【作者】 张际亮；

【导师】 郦剑；

【作者基本信息】 浙江大学 ， 材料加工工程， 2008， 博士

【摘要】 金属基陶瓷涂层既有金属的韧性、强度、导电性等性能,又有陶瓷材料高硬度、高强度、耐磨、耐高温、耐腐蚀等优点,在航天、航空、电力、电子等工业中得到广泛应用。大量研究表明硅氧化合物陶瓷膜层具有特殊的光学、电学、力学等性能,广泛应用于光电功能器件、集成电路、高阻隔材料等领域。通过CVD技术制备金属铝基硅氧化物陶瓷膜层,是一个尚未进行研究的领域,技术瓶颈在于常规CVD技术的工艺温度高于铝的熔点。本论文研究开发低温常压化学气相沉积（APCVD）技术,在铝及其合金基底上成功制备硅氧化物陶瓷薄膜;采用多种检测技术对表面结构性能进行表征;探讨了薄膜的形核机理,对经典形核理论进行修正,提出了形核模型。通过对基底预处理以及工艺参数的研究,系统考察薄膜生长组织和表面形貌的影响因素,沉积温度对薄膜厚度的影响呈单峰状,最佳沉积温度为400℃;最佳沉积气体流量为硅烷稀释气流量0.2L/min,空气0.3L/min;载气（氮气）流量同薄膜的生长速率呈线性关系,最佳流量为2L/min;薄膜厚度变化随沉积时间增加线性增大;薄膜SEM表面形貌由大量的球状或等轴状硅氧化物颗粒镶嵌堆垛而成,颗粒间存在间隙;随着沉积时间的增加,颗粒发生融合长大,间隙体积减少。沉积薄膜后续退火有助于薄膜表面发育完整,减少孔隙,使硅氧化物球状颗粒发生融合粗化长大;退火温度越高,保温时间越长,薄膜颗粒融合长大越充分。退火可使薄膜中发生铝、硅、氧原子互扩散,改变薄膜结构,增强了薄膜与铝基的结合力。铝硅氧化物薄膜在反应温度下能够自发进行沉积生长。薄膜同基底结合部位原子互扩散过程中能够形成稳定的Al-O-Si复杂晶体结构,促进表面形核和长大;薄膜形核率以及生长速率同气压、温度、界面能、界面接触角、沉积表面扩散激活能、气相反应形核能垒、表面解附能等有关。由于APCVD技术气压高,温度低,气相反应能垒小,沉积形核率高,因此薄膜呈现非晶态具有各种缺陷以及悬挂键。硅氧化物薄膜表层O/Si原子比稳定在2.2—2.4之间,证明该结构中的氧除了与硅键合外,还以OH基团存在,形成Si-OH结构;该表层O/Si原子比与沉积时间没有直接关系。薄膜存在成分过渡层,有铝、硅、氧原子的互扩散现象;铝和硅原子通过氧原子形成桥连的Al-O-Si键合结构,局部区域组成复杂类尖晶石结构,也对薄膜同基底的紧密结合起重要作用;铝基硅氧化物薄膜大部分为非晶态结构,表层局部区域还发现晶态的SiO₂结构生成。铝基硅氧化物薄膜具有胞状组织形貌,胞状组织具有交叠层片亚结构。其生长机理是:硅烷和氧气在铝基表面反应生成硅氧化物微粒,与铝基表面的新鲜氧化铝结合成为成膜核心;后续的气源分子依附形核点继续反应,使初生晶核发育长大,形成的岛状硅氧化物分子团,在三维竞争生长过程中,因硅氧化物与铝基表面的新鲜氧化铝键合力较强,两者“浸润”性能较好,XY方向上生长速度大于Z方向,岛状单元的长大形成亚结构层片,相互接触,构成胞状组织的底层;这种形核—长大—融合的层片生长过程反复进行,构成具有层片式亚结构的胞状组织。铝基硅氧化物薄膜的亚结构层片由Si-O-Si无规网络环状结构组成,还包含硅悬挂键、Si-Si共价键以及Si-OH键合结构,产生原因是Si-O-Si键合中的桥氧产生空位,形成硅悬挂键结构;部分硅悬挂键通过相互键合形成“≡Si—Si≡”共价键结构,部分通过获取气相中OH集团和氢原子形成Si-OH结构及Si-H结构。研究并分析了铝基硅氧化物薄膜性能及机理。划痕实验载荷达到80N,切应力达到1.24GPa时,薄膜仍未发生剥落,这种良好的结合力依靠氧同铝硅的强烈键合作用和铝硅氧原子发生互扩散。铝基硅氧化物薄膜能有效提高样品表面硬度,但由于薄膜表面存在孔隙,且硅氧化物薄膜表面容易在外力作用发生坍塌挤压;随着载荷压力的增大,薄膜将随基底一起发生塑性形变。硅氧化物薄膜能有效提高铝及铝合金表面的耐磨性,磨损机理是对磨时,薄膜表面发生坍塌挤压,形成细小的硅氧化物陶瓷碎片或粉末充当磨粒,形成磨粒磨损;磨损量的变化具有线性变化规律。铝基硅氧化物陶瓷薄膜在紫外光到红外光波段具有很好的光吸收性能,反射率均低于30%;吸收光的原因是由于薄膜由大量硅氧化物颗粒堆跺而成,颗粒间存在孔隙,光线进入内部空洞后通过不断反射,延长了光线的传播距离,消耗一部分能量;非晶态薄膜内部存在大量不同类型缺陷,悬挂键、氧空位等结构缺陷都会吸收不同波长的光,显著降低薄膜的光学反射率。以激光作为激发光源,薄膜呈现大范围波段的光致发光,发光机理是薄膜中大量的缺陷结构在激光激发下产生电子跃迁发光,呈白色荧光;铝合金基底的硅氧化物薄膜发光强度要高于纯铝基底,原因是铝合金基底含有其他元素成分,在制备薄膜的过程中扩散到薄膜内部,引起薄膜内部缺陷结构的变化。铝基硅氧化物薄膜表面具有良好的聚乙烯热喷涂工艺性,由于硅氧化物薄膜表面孔隙率较高,部分粘流态的聚乙烯进入到薄膜孔洞中,增大了聚乙烯薄膜同硅氧化物薄膜的附着力。更多还原

【Abstract】 Ceramic film coated on metallic substrate, widely used in aerospace, aviation, electronics and electrics, has high toughness, intensity and conductibility of the metal and high hardness, good wear resistance, heat resistance and corrosion resistance of the ceramic. The silicon rich oxide （SRO） has good properties of hardness, insulation, thermal conduction, etc; and many studies of it have been carried out on optical, electronics, mechanics and engineering performances. This accommodate the SRO a widely use in photo electricity apparatus, integrate circuit, barrier materials, etc. Having many potential applications, this research have not been widely studied with a technical difficulty.In this dissertation, a new kind of SRO film is deposited on Al and Al alloy substrate by low temperature APCVD approach. The pretreatment and the process parameters are studied. The results show that, with the increase of temperature, there is an optimal point at about 400°C. The flux rate of the diluted silane and air are fixed at 0.2 L/min and 0.3 L/min optimally. The growth rate of the SRO film increases with the flux rate of nitrogen carrier, which is fixed at 2 L/min. The thickness of the film increases with the deposition time increasing. SEM results demonstrate the various morphologies of the SRO film in different conditions. The film surface is stacked and packed up by a number of SRO cell units with some gaps. The growth process is