Elastic anisotropy of γ'-Fe4N and elastic grain interaction in γ'-Fe4N1-y layers on α-Fe: first-principles calculations and diffraction stress measurements
Elastic anisotropy of γ'-Fe4N and elastic grain interaction in γ'-Fe4N1-y layers on α-Fe: first-principles calculations and diffraction stress measurements
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DOI：
10.1016/j.actamat.2007.07.001
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发表时间：
2007-10
期刊：
影响因子：
9.4
通讯作者：
T. Gressmann;M. Wohlschlögel;S. Shang;U. Welzel;A. Leineweber;E. Mittemeijer;Zhen Liu
中科院分区：
文献类型：
--
作者：
T. Gressmann;M. Wohlschlögel;S. Shang;U. Welzel;A. Leineweber;E. Mittemeijer;Zhen Liu
用第一性原理方法，用密度泛函理论计算了立方{Gamma}‘-Fe{sub4}N(面心立方(Fcc)型铁亚结构)的三个独立单晶弹性刚度常数C{sub11}=307.2 Gpa，C{sub12}=134.1 Gpa和C{sub44}=46.0GPa.Zener弹性-各向异性之比A=2C{sub44}/(C{sub11}-C{sub12})=0.53，明显小于1，表明为最硬的方向，而所有面心立方金属都表现为A>；1。这种弹性各向异性归因于N在八面体间隙位上的有序分布。从{α}-Fe上的{Gamma}‘-Fe{sub4}N{sub1-y}层中记录的一组不同的hk L反射的X射线衍射晶格应变测量证实了{Gamma}’-Fe{sub4}N{sub1-y}弹性各向异性的‘反常’。应力评估是基于由计算的单晶弹性常数C{subij}确定的有效X射线弹性常数，并允许Reuss和Voigt模型之间的颗粒相互作用来进行的，产生与表面平行的约-670 Mpa的压应力。
The three independent single-crystal elastic-stiffness constants C{sub ij} of cubic {gamma}'-Fe{sub 4}N (face-centred cubic (fcc)-type iron substructure) have been calculated by first-principles methods using the density functional theory: C{sub 11} = 307.2 GPa, C{sub 12} = 134.1 GPa and C{sub 44} = 46.0 GPa. The Zener elastic-anisotropy ratio, A = 2C{sub 44}/(C{sub 11} - C{sub 12}) = 0.53, is strikingly less than 1, implying <1 0 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 {gamma}'-Fe{sub 4}N{sub 1-y} layers on top of {alpha}-Fe confirmed the 'abnormal' elastic anisotropy of {gamma}'-Fe{sub 4}N{sub 1-y}. 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 ij} and allowing a grain interaction intermediate between the Reuss and the Voigt models.