The random distribution of crystallographic directions in coarse-grained alloys affects ultrasonic testing by increasing which phenomenon?

• A. Acoustic noise levels
• B. Scattering of sound
• C. Attenuation
• D. All of the above

Answer: (D)

When grains are randomly oriented in a coarse-grained alloy, the ultrasonic wave encounters many impedance mismatches at grain boundaries, turning the beam into multiple scattered components. This scattering disrupts the coherent signal along the path, increasing the background fluctuations and thus acoustic noise in the received signal. The energy that is scattered away from the main path also contributes to higher attenuation, since more energy is lost from the direct wave and can be absorbed or dissipated at boundaries. Because random grain orientations amplify both scattering and the energy loss, all of these effects rise together. So the phenomenon increased is all of the above.