Nondestructive measurement of mill-scale thickness on steel by terahertz time-of-flight tomography

SURFACE & COATINGS TECHNOLOGY

卷:393

Article

Zhai, Min^1,2  Locquet, Alexandre^1,2  Roquelet, Cyrielle³  Alexandre, Patrice³  Daheron, Laurence³  Citrin, D. S.^1,2 

[1] Georgia Tech Lorraine, Georgia Tech CNRS UMI2958, 2 Rue Marconi, F-57070 Metz, France

[2] Georgia Inst Technol, Sch Elect & Comp Engn, Atlanta, GA 30332 USA

[3] ArcelorMittal Maizieres Res SA, Voie Romaine, F-57280 Maizieres Les Metz, France

关键词: Nondestructive testing;    Nondestructive evaluation;    Terahertz imaging;    Terahertz reflectometry;    Oxide coatings;    Coated metal;   

DOI  :  10.1016/j.surfcoat.2020.125765

来源: Elsevier

【 摘 要 】

We measure in a nondestructive and noncontact fashion the thicknesses of three scale films with thicknesses 28.5 +/- 1.4 mu m, 13.4 +/- 0.9 mu m, and 5.1 +/- 0.3 mu m on steel substrates employing terahertz time-of-flight tomography combined with advanced signal-processing techniques. Wiistite is the dominant phase in the scale films, though magnetite and hematite are also present. Because wiistite is electrically insulating, the incident terahertz electromagnetic pulses largely penetrate into the scale film; however, the pulses are entirely reflected by the underlying electrically conductive steel substrate. Because the film layers are thin, in some cases optically thin, the distinct pulses reflected at the air/scale and scale/steel interfaces overlap in time and thus are not visually evident in the reflected terahertz signal, necessitating the use of deconvolution techniques to recover the sample structure. We compare the merits of three deconvolution techniques, one unsuccessful (frequency-wavelet domain deconvolution) and two successful (sparse deconvolution and autoregressive extrapolation), to characterize the thicknesses of these scale films.

【 授权许可】

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