He Yang, Li Bin, Wang Chongmin, Mao Scott X
Department of Mechanical Engineering and Materials Science, University of Pittsburgh, Pittsburgh, PA, 15261, USA.
Department of Chemical and Materials Engineering, University of Nevada, Reno, NV, 89557, USA.
Nat Commun. 2020 May 18;11(1):2483. doi: 10.1038/s41467-020-16351-0.
Design and processing of advanced lightweight structural alloys based on magnesium and titanium rely critically on a control over twinning that remains elusive to date and is dependent on an explicit understanding on the twinning nucleation mechanism in hexagonal close-packed (HCP) crystals. Here, by using in-situ high resolution transmission electron microscopy, we directly show a dual-step twinning nucleation mechanism in HCP rhenium nanocrystals. We find that nucleation of the predominant {1 0 -1 2} twinning is initiated by disconnections on the Prismatic│Basal interfaces which establish the lattice correspondence of the twin with a minor deviation from the ideal orientation. Subsequently, the minor deviation is corrected by the formation of coherent twin boundaries through rearrangement of the disconnections on the Prismatic│Basal interface; thereafter, the coherent twin boundaries propagate by twinning dislocations. The findings provide high-resolution direct evidence of the twinning nucleation mechanism in HCP crystals.
基于镁和钛的先进轻质结构合金的设计与加工，关键依赖于对孪晶的控制，而迄今为止这一控制仍难以实现，并且这取决于对六方密排（HCP）晶体中孪晶成核机制的明确理解。在此，通过使用原位高分辨率透射电子显微镜，我们直接展示了HCP铼纳米晶体中的双步孪晶成核机制。我们发现，主要的{1 0 -1 2}孪晶的成核是由棱柱面│基面界面上的位错断开引发的，这些位错断开建立了孪晶与理想取向稍有偏差的晶格对应关系。随后，通过棱柱面│基面界面上的位错断开重排形成共格孪晶界来校正微小偏差；此后，共格孪晶界通过孪晶位错传播。这些发现为HCP晶体中的孪晶成核机制提供了高分辨率的直接证据。
