Aero-engine blade surface coating defect and thickness detection method

Abstract

The invention relates to the technical field of aero-engine nondestructive testing, and discloses a method for detecting defects and thickness of a surface coating of an aero-engine blade. The invention designs a novel acoustic impedance sensor special for a blade coating, the novel acoustic impedance sensor comprises a plurality of independently controlled transduction units, each transduction unit has multi-band detection capability, main resonant frequencies of different transduction units are configured in a differentiated manner, and during detection, the novel acoustic impedance sensor is coupled to the surface of a blade; the material state is reversely deduced by measuring the energy absorption spectrum of broadband sound waves in the coating, and the blade surface coating defect and thickness detection is achieved.

Description

Technical Field

[0001] This invention relates to the field of non-destructive testing technology for aero-engines, and in particular to a method for detecting defects and thickness of coatings on the surface of aero-engine blades. Background Technology

[0002] As a core hot-end component, aero-engine blades operate in extreme environments for extended periods, enduring the combined effects of high temperature, high pressure, and complex mechanical loads. To improve their heat resistance, modern blades commonly employ thermal barrier coating technology, coating ceramic materials onto the surface of a high-temperature alloy substrate. However, the significant difference in thermal expansion coefficients between the metal substrate and the ceramic coating leads to severe thermal mismatch stress under high-temperature cyclic conditions, causing the coating to crack, peel, or even detach entirely, directly impacting the engine's safety and reliability. Research indicates that coating failure is a major cause of turbine blade failure, and early detection of coating defects can significantly reduce maintenance costs; therefore, developing high-precision detection technologies is of paramount importance.

[0003] Currently, non-destructive testing of blade coatings mainly relies on methods such as ultrasound, eddy current, and infrared thermography, but these technologies all have significant limitations. Ultrasonic testing has limited resolution for ultrathin coatings and poor applicability on complex curved surfaces; eddy current technology is only applicable to conductive substrates and is essentially ineffective for defects in the insulating ceramic coating itself and the debonding state of the coating / substrate interface; while infrared thermography can quickly scan the surface, it is insensitive to key parameters such as interfacial bonding strength. Furthermore, the micron-level thickness of the ceramic coating and the nanometer-level diffusion region at the interface further increase the difficulty of detection. Traditional methods struggle to identify microcracks or interfacial debonding, and these micro-defects are precisely the root cause of rapid propagation under thermal cycling loads, ultimately leading to coating system failure. Therefore, to improve flight safety, ensure blade integrity, and achieve the economic benefits of green manufacturing and remanufacturing, it is imperative to find a safe, reliable, and pollution-free method for detecting cracks / discontinuities in blade ceramic layers. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a method for detecting defects and thickness in the surface coating of aero-engine blades. This invention is implemented as follows:

[0005] A method for detecting defects and thickness in the surface coating of aero-engine blades, employing a novel array-type acoustic impedance sensor specifically designed for blades to scan and detect the coating area, includes the following steps:

[0006] S1. Couple the novel array-type acoustic impedance sensor to the surface of the blade to be tested;

[0007] S2. Control each transducer unit in the novel array acoustic impedance sensor to sequentially emit broadband excitation sound waves covering low frequency, medium frequency, and high frequency.

[0008] S3. Real-time acquisition of energy attenuation data of sound waves in the coating at various frequency bands, generating sound energy absorption spectrum;

[0009] S4. Based on the inversion calculation of the acoustic energy absorption spectrum, the thickness distribution and internal defect information of the coating are output simultaneously;

[0010] in:

[0011] The novel array-type acoustic impedance sensor includes multiple independently controlled transducer units;

[0012] The transducer unit includes, from bottom to top, a flexible substrate, a cavity structure, a vibrating thin film, a piezoelectric layer, a frequency division electrode group, and an acoustic impedance matching layer;

[0013] The vibrating diaphragm covers the cavity structure, and the piezoelectric layer is disposed on the upper surface of the vibrating diaphragm;

[0014] The frequency division electrode group includes low-frequency, medium-frequency and high-frequency electrodes that are insulated from each other, and respectively cover different regions of the piezoelectric layer to achieve multi-frequency excitation;

[0015] The acoustic impedance value of the acoustic impedance matching layer is between that of the piezoelectric layer material and the coating material.

