Hot corrosion dynamic calibration method based on nickel-based superalloy coating

Abstract

The invention discloses a hot corrosion dynamic calibration method based on a nickel-based superalloy coating, and belongs to the technical field of coating hot corrosion evaluation. The method comprises the following steps of: firstly, preheating an alloy test piece and a calibration test piece by adopting an aluminum oxide ceramic piece with the same size as an alloy coating test piece as the calibration test piece; depositing salt films with the same thickness on the surfaces of the preheated alloy coating test piece and the calibration test piece by adopting a salt coating method to obtain a salt film test piece and a salt film calibration piece; secondly, carrying out a long-period hot corrosion test when the temperature is higher than the melting point of the salt film to obtain hot corrosion data of the salt film test piece and the salt film calibration piece, and drawing a unit area weight change curve of the salt film test piece and the salt film calibration piece in the hot corrosion process; and finally, the volatilization amount of the hot salt is obtained through the salt film calibration piece, and the thermal corrosion kinetic curve of the salt film test piece is calibrated. The dynamic difference caused by hot salt volatilization in the hot corrosion process can be calibrated, and hot corrosion damage evaluation of the nickel-based high-temperature alloy coating in the environment with the temperature higher than the melting point of hot salt can be achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of thermal corrosion assessment of nickel-based high-temperature alloy coatings, and relates to a calibration method based on the corrosion kinetics of nickel-based high-temperature alloy coatings, and in particular to a calibration method for hot salt volatilization based on the thermal corrosion kinetics of coatings above 900°C. Background Art

[0002] Nickel-based high-temperature alloys have become the main manufacturing materials for turbine blades on gas turbines due to their good high-temperature strength, oxidation resistance and corrosion resistance. With the rapid development of the marine field, the performance requirements for engines are getting higher and higher, and the surface service temperature is rising. It is necessary to coat the engine surface with a high-temperature protective coating to meet the working environment requirements. Among them, the MCrAlY coating has good plasticity, fatigue resistance and corrosion resistance, and has become the main protective coating for gas turbine blades. However, for gas turbine blades that have been in service for a long time in the marine field, the NaCl salt particles in the atmosphere react with sulfur-containing gas at high temperatures, and a layer of salt film (mainly Na2SO4+NaCl) is deposited on the surface of the blades, causing severe thermal corrosion, destroying the complete structure of the blade surface coating, and greatly limiting the service life of the blades. According to the alloy service temperature and the state of the salt film, thermal corrosion can be divided into low-temperature thermal corrosion (650℃-800℃) and high-temperature thermal corrosion (850℃-950℃).

[0003] At present, the salt coating method can evenly deposit a layer of mixed salt film on the surface of the alloy, which is not easy to peel or flake off, can well simulate the thermal corrosion environment, and has become a universal thermal corrosion test method. The alloy coating after the salt film is coated is used for thermal corrosion test, and the thermal corrosion kinetic curve is obtained at the same time, which can evaluate the degree of coating damage to a certain extent. However, the current conventional thermal corrosion weighing method for the study of corrosion kinetic behavior believes that under the combined action of sulfidation, oxidation, alkaline fluxing and other mechanisms, the molten salt elements diffuse quickly into the matrix and the oxides are porous and loose, resulting in the shedding of oxides, thereby causing the overall weight loss of the alloy coating. However, in the thermal corrosion test environment above 900°C, the mixed salt film on the surface of the coating is in a molten state, and there is a large amount of volatilization. The existing conventional weighing method does not consider the mass influence of the molten salt volatilization.

[0004] Therefore, when conducting thermal corrosion tests in an environment above the melting point of the mixed salt, the effect of hot salt volatilization on the determination of thermal corrosion kinetics cannot be ignored, but the existing technologies are unable to calibrate the volatilization amount of the hot salt itself when determining the thermal corrosion kinetics curve. Summary of the invention

