DETECTION OF HARD INTERMETALLICS IN BETA-QUENCHED AND THERMALLY AGED ZIRCALOY-2 USING ULTRASONIC MEASUREMENTS

Zircaloy-2 is widely used for critical core components in the pressuri sed heavy water reactors. Components of Zircaloy-2 are usually fabrica ted from the beta-quenched billets. Proper quenching treatment must be ensured to avoid the rejection of finished products made from Zircalo y-2. Metallographic techniques are used for this purpose. However, it is advantageous to use nondestructive testing (NDT) techniques such as ultrasonics. In this work, laboratory investigations are carried out on the feasibility for the assessment of the acceptability of the beta -quenched microstructure using ultrasonic attenuation and velocity mea surements in the frequency range 2-100 MHz. Precise velocity measureme nts with an accuracy of 0.2 ns by cross-correlation technique have bee n made in this study. Results indicate that low frequency (2-10 MHz) u ltrasonic velocity measurements using both longitudinal and transverse waves are useful for revealing the presence of hard intermetallics. H igh-frequency (75 and 100 MHz) ultrasonic velocity measurements are us eful for revealing the early-stage dissociation of beta-quenched marte nsite to alpha-phase. Ultrasonic measurements are also correlated with hardness and density measurements in addition to microstructural feat ures. As compared to the attenuation measurements, velocity measuremen ts are more reliable and repeatable for microstructural characterisati on of Zircaloy-2. (C) 1998 Elsevier Science B.V. All rights reserved.