Elastic anisotropy of γ′-Fe<sub>4sub>N and elastic grain interaction in γ′-Fe<sub>4sub>N<sub>1−ysub> layers on α-Fe: First-principles calculations and diffraction stress measurements
- 作者：T. Gressmann ; M. Wohlschlö ; gel ; S. Shang ; U. Welzel ; A. Leineweber ; E.J. Mittemeijer ; Z.-K. Liu
- 关键词：X-ray diffraction (XRD) ; Nitrides ; Elastic behaviour ; Residual stresses ; First-principles electron theory
- 刊名：Acta Materialia
- 出版年：2007
- 期刊代码：1_13596454
- 类别：ms
- 出版时间：October 2007
- 卷：55
- 期：17
- 页码：5833-5843
- 文件大小：540 K
摘要
The three independent single-crystal elastic-stiffness constants C<sub>ijsub> of cubic γ′-Fe<sub>4sub>N (face-centred cubic (fcc)-type iron substructure) have been calculated by first-principles methods using the density functional theory: C<sub>11sub> = 307.2 GPa, C<sub>12sub> = 134.1 GPa and C<sub>44sub> = 46.0 GPa. The Zener elastic-anisotropy ratio, A = 2C<sub>44sub>/(C<sub>11sub> − C<sub>12sub>) = 0.53, is strikingly less than 1, implying 
direct.com/scidirimg/entities/2329.gif" alt="left angle bracket" border=0>1 0 0direct.com/scidirimg/entities/232a.gif" alt="right-pointing angle bracket" border=0> as stiffest directions, whereas all fcc metals show A > 1. This elastic anisotropy is ascribed to the ordered distribution of N on the octahedral interstitial sites. X-ray diffraction lattice-strain measurements for a set of different h k l reflections recorded from γ′-Fe<sub>4sub>N<sub>1−ysub> layers on top of α-Fe confirmed the “abnormal” elastic anisotropy of γ′-Fe<sub>4sub>N<sub>1−ysub>. Stress evaluation, yielding a compressive stress of about −670 MPa parallel to the surface, was performed on the basis of effective X-ray elastic constants determined from the calculated single-crystal elastic constants C<sub>ijsub> and allowing a grain interaction intermediate between the Reuss and the Voigt models.