铜及铜铝合金中晶界、孪晶界的变形与剪切疲劳开裂机制研究

The role of grain boundaries (GBs) in plastic deformation and fatigue damage of materials is one of the important frontiers and hotspots in the research field of material science. It is well-known that high-angle GBs are always the preferential fatigue cracking sites, independent on the angles between the high-angle GBs and the loading axis. Fortunately, the fatigue cracking behaviors of twin boundaries (TBs) vary with their inclination angles with respect to the loading axis and thus could be tuned. The key point is that the fatigue cracking of inclined TB is concerned with the shearing effect of the slip bands (SBs) nearby, which is different from conventional fatigue cracking of high-angle GBs with the impingement of SBs. Especially when the TB is inclined at 45° to the loading direction, the SBs parallel to the TB concentrate at the TB showing strong strain localization. In this project, Cu and Cu-Al alloys bicrystals with a TB will be employed to investigate the effect of stacking fault energy (SFE) on the deformation homogeneity of the bicrystals and the fatigue cracking behavior of the TBs. By combined consideration of the shear fatigue cracking behaviors of {111} high-angle GB as well as the TB, the rule and micromechanism of interfacial shear fatigue cracking will be proposed. On the other hand, investigations on the roles of the {111} GB and TB in the deformation of bicrystal micropillars will be performed. Wherein, the shear deformation of the {111} GB and TB will be explored in order to deeply understand their shear fatigue cracking behavior. It is hoped that the above investigations could expand our knowledge on the deformation and fatigue cracking behaviors of interfaces, which could finally provide experimental and theoretical foundations for the interfacial design in optimizing mechanical properties of materials.

深入理解材料塑性变形与疲劳损伤的晶界效应是材料研究领域的重要和热点问题。研究发现，普通大角晶界疲劳开裂行为与取向无关，而共格孪晶界疲劳开裂行为具有一定的取向性与可调节性。其中较为关键的是，不同于常见大角晶界的撞击型疲劳开裂，倾斜孪晶界在两侧滑移带的剪切作用下萌生疲劳裂纹，并伴随明显的应变局部化现象。本项目拟选用含共格孪晶界的纯铜与单相铜铝合金双晶，研究合金成分（层错能）变化对双晶变形均匀性以及孪晶界剪切疲劳开裂行为的影响；对比分析铜双晶中倾斜{111}大角晶界和孪晶界的剪切疲劳开裂行为及微观机制的差异，总结晶界的剪切疲劳开裂规律；另外，研究小尺度下{111}大角晶界、孪晶界在双晶变形中的作用，探索晶界与孪晶界抵抗变形能力的差异，辅助理解二者的剪切疲劳开裂行为。希望通过本项目的研究，扩展人们对晶界变形与疲劳开裂机制的认识，为材料界面优化设计提供实验与理论依据。

深入理解材料塑性变形与疲劳损伤的晶界效应是材料研究领域的重要和热点问题。研究发现，普通大角晶界疲劳开裂行为与取向无关，而共格孪晶界疲劳开裂行为具有一定的取向性与可调节性。其中较为关键的是，不同于常见大角晶界的撞击型疲劳开裂，倾斜孪晶界在两侧滑移带的剪切作用下萌生疲劳裂纹，并伴随明显的应变局部化现象。本项目对孪晶界取向以及层错能对孪晶界疲劳开裂行为的影响机制进行了系统总结整理；对含特殊大角晶界和非共格孪晶界以及小角晶界的双晶样品进行了疲劳实验，研究了位错撞击作用下晶界疲劳开裂阻力的差异；选用纯铜与单相铜铝合金单晶，研究合金成分（层错能）变化对滑移带疲劳开裂行为的影响；另外，研究小尺度下孪晶界在双晶变形中的作用，探索孪晶界抵抗变形能力的差异。本项目的研究结果，扩展了人们对滑移带疲劳开裂机制以及晶界变形与疲劳开裂机制的认识，为材料界面优化设计提供实验与理论依据。