论文标题
MG-ZN合金中降水的第一原理分析
First principles analysis of precipitation in Mg-Zn alloys
论文作者
论文摘要
通过第一原理计算分析了MG-ZN合金中的降水。确定了对称不同的HCP MG1-XZNX（0 <x <1）构型的形成能，并从凸船体中鉴定出与基质相干的Guinier-Preston区域的潜在候选物。最有可能的结构根据沿基平面的界面能进行排名。此外，计算了实验中报道的几个阶段的形成能和振动熵贡献（MG4ZN7，MGZN2立方体，MGZN2六角形，MG21ZN25和MG2ZN11）。 MG4ZN7，MGZN2立方体和MGZN2六角形薰衣草相的形成能非常接近，因为它们是由菱形和六角晶格单元的不同排列形成的。得出的结论是，β_1^'沉淀是由所有这些沉淀物形成的。然而，几何布置的差异导致熵能贡献的变化，从而确定了高温稳定性。发现MGZN2六角形液相是高温下最稳定的相位，因此，β_1^'沉淀物倾向于以较高的衰老温度或更长的衰老时间转变为β_2^'（MGZN2六角形）沉淀。最后，发现平衡β相（MG21ZN25）是一个远程阶，由于触发从短距离阶相β_2^'到β的转换所需的动力学过程，因此沉淀了最后一个。
Precipitation in Mg-Zn alloys was analyzed by means of first principles calculations. Formation energies of symmetrically distinct hcp Mg1-xZnx (0 < x < 1) configurations were determined and potential candidates for Guinier-Preston zones coherent with the matrix were identified from the convex hull. The most likely structures were ranked depending on the interface energy along the basal plane. In addition, the formation energy and vibrational entropic contributions of several phases reported experimentally (Mg4Zn7, MgZn2 cubic, MgZn2 hexagonal, Mg21Zn25 and Mg2Zn11) were calculated. The formation energies of Mg4Zn7, MgZn2 cubic, and MgZn2 hexagonal Laves phases were very close because they were formed by different arrangements of rhombohedral and hexagonal lattice units. It was concluded that β_1^' precipitates were formed by a mixture of all of them. Nevertheless, the differences in the geometrical arrangements led to variations in the entropic energy contributions which determined the high temperature stability. It was found that the MgZn2 hexagonal Laves phase is the most stable phase at high temperature and, thus, β_1^' precipitates tend to transform into the β_2^' (MgZn2 hexagonal) precipitates with higher aging temperature or longer aging times. Finally, the equilibrium βphase (Mg21Zn25) was found to be a long-range order that precipitates the last one on account of the kinetic processes necessary to trigger the transformation from a short-range order phase β_2^' to β.
