STRUCTURE OF SURFACE-WAVE ON COARSE-GRAINED NICKEL OBSERVED BY ACOUSTIC SPECTRO-MICROSCOPY

The surface wave structure is investigated by using acoustic spectro-m icroscopy for various coarse-grained nickel crystals with low symmetry . Experimentally measured angular distributions of the surface wave ve locity are in fairly good agreement with the theoretically calculated ones. Although the measured surface wave velocity dispersions are inde pendent of the ultrasonic frequency within a range from 40 MHz to 140 MHz, the surface wave attenuation has significant dependency. It may b e noted in our methodology that, not only the Rayleigh surface wave ve locity distributions but also the pseudo-surface wave velocity distrib utions can be determined for linking the elastic anisotropy with cryst allographic orientations. A systematic examination through direct meas urement and evaluation of the surface wave structure reveals that the angular dispersion of pseudo-surface wave velocity is more sensitive t o crystallographic orientations than that of Rayleigh surface wave vel ocity.