超音速等离子喷涂Fe基合金层疲劳损伤声发射信号的处理与分析

Processing and Analysis of Fatigue Damage Acoustic Emission Signals of Iron-Based Alloy Coating Prepared by Supersonic Plasma Spraying

为了通过对声发射信号的处理来诊断涂层接触疲劳损伤,采用超音速等离子喷涂在淬火45钢上制备了Fe基合金涂层,采用扫描电镜及其附带的能谱仪观察涂层形貌、分析涂层成分;在球盘式滚动接触疲劳试验机上进行接触疲劳试验,借助声发射系统采集涂层接触疲劳失效前和失效时的声发射信号;采用小波变换和经验模态分解对声发射信号在不同尺度上进行分解和重构,提取了包含疲劳损伤信息的波形和频率特征。结果表明:Fe基合金涂层结构致密,存在少量孔隙,在沉积粒子边界处存在少量微观裂纹,孔隙率为2.753 5%,等离子喷涂过程中,Fe,Cr和Si只发生少量的烧损且在涂层内分布均匀;接触疲劳失效前的声发射信号以连续型为主,失效时以突发型为主,采用小波变换和经验模态分解均可获得涂层接触疲劳失效前和失效时较为纯净的疲劳损伤声发射信号;2种方法重构的涂层接触疲劳失效前和失效时声发射信号波形相似,经验模态分解方法对400 kHz以上高频和100 kHz以下低频干扰信号的滤除效果明显不及小波变换。

Fe-based alloy coating was prepared on plain carbon steel( 45) substrate by supersonic plasma spraying. A scanning electron microscope equipped with an energy dispersive spectrometer was performed to observe the morphology and determine the elemental composition of as-prepared Fe-based alloy coating. Moreover,a ball-on-disc contact fatigue tester was employed to conduct contact fatigue test,and the typical acoustic emission signals before and upon contact fatigue failure of the coating were collected with an acoustic emission system. Furthermore,the acoustic emission signals were decomposed and reconstructed at different scales by wavelet transform and empirical mode decomposition; and the waveform and frequency feature of the acoustic emission signals covering fatigue damage information were acquired. Results indicated that as-prepared Fe-based alloy coating had dense structure and contained a small amount of pores. Besides,there existed a small amount of microcracks at the boundaries of the deposited particulates,and the porosity of the Fe-based alloy coating was 2. 76%. Moreover,a small amount of Cr and Si were burned during the plasma spraying process,and they were uniformly distributed in as-obtained Fe-based alloy coating. Continuous type of acoustic emission signal was dominant before contact fatigue failure,and burst type of acoustic emission signal was dominant upon contact fatigue failure. Furthermore,after being reconstructed by wavelet transform and empirical mode decomposition,the acoustic emission signals before and upon fatigue failure exhibited similar waveforms; and wavelet transform method was obviously advantageous over empirical mode decompositionmethod in terms of the filtering effect for interference signals above a high frequency of 400 kHz and a low frequency of below 100 kHz.