[0016] Furthermore, the transducer unit is configured such that the direction of sound wave propagation is perpendicular to the coating surface; the main resonant frequency of each transducer unit is configured differently, specifically: the main resonant frequency interval between adjacent transducer units is greater than one octave; the main resonant frequency refers to the overall resonant peak frequency of the transducer unit when there are no partitioned electrodes.

[0017] Furthermore, the frequency-divided electrode group achieves multi-band excitation through the following frequency partitioning:

[0018] The frequency range of the acoustic waves excited by the low-frequency electrode is 10kHz-100kHz.

[0019] The frequency range of the acoustic waves excited by the intermediate frequency electrode is 100kHz-1MHz;

[0020] The frequency range of the acoustic waves excited by the high-frequency electrode is 1MHz-20MHz.

[0021] Furthermore, the inversion calculation is achieved by establishing an acoustic impedance gradient distribution model, which converts the energy attenuation into the change in material acoustic impedance.

[0022] Furthermore, the inversion calculation includes:

[0023] When the acoustic energy absorption spectrum shows abnormal attenuation in a specific frequency band, a microcrack defect is determined.

[0024] When the characteristic peak of the acoustic energy absorption spectrum undergoes a frequency shift, the thickness anomaly is determined based on the pre-calibrated thickness-frequency shift relationship.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0026] This invention innovatively proposes a novel acoustic inspection method for the surface coating of aero-engine blades. It uniquely designs a novel acoustic impedance sensor specifically for blade coatings, comprising multiple independently controlled transducer units, each capable of multi-band frequency sweep detection. The differentiated main resonant frequencies among different transducer units ensure spatial detection resolution. During inspection, the novel acoustic impedance sensor is coupled to the blade surface without disassembly. The inspection process does not rely on defect echoes; instead, it infers the material state by measuring the energy absorption spectrum of broadband acoustic waves in the coating, enabling reliable simultaneous detection of both coating defects and thickness. This invention achieves a comprehensive advantage of "non-destructive, high precision, high efficiency, and low cost" in in-situ inspection of aero-engine blade coatings, significantly improving engine maintenance safety and economy, and possessing broad engineering application prospects. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the present invention or the prior art, or to provide a simple description of the drawings used in the prior art, it is obvious that those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0028] Figure 1 This is a schematic diagram of the blade to be tested in this embodiment.

[0029] Figure 2 This is a schematic diagram of the detection method in this embodiment.

[0030] Figure 3 This is a schematic diagram of the array of the novel acoustic impedance sensor in this embodiment.

[0031] Figure 4 This is a schematic diagram of the control and acquisition system in this embodiment.

[0032] Figure 5 This is a schematic diagram of the transducer unit structure of the novel acoustic impedance sensor in this embodiment.

[0033] Base-10;

[0034] Transducer unit-100; 101-Flexible substrate; 102-Cavity structure; 103-Vibrating thin film; 104-Piezoelectric layer; 105-Frequency dividing electrode group; 106-Acoustic impedance matching layer. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention.

[0036] Taking the working blade of a high-pressure turbine of a certain type of aero-engine as an example, this embodiment is implemented under the in-situ conditions of the entire engine. Figure 1 As shown, the blade under test is a high-temperature alloy eddy current working blade with a ceramic layer bonded to its surface.

[0037] This embodiment uses a novel array-type acoustic impedance sensor specifically designed for blades to scan and detect the coating area, referring to... Figure 2 This includes the following steps:

[0038] S1. Couple a novel array-type acoustic impedance sensor specifically designed for blade coating onto the surface of the blade to be tested. Specifically, the sensor can be mounted and attached to the surface of the area to be tested on the blade using an adaptive bonding mechanism (such as pneumatic adsorption).