supposed to be followed: After silane and oxygen chemical reacted and nucleated on the surface, the nascent nucleus grow up and present a spherical or equaxial shape cell packed on the surface. The cells press each other and stack up with some gaps. With the increase of deposition time or the proceeding of anneal, the cells coalescence and grow up with a contraction of the gaps.The SRO film cured and developed after the anneal process has been investigated in this dissertation. SRO cell units grow up and coalescence in anneal process, formed in chain-like or layer-like morphology. With the increase of anneal temperature and heat preservation time, much more cell units coalescence and grow up. Besides, due to the Al, Si and 0 atoms inter diffusion between the SRO film and the substrate, the film thickness increases in the anneal process.Thermal dynamics and kinetics analysis shows that: the APCVD reaction of the SRO film is spontaneous under the optimal process condition; the Al-O-Si complicated crystalline structure is formed by the inter-diffusion of the Al, Si, 0 atoms. The velocity of nucleation and film growth is dependent of pressure, temperature, interfacial energy, interfacial contact angel, diffusional activation energy of the deposited surface, nucleation energy barrier of the vapor reaction, surface desorption energy, etc. Because the atmospheric pressure is higher than usual CVD and the nucleation energy barrier of the vapor reaction is low, the reaction in this experiment is very acute. This leads to a high nucleation rate and a non-crystalline microstructure. Besides, high reaction rate increases the Si dangling bonds and the density of defects in SRO film.XPS results show that the O/Si ratio of the different region in the SRO film stabilized at 2.2 - 2.4. It is indicated that there are many Si-OH bonds in the film and the composition does nothing with the deposition time. There are much more Si-OH bonds in the near surface region than in the interior, because of the saturation of the OH in vapor phase and absent of the dehydration inside the film. The results also show that there is a widely transition layer between the SRO film and the substrate, indicated the inter-diffusion of the Al atoms and Si, 0 atoms. The Al and Si atoms supposed to be formed an Al-O-Si bonding structure and the 0 atoms play a role of bridge oxygen. A complicated spinel like crystalline structure is formed in some oxygen rich region and shows a great bonding ability to the substrate. XRD results show that a crystalline SiO₂ microstructure is also appeared in some oxygen rich region with the absent of Al atoms.The TEM, TED and HRTEM results show that the SRO film is not totally non-crystalline but with a little crystalline structure in some oxygen rich region. This is from the beginning of the film growth; the surface of the substrate is coated with a layer of alumina and offers an oxygen rich environment; so in the nascent SRO film, the silicon dangling bonds are very easy to be saturated by the oxygen in the alumina and some of them grow up in crystalline structure with atoms migration or diffusion. The experiments prove that the formation of the crystalline structure is independent of the deposition time.TEM results show that the full growth process supposed to be a series of nucleation and growth: After silane and oxygen reacted on the surface, the nucleus grow up with the continuously supply of feed gas and formed an island-like micro structure; Because of the strong bonding between the SRO, the wetting ability of the