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

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 throu...

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Bibliographic Details
Published in:Acta materialia 2019-04, Vol.168 (C), p.331-342
Main Authors: Yang, Ping-Jiong, Li, Qing-Jie, Tsuru, Tomohito, Ogata, Shigenobu, Zhang, Jie-Wen, Sheng, Hong-Wei, Shan, Zhi-Wei, Sha, Gang, Han, Wei-Zhong, Li, Ju, Ma, Evan
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Language:English
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Summary: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. [Display omitted]
ISSN:1359-6454
1873-2453
DOI:10.1016/j.actamat.2019.02.030