| 题名 | 脉冲紫外激光表面消融硬质合金及其应用研究 |
| 作者 | 李铁军 |
| 学位类别 | 博士 |
| 答辩日期 | 2002 |
| 授予单位 | 中国科学院上海光学精密机械研究所 |
| 导师 | 楼祺洪 |
| 关键词 | 脉冲紫外激光 激光表面消融 硬质合金 金刚石涂层 结合强度 |
| 其他题名 | Study on Surface Ablation of Hardmetal with Pulsed UV Laser and It' s Application |
| 中文摘要 | 本工作的目的在于研究一种新的激光表面预处理技术以提高金刚石涂层刀具的结合强度。本文首先从实验上研究了金属钻在3O8nm脉冲紫外激光照射下，消融特性随激光能量密度、焦斑大小、脉冲数目等参数的变化规律。其次，提出了改进的热模型，即在热模型中合理考虑了激光辐照金属钻表面时产生的蒸汽羽对激光能量的吸收，并依据该模型采用数值计算的方法从理论上模拟了308nm脉冲紫外激光表面消融金属钻的物理过程，得到了表面温度随时间、空间的变化关系以及消融速率同激光能量密度的变化关系，并同实验结果进行了对比。研究结果表明：在合理考虑了蒸气羽对入射激光脉冲能量的吸收以后，理论数值计算得到的结果同实验结果较好地符合，这说明我们在热模型中引入蒸气羽对入射激光脉冲能量的吸收还是基本合理的。在上述研究结果的基础上，从实验上对钻基碳化钨硬质合金的脉冲紫外激光表面消融过程进行了详细的研究。主要利用扫描电镜、X光衍射等先进分析手段，对消融过程中硬质合金的表面形貌、相结构等特性同激光能量密度、激光累积脉冲数等激光参数的变化关系进行了深入细致的研究。发现硬质合金表面形貌随激光能量密度的变化而有很大的不同。在特定的激光能量密度范围内（如2.5J／cm2左右），脉冲紫外激光对硬质合金的表面消融将会产生一种具有"峰一谷"相间特征的特殊表面形貌，而太高或太低的激光能量密度都不会使硬质合金表面产生这种特殊的表面形貌。同时，在激光能量密度为2.5J／cm2的条件下，被消融硬质合金的表面形貌及表面组成随激光脉冲数目的累积而有所变化。研究结果表明：在激光能量密度为2.5J／cm2的条件下，硬质合金表面层中金属钻的选择性消融是被消融硬质合金表面产生特殊"峰一谷"表面形貌的主要原因。同时，累积激光脉冲数目也是影响硬质合金表面"峰一谷＂相间特殊表面形貌的重要因素之一。从有利于提高后续金刚石涂层结合强度的角度出发，要在硬质合金表面获得"峰一谷"的空间对比度较大，同时硬质合金表面层中的钻成份含量最少的理想表面形貌，必须将照射的累积激光脉冲数目控制在300个激光脉冲左右。在进一步的工作中，利用激光诱导的光学发射光潜技术详细研究了脉冲紫外激光表面消融钻基碳化钨硬质合金过程中的发光现象。研究结果表明：在激光能量密度为2.5J／cm2的条件下，硬质合金的脉冲激光消融过程确实存在着钻成份含量随激光脉冲的累积迅速下降的现象。硬质合金脉冲激光消融过程中钻成份的选择性消融现象在这里通过光谱学的手段得到了验证。最后，在经过脉冲紫外激光表面消融处理的硬质合金表面用CVD方法制备了金刚石涂层，利用Ramnan、SEM以及硬度计刘涂层质量、涂层与硬质合金基体的结合强度进行了分析测试，并选用耐"磨的碳化硅增强铝合金材料对涂层刀具进行了实际切削性能测试。实验结果表明：与传统酸浸蚀预处理相比，经过脉冲紫外激光表面消融预处理后制备的金刚石涂层刀具其涂层与衬底之间的结合强度确实得到了显著的提高。经过300个激光脉冲表面消融预处理的金刚石涂层刀具其耐用度比只经过传统酸浸蚀预处理制备的金刚石涂层刀具相应值提高了3.5倍，比普通硬质合金刀具则要高6倍以上。在实验中金刚石涂层刀具结合强度的提高与脉冲紫外激光表面消融预处理在实验中的应用是有着非常密切的关系的，正是脉冲激光表面消融在硬质合金表面产生的特殊表面形貌导致了通过脉冲激光消融预处理得到的金刚石涂层刀具其结合强度得到了较大程度的提高。在硬质合金的脉冲激光表面消融处理过程中所累积的激光脉冲数目对于制备的金刚石涂层结合强度有着较大的影响。为了制备出结合强度较高的金刚石涂层刀具，在硬质合金衬底的脉冲激光表面消融预处理中必须控制好照射的激光脉冲数目。在我们的实验条件下，由实验得到的对应最高涂层结合强度的最佳激光脉冲照射数目在300左右。 |
| 英文摘要 | The aim of this study is to develop a novel substrate pretreatment method for adhesion improvement of diamond coating tools. In this work, the ablation of cobalt with a 308nm pulsed UV laser has been investigated. The ablation rate was measured. The dependence of ablation rate on laser fluence, spot area and pulse number have been studied. Moreover, numerical calculations based on an improved thermal model were presented, which describe the process of target heating and ablation of cobalt during irradiation by a 308nm pulsed UV laser and the attenuation of laser by vapor has been taken into account in this model. The temperature distribution beneath the surface of target and the temporal evolution of surface temperature were given. The dependence of ablation rate on laser fluence was also studied based on this improved thermal model. It has shown that the calculated ablation rate was in good agreement with the experimental results, which indicated that our model considering proper vapor attenuation should be a good description of this laser ablation process. Surface ablation of cobalt cemented tungsten carbide hardmetal has been carried out by using a 308nm pulsed UV laser. The influence of ablation rate, surface morphology as well as surface phase structure on laser conditions including laser irradiance and pulse number has been investigated respectively by using SEM and XRD. The experimental results showed that the surface morphology and phase structure of irradiated surface layer varied greatly with different laser conditions. It was found that at laser fluence of 