Nonlinear ultrasonic detection system and detection method for porosity of thermal barrier coating of turbine blade

Abstract

The invention discloses a nonlinear ultrasonic detection system and a nonlinear ultrasonic detection method for porosity of a thermal barrier coating of a turbine blade, and belongs to the field of nonlinear ultrasonic nondestructive detection. The low-pass filter inputs filtered multi-cycle sinusoidal pulse string signals to the transmitting probe to excite the transmitting probe to transmit ultrasonic waves, and the transmitting and receiving probes are installed in a transmitting probe cabin and a receiving probe cabin of the probe tool to form ultrasonic Rayleigh waves propagating in the length direction of the blade; a receiving probe receives a Rayleigh wave signal in the blade, a relevance model of the nonlinear coefficient of the Rayleigh wave and the porosity is established, nonlinear ultrasonic Rayleigh wave representation of the porosity is achieved, and a new effective solution is provided for nondestructive testing of the porosity of the thermal barrier coating.

Description

Technical Field

[0001] The present invention mainly relates to the field of non - linear ultrasonic detection of the porosity of thermal barrier coatings for turbine blades, and particularly relates to a non - linear ultrasonic detection system and method for the porosity of thermal barrier coatings for turbine blades. Background Technique

[0002] Thermal barrier coatings can improve the ultra - high - temperature heat - insulation performance of turbine blades, increase the thrust - to - weight ratio, fuel efficiency of aero - engines, and extend the service life. During the extreme service process of long - term high temperature and high pressure, due to the action of alternating loads and thermal stresses, the microstructure of thermal barrier coatings changes, new pores are generated inside the coatings, and the existing large - size pores expand and connect to form larger - size pores, resulting in an increase in the overall porosity of the coatings. The continuous expansion of large - size pores will eventually develop into micro - cracks, causing the failure of thermal barrier coatings. Therefore, it is particularly important to characterize the porosity of thermal barrier coatings for ensuring the service inspection of turbine blades.

[0003] The thickness of thermal barrier coatings is in the micron range. Conventional ultrasonic detection techniques are limited by the detection blind zone and are difficult to perform near - surface detection; the pore sizes are mostly in the nanometer and micron ranges, and linear ultrasonic detection methods are insensitive to the changes in the microstructure of pores in thermal barrier coatings; the complex curved surface structure of turbine blades also causes problems such as poor ultrasonic sound coupling, poor detection accuracy, and low efficiency. Summary of the Invention

[0004] Aiming at the problems that existing ultrasonic detection techniques are difficult to detect the changes in the microstructure of pores in thermal barrier coatings, and are affected by complex curved surface structures, resulting in difficult sound coupling, poor detection accuracy, and low efficiency, the present invention discloses a non - linear ultrasonic detection system and method for the porosity of thermal barrier coatings for turbine blades. By constructing a dedicated non - linear ultrasonic detection system, developing a dedicated detection probe and probe tooling, and combining the dual - probe transmitting and receiving method to efficiently collect non - linear ultrasonic Rayleigh wave detection signals of pores in thermal barrier coatings for turbine blades, extracting the non - linear coefficient of ultrasonic Rayleigh waves and establishing a mapping model between porosity and non - linear coefficient, non - destructive detection of the porosity of thermal barrier coatings for turbine blades is realized, which has important engineering significance for improving the quality control ability of blade thermal barrier coatings.

[0005] The technical solution is as follows:

[0006] In a first aspect, a non - linear ultrasonic detection system for the porosity of thermal barrier coatings for turbine blades includes: a low - pass filter, a probe tooling, a transmitting probe, and a receiving probe.

[0007] The low - pass filter uses a filtered multi - cycle sine pulse train signal to excite a dedicated probe to emit ultrasonic waves. The number of cycles of the sine pulse train signal is 10, the excitation voltage is 400V, and it is modulated by a Hanning window.

[0008] The low-pass filter is a low-pass filter with a cut-off frequency of 2.5 MHz.

[0009] The central frequency of the transmitting probe is 2 MHz, and the diameter of the piezoelectric wafer is 3 mm; the central frequency of the receiving probe is 4 MHz, the diameter of the piezoelectric wafer is 3 mm, and the outer diameter of the transmitting and receiving probe housing is 6 mm.

[0010] A probe cabin is provided on the probe tooling, and the probe cabin includes a transmitting probe cabin and a receiving probe cabin.

