Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
10128636 | Materials Characterization | 2018 | 10 Pages |
Abstract
A novel method of producing nanograined Ni-rich superelastic NiTi alloys in sheet form was proposed using a combination of severe plastic deformation via high-ratio differential speed rolling (HRDSR) and post-deformation annealing. The HRDSR-processed microstructure was composed of heavily deformed austenite and martensite grains, and amorphous phases. After annealing at 673â¯K, the severely deformed microstructure with no functional properties evolved to the nanograined structure (20-70â¯nm) composed of austenite and martensite nanograins and sub-nanograins through static recovery or continuous static recrystallization process. The nanograined microstructure had a high resistance to martensitic transformation upon cooling and slip deformation during straining. As a result, the HRDSR-processed alloy annealed at 673K exhibited superior superelasticity compared to the alloys with coarse grains. At the higher annealing temperature of 873â¯K, the micron-sized recrystallized grains with low dislocations developed through discontinuous static recrystallization process. In this case, deformation during straining was governed by the detwinning of twinned martensite, and as a result, shape memory effect was more significantly pronounced than superelasticity.
Keywords
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Physical Sciences and Engineering
Materials Science
Materials Science (General)
Authors
Y.G. Lim, S.H. Han, E. Choi, W.J. Kim,