Abstract
Vacancy-mediated climb models cannot account for the fast, direct coalescence of dislocation loops seen experimentally. An alternative mechanism, self climb, allows prismatic dislocation loops to move away from their glide surface via pipe diffusion around the loop perimeter, independent of any vacancy atmosphere. Despite the known importance of self climb, theoretical models require a typically unknown activation energy, hindering implementation in materials modeling. Here, extensive molecular statics calculations of pipe diffusion processes around irregular prismatic loops are used to map the energy landscape for self climb in iron and tungsten, finding a simple, material independent energy model after normalizing by the vacancy migration barrier. Kinetic Monte Carlo simulations yield a self climb activation energy of 2 (2.5) times the vacancy migration barrier for 1/2〈111〉 (〈100〉) dislocation loops. Dislocation dynamics simulations allowing self climb and glide show quantitative agreement with transmission electron microscopy observations of climbing prismatic loops in iron and tungsten, confirming that this novel form of vacancy-free climb is many orders of magnitude faster than what is predicted by traditional climb models. Self climb significantly influences the coarsening rate of defect networks, with important implications for post-irradiation annealing.
Highlights
Dislocation glide dominates plastic flow at low homologous temperatures, but confinement to a glide surface significantly restricts the evolution of a defect network[1]
An alternative ‘self climb’ model was proposed to account for these puzzling observations[5,10,12,13,14], where loops are able to migrate in their habit plane due to the diffusion of self interstitial atoms (SIA) around the loop perimeter, 1CCFE, Culham Science Centre, Abingdon, Oxon, OX14 3DB, UK. 2Department of Materials Science, Faculty of Science and Engineering, Shimane University, 1060 Nishikawatsu, Matsue 690-8504, Japan. 3Research Center for UltraHigh Voltage Electron Microscopy, Osaka University, 7-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan. 4Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, 2-2-1 Katahira, Aoba-ku, Sendai 980-8577, Japan
We have derived and calculated a quantitative mobility law for self climb, by mapping out the energy landscape for pipe diffusion around a large number of randomly shaped prismatic dislocation loops in two different bcc metals which can be explored in kinetic Monte Carlo simulations
Summary
Dislocation glide dominates plastic flow at low homologous temperatures, but confinement to a glide surface significantly restricts the evolution of a defect network[1]. Dislocation climb, which requires concurrent mass transport, is typically much slower than glide but allows migration off the glide surface, giving rise to a wide range of important plasticity mechanisms including network coarsening[2,3] and creep[4]. VMC is controlled by the large mechanisms are only expected to be active at high homologous temperatures[4]. It has long been recognized[5,6,7,9,10] that prismatic loops can migrate away from their glide cylinder, with no observable change in size, driving loop coalescence. An alternative ‘self climb’ model was proposed to account for these puzzling observations[5,10,12,13,14], where loops are able to migrate in their habit plane due to the diffusion of self interstitial atoms (SIA) around the loop perimeter, www.nature.com/scientificreports/
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