[0005] In view of the above shortcomings of the existing research, the purpose of the present invention is to provide a method for calibrating the thermal corrosion dynamics by considering the volatilization amount of molten salt when the coating is subjected to thermal corrosion measurement at above 900°C. The method calibrates the thermal corrosion dynamics.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A corrosion kinetics calibration method based on a nickel-based high-temperature alloy coating. The thermal corrosion kinetics calibration method comprises the following steps: first, an alumina ceramic sheet of the same size as the alloy coating test piece is used as a calibration test piece to preheat the alloy test piece and the calibration test piece. A salt film of the same thickness is deposited on the surface of the preheated alloy test piece and the calibration test piece by a salt coating method to obtain a salt film test piece and a salt film calibration piece; secondly, a long-term thermal corrosion test is carried out at a temperature above the melting point of the salt film to obtain thermal corrosion data of the salt film test piece and the salt film calibration piece, and a weight change curve per unit area of ​​the salt film test piece and the salt film calibration piece during the thermal corrosion process is plotted. Finally, the volatilization amount of the hot salt itself is obtained through the salt film calibration piece, and the thermal corrosion kinetics curve of the salt film test piece (alloy coating) is calibrated. Specifically, the following steps are included:

[0008] Step S1, preheating the alloy coating test piece and the alumina ceramic piece to obtain the alloy test piece and the calibration test piece before the salt film is deposited; wherein the alloy coating test piece obtains the alloy test piece, and the alumina ceramic piece obtains the calibration test piece.

[0009] Step S2, performing salt film deposition treatment on the alloy test piece and the calibration test piece after the treatment in step S1, respectively, to obtain a salt film test piece and a salt film calibration piece, placing the salt film test piece and the salt film calibration piece in corundum crucible containers of the same size, respectively, and weighing the initial total mass; the parameters of the salt film deposition treatment of the two are the same.

[0010] Step S3, performing long-period thermal corrosion tests on the salt film test piece and the salt film calibration piece respectively, and using the mid-course sampling method to obtain thermal corrosion data of the salt film test piece and the thermal corrosion data of the salt film calibration piece respectively; the parameters of the long-period thermal corrosion tests of the two are the same.

[0011] Step S4, based on the two sets of thermal corrosion data obtained in step S3, respectively obtain the unit area weight changes of the salt film test piece and the salt film calibration piece at different thermal corrosion moments, and draw 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 thermal corrosion time, the weight change of the alloy coating after the calibrated hot salt volatilization amount is subtracted from the weight change of the salt film test piece by the weight change of the salt film calibration piece, to obtain the weight change of the alloy coating after the calibrated hot salt volatilization amount during the thermal corrosion time; and draw a thermal corrosion kinetic curve of the alloy coating after the calibrated hot salt volatilization amount during the long-period thermal 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°C-130°C, the preheating temperature of the alumina ceramic piece is the same as the thermal corrosion test temperature, and 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 by 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 thickness of the salt film is 1.0 mg / cm 2 -3.0mg / cm 2 It is appropriate;

[0016] Furthermore, in step S2, the salt coating method is specifically a thermal spraying method: after the alloy test piece and the calibration test piece are placed on a heated nickel plate for heating, an atomizing spray gun is used to evenly deposit the prepared mixed salt solution on the upper and lower surfaces of the test piece; the mixed salt solution is composed of NaCl and Na2SO4, wherein the weight percentage of NaCl is 0% to 25%, and the rest is Na2SO4.

[0017] Further, in step S3, the thermal corrosion test temperature of the long-period thermal corrosion test is higher than the melting point of the mixed salt film;

[0018] Furthermore, in step S3, the mid-sampling method is to take out the test piece at regular intervals, weigh the total weight of the test piece and the crucible container, and put it back into the muffle furnace after the weighing is completed to continue the next cycle of hot corrosion test;

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

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

[0021] (2) The present invention can take into account the amount of hot salt volatilization during the hot corrosion test of the nickel-based alloy coating in an environment above the melting point of the molten salt, realize the calibration of the hot corrosion kinetic curve, improve the reliability of the hot corrosion experimental data, and provide a new research method for in-depth understanding of the hot corrosion behavior of the alloy coating. It has been verified that this method is feasible and provides an evaluation basis for the corrosion rate of the nickel-based alloy coating under different conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1It is a schematic flow chart of the corrosion dynamics calibration method of the nickel-based alloy coating of the present invention;

[0023] Figure 2 The schematic diagram of the position structure of the salt film test piece and the salt film calibration piece of the present invention when conducting a thermal corrosion test, wherein: 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 weight per unit area variation curve of the salt film test piece and the salt film calibration piece in Examples 1 to 3 of the present invention during the thermal corrosion process;

[0025] Figure 4 The thermal corrosion kinetic curves of the alloy coating test pieces in Examples 1 to 3 of the present invention after calibrating the hot salt volatilization amount;

[0026] Figure 5 The weight per unit area variation curve of the salt film test piece and the salt film calibration piece in Example 4 of the present invention during the thermal corrosion process;

[0027] Figure 6 This is the thermal corrosion kinetics curve of the alloy coating test piece in Example 4 of the present invention after calibrating the hot salt volatilization amount. DETAILED DESCRIPTION

[0028] In order to make those skilled in the art 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 in conjunction with the accompanying drawings. It should be understood that the described implementation cases are only used to explain the present invention and are not used to limit the scope of the present invention.

