First Order Pyramidal Slip of $$1/3\ \langle 1\bar{2}10\rangle $$ 1
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INTRODUCTION
HEXAGONAL close-packed (hcp) Zirconium is an important material for the nuclear industry where it is used as structural component in nuclear reactors. In particular, the cladding of nuclear fuel is made of zirconium alloys. Like most crystalline material, the mechanical behavior is mainly driven by dislocations motion. In a-zirconium, dislocations with Burgers vector ! a ¼ 1=3 ½1 210, named hai dislocations, are the most frequently observed with transmission electron microscopy.[1–3] These dislocations glide principally in prismatic f10 10g planes[2,4,5] due to a lower critical resolved shear stress than in the basal and pyramidal planes.[1,3,6–9] At low temperature, screw components of hai dislocations can be distinguished as long rectilinear segments while mixed and edge components are observed in their equilibrium state as curved lines. This is because screw dislocations have a larger lattice friction opposing their motion and making them less mobile compared to mixed and edge dislocations.[1–3] For this reason, screw dislocations with Burgers vector ! a control the material plasticity at low temperature and are mostly considered in the literature. In addition, experiments show that the ease of glide of hai screw dislocations in the prismatic planes is strongly temperature-dependent and also decreases when the amount of impurities such as oxygen, sulfur, and carbon, increases in the material.[3,5,10–12] At higher temperatures and strain levels, secondary slip systems are activated such as 1=3 h1 213i first order pyramidal slip,[13] which has been evidenced at room temperature as an important glide system to accommodate the crystal deformation along the h0001i direction. Thermal activation also enhances hai dislocation crossslip. Experimental evidence shows that above 300 K NERMINE CHAARI, Ph.D. Student, and EMMANUEL CLOUET, Ph.D. Researcher, are with the CEA, DEN, Service de Recherches de Me´tallurgie physique, Gif-sur-Yvette 91191, France. Contact e-mail: [email protected] DAVID RODNEY, Professor, is with Institut Lumie`re Matie`re, Universite´ Lyon 1, CNRS, UMR 5306, Villeurbanne 69622, France. Manuscript submitted March 31, 2014. Article published online September 30, 2014 5898—VOLUME 45A, DECEMBER 2014
(573 C), screw dislocations with Burgers vector ! a ¼ 1=3 ½1210 initially gliding in the prismatic planes, may leave their habit plane to glide in a first order pyramidal f1011g plane (p1 ),[3,10,14] or less frequently in a basal f0001g plane.[6,15–17] Screw hai dislocations cross-slip is more frequently observed with increasing impurity content, especially with oxygen, while the hardening effect due to impurities manifests itself on the prismatic glide,[3,5,10,11] as mentioned above. The same dislocation behavior has also been evidenced in titanium,[18–23] a transition metal with similar properties to zirconium. In agreement with the experiments, atomistic simulations have established that, in pure zirconium, a screw dislocation with Burgers vector ! a dissociates spontaneously in the
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