A method and system for determining a failure criterion of a thermal barrier coating

Abstract

The present invention discloses a method and system for determining a failure criterion of a thermal barrier coating, relating to the technical field of thermal barrier coating detection. After placing a thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectral signal of the thermal barrier coating sample, a fast Fourier transform is performed on the time-domain spectral signal to obtain a frequency-domain signal; then, the thermal barrier coating sample is heated at a set temperature for a certain period of time, cooled to room temperature, and the above operations are continuously repeated until frequency-domain information is obtained to generate a frequency spectrum diagram, and then the positions of the frequency spectrum characteristic peaks at different heating times are determined; then, the change slope is determined based on the positions of the frequency spectrum characteristic peaks of different curves at different times; finally, the failure criterion of the thermal barrier coating is determined based on the change slope. The detection method is simple and fast, highly operable, and has high detection efficiency, and is applicable to the failure judgment of thermal barrier coatings on aeroengine blades.

Description

Technical Field

[0001] The present invention relates to the field of thermal barrier coating detection, and particularly to a method and system for determining the failure criterion of a thermal barrier coating. Background Art

[0002] Thermal Barrier Coatings (TBCs) technology is one of the three key technologies for increasing the working temperature of aero-engine blades. The thermal barrier coating system consists of a ceramic layer (Top Coatings, TC), a thermally grown oxide layer (Thermally Grown Oxide, TGO), and a bond coat (Bond Coatings, BC). Among them, the ceramic layer has excellent heat insulation performance, and its heat insulation effect is related to factors such as its thickness and sintering. During service, due to the action of high temperature and stress, the ceramic layer will first undergo damage and thinning, phase change, and cracking failure. Moreover, as the service time prolongs, the TGO gradually thickens, which will also become a crack source, resulting in the failure of the entire thermal barrier coating system. Therefore, studying the above failure problems has become the key to improving the life of thermal barrier coatings. The common non-destructive testing methods in the current thermal barrier coating field are shown in Table 1.

[0003] Table 1 Common non-destructive testing methods in the current thermal barrier coating field

[0004]

[0005]

[0006] Terahertz Time Domain Spectroscopy (THz-TDS) has the advantages of convenient extraction of optical constants, non-ionization, non-destruction, high imaging resolution, and ability to perform depth imaging, and has broad application prospects in the non-destructive testing of the ceramic layer of TBCs. The application of THz-TDS technology in non-destructive testing has been recognized, but there are few reports on this technology in the field of TBCs.

[0007] THz-TDS technology can achieve precise measurement of the thickness of TBCs coatings. Fukuchi et al. measured the refractive index of samples by THz-TDS and calculated the coating thickness according to the time difference Δt between two adjacent reflections of the terahertz wave on the surface of the ceramic layer. The results show that the thicknesses (300 - 620 μm) of 6 TBCs samples measured by this method are consistent with the thicknesses measured by a microscope. To improve the measurement accuracy of THz-TDS technology, Krimi et al. proposed a self-calibration method for measuring the thickness of the ceramic layer. For a coating with a thickness of 311 μm, the maximum measurement deviation of this method is about 3 μm, that is, the relative deviation is about 1%.

[0008] In the aspect of TBCs degradation detection, Chen et al. used THz-TDS technology to study the evolution process of interface defects between the TGO layer, ceramic layer and metal layer, and proved that THz-TDS technology has the potential to predict the failure of thermal barrier coatings on turbine blades; White et al. studied the application of THz-TDS imaging technology in the field of TBCs. By performing two-dimensional imaging on TBCs of aero-engine turbine blades, the abnormal regions of the YSZ layer were resolved. Watanabe et al. evaluated the transmittance and dielectric properties of the ceramic layer of plasma-sprayed TBCs by THz-TDS, indicating that THz-TDS technology is not only applicable to the non-destructive evaluation of the microstructure of YSZ-TBCs, but also can detect the microstructure changes (such as densification) caused by coating sintering in high-temperature environments.

[0009] At present, the non-destructive testing of thermal barrier coatings by THz-TDS is in its infancy. The existing research on the application of terahertz technology in the field of thermal barrier coatings is all focused on the measurement of coating thickness and the rough prediction of defects. It mainly focuses on the time-domain spectral information of terahertz, and the data extraction and processing process is complex, and there is no quantitative criterion for coating failure. Summary of the Invention

[0010] To solve the above problems existing in the prior art, the present invention provides a method and system for determining the failure criterion of thermal barrier coatings.

