Journal
INTERNATIONAL JOURNAL OF SOLIDS AND STRUCTURES
Volume 221, Issue -, Pages 31-41Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.ijsolstr.2020.02.027
Keywords
Energy partition; Phase transition at nano-scale; Shape memory alloys; Grain size effects; Molecular dynamics simulation
Categories
Funding
- National Natural Science Foundation of China [11532010, 11772236]
- RGC of Hong Kong SAR (GRF) [16215218]
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As the grain size decreases, fundamental changes in phase transition behavior of nanocrystalline NiTi shape memory alloys occur, characterized by a transition from atomic interface friction in phase transition to plastic deformation caused by grain boundary sliding.
Nanocrystalline NiTi shape memory alloys show fundamental changes in phase transition behavior when the grain size is reduced down to nano-scale (grain size <30 nm). However, due to the extreme difficulties of in-situ experimental observation, universally acknowledged physical mechanisms and detailed microstructures at atomic level are still not clear. In this paper, detailed microstructure images and quantified energy partition at atomic level during stress-induced phase transition are obtained by molecular dynamics simulation. Phase transition is gradually suppressed and incomplete phase transition occurs as grain size decreases. The potential energy landscape of the nanocrystalline system changes significantly from nonconvex to convex, which leads to corresponding changes in stress-strain response and microstructural evolution. With decreasing grain size, the interface (grain boundary and phase boundary) energy makes much more contributions in variation of the system potential energy than the crystallite (austenite and martensite) energy. The mechanism of energy dissipation changes from atomic interface friction in phase transition to plastic deformation caused by grain boundary sliding. It is the gradual dominance of interfacial energy terms in total potential energy that leads to the observed fundamental changes of phase transition behavior in nanocrystalline NiTi. (C) 2020 Elsevier Ltd. All rights reserved.
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