B2型Ti-Al-X合金相稳定性与力学性质的第一原理计算

First-principles calculation on the stability and mechanical properties of B2-Ti-Al-X alloys

采用基于密度泛函理论的第一原理赝势平面波方法,计算了B2-Ti-Al-X(X=Cr、Mo、Nb、W、Zr和Hf)晶体的电子与能态结构及其弹性性质,通过合金形成热和Born稳定性判据考察了过渡金属元素X在B2-TiAl晶体中的择优占位趋势与力学稳定性,并采用Cauchy压力参数(C12-C44)和B/C44比值表征和评判了X对B2型Ti-Al-X合金延性的影响。结果表明:Cr、Mo、Nb、Zr和W在B2-TiAl晶体中优先占据Al点阵位,Hf则主要占据Ti点阵位。添加Cr、W或Zr后,B2型Ti4Al3Zr、Ti4Al3W和Ti4Al3Cr合金的延性相对于γ型TiAl合金有所提高,B2-TiAl合金的Nb、Mo或Hf合金化则没有这种韧化效果。

Using the first-principles pseudo-potential plane wave method,the electronic structures,energetics and the elastic moduli of B2-Ti-Al-X（X=Cr,Mo,Nb,W,Zr and Hf） crystals are calculated.The site preference of TM elements X in B2-TiAl crystal and the mechanical stability of these B2 phases with preferential site of X are also investigated by a comparison of the heats of formation and the Born Criterion of stability.The Cauchy pressures（C12-C44） and the ratios of B/C44have been adopted to characterize and assess the ductile/brittle behaviors of B2-Ti-Al-X phases.The results show Cr,Mo,Nb,Zr and W prefer to occupy Al sites in B2-TiAl crystal,and Hf mainly substitutes for Ti atoms.The ductility of B2-TiAl alloys with the addition of Cr,W or Zr is evidently improved relative to γ-TiAl alloys,whereas no toughening effect can be seen for the addition of Nb,Mo or Hf in B2-TiAl alloys.