Structure Analysis of a Long Period Stacking Ordered Phase in Mg-Al-Gd Alloys

Yokobayashi, Hideyuki; Kishida, Kyosuke; Inui, Haruyuki; Yamasaki, Michiaki; Kawamura, Yoshihito

doi:10.1557/opl.2011.36

Cited by 18 publications

(23 citation statements)

References 12 publications

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“…9,10) Before the system reaches the final structure, some intermediate states possibly exist. For example, in an early stage of the microstructure development, rare earth atoms and transition metal atoms in the alloys are randomly distributed on the hcp-Mg lattices.…”

Section: Introductionmentioning

confidence: 99%

Thermodynamic Analysis of the Mg–RE–Zn (RE = Y, La) Ternary hcp Phase Using the Cluster Variation Method

2013

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In this study, thermodynamic properties of the MgREZn (RE = Y, La) ternary hcp phase at finite temperature have been investigated by means of first-principles calculations combined with the cluster variation method (CVM). Free energy calculation, including the configurational entropy, shows that the MgYZn ternary hcp phase has a tendency to phase separation. Conversely, the MgLaZn ternary system does not exhibit such behavior even around room temperature. Furthermore, the calculated spinodal region extends to a broader composition range and the maximal spinodal temperature reaches above 1000 K for the MgYZn system. Conversely, the spinodal region for the MgLaZn system is a limited narrow region near the Mg-rich side, and the maximal spinodal temperature is 300 K. Formation enthalpies calculated on the basis of recent information from structure analyses do not show a definite difference in these two ternary systems. Therefore, we propose that the dominant factors in the formation of a novel long period stacking ordered structure include spinodal decomposition as well as structure transformation from 2H to other structures having periodic stacking faults.

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Section: Introductionmentioning

confidence: 99%

Thermodynamic Analysis of the Mg–RE–Zn (RE = Y, La) Ternary hcp Phase Using the Cluster Variation Method

2013

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“…Considering that the reported stable periodicity for the sample having ¡-Mg + LPSO two phase microstructure is 14H, 15,25) higher cooling rate in the L+¡-Mg region leads to insufficient mixing in the liquid region and formation of LPSO at higher concentration. The peak position corresponding to the in-plane ordering is much lower than the ideal 2 ffiffi ffi 3 p a position, 4) as reported for 6-9 and 1-2 alloys. To examine the profile at the initial state of formation of LPSO during cooling, three profiles are extracted from Fig.…”

Section: ¹1mentioning

confidence: 49%

“…4,7) In contrast, several works using synchrotron radiation 4,16,17) and scanning probe microscopy 22) showed that the periodicity that appears first in the alloy system does not necessarily the most stable one, and the in-plane order structure in the segregated layer may change with time, temperature and composition.…”

Section: Introductionmentioning

confidence: 99%

Stability of Long-Period Stacking Ordered Structures at Elevated Temperatures Examined by Multicolor Synchrotron Radiation X-ray Scattering/Diffraction Measurements

et al. 2015

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Stability of long-period stacking ordered (LPSO) structures of Mg-Zn-Y ternary alloys at elevated temperatures was examined by multicolor synchrotron radiation small-and medium-angle scattering/diffraction. The LPSO structures directly melted during heating, and the formation of LPSO was observed from supercooled liquid. The temperatures of complete dissolution and the onset of formation of LPSO phases were measured by monitoring the first diffraction peak of 14H, 18R and 10H compositional modulation. The stability of composition modulation in c axis direction was found to be the same as that of L1 2 cluster ordering in the segregation layer in both heating and cooling processes, i.e., dissolution and formation. Supercooling of LPSO was obtained for the heating/cooling rate of 10 K/min.

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“…8) Yokobayashi et al found that the completely ordered L1 2 -type structure in the orderdisorder type LPSO structure in MgAlGd alloys. 9) Recently, Egusa et al showed a revised crystalline structure of 18R-and 14H-type LPSO in Mg 97 Zn 1 RE 2 (RE = Y, Er) and Mg 85 Zn 6 Y 9 alloys. 10) Based on the diffuse scattering pattern in the electron diffraction patterns, they concluded that L1 2 -type clusters align in inplane short range order.…”

Section: )mentioning

confidence: 99%

Structural and Compositional Modulation in Transformation of LPSO Structure in Mg97Zn1Y2 Cast Alloys

et al. 2013

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This study investigated modulation of the long period stacking order (LPSO) structure in aged Mg 97 Zn 1 Y 2 alloys using conventional transmission electron microscopy (TEM) and aberration-corrected high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM). The irregular stacking sequence of a fragment of 24R-type LPSO acts as a catalyst for the transformation from 18R-to 14H-type LPSO. The elementary step of the transformation from 18R-to 24R-type takes place by the ledge-pair movement on different (0001) Mg planes with Shockley partial dislocations. Each ledge has a transition region in front of it. The transition regions are HCP-type stacking sequence with lower Zn and Y concentrations than those of the FCC-type enrichment layer. The solute elements migrate easily in the region, where solute elements produce a kind of diffusion field. Therefore, structural modulation occurs by a mechanism resembling diffusionaldisplacive transformation. Local strain analysis using HAADF-STEM images has elucidated that lattice spacing of (0001) Mg in the FCC-type enrichment layer is shorter than that in the HCP-type transition region. These structural and compositional irregularities are an elementary step in the transformation of LPSO in Mg 97 Zn 1 Y 2 alloys. A diffusionaldisplacive type transformation mechanism in LPSO has been proposed.

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Structure Analysis of a Long Period Stacking Ordered Phase in Mg-Al-Gd Alloys

Cited by 18 publications

References 12 publications

Thermodynamic Analysis of the Mg–RE–Zn (RE = Y, La) Ternary hcp Phase Using the Cluster Variation Method

Thermodynamic Analysis of the Mg–RE–Zn (RE = Y, La) Ternary hcp Phase Using the Cluster Variation Method

Stability of Long-Period Stacking Ordered Structures at Elevated Temperatures Examined by Multicolor Synchrotron Radiation X-ray Scattering/Diffraction Measurements

Structural and Compositional Modulation in Transformation of LPSO Structure in Mg<sub>97</sub>Zn<sub>1</sub>Y<sub>2</sub> Cast Alloys

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Structure Analysis of a Long Period Stacking Ordered Phase in Mg-Al-Gd Alloys

Cited by 18 publications

References 12 publications

Thermodynamic Analysis of the Mg&ndash;RE&ndash;Zn (RE = Y, La) Ternary hcp Phase Using the Cluster Variation Method

Thermodynamic Analysis of the Mg&ndash;RE&ndash;Zn (RE = Y, La) Ternary hcp Phase Using the Cluster Variation Method

Stability of Long-Period Stacking Ordered Structures at Elevated Temperatures Examined by Multicolor Synchrotron Radiation X-ray Scattering/Diffraction Measurements

Structural and Compositional Modulation in Transformation of LPSO Structure in Mg<sub>97</sub>Zn<sub>1</sub>Y<sub>2</sub> Cast Alloys

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Thermodynamic Analysis of the Mg–RE–Zn (RE = Y, La) Ternary hcp Phase Using the Cluster Variation Method

Thermodynamic Analysis of the Mg–RE–Zn (RE = Y, La) Ternary hcp Phase Using the Cluster Variation Method