[0029] like Figure 1 As shown, a thermal corrosion kinetics calibration method based on a nickel-based high-temperature alloy coating comprises the following steps:

[0030] Step S1, performing a preheating test on the alloy coating test piece and the alumina ceramic piece to obtain an alloy test piece and a calibration test piece before salt film deposition; wherein the alloy coating test piece obtains the alloy test piece, and the alumina ceramic piece obtains the 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°C-130°C, the preheating temperature of the calibration test piece and the corundum crucible container is the same as the thermal corrosion test temperature, and the preheating is repeated until the weight of the alloy coating test piece and the alumina ceramic piece does not change, and the calibration test piece has the same size as the alloy test piece.

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

[0033] Step S2, depositing salt film on the alloy test piece and the calibration test piece after the treatment in step S1, respectively, to obtain a salt film test piece and a salt film calibration piece. The salt film test piece and the salt film calibration piece are placed in a corundum crucible container of the same size, respectively, and the initial total mass is weighed;

[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 by a salt coating method, and the processing parameters for depositing the salt film 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 evenly deposit the prepared mixed salt solution on the upper and lower surfaces of the alloy test piece and the calibration test piece in multiple times to ensure that a salt film of the same thickness is formed on the surface of the salt film test piece and the salt film calibration piece. The salt film thickness is 1.0 mg / cm 2 -3.0mg / cm 2 The mixed salt solution is composed of NaCl and Na2SO4, wherein the weight percentage of NaCl is 0% to 25% and the rest is Na2SO4. The salt film test piece and the salt film calibration piece are respectively placed in a corundum crucible container and moved to a constant temperature drying oven to dry until the total weight does not change, and the initial total weight of the salt film test piece and the corundum crucible container and the initial total weight of the salt film calibration piece and the corundum crucible container are respectively weighed.

[0036] Step S3, performing a long-period thermal corrosion test on the salt film test piece and the salt film calibration piece, and obtaining thermal corrosion data by adopting a mid-course sampling method; the parameters of the long-period thermal corrosion tests of the two pieces are the same.

[0037] In one or more embodiments of the present invention, in step S3, the thermal corrosion test temperature is higher than the melting point of the salt film, and the mid-course 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 thermal corrosion testing.

[0038] Specifically, in one or more embodiments of the present invention, the thermal corrosion test temperature is 950°C and 900°C, and the intermediate 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 thermal corrosion data obtained in step S3, respectively plotting 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 thermal corrosion time;

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

[0041] The specific scheme is given in detail by the following embodiments:

[0042] Example 1

[0043] The mixed salt composition is 75wt.% Na2SO4+25wt.% NaCl, the alloy coating test piece is DZ411 nickel-based high-temperature alloy with MCrAlY coating on the surface, an alumina ceramic piece is used as a calibration test piece, and a number of small round corundum crucibles and large square corundum crucibles are used as spare parts.

[0044] The first step is to preheat the alloy coating test piece in a 130°C dry environment using a constant temperature drying oven. When the mass of the alloy coating test piece does not change, the alumina ceramic test piece and all the crucible containers used are preheated in a 950°C high temperature environment for a long enough time to ensure that the mass does not change, so as to remove the residual moisture therein; wherein, the size of the ceramic calibration piece should be the same as that of the alloy coating test piece, and in all implementation cases, its size is 8mm×8mm×2mm. The preheated alloy test piece and the calibration test piece are weighed separately. To ensure the accuracy of the weighing, weigh 5 times each time, and take the average value as the initial mass of the alloy coating test piece and the calibration test piece.

[0045] The second step is to prepare a mixed salt solution of 75wt.% Na2SO4+25wt.% NaCl, place the alloy test piece and the calibration test piece on a heated nickel plate at 80°C, and use an atomizing spray gun to evenly deposit the prepared mixed salt solution on the upper and lower surfaces of the test piece and the calibration test piece in multiple times to ensure that the thickness of the salt film deposited on the surface of the salt film test piece and the salt film calibration piece is 3.0±0.2mg / cm 2 .

