On the structure and role of βF′ in β1 precipitation in Mg–Nd alloys. (July 2017)

• Record Type: Journal Article
• Authors: Liu, H.; Zhu, Y.M.; Wilson, N.C.; Nie, J.F.
• Is Part Of: Acta materialia. Volume 133(2017)
• Page Start: 408
• Page End: 426
• Publication Date: 2017-07
• Subjects: Magnesium alloys -- Precipitate -- HAADF-STEM -- DFT -- Phase field simulation; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2017.03.065
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: The crystal structure and atomic coordinates of β F ′ in aged samples of a Mg–3wt.%Nd alloy are examined using high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and the first-principles density functional theory (DFT). It is found that the lattice parameters and the atomic positions in the orthorhombic β F ′ unit cell deviate from the atomic model that has been generally accepted. The newly proposed β F ′ structure is similar to that of β1 which also forms in the alloy, and a simple atomic replacement and structural relaxation can transform the structure of β F ′ to that of β1 . A specific variant of the β F ′ phase is often observed to be attached to the end of a β1 precipitate after ageing for longer time. The stress field analysis and interaction energy calculations indicate that this attachment can reduce the stress field around the end facet of the β1 precipitate and may influence β1 lengthening. DFT computation results suggest that the β F ′ phase is more stable than β′, but less stable than β1, in the Mg–Nd system, and this finding is extendable to other Mg–RE (where RE represents rare earth elements) systems such as Mg–La, Mg–Ce, Mg–Pr, Mg–Pm, Mg–Sm and Mg–Eu alloys. Graphical abstract: Image