【作者】 周玉锋；

【导师】 韩杰才； 张宇民；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2008， 博士

【摘要】 应烧结碳化硅是一种综合性能优良的反射镜材料,它由两种硬度不同的材料组成,普通的机械加工方式不能或很难使其表面光洁度达到很高的水平。本研究采用在其表面沉积致密层的方法来提高表面光洁度。为降低实验成本,提高研究针对性,在进行致密层沉积之前,首先使用计算机模拟的方法对致密层沉积参数对其性能的影响进行了分析(包括使用蒙特卡罗法模拟致密层的沉积过程、分子动力学方法计算致密层与衬底之间的相互作用能、有限元分析方法分析致密层-衬底系统的应力状态),然后根据模拟分析结果进行了致密层的沉积,并对其性能进行了研究。根据沉积过程模拟结果可知,在高温下沉积所得致密层与衬底之间的结合状况及其致密度得以改善。另外,分子动力学的计算结果显示:随着沉积温度的升高,致密层与衬底之间的相互作用能也随之升高。然而,有限元分析结果显示,致密层-衬底系统中热应力随沉积温度升高而升高,且与温度差成正比-这将对系统的稳定性产生不利影响。同时,在对不同温度下制备的致密层进行致密层-衬底的断面进行观察时发现,沉积温度对磁控溅射法制备的硅致密层与衬底之间的结合情况影响并不明显。据此,本研究最终选择硅致密层的沉积温度为200℃,尽可能降低了致密层-衬底系统中的应力水平。另外,从沉积过程模拟结果来看,随着衬底表面粗糙度的升高,衬底与致密层之间的结合情况、致密层的致密度变差。因此在沉积致密层之前,需要将衬底表面粗糙度降低到所能达到的最低程度。不同表面粗糙度的衬底上制备的致密层的研究显示:在粗糙衬底表面上制备的致密层具有较高的应力水平,部分致密层在自然放置的条件下便出现自然脱落的现象。根据理论分析结果,在本文中选用在低粗糙度的衬底上制备硅致密层。本文还研究了致密层厚度对致密层-衬底系统中应力属性的影响。根据有限元的分析结果可知,随着致密层厚度的增加,致密层中应力水平随之降低,但降低的速率随着厚度的增加而减小。分析结果与文献结果相符。实验结果也表明,在各种测试中,厚度为12μm的致密层都表现出较高的综合性能。致密层的结构对其加工后得到的表面粗糙度有一定影响。非晶硅含量越高,所得致密层抛光后表面粗糙度越低。通过分子动力学研究发现,在200℃时沉积的硅致密层具有最高的非晶硅含量,而其他试验温度下制备的硅致密层中非晶硅的含量均低于此值。对致密层表面进行抛光后发现,200℃下制备的硅致密层的表面粗糙度值最低。本文还对由电子束物理气相沉积法、离子束增强化学气相沉积法制备的硅致密层和化学气相沉积法制备的碳化硅致密层的性能进行了测试,并与由磁控溅射法制备的硅致密层的性能进行比较。结果发现,在本文所使用的四种方法中,磁控溅射法是制备反应烧结碳化硅致密层最适宜的方法。更多还原

【Abstract】 The reaction-bonded silicon carbide (RB-SiC) is a kind of mirror material withexcellent comprehensive properties. RB-SiC is composed of two kinds of materi-als with different hardness, and it is hard or impossible to obtain very high surfacesmoothness for normal machining. The deposition of tectum was used to improvethe surface smoothness of RB-SiC in present research. In order to reduce cost andimprove the pertinence of experiments, the computer simulations were used to get theoptimized parameter of deposition. The simulation methods include the Monte Carlofor deposition process, the Molecular dynamics simulation for interaction energy andthe Finite Element Analysis method for simulation of stress state. The deposition ofthe tectum is prepared by magnetron sputtering based on the optimized parameters,and then, the properties of the tectum were studied. It could be known that the adhe-sion of the tectum to substrate and the density of the tectum were all improved whenthe deposition temperature increased. Besides which, the results of molecular dynam-ics simulation indicated that the interactive energy between the tectum and substrateincreased with the increasing deposition temperature. However, the results of FEAshowed that the higher deposition temperature led to higher stress, which is in directproportion with the difference between the deposition and room temperature, in thetectum-substrate system. And the higher stress will do harm to the stability of thetectum-substrate system. At the same time, the effect of the deposition temperatureon the adhesion of the tectum to substrate is weak, as indicated by the morphology ofintercross section. Therefore, the deposition temperature was set as 200℃in orderto reduce the stress in the tectum-substrate system.Furthermore, the higher surface roughens of substrate could result in lower adhe-sion of the tectum to substrate and the weaker density of the tectum as indicated by thedeposition simulation of the tectum. Therefore, the surface roughness of the substrateshould be reduced as low as possible before the deposition process. Besides which,the study on the tectum on substrates with different surface roughness shown that thestress level increased with the increasing surface roughness of substrate, and the de-lamination will appear when the specimen were put in air at room temperature. As a result of which, the tectum should be deposited on the substrate with lower surfaceroughness.The effects of the tectum thickness on the properties, such as the value and dis-tribution, of the stress in the tectum-substrate system were studied. As indicted bythe FEA results, the stress in the tectum decreased at a rate slowing down with theincreasing tectum thickness. And the conclusion agrees well with the results providedby literatures, and the results of our experiments shown that the tectum with thicknessequal to 12μm had a excellent comprehensive properties.The crystal structure could affect the surface roughness of polished tectum, andthe surface roughness of tectum prepared at 200 ?C could reach a higher level if thecontent of a-Si is higher. It could be found that content of a-Si is the highest amongthe specimen prepared at different temperature. The surface roughness of the polishedtectum prepared at 200?C was the lowest among that prepared at other temperatures.The properties of the silicon tectum prepared by electron beam physical vapordeposition, plasma enhanced chemical vapor deposition and the silicon carbide tectumprepared by chemical vapor deposition were studied. And the comparison betweenthose methods and magnetron sputtering has been made, and the result of comparisonindicated that the magnetron sputtering is most suitable method among four methods.更多还原