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The Influence of the R-Phase on the Superelastic Behavior of NiTi

Duerig, T. W. and Bhattacharya, K. (2015) The Influence of the R-Phase on the Superelastic Behavior of NiTi. Shape Memory and Superelasticity, 1 (2). pp. 153-161. ISSN 2199-384X.

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Approximately equiatomic Ni–Ti alloys, or Nitinol, can transform upon cooling or when stressed from a parent ordered cubic (B2) Austenite phase into two martensitic structures: a monoclinic structure commonly referred to as simply martensite and a rhombohedrally distorted martensite referred to as the R-phase. While the former is often more stable, the R-phase presents a substantially lower barrier to formation, creating an interesting competition for the succession of Austenite. This competition has markedly different outcomes depending upon whether Austenite instability is caused by cooling or by the application of stress. While medical applications are generally used isothermally, most characterization is done using thermal scans such as differential scanning calorimetry. This leads to frequent and significant misunderstandings regarding plateau stresses in particular. The purpose of this paper is to discuss the competition between these two martensites as the parent Austenite phase loses stability, and to clarify how tests can be properly conducted and interpreted to avoid confusion. To that end, the examples shown are not selected to be ideal or theoretical, but rather to illustrate complexities typical of those found in medical devices, such as cold worked conditions that make peaks difficult to interpret and “plateaus” ill-defined. Finally, a stress-induced M ⇒ R ⇒ M sequence will be discussed.

Item Type:Article
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Bhattacharya, K.0000-0003-2908-5469
Additional Information:© 2015 ASM International. First Online: 16 May 2015.
Subject Keywords:Martensite; NiTi materials; Mechanical behavior; Pseudoelasticity; Superelasticity; Transformation temperature
Issue or Number:2
Record Number:CaltechAUTHORS:20170616-104220103
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Official Citation:Duerig, T.W. & Bhattacharya, K. Shap. Mem. Superelasticity (2015) 1: 153. doi:10.1007/s40830-015-0013-4
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:78275
Deposited By: Tony Diaz
Deposited On:16 Jun 2017 19:12
Last Modified:03 Oct 2019 18:07

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