The impact of a chromium (Cr) coating on the elastic guided waves propagating in zirconium alloy (called M5 Framatome and referred to as M5 hereafter) nuclear cladding tubes is studied both theoretically and experimentally. Longitudinal modes are measured on different 9.5 mm–diameter tubes by a non-contact laser ultrasonic technique. These modes are calculated using the M5 elastic constants determined from x-ray diffraction measurements. Since Cr has a much higher shear wave velocity than the M5 alloy, the dispersion of observed guided modes is significantly modified by the coating. In the mid-frequency range, characterized by shear wavelengths on the order of the tube thickness, the second longitudinal mode appears to be particularly sensitive to the coating. In a higher frequency range, it is observed that modes are well measured in a frequency-wavenumber domain corresponding to the leaky surface wave of a Cr coated infinite M5 substrate. A simple but effective model predicts the observability of each mode, in good qualitative agreement with experimental observations.
Diboune et al. (Thu,) studied this question.