超过饱和固溶W-B合金力学性质的第一性原理研究

First principles study on mechanical properties of supersaturated solid solution W-B alloy

针对小原子元素在金属合金中可同时提高硬度和韧性的现象,本文采用基于第一性原理方法,研究了W-B合金的超过饱和固溶结构和力学性能.计算结果表明:无论是几何结构的晶格畸变,还是热力学上的结合能,B原子以置换形式固溶于W晶体中均优于其他固溶形式,这主要是由于置换B原子与周围W原子形成以共价型为主兼有离子型的键合作用.在合金中添加B元素虽然降低了合金材料的弹性模量,杨氏模量由414.34 GPa降低至338.36 GPa,但却显著增加了材料的韧性,B/G值由1.97提高到2.30(纯W晶体相较于B含量6.25 at.%时).并且合金的各向异性显著地减弱.另外,合金中B元素的添加,还使得材料理想剪切强度和最大应变值也得到了增加,分别由原来的19.981 GPa和0.187增加至21.814 GPa和0.209.这说明B元素在W合金中的超过饱和固溶不仅增加了合金的强度,还提高了合金的韧性.

In view of the phenomenon that small atomic elements could improve both hardness and toughness in metal alloys,the supersaturated solid solution structures and mechanical properties of W-B alloy were studied by the first-principles calculation.The results show that for both of lattice distortion of geometric structure and binding energy,the substitutional solid solution of B atom is better than other solid solution forms in W crystal.This is mainly because the substitutional atom B and the surrounding W atoms form covalent bond and small amount ionic bonds.In addition,the addition of B decreases the elastic modulus of the alloy from 414.34 Gpa to 338.36 Gpa,but significantly increases the toughness of the alloy,and the B/G value increases from 1.97 to 2.30(from pure W to the content of B with 6.25 at.%).At the same time,the anisotropy of the alloy decreases significantly.In addition,the addition of B atom in the W-B alloy increases the ideal shear strength and the maximum strain value from 19.981 Gpa and 0.187 to 21.814 Gpa and 0.209,respectively.These show that the supersaturated solution of B in W alloy not only strengthens the strength of the alloy,but also improves the toughness of the alloy.