Collaborative Research: Feasibility and Fundamentals of Femtosecond-Laser Shock Peening Without Protective Coating in Air Environment

激光诱导的局部冲击波可以在金属表面产生压应力，从而提高零件的硬度和疲劳度，而不会改变其整体材料特性。这种纳秒激光冲击强化工艺需要一种保护涂层来对抗热影响区，并需要一种限制介质来促进冲击波。该研究将调查飞秒激光冲击喷丸工艺的能力，该工艺具有更高的能量密度，在不需要保护涂层和限制层的情况下实现相同的结果。消除涂层和限制层将显著降低设置复杂性和制造成本。在飞秒激光喷丸过程中发生的基本物理机制上获得的知识将被利用来实现更高分辨率的工艺，该工艺能够处理比目前纳秒激光喷丸更广泛的材料。这种先进的制造能力将有助于提高美国的竞争力，因为它可以应用于先进的精密仪器、3D打印技术、生物医学植入物和微机械系统的开发。除了为研究生提供先进的制造业专业知识外，研究成果将被纳入课程模块和教育推广活动，旨在为代表性不足的少数民族，以进一步鼓励更多合格的人进入制造业劳动力。研究目的是了解飞秒激光冲击强化的基本机制和局限性，没有保护涂层在空气环境中。为了实现这两个过程相关的非平衡电子动力学，超高应变率变形机制将进行研究。一种独特的原位测量方法将被用来捕捉飞秒激光冲击硬化不锈钢304和铝6061样品过程中发生的等离子体动力学。微观结构的演变将被表征，以研究在压力和应变率下的变形动力学，同时测量表面形态、残余应力、表面硬度和疲劳，以测试该过程的有效性。混合数值模型，通过实验验证，将被用来进一步了解潜在的机制。Fokker-Planck模型将专注于揭示非平衡电子动力学。从这个模型的输出将被纳入一个流体动力学模型，以预测所产生的等离子体的形成和冲击波的产生。冲击波信息将被集成到有限元模型中，以帮助预测金属在超高应变率冲击下的变形过程。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。

Laser induced, localized shock waves can generate compressive stresses in a metal's surface that improve the hardness and fatigue of the part without altering its bulk material properties. This process, nanosecond laser shock peening, requires a protective coating to combat the heat affect zone, and a confining medium to promote the shock waves. The research will investigate the ability of a femtosecond laser shock peening process, which has higher energy density, to achieve the same result without the need for the protective coating and confinement layer. Eliminating the coating and confinement layer will significantly reduce setup complexity and manufacturing costs. Knowledge gained on the fundamental physical mechanisms occurring during femtosecond laser peening will be leveraged to realize a higher resolution process capable of processing a broader range of materials than currently possible by nanosecond laser peening. This advanced manufacturing capability will contribute to the competitiveness of the US by finding application in the development of progressive precision instrumentation, 3D-printing technologies, biomedical implants, and micro-mechanical systems. In addition to providing graduate students with advanced manufacturing expertise, the research results will be integrated into both course modules and educational outreach activities aimed at underrepresented minorities to further encourage more qualified people into the manufacturing work force. The research objective is to understand the fundamental mechanisms and limitations of femtosecond laser shock peening without a protective coating in an air environment. To achieve this both process related non-equilibrium electron dynamics, and super-high strain-rate deformation mechanisms will be investigated. A unique in-situ measurement method will be used to capture the plasma dynamics occurring during femtosecond laser shock peening of stainless steel 304 and aluminum 6061 samples. The microstructure evolution will be characterized to study the deformation dynamics under ultrahigh pressure and stain rate, while the surface morphology, residual stress, surface hardness, and fatigue will be measured to test the effectiveness of the process. Hybrid numerical models, validated by experiments, will be utilized to further understand the underlying mechanisms. A Fokker-Planck model will focus on revealing non-equilibrium electron dynamics. Outputs from this model will be incorporated into a hydrodynamic model to predict the resultant plasma formation and shock wave generation. The shock wave information will be integrated into a finite element model to assist in predicting the deformation process of metals subjected to super-high strain-rate impacts.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.