On the Structure, Transformation and Deformation of Long-Period Stacking Ordered Phases in Mg-Y-Zn Alloys

Nie, Jian Feng; Zhu, Yuman; Morton, A. J.

doi:10.1007/s11661-014-2301-6

Cited by 131 publications

(62 citation statements)

References 42 publications

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“…Type I includes Y, Dy, Ho and Er, and the LPSO phase is reported to form during solidification in these ternary systems 7 . The LPSO phase formed during solidification is generally based on the 18 R -type stacking and it transforms into that based on the 14 H -type stacking upon annealing 4,7,12–14 . On the other hand, type II includes Gd, Tb and Tm, and the LPSO phase of the 14 H -type is reported to form during annealing while it is absent immediately after solidification 5,8 .…”

Section: Introductionmentioning

confidence: 99%

A formation criterion for Order-Disorder (OD) phases of the Long-Period Stacking Order (LPSO)-type in Mg-Al-RE (Rare Earth) Ternary Systems

Kishida

Yokobayashi

Inui

2017

Sci Rep

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The formation of OD (order-disorder) phases of the LPSO (long-period stacking ordered)-type in Mg-Al-RE (RE (rare earth) = Y, La, Ce, Nd, Sm, Dy, Ho, Er and Yb) ternary systems has been investigated for both as-solidified and annealed conditions. The OD phase is found to form in those systems with RE = Y, Nd, Sm, Dy, Ho and Er. The Mg-Al-RE OD phase formed is of the 18R-LPSO-type consisting of 6-layer structural blocks with the RE enrichment occurring in the four consecutive atomic layers in the structural block in the form of the Al6RE8 L12-type atomic clusters. The Mg-Al-RE OD phases are found to be stabilized by the inclusion of any atoms (either Mg, Al or RE) in the central site of the Al6RE8 L12-type atomic cluster. The occupancy ratio of the central site among Mg, Al and RE atoms varies with the RE element, so that the occupancy ratio of RE atoms increases with the increase in the atomic number of the RE element in particular for the late rare-earth elements. Based on the results obtained, a criterion based on the volume of the Al6RE8 atomic cluster is proposed to predict the formation of the Mg-Al-RE OD phases.

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Section: Introductionmentioning

confidence: 99%

A formation criterion for Order-Disorder (OD) phases of the Long-Period Stacking Order (LPSO)-type in Mg-Al-RE (Rare Earth) Ternary Systems

Kishida

Yokobayashi

Inui

2017

Sci Rep

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“…Besides solute pinning on dislocations, the pinning effect of solute atoms on TB has attracted attention recently [37,38]. The coherent twin boundary (CTB) associated with a twin plane is a highly symmetric interface between two crystals, often with one crystal the mirror image of the other.…”

Section: Introductionmentioning

confidence: 99%

First-principles study of energy and atomic solubility of twinning-associated boundaries in hexagonal metals

2015

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Twinning-associated boundaries (TB), f1 0 1 ng coherent twin boundaries (CTB) and the coherent basal-prismatic (CBP) boundary in six hexagonal metals (Cd, Zn, Mg, Zr, Ti and Be) are studied using first-principles density function theory, with the focus on the structural character of TB and the solute's solubility at TB. Regarding the structure and energy of TB, the formation of TB is associated with the creation of an excess volume. All six metals show positive excess volume associated with ð1 0 1 1Þ and ð1 0 1 3Þ CTB, but the excess volume associated with ð1 0 12Þ CTB and CBP can be positive or negative, depending on the metal. The ð1 0 1 2Þ CTB has higher excess energy than ð1 0 1 1Þ and ð1 0 1 3Þ CTB for metals with c=a < ffiffiffiffiffiffiffi ffi 8=3 p , but lower for metals with c=a > ffiffiffiffiffiffiffi ffi 8=3 p . More interestingly, CBP has lower excess energy than ð1 0 1 2Þ CTB for all metals. This is consistent with the recent finding concerning the pure-shuffle nucleation mechanism of ð1 0 1 2Þ twins. To understand solubility at TB, the solubility of solute atoms in Mg, Ti and Zr is calculated for solute positions in bulk, ð1 0 1 2Þ CTB and CBP boundaries. In general, solute atoms have better solubility at CTB and CBP than in bulk. Interestingly, the solubility of solute atoms changes linearly with normal strain at CBP, increasing with normal strain for solute atoms with a greater metallic radius than the matrix, and decreasing with normal strain for solute atoms with a smaller metallic radius than the matrix. This suggests that the distribution of solute atoms in bulk, CTB and CPB boundaries varies with stress state and, in turn, affects the mobility of TB.

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“…It seems that the degree of chemical ordering of the 18R and 14H phases depends on the composition of the alloys and heat treatment conditions. [23] Precipitation hardening is the most effective way to improve alloy strength. In particular, it was found more than fifty years ago that the addition of Ag could considerably increase the age-hardening response and hence mechanical properties of Mg-Nd alloys and this led to the development of the commercial alloy QE22 (Mg-2.5 wt pctAg-2 wt pctNd-0.7 wt pctZr).…”

Section: Introductionmentioning

confidence: 99%

Precipitation in a Ag-Containing Mg-Y-Zn Alloy

Zhu

Oh-ishi

Wilson

et al. 2015

Metall Mater Trans A

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The precipitation in a Mg-6Y-2Ag-1Zn-0.6Zr (wt pct) alloy during isothermal aging at and above 473 K (200°C) has been examined systematically using conventional transmission electron microscopy, high-angle annular dark-field scanning transmission electron microscopy, and three-dimensional atom probe. The precipitation involves the formation of G.P. zones, metastable c¢¢ and c¢ phases, and equilibrium 14H and d phases. The G.P. zones are a single atomic layer on (0001) a . The c¢¢ is the key strengthening phase and it has an ordered hexagonal structure (P6/mmm, a = 0.556 nm, c = 0.424 nm). The c¢¢ forms as (0001) a plates with a thickness of a single unit cell height and tends to develop into stacks with irregular spacing when the alloy is exposed to longer aging time at 473 K (200°C). The c¢¢ is gradually replaced by c¢ and 14H during prolonged aging at 473 K (200°C) and/or temperatures above 473 K (200°C). The equilibrium d phase is also found in grain boundaries. The results are compared with findings in other but similar alloy systems, and approaches for enhancing c¢¢ nucleation rate and hence further improvement in alloy age-hardening response are discussed. The effects of Ag on precipitation are also discussed.

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On the Structure, Transformation and Deformation of Long-Period Stacking Ordered Phases in Mg-Y-Zn Alloys

Cited by 131 publications

References 42 publications

A formation criterion for Order-Disorder (OD) phases of the Long-Period Stacking Order (LPSO)-type in Mg-Al-RE (Rare Earth) Ternary Systems

A formation criterion for Order-Disorder (OD) phases of the Long-Period Stacking Order (LPSO)-type in Mg-Al-RE (Rare Earth) Ternary Systems

First-principles study of energy and atomic solubility of twinning-associated boundaries in hexagonal metals

Precipitation in a Ag-Containing Mg-Y-Zn Alloy

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