NiAl力学性质合金化效应的第一原理计算

采用第一原理赝势平面波方法,计算几种合金化元素X(X=Cr、Mn、Fe、Co和Cu)与不同Fe含量(0,3.125%,4.167%,6.25%,摩尔分数)(NiFe)Al超胞的几何与电子结构,并采用如下几个力学参数:弹性常数C44、Cauchy压力参数(C12-C44)、弹性模量E和剪切模量G及比值G/B0等,表征和评判了合金化元素X与不同Fe含量对NiAl金属间化合物延性与硬度的影响。结果表明:高浓度(6.25%)合金化虽可提高NiAl晶体的硬度,但却导致NiAl延展性降低,合金化后NiAl硬度增加的次序为:(Ni7Mn)Al8>(Ni7Co)Al8>(Ni7Fe)Al8>(Ni7Cr)Al8>(Ni7Cu)Al8>NiAl,其延性降低次序则与硬度增加次序相反;随着Fe含量的升高,NiAl晶体的硬度增加,但其使硬度增加的上限约为4%,而随着Fe含量的降低,NiAl晶体的延性逐步增大,当Fe含量低到一定程度时,可改善NiAl晶体的本征脆性。

Alloying effects of mechanical properties of B2-NiAl intermetallic compound calculated by first-principles method

Using the first-principles pseudopotential plane-wave methods based on the density functional theory,the geometric and electronic structures of(NiX)Al supercells with different alloying elements X(X=Cr,Mn,Fe,Co and Cu) or different Fe contents,e.g.0,3.125%,4.167% and 6.25%(mole fraction) are calculated.Several mechanical properties parameters such as elastic constant C_(44),Cauchy pressure parameter(C_(12)-C_(44)),elastic modulus E,the shear modulus G and their ratio G/B_0 are used to characterize and assess the effect of alloying element and Fe content on the ductility and hardness of NiAl intermetallic compounds,respectively.The result shows that high addition of alloying element X(6.25%) can not enhance the ductility of NiAl intermetallic compound although it makes the hardness of NiAl improve as following order: NiAl<(Ni_7Cu)Al_8<(Ni_7Cr)Al_8<(Ni_7Fe)Al_8<(Ni_7Co)-Al_8<(Ni_7Mn)Al_8.And the decreasing order of ductility of NiAl induced by alloying element X is opposite to their hardness increasing order.With the increase of Fe content,the hardness of NiAl is elevated.And the upper limit making the hardness of NiAl increase is about 4%.Meanwhile a gradual improvement of the ductility of NiAl is also observed as Fe addition content decreases.From this variation tendency of the ductility of NiAl versus Fe content,a deduction is made.The intrinsic embitterment of NiAl can be restrained if Fe content is enough low.