【作者】 佟艳群；

【导师】 张永康；

【作者基本信息】 江苏大学 ， 机械电子工程， 2014， 博士

【摘要】 高效环保的激光去除金属氧化物技术,是近年来激光技术应用的重点发展方向之一。它以激光作为加工工具,在去除金属氧化物的同时形成高性能的表面质量,提高界面结合强度等表面性能,具有便于与焊接设备集成、去除度高、定域性好、操作方便等优势,可在大型海洋工程装备、船舶制造、全自动化工业生产等领域推广应用。激光与金属或金属氧化物之间的作用,包含光子-电子-声子-等离子体等微观粒子之间的相互作用,目前机理研究主要集中在仿真模拟,激光去除机理存在巨大的理论研究空间。金属表面在激光作用下允许发生一定程度的永久性特征变化,激光能量选取是否合理不能单纯用激光损伤阈值判断,需要综合分析激光去除后的金属表面质量；对于大面积金属氧化物的去除,采用高速的激光扫描系统,但去除效果的影响因素很多,很难通过常用的试错实验选取工艺参数,比如激光光斑叠加的热效应影响,材料表面会再次被氧化,需要采用有效的方法选取最优工艺参数,因此激光去除技术存在巨大的技术研究空间。本文开展激光去除金属氧化物的基础研究,主要研究内容有：(1)分析激光去除金属氧化物的微观过程,揭示激光去除金属氧化物的物理机制。基于激光烧蚀理论,研究激光作用下金属和金属氧化物的温升规律,分析激光能量、激光脉宽等参数的影响。检测激光去除金属氧化物的微观过程,分析激光等离子体光谱谱线成分和强度变化,研究激光烧蚀分解表面物质发生的物理化学效应,分析出激光与金属氧化物之间的作用机理；检测激光去除过程的等离子体冲击波传播特性,分析材料表面的弹性变形过程,研究激光去除过程的弹性振动效应。结合形貌分析,提出金属氧化物的激光去除机理是激光烧蚀的物理化学效应和弹性振动效应共同作用的结果,为激光工艺参数的选取和在线监测技术提供依据。(2)构建适合工业应用需求的在线监测系统,实时分析激光去除程度。成本低、操作简单、稳定性好、对平台和环境要求低等使用条件,是工业应用对在线监测系统的要求。采用光电二极管、宽带麦克风等常用设备,实现对激光诱导等离子体发光信号和声波信号的检测。采用等离子体发光强度峰值的变化趋势,以及声波持续时间的变化趋势,表征出金属氧化物是否去除干净。采用BiDoseResp模型,分析发光强度峰值与作用激光能量的关系,计算出基体损伤能量阈值等关键数据,验证激光去除机理,并为工艺参数的选取提供依据。(3)建立激光去除效果的评价准则。定义激光去除效果评价参数,如去除干净、去除度、良好的表面形貌等,采用肉眼观察或JSM-7001F型扫描电镜及能谱分析仪、DM2500M型光学显微镜、Surface130A表面粗糙度仪等各种表面性能测试设备,分析激光去除后金属表面质量,参考已有传统去除手段的评价准则,提出表面质量的评估方法,为激光去除效果的评价建立准则。(4)提出系统选取最优工艺参数的有效方法：由机理分析入手,以检测技术为辅,确定因素及水平,根据表面质量评估,结合正交试验和优化工艺,获取最优工艺参数。构建高速激光去除系统,研究激光能量和激光扫描速度等工艺参数对激光去除效果的影响,得出很难通过试错实验来确定最优工艺参数的结论。采用正交试验方法,根据机理分析和在线监测结果,确定正交试验的因素及水平区间,采用L9(34)正交试验方案,初步判断出较优的参数水平区间。根据表面质量评估准则,进一步优化工艺参数,获取最优工艺参数：当氧化层厚度约30μm时,激光功率为20W,扫描速度为3000mm/s,激光作用次数2次。在最优工艺参数下,金属氧化物被去除干净,去除度达到100%；分析横截面金相具体形态,表面同内部相比没有发生变化；凹坑底部的硬度小于凹坑顶部的硬度,均大于金属基体的硬度；在凹坑底部观察到微纳米多级精细结构的表面形貌。本文的研究结果对金属氧化物的激光去除技术、激光诱导等离子体行为的检测以及激光与物质相互作用的机理研究均具有一定的促进作用。更多还原

