飞秒激光烧蚀金箔机理及模拟分析

研究了在不同能量密度的单脉冲飞秒激光下烧蚀金箔的过程。讨论在不同能量密度的飞秒激光烧蚀下对电声相互作用,结合双温模型在有限差分法下模拟出的数据图,从模拟结果中得出能量密度与飞秒激光烧蚀的关联,进一步结合实验结果,分析飞秒激光能量密度是金箔的加工效率以及加工质量的主要因素,从而表明飞秒激光能量密度对于飞秒激光烧蚀材料的研究具有很大意义。     

飞秒激光烧蚀铝片的热弛豫效应模拟与实验研究

研究了在不同能量密度的单脉冲飞秒激光下烧蚀铝片的过程。通过分析基于双温模型有限差分法所模拟出的数据图,并结合飞秒激光烧蚀实验的结果,从而研究不同激光能量密度与铝片烧蚀之间的联系。研究表明：飞秒激光能量密度与飞秒激光烧蚀的关联,而实验所测的结果进一步表明了提升飞秒激光能量密度对加工铝材料的加工效率以及加工质量的影响。通过研究和实验结果能够得出随着飞秒激光能量密度的增加,飞秒激光烧蚀期间铝材料的热弛豫过程将加长,烧蚀强度也将有所增加,同时铝材料加工后得出形貌质量也将有所提高,这个结论对于飞秒激光烧蚀金属材料的研究具有一定的意义。     

激光表面硬化及其数值模拟研究概况

激光表面硬化技术可以大幅提高产品质量,显著延长产品的使用寿命,具有良好的经济效益。本文对激光表面硬化及数值模拟的情况进行概述,主要介绍了激光表面硬化技术的强化机理、特点及其在国内外的发展应用;论述了激光表面硬化数值模拟在国内外的研究现状及存在的问题;并对激光表面硬化及数值模拟进行了总结和展望。     

CrNiMo钢激光淬火处理的抗烧蚀性能研究

通过激光淬火表面强化技术,在CrNiMo钢表面形成马氏体相变的表面强化薄层.采用小电流累积烧蚀方法分解了材料烧蚀过程;对比分析相同烧蚀条件下CrNiMo钢在激光处理与未经激光处理的表面烧蚀形貌及其烧蚀质量差.结果表明:激光淬火确实能提高材料的抗烧蚀性能.     

飞秒激光加工参数对RB-SiC表面形貌的影响

目的 揭示飞秒激光加工参数对反应烧结碳化硅(Reaction-Bounded Silicon Carbide,RB-SiC)表面形貌的影响规律。方法 通过改变激光能量密度和有效脉冲数,研究RB-SiC表面烧蚀槽的形貌变化规律,确定飞秒激光加工RB-SiC的去除机理。采用扫描电镜、共聚焦显微镜、X射线能谱仪和拉曼光谱仪分析RB-SiC烧蚀前后的表面形貌演变行为。结果 激光能量密度在0.62~10.48 J/cm²时,Si富集区域形成凹陷结构,SiC颗粒区域形成周期性结构(Laser-Induced Periodic Surface Structures,LIPSS),周期约为970 nm。随着激光能量密度的增加,凹陷结构扩大加深,表面球形纳米颗粒增多,烧蚀槽宽度呈对数增长。有效脉冲数在69~ 1 379,Si富集区域的去除量高于SiC颗粒区域的去除量。随着有效脉冲数增加,烧蚀槽深度显著加深,凹陷结构扩展成深坑结构,飞溅至烧蚀槽外侧的纳米颗粒聚集成团簇物,由Si、SiC和非晶态SiO2构成的沉积物在烧蚀槽边缘形成堆积层。结论 降低激光能量密度能够减少RB-SiC表面凹陷和纳米颗粒,有助于提升烧蚀形貌的一致性。增加有效脉冲数会促进烧蚀槽底部深坑结构的产生,进而扩大Si与SiC去除量之间的差异。     

激光熔覆对Cu抗烧蚀性能的影响

应用激光熔覆法使Ti粉和B4C粉在铜基体表面发生原位反应形成了熔覆层,通过XRD分析确定了熔覆层相组成为TiB2/Cu。熔覆层试样和纯Cu的抗电弧烧蚀实验在自制设备上进行,并采用SEM观察了电弧烧蚀表面的形貌。研究结果表明,随着电弧烧蚀次数的增加,熔覆层试样表面电弧烧蚀和氧化现象并不明显,烧蚀孔洞少且小,没有液态金属喷溅现象;而纯铜试样表面变得较为粗糙,电弧作用的中心处烧蚀氧化严重,有大量的烧蚀坑存在,并且出现液态金属飞溅现象。因此,相对纯铜,TiB2/Cu复合涂层电弧烧蚀显著降低,抗电弧烧蚀性能明显提高。     

