Nonlinear Ultrasonic Detection And Microscopic Observation Of Microstructure Damage Of Steam Turbine Blades

Steam turbine blades are made of 0Cr17Ni4Cu4 Nb stainless steel.After the steel is treated at different aging temperatures,changes in the precipitated phase may cause its mechanical properties and other properties to not meet the requirements of the blade.Further,the steam turbine blade easy to produce fatigue damage during operation,and in severe breakage caused by "speed" accident.At present,when magnetic particle and ultrasonic flaw detection methods are used to detect blades,only macro-cracks,open-welds and other damage can be detected,and microstructure damage such as dislocations and micro-cracks due to fatigue damage cannot be detected.The source of the subject of this article is the National Natural Science Foundation project "Research on Nonlinear Rayleigh Wave Detection Method of Microstructure Damage on Steam Turbine Blade Surface" undertaken by Henan University of Technology.Aiming at the non-destructive testing of microstructure damage of steam turbine blades,a series of non-linear ultrasonic non-destructive testing experiments were carried out with steam turbine blade manufacturing materials as the test object.The effects of precipitation phase changes and different fatigue damage levels on the ultrasonic non-linear coefficients were studied respectively.Further,the current detection and nonlinear Rayleigh wave ultrasonic signal processing problems were analyzed and studied.The main research contents are as follows:(1)Using the RAM-5000 SNAP nonlinear ultrasonic testing equipment,filters,ultrasonic probes and other instruments and homemade fixtures,a nonlinear ultrasonic longitudinal wave detection system and a nonlinear ultrasonic Rayleigh wave detection system were built.(2)Aiming at the problem of large differences in mechanical properties of turbine blade materials under different aging temperature treatments,a non-linear ultrasonic longitudinal wave detection experiment of test pieces with different aging treatment temperatures was carried out;Combined with microscopic observation experiments and hardness measurement results,the influence of the change of the precipitated phase inside the material structure onthe nonlinear coefficient of ultrasound was analyzed.(3)The non-linear ultrasonic Rayleigh wave detection experiments of specimens with different fatigue damage levels were carried out using the turbine blade material as the test object,and the trend of ultrasonic nonlinear coefficients under different fatigue damage levels was obtained.In addition,in view of the problem of small ultrasonic nonlinear coefficients in the test,the experiments of reverse phase relative excitation Rayleigh wave detection of different fatigue damage specimens were carried out,and the test results were compared with the results of nonlinear ultrasonic Rayleigh wave detection.(4)Aiming at the problem of inaccurate FFT processing results when the number of excitation signal cycles is small,a nonlinear ultrasonic signal processing method based on the least square method is studied and its feasibility is verified by numerical simulation.