Physical Acoustics and the Properties of Solids

The techniques of physical acoustics have been applied in determining the elastic properties and internal friction of polycrystal and single crystal metals, glasses, nonmetallic crystals, high polymer materials, and ceramics. They have been used as tools in investigating such solid state phenomena as grain and domain boundary effects in metals and ferromagnetic and ferroelectric materials, in the diffusion of atoms, molecules and vacancies through a solid, in the motion of imperfections such as dislocations and have even detected an interaction between the lattice sound vibrations and free electrons in metals at low temperatures. These effects are studied by techniques varying from the vibrations of torsional pendulums at frequencies below 1 cy to frequencies as high as 300 Mc by ultrasonic pulsing methods and have employed strain values from 10−8 to 10−2. Four examples of these techniques are discussed in the present paper. These include diffusions of nitrogen and carbon atoms in iron, the motion of domain walls in ferromagnetic nickel, the interaction of lattice vibrations with free electrons at low temperatures and the use of high strain values in studying internal friction and fatigue in metals. These examples were chosen because they result in definitely explained effects which are indicative of typical processes occurring in solids.