4.7 Article

Mechanical response of dislocation interaction with grain boundary in ultrafine-grained interstitial-free steel

期刊

ACTA MATERIALIA
卷 206, 期 -, 页码 -

出版社

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2021.116621

关键词

Ultrafine-grained interstitial-free steel; TEM in-situ compression test; Dislocation interaction with grain boundary; Dislocation source; Dislocation density

资金

  1. KAKENHI from the Japan Society for the Promotion Science (JSPS) [JP16H06366, JP18H01696]
  2. Elements Strategy Initiative for Structural Materials (ESISM) through the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan [JPMXP01121010 0 0]

向作者/读者索取更多资源

This study investigates the motion of dislocations and their interactions with grain boundaries in ultrafine-grained IF steel under tensile and compressive conditions. Before macro-yielding, dislocations move towards grain boundaries and are absorbed, leading to a decrease in dislocation density; after macro-yielding, dislocations emit from grain boundaries, resulting in hardening effects and discontinuous yielding behavior.
Interstitial-free (IF) steel with ultrafine-grained (UFG) size was used to clarify the underlying mechanisms of the 'extra-hardening' behavior from the Hall-Petch plot and the discontinuous yielding behavior from axial tensile tests. Using transmission electron microscopy (TEM) at different tensile strains, it was found that the TEM micrographs for the bulk sample of the UFG IF steel showed a decrease in dislocation density in the grain interior after experiencing a micro tensile strain of 1.0% before macro-yielding. Additionally, an increase in dislocation density was found in the grain interior, with a micro tensile strain of 15% in the necking region after macro-yielding. In-situ compression tests in a TEM for micropillars were performed to directly observe the motion of dislocations and corresponding interactions with grain boundaries in UFG IF steel. Before macro-yielding, pre-existing dislocations in the grain interior moved toward the grain boundary, wherein they were then absorbed. The dislocation density decreased significantly due to the annihilation, which was accompanied by an increase in load during pre-yielding. The decrease in dislocation density in the grain interior of the micropillar is consistent with the results obtained from the bulk sample. After macro-yielding, the burst-like dislocation emission emerged from the grain boundary, leading to a yield drop and a discontinuous yielding behavior. Furthermore, the higher yield stress and the yield drop in the UFG IF steel can be understood by the decrease in dislocation density according to a combination of the Orowan model as well as the Johnston-Gilman model. (C) 2021 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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