Zhang Yong, He Chenyun, Yu Qin, Li Xiao, Wang Xiaogang, Zhang Yin, Wang Ji, Jiang Chao, Jia Yunfei, Zhang Xian-Cheng, Sun Binhan, Ritchie Robert O, Tu Shan-Tung
Key Laboratory of Pressure Systems and Safety, Ministry of Education, School of Mechanical and Power Engineering, East China University of Science and Technology, Shanghai, 200237, China.
Department of Materials Science and Engineering, University of California, Berkeley, CA, 94720, USA.
Nat Commun. 2024 Aug 12;15(1):6917. doi: 10.1038/s41467-024-51423-5.
Fatigue failure is invariably the most crucial failure mode for metallic structural components. Most microstructural strategies for enhancing fatigue resistance are effective in suppressing either crack initiation or propagation, but often do not work for both synergistically. Here, we demonstrate that this challenge can be overcome by architecting a gradient structure featuring a surface layer of nacre-like nanolaminates followed by multi-variant twinned structure in pure titanium. The polarized accommodation of highly regulated grain boundaries in the nanolaminated layer to cyclic loading enhances the structural stability against lamellar thickening and microstructure softening, thereby delaying surface roughening and thus crack nucleation. The decohesion of the nanolaminated grains along horizonal high-angle grain boundaries gives rise to an extraordinarily high frequency (≈1.7 × 10 times per mm) of fatigue crack deflection, effectively reducing fatigue crack propagation rate (by 2 orders of magnitude lower than the homogeneous coarse-grained counterpart). These intriguing features of the surface nanolaminates, along with the various toughening mechanisms activated in the subsurface twinned structure, result in a fatigue resistance that significantly exceeds those of the homogeneous and gradient structures with equiaxed grains. Our work on architecting the surface nanolaminates in gradient structure provides a scalable and sustainable strategy for designing more fatigue-resistant alloys.
疲劳失效始终是金属结构部件最关键的失效模式。大多数提高抗疲劳性能的微观结构策略在抑制裂纹萌生或扩展方面是有效的，但通常不能同时协同作用于两者。在此，我们证明了通过构建一种梯度结构可以克服这一挑战，该梯度结构在纯钛中具有类似珍珠母的纳米层状表面层，随后是多变体孪晶结构。纳米层状层中高度规整的晶界对循环载荷的极化调节增强了结构对层片增厚和微观结构软化的稳定性，从而延迟了表面粗糙度增加，进而延迟了裂纹形核。纳米层状晶粒沿水平大角度晶界的脱粘产生了极高频率（≈1.7×10次/毫米）的疲劳裂纹偏转，有效降低了疲劳裂纹扩展速率（比均匀粗晶对应物低2个数量级）。表面纳米层的这些有趣特性，以及在亚表面孪晶结构中激活的各种增韧机制，导致其抗疲劳性能显著超过具有等轴晶粒的均匀和梯度结构。我们在梯度结构中构建表面纳米层的工作为设计更抗疲劳的合金提供了一种可扩展且可持续的策略。