激光熔覆层冲刷腐蚀研究现状

冲刷腐蚀广泛发生在石油、化工等领域,并致使设备材料发生损伤或失效。材料经激光熔覆后得到具有特殊化学、力学性能,并能与基体材料形成冶金结合的涂层。从激光熔覆层冲刷腐蚀行为研究方法出发,简要概括了现场测试法、数值模拟法以及通过模拟真实工况进行实验室研究的三大类实验装置的优缺点,并对目前用于激光熔覆层冲刷腐蚀行为的表征方法进行了总结。然后介绍了激光熔覆层冲刷腐蚀机理的研究现状:冲刷腐蚀机制由电化学腐蚀、机械力磨损及二者交互作用构成,其中冲刷主要通过正应力和切应力两种侵蚀机制对腐蚀产生促进作用,而腐蚀则通过弱化涂层表面促进冲刷。随后,总结了激光熔覆层冲刷腐蚀行为的影响因素,并对熔覆材料自身因素、流体因素(流速、冲蚀角、固体颗粒及pH值、温度等)对激光熔覆层冲刷腐蚀行为的影响规律进行了分析和归纳。最后,基于冲刷腐蚀机理研究现状,从研究方法及影响因素等方面总结了目前激光熔覆层冲刷腐蚀研究中存在的问题,同时对未来的研究趋势进行了展望。     

激光防护材料及其在涂层中的应用研究进展

激光武器由于打击能量大、打击精度高、抗干扰能力强等优势已成为各军事强国竞相研究的技术领域。相应地如何开展激光防护工作成为科研人员亟须解决的难题,而之前对于激光防护材料及其在涂层中的应用研究进展仍未有较全面的归纳总结。首先介绍激光武器的优越性能和激光防护的重要意义;接着总结激光防护机制,包括激光与材料相互作用机理和三种激光对材料的破坏形式,提出激光防护材料的原理和要求,并归纳激光防护材料的研究进展,包括高反射率材料、耐烧蚀材料,以及相变材料等的防护特点和防护效果。随后归纳这几种材料在涂层中的应用研究进展。最后指出目前激光防护技术存在的局限性,并探讨激光防护材料未来的研究方向。根据激光与材料的作用机理,分别从高反射、耐烧蚀和激光软防护方面对防护材料进行综述,并分别综述各类材料在涂层中的应用,对防护材料的发展方向进行展望。填补了对于激光防护材料及其在涂层中应用研究进展总结的空白,可为激光防护新技术的发展提供借鉴。     

激光熔覆熔池温度场及流场数值模拟研究进展

简述了激光熔覆熔池的受力,包括表面张力、黏性剪力、重力以及保护气压力等,并从组织生长和熔池流淌对熔覆层的形成机理作了简要分析。同时,对激光熔覆仿真模拟中采用的不同热源模型的能量分布规律和方程进行了归纳,包括表面高斯热源、表面环形热源、高斯体热源、椭圆球热源、组合体热源等。在此基础上,分类评述了近年来国内外激光熔覆熔池温度场及流场的数值模拟方面的研究进展,并分析了各种热源模型的优势及不足,总结了不同热源的适用环境及获得的温度场、流场分布规律。此外,对熔池自由液面的研究方法进行了总结,归纳了温度场流场数值模拟模型的验证方法。同时,针对激光熔覆熔池数值模拟研究存在的问题,分别从数值模型、边界条件等方面进行了归纳,最后对其未来的发展方向进行了展望。     

飞秒激光刻蚀对纳米金刚石薄膜表面微观特性的影响

利用飞秒激光对纳米金刚石涂层进行刻蚀试验,通过改变激光的重复频率,输出功率以及焦点扫描速度,研究不同的激光加工参数对金刚石涂层烧蚀结果的影响。利用白光干涉仪器、SEM、拉曼光谱仪研究了飞秒激光刻蚀后涂层表面微观粗糙度、微观形貌以及碳相结构变化。采用面积推算法计算出扫描速度1 mm/s,有效脉冲数为90时的烧蚀阈值。结果表明：金刚石涂层表面飞秒激光诱导的条纹状结构周期（LIPSS）接近飞秒激光波长,改变飞秒激光重复频率对涂层表面形貌修饰影响不大;由于烧蚀饱和作用,飞秒激光功率增加至80 mW过程中涂层表面微观粗糙度持续减小随后维持在325 nm左右;激光扫描速度的增大可使LIPSS特征消失,当扫描速度增加至1.4 mm/s后,涂层表面微观粗糙度不再继续降低而是随着速度的增大而增大。激光诱导的金刚石涂层表面石墨化程度越高,涂层表面微观粗糙度则越低;当有效脉冲数为90时纳米金刚石薄膜的飞秒激光烧蚀阈值为0.138 J/cm²。     

