Study on the Change Law of Transverse Ultrasonic Velocity in a High Temperature Material

ABSTRACT The propagation velocity of a transverse ultrasonic wave is influenced by the temperature of the testing materials. In other words, it directly affects the accuracy of thickness measurement and flaw detection as well as the validity of the focal law during the high-temperature ultrasonic inspection. For the above reasons, an electromagnetic acoustic transducer (EMAT) was adopted in this study to measure the transverse ultrasonic velocities of several metallic specimens when heated to the temperatures of the order of 700°C. EMAT was particularly favored for use in this study owing to its non-contact and couplant-free characteristics. The reliability of the collected data and experimental stability were verified via the establishment of a high-temperature experimental system as well as analysis of the measurement error and uncertainty. By comparing ferromagnetic and non-ferromagnetic materials using this system, it can be found that the transverse ultrasonic velocity of ferromagnetic materials decreases in a nonlinear “step-like” manner with the temperature. Therefore, results obtained from this study indicates that the velocity–temperature relationship of different materials does not follow the same law. Besides, the curves tested in this study can serve as a ready references to facilitate nondestructive inspections of materials at high temperatures.