title: Shape-memory transformations of NiTi: minimum-energy pathways between austenite, martensites, and kinetically limited intermediate states.
abstract: NiTi is the most used shape-memory alloy; nonetheless, a lack of understanding remains regarding the associated structures and transitions, including their barriers. Using a generalized solid-state nudged elastic band method implemented via density-functional theory, we detail the structural transformations in NiTi relevant to shape memory: those between a body-centered orthorhombic (bco) ground state and a newly identified stable austenite ("glassy" B2-like) structure, including energy barriers (hysteresis) and intermediate structures (observed as a kinetically limited R phase), and between martensite variants (bco orientations). All results are in good agreement with available experiment. We contrast the austenite results to those from the often-assumed, but unstable B2. These high- and low-temperature structures and structural transformations provide much needed atomic-scale detail for transitions responsible for NiTi shape-memory effects.
authors.affiliation: The Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011-3020, USA.
authors.forename: N A
authors.initials: NA
authors.lastname: Zarkevich
authors.affiliation: The Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011-3020, USA and Materials Science & Engineering, Iowa State University, Ames, Iowa 50011-2300, USA.
authors.forename: D D
authors.initials: DD
authors.lastname: Johnson