Concurrent Enhancement of Fatigue Life and Corrosion Resistance via Laser Shock Peening

该研究项目涉及与激光冲击强化（LSP）引起的表面变形相关的基础科学，以及激光冲击强化在提高金属部件抗应力腐蚀开裂（SCC）能力方面的应用，以及激光冲击强化对疲劳寿命的影响。SCC是一种腐蚀环境中拉伸载荷的组合导致过早失效的现象。这种失效通常是突然的、灾难性的，并且发生在远低于材料屈服强度的载荷水平下，因此很难预测。根据材料和环境的不同，SCC可以通过不同的机制发生，因此需要确定缓解方法。使用LSP在表面产生的冲击波传递压残余应力，没有热效应，传统上用于提高材料的疲劳寿命。它们还会引起微观结构水平的其他变化，这可能有助于同时减轻SCC。提高材料性能将增强现有技术的能力，有可能使它们在更高的拉伸载荷下工作更长时间。此外，表面处理方法可以应用于不同的材料和几何结构，从而为从核反应堆到石油生产到医疗设备等许多行业提供有效的解决方案。因此，该研究具有显著的广度，并对经济福利和国家安全产生直接而积极的影响。通过与全国黑人工程师协会（National Society of Black Engineers）等少数群体建立联系，将招募到代表性不足的学生。来自曼哈顿北部和布朗克斯附近学校的高中生和STEM教师将参与“伸出手”和“让进来”活动的创新结合。该项目将阐明允许变形过程具有应力腐蚀开裂（SCC）缓解效益的机制。对激波诱导的微结构变化与SCC路径之间相互作用的基本理解将得到发展。氢已被确定为驱动SCC的主要成分，因此氢进入表面和吸收氢在晶格内的传播将更好地理解。移动位错的移动有助于裂纹扩展。这两种成分都会受到激波处理过程中形成的位错胞结构的影响。此外，还将从基本的角度研究变形过程中电化学对SCC及其缓解的影响。最后，该项目将对LSP对疲劳寿命的影响与抗SCC能力之间的平衡进行科学研究。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。

This research project addresses the fundamental science associated with surface deformations induced by laser shock peening (LSP), and their use to improve the stress corrosion cracking (SCC) resistance of metallic components in addition to LSP's well-known effect on fatigue life. SCC is a phenomenon where the combination of a tensile load in a corrosive environment causes premature failure. This failure is often sudden, catastrophic and occurs at loading levels far below a material's yield strength, making it difficult to predict. Depending on the material and environment, SCC can occur through different mechanisms, thus there is a need to identify mitigation approaches. Shockwaves generated on the surface using LSP impart compressive residual stresses, without thermal effects, and have traditionally been used to improve the material's fatigue life. They also induce other changes at the microstructural level, which may help mitigate SCC concurrently. Improving material performance will enhance the capability of existing technologies, potentially by allowing them to operate at higher tensile loads for longer times. In addition, the surface treatment methodology can be applied to different materials and geometric configurations, thus providing effective solutions for many industries ranging from nuclear reactors to oil production to medical devices. As such, the research has significant breadth and directly and positively impacts economic welfare and national security. By networking with minority groups such as National Society of Black Engineers, underrepresented students will be recruited. High school students and STEM teachers from neighborhood schools in northern Manhattan and the Bronx will be engaged in an innovative combination of "reach out" and "let in" activities.This project will set forth the mechanisms that allow deformation processes to have stress corrosion cracking (SCC) mitigation benefits. Fundamental understanding of the interaction between the shockwave-induced microstructural changes and the SCC pathways will be developed. Hydrogen has been identified as a major component driving SCC, and thus entry of hydrogen into the surface and propagation of absorbed hydrogen within the lattice will be better understood. Movement of mobile dislocations can contribute to crack propagation. Both of these components will be influenced by dislocation cell structures formed during shockwave processing. In addition, the electrochemical effects of the deformation process on SCC and their mitigation will be studies in a fundamental approach. Finally the project will perform scientific investigation into the balance between LSP's effect on fatigue life and SCC resistance.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.