis of the mass change curves per unit area shows that when the salt film composition is 100 wt.% Na₂SO₄, both the salt film test piece and the salt film calibration piece exhibit mass loss characteristics during hot corrosion. After calibration by hot salt volatilization, the hot corrosion kinetic curve of the alloy coating test piece in a 100 wt.% Na₂SO₄ salt film environment is shown below. Figure 4 The data shows a continuous increasing trend in mass per unit area, indicating that the alloy coating actually underwent a weight gain process during hot corrosion.

[0053] Example 4

[0054] In Example 1, the preheating temperature of the alloy coating test piece in the first step was changed to 110℃, and the preheating temperature of the ceramic test piece and the corundum crucible container was changed to 900℃. In the second step, the salt film thickness was changed to 1.0 ± 0.2 mg / cm². 2 The long-cycle hot corrosion test temperature was changed to 900℃, all other settings remained unchanged. (See attached...) Figure 5 Analysis of the mass change curve per unit area shows that when the salt film composition is 75 wt.% Na₂SO₄ + 25 wt.% NaCl, the salt film thickness is 1.0 mg / cm. 2 At that time, both the salt film test piece and the salt film calibration piece exhibited mass loss characteristics during the hot corrosion process. After calibration by hot salt volatilization, the hot corrosion kinetic curve of the alloy coating test piece ( Figure 6 The data shows a continuous increasing trend in mass per unit area, indicating that the alloy coating actually underwent a weight gain process during hot corrosion.

[0055] The above embodiments are only used to illustrate the implementation of the present invention and are not intended to limit the scope of the present invention. It should be noted that those skilled in the art can still make adjustments to the specific implementation schemes of the above specific embodiments, or modify or replace some features therein without departing from the concept scope of the present invention, and all such adjustments and modifications or replacements are within the protection scope of the present invention.

Claims

1. A method for calibrating the thermal corrosion kinetics of nickel-based superalloy coatings, characterized in that, The aforementioned thermal corrosion kinetics calibration method includes the following steps: Step S1: Using an alumina ceramic sheet of the same size as the alloy coating test piece as a calibration test piece, a preheating test is performed on the alloy coating test piece and the alumina ceramic sheet to obtain the alloy test piece and the calibration test piece before salt film deposition. Step S2: A salt film of the same thickness is deposited on the surface of the preheated alloy test piece and the calibration test piece using the salt coating method to obtain a salt film test piece and a salt film calibration piece. Step S3: Perform long-cycle hot corrosion tests on the salt film test piece and the salt film calibration piece respectively to obtain hot corrosion data of the salt film test piece and the salt film calibration piece; Step S4: Based on the two sets of hot corrosion data obtained in step S3, obtain the change in unit area mass of the salt film test piece and the salt film calibration piece at different hot corrosion times, and plot the unit area weight change curves of the salt film test piece and the salt film calibration piece during the hot corrosion process. Step S5: Obtain the amount of hot salt volatilization using a salt film calibration plate, and calibrate the thermal corrosion kinetics curve of the salt film test plate. In step S3, the hot corrosion test temperature of the long-cycle hot corrosion test is higher than the melting point of the mixed salt film. Specifically, step S5 involves: based on the weight change curve obtained in step S4, subtracting the weight change of the salt film test piece from the weight change of the salt film calibration piece at the same hot corrosion time to obtain the weight change of the alloy coating after the calibrated hot salt volatilization amount at that hot corrosion time; and plotting the hot corrosion kinetic curve of the alloy coating after the calibrated hot salt volatilization amount during the long-cycle hot corrosion process.

2. The thermal corrosion kinetics calibration method based on nickel-based superalloy coatings according to claim 1, characterized in that, In step S1, the size of the calibration test piece is the same as that of the alloy test piece; the preheating temperature of the alloy coating test piece is 110℃-130℃, and the preheating temperature of the alumina ceramic sheet is the same as that of the hot corrosion test. The alloy test piece and the calibration test piece are repeatedly preheated until the weight does not change.

3. The thermal corrosion kinetics calibration method based on nickel-based superalloy coatings according to claim 1, characterized in that, In step S2, the alloy test piece and calibration test piece processed in step S1 are subjected to salt film deposition treatment to obtain salt film test piece and salt film calibration piece. The salt film test piece and salt film calibration piece are placed in corundum crucible containers of the same size and the initial total mass is weighed. The parameters for salt film deposition are the same for both.

4. The thermal corrosion kinetics calibration method based on nickel-based high-temperature alloy coatings according to claim 1, characterized in that, In step S2, the salt film thickness is 1.0 mg / cm. 2 -3.0mg / cm 2 .

5. The thermal corrosion kinetics calibration method based on nickel-based superalloy coatings according to claim 1, characterized in that, The salt coating method in step S2 is specifically a thermal spraying method: after heating the alloy test piece and the calibration test piece on a heated nickel plate, the prepared mixed salt solution is uniformly deposited on the upper and lower surfaces of the test piece using an atomizing spray gun; the mixed salt solution is composed of NaCl and Na2SO4, wherein the weight percentage of NaCl is 0% to 25%, and the remainder is Na2SO4.

6. The thermal corrosion kinetics calibration method based on nickel-based superalloy coatings according to claim 1, characterized in that, In step S3, during the long-cycle hot corrosion test, the mid-course sampling method is used to obtain the hot corrosion data of the salt film test piece and the hot corrosion data of the salt film calibration piece, respectively. The parameters for the long-cycle hot corrosion tests of both are the same.

7. The thermal corrosion kinetics calibration method based on nickel-based superalloy coatings according to claim 6, characterized in that, The intermediate sampling method involves taking out the test piece at regular intervals, weighing the total weight of the test piece and the crucible container, and then putting it back into the muffle furnace to continue the next cycle of hot corrosion test.

Images