Er对镁合金固溶强化作用的第一性原理研究

First-Principles Study on Solid Solution Strengthening Effect of Er on Mg Alloy

采用虚拟晶胞近似方法控制固溶体中的Er含量，基于密度泛函理论的第一性原理赝势方法研究了Er对Mg-zEr（x=1at．％～6at．％）固溶体的固溶强化作用。计算结果表明：Mg-xEr（x=1at．％～6at．％）固溶体的体模量（B）随Er含量的增加而逐渐增大，当Er含量为4at．％时体模量达到最高值，之后基本保持不变。剪切模量（G）和杨氏模量（E）随Er含量的增加而降低，当Er含量达到6％时，又略微增大。6种固溶体的5／B值均小于0．57，都是韧性材料。Er掺杂量为1at．％～5at．％的区间内，随Er含量的增加，固溶体的G／B值明显降低，泊松比（v）增大，合金韧塑性提高；当Er含量继续增大到6at．％，固溶体的C／B值有所升高，泊松比（v）减小，合金韧塑性下降。随着Er含量的增加，态密度整体向低能级区域移动，费米能级低能级区域的成键电子数逐渐增多，同时底带宽度明显变宽，合金成键能力增强。在Er含量为1at．％～2at．％的区间内，受Er-4f电子影响总态密度图中出现了明显的赝能隙，费米能级在赝能隙高能侧，合金电子跃迁困难。当Er含量大于2at．％时，赝能隙变得不明显，费米能级处的态密度值比较高，合金活性增强。

The method of virtual crystal approximation is deployed to control the content of Er in solid so- lution and the first-principle pseudopotential plane wave （PPW） method based on the density functional theory is uses to study the solid solution strengthening effect of Er on Mg-xEr（x= 1 at. %--6 at. %） solid solution. The results indicate that the bulk modulus（B） raises with the increasing content of Er, which peaks at 4 at. % Er and remains at almost same level afterwards. Young% modulus（E） and shear modulus（G） drop with the increment of Er content, while they increase slightly when Er content reaches 6 at. %. The G/B values of six Mg-xEr（x=l at. % 6 at. %） solid solutions are less than 0.57, all theMg solid solutions are ductile materials. With the increasing of Er doped amount in the range of 1 at. %-5 at. %, the G/B value of solid solution decreases significantly, while Poisson ratio （v） increa- ses and the toughness and plasticity of the solid solutions increase. When Er content increases to 6 at. %, the G/B value of solid solution decreaseds to some extent, while v increaseds, and the toughness and plasticity of the solid solutions increase. As the amount of Er increases, the density of state （DOS） moves to the low-energy region as a whole, and the average quantity of bonding electron at low-energy region of Fermi level grows and the bottom band widens simultaneously, resulting in greater bonding ca- pacity. Affected by electrons in the 4f orbital, a clear pseudogap turns up in the total density of state （TDOS） figure when Er content is between 1 at. %--2 at. %. The Fermi level is at the high-energy re- gion of pseudogap where the electronic transition is hard to achieve. When Er content is higher than 2 at. %, the pseudogap turns blur and DOS at the Fermi level is high, which means the activity of these solid solutions is increased.