Structural studies of stacking variants in Mg-base Friauf–Laves phases

Komura, Y.; Tokunaga, Katsushi

doi:10.1107/s0567740880006565

Cited by 206 publications

(93 citation statements)

References 6 publications

(11 reference statements)

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“…[64] Another hexagonal structure (a = 0.556 nm, c = 0.521 nm) was also reported for b 0 1 , [59] but it has not been confirmed so far. The orientation relationships for these two precipitate phases are that 0001…”

Section: Phase Equilibria and Precipitationmentioning

confidence: 95%

Precipitation and Hardening in Magnesium Alloys

Nie

2012

Metall Mater Trans A

1,354

519

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Magnesium alloys have received an increasing interest in the past 12 years for potential applications in the automotive, aircraft, aerospace, and electronic industries. Many of these alloys are strong because of solid-state precipitates that are produced by an age-hardening process. Although some strength improvements of existing magnesium alloys have been made and some novel alloys with improved strength have been developed, the strength level that has been achieved so far is still substantially lower than that obtained in counterpart aluminum alloys. Further improvements in the alloy strength require a better understanding of the structure, morphology, orientation of precipitates, effects of precipitate morphology, and orientation on the strengthening and microstructural factors that are important in controlling the nucleation and growth of these precipitates. In this review, precipitation in most precipitation-hardenable magnesium alloys is reviewed, and its relationship with strengthening is examined. It is demonstrated that the precipitation phenomena in these alloys, especially in the very early stage of the precipitation process, are still far from being well understood, and many fundamental issues remain unsolved even after some extensive and concerted efforts made in the past 12 years. The challenges associated with precipitation hardening and age hardening are identified and discussed, and guidelines are outlined for the rational design and development of higher strength, and ultimately ultrahigh strength, magnesium alloys via precipitation hardening.

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Section: Phase Equilibria and Precipitationmentioning

confidence: 95%

Precipitation and Hardening in Magnesium Alloys

Nie

2012

Metall Mater Trans A

1,354

519

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“…The crystal structure of Eu2Ga3Ir adopts Mg 2 Cu 3 Si type [1] realizing an ordered variant of the hexagonal Laves phase MgZn 2 [2][3][4]. Europium atoms occupy positions of Mg species (4f), gallium and iridium are located in the 6h and 2a sites, respectively.…”

Section: Discussionmentioning

confidence: 99%

Crystal structure of dieuropium trigallium iridium, Eu2Ga3Ir

Sichevych

Prots

Schnelle

et al. 2006

Zeitschrift Für Kristallographie - New Crystal Structures

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Source of materialStarting materials for the preparation (total sample mass 1 g) were ingots of europium (Hunan Institute of Rare Earth Metal Materials, 99.9 %), gallium lumps (Chempur, 99.999 %) and iridium foil (Lamprecht, 99.9 %). Europium was redistilled in vacuum before using. The elemental components were mixed in stoichiometric ratio and sealed into a tantalum tube under an argon pressure of about 800 mbar. The tantalum tube was subsequently closed in a silica ampule to prevent oxidation of tantalum at high temperatures. The synthesis was performed by slow heating of the reaction mixture to 900°C, annealing for 48 h, lowering the temperature (2 K/h) to 600°C, annealing for 2 weeks and quenching in cold water. A platelet-like single crystal was mechanically extracted from annealed sample with stoichiometric composition. Experimental detailsLattice parameters were obtained by least-squares fitting of 29 reflections extracted from X-ray powder diffraction Guinier data using CoK a1 radiation (l = 1.788965 Å) and LaB 6 as the internal standard (a = 4.15692 Å). ) [6,7]. Similar close EuEu contacts also were observed in the isotypic europium indides EuIn 1.28 Pd 0.72 and EuIn 1.44 Pt 0.56 [8]. The gallium and iridium species form rows of face-and corner-sharing tetrahedra along the c axis. The distances within these tetrahedra of d(IrGa) = 2.676(2) Å and d(GaGa) = 2.707(4) Å are considerably shorter as GaGa interactions between the chains of 2.972(4) Å, so that we suggest an one-dimensional character of [IrGa] polyanion in the Eu 2 Ga 3 Ir structure, contrary to the usual interpretation of the Laves phases. In the early work [9], it was shown that, additionally to the size effect in the Laves phases, a low valence electron concentration (VEC) stabilizes the formation of the alloys with cubic MgCu 2 (C15) structure [10], the alloys with the high electron concentration crystallize with the hexagonal MgZn 2 atomic arrangement (C14). This agrees very well for the pseudobinary EuIr 2EuGa2 system. Whereas the binary EuIr 2 compound ([11], low VEC) adopts the MgCu 2 structure, Eu2Ga3Ir (higher VEC) crystallizes in the hexagonal C14 type. At the temperatures 90 K < T < 400 K, the susceptibility (m 0(H) = 1 T) follows a Curie-Weiss law with an effective magnetic moment m eff = 8.18 m B /Eu-atom and Qp = +3.6(1) K. The effective moment indicates that Eu is in the ). Electrical resistivity data indicate metallic conduction in Eu 2 Ga 3 Ir with r (300 K) approx. 150 mW cm and r 0 approx. 50 mW cm. The 4f 7 configuration of europium is confirmed by Eu-L III X-ray absorption spectroscopy, showing only one maximum in the spectrum at the expected position of about 6980 eV. This value is by 8 eV smaller than observed for the standard Eu 2O3 with electronic configuration 4f 6 (Eu Discussion 3+).

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“…In the course of their investigations several stacking variants were found in addition to the three fundamental structures of C14, C15 and C36. Komura & Tokunaga (1980) have refined the structures of MgZn 2, MgNi 2, MgZn2-0.03MgAg2(8H), MgZnz-0.07MgAg 2 (9R) and MgZn2-0.10MgAg / (10H) using a full-matrix least-squares method.…”

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confidence: 99%