interface is enhanced and bring out a result of that the growth rate of X-Y direction is faster than that of Z direction; The island-like micro structures develop and construct a laminar structure when they contact. With the repeat of the nucleation, growth and coalescence, the laminar structures stack up and show a SEM morphology of SRO cells.PL and IR results show that, the microstructure of SRO film is constructed of many Si-O-Si irregular ring nets with a lot of Si dangling bonds, Si-Si bonds and Si-OH bonds in it. Because of the bridge oxygen vacancies in the Si-O-Si bond, the Si dangling bonds are formed; some neighbors of them connect and form Si-Si bonds; a few of them form Si-OH bonds or Si-H bonds by saturated of the OH group or H atoms in the vapor phase. The PL results show that the impurities in the SRO film increase the density of the defects. This consequence can induce the photoluminescence intensity. The results also show that the film microstructure is more complicated with the increase of deposition time.In this dissertation, the bonding property, mechanics, wear and optical absorption performances of the SRO film deposited on Al or Al alloy substrates are studied, respectively. The nick test shows that the SRO film is still not scaled out of the substrate in the condition of an 80 N load and a 1.24 GPa shear stress. It is definitely that this good bonding performance bases on the strong bonding ability between Al-O and Si-O. The micro Vicker’s hardness measurement and the impress observation shows that the hardness of Al and Al alloy is obviously increased by deposited a coating of SRO film on it. Due to the brittle and porous property, the SRO film is very easy to be collapsed and fragmentized. This results in a irregular shape of the impress. With the increase of the load, the SRO film is plastic deformed with the substrate deformation. The results of wear experiment show that the wear resistant property of the Al or Al alloy is effectively enhanced by deposited a coating of SRO film. The wear mechanism indicates that the SRO cell units are easy to be collapsed and press to fill the gaps. The tiny granules formed in this process play a role of abrasive grains and wear the substrate. The wear loss increases linearly with the increase of wear time and the wear rate decreases with the increase of deposition time.UV-VIS and IR reflection results show that the SRO film deposited on Al or Al alloy present an excellent optical absorption in the wave length scale from ultraviolet to middle infrared. The reflection rates are basically below 30%. The reasons of the absorption are: Firstly, the ray is scattered reflected because of the surface fluctuation; Secondly, the gaps among the packed SRO cell units; Then, the energy of the ray is consumed due to the increase of transmission distance; Besides, much ray of different wave length is absorbed due to the dangling bonds, oxygen vacancies and other defects. PL results show that the SRO film is photo luminescent in large scale under laser activation. The mechanism is the transition of electrons in defects under laser activation. The results also show that the photo luminescent intensity of Al alloy is great than that of Al, because there are much more defects formed in the SRO film due to the diffusion of other element.A heat spray process of PE has also been carried out after SRO film deposition. The results show that the sticky PE enter the gaps among the SRO cell units and consequently increases the adhesion of the PE coatings to the SRO film.更多还原