CAREER: Understanding the Role of Cu-Containing Secondary Phase Particles in Enhancing the Resistance to the Environmental Acceleration to Fatigue in Age-Hardenable Al Alloys

非技术总结：为了解决全球气候变化的生存危机和我们老化的基础设施，需要大幅提高基础设施中使用的金属的可持续利用（例如用于飞机、汽车和桥梁的铝以及用于船舶、汽车、桥梁和核废料储存的钢）。在考虑金属的可持续利用时，一个主要问题是通过腐蚀过程造成的环境退化，需要在环境退化（特别是腐蚀和相关的开裂）和材料科学方面受过教育的工程师。在日常生活中，腐蚀最容易被视为生锈；但在老化的基础设施中，它可能看不到，并导致灾难性的故障，严重限制工程金属结构的可持续长期使用。这项研究有助于理解为什么一些铝基金属天生就比其他金属具有更好的抗环境加速开裂和相关失效的能力。可以利用这些知识来提高性能，并长期可持续地使用具有较低环境抗开裂性的金属。通过这些研究努力，一名研究生和5年本科生研究经验（REU）和教师研究经验（RET）的参与者被介绍和培训腐蚀和材料科学。此外，随着研究团队开发与腐蚀相关的演示和社交媒体视频，广泛的学生和未来的工程师将接触到材料科学和腐蚀。最后，这项研究将在PI在俄亥俄州立大学的研究实验室（哥伦布当地的K-12学校）和俄亥俄州的教育重点大学维滕贝格大学（Wittenberg University）之间建立联系，这将远远超出短期目标。技术概述：腐蚀和环境辅助开裂（EAC）在可持续发展中起着关键作用。腐蚀和EAC的研究和教育对于确保我们的社会解决金属的可持续使用问题以节约能源和减少消耗至关重要。研究已经证实，一些时效硬化铝合金比其他铝合金具有更好的抗EAC性能，但其潜在机制尚未得到证实。具体来说，Al- cu基铝合金天生就比Al- zn基铝合金更能抵抗环境加速疲劳裂纹扩展。本研究验证了具有促进Cu在腐蚀过程中再沉积的冶金二次相的时效硬化铝合金（Al-Cu基铝合金）具有内在的抵抗环境加速疲劳裂纹扩展的能力，这是由于裂纹尾迹表面Cu富集催化了裂纹环境中的阴极反应。7xxx时效硬化铝合金具有较高的易感性，这一特性可自我缓解导致EAC发生的不利酸性环境。酸性较低的裂纹溶液pH值通过稳定裂纹尖端钝化膜降低了裂纹尖端H的吸收，从而降低了环境敏感性和腐蚀疲劳敏感性。下面的方法被用来检验这个假设。首先，断裂力学方法被用来探测特定Zn、Mg和Cu浓度的铝合金的腐蚀疲劳敏感性，作为疲劳加载频率和加载波形的函数。此外，利用插入断裂力学样品的微型柔性pH电极，直接探测裂纹尖端附近的pH值。最后，作为最后的确认，裂纹尖端的pH值被改变以促进或减轻腐蚀疲劳。这项研究由一个团队进行，包括首席研究员，一名赞助的研究生，以及RET和REU参与者，目的是在整个研究项目中培养和参与一个多元化的团队。该研究团队还共同合作开发与腐蚀相关的材料科学演示，这些演示将在REU和RET的国内机构以及俄亥俄州立大学的材料科学导论课程中部署。社交媒体视频也正在制作中，以展示先进的演示和多样化的研究团队，他们的使命是教育腐蚀科学及其如何影响可持续性。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-Technical Summary: In order to address the existential crisis of global climate change and our aging infrastructure, dramatically improving the sustainable use of metals utilized in our infrastructure (examples include aluminum used for aircraft, automobiles, and bridges and steels used for ships, automobiles, bridges, and nuclear waste storage) is required. A major problem when considering the sustainable use of metals is environmental degradation through corrosion processes and the need for engineers educated in both environmental degradation (specifically corrosion and related cracking) and materials science. In everyday life, corrosion is most easily seen as rust; but in aging infrastructure it can go unseen and cause catastrophic failures that severely limit sustainable long-term use of engineered metal structures. This research pushes to understand why some aluminum based metals have inherently better resistance to the environmental acceleration of cracking and associated failures than others. Knowledge that could be utilized to improve the performance and the long term sustainable use of metals that have lower environmental resistance to cracking. Through these research endeavors, a graduate student and 5 years of REU (Research Experience of Undergraduates) and RET (Research Experience for Teachers) participants are being introduced to and trained in corrosion and materials science. Additionally, a wide range of students and future engineers are being exposed to materials science and corrosion as the research team develops corrosion related demos and social media videos. Finally, this research is establishing bonds between the PI’s research lab at The Ohio State University, a local Columbus K-12 school, and an education focused university in Ohio, Wittenberg University, which will go far beyond the short-term goals. Technical Summary: Corrosion and environment assisted cracking (EAC) play critical roles in sustainability. Research and education in corrosion and EAC is critical to ensuring our society addresses the sustainable use of metals to save energy and reduce consumption. Research has established that some age-hardenable aluminum alloys have better resistance to EAC than others, but an underlying mechanism for this has yet to be confirmed. Specifically, Al-Cu based Al alloys are inherently more resistant to the environmental acceleration of fatigue crack growth than Al-Zn based Al alloys. This research tests the hypothesis that age-hardenable Al alloys with metallurgical secondary phases that promote Cu re-depostion during corrosion (Al-Cu based Al alloys) have an intrinsic resistance to the environmental acceleration to fatigue crack growth as a result of crack wake surface Cu enrichment catalyzing cathodic reaction(s) within the crack environment. This self-mitigates the adverse acidic environment established to drive EAC in 7xxx age-hardenable Al alloys, which are of higher susceptibility. The less acidic crack solution pH reduces environmental sensitivity and corrosion fatigue susceptibility by reducing crack tip H uptake through the stabilization of a crack tip passive film. The following approaches are being used to test this hypothesis. First, fracture mechanics approaches are being utilized to probe corrosion fatigue sensitivity of Al alloys with specific Zn, Mg, and Cu concentrations as a function of fatigue loading frequency and load waveform. In addition, near crack tip pH is being directly probed utilizing mini-flexible pH electrodes inserted into the fracture mechanics samples. Finally, crack tip pH is being altered to either promote or mitigate corrosion fatigue as a final confirmation. This research is being performed by a team that includes the principal investigator, a sponsored graduate student, and RET and REU participants with the goal of training and engaging a diverse team throughout the research program. Together this research team is also collaboratively developing corrosion related materials science demos that will be deployed at the REU’s and RET’s home institutions and in the Introduction to Materials Science course at The Ohio State University. Social media videos are also being created to showcase the developed demos and the diverse research team with the mission of educating on the science of corrosion and how it impacts sustainability.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.