飞秒激光诱导超快超高压冲击加载下金属箔材塑性成形机理及方法

The mechanisms of ultrafast laser-matter interaction, are different from those of long-pulse lasers(pulse width>100ps)，which makes the formation mechanisms and characteristics of femtosecond laser -induced shockwaves differ significantly from nanosecond laser .So the plastic forming technology based on ultrafast laser-induced shockwave demonstrates distinct features: very small thermal effects, high precision, and easy to control. And this technology has unique advantages over other plastic forming methods and huge potential applications in the field of micro-fabrication..This project intends to study the fundermental theory and technology of plastic forming based on ultrafast laser-induced shockwaves.The theoretical models of ultrafast laser inducing mechanical shockwaves, and coupling shockwaves into metal targets will be established and then these processes be numerically simulated. The spatial and temporal evolutions of plasma and shockwave will also be experimentally monitored.Then we will carry out single-point and single-line scanning laser shock experiments. Through the above mentioned researches, the project intends to explore the forming mechanisms of ultrafast laser-induced shockwave, the temporal and spatial evolution characteristics of shockwave, plastic deformation mechanisms of metal foil, and the influences of laser parameters on the plastic deformation. Through optimizing the process parameters,the expected local plastic deformation can be realized firstly.Based on the obtained optimization results of sing-point and single-line scanning laser shock experiments, we will research the technology of controlling forming shape and deformation of metal foil through multiple and multi-channel scanning and appropriately designing and matching process parameters of each scan .The databases of optimized process parameters and process plans of dielessly forming typical surface shapes will be established.. The theory, process and technology research results obtained in this project will lay the theoretical and technical foundations for the application of ultrafast laser shock processing technology in the field of micro-fabrication.

飞秒激光与靶材作用机理不同于长脉冲（脉宽>100ps）激光，这使得飞秒激光诱导冲击波形成机制及冲击波特性显著不同于纳秒激光诱导冲击波，基于飞秒激光诱导冲击波的加工方法具有热效应极小、精度高、可控性强等特点，在微制造领域具有独特优势。本项目拟研究基于飞秒激光诱导力学冲击波的金属箔材塑性成形基础理论和工艺技术。通过建立飞秒激光－冲击波－靶材的耦合数学模型和数值研究、实时监测等离子体和冲击波时空演变、实施单点和单道扫描激光冲击实验，研究飞秒激光诱导冲击波的形成机制、激光参数对冲击波特性的影响规律、超快超高压冲击加载下金属箔材的塑性变形机制、以及激光参数对箔材塑性变形特征和变形量的影响规律。在获得单点和单道扫描激光冲击优化工艺参数基础上，研究通过合理设计和匹配多道次扫描工艺参数，控制箔材形状和变形量，获得优化工艺参数库和典型曲面无模成形工艺方案库，为超快激光冲击塑性成形在微制造领域的应用奠定基础。

飞秒激光与物质相互作用具有过程超快、热效应小等特性，这使得飞秒激光加工在高精度制造领域具有独特优势。本项目围绕金属箔材飞秒激光冲击成形，研究了飞秒激光与物质相互作用的特性（包括温度场、冲击波等）、箔材的飞秒激光冲击成形工艺、成形精度的影响因素和规律、超快超高压条件下箔材的塑性变形机制、靶材表面微缺陷形成机理等。项目获得的主要结论如下：（1）激光能量密度显著影响电子-晶格耦合时间，能量密度增加会使耦合时间超过靶材热扩散的特征时间，材料发生热烧蚀，进而改变飞秒激光加工特性。（2）约束层和吸收层是影响冲击成形效果的重要因素。超快激光冲击成形过程中，约束层有两种典型破坏机制：非线性烧蚀和机械胀裂。为保证冲击效果，非线性烧蚀必须要避免。吸收层应优选声阻抗值最接近“最佳声阻抗值”的材料。（3）脉宽是飞秒激光冲击成形的重要工艺参数。材料对超快超高压冲击波的响应具有局域性特征，即脉冲宽度越短，光束直接作用区外的弯曲影响区越小。因此，脉冲宽度是影响激光冲击成形精度和可控性的重要因素，缩小激光脉冲宽度，有利于提高成形精度；但是，脉冲宽度过短，激光峰值功率密度过高，会导致约束层非线性烧蚀，也会削弱成形效果。（4）超快超高压冲击加载下，高应变率和超高压载荷使得层错和孪晶成为铜靶材的重要塑性变形机制；短、离散位错线和大量平行平直位错滑移线是高层错能铝靶材内微观组织特征。上述现象与纳秒激光冲击，以及低应变率塑性变形截然不同。（5）靶材表面凸起微缺陷是吸收层背面不均匀粘结层调制冲击波的结果，弄清该机理为激光冲击后靶材表面质量控制提供了依据。项目研究成果为飞秒激光冲击塑性成形在微制造领域的应用奠定了基础。