[0011] The included angles between the probe cabin and the bottom surface of the probe tooling are both 35°;

[0012] The diameter of the probe cabin is 6.2 mm;

[0013] The transmitting probe and the receiving probe are respectively installed in the transmitting probe cabin and the receiving probe cabin, and the longitudinal distance between the intersection points of the acoustic beam main axes of the transmitting probe and the receiving probe on the blade surface is 30 mm.

[0014] In a second aspect, a method for non-linear ultrasonic detection of the porosity of a thermal barrier coating on a turbine blade is provided. The method is realized by exciting and receiving ultrasonic Rayleigh waves in the blade according to a non-linear ultrasonic detection system for the porosity of the thermal barrier coating on a turbine blade. The method includes:

[0015] (1) Adjust the position of the tooling according to the surface profile of the thermal barrier coating on the turbine blade, so that the plane where the tooling and the probe are located is perpendicular to the detection surface of the thermal barrier coating, and a water distance of 10 mm is maintained between the ends of the transmitting probe and the receiving probe and the blade surface;

[0016] (2) Collect Rayleigh wave detection signals;

[0017] (3) Perform Fourier transform on the collected Rayleigh wave detection signals and calculate the non-linear coefficient β':

[0018]

[0019] A 1 is the amplitude of the 2 MHz fundamental wave, A 2 is the amplitude of the 4 MHz second harmonic, and β' is the Rayleigh wave non-linear coefficient.

[0020] (4) Establish a correlation model between the porosity measured by the metallographic test and the non-linear coefficient, and quantitatively evaluate the porosity y% from the non-linear coefficient accordingly:

[0021] y% = 10.22909 - 66.52225β + 61.83264β 2

[0022] Compared with the prior art, the advantages of the present invention are:

[0023] Through precise planning of the fixture position and scanning path, high-precision and high-reliability detection of complex detection surfaces can be achieved;

[0024] The nonlinear ultrasonic Rayleigh wave technology can comprehensively and rapidly scan the thermal barrier coating in a short time, improving the detection efficiency;

[0025] Traditional detection methods may lead to misjudgment or missed detection due to limitations such as environmental factors and equipment accuracy. Based on the nonlinear ultrasonic Rayleigh wave technology, by calculating the physical quantity of the nonlinear coefficient, external interference can be excluded to a certain extent, improving the accuracy and reliability of detection. Description of the Drawings

[0026] Figure 1 is the detection principle diagram provided by the embodiment of the present application;

[0027] Figure 2 is the schematic diagram of the Hanning window modulation signal provided by the embodiment of the present application;

[0028] Figure 3 is the spectrum diagram of the Rayleigh wave detection signal provided by the embodiment of the present application;

[0029] Figure 4 is the nonlinear coefficient - porosity curve provided by the embodiment of the present application

[0030] Figure 5 is the measurement result diagram of the metallographic method provided by the embodiment of the present application. Detailed Embodiment

[0031] The present invention will be further described below in conjunction with the drawings in the specification and specific embodiments.

[0032] The nonlinear ultrasonic detection system for the porosity of the thermal barrier coating of the turbine blade includes: a low-pass filter, a probe fixture 1; the probe fixture 1 is provided with a transmitting probe cabin and a receiving probe cabin; the probe 2 includes a transmitting probe and a receiving probe, and the transmitting probe and the receiving probe are respectively installed in the transmitting probe cabin and the receiving probe cabin.

[0033] Adjust the position of the probe fixture 1 according to the surface profile of the thermal barrier coating of the turbine blade, as Figure 1 shown, make the plane where the probe fixture 1 and the probe 2 are located perpendicular to the detection surface of the thermal barrier coating, keep a water distance of 10 mm between the ends of the transmitting probe and the receiving probe and the surface of the blade 3, and the longitudinal distance between the intersection points of the main axes of the sound beams emitted by the transmitting probe and the receiving probe on the surface of the blade 3 is 30 mm.

[0034] A 10-cycle, Hanning-window-modulated sinusoidal excitation electrical signal is output to a 2 MHz transmitting probe through a 2.5 MHz low-pass filter; the ultrasonic wave transmitted by the transmitting probe generates a Rayleigh wave signal on the blade 3, and after propagating 30 mm, it is received by a 4 MHz receiving probe through a water coupling layer. The received Rayleigh wave signal is as Figure 2 shown.

