Grain-Boundary Relaxations in Copper-Gold Alloys

Abstract

Strong damping and modulus effects have been observed using a torsional pendulum in very pure, coarse-grained copper, gold, and seven completely miscible copper-gold alloys. In Cu and Au a high-temperature relaxation peak increases with increasing grain size and stabilizes at 470 and 230 degC, respectively, above the orthodox grain-boundary damping peaks. Related damping peaks were also measured in the alloys with activation energies distributed between Cu and Au, decreasing with increasing Au content. All alloys showed stronger relaxation effects than pure Cu and Au, with a maximum at cu3Au. It is suggested that this high-temperature peak results from grain-boundary sliding and that the relaxation time and strength in Cu and Au are controlled by irregularities in the grain boundaries. Adsorption of solute atoms on the alloy boundaries will influence these irregularities and facilitate greater sliding.