Internal Friction of Metals at Very High Temperatures

Abstract

In connection with the study of the internal friction peak (versus temperature) associated with the viscous behavior of grain boundaries in metals, some other effects were observed at higher temperatures causing an additional internal friction in superposition with the high temperature branch of this internal friction peak. This additional internal friction at high temperatures was found to have its origins in some effects of cold-working introduced in the interior of the grains which remains even after the complete recrystallization of the cold-worked specimens. It increases with the amount of cold-work the specimen was subjected to before and after recrystallization; it decreases with annealing at successively higher temperatures until a stable value is reached; and it increases with the precipitated impurity content in the specimen. This high temperature internal friction was found to be very high in an aged specimen of high purity aluminum alloyed with 4 percent of copper. These observations are consistent with the viewpoint that this internal friction is caused by the presence of dislocations in the interior of the specimen although the mechanism of giving rise to the internal friction is unknown. It is pointed out that a study of high temperature creep under very low stress may be conveniently carried out through the internal friction measurements described.