[0035] The Fourier transform is performed on the collected Rayleigh wave signal to obtain a spectral distribution diagram as Figure 3 . The center frequency of the fundamental wave is 1.98 MHz, and the center frequency of the second harmonic is 4.01 MHz. Generally, the peak frequency of the second harmonic is about twice that of the fundamental wave peak frequency, which conforms to the mutual relationship between the second harmonic and the fundamental wave in the frequency domain distribution. The amplitude of the 2 MHz fundamental wave is 7.73 V, and the amplitude of the 4 MHz second harmonic is 0.14 V. According to the calculation of Equation (1), the nonlinear coefficient β’ is 0.00234.

[0036]

[0037] A 1 is the amplitude of the 2 MHz fundamental wave, A 2 is the amplitude of the 4 MHz second harmonic, and β’ is the Rayleigh wave nonlinear coefficient.

[0038] The correlation model between the porosity measured by the metallographic test and the nonlinear coefficient is as Figure 4 shown, and based on this, the porosity is quantitatively evaluated by the nonlinear coefficient. Specifically:

[0039] y% = 10.22909 - 66.52225β + 61.83264β 2 (2)

[0040] Substituting the nonlinear coefficient β’ into Equation (2) gives a porosity of 10.07%.

[0041] The propagation path of the Rayleigh wave in the thermal barrier coating specimen of the turbine blade is dissected, and the metallographic method is used to measure the coating porosity. The overall porosity is 9.69%, and the measurement result is as Figure 5 shown. The relative error between the actual measured value of the porosity and the theoretical calculated value is only 3.9%.

Claims

1. Nonlinear ultrasonic detection system for porosity of thermal barrier coating of turbine blades, characterized by: include: A low-pass filter and a probe tooling; a transmitting probe cabin and a receiving probe cabin are arranged on the probe tooling; a transmitting probe cabin and a receiving probe are respectively installed in the transmitting probe cabin and the receiving probe cabin.

2. The nonlinear ultrasonic detection system for porosity of thermal barrier coating of turbine blades according to claim 1, characterized in that: The low-pass filter uses the filtered multi-cycle sinusoidal pulse train signal to excite the transmitting probe to transmit ultrasonic waves; The low-pass filter has a cut-off frequency of 2.5 MHz.

3. The nonlinear ultrasonic detection system for porosity of thermal barrier coating of turbine blades according to claim 2, characterized in that: The number of cycles of the sinusoidal pulse train signal is 10, the excitation voltage is 400V, and it is modulated by a Hanning window.

4. The nonlinear ultrasonic detection system for porosity of thermal barrier coating of turbine blades according to claim 1, characterized in that: The central frequency of the transmitting probe is 2MHz, and the diameter of the piezoelectric chip is 3mm; the central frequency of the receiving probe is 4MHz, and the diameter of the piezoelectric chip is 3mm, and the outer shell diameters of the transmitting probe and the receiving probe are 6mm.

5. The nonlinear ultrasonic detection system for porosity of thermal barrier coating of turbine blades according to claim 1, characterized in that: The angles between the transmitting probe cabin and the receiving probe cabin and the bottom surface of the probe tooling are both 35°; The diameter of the transmitting probe cabin and the receiving probe cabin are both 6.2mm; The longitudinal distance between the main axes of the sound beams emitted by the transmitting probe and the receiving probe and the intersection point on the blade surface is 30mm.

6. A nonlinear ultrasonic detection method for porosity of thermal barrier coatings of turbine blades, characterized in that: The method is implemented by using the nonlinear ultrasonic detection system for porosity of thermal barrier coating of turbine blades according to any one of claims 1 to 5 to excite and receive ultrasonic Rayleigh waves in the blades, and the method comprises the following steps: (1) Adjust the position of the tooling according to the surface profile of the thermal barrier coating of the turbine blade, so that the plane where the tooling and the probe are located is perpendicular to the thermal barrier coating detection surface, and the blade surface of the transmitting probe and the receiving probe ends are kept at a water distance of 10 mm; (2) collecting Rayleigh wave detection signals; (3) Perform Fourier transform on the collected Rayleigh wave detection signal and calculate the nonlinear coefficient β': A1 is the 2MHz fundamental amplitude, A2 is the 4MHz second harmonic amplitude, and β' is the Rayleigh wave nonlinear coefficient; (4) Evaluate the porosity y% based on the correlation model between porosity and nonlinear coefficient: y％＝10.22909-66.52225β+61.83264β 2 。

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