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Phase-field-crystal study of grain boundary premelting and shearing in bcc iron

机译：bcc铁中晶界预熔和剪切的相场晶体研究

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摘要

We use the phase-field-crystal (PFC) method to investigate the equilibrium premelting and nonequilibrium shearing behaviors of [001] symmetric tilt grain boundaries (GBs) at high homologous temperature over the complete range of misorientation 0 < θ < 90° in classical models of bcc Fe. We characterize the dependence of the premelted layer width W as a function of temperature and misorientation. In addition, we compute the thermodynamic disjoining potential whose derivative with respect to W represents the structural force between crystal-melt interfaces due to the spatial overlap of density waves. The disjoining potential is also computed by molecular dynamics (MD) simulations, for quantitative comparison with PFC simulations, and coarse-grained amplitude equations (AE) derived from PFC that provide additional analytical insights. We find that, for GBs over an intermediate range of misorientation (θ_(min) < θ < θ_(man)), W diverges as the melting temperature is approached from below, corresponding to a purely repulsive disjoining potential, while for GBs outside this range (9 < 9_(min) or θ_(mix) < θ < 90°) W remains finite at the melting point. In the latter case, W corresponds to a shallow attractive minimum of the disjoining potential. The misorientation range where W diverges predicted by PFC simulations is much smaller than the range predicted by MD simulations when the small dimensionless parameter e of the PFC model is matched to liquid structure factor properties. However, it agrees well with MD simulations with a lower e value chosen to match the ratio of bulk modulus and solid-liquid interfacial free energy, consistent with the amplitude-equation prediction that θ_(min)and 90° -θ_(max) scale as ~∈~(1/2). The incorporation of thermal fluctuations in PFC is found to have a negligible effect on this range. In response to a shear stress parallel to the GB plane, GBs in PFC simulations exhibit coupled motion normal to this plane or sliding. Furthermore, the coupling factor exhibits a discontinuous change as a function of θ that reflects a transition between two coupling modes. Sliding is only observed over a range of misorientation that is a strongly increasing function of temperature for T/ T_M ≥0.8 and matches roughly the range where W diverges at the melting point. The coupling factor for the two coupling modes is in excellent quantitative agreement with previous theoretical predictions [Cahn, Mishin, and Suzuki, Acta Mater. 54, 4953 (2006)].
机译：我们使用相场晶体（PFC）方法来研究[001]对称倾斜晶界（GBs）在高同源温度下在整个取向错误0 <θ<90°的完整范围内的平衡预熔融和非平衡剪切行为。密件抄送铁的模型。我们将预熔融层宽度W的依赖性描述为温度和取向错误的函数。另外，我们计算了热力学解离势，其相对于W的导数表示由于密度波的空间重叠而导致的晶体熔体界面之间的结构力。还通过分子动力学（MD）模拟计算分离的势能，以便与PFC模拟进行定量比较，并从PFC导出的粗粒度振幅方程（AE）提供了更多的分析见解。我们发现，对于取向失常的中间范围（θ_（min）<θ<θ_（man））的GB，随着从下方接近熔化温度，W发生发散，这对应于纯排斥相分离的电势，而GBs在此范围之外熔点（9 <9_（min）或θ_（mix）<θ<90°）范围保持在有限。在后一种情况下，W对应于分离电位的浅的吸引最小值。当PFC模型的小无量纲参数e与液体结构因子属性匹配时，PFC模拟预测的W偏离的取向差范围远小于MD模拟预测的取向差范围。但是，它与MD模拟非常吻合，选择较低的e值来匹配体积模量和固液界面自由能的比率，这与θ_（min）和90°-θ_（max）标度的振幅方程预测一致为〜∈〜（1/2）发现在PFC中引入热波动对该范围的影响可忽略不计。响应平行于GB平面的剪应力，PFC模拟中的GB表现出垂直于该平面或滑动的耦合运动。此外，耦合因子表现出作为θ函数的不连续变化，反映了两个耦合模式之间的过渡。仅在方向不正确的范围内观察到滑动，这是温度在T / T_M≥0.8时急剧增加的函数，并且大致与W在熔点处发散的范围相匹配。两种耦合模式的耦合因子与先前的理论预测[Cahn，Mishin和Suzuki，Acta Mater。 54，4953（2006）]。

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  • 来源
    《Physical review》 |2013年第2期|024110.1-024110.22|共22页
  • 作者

    Ari Adland; Alain Karma; Robert Spatschek; Dorel Buta; Mark Asta;

  • 作者单位

    Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts 02115, USA;

    Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts 02115, USA;

    Max-Planck-lnstitut fur Eisenforschung GmbH, D-40237 Dusseldorf, Germany;

    Department of Materials Science and Engineering, University of California, Berkeley, California, 94720 USA;

    Department of Materials Science and Engineering, University of California, Berkeley, California, 94720 USA;

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  • 原文格式 PDF
  • 正文语种 eng
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  • 关键词

    grain and twin boundaries; solidification; noise;

    机译：晶界和孪晶界;凝固;噪声;

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