Formation of high-strength β′ precipitates in Mg–RE alloys: The role of the Mg/β″ interfacial instability. (15th January 2015)

• Record Type: Journal Article
• Authors: Issa, A.; Saal, J.E.; Wolverton, C.
• Is Part Of: Acta materialia. Volume 83(2015)
• Page Start: 75
• Page End: 83
• Publication Date: 2015-01-15
• Subjects: Magnesium alloys -- Rare-earths -- Precipitation strengthening -- Density functional theory -- Interfacial energy; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2014.09.024
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Aging reactions in Mg–RE alloys strengthen magnesium, due to the formation of metastable β ″ and β ′ precipitates. We use first-principles calculations to critically assess binary Mg–RE (RE = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm and Y) aging reactions, metastable phases and interfacial energy. We find the following. (i) Our calculations correctly predict the formation of different variants of β ′ phases for Mg–RE systems across the RE series. (ii) Surprisingly, the Mg/ β ″ prismatic interfaces are unstable, with a negative interfacial energy. (iii) This interfacial instability implies the existence of a more energetically stable compound than β ″, which we show to be the β ′ precipitate. By exposing the link between Mg/ β ″ prismatic interfaces and the β ′ structure, we propose that β ′ phase formation is due to an energetic preference for an ordered arrangement of Mg and β ″ . (iv) Our Mg/ β ″ interfacial energy results also indicate that atomically thin β ″ planar Guinier–Preston zones can form as a precursor to β ′ precipitation.