Effect of Dislocations on Ultrasonic Wave Attenuation in Metals

T h e present paper is a chapter of a new book entitled " U l t r a sonics in Solids", which is scheduled for publication by D. Van Nostrand in 1956. 903 904 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1955 from one position to another. This energy is somewhat less than the bulk diffusion energy on account of the strains in the grain boundary. Highly worked metals show two other effects due to dislocations, called the Roster effect and the viscosity effect. It appears that these are due to zig zag dislocations which do not lie in minimum energy positions. In the course of time free dislocations become pinned and the Koster effect disappears. INTRODUCTION Metals are used very considerably in conducting sound waves in such applications as mechanical filters, reed relays, low frequency delay lines, and ultrasonic processing devices. In all of these devices, the energy loss and the stability of the elastic properties of the metals are of prime importance. The causes of energy losses and instabilities in all solid materials are associated with the molecular motions that can take place under thermal agitation and under the stresses that are applied to the materials. For metals, most of the irreversible processes have been interpreted in terms of a type of imperfection known as a dislocation. While it is not within the scope of this book to discuss dislocation theory in detail,1 a short introduction is given in order to provide a background for the ultrasonic measurements discussed in this chapter.