Phase stability and transformations in NiTi from density functional theory calculations

Karthik Guda Vishnu, Purdue University - Main Campus
Alejandro Strachan, Purdue University - Main Campus

Date of this Version

2-2010

Citation

DOI: 10.1016/j.actamat.2009.09.019

This document has been peer-reviewed.

 

Abstract

We used density functional theory to characterize various crystalline phases of NiTi alloys: (i) high-temperature austenite phase B2; (ii) orthorhombic B19; (iii) the monoclinic martensite phase B19'; and (iv) a body-centered orthorhombic phase (BCO), theoretically predicted to be the ground state. We also investigated possible transition pathways between the various phases and the energetics involved. We found B19 to be metastable with a 1 meV energy barrier separating it from B19. Interestingly, we predicted a new phase of NiTi, denoted B19 '', that is involved in the transition between B19' and BCO. B19 '' is monoclinic and can exhibit shape memory; furthermore, its presence reduces the internal stress required to stabilize the experimentally observed B19' structure, and it consequently plays a key role in NiTi's properties.

Discipline(s)

Engineering | Nanoscience and Nanotechnology

 

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