面心立方金属材料孪晶界面疲劳开裂机制的计算模拟

Experimental observations and theretical studies about bicrystals with different twin boundaries (TBs) uncover that the mechanisms of fatigue cracking are mainly determined by the interaction between TBs and dislocations with complicated configureations in face-centered cubic metals and alloys, and that they could be a function of the loading orientation and stacking faut energy. However, experimental results cannot be fully understood because of the lack of derect evidence of fatigue cracking at atomic scale. For atomistic simulations, molecular dynamics and first principles are performed to investigate the dynamic process of the boundary-dislocation interaction and the related fatigue cracking behaviors in the vicinity of TBs, such as: 1) the interaction between TBs and dislocations with different configurations (a single dislocation, piled-up dislocations and PSB ladder), 2) the underlying causes of the influence of loading orientation and stacking fault energy on the interaction between TBs and dislocations, and 3) the evolution process from the damage due to the boundary-dislocation interaction to crack initiation and propagation. In order to verify the present modeling results, a series of experimental observations of deformation microstructures are needed by scanning electron microscopy and transmission electron microscopy, especially during in situ straining experiments, to reveal dislocation reactions, slip band distributions, dislocation structures of TBs，crack initiation and so on. The results from atomistic modeling together with experimental observations serve to validate theoretical models about the influence of different TBs on the fatigue cracking mechanisms of face-centered cubic metals and alloys, and further enhance our understanding of the role of TBs on strengthening, toughening and fatigue fracture of materials.

面心立方金属双晶样品疲劳实验观测与理论分析表明，孪晶界面开裂方式主要取决于孪晶界面与复杂组态位错交互作用所造成的应变局部化，与加载取向和层错能密切相关。然而，由于缺乏直接证据，现有的实验观测和理论分析不足以揭示孪晶界面疲劳开裂的微观机制，需要借助原子尺度模拟计算，它可以动态揭示孪晶界面与复杂组态位错交互作用以及所导致的开裂过程。本研究工作主要包括：1）单一特定位错或复杂组态位错与孪晶界面的交互作用；2）层错能和加载取向对界面-位错交互作用的影响；3）孪晶界面与位错交互作用所引起的裂纹萌生与扩展机制。为了验证模拟结果，在已有的实验基础上也会补充关于位错和裂纹的定量实验分析。最终，在综合模拟计算、实验观测和理论分析的基础上，建立疲劳实验中孪晶界面微观开裂机制并定量描述之，为探索孪晶界面强韧化机制、疲劳损伤机制和界面工程优化设计提供实验证据。

孪晶界面一方面可以作为界面阻碍位错运动，另一方面又可以作为滑移面吸收位错并使其产生交滑移。在过去的研究中，位错组态和交滑移机制很少定量考虑，因此，本项目选择具有不同层错能面心立方材料，结合实验（以Cu和Cu-Al合金为主）和原子尺度模拟计算（以Cu以及Ni和Ag为主）对孪晶界面与复杂组态位错交互作用进行系统研究，揭示孪晶界面开裂行为。原子尺度模拟计算主要研究面心立方系统中位错的滑移、孪晶、交滑移和位错组态等，以及与孪晶界面间的交互作用等，主要研究成果包括：1）证明了位错组态是影响位错分解以及交滑移的重要因素，实验中也发现复杂组态位错与孪晶界面的交互作用；2）确定了层错能和加载取向对位错分解有函数关系，超出弹性力学可以预测的范围，影响位错-孪晶交互作用；3）证明了位错在特定取向下容易被孪晶界面吸收并发生堆积，是裂纹萌生的重要机制。在综合模拟计算、实验观测和理论分析的基础上，建立了疲劳实验中孪晶界面微观开裂机制并定量描述之，为探索孪晶界面强韧化机制、疲劳损伤机制和界面工程优化设计提供了研究基础。