Mobility of <c+a> dislocations in zirconium

TL;DR

This study investigates the glide behavior of <c+a> dislocations in zirconium, revealing their exclusive glide in pyramidal planes, the influence of lattice friction, and the effects of solute atoms, through in situ TEM experiments.

Contribution

It provides new insights into <c+a> dislocation glide mechanisms and the role of lattice friction and solutes in zirconium, which were previously not well understood.

Findings

<c+a> dislocations glide in pyramidal planes with cross-slip.

Lattice friction strongly opposes <c+a> dislocation glide along <a> directions.

Solute atoms contribute to lattice friction effects.

Abstract

Plasticity in hexagonal close-packed zirconium is mainly controlled by the glide of dislocations with 1/3<1-210> Burgers vectors. As these dislocations cannot accommodate deformation in the [0001] direction , twinning or glide of <c+a> dislocations, i.e. dislocations with 1/3<1-213> Burgers vector, have to be activated. We have performed in situ straining experiments in a transmission electron microscope to study the glide of <c+a> dislocations in two different zirconium samples, pure zirconium and Zircaloy-4, at room temperature. These experiments show that <c+a> dislocations exclusively glide in first-order pyramidal planes with cross-slip being activated. A much stronger lattice friction is opposing the glide of <c+a> dislocations when their orientation corresponds to the <a> direction defined by the intersection of their glide plane with the basal plane. This results in long dislocations straightened along <a> which glide either viscously or jerkily. This <a> direction governs the motion of segments with other orientations, whose shape is merely driven by the minimization of the line tension. The friction due to solute atoms is also discussed.