Heterogeneous structure consisting of brittle-zones (BZs) rich of carbon nanotubes (CNTs) and ductile-zones (DZs) free of CNTs, was an effective way to improve the strength-ductility of CNT reinforced Al (CNT/Al) composites. Two heterogeneous CNT/2009Al composites with coarse grain (CG, ~2 μm) DZs or ultra-fine grain (UFG, ~500 nm) DZs were fabricated and achieved enhanced strength-ductility. However, the heterogeneous composite with CG DZs had a lower high-cycle fatigue strength as well as fatigue strength/tensile strength ratio than the uniform composite, while the heterogeneous composite with UFG DZs exhibited the increased fatigue strength and the same level of fatigue strength/tensile strength ratio compared to the uniform composite. It was found that the improved fatigue properties for the heterogeneous composite with the UFG DZs could attribute to two reasons. Firstly, the UFG for the DZs significantly increased the strength of DZs, which effectively reduced the strain localization in the DZs. Secondly, the dislocations piling up at the grain boundaries of the BZs, as well as the stress concentration at the boundaries between the DZs and BZs were relieved due to the coordinated micro-strain for the heterogeneous structure. This provided a simple strategy for the structural design of heterogeneous composites with high fatigue strength.

由富含碳纳米管 (CNT) 的脆区 (BZ) 和不含 CNT 的延展区 (DZ) 组成的异质结构是提高 CNT 增强铝 (CNT/Al) 复合材料强度-延展性的有效方法。制造了两种具有粗晶粒（CG，~2 μm）DZ 或超细晶粒（UFG，~500 nm）DZ 的异质 CNT/2009Al 复合材料，并实现了增强的强度-延展性。然而，具有CG DZs的异质复合材料的高周疲劳强度以及疲劳强度/拉伸强度比低于均匀复合材料，而具有UFG DZs的异质复合材料表现出更高的疲劳强度和相同水平的疲劳强度/与均匀复合材料相比的抗拉强度比。研究发现，具有 UFG DZ 的异质复合材料改善的疲劳性能可归因于两个原因。首先，用于 DZs 的 UFG 显着增加了 DZs 的强度，有效地减少了 DZs 中的应变局部化。其次，由于异质结构的协调微应变，BZs晶界处堆积的位错以及DZs和BZs边界处的应力集中得到缓解。这为具有高疲劳强度的异质复合材料的结构设计提供了一种简单的策略。由于异质结构的协调微应变，DZs和BZs边界处的应力集中得到缓解。这为具有高疲劳强度的异质复合材料的结构设计提供了一种简单的策略。由于异质结构的协调微应变，DZs和BZs边界处的应力集中得到缓解。这为具有高疲劳强度的异质复合材料的结构设计提供了一种简单的策略。