Theory of Ultrasonic Backscatter From Multiphase Polycrystalline Solids
Ultrasound scatters from the microscopic single crystals that constitute polycrystalline solids. The scattering originates from crystallite-crystallite variations in the density and elastic constants. For single-phase materials, each crystallite has the same density and the same crystalline symmetry. Hence, in single-phase materials scattering arises from the variation in velocity, which in turn is due to the anisotropy of the elastic constants and the more or less random orientation of the crystallites [1,2]. The situation is considerably more complicated in multiphase alloys where the density, the crystal symmetry and the elastic constants vary from crystallite to crystallite.