[0011] To achieve the above object, the present invention provides the following solutions:

[0012] A method for determining the failure criterion of thermal barrier coatings, comprising:

[0013] Placing a thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectral signal of the thermal barrier coating sample;

[0014] Performing a fast Fourier transform on the time-domain spectral signal to obtain a frequency-domain signal;

[0015] After heating the thermal barrier coating sample at a set temperature for a certain time, taking out the thermal barrier coating sample and air-cooling it to room temperature, then returning to execute "placing the thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectral signal of the thermal barrier coating sample" to obtain frequency-domain information; the frequency-domain information is composed of frequency-domain signals at different times;

[0016] Generating a frequency spectrum diagram based on the frequency-domain information;

[0017] Extracting the positions of the frequency spectrum characteristic peaks of different curves in the frequency spectrum diagram;

[0018] Obtaining the position of the as-prepared peak; the position of the as-prepared peak is the position of the frequency spectrum characteristic peak obtained when the thermal barrier coating sample is not heated;

[0019] Determine the change slope based on the position of the as-prepared peak and the positions of the characteristic peaks in the frequency spectra of different curves;

[0020] Determine the failure criterion for the thermal barrier coating based on the change slope.

[0021] Preferably, placing the thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain frequency spectrum signal of the thermal barrier coating sample specifically includes:

[0022] Place the thermal barrier coating sample on the sample stage of the terahertz time-domain spectroscopy system, introduce nitrogen gas, and when the humidity in the terahertz time-domain spectroscopy system is detected to be less than a preset humidity value, irradiate the terahertz wave vertically on the position to be measured of the thermal barrier coating sample to generate the time-domain frequency spectrum signal.

[0023] Preferably, the preset humidity value is 3%.

[0024] Preferably, the change slope is y:

[0025] where a is the position of the as-prepared peak, and Xi is the position of the characteristic peak in the frequency spectrum of curve i.

[0026] Preferably, taking the change slope greater than a preset value as the critical point for determining the failure of the thermal barrier coating.

[0027] Preferably, the preset value is 14%.

[0028] According to the specific embodiments provided by the present invention, the following technical effects are disclosed by the present invention:

[0029] The method for determining the failure criterion of the thermal barrier coating provided by the present invention places the thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain frequency spectrum signal of the thermal barrier coating sample, and then performs a fast Fourier transform on the time-domain frequency spectrum signal to obtain the frequency-domain signal; then, heat the thermal barrier coating sample at a set temperature for a certain period of time, take out the thermal barrier coating sample and air-cool it to room temperature, and then return to the step of obtaining the time-domain frequency spectrum signal until the frequency-domain signals at different times are obtained to generate frequency-domain information. After generating a frequency spectrum diagram based on the frequency-domain information, determine the positions of the characteristic peaks in the frequency spectra at different heating times; then, determine the change slope based on the position of the as-prepared peak (the peak position corresponding to a heating time of 0) and the positions of the characteristic peaks in the frequency spectra of different curves; finally, determine the failure criterion of the thermal barrier coating based on the change slope. The detection method provided by the present invention belongs to a non-contact non-destructive detection method, which is simple and fast, highly operable, and has high detection efficiency, and is suitable for the failure judgment of thermal barrier coatings on aeroengine blades.

[0030] Corresponding to the method for determining the failure criterion of the thermal barrier coating provided above, the present invention provides a system for determining the failure criterion of the thermal barrier coating, and the system includes:

[0031] Time-domain spectrum signal acquisition module, which is used to place a thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectrum signal of the thermal barrier coating sample;

[0032] Frequency-domain signal determination module, which is used to perform fast Fourier transform on the time-domain spectrum signal to obtain a frequency-domain signal;

[0033] Frequency-domain information acquisition module, which is used to heat the thermal barrier coating sample at a set temperature for a certain period of time, then take out the thermal barrier coating sample and air-cool it to room temperature, and then return to execute "place the thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectrum signal of the thermal barrier coating sample" to obtain frequency-domain information; the frequency-domain information is composed of frequency-domain signals at different times;

[0034] Frequency spectrum diagram generation module, which is used to generate a frequency spectrum diagram based on the frequency-domain information;

[0035] Peak position extraction module, which is used to extract the positions of the frequency spectrum characteristic peaks of different curves in the frequency spectrum diagram;

[0036] Peak position acquisition module, which is used to obtain the as-prepared peak position; the as-prepared peak position is the position of the frequency spectrum characteristic peak obtained when the thermal barrier coating sample is not heated;

[0037] Change slope determination module, which is used to determine the change slope based on the as-prepared peak position and the positions of the frequency spectrum characteristic peaks of different curves;

[0038] Failure criterion determination module, which is used to determine the thermal barrier coating failure criterion based on the change slope.

