Jian Yongxin, Huang Zhifu, Wang Yu, Xing Jiandong
State Key Laboratory for Mechanical Behavior of Materials, School of Materials Science and Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
Shaanxi Special Equipment Inspection and Testing Institute, Xi'an 710048, China.
Materials (Basel). 2020 Sep 23;13(19):4221. doi: 10.3390/ma13194221.
First-principles calculations based on density functional theory (DFT) have been performed to explore the effects of Si, Cr, W, and Nb elements on the stability, mechanical properties, and electronic structures of MoAlB ternary boride. The five crystals, with the formulas of MoAlB, MoAlSiB, MoCrAlB, MoWAlB, and MoNbAlB, have been respectively established. All the calculated crystals are thermodynamically stable, according to the negative cohesive energy and formation enthalpy. By the calculation of elastic constants, the mechanical moduli and ductility evolutions of MoAlB with elemental doping can be further estimated, with the aid of B/G and Poisson's ratios. Si and W doping cannot only enhance the Young's modulus of MoAlB, but also improve the ductility to some degree. Simultaneously, the elastic moduli of MoAlB are supposed to become more isotropic after Si and W addition. However, Cr and Nb doping plays a negative role in ameliorating the mechanical properties. Through the analysis of electronic structures and chemical bonding, the evolutions of chemical bondings can be disclosed with the addition of dopant. The enhancement of B-B, Al/Si-B, and Al/Si-Mo bondings takes place after Si substitution, and W addition apparently intensifies the bonding with B and Al. In this case, the strengthening of chemical bonding after Si and W doping exactly accounts for the improvement of mechanical properties of MoAlB. Additionally, Si doping can also improve the Debye temperature and melting point of the MoAlB crystal. Overall, Si element is predicted to be the optimized dopant to ameliorate the mechanical properties of MoAlB.
基于密度泛函理论（DFT）进行了第一性原理计算，以探究Si、Cr、W和Nb元素对MoAlB三元硼化物的稳定性、力学性能和电子结构的影响。分别建立了化学式为MoAlB、MoAlSiB、MoCrAlB、MoWAlB和MoNbAlB的五种晶体。根据负结合能和生成焓，所有计算得到的晶体在热力学上都是稳定的。通过弹性常数的计算，借助B/G和泊松比，可以进一步估计MoAlB在元素掺杂时的力学模量和延展性演变。Si和W掺杂不仅可以提高MoAlB的杨氏模量，还能在一定程度上改善其延展性。同时，添加Si和W后，MoAlB的弹性模量有望变得更加各向同性。然而，Cr和Nb掺杂对改善力学性能起到负面作用。通过电子结构和化学键分析，可以揭示掺杂剂添加后化学键的演变。Si取代后，B-B键、Al/Si-B键和Al/Si-Mo键增强，添加W明显增强了与B和Al的键合。在这种情况下，Si和W掺杂后化学键的强化恰好解释了MoAlB力学性能的改善。此外，Si掺杂还可以提高MoAlB晶体的德拜温度和熔点。总体而言，预测Si元素是改善MoAlB力学性能的最佳掺杂剂。
