Post-yielding dislocation retraction of nano-lamellar TiAl single crystals

HG Xiang and WL Guo, SCIENCE CHINA-PHYSICS MECHANICS & ASTRONOMY, 64, 264611 (2021).

DOI: 10.1007/s11433-021-1697-2

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 of 1.03 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.

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