[0046] In the third step, place the salt film test piece and the salt film calibration piece in a round corundum crucible container respectively, and transfer them to a constant temperature drying oven to dry to constant weight. Weigh the total weight of the salt film test piece together with the round corundum crucible container and the total weight of the salt film calibration piece together with the crucible container respectively, and record them as the initial mass m0 of the salt film test piece and the salt film calibration piece. Place all the round crucibles containing the test pieces in a large square crucible (such as the attached Figure 2) and transferred as a whole to a muffle furnace for a long-term hot corrosion test at 950°C. During the hot corrosion test, the sample pieces and crucibles were taken out 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 weighed. t When weighing, take the average of 5 weighing results as the final recorded value.

[0047] Step 4: Based on the thermal corrosion data obtained in step 3 and the surface area A (cm 2 ), calculate the unit area mass change W of the salt film test piece and the salt film calibration piece at each thermal corrosion moment = (m t -m0) / A, unit is mg / cm 2 . Draw the weight change curve of the salt film test piece and the salt film calibration piece per unit area. Figure 3 When the salt film composition is 75wt.%Na2SO4+25%wt.%NaCl, both the salt film test piece and the salt film calibration piece show mass loss characteristics during the thermal corrosion process.

[0048] The fifth step is to obtain the weight change curve obtained in the fourth step, and at the same hot corrosion time, the weight change per unit area of ​​the salt film calibration piece is subtracted from the weight change per unit area of ​​the salt film test piece to obtain the weight change per unit area of ​​the alloy coating test piece after the calibrated hot salt volatilization during the hot corrosion time. Finally, the hot corrosion kinetic curve of the alloy coating after the calibrated hot salt volatilization during the long-term hot corrosion process is drawn; Figure 4 After hot salt volatilization calibration, the thermal corrosion kinetic curve of the alloy coating test piece in 75wt.%Na2SO4+25%wt.%NaCl salt film environment ( Figure 4 ) shows that the mass per unit area shows a continuous increasing trend, indicating that the alloy coating actually undergoes a significant mass gain phenomenon during the hot corrosion process.

[0049] Example 2

[0050] The composition of the mixed salt solution in the second step of Example 1 was changed to 95wt.% Na2SO4+5wt.% NaCl, and the other components remained unchanged. Figure 3 , through the analysis of the mass change curve per unit area, it can be seen that when the salt film composition is 95wt.%Na2SO4+5wt.%NaCl, the salt film test piece and the salt film calibration piece both show mass loss characteristics during the hot corrosion process. After hot salt volatilization calibration, the hot corrosion kinetic curve of the alloy coating test piece in the 95wt.%Na2SO4+5wt.%NaCl salt film environment ( Figure 4 ) shows that the mass per unit area shows a continuous increasing trend, indicating that the alloy coating actually undergoes a weight gain process during the hot corrosion process.

[0051] Example 3

[0052] The composition of the mixed salt solution in the second step of Example 1 was changed to 100 wt.% Na2SO4, and the other components remained unchanged. Figure 3 , through the analysis of the mass change curve per unit area, it can be seen that when the salt film composition is 100wt.%Na2SO4, the salt film test piece and the salt film calibration piece both show mass loss characteristics during the hot corrosion process. After hot salt volatilization calibration, the hot corrosion kinetic curve of the alloy coating test piece in the 100wt.%Na2SO4 salt film environment ( Figure 4 ) shows that the mass per unit area shows a continuous increasing trend, indicating that the alloy coating actually undergoes a weight gain process during the hot corrosion process.

[0053] Example 4

[0054] In the first step of Example 1, the preheating temperature of the alloy coating test piece was changed to 110°C, the preheating temperature of the ceramic test piece and the corundum crucible container was changed to 900°C, and the salt film thickness in the second step was changed to 1.0±0.2 mg / cm 2 , the long-term thermal corrosion test temperature was changed to 900℃, and the other parameters remained unchanged. Figure 5 According to the change curve of unit area mass, when the salt film composition is 75wt.%Na2SO4+25%wt.%NaCl, the thickness of the salt film is 1.0mg / cm 2 When the salt film test piece and the salt film calibration piece both show mass loss characteristics during the hot corrosion process. After hot salt volatilization calibration, the hot corrosion kinetic curve of the alloy coating test piece ( Figure 6 ) shows that the mass per unit area shows a continuous increasing trend, indicating that the alloy coating actually undergoes a weight gain process during the hot corrosion process.

