Titanium α−ω phase transformation pathway and a predicted metastable structure

As titanium is a highly utilized metal for structural lightweighting, its phases, transformation pathways (transition states), and structures have scientific and industrial importance. Using a proper solid-state nudged elastic band method employing two climbing images combined with density functional theory DFT + U methods for accurate energetics, we detail the pressure-induced α (ductile) to ω (brittle) transformation at the coexistence pressure. We find two transition states along the minimal-enthalpy path and discover a metastable body-centered orthorhombic structure, with stable phonons, a lower density than the end-point phases, and decreasing stability with increasing pressure. Disciplines Condensed Matter Physics | Engineering Physics | Metallurgy Comments This article is from Physical Review B 93 (2016): 020104(R), doi:10.1103/PhysRevB.93.020104. Posted with permission. This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/ameslab_pubs/385 RAPID COMMUNICATIONS PHYSICAL REVIEW B 93, 020104(R) (2016) Titanium α-ω phase transformation pathway and a predicted metastable structure N. A. Zarkevich1,* and D. D. Johnson1,2,† 1Ames Laboratory, US Department of Energy, Ames, Iowa 50011-3020, USA 2Departments of Materials Science & Engineering and Physics, Iowa State University, Ames, Iowa 50011-2300, USA (Received 14 October 2015; revised manuscript received 15 December 2015; published 15 January 2016) As titanium is a highly utilized metal for structural lightweighting, its phases, transformation pathways (transition states), and structures have scientific and industrial importance. Using a proper solid-state nudged elastic band method employing two climbing images combined with density functional theory DFT+U methods for accurate energetics, we detail the pressure-induced α (ductile) to ω (brittle) transformation at the coexistence pressure. We find two transition states along the minimal-enthalpy path and discover a metastable body-centered orthorhombic structure, with stable phonons, a lower density than the end-point phases, and decreasing stability with increasing pressure. DOI: 10.1103/PhysRevB.93.020104