Structure of surface wave on coarse-grained nickel observed by acoustic spectro-microscopy

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