ABSTRACT

The effect of crystallographically oriented, unidirectional concentration gradients on spinodal decomposition in cubic crystalline solids with elastic and interfacial energy anisotropy is discussed. Phase-field simulations reveal that the kinetics of spinodal decomposition occurring in such systems is dependent on the degree of misorientation between the direction of composition gradient and the preferred crystallographic orientation for growth of spinodal fluctuations; the larger is the misorientation, the slower the kinetics. This phenomenon has been used to explain the well-known grain-orientation-dependent N-uptake kinetics observed during nitriding of metallic alloys. Several plausible causes have been proposed in the literature for the grain-orientation-dependent N-uptake kinetics during nitriding. However, this study reveals that this phenomenon is observed exclusively and without exception in alloy systems having a spinodal instability. The N-uptake kinetics in such systems is known to be dependent on the kinetics of spinodal decomposition. Consequently, anisotropic spinodal decomposition kinetics occurring owing to the presence of a surface-directed N-composition gradient in poly-crystalline metals has been shown to be a more fundamental cause for the phenomenon.

摘要

讨论了晶体取向的单向浓度梯度对具有弹性和界面能各向异性的立方晶体固体中的旋节线分解的影响。相场模拟表明，在此类系统中发生的旋节线分解动力学取决于成分梯度方向与旋节线波动生长的首选晶体取向之间的错误取向程度；方向错误越大，动力学越慢。这种现象已被用来解释在金属合金渗氮过程中观察到的众所周知的晶粒取向依赖的 N 吸收动力学。在文献中已经提出了几种可能的原因，用于氮化过程中晶粒取向依赖的 N 吸收动力学。然而，该研究表明，这种现象仅在具有旋节线不稳定性的合金系统中观察到，无一例外。已知此类系统中的 N 吸收动力学取决于旋节线分解的动力学。因此，由于多晶金属中存在表面定向的 N 组成梯度而发生的各向异性旋节线分解动力学已被证明是该现象的更根本原因。