【Abstract】 Laser removal technology is one of the key development directions of laser application technology due to its high efficiency and environmentally friendlyness. As a processing tool, the laser is used to generate the the high quality surface after the removal of metal oxides and improve the surface performance, such as the interfacial bonding strength. This technology has many advantages, such as easy integration with welding equipment, high removal degree, good locality and easy operation, et al. It can be used in many fields such as large marine engineering equipment, ship building, automatic industry production, et al.The mechanisms between the laser and the metal or metal oxide are the interaction between individual particles including photons, electrons, phonon and plasma. The research emphasis at present is focused on the simulation analysis. There is a huge theory study space of the laser removal mechanisms. The metal surface performances are changed permanently to some extent by laser. The reasonableness of laser energy selection can not be judged simply by the laser-damaged threshold, but by the surface quality analysis after laser removal. The high speed laser scanning system is used to remove the large area metal oxides. But there are many factors affecting the removal efficiency. It is difficult to select the process parameters through the trial experiments, such as the heating effect of laser superposition and reoxidation. The parameters selection must give consideration to the laser removal effect and efficiency. There is a huge technical study space of the laser removal technology.The fundamental research of the laser removal technology is carried out in this dissertation. Four major results are listed as follows:(1)The microscopic process of laser removal is analyzed and the physical mechanism of the laser removal of metal oxides was revealed.Temperature rise laws of laser interaction with metal or metal oxides is calculated and the effects of the parameters such as laser power and laser pulse width are analyzed based on the theory of laser ablation. Experimental research on the microcosmic process characteristics of laser removal is carried out through testing the laser induced plasma spectral line and intensity changes. The physical and chemical reaction of surface material decomposition by laser ablation is investigated and the mechanism of interaction between laser and metal oxides is analyzed. The propagation characteristics of laser plasma shock wave are detected in the laser removal process. The elastic deformation process of the material surface is analyzed and the elastic vibration effect of the laser removal process is investigated. Combined with the morphology analysis, we proposed that the physical mechanism of the laser removal of metal oxides is the combined effect of the physicochemical effect and the elastic vibration effect. Those provide the basis for the laser processing parameters selection and the on-line monitoring technology.(2) The on-line monitoring system of laser removal process suitable for industrial application requirements is built up.The requirements of the on-line monitoring system for industrial applications are of several advantages, such as low cost, simple operation, good stability and low requirement for experiment platform and environment condition. Some common equipment such as the photodiode and broadband microphone are applied to deceting the macro-signal of laser induced plasma. The variation trends of the light intensity of laser induced plasma and the duration of the sound signal are symbolized to characterize whether the metal oxide is removed totally. The relationship between the peak signal of the light intensity and the laser energy is analyzed through BiDoseResp model. The laser energy damage threshold of the body material is calculated. The mechanism of laser removal is verified. All the above mentioned provide the basis for the processing parameters selection.(3) The evaluation rules of the laser removal effect are established.The evaluation parameters of the laser removal effect are defined, such as the clean removal, the removal ratio, the good surface topography, et al. The surface quality after the laser removal is analyzed through visual inspection and various test equipments such as JSM-7001F scanning electron microscopy (SEM) and energy spectrum analyzer, DM2500M optical microscope and Surface130A surface rough meter. An evaluation method of the surface quality is put forward according to the evaluation criterion of the traditional means. The evaluation criterion of laser removal effect of is established.(4) An effective method of the optimum technique parameters selection is put forward. The factors and levels are established by analyzing the mechanism and on-line monitoring. The optimum technique parameters are obtained by the orthogonal experiment and optimization process according to the evaluation criterion of the surface qualityThe high speed laser removal system is built and the impact on the laser removal effectiveness of the laser repetition frequency, laser energy, laser scanning speed is experimentally investigated. We propose that it is difficult to obtain the optimum technique parameters by the trial and error test. The orthogonal experiment method is used and its experimental factors and levels are obtained by the mechanism analysis and online monitoring results. The orthogonal experiment scheme L9(34) is used and the optimal parameters and levels are preliminary obtained. The optimum technique parameters are obtained through process optimization and according to the assessment criteria of surface quality. Under the optimum technique parameters:oxide thickness30μm, laser power20W, laser scanning speed3000mm/s, laser action number2, the effect of laser removal is ideal and the laser removal ratio is100%. The metallic phase of the cross section on the surface is the same as that in the body. The hardness at the bottom of the craters is smaller than that at the top of the craters and both are higher than on the body material. The surface topography of micro/nano multistage fine structure is observed at the bottom of the craters.The research results of this dissertation are favorable to the laser removal technology of the metal oxide, the detection of the laser induced plasma behavior and the interaction mechanism of laser and matter.更多还原