Although at first nothing appears wrong with the idea, and the metal crystal will come out of the ultrasound in one piece, it can immediately be trashed after this treatment. The ultrasound couples into the crystal lattice and tends to induce polycrystallinity in the surface region of the crystal. The degree to which this occurs depends on the material and the details of the ultrasound treatment. Once the polycrystalline region is formed, annealing it will lead to a further recrystallization in the surface region.