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.
Original language | English (US) |
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Pages (from-to) | 75-83 |
Number of pages | 9 |
Journal | Acta Materialia |
Volume | 83 |
DOIs | |
State | Published - Jan 15 2015 |
Funding
We gratefully acknowledge the support of the Ford–Boeing–Northwestern (FBN) alliance, award No. 81132882 . J.E.S. acknowledges support by the US Department of Energy, Office of Basic Energy Sciences through grant DE-FG02-98ER45721 .
Keywords
- Density functional theory
- Interfacial energy
- Magnesium alloys
- Precipitation strengthening
- Rare-earths
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Polymers and Plastics
- Metals and Alloys