[0055] The above embodiments are only used to illustrate the implementation methods of the present invention and are not considered to be limiting of the scope of the present invention. It should be pointed out that those skilled in the art can make adjustments to the above specific embodiments or modify or replace some of the features therein without departing from the scope of the present invention, all of which fall within the protection scope of the present invention.

Claims

1. A thermal corrosion kinetics calibration method based on nickel-based high-temperature alloy coating, characterized in that: The thermal corrosion kinetics calibration method comprises the following steps: Step S1, using an alumina ceramic sheet of the same size as the alloy coating test sheet as a calibration test sheet, performing a preheating test on the alloy coating test sheet and the alumina ceramic sheet to obtain an alloy test sheet and a calibration test sheet before salt film deposition; Step S2, using a salt coating method to deposit a salt film of the same thickness on the surfaces of the preheated alloy test piece and the calibration test piece to obtain a salt film test piece and a salt film calibration piece; Step S3, respectively performing a long-period thermal corrosion test on the salt film test piece and the salt film calibration piece to obtain thermal corrosion data of the salt film test piece and the salt film calibration piece; Step S4, based on the two sets of thermal corrosion data obtained in step S3, respectively obtain the unit area weight changes of the salt film test piece and the salt film calibration piece at different thermal corrosion moments, and draw the unit area weight change curves of the salt film test piece and the salt film calibration piece during the thermal corrosion process; Step S5, obtaining the volatilization amount of the hot salt itself through the salt film calibration piece, and calibrating the thermal corrosion kinetic curve of the salt film test piece.

2. A thermal corrosion kinetics calibration method based on nickel-based high-temperature alloy coating according to claim 1, characterized in that: In step S1, the size of the calibration test piece is consistent with the size of the alloy test piece; the preheating temperature of the alloy coating test piece is 110°C-130°C, and the preheating temperature of the alumina ceramic piece is the same as the thermal corrosion test temperature. 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 high-temperature alloy coating according to claim 1 is characterized in that: In the step S2, the alloy test piece and the calibration test piece after the treatment in step S1 are respectively subjected to salt film deposition treatment to obtain a salt film test piece and a salt film calibration piece, and the salt film test piece and the salt film calibration piece are respectively placed in a corundum crucible container of the same size, and the initial total mass is weighed; The parameters of the salt film deposition process are the same for both.

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

5. The thermal corrosion kinetics calibration method based on nickel-based high-temperature alloy coating according to claim 1 is characterized in that: The salt coating method in step 2 is specifically a thermal spraying method: after the alloy test piece and the calibration test piece are placed on a heated nickel plate for heating, an atomizing spray gun is used to evenly deposit the prepared mixed salt solution on the upper and lower surfaces of the test piece; the mixed salt solution is composed of NaCl and Na2SO4, wherein the weight percentage of NaCl is 0% to 25%, and the rest is Na2SO4.

6. The thermal corrosion kinetics calibration method based on nickel-based high-temperature alloy coating according to claim 1 is characterized in that: In the step S3, during the long-period thermal corrosion test, the thermal corrosion data of the salt film test piece and the thermal corrosion data of the salt film calibration piece are respectively obtained by using the midway sampling method; The parameters of the long-term hot corrosion tests of the two are the same.

7. A thermal corrosion kinetics calibration method based on nickel-based high-temperature alloy coating according to claim 6, characterized in that: The mid-course sampling method is to take out the test piece at regular intervals, weigh the total weight of the test piece and the crucible container, and put it back into the muffle furnace after weighing to continue the next cycle of hot corrosion test.

8. The thermal corrosion kinetics calibration method based on nickel-based high-temperature alloy coating according to claim 1 is characterized in that: In the step S3, the thermal corrosion test temperature of the long-period thermal corrosion test is higher than the melting point of the mixed salt film.

9. The thermal corrosion kinetics calibration method based on nickel-based high-temperature alloy coating according to claim 1 is characterized in that: The step S5 specifically comprises: based on the weight change curve obtained in step S4, at the same hot corrosion time, the weight change of the alloy coating after calibrating the hot salt volatilization amount at the hot corrosion time is obtained by subtracting the weight change of the salt film test piece from the weight change of the salt film calibration piece; The hot corrosion kinetics curve of the alloy coating after calibrating the hot salt volatilization amount during long-term hot corrosion was drawn.

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