Ultrasonic Attenuation and Velocity in Hot Specimens by the Momentary Contact Method with Pressure Coupling, and Some Results on Steel to 1200°C

The momentary contact pulse-echo method with pressure coupling has been extended to the measurement of ultrasonic attenuation in hot specimens. Previously, only velocity was measured. In the present method, the specimen is contacted momentarily by one end of a cool buffer rod about three times as long as the specimen. A piezoelectric transducer on the other end of the buffer rod transmits an ultrasonic signal and receives echoes from the buffer/specimen interface and from the free end of the specimen. The echoes are displayed on an oscilloscope and recorded by a camera. Three echoes are required to define both the attenuation coefficient in the specimen and the reflection coefficient at the buffer/specimen interface. Our results in steel show that the solution and precipitation of carbides affect the velocity drastically, while the attenuation is affected by at least one of the following: (1) magnetism, (2) recrystallization, or (3) carbon solubility, and also by grain growth at elevated temperatures.