【作者】 冯丽萍；

【导师】 刘正堂；

【作者基本信息】 西北工业大学 ， 材料学， 2006， 博士

【摘要】 头罩是红外制导空-空导弹的重要部件，蓝宝石具有的一系列优异性能，决定了它是目前作为中波红外窗口／头罩的最佳材料。然而，限于目前的材料制备和加工技术水平，蓝宝石的红外透过率明显低于理论值并且透过率随着环境条件的恶化而降低。另外，蓝宝石的高温强度大幅度下降，大大限制了其抗热震性等其它性能的发挥。因此蓝宝石作为新一代窗口／头罩材料是有待于改善和提高的。在蓝宝石表面制备红外增透保护膜是提高其透过性能、改善其高温强度及提高其耐久性的有效方法。由于SiO₂膜折射率低（1.41）、可宽波段透过、吸收小、化学稳定性好等优良性能，而被用作蓝宝石的增透保护膜系。Si₃N₄膜的折射率稍大（1.99），可与低折射率的SiO₂膜结合用于红外增透保护膜系中。本论文把SiO₂、SiO₂／Si₃N₄用作蓝宝石衬底的红外增透保护膜系，采用射频磁控反应溅射法在蓝宝石衬底上设计并制备出SiO₂单层及SiO₂／Si₃N₄双层膜系，对薄膜的制备工艺及性能进行了系统研究。论文的主要研究内容和结果如下：在蓝宝石衬底上设计了SiO₂、SiO₂／Si₃N₄、SiO₂／Si₃N₄／SiO₂等单层及多层增透保护膜系。蓝宝石衬底双面镀单层及多层膜系，可实现3～5μm波段的宽波段增透，满足红外窗口对透过性能的使用要求。采用磁控反应溅射法在蓝宝石衬底上制备了SiO₂薄膜和Si₃N₄薄膜。揭示了主要工艺参数对SiO₂薄膜的沉积速率、附着性能、内应力和红外透过等性能的影响规律，优化出制备SiO₂薄膜的工艺参数。研究了主要工艺参数对Si₃N₄薄膜中O含量及薄膜红外光谱的影响规律，对Si₃N₄薄膜的成分、结构和性质进行分析，从而制备出低O含量、满足化学计量比的Si₃N₄薄膜。根掘膜系设计的结果，在蓝宝石衬底上双面制备出SiO₂单层增透膜系和SiO₂／Si₃N₄双层增透膜系。镀膜后蓝宝石在3～5μm波段的平均透过率净增加大于9.0％，均可满足使用需求。进行了蓝宝石头罩镀膜的试验研究。利用磁控反应溅射法成功地在蓝宝石头罩上镀制出SiO₂增透保护膜系。单面镀膜后头罩在3～5μm波段的平均透过率净增加大于4.0％，透过率的不均匀性小于2.0％，满足了使用要求。采用旋转臂雨蚀试验装置对SiO₂／Sapphire试样进行了雨蚀试验，并对试样表面的损伤情况进行了光学显微观察、对试样的红外透过率进行了研究。旋转臂雨蚀试验结果表明，SiO₂膜与蓝宝石衬底结合牢固，镀SiO₂膜蓝宝石试样在3～5μm波段的平均透过率下降量均小于1％，雨蚀测试后镀膜蓝宝石的平均透过率仍明显高于未镀膜蓝宝石的平均透过率，SiO₂膜系具有一定的抗雨蚀性。针对所制备的SiO₂薄膜及SiO₂／Si₃N₄双层膜系，测试了不同温度下镀膜与未镀膜蓝宝石的三点弯曲强度。发现在相同的测试温度下，镀膜蓝宝石的平均抗弯强度要高于未镀膜蓝宝石的平均抗弯强度。在800℃时，镀SiO₂／Si₃N₄膜蓝宝石试样的抗弯强度是未镀膜蓝宝石试样的1.4倍；镀SiO₂膜蓝宝石试样的抗弯强度为未镀膜蓝宝石试样的1.5倍。探讨了镀膜可以改善蓝宝石强度的机理。分析认为，在室温下镀膜对蓝宝石强度的改善主要有两方面的原因，一是改善了蓝宝石的表面质量，二是改变了蓝宝石的表面应力状态。在高温下镀膜除改善了蓝宝石的表面质量外，有效地降低了弯曲测试中的表面接触压缩应力，在一定程度上抑制了蓝宝石晶体中缺陷的产生，明显改善了蓝宝石的高温强度。更多还原

