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首页> 外文期刊>Materials transactions >Key Factor for the Transformation from hcp to 18R-Type Long-Period Stacking Ordered Structure in Mg Alloys
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Key Factor for the Transformation from hcp to 18R-Type Long-Period Stacking Ordered Structure in Mg Alloys

机译：镁合金中HCP至18R型长期堆叠结构的关键因素

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Cast Mg85Y9Zn6 has an 18R-type LPSO structure. However, Mg85Y9Zn6 recovered after being subjected to a loading pressure of 7 GPa at 973K 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 Mg-Y-Zn 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.
机译：铸造MG85Y9ZN6具有18R型LPSO结构。然而，在973K处经过7GPa的负载压力后回收的Mg85Y9ZN6显示了由面向中心的立方（FCC）结构组成的细双相结构，所述立方（FCC）结构显示出超晶格（D0（3））以及六边形关闭 - 包装结构（HCP：2H）。在加热环境压力期间，D0（3）/ HCP结构在加热期间转化为18R型LPSO。在该研究中，通过原位XRD和第一原理计算讨论了来自D0（3）/ HCP结构到18R型LPSO结构的转换过程。首先，晶格体积为2H，随着温度的增加而增加，因为从D0（3）相中发射到2H格中的Zn和Y。在2小时伸展后，由于随机堆叠故障的插入（SFS），该结构由于随机堆叠故障（SFS）而塌陷。然后，发生了18R型LPSO结构的形成。基于纯MG的第一原理计算，2H晶格的体积膨胀导致转换为18R结构。此外，Mg-Y-Zn三元系统中HCP和FCC结构的自由能量计算结果表明，Suzuki效应发生了y和Zn原子对SFS上的偏析。在具有本地FCC结构的SF层中，这些隔离的Y和Zn原子在堆叠和化学调制之间产生协同作用。目前的结果坚持认为，首先发生2h晶格的体积增加，然后发生从HCP结构到18R堆叠的变换。

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