Ultrasonic Attenuation in Hot Specimens by the Momentary Contact Method with Pressure Coupling

Abstract

The momentary contact method previously used for ultrasonic velocity measurements and flaw detection in hot specimens has been extended to the measurement of ultrasonic attenuation. In this method, a cool buffer rod is brought into contact with the hot specimen for a few milliseconds. A transducer on the cool end of the buffer rod transmits an ultrasonic pulse down the buffer rod and receives the echoes from the buffer/specimen interface and from the multiple reflections within the specimen. From the first three returning echoes, the attenuation in the specimen and the interface reflection coefficient are computed. Acoustic coupling at the interface is brought about by pressure alone for both longitudinal and shear waves without any bonding agent. The utility of the method is illustrated by measurements on SAE 52100 alloy steel in which the curie temperature was detected by a peak in attenuation in the ferromagnetic region followed immediately by a dip in attenuation in the paramagnetic region. At higher temperatures, grain growth is detected. [This work was supported by the Office of Naval Research, Code 468.]