TY - JOUR
T1 - Formation of high-strength β ′ precipitates in Mg-RE alloys
T2 - The role of the Mg/β ″ interfacial instability
AU - Issa, A.
AU - Saal, J. E.
AU - Wolverton, C.
N1 - Funding Information:
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 .
Publisher Copyright:
© 2014 Acta Materialia Inc.
PY - 2015/1/15
Y1 - 2015/1/15
N2 - 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.
AB - 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.
KW - Density functional theory
KW - Interfacial energy
KW - Magnesium alloys
KW - Precipitation strengthening
KW - Rare-earths
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U2 - 10.1016/j.actamat.2014.09.024
DO - 10.1016/j.actamat.2014.09.024
M3 - Article
AN - SCOPUS:84908320299
SN - 1359-6454
VL - 83
SP - 75
EP - 83
JO - Acta Materialia
JF - Acta Materialia
ER -