[0039] Reference Figure 2 The specific structure of the novel array-type acoustic impedance sensor is as follows:

[0040] The novel array-type acoustic impedance sensor employs a 5×5 array of 25 transducer units 100 on a substrate 10, with a center-to-center distance of 2mm between adjacent units. The sound beam is focused and scanned through electronic control. In this embodiment, the transducer unit 100 is configured such that the direction of sound wave propagation is perpendicular to the surface of the coating of the blade to be tested.

[0041] Reference Figure 3 Each transducer unit 100 includes, from bottom to top, a flexible substrate 101, a cavity structure 102, a vibrating film 103, a piezoelectric layer 104, a frequency-dividing electrode group 105, and an acoustic impedance matching layer 106. The vibrating film 103 covers the cavity structure 102, and the piezoelectric layer 104 is disposed on the upper surface of the vibrating film 103. The frequency-dividing electrode group 105 includes a low-frequency electrode 105a, a mid-frequency electrode 105b, and a high-frequency electrode 105c that are mutually insulated and respectively cover different regions of the piezoelectric layer 104. The acoustic impedance value of the acoustic impedance matching layer 106ca is between that of the piezoelectric layer material and the coating material, which can reduce sound wave diffusion and ensure the detection resolution of surface microcracks.

[0042] Reference Figure 4The system is configured with a control and acquisition system 200, including an FPGA module 201, a power amplifier 202, a high-speed ADC 203, and a host computer 204. The FPGA module 201 is independently connected to the low-frequency electrode 105a, the medium-frequency electrode 105b, and the high-frequency electrode 105c to realize multi-band frequency sweep excitation.

[0043] The main resonant frequencies of each transducer unit 100 are configured differently, as detailed below:

[0044] The 25 transducer units 100 are partitioned along the Y direction with main resonant frequencies. The main resonant frequency refers to the overall resonant peak frequency of the transducer unit when the electrodes are not partitioned, as detailed below:

[0045] Line 1: 0.25MHz;

[0046] Line 2: 0.60MHz;

[0047] Line 3: 1.40MHz;

[0048] Line 4: 2.50MHz;

[0049] Line 5: 3.20MHz.

[0050] The main resonant frequencies of adjacent units are spaced more than one octave apart to ensure complementary frequency domain information, non-overlapping frequency bands of adjacent units, elimination of sound field crosstalk, and improvement of array spatial resolution.

[0051] S2. Control each transducer unit in the novel array-type acoustic impedance sensor to sequentially emit broadband excitation sound waves covering low, mid, and high frequencies, achieving multi-band frequency sweep excitation. FPGA module 201 controls each transducer unit 100 to sequentially execute the following frequency sweep excitation:

[0052] Low-frequency electrode 115a: 10kHz–100kHz, in 2kHz increments;

[0053] Intermediate frequency electrode 115b: 100kHz–1MHz, in 5kHz increments;

[0054] High-frequency electrode 115c: 1MHz–20MHz, in 20kHz increments.

[0055] Each frequency point outputs a 10-cycle sine wave with a pulse repetition frequency of 1kHz.

[0056] The low-frequency band can penetrate the entire coating and sensitively detect interfacial delamination; the mid-frequency band is most sensitive to thickness changes; and the high-frequency band can distinguish micron-level cracks. The complementarity of the three frequency bands greatly reduces the error in thickness measurement and crack detection.

[0057] S3, the high-speed ADC 203 collects the energy attenuation data of sound waves in the coating in real time at a sampling rate of 50MHz, and transmits it to the host computer 204 to generate the sound energy absorption spectrum.

