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，以及它们用于提高金属部件的应力腐蚀开裂（SCC）抗性，以及LSP对疲劳寿命的众所周知的影响。SCC是一种在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，使得难以预测。 根据材料和环境的不同，SCC可能通过不同的机制发生，因此需要确定缓解方法。使用LSP在表面上产生的冲击波赋予压缩残余应力，而没有热效应，并且传统上用于提高材料的疲劳寿命。它们还在微观结构水平上引起其他变化，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，可能使它们能够在更高的拉伸载荷下运行更长的时间。此外，表面处理方法可以应用于不同的材料和几何构型，从而为从核反应堆到石油生产再到医疗设备的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，并直接和积极影响经济福利和国家安全。通过与全国黑人工程师协会等少数群体建立联系，将招募代表性不足的学生。来自北方曼哈顿和布朗克斯社区学校的高中生和STEM教师将参与“伸出手”和“让进”活动的创新组合。该项目将阐述使变形过程具有应力腐蚀开裂（SCC）缓解效益的机制。冲击波引起的微观结构的变化和SCC途径之间的相互作用的基本理解将被开发。氢已被确定为驱动SCC的主要组分，因此将更好地理解氢进入表面和吸收的氢在晶格内的传播。移动的位错的移动可有助于裂纹扩展。 这两种成分都将受到冲击波处理过程中形成的位错胞结构的影响。此外，变形过程中的电化学效应对应力腐蚀开裂及其缓解将是一个基本的方法进行研究。最后，该项目将对LSP对疲劳寿命和SCC抗性之间的平衡进行科学调查。该奖项反映了NSF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.