Sandia National Laboratories, Albuquerque, NM, USA.
Center for Integrated Nanotechnologies, Sandia National Laboratories, Albuquerque, NM, USA.
Nature. 2023 Aug;620(7974):552-556. doi: 10.1038/s41586-023-06223-0. Epub 2023 Jul 19.
Fatigue in metals involves gradual failure through incremental propagation of cracks under repetitive mechanical load. In structural applications, fatigue accounts for up to 90% of in-service failure. Prevention of fatigue relies on implementation of large safety factors and inefficient overdesign. In traditional metallurgical design for fatigue resistance, microstructures are developed to either arrest or slow the progression of cracks. Crack growth is assumed to be irreversible. By contrast, in other material classes, there is a compelling alternative based on latent healing mechanisms and damage reversal. Here, we report that fatigue cracks in pure metals can undergo intrinsic self-healing. We directly observe the early progression of nanoscale fatigue cracks, and as expected, the cracks advance, deflect and arrest at local microstructural barriers. However, unexpectedly, cracks were also observed to heal by a process that can be described as crack flank cold welding induced by a combination of local stress state and grain boundary migration. The premise that fatigue cracks can autonomously heal in metals through local interaction with microstructural features challenges the most fundamental theories on how engineers design and evaluate fatigue life in structural materials. We discuss the implications for fatigue in a variety of service environments.
金属的疲劳涉及在重复机械负载下裂纹的逐渐扩展和渐进式失效。在结构应用中，疲劳占服役失效的 90%。疲劳的预防依赖于实施大的安全系数和低效的过度设计。在传统的抗疲劳冶金设计中，微结构的开发旨在阻止或减缓裂纹的扩展。裂纹扩展被认为是不可逆的。相比之下，在其他材料类别中，基于潜在的愈合机制和损伤逆转的方法提供了一种有吸引力的替代方法。在这里，我们报告纯金属中的疲劳裂纹可以进行固有自愈合。我们直接观察到纳米级疲劳裂纹的早期扩展，正如预期的那样，裂纹在局部微观结构障碍处扩展、转向和停止。然而，出人意料的是，我们还观察到裂纹通过一种可以描述为裂纹面冷焊的过程进行愈合，这是局部应力状态和晶界迁移共同作用的结果。疲劳裂纹可以通过与微观结构特征的局部相互作用在金属中自动愈合的前提，挑战了工程师在设计和评估结构材料疲劳寿命时所依据的最基本理论。我们讨论了这一发现对各种服役环境中疲劳的影响。