[0058] S4. Based on the inversion calculation of the acoustic energy absorption spectrum, the thickness distribution and internal defect information of the coating are output simultaneously;

[0059] The steps for inversion calculation are as follows:

[0060] 1. Establish an acoustic impedance gradient distribution model

[0061] The acoustic impedance gradient distribution model is used to convert energy attenuation into changes in the material's acoustic impedance. Specifically, the acoustic impedance gradient distribution model is as follows:

[0062]

[0063] Where Z(x) is the equivalent acoustic impedance at position x, ΔE is the energy attenuation, A(f) is the frequency correlation correction coefficient, and k is the sensor calibration constant.

[0064] 2. Defect Judgment

[0065] Microcrack defects are identified when the acoustic energy absorption spectrum shows abnormal attenuation in a specific frequency band.

[0066] When the characteristic peaks of the acoustic energy absorption spectrum undergo frequency shift, the thickness anomaly is determined based on the pre-calibrated thickness-frequency shift relationship.

[0067] This embodiment can achieve high-precision synchronous detection of coating thickness and defects without disassembling the engine or damaging the blades.

[0068] The advantages of the detection method and system of the present invention are as follows: the same acoustic energy absorption spectrum is used for inversion, and the thickness calculation and defect identification share the same set of original data, which eliminates the system errors introduced by multiple devices and multiple parameters, and significantly improves the reliability and comparison consistency.

[0069] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A method for detecting defects and thickness of surface coating on aero-engine blades, characterized in that, A novel array-type acoustic impedance sensor specifically designed for blades is used to scan and detect the coating area, including the following steps: S1. Couple the novel array-type acoustic impedance sensor to the surface of the blade to be tested; S2. Control each transducer unit in the novel array acoustic impedance sensor to sequentially emit broadband excitation sound waves covering low frequency, medium frequency, and high frequency. S3. Real-time acquisition of energy attenuation data of sound waves in the coating at various frequency bands, generating sound energy absorption spectrum; S4. Based on the inversion calculation of the acoustic energy absorption spectrum, the thickness distribution and internal defect information of the coating are output simultaneously; in: The novel array-type acoustic impedance sensor includes multiple independently controlled transducer units; The transducer unit includes, from bottom to top, a flexible substrate, a cavity structure, a vibrating thin film, a piezoelectric layer, a frequency division electrode group, and an acoustic impedance matching layer; The vibrating diaphragm covers the cavity structure, and the piezoelectric layer is disposed on the upper surface of the vibrating diaphragm; The frequency division electrode group includes low-frequency, medium-frequency and high-frequency electrodes that are insulated from each other, and respectively cover different regions of the piezoelectric layer to achieve multi-frequency excitation; The acoustic impedance value of the acoustic impedance matching layer is between that of the piezoelectric layer material and the coating material.

2. The detection method according to claim 1, characterized in that: The transducer unit is configured such that the direction of sound wave propagation is perpendicular to the coating surface; The main resonant frequency of each transducer unit is configured differently, specifically: the main resonant frequency interval between adjacent transducer units is greater than one octave. The main resonant frequency refers to the overall resonant peak frequency of the transducer unit when there are no partitioned electrodes.

3. The detection method according to claim 1, characterized in that: The frequency-division electrode group achieves multi-band excitation through the following frequency partitioning: The frequency range of the acoustic waves excited by the low-frequency electrode is 10kHz-100kHz. The frequency range of the acoustic waves excited by the mid-frequency electrode is 100kHz-1MHz; The frequency range of the acoustic waves excited by the high-frequency electrode is 1MHz-20MHz.

4. The detection method according to claim 1, characterized in that, The inversion calculation is achieved by establishing an acoustic impedance gradient distribution model, which converts the energy attenuation into the change in material acoustic impedance.

5. The detection method according to claim 4, characterized in that, The inversion calculation includes: When the acoustic energy absorption spectrum shows abnormal attenuation in a specific frequency band, a microcrack defect is determined. When the characteristic peak of the acoustic energy absorption spectrum undergoes a frequency shift, the thickness anomaly is determined based on the pre-calibrated thickness-frequency shift relationship.

Images