SAM STUDY ON PLASMA-SPRAYED CERAMIC COATINGS

Scanning acoustic microscopy (SAM) is a relatively new non-destructive technique, which uses sound to create visual images of variations in the mechanical properties of samples that may be opaque optically. A 1 50 MHz reflection type SAM was used to detect the defects of thermally sprayed ceramic coatings in the present paper. It is found that the p orosity-type defects in the coatings can be detected nondestructively. The defects are revealed as the white regions, and the substrates as the gray region in SAM images. The features of each white region corre sponding to various defects are different too. Four types of arrangeme nt patterns of the white regions are concluded based on many observati ons. The contrast mechanism of defects in SAM images are illustrated b y calculating the reflection coefficient at the interface of the air a nd the coating matrix.