Contribution of grain boundaries with matching planes to internal friction

Abstract

In nanocrystalline metals, there are grain boundaries that, under the influence of shear stresses applied along them, move along the normal. Such boundaries combine two types of the grain boundary deformation – mutual grain slippage along the boundary and its migration. This relationship is easily explained in the model of intercrystalline boundaries with mating crystallographic planes. By solving the differential equation under the action of alternating voltage, the functional dependence of the boundary displacement on the coordinate and time is found. Based on this, the value of the energy dissipated during the oscillation period and the expression for the internal friction caused by the contribution of such boundaries are found. It has the character of a Debye peak. The activation energy of the process is equal to the activation energy of the grain boundary self-diffusion. An atomic mechanism of the boundary motion is proposed, which is based on diffusion processes between extended steps of atomic scale in the boundary.

Keywords

• grain boundaries
• crystallites
• matching planes
• boundary migration
• diffusion
• vacancies
• relaxation time