Mechanism of hardening and damage initiation in oxygen embrittlement of body-centred-cubic niobium

PJ Yang and QJ Li and T Tsuru and S Ogata and JW Zhang and HW Sheng and ZW Shan and G Sha and WZ Han and J Li and E Ma, ACTA MATERIALIA, 168, 331-342 (2019).

DOI: 10.1016/j.actamat.2019.02.030

Body-centred-cubic metallic materials, such as niobium (Nb) and other refractory metals, are prone to embrittlement due to low levels of oxygen solutes. The mechanisms responsible for the oxygen-induced rampant hardening and damage are unclear. Here we illustrate that screw dislocations moving through a random repulsive force field imposed by impurity oxygen interstitials readily form cross-kinks and emit excess vacancies in Nb. The vacancies bind strongly with oxygen and screw dislocation in a three-body fashion, rendering dislocation motion difficult and hence pronounced dislocation storage and hardening. While self-interstitials anneal out fast during plastic flow, the vacancy- oxygen complexes are stable against passing dislocations. The debris in fact amplify the random force field, facilitating the generation of even more defects in a self-reinforcing loop. This leads to unusually high strain hardening rates and fast breeding of nano-cavities that underlie damage and failure. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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