Mobility of 〈c+a〉 dislocations in zirconium

Abstract

Plasticity in hexagonal close-packed zirconium is mainly controlled by the glide of dislocations with 1/3 1210 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 1213 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.

Machine learning for metallurgy V: A neural-network potential for zirconium

“…The experimental consensus is that ⟨c + a⟩ glide occurs along the pyramidal I-w plane [73][74][75][76][77][78][79] and not the pyramidal II plane. Only Long et al [78] observed a dislocation with pyramidal II glide, but this result is suspected to be due to the presence of Nb [79]. The NNP4 predicts a stable ⟨c + a⟩ screw dislocation on the pyramidal I-w plane.…”

Atomistically informed dislocation dynamics simulations: application to dislocation-loop interactions in zirconium

“…From experimental investigations, it is known that these loops have a ⟨a⟩ = 1/3 ⟨1 1 2 0⟩ Burgers vector and are located close to the prismatic habit planes of the hexagonal close packed (HCP) structure [4][5][6][7][8][9]. Furthermore, it is experimentally assessed that easy dislocation glide occurs on the prismatic slip systems [10][11][12][13][14][15], basal and ⟨c + a⟩ pyramidal being the main secondary slip systems [13,[15][16][17]. The change of mechanical properties after irradiation is essentially the result of the interactions between gliding dislocations and these numerous loops, which act as obstacles against dislocation glide.…”