[0039] Since the technical effects achieved by the thermal barrier coating failure criterion determination system provided by the present invention are the same as those achieved by the thermal barrier coating failure criterion determination method provided above, they will not be elaborated here. Description of the Drawings

[0040] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required in the embodiments. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0041] Figure 1 It is a flowchart of the thermal barrier coating failure criterion determination method provided by the present invention;

[0042] Figure 2 It is a typical spectrum frequency spectrum diagram provided by an embodiment of the present invention;

[0043] Figure 3The figure shows the change of the spectral peak position of the YSZ coating sample with the thermal exposure time at 1150° when the thickness is 213μm provided by the embodiment of the present invention;

[0044] Figure 4 The figure shows the change of the spectral peak position of the YSZ coating sample with the thermal exposure time at 1150° when the thickness is 197μm provided by the embodiment of the present invention;

[0045] Figure 5 The figure shows the change of the spectral peak position of the YSZ coating sample with the thermal exposure time at 1150° when the thickness is 122μm provided by the embodiment of the present invention;

[0046] Figure 6 The figure shows the change of the spectral peak position of the YSZ coating sample with the thermal exposure time at 1150° when the thickness is 133μm provided by the embodiment of the present invention;

[0047] Figure 7 The figure shows the change of the spectral peak position of the YSZ coating sample with the thermal exposure time at 1150° when the thickness is 118μm provided by the embodiment of the present invention;

[0048] Figure 8 The structural schematic diagram of the thermal barrier coating failure criterion determination system provided by the present invention. Detailed implementation manners

[0049] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0050] The purpose of the present invention is to provide a method and system for determining the thermal barrier coating failure criterion, which can solve the problems in the prior art such as the complex data extraction and processing process and the lack of quantitative criteria for coating failure.

[0051] To make the above objects, features, and advantages of the present invention more obvious and understandable, the present invention will be further described in detail below in conjunction with the accompanying drawings and specific implementation manners.

[0052] As Figure 1 shown, the method for determining the thermal barrier coating failure criterion provided by the present invention includes:

[0053] Step 100: Place the thermal barrier coating sample in the terahertz time-domain spectroscopy system to obtain the time-domain spectral signal of the thermal barrier coating sample; among them, the acquisition process of the time-domain spectral signal can be:

[0054] Step 100-1: Place the thermal barrier coating sample on the sample stage of the terahertz time-domain spectroscopy system;

[0055] Step 100-2: Introduce high-purity nitrogen gas and detect that the humidity inside the detection device is less than the preset humidity value (e.g., 3%) to remove the influence of water vapor on the signal;

[0056] Step 100-3: Adjust the sample stage and synchronously monitor the time-domain spectrum signal to make the terahertz wave perpendicularly irradiate the surface of the thermal barrier coating sample at the position to be measured, so as to obtain the maximum value of the time-domain signal intensity;

[0057] Step 101: Perform a fast Fourier transform on the time-domain spectrum signal to obtain a frequency-domain signal;

[0058] Step 102: Heat the thermal barrier coating sample at a set temperature for a certain period of time, then take out the thermal barrier coating sample and air-cool it to room temperature, and then return to execute Step 100 to obtain frequency-domain information; the frequency-domain information is composed of frequency-domain signals at different times;

[0059] Based on the above example content, the implementation process of Step 102 is to take out the sample, place it in a tube furnace, heat it at a high temperature for a certain period of time, take it out and air-cool it to room temperature, and then repeat the operation steps from Step 100-1 to Step 100-3.

[0060] Step 103: Generate a frequency spectrum diagram based on the frequency-domain information; specifically, plot a frequency spectrum diagram with the frequency (Frequency / THz) of the frequency-domain information of the sample heated for different times as the abscissa and the amplitude as the ordinate.

[0061] Step 104: Extract the positions of the frequency spectrum characteristic peaks of different curves in the frequency spectrum diagram;

[0062] Step 105: Obtain the position of the as-prepared state peak; the position of the as-prepared state peak is the position of the frequency spectrum characteristic peak obtained when the thermal barrier coating sample is not heated (heating time is 0);

[0063] Step 106: Determine the change slope based on the position of the as-prepared state peak and the positions of the frequency spectrum characteristic peaks of different curves; where the change slope is y:

[0064] In the formula, a is the position of the as-prepared state peak, and Xi is the position of the frequency spectrum characteristic peak of curve i.

