Study On Detection Method Of NiCoCrAlYTa Six-membered Coating Thickness By Ultrasonic Microscopy Imaging

Aeroengine turbine blades have long service in harsh conditions and are prone to hot and high temperature oxidation.NiCoCrAlYTa six-membered coating as an important high-temperature protective coating on the surface of turbine blades can provide effective anti-oxidation and thermal protection for the blade matrix.Since the thickness of the coating directly affects the working performance of the blade,accurate measurement of its thickness will have a significant impact on the overall operational performance and reliability of the aeroengine.It is difficult to extract the characteristic information reflecting the thickness of the coating effectively.Therefore,this paper proposes a high frequency(15-100MHz)ultrasonic microscopic imaging detection method,which is based on both theoretical analysis and experimental test.Study on the Detection of Coating Thickness.Firstly,according to the physical properties of the NiCoCrAlYTa six-membered coating and the blade matrix material,the acoustic characteristics of the coating and the matrix were analyzed theoretically,and the influence of the acoustic characteristics between the coating and the substrate on the high-frequency ultrasonic detection signal was studied.Secondly,according to the propagation characteristics of ultrasonic waves in the thin layer structure,the acoustic intensity reflectance and sound transmittance of the ultrasonic wave at the water / coating / substrate interface are calculated and analyzed theoretically.The frequency of ultrasonic wave propagation in the process of thin layer structure Offset and reflection echo aliasing.Thirdly,in the simulation verification experiment,the matching tracking algorithm is used to match the simulation signal to obtain the simulated mother wave packet with good matching effect.The convolution filter technique is used to convolve the mother wave packet and the simulation detection signal effectively.Frequency offset phenomenon;the use of wave packet decomposition technology,the successful decomposition of the aliasing signal extracted,and fully verify the feasibility of the method.Finally,a rectangular coating of NiCoCrAlYTa was prepared by low pressure plasma spraying technique.The experimental specimen was studied by ultrasonic microscopy.The experimental instrument selected ultrasonic microscope,ultrasonic transducer selection frequency of 50 MHz.First,the original detection data is obtained by Z-scan method,and the detection data of the decryption process are analyzed and processed by MATLAB software.Then,the echo signal reflecting the water / coating / substrate interface is decomposed and extracted by narrow pulse Replacement,complete the ultrasonic feature imaging,and imaging results and coating thickness characteristics of the information obtained by comparing the thickness of the results.Finally,the accuracy of the detection method was verified by comparing with the results of scanning electron microscopy(SEM).The results show that the ultrasonic microscopy imaging method can effectively measure the thickness of NiCoCrAlYTa six-membered coating on the turbine blade surface.