Vacancy-mediated ω-assisted α-phase formation mechanism in titanium–molybdenum alloy. (15th January 2015)

• Record Type: Journal Article
• Authors: Kim, Sung-Hwan; Kang, Sung Jin; Park, Min-Ho; Yang, Cheol-Woong; Lee, Hu-Chul; Han, Heung Nam; Kim, Miyoung
• Is Part Of: Acta materialia. Volume 83(2015)
• Page Start: 499
• Page End: 506
• Publication Date: 2015-01-15
• Subjects: Titanium alloys -- Vacancy ordering -- Phase transformation -- Z-contrast -- Density functional theory; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2014.10.022
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: This study investigates the mechanism of the ω-to-α phase transformation in a titanium–molybdenum alloy. Using aberration-corrected high annular angle dark-field scanning transmission electron microscopy and density functional theory (DFT), the authors demonstrate that the ω-to-α phase transformation is mediated by vacancy ordering. Atomic resolution Z-contrast images display high- and low-contrast regions in a single ω precipitate, and it was found that the low Z-contrast regions are composed of an unknown structure, which differs significantly from the ω-phase crystal structure. DFT calculations show that the vacancies could be stabilized by Mo and should preferably be assembled with ordering. The relaxed ω-phase structure with ordered defects explains the intricate atomic images in the low Z-contrast regions of the ω phase. It was found that this distorted ω phase with defects is similar to the hexagonal α-phase structure with vacancies. It was confirmed that these vacancies could easily be occupied by Ti atoms and could form a perfect α phase.