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Hidden pathway and defect generation during structural phase transformations

Date: 03.05.2016
Time: 1:00 p.m.
Place: ICAMS Advanced Discussions 2016, Bochum, Germany

Yunzhi Wang, Department of Materials Science and Engineering, The Ohio State University, Columbus, USA
Yipeng Gao, The Ohio State University, Columbus, USA

Structural phase transformations, no matter reversible or irreversible, are commonly accompanied by the generation of various types of defects including dislocations and grain boundaries. We show in this work that the types of defects are not only associated with the symmetry of the parent and product crystals, but also dictated by the transformation pathways between the two crystals. In particular, hidden non-phase-transformation pathways (NPTPs) are identified through crystal symmetry analysis in some familiar material systems including steels and NiTi shape memory alloys. Such NPTPs are found to be responsible for defect generation and the defects generated are found to have distinctive characteristics and could be activated at a stress level much lower than the yield stress. Such an intrinsic connection between phase transformation and defect generation provides a rigorous theoretical foundation for fundamental understanding of defect generation during structural phase transformations and for crystallographic design of domain and defect structure engineering through structural phase transformations.

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