TY - JOUR
T1 - Key factor for the transformation from Hcp to 18R-type long-period stacking ordered structure in Mg alloys
AU - Matsushita, Masafumi
AU - Nagata, Takafumi
AU - Bednarcik, Jozef
AU - Nishiyama, Norimasa
AU - Kawano, Shoya
AU - Iikubo, Satoshi
AU - Kubota, Yuji
AU - Morishita, Ryo
AU - Irifune, Tetsuo
AU - Yamasaki, Michiaki
AU - Kawamura, Yoshihito
AU - Enoki, Masanori
AU - Ohtani, Hiroshi
N1 - Funding Information:
We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Parts of this research (in-situ XRD studies) were carried out at P02.1 beamline of PETRA III storage ring under proposal No. I-20140354. This study was supported by a Grant-in-Aid for Scientific Research (No. 16K06706), JKA and its promotion funds from the KEIRIN race (No. 2018 M128), the Grant “Synchronized LPSO” (No. 23109007) from MEXT/JSPS, and a Grant-in-Aid for “Materials science under ultra-high pressure” from Ehime University. One of the authors (H.O.) appreciates the financial support of the JST’s Advanced Low Carbon Technology Research and Development Program (ALCA).
Publisher Copyright:
©2018 The Japan Institute of Metals and Materials.
PY - 2019
Y1 - 2019
N2 - Cast Mg 85 Y 9 Zn 6 has an 18R-type LPSO structure. However, Mg 85 Y 9 Zn 6 recovered after being subjected to a loading pressure of 7 GPa at 973 K shows a fine dual-phase structure composed of a face-centered cubic (fcc) structure showing a superlattice (D0 3 ), as well as a hexagonal close-packed structure (hcp:2H). The D0 3 /hcp structure transformed to 18R-type LPSO during heating at ambient pressure. In this research, the transformation process from the D0 3 /hcp structure to 18R-type LPSO structure was discussed by means of in situ XRD and first-principles calculation. At first, lattice volume of 2H increased with an increase in the temperature, because of the Zn and Y emitted from the D0 3 phase into the 2H lattice. After the volume expansion of 2H lattice, the structure collapsed due to insert of random stacking faults (SFs). Then, a formation of 18R-type LPSO structure occurred. Based on a first-principles calculation for pure Mg, volume expansion of the 2H lattice causes the transformation to an 18R structure. Furthermore, the results of free energy calculations for the hcp and fcc structures in the MgYZn ternary system show that the segregation of Y and Zn atoms on SFs occurs by the Suzuki effect. These segregated Y and Zn atoms in SF layers, which have a local fcc structure, create a synergy between the stacking and chemical modulations. Present result insists that the volume increase of 2H lattice takes place first, and then the transformation from the hcp structure to 18R stacking occurs. [doi:10.2320/matertrans.M2018213]
AB - Cast Mg 85 Y 9 Zn 6 has an 18R-type LPSO structure. However, Mg 85 Y 9 Zn 6 recovered after being subjected to a loading pressure of 7 GPa at 973 K shows a fine dual-phase structure composed of a face-centered cubic (fcc) structure showing a superlattice (D0 3 ), as well as a hexagonal close-packed structure (hcp:2H). The D0 3 /hcp structure transformed to 18R-type LPSO during heating at ambient pressure. In this research, the transformation process from the D0 3 /hcp structure to 18R-type LPSO structure was discussed by means of in situ XRD and first-principles calculation. At first, lattice volume of 2H increased with an increase in the temperature, because of the Zn and Y emitted from the D0 3 phase into the 2H lattice. After the volume expansion of 2H lattice, the structure collapsed due to insert of random stacking faults (SFs). Then, a formation of 18R-type LPSO structure occurred. Based on a first-principles calculation for pure Mg, volume expansion of the 2H lattice causes the transformation to an 18R structure. Furthermore, the results of free energy calculations for the hcp and fcc structures in the MgYZn ternary system show that the segregation of Y and Zn atoms on SFs occurs by the Suzuki effect. These segregated Y and Zn atoms in SF layers, which have a local fcc structure, create a synergy between the stacking and chemical modulations. Present result insists that the volume increase of 2H lattice takes place first, and then the transformation from the hcp structure to 18R stacking occurs. [doi:10.2320/matertrans.M2018213]
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U2 - 10.2320/matertrans.M2018213
DO - 10.2320/matertrans.M2018213
M3 - Article
AN - SCOPUS:85060188466
SN - 1345-9678
VL - 60
SP - 237
EP - 245
JO - Materials Transactions
JF - Materials Transactions
IS - 2
ER -