Ultrasonic attenuation in plasma-sprayed coating materials

Measurements have been made of the attenuation in thin samples of plasma-sprayed molybdenum, nickel aluminide and aluminium coating materials in the frequency range 2.5 to 15 MHz. It has been found that attenuation is dependent on the structure of the coatings and in particular on porosity. Interference effects in such thin samples are shown to be unimportant because of their high attenuations. An analysis of ultrasonic attenuation through thin samples is presented.