Anisotropic failure behavior of ordered intermetallic TiAl alloys under pure mode-I loading
Anisotropic failure behavior of ordered intermetallic TiAl alloys under pure mode-I loading
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DOI：
10.1088/1361-651x/aba738
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发表时间：
2020-09-01
影响因子：
1.8
通讯作者：
Janisch, Rebecca
中科院分区：
文献类型：
--
作者：
Neogi, Anupam;Alam, Masud;Janisch, Rebecca
金属材料断裂是脆性解理断裂还是韧性断裂主要取决于裂纹尖端解理与位错发射之间的竞争。基于线弹性断裂力学（LEFM）的Griffith准则和Rice的位错发射准则对于确定各向同性晶体金属中可能的裂纹尖端扩展机制是足够可靠的。然而，当考虑非立方各向异性固体时，这些标准的适用性是值得怀疑的，例如，有序的金属间TiAl相，其中滑移系统是有限的，弹性各向异性是明显的。我们使用大规模的原子模拟研究面心四面体TiAl和六方体Ti3Al的脆性与韧性失效机制，并将我们的研究结果与基于LEFM的弹性各向异性增强标准的预测进行比较。我们观察到，扩大格里菲斯和赖斯准则是可靠的，确定方向相关的裂纹尖端机制，如果所有可用的位错滑移系统被考虑在内。然而，原子模拟是必要的，以了解裂纹钝化由于混合机制，或剪切不稳定性以外的位错发射。我们的系统研究的结果可以作为修改格里菲斯/赖斯标准，以纳入这些影响的基础。
Whether a metallic material fractures by brittle cleavage or by ductile rupture is primarily governed by the competition between cleavage and dislocation emission at the crack tip. The linear elastic fracture mechanics (LEFM) based criterion of Griffith, respectively the one for dislocation emission of Rice, are sufficiently reliable for determining the possible crack tip propagation mechanisms in isotropic crystalline metals. However, the applicability of these criteria is questionable when non-cubic, anisotropic solids are considered, as e.g. ordered intermetallic TiAl phases, where slip systems are limited and elastic anisotropy is pronounced. We study brittle versus ductile failure mechanisms in face-centered tetragonal TiAl and hexagonal Ti3Al using large-scale atomistic simulations and compare our findings to the predictions of LEFM-based criteria augmented by elastic anisotropy. We observe that the augmented Griffith and Rice criteria are reliable for determining the direction dependent crack tip mechanisms, if all the available dislocation slip systems are taken into account. Yet, atomistic simulations are necessary to understand crack blunting due to mixed mechanisms, or shear instabilities other than dislocation emission. The results of our systematic study can be used as basis for modifications of the Griffith/Rice criteria in order to incorporate such effects.