[0065] Step 107: Determine the failure criterion of the thermal barrier coating based on the change slope. Pay attention that during the service process of the thermal barrier coating sample, when the value of the change slope y is greater than 14%, it is a sharp change stage. After that, the coating will quickly peel off. Therefore, the criterion that the change slope y is 14% is used as the critical point for judging the coating failure.

[0066] Terahertz time-domain spectroscopy tests were carried out on thermal barrier coating samples with different high-temperature thermal exposure times to obtain time-domain spectral data. Then, the obtained data were subjected to fast Fourier transform to obtain frequency spectral curves (as shown in Figure 2 , where different line types represent different times). The peak values of each curve in Figure 2 were extracted, and a curve showing the variation of the frequency values with time as shown in Figures 3 - 7 was plotted. As can be seen from Figures 3 - 7 , when the characteristic peak of the sample shows a sharp decline, the coating of the thermal barrier coating sample is facing failure and peeling. Further experiments were carried out, and the coating peeled off after the next test.

[0067] Among them, Figures 3 - 7 the corresponding y values of the thermal barrier coating samples are shown in Table 2.

[0068] Table 2 y-value table corresponding to thermal barrier coating samples

[0069]

[0070]

[0071] In Table 2, 1h - 30h represents the heating time.

[0072] Based on the above description, the thermal barrier coating sample of the present invention is placed at the position to be measured in the reflection module of the terahertz time-domain spectroscopy system (TeraHertz Time Domain Spectral system, THz-TDS), and the time-domain spectral signal of the sample is obtained at the marked position [abscissa time (Time / ps), ordinate signal (Signal / nA)]. The obtained data are subjected to fast Fourier transform (Fast Fourier Transform, FFT) to obtain frequency-domain information, and the converted frequency-domain information is used to plot a graph (abscissa Frequency / THz, ordinate Amplitude) to obtain the frequency spectrum graph of the sample. The sample is placed in a tube furnace for heating, and the sample is taken and placed at high temperature. When the sample cools to room temperature, it is placed at the same position to be measured in the THz-TDS again for testing. This operation is repeated to obtain the variation of the frequency spectrum characteristic peak with the thermal exposure time during different high-temperature thermal exposure times. The position of the characteristic peak is statistically analyzed, and a graph of the change amount of the characteristic peak position is monitored to evaluate the peeling failure of the thermal barrier coating. The detection method provided by the present invention belongs to non-contact non-destructive detection. The detection method is simple and fast, has high operability, and high detection efficiency, and is applicable to the failure judgment of thermal barrier coatings on aero-engine blades.

[0073] Corresponding to the above-provided method for determining the failure criterion of the thermal barrier coating, the present invention provides a system for determining the failure criterion of the thermal barrier coating, as shown in Figure 8As shown in the figure, the system includes: a time-domain spectrum signal acquisition module 900, a frequency-domain signal determination module 901, a frequency-domain information acquisition module 902, a frequency spectrum diagram generation module 903, a peak position extraction module 904, a peak position acquisition module 905, a change slope determination module 906, and a failure criterion determination module 907.

[0074] Among them, the time-domain spectrum signal acquisition module 900 is used to place the thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectrum signal of the thermal barrier coating sample;

[0075] The frequency-domain signal determination module 901 is used to perform a fast Fourier transform on the time-domain spectrum signal to obtain a frequency-domain signal;

[0076] The frequency-domain information acquisition module 902 is used to heat the thermal barrier coating sample at a set temperature for a certain period of time, then take out the thermal barrier coating sample and air-cool it to room temperature, and then return to execute "placing the thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectrum signal of the thermal barrier coating sample" to obtain frequency-domain information; the frequency-domain information is composed of frequency-domain signals at different times;

[0077] The frequency spectrum diagram generation module 903 is used to generate a frequency spectrum diagram based on the frequency-domain information;

[0078] The peak position extraction module 904 is used to extract the positions of the frequency spectrum characteristic peaks of different curves in the frequency spectrum diagram;

[0079] The peak position acquisition module 905 is used to obtain the as-prepared peak position; the as-prepared peak position is the position of the frequency spectrum characteristic peak obtained when the thermal barrier coating sample is not heated;

[0080] The change slope determination module 906 is used to determine the change slope based on the as-prepared peak position and the positions of the frequency spectrum characteristic peaks of different curves;

[0081] The failure criterion determination module 907 is used to determine the thermal barrier coating failure criterion based on the change slope.

