热暴露 APS 与 EB-PVD YSZ 热障涂层的太赫兹时域光谱与成像表征

Due to different microstructures, atmospheric plasma sprayed (APS) and electron beam physical vapor deposited (EB-PVD) yttria-stabilized zirconia (YSZ) thermal barrier coatings may present different responses under thermal exposure. In order to better monitor the changes in coating structure and quality, in this study, as the non-destructive testing method, terahertz time-domain spectroscopy and imaging technology were used to characterize and compare the effects of thermal exposure conditions on APS and EB-PVD YSZ coatings. The results show that before thermal exposure, APS coatings exhibit a lamellar structure with more pores and scattering interfaces, leading to weaker secondary echoes and less distinguishable multiple reflections. In contrast, EB-PVD coatings present a more regular columnar structure, clearer multiple echoes, and a more uniform spatial response. After exposed at 1100 K, APS coatings show exposure-duration-dependent changes, including variations in the amplitude and width of the secondary echo, degraded waveform quality, increased THz-derived thickness, and enhanced spatial nonuniformity in THz imaging. By comparison, EB-PVD coatings exposed at 1100 K for 10 h, 20 h, and 40 h maintain clearer primary and secondary echoes, weaker waveform degradation, and relatively stable spatial uniformity, indicating a more stable THz response with increasing exposure duration. When the exposure temperature increases to 1300 K, APS coatings exhibit broader waveforms and a more irregular bottom interface. For EB-PVD coatings, exposure at 1300 K results in decreased echo amplitude and shortened time-of-flight, corresponding to reduced THz-derived thickness, while the overall spatial uniformity remains relatively stable. These results demonstrate that THz-TDS combined with two-dimensional and three-dimensional imaging is suitable for rapid, nondestructive, and spatially resolved characterization of thermally exposed YSZ coatings prepared by different deposition methods.