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：为了应对全球气候变化和我们老化的基础设施的生存危机，需要大幅提高我们基础设施中使用的金属的可持续利用(例如，用于飞机、汽车的铝，以及用于船舶、汽车、桥梁和核废料储存的桥梁和钢材)。在考虑金属的可持续使用时，一个主要问题是通过腐蚀过程造成的环境退化，以及需要受过环境退化(特别是腐蚀和相关开裂)和材料科学教育的工程师。在日常生活中，腐蚀最容易被视为铁锈；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，严重限制了工程金属结构的可持续长期使用。这项研究推动理解为什么一些铝基金属天生就比其他金属更能抵抗环境加速开裂和相关故障的能力。可用于改善环境抗裂性较低的金属的性能和长期可持续使用的知识。通过这些研究工作，一名研究生和5年的REU(本科生研究经验)和RET(教师研究经验)参与者被介绍到腐蚀和材料科学方面并接受培训。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，大量学生和未来的工程师将接触到材料科学和腐蚀。最后，这项研究正在俄亥俄州立大学(俄亥俄州立大学)的研究实验室和俄亥俄州一所专注于教育的大学威滕贝格大学(Wittenberg University)之间建立联系，这将远远超出短期目标。技术综述：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方面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以节约能源和降低消耗至关重要。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。具体地说，Al-Cu基铝合金比Al-Zn基铝合金具有更强的抗环境疲劳裂纹扩展加速能力。本研究验证了时效硬化铝合金(Al-Cu基铝合金)的假设，即含有促进腐蚀过程中铜再沉积的冶金第二相的时效硬化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铜的富集化催化了裂纹环境中的阴极反应(S)。这自我缓解了为驱动7xxx时效硬化铝合金的EAC而建立的不利的酸性环境，这些铝合金具有更高的敏感性。酸性较弱的裂纹溶液pH通过稳定裂纹尖端钝化膜来减少裂纹尖端的吸氢量，从而降低环境敏感性和腐蚀疲劳敏感性。以下方法被用来检验这一假设。首先，利用断裂力学方法研究了特定锌、镁、铜含量的铝合金的腐蚀疲劳敏感性随疲劳加载频率和加载波形的变化规律。此外，利用插入断裂力学样品的微型柔性pH电极，可直接探测裂纹尖端附近的pH。最后，裂纹尖端的pH值正在改变，以促进或减轻腐蚀疲劳，作为最终确认。这项研究由一个团队进行，该团队包括首席研究员、一名受资助的研究生以及RET和REU参与者，目标是在整个研究计划中培训和吸引不同的团队。该研究团队还在合作开发与腐蚀相关的材料科学演示，这些演示将部署在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。还在制作社交媒体视频，以展示开发的演示和不同的研究团队，其使命是教育腐蚀科学及其如何影响可持续发展。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势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.