2.5J/cm2, the surface morphology characterized a uniform framework pattern of "hill-valleys" which differed greatly with surface morphology at fluence far from 2.5J/cm2. At laser fluence of 2.5J/cm2, there was a considerable variation both in surface morphology and phase structure of irradiated surface layer with the accumulation of laser shots. It was concluded that the effect of selective removal of cobalt from surface layer of tungsten carbide hardmetal should be chiefly responsible for the undulating surface morphology generated at laser fluence of 2.5J/cm2. In the meantime, the total number of laser shots applied in this surface ablation process should be another important factor, which may give considerable influence on surface morphology of hardmetal. Moreover, surface ablation of cobalt cemented tungsten carbide hardmetal with pulsed UV laser has been in situ diagnosed by using the technique of laser induced optical emission spectroscopy. It was found that, at laser fluence of 2.5J/cm2, there was a fall-off of cobalt lines with the accumulation of laser shots which indicated the dramatic decreasing of the amount of cobalt binder in surface layer of irradiated tungsten carbide. Thus, by using the technique of laser induced optical emission spectroscopy, it has been confirmed that there was selective removal of cobalt binder during surface ablation of tungsten carbide hardmetal at proper laser fluence. Finally, pulsed UV laser surface ablation has been applied in substrate pretreatment in order to obtain good adhesion of diamond coating grown on cobalt cemented tungsten carbide hardmetal. The dependence of diamond coating's adhesion on different shots of pulsed UV laser substrate pretreatment has been studied experimentally. The results were compared with diamond coating deposited by using traditional acid-etching substrate pretreatment. It was shown that adhesion of diamond coating grown on tungsten carbide hardmetal has been greatly improved by using pulsed-UV-laser substrate pretreatment. The life time for diamond coating grown on hardmetal with 300-shot pulsed-UV-laser substrate pretreatment has been 3.5 times longer than that for diamond coating fabricated through traditional acid-etching pretreatment and 6 times longer than that for commercial tungsten carbide hardmetal. It has been demonstrated that pulsed-UV-laser substrate pretreatment should be a feasible and effective method for improving adhesion of diamond coating on cobalt cemented tungsten carbide hardmetal. It is the characteristic surface morphology produced by pulsed-UV-laser surface ablation that subsequently results in this improved adhesion of diamond coating grown on tungsten carbide hardmetal. The number of laser shots being used in substrate pretreatment has a great influence to the adhesion of diamond coating deposited on tungsten carbide hardmetal. One should always apply proper number of laser shots in pulsed-UV-laser substrate pretreatment when seeking for the optimal adhesion of diamond coating on tungsten carbide hardmetal. In this work, the corresponding number of laser shots for the optimal adhesion of diamond coating has found to be 300 laser shots. |
| 语种 | 中文 |
| 内容类型 | 学位论文 |
| 源URL | [http://ir.siom.ac.cn/handle/181231/15466]  |
| 专题 | 上海光学精密机械研究所_学位论文 |
| 推荐引用方式 GB/T 7714 | 李铁军. 脉冲紫外激光表面消融硬质合金及其应用研究[D]. 中国科学院上海光学精密机械研究所. 2002. |
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