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Identification of the Velocity, Thickness and Interfacial Roughness of Coating Using Full Time-domain URCPS: Cross-correlation-based Inverse Problem

[+] Author and Article Information
Zhiyuan Ma

NDT & E Laboratory, Dalian University of Technology, Dalian 116024, China
Zhiyma@dlut.edu.cn

L. Lin

NDT & E Laboratory, Dalian University of Technology, Dalian 116024, China
Linli@dlut.edu.cn

Shijie Jin

NDT & E Laboratory, Dalian University of Technology, Dalian 116024, China
jinshijie@dlut.edu.cn

M.K. Lei

Surface Engineering Laboratory, School of Materials Science and Engineering, Dalian University of Technology, Dalian 116024, China
mklei@dlut.edu.cn

1Corresponding author.

ASME doi:10.1115/1.4042177 History: Received August 28, 2018; Revised December 02, 2018

Abstract

Aim at characterizing interfacial roughness of thin coatings with unknown sound velocity and thickness, we derive a full time-domain ultrasonic reflection coefficient phase spectrum (URCPS) as a function of interfacial roughness based on the phase screen approximation theory. The constructed URCPS is used to determine the velocity, thickness, and interfacial roughness of specimens through the cross-correlation algorithm. The effect of detection frequency on the roughness measurement is investigated through the finite element method. A series of simulations were implemented on Ni-coating specimens with a thickness of 400 µm and interfacial roughness of 1.9~39.8 µm. Simulation results indicated that the measurement errors of interfacial roughness were less than 10% when the roughness satisfies the relationship of Rq=1.6%?~10.0%?. The measured velocity and thicknesses were in good agreement with those imported in simulation models with less than 9.3% error. Ultrasonic experiments were carried out on two Ni-coating specimens through a flat transducer with an optimized frequency of 15 MHz. Compared with the velocities measured by time-of-flight method, the relative errors of inversed velocities were all less than 10%. The inversed thicknesses were in good agreement with those observed by optical microscopy with less than 10.9% and 7.6% error. The averaged interfacial roughness determined by the ultrasonic inversion method were 16.9 µm and 30.7 µm, respectively. The relative errors were 5.1% and 2.0% between ultrasonic and confocal laser scanning microscope method, respectively.

Copyright (c) 2018 by ASME
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