【Abstract】 Domes are important components of infrared guide air-to-air missiles. Sapphire has many excellent properties that it is superior to other current and emerging materials for window and dome applications. However, the transmission in mid-wave IR of sapphire limited by the level of preparation and fabrication process can not reach what we expected and it decrease at harsh environments. In addition, the decrease in the mechanical strength of sapphire with increasing temperature is unusually rapid, in comparison to that in most ceramic materials. Resistance to thermal stress is limited by a loss of mechanical strength at elevated temperature. Hence, sapphire is a new window and dome material that needed to be refined and improved. Depositing IR antireflective and protective thin films on sapphire is an effective method to improve its IR transmittance, high temperature strength and durability. Silicon Dioxide films has been used as antireflective and protective thin film of sapphire because of its desirable properties, such as small refractive index, transparency over broad wave band, low absorption, and chemical stability, etc. Silicon Nitride has big refractive index of～1.99, and Si₃N₄ film can be used as antireflective film system by combination with SiO₂ film which has low refractive index.In this article, SiO₂ coatings and double layer films of SiO₂/Si₃N₄ are used as IR antireflective and protective film systems for sapphire. Single layer films of SiO₂ and two-layer films of SiO₂/Si₃N₄ have been designed and prepared on sapphire （α-Al₂O₃） by radio frequency magnetron reactive sputtering. The depositing processes and properties of the films are studied systematically. The main contents and results are listed as follows:Anti-reflective and protective films of SiO₂, SiO₂/Si₃N₄, and SiO₂/Si₃N₄/SiO₂ are designed on the sapphire substrate. The design results explain that sapphire coated on both sides can transmit over a wide waveband from 3 to 5urn for all the designs, which can meet the transmission requirements of missile dome in infrared application.SiO₂ and Si₃N₄ films have been prepared on sapphire substrate by radio frequency magnetron reactive sputtering. Preparations of SiO₂ films with RF magnetron reactive sputtering are studied systematically, influences of processing parameters on the deposition rate, adherence, internal stress, and infrared transmission of SiO₂ film are discovered, and optimized parameters are obtained. The influences of processing parameters on the oxygen content and the infrared spectra of sapphire coated with Si₃N₄ films were measured using a Fourier Transform Infrared （FTIR） spectrometer. Composition and structure of Si₃N₄ films was analyzed by X-ray photoelectron spectroscopy （XPS） and X-ray diffraction （XRD）, respectively. The pure Si₃N₄ films have been obtained.According to the films design, sapphires have been coated with single layer films of SiO₂ and two-layer films of SiO₂/Si₃N₄ on two sides. The average transmittance can be increased 9.0% at a wavelength from 3 to 5μm for all the coated sapphires. The transmission of coated sapphire can meet the requirements of missile dome in infrared application. Preparing films on sapphire domes have been studied. The SiO₂ films were firstly deposited on the dummy dome and sapphire dome by RRFS. The average transmittance in 3～5μm waveband of coated dome can increase 4.0％and the transmittance variation in whole dome area is less than 2.0％, all these meet the requirements of sapphire domes in infrared application.Rain erosion experiments were carried on a whirling arm rig provided by Chinese Aerodynamics Research Institute. Whirling-arm rain erosion results express that SiO₂ coating was strongly bonded to the sapphire substrate during impact. After rain erosion, the decreases in normalized transmission were less than 1％for designed SiO₂ films, and sapphires coated with SiO₂ films had a higher transmittance than uncoated ones. It explains that SiO₂ films can satisfy the rain-erosion-resistant requirements of sapphire substrate in use.For the two films design, the flexure strength of coated and uncoated sapphire samples has been studied by 3-point bending tests at room temperature and high temperatures. The designed single layer of SiO₂ film and two-layer of SiO₂/Si₃N₄ films can strengthen sapphire at the same test temperatures. Flexure tests reveal that SiO₂ coatings and SiO₂/Si₃N₄ films increase the strength of c-axis sapphire by a factor of about 1.5 and 1.4, respectively, at 800℃.The mechanism that films can strengthen sapphire were discussed and analyzed. Two factors could contribute to the effect of films increased the strength of sapphire at ambient temperature. The coatings can improve the surface morphology and reduce the surface roughness of sapphire substrate. A second effect could be that the stress state of sapphire surface is changed from tensile to compressive by the coatings. Films can improve the surface quality and reduce the contact compressive stress along the c-axis of sapphire samples at elevated temperatures, which maybe restrain the twins to be produced so as to increase the flexure strength of sapphire at high temperatures.更多还原