[0082] The present invention mainly protects the left shift trend of the frequency values of the frequency spectrum characteristic peaks between 0.1-1.4 THz of the YSZ thermal barrier coating as the high-temperature service time extends. When the defined parameter reaches more than 14%, it can be determined that the coating is facing failure.

[0083] In this specification, each embodiment is described in a progressive manner. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. For the system disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the description of the method part.

[0084] In this article, specific examples are used to illustrate the principles and implementation manners of the present invention. The description of the above embodiments is only used to help understand the method of the present invention and its core idea; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manners and application scopes. In summary, the content of this specification should not be construed as a limitation on the present invention.

Claims

1. A method for determining the failure criterion of a thermal barrier coating, characterized in that, it includes: Placing a thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectral signal of the thermal barrier coating sample; Performing a fast Fourier transform on the time-domain spectral signal to obtain a frequency-domain signal; After heating the thermal barrier coating sample at a set temperature for a certain period of time, taking out the thermal barrier coating sample and air-cooling it to room temperature, then returning to execute "Placing the thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectral signal of the thermal barrier coating sample" to obtain frequency-domain information; the frequency-domain information is composed of frequency-domain signals at different times; Generating a frequency spectrum diagram based on the frequency-domain information; Extracting the positions of the frequency spectrum characteristic peaks of different curves in the frequency spectrum diagram; Obtaining the peak position in the as-prepared state; the peak position in the as-prepared state is the position of the frequency spectrum characteristic peak obtained when the thermal barrier coating sample is not heated; Determining the change slope based on the peak position in the as-prepared state and the positions of the frequency spectrum characteristic peaks of different curves; Determining the failure criterion of the thermal barrier coating based on the change slope.

2. The method for determining the failure criterion of a thermal barrier coating according to claim 1, characterized in that, The step of placing the thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectral signal of the thermal barrier coating sample specifically includes: Placing the thermal barrier coating sample on the sample stage of the terahertz time-domain spectroscopy system, introducing nitrogen gas, and when detecting that the humidity in the terahertz time-domain spectroscopy system is less than a preset humidity value, irradiating the terahertz wave vertically on the position to be measured of the thermal barrier coating sample to generate the time-domain spectral signal.

3. The method for determining the failure criterion of a thermal barrier coating according to claim 2, characterized in that, The preset humidity value is 3%.

4. The method for determining the failure criterion of a thermal barrier coating according to claim 1, characterized in that, The change slope is y: Among them, a is the position of the peak in the as-prepared state, and Xi is the position of the characteristic peak of the frequency spectrum of curve i.

5. The method for determining the failure criterion of a thermal barrier coating according to claim 1, characterized in that, Taking the change slope greater than a preset value as the critical point for determining the failure of the thermal barrier coating.

6. The method for determining the failure criterion of a thermal barrier coating according to claim 5, characterized in that, The preset value is 14%.

7. A system for determining the failure criterion of a thermal barrier coating, characterized in that, it includes: A time-domain spectral signal acquisition module for placing a thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectral signal of the thermal barrier coating sample; A frequency-domain signal determination module for performing a fast Fourier transform on the time-domain spectral signal to obtain a frequency-domain signal; A frequency-domain information acquisition module for heating the thermal barrier coating sample at a set temperature for a certain period of time, taking out the thermal barrier coating sample and air-cooling it to room temperature, then returning to execute "Placing the thermal barrier coating sample in a terahertz time-domain spectroscopy system to obtain the time-domain spectral signal of the thermal barrier coating sample" to obtain frequency-domain information; the frequency-domain information is composed of frequency-domain signals at different times; A frequency spectrum diagram generation module for generating a frequency spectrum diagram based on the frequency-domain information; A peak position extraction module for extracting the positions of the frequency spectrum characteristic peaks of different curves in the frequency spectrum diagram; A peak position acquisition module, configured to acquire the as-prepared peak position; the as-prepared peak position is the position of the frequency spectrum characteristic peak obtained when the thermal barrier coating sample is not heated; A change slope determination module, configured to determine the change slope based on the as-prepared peak position and the positions of the frequency spectrum characteristic peaks of different curves; A failure criterion determination module, configured to determine the thermal barrier coating failure criterion based on the change slope.

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