Thermomechanical properties of Ni-Ti shape memory wires containing nanoscale precipitates induced by stress-assisted ageing.

Cong,DY, Saha,G and Barnett,MR 2014, Thermomechanical properties of Ni-Ti shape memory wires containing nanoscale precipitates induced by stress-assisted ageing., Acta Biomaterialia, vol. 10, no. 12, pp. 5178-5192, doi: 10.1016/j.actbio.2014.08.017.

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Title Thermomechanical properties of Ni-Ti shape memory wires containing nanoscale precipitates induced by stress-assisted ageing.
Author(s) Cong,DY
Barnett,MRORCID iD for Barnett,MR
Journal name Acta Biomaterialia
Volume number 10
Issue number 12
Start page 5178
End page 5192
Publisher Elsevier
Place of publication England
Publication date 2014-12
ISSN 1878-7568
Keyword(s) Phase transformation
Shape memory alloys
Thermomechanical properties
Twin boundary movement
Science & Technology
Engineering, Biomedical
Materials Science, Biomaterials
Materials Science
Summary This paper systematically examines the thermomechanical properties and phase transformation behaviour of slightly Ni-rich Ni-Ti biomedical shape memory wires containing homogeneously distributed nanoscale precipitates induced by stress-assisted ageing. In contrast to previous studies, particular attention is paid to the role of precipitates in impeding twin boundary movement (TBM) and its underlying mechanisms. The size and volume fraction of precipitates are altered by changing the ageing time. The martensitic transformation temperatures increase with prolonged ageing time, whereas the R-phase transformation temperature remains relatively unchanged. The stress-strain behaviour in different phase regions during both cooling and heating is comprehensively examined, and the underlying mechanisms for the temperature- and thermal-history-dependent behaviour are elucidated with the help of the established stress-temperature phase diagram. The effect of precipitates on TBM is explored by mechanical testing at 133K. It is revealed that the critical stress for TBM (σcr) increases with increasing ageing time. There is a considerable increase of 104MPa in σcr in the sample aged at 773K for 120min under 70MPa compared with the solution-treated sample, owing to the presence of precipitates. The Orowan strengthening model of twinning dislocations is insufficient to account for this increase in σcr. The back stress generation is the predominant mechanism for the interactions between precipitates and twin boundaries during TBM that give rise to the increase in σcr. Such results provide new insights into the thermomechanical properties of precipitate containing Ni-Ti biomedical shape memory wires, which are instructive for developing high-performance biomedical shape memory alloys.
Language eng
DOI 10.1016/j.actbio.2014.08.017
Field of Research 091205 Functional Materials
Socio Economic Objective 861299 Fabricated Metal Products not elsewhere classified
HERDC Research category C1 Refereed article in a scholarly journal
ERA Research output type C Journal article
Copyright notice ©2014, Elsevier
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Document type: Journal Article
Collections: Institute for Frontier Materials
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