The background internal friction of cold-worked iron single crystals

Abstract

The internal friction of cold-worked α-iron single crystals with solute nitrogen was measured by a flexure mode of some hundreds Hz. The magnitude of the background internal friction above the Snoek peak temperature is found to depend on a crystallographic orientation. This orientation dependence agrees with that of the Snoek peak, and the magnitude of the internal friction seems to increase with nitrogen content and with the degree of cold-work. Comparing this result with low frequency experiments, this internal friction can be attributed to relaxation. It is thought that the background internal friction is a superposition of Snoek type relaxations, caused by solute nitrogen near screw dislocations. Solute nitrogen near a dislocation interacts elastically with it according to G. Schoeck and M. Mondino. Nitrogen atoms in such a region diffuse with larger activation energy than in a dislocation free matrix, and the activation energy decreases with a distance from a dislocation. So there is possibility of appearance of many Snoek peaks with different peak temperature. Assuming a reasonable value of binding energy between nitrogen and a dislocation, it could be verified that these Snoek peaks were superposed and made the background internal friction.