Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 118, Issue 37, Pages -Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.2110596118
Keywords
brittle; ductile; dislocation; mobility
Categories
Funding
- Xi'an Jiaotong University
- National Natural Science Foundation of China [51971170, 51922082]
- 111 Project of China [BP2018008]
- Innovation Project of Shaanxi Province [2017KTPT-12]
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Body-centered cubic metals exhibit a ductile-to-brittle transition at a critical temperature, controlled by the ratio of screw dislocation velocity to edge dislocation velocity. A physical model shows the importance of coordinated movement of screw and edge dislocation segments for sustaining dislocation multiplication. High relative mobility is crucial for the transition of dislocation sources from disposable to regeneratable ones.
Body-centered cubic metals including steels and refractory metals suffer from an abrupt ductile-to-brittle transition (DBT) at a critical temperature, hampering their performance and applications. Temperature-dependent dislocation mobility and dislocation nucleation have been proposed as the potential factors responsible for the DBT. However, the origin of this sudden switch from toughness to brittleness still remains a mystery. Here, we discover that the ratio of screw dislocation velocity to edge dislocation velocity is a controlling factor responsible for the DBT. A physical model was conceived to correlate the efficiency of Frank-Read dislocation source with the relative mobility of screw versus edge dislocations. A sufficiently high relative mobility is a prerequisite for the coordinated movement of screw and edge segments to sustain dislocation multiplication. Nanoindentation experiments found that DBT in chromium requires a critical mobility ratio of 0.7, above which the dislocation sources transition from disposable to regeneratable ones. The proposed model is also supported by the experimental results of iron, tungsten, and aluminum.
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