In-situ TEM investigation of structural transformation from LEDS to twin in fatigued Cu single crystal during annealing

ABSTRACT

Low-energy dislocation structure is one classical self-organised dislocation pattern, among which persistent slip band (PSB) ladders is the most representative. Periodically distributed PSB ladders consist of two phases: matrix phase and pattern phase. In the new two-phase model, the appearance of pattern phase results in the softening of PSBs with lower elastic constant. The formation of PSB ladders reflects two kinds of dynamic equilibriums: (i) bowing out and annihilation between unlike screw dislocations; (ii) multiplication and annihilation between unlike edge dislocations in the rung. Subsequently, in-situ annealing experiments indicate that most of the dislocations are annihilated and a few dislocations rearrange to result in the nucleation and growth of the twin. In a word, both the evolution of dislocation patterns and the transition from LEDS to twin structures are the process of energy redistribution. Controlling the stored energy per unit area will effectively improve the formation of distribution of defects, which will benefit to design the metallic materials based on the defect-engineering strategy.

KEYWORDS:

• In-situ TEM
• low-energy dislocation structure
• PSB ladders
• annealing twins
• Cu single crystals

Acknowledgements

The authors are grateful to Prof. S. X. Li and Prof. X. W. Li for their good suggestions and advices. Thanks are also due to H. H. Su, Q. Q. Duan, J. L. Wen and G. Yao for their assistance in the fatigue experiments and dislocation observations.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by the Alexander von Humboldt Foundation, the National Natural Science Foundation of China (NSFC) [grant numbers 51001104; 51331007], and the National Basic Research Program of China under Grant No. 2017YFA0700704.