Design Of Triaxial Ultrasound Scanning System For High Velocity Oxygen Fuel Sprayed Iron-based Amorphous Coatings

Iron-based amorphous coatings had strong resistance to wear and corrosion and were widely used in important steel equipment.However,iron-based amorphous coatings were usual y prepared under high temperature conditions,resulting in hazardous defected due to the incorporation of impurities,air gaps,and cracks due to cooling.Moreover,the coefficient of thermal expansion of the coating material and the matrix material were usually not the same,so the coating and the matrix often fail to match during the preparation process,resulting in peeling and delamination of the coating and the substrate.Therefore,in order to ensure the normal operation of the equipment,the quality evaluation of the coating was very important.Compared with other spraying methods,the iron-based amorphous coating prepared by the supersonic flame spraying(HVOF)technology had certain advantages in performance and the like.In the detection method of HVOF coating,since non-destructive testing did not damage the structure of the material itself,it had been widely used,and the ultrasonic immersion ultrasonic method in ultrasonic testing had strong penetrating ability,fast response speed and easy automation.Features,very suitable for the detection of coating materials.Ultrasonic automatic scanning detection had the advantages of convenient display and rapid detection,and had become a commonly used technique for coating detection.In this paper,a high-frequency water-immersed ultrasonic scanning system for supersonic flame-sprayed iron-based amorphous coatings was designed,and the detection of coatings was realized.The system mainly included data acquisition module,host computer,mechanical scanning platform and motion control module to realize signal acquisition and waveform display.At the same time,it could realize precise motion control in the three-axis direction(minimum motion step size is 0.05mm);the scanning speed was adjustable,the range was from 0.06mm/s to 200mm/s;the pulse repetition frequency ranged from 100 Hz to 5000 Hz.The excitation voltage could be manually selected as 100 V,200V,300 V and 400 V with a gain range of 0 to 50 dB.The sampling frequency was 200 MHz and could match ultrasonic probes from 0.1MHz to 200 MHz.The system enabled C-scanning of HVOF coated samples and onedimensional display of the acquired signals on a software panel.In addition,the propagation characteristics of ultrasonic waves in HVOF ironbased amorphous coatings were analyzed.Since the composition of the HVOF coating was similar to that of the iron base,the reflection signal of the ultrasonic wave passing through the interface was very weak;and because the coating was very thin,the watercoating interface and the coating in the collected echo signal were caused.The layersubstrate reflection signals were aliased together and the coating information from the echo could not be directly analyzed.This was a big problem to be solved in this article.In this regard,the wave packet decomposition method was proposed in this paper and applied to the thickness measurement of HVOF iron-based amorphous coating for the first time.The echo signal of the aliased coating collected by the experiment was decomposed,and a series of wave packets reflecting the structural state of each layer of the material were obtained.At the same time,the detected echo signals of each interface were extracted and analyzed,and the narrow pulse signal was used for replacement.A narrow pulse matrix diagram is obtained,which improves the signal-to-noise ratio of the detection.The propagation time of the ultrasonic wave in the coating was calculated,and the structure of the obtained iron-based amorphous coating was characterized.Based on the thickness of the coating measured by scanning electron microscopy(SEM),the sound velocity of the middle coating of one of the samples was calculated,and the respective thickness results were calculated using the speed of sound and the ultrasonic propagation time in the other samples.Finally,the coating thickness results were compared with the SEM metalographic results,and the error were calculated to measure the effectiveness of the method and the coating quality of the material.