Micro-Scale Laser Shock Processing with Controlled Mechanical Properties, Microstructure and Fatigue Performance

激光冲击处理(LSP)，又称激光喷丸，是一种利用定向激光脉冲将有益的残余压缩应力施加到金属零件表面的过程。零件被处理在容易过早故障的特定区域。它是在70年代初被S接受的，目前正在生产使用毫米级激光的涡轮叶片等零部件。在微系统设计和制造取得快速进展的推动下，微尺度液晶光斑(即使用几微米大小的激光光斑)的初步研究表明是可行的。虽然微系统中的主要材料是硅，但金属厚膜和薄膜结构往往是不可或缺的一部分。其中一些金属微结构，如MEMS致动器、金属涂层微型齿轮、微型医疗植入物、微型开关和继电器，在使用中会承受循环载荷。因此，该项目的目标是提高微尺度LSP技术的知识水平，并开发可靠的能力来修改微系统中的金属结构，使其具有可控的机械性能、微结构和疲劳性能。更具体地说，本项目的目的是(1)通过适当考虑对微尺度重要的现象，并通过考虑块体、厚膜和薄膜材料，来开发对微尺度LSP的更好的理解和可靠的预测能力；(2)设计和适当地执行积极的实验计划，以补充建模工作，并为进一步的发展积累实验数据。该计划将研究适合于相关微观尺度的表征方法，以测量残余应力分布；以及量化LSP引起的微观结构变化的方法。这项研究引起了业界的极大兴趣，IBM、LSP Technologies和布鲁克海文国家实验室的支持将提供知识和特性交流。通过纽约市地区专业协会的地方分会向不同的本科生群体进行教育推广，将加强招收和留住这些工程专业学生的努力。

Laser shock processing (LSP), also known as laser peening, is a process in which beneficial compressive residual stress is imparted into surface layer of metallic parts by directed laser pulses. Parts are treated the specific areas prone to premature failures. It was incepted in early 70's and is currently in production for parts such as turbine blades using millimeter-sized laser beams. Motivated by the rapid progress being made in microsystem design and fabrication, preliminary studies on micro-scale LSP (i.e., using laser spot size of a few microns) have shown feasibility. While the dominant material in microsystems is silicon, metallic thick- and thin-film structures are often an integral part. Some of these metallic microstructures, such as MEMS actuators, metal-coated micro-gears, micro medical implants, micro-switches, and relays, experience cyclic loads in service. The goal of the project is thus to advance the state of knowledge in micro-scale LSP technology, and to develop reliable ability to modify metallic structures in microsystems, with controlled mechanical proper-ties, microstructures and fatigue performance. More specifically, the aims of this project are (1) to de-velop better understanding and reliable prediction capabilities for the micro-scale LSP by properly consid-ering phenomena important to the micro scale concerned, and by considering both bulk, thick- and thin-film materials; and (2) to design and properly execute an aggressive experimental program to complement the modeling effort and to accumulate experimental data for further development. This program will in-vestigate characterization methods appropriate for the micro-scale concerned to measure residual stress distribution; and methods to quantify microstructure change caused by LSP. This research is of substantial interest to industry, and support from IBM, LSP Technologies and Brookhaven National Lab will provide intellectual and characterization exchanges. Education outreach to a diverse group of undergraduate stu-dents through local chapters of professional societies in the New York City area will enhance efforts to recruit and retain these students in engineering.