Theoretical and experimental study of energy transportation and accumulation in femtosecond laser ablation on metals

The energy transportation and accumulation effect for femtosecond (fs) laser ablation on metal targets were studied using both theoretical and experimental methods. Using finite difference method, numerical simulation of energy transportation characteristics on copper target ablated by femtosecond laser was performed. Energy accumulation effects on metals of silver and copper ablated by an amplified Ti: sapphire femtosecond laser system were then studied experimentally. The simulated results show that the electrons and lattices have different temperature evolvement characteristics in the ablation stage. The electron temperature increases sharply and reaches the maximum in several femtoseconds while it needs thousands of femtoseconds for lattice to reach the maximum temperature. The experimental results show that uniform laser-induced periodic surface structures (PSS) can be formed with the appropriate pulsed numbers and laser energy density. Electron-phonon coupling coefficient plays an important role in PSS formation in different metals. Surface ripples of Cu are more pronounced than those of Au under the same laser energy density.     

纳米材料的激光制备技术

本文综述了纳米材料的激光制备方法。其中重点介绍了激光消融法制备纳米颗粒、纳米纤维、纳米薄膜的原理和现状。     

Potential and limitations of laser technology in restoration of metallic objects of art and cultural heritage

Potential applications of laser techniques, such as precision cutting, micro welding, and ablation of stains, are presented. Concerning laser beam ablation, we explain the mechanism, and then discuss potential applications (cleaning of gilded or solid metal surfaces, cleaning of verdigris) and limits (thinning of verdigris, removing rust from verdigris). This research has been performed within the frame of a joint project sponsored by Deutsche Bundesstiftung Umwelt (DBU, German Foundation for the Environment) as well as in immediate co‐operation with restorers. The presentation of these results is to propose laser technology as a promising option to be taken into account in planning and doing restoratory work.     

A time based method for predicting the workpiece surface micro-topography under pulsed laser ablation

The generation of micro-features in a predictable and repeatable manner by use of pulsed laser ablation requires an understanding of the temporal and energetic distributions of the laser beam upon the workpiece surface. Modelling the response of the material to known energetic and kinematic parameters of the pulsed laser ablation process can be carried out in a discretised time-based approach, allowing the workpiece topography to be simulated mathematically to reflect a real-life process. Considerations of the antecedent workpiece surface texture such as increases in irradiated area due to the surface gradient, and increases in laser spot size due to beam divergence throughout the elevation of the workpiece are used to predict energy densities and hence the resultant ablated depth and texture of the targeted surfaces. A fully calibrated Yb:YAG pulsed fibre laser (SPI G3.0 RM) was used to validate the model on three materials, highlighting the models strengths for different material types. It was found that Ni based workpieces presented redeposition phenomena under these laser ablation conditions. To analyse the model without redeposition, validations trials on materials that do not present such side effects, e.g. diamond, were carried out and differences were found to be up to 9.39%.     

An investigation of the synthesis of metallic nano-particles by laser ablation

A numerical model is proposed to simulate the deposition process of the metallic particles under laser irradiation, in order to investigate the formation mechanism of the nano-particles for the mass production. The deposition of nano-particles has been effectively made by a Q-switched laser irradiation of nickel substrate. In the analysis of the localized ablation phenomenon, which was induced by a high peak power laser, the deposition of nickel nano-particles with narrow size distribution has been examined. The analysis of fabrication mechanisms has been studied for the process design from the macroscopic to microscopic views and the process characteristics of the laser ablation for the nano-particle deposition has been verified experimentally and numerically.     

激光冲击强化的影响参数与发展应用

激光冲击强化是一种先进表面技术,其利用激光诱导形成的等离子冲击波对金属材料进行强化,因具有强化效果更佳、可操控性更强和适用性更好等技术优势,得到了越来越广泛的应用与研究,对提高部件的疲劳性能和延长材料使用寿命具有重要作用。简要介绍了激光冲击强化技术的发展概况,分别从激光工艺参数、约束层与吸收保护层、冲击角度等影响参数进行了重点分析与总结。激光工艺参数是影响强化效果的最重要因素,选取最佳的激光功率密度、最优的光斑搭接率、适当的冲击次数以及合适的脉冲宽度可以明显提高强化效果。针对不同的材料形态,应选取合适的约束层和吸收保护层,提高激光透光率的同时防止材料表面烧蚀。此外还需考虑激光冲击强化的冲击角度,选择合适的冲击角度,能够对复杂的结构进行强化。综合考虑激光冲击强化的影响参数,可为得到最佳激光冲击强化效果提供重要的理论参考。