摘要
The perfect single crystal has ultra-high strength but is often accompanied by catastrophic failures after yielding.This study reveals that nano-lamellar TiAl single crystals alleviate the catastrophic failure due to a post-yielding dislocation retraction through atomistic simulations and theoretical analyses.This dislocation retraction leads to a retained post-yielding strength of1.03 to 2.33 GPa(about 50%of the yielding strength).It is shown that this dislocation retraction is caused by local stress relaxation and interface-mediated image force.The local stress relaxation is due to successive dislocation nucleation in different slip systems,and the interface-mediated image force is caused by the heterogeneous interface.Based on dislocation theory,this study demonstrates that the size effect also plays a vital role in dislocation retraction.Theoretical modeling shows that the dislocation retraction occurs when the lamellar thickness is less than approximately 12 nm.Additionally,the post-yielding dislocation retraction is more pronounced at higher temperatures,making it more effective in alleviating catastrophic failures.These findings demonstrate a viable option for avoiding catastrophic failure of single crystals through nanoscale-lamellar design.
基金
supported by the National Key Research and Development Program of China(Grant No.2019YFA0705400)
the National Natural Science Foundation of China(Grant No.51535005)
the Research Fund of State Key Laboratory of Mechanics and Control of Mechanical Structures(Grant No.MCMS-I-0419K01)
the Fundamental Research Funds for the Central Universities(Grant Nos.NJ2020003,and NZ2020001)
a Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions。