难熔陶瓷中滑移诱导裂纹钝化的描述符
Descriptor for slip-induced crack-blunting in refractory ceramics
AI总结：
该研究针对难熔陶瓷脆性与塑性竞争问题，以Ti-N体系为对象开展原子尺度模拟，验证了半经验原子间势，揭示了滑移诱导裂纹钝化的机制，并提出Iplast描述符可用于排序陶瓷的位错介导裂纹钝化能力。
摘要：
理解难熔陶瓷中脆性与塑性的竞争关系，对于辅助设计抗断裂性能提升的硬质材料具有重要意义。受TiN陶瓷中位错活动产生裂纹屏蔽的实验观测[Int J Plast 27 (2011) 739]启发，我们开展了全面的原子尺度研究，以明确Ti-N体系中脆性和滑移诱导塑性的作用机制。首先，我们采用密度泛函理论计算得到的解理格里菲斯应力强度（KIc）和位错发射赖斯应力强度（KIe）结果，以及300至1200 K温度下完整和含缺陷TiN晶格的从头算分子动力学力学测试模拟结果，验证了一种半经验原子间势的可靠性。计算得到的KIc和KIe值表明TiN具有本征脆性，因为KIc远小于KIe。然而，可通过纳米尺度建模可靠预测宏观力学性能的KI控制分子静力学模拟显示，裂纹锐度降低和/或阴离子空位的存在能够促进滑移塑性。对受拉的带缺口Ti-N超胞模型开展的经典分子动力学模拟，为有限温度下脆性与塑性的竞争提供了定性认识。尽管多数情况下会发生裂纹扩展，但缺口尖端处足够快速的切应力累积，可通过位错的形核与发射延缓或阻止断裂。此外，我们发现含缺陷TiN晶格中出现滑移诱导塑性并导致裂纹钝化的概率，与完整Ti-N晶体的理想拉伸/剪切强度比（Iplast）相关。我们提出，在评估陶瓷通过位错介导的塑性在有限温度下钝化裂纹的能力时，应考虑将Iplast描述符作为排序指标。
英文摘要：
Understanding the competition between brittleness and plasticity in refractory ceramics is of importance for aiding design of hard materials with enhanced fracture resistance. Inspired by experimental observations of crack shielding due to dislocation activity in TiN ceramics [Int J Plast 27 (2011) 739], we carry out comprehensive atomistic investigations to identify mechanisms responsible for brittleness and slip-induced plasticity in Ti-N systems. First, we validate a semi-empirical interatomic potential against density-functional theory results of Griffith and Rice stress intensities for cleavage (KIc) and dislocation emission (KIe) as well as ab initio molecular dynamics mechanical-testing simulations of pristine and defective TiN lattices at temperatures between 300 and 1200 K. The calculated KIc and KIe values indicate intrinsic brittleness, as KIc<<KIe. However, KI-controlled molecular statics simulations - which reliably forecast macroscale mechanical properties through nanoscale modelling - reveal that slip-plasticity can be promoted by a reduced sharpness of the crack and/or the presence of anion vacancies. Classical molecular dynamics simulations of notched Ti-N supercell models subject to tension provide a qualitative understanding of the competition between brittleness and plasticity at finite temperatures. Although crack growth occurs in most cases, a sufficiently rapid accumulation of shear stress at the notch tip may postpone or prevent fracture via nucleation and emission of dislocations. Furthermore, we show that the probability to observe slip-induced plasticity leading to crack-blunting in flawed Ti-N lattices correlates with the ideal tensile/shear strength ratio (Iplast) of pristine Ti-N crystals. We propose that the Iplast descriptor should be considered for ranking the ability of ceramics to blunt cracks via dislocation-mediated plasticity at finite temperatures.
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