Ce与Cr协同作用B2-NiAl合金力学性能的理论研究

本文采用第一性原理赝势平面波方法,基于虚拟晶体势函数近似(VCA),研究了不同浓度x (x=0~2.2%,原子百分比)的Ce和Cr 单独及协同合金化对B2-NiAl晶体弹性模量E、剪切模量G、 Cauchy压力参数及G/B0比值的影响。结果表明：Cr占据Ni原子位能显著提高B2-NiAl合金的剪切模量G和弹性模量E, 而Ce占据Al原子位则能降低其合金的G和E；随着合金化浓度提高到2.1%,Cr占据Al原子位能改善B2-NiAl合金的延性,而当Ce取代Al原子位协同Cr取代Al原子位时,对其延性的改善效果比各自单独合金化的效果更显著,且以合金化浓度为2.0%时为最佳效果。这一理论计算很好的重现了实验中Ce与Cr协同合金化明显提升B2-NiAl合金室温延性的现象。电子态密度分析显示,Cr原子或者Cr协同Ce原子能够削弱B2-NiAl晶体当中的Ni(d)-Ni(d)主要成键峰的杂化效应,降低主要成键峰的方向性。

First-Principles Study on Mechanical Properties of B2-NiAl Intermetallic Compound Alloyed by Ce cooperation with Cr

The effect of alloying concentration x (x=0~2.2%,atom fraction) to several parameters such as Cauchy pressure, Elastic modulus E, the shear modulus G and their ratio G/B₀ of B₂-NiAl supercells alloyed by Cr and Ce, alone or together, are calculated in the framework of Virtual Crystal Approximation by the first-principles pseudopotential plane-wave method. The shear modulus G and elastic modulus E of B₂-NiAl alloy were significantly increased when Cr occupied the Ni atom site in B₂-NiAl crystals, while the G and E will be reduced when Ce occupied the Al atom site. With the alloying concentration increased to 2.1%, the ductility of B₂-NiAl crystals can be improved with Cr occupied the Al atom site. It is worth emphasizing that the ductility of B₂-NiAl crystals was improved more significantly when Ce and Cr replaced Al atom site simultaneously than that alloyed by Ce or Cr alone, especially the alloying concentration x is 2.0%. The electronic density of states shows that Cr atoms or Cr cooperation with Ce atoms all can weaken the hybridization effect of the main bonding peaks of Ni(d)-Ni(d) and decrease the directivity of the main bonding peaks in B₂-NiAl crystal. The calculation result herein explains the phenomenon that the room temperature ductility of B2-NiAl alloy is enhanced obviously alloyed by Cr or Cr cooperation with Ce.