Metadynamic Simulations to determine the free energy profile of shear in Aluminium single crystals and at grain boundaries

金属和合金中的晶界影响材料的变形能力和强度。它们与位错相互作用，代表微结构中裂纹可能成核的薄弱环节。 因此，要理解和预测宏观强度和塑性变形的多金属在有限的温度下，知识的滑动障碍，和剪切强度的晶界的微观结构是必要的。这方面的知识可以从广义堆垛层错能面（“伽马”面）的计算中获得，这也使我们深入了解晶界与位错的相互作用。“γ”-表面可以通过从头计算电子结构计算以高精度确定。然而，在这个能量超曲面的计算中，原子位置的弛豫必须被约束，因此能量势垒和能量与位移的导数，即应力，被高估。 在这个项目中，我们将改进传统的“伽马”表面方法，并将其扩展到有限的温度，通过推导自由能表面的剪切铝单晶和晶界的原子模拟采用metadaptics方法。

Grain boundaries in metals and alloys influence the deformability and strengthof the material. They interact with dislocations and represent weak links in the microstructure at which cracks can nucleate. Thus, to understand and to predict macroscopic strength and plastic deformation of polycrystallinemetals at finite temperatures, knowledge of sliding barriers for, and the shear strength of grain boundaries in the microstructure is necessary. This knowledge can be gained from calculations of the generalized-stacking-fault-energy surface ("gamma"-surface), which also give insight into the interaction of grain boundaries with dislocations. "gamma"-surfaces can be determined with high accuracy by means of ab-initio electronic structure calculations. However, in the calculations of this energy hypersurface, the relaxation of atomic positions have to be constrained, thus energy barriers and the derivatives of energy vs. displacement, i.e. the stress, are overestimated. In this project we will improve the conventional "gamma"-surface method and extend it to finite temperatures by deriving the free energy surface for shear in aluminium single crystals and at grain boundaries from atomistic simulations employing the metadynamics method.