晶体取向和晶界对γ-TiAl合金纳米压痕行为的影响

Effects of Crystal Orientations and Grain Boundaries on Nanoindentation Behavior of γ-TiAl Alloys

摘要:

为了阐述γ-TiAl的变形机理，采用纳米压痕实验和晶体塑性有限元模拟研究晶体取向和晶界对γ-TiAl合金机械性能的影响。建立了晶体塑性本构模型，得到了γ-TiAl合金单晶及晶界处的载荷-位移曲线、硬度和杨氏模量。模拟数据与实验数据的误差较小，证实了纳米压痕可以很好地验证晶体塑性本构参数。基于上述模型，讨论了各晶粒和晶界压痕周围的堆积形貌，分析了不同晶体取向下累积剪切应变的分布、滑移系的启动情况、晶界与位错滑移的相互作用。结果表明，由于压头的几何形状、材料滑移系统和累积剪切应变分布之间的耦合作用，γ-TiAl合金的力学响应和堆积行为表现出显著的各向异性。此外，晶界与位错滑移的相互作用显著改变了位错的分布，进而影响了材料的流动，对材料力学响应和塑性变形起着至关重要的作用。晶界吸收了部分位错，改变了压痕下塑性变形的分布特征，导致其硬度降低，材料堆积形貌发生改变，堆积减少。

Abstract:

To elucidate the deformation mechanisms of γ-TiAl, the nanoindentation experiments and crystal plasticity finite element (CPFE) simulation were employed to investigate the effects of crystal orientations and GBs on the mechanical properties of γ-TiAl alloys. A crystal plasticity constitutive model was developed, and load-displacement curves, hardness, and Young's modulus were obtained for both single grains and GBs in γ-TiAl alloys. Based on the aforementioned model, this study investigated the distribution patterns of surface morphology around the indentation sites of individual grain and GBs. It also analyzed the cumulative shear strain distribution, slip system activation, and the interaction between GBs and dislocation slip for various crystal orientations. The results indicate that the mechanical response and pileup behavior exhibit significant anisotropy due to the interplay among the indenter geometry, material slip systems, and cumulative shear strain distribution. Moreover, the interaction between GBs and dislocation slip substantially alters dislocation distribution, thereby influencing material flow and playing a critical role in the mechanical response and plastic deformation of the material.