【作者】 马彬；

【导师】 李垚；

【作者基本信息】 哈尔滨工业大学 ， 材料学， 2010， 博士

【摘要】 临近空间飞行器已经成为了各国研究的热点,该飞行器飞行环境的特殊性和飞行特点对新型表面防热技术的需求也迫在眉睫。本论文主要是利用三维光子晶体对光的可控可调的特点,设计出适用于在临近空间运行的飞行器的高辐射涂层。在镍基高温合金表面设计出了底层为三维多孔镍/氧化钇稳定氧化锆（YSZ）复合结构,表层为SiC涂层的防热结构,在本结构中三维镍结构可以对光有高的反射率,将传播到其表面的光向外部反射,来增强表面SiC涂层的发射率。本论文首先利用不同的制备工艺制备出了基于三维镍结构的辐射防热涂层,并通过SEM、XPS、Raman、PL等测试手段分析了涂层的成分、微观组织及表面粗糙度等;利用纳米压痕试验和纳米划痕试验对涂层的力学性能进行了表征;利用光分光光度计对涂层的光学性能进行了表征;利用傅里叶红外光谱仪测试了防热涂层在高温下的发射率,并对影响发射率的因素进行了分析。通过垂直沉降法,在镍合金基体上制备了质量较好的聚苯乙烯模板,在大范围内聚苯乙烯球为最稳定的有序密堆六方排列。然后基于模板技术,利用电沉积方法制备三维镍结构。在沉积时间较短（1min）时,得到的为二维镍结构;沉积时间大于3min后得到的为三维镍结构,其中孔按照密堆六方排列,孔径与聚苯乙烯球直径相符,没有收缩。40℃温度下沉积得到的镍薄膜的孔形圆,孔壁光滑。随着沉积温度的升高,孔变形,孔壁变粗糙。不同的电流密度下,镍会沿着不同的晶向生长,其颗粒大小也有相应的变化。通过对电沉积参数的研究得出:在电沉积温度为40℃,电流密度为30mA·cm-2,沉积时间大于3min的条件下,可以制备质量较好的三维镍结构。试样拉伸伸长10%后,三维镍结构薄膜没有脱落,说明镍薄膜与基体结合牢固;拉伸后孔的变形量小于10%,说明为弹塑性变形,拉伸卸载后形状有所恢复。通过力学测试和计算得出,未拉伸前的三维镍结构薄膜的平均硬度和弹性模量分别为0.99GPa和23.52GPa;拉伸后的硬度和弹性模量分别是0.88GPa和22.68GPa。通过划痕试验,1000μN的固定载荷下在薄膜表面划6μm,薄膜没有剥落。制备的三维镍结构具有很好的塑性和抗压性能,膜基结合牢固。三维镍结构薄膜的反射率随着波长的增大而增加,高达78%。三维镍结构薄膜的反射率随着沉积电流密度的变化而变化。由30mA·cm^-2沉积的三维镍结构薄膜的反射率较高。三维镍结构的反射率不但与其孔的结构有关,还与镍颗粒大小有关。通过溶胶凝胶的方法,将YSZ先驱在600℃下煅烧后2h后在三维镍结构中制备了单一立方相YSZ涂层,YSZ涂层颗粒均匀,涂层致密。磁控溅射工艺制备的SiC涂层主要以非晶物质为主,含有大量的Si-C键和C-C键,还有少量的Si-O键和Si-Si键。其中Si-C键主要是非晶碳化硅也含有少量6H-SiC,C-C键是以sp2非晶碳（石墨）形式存在。制备的SiC涂层颗粒均匀,大约在500nm左右,涂层表面平整致密,没有明显的空隙或者缺陷。在300℃、600℃、900℃、1050℃下对制备的SiC涂层进行了真空热处理2h,在热处理过程中富余的C-C键与Si-Si键或者是Si-C键中空键搭联,这样Si-C键增多,C-C键减少,说明热处理有利于提高SiC的结晶程度。600℃温度以下热处理后SiC涂层中的小晶粒逐渐聚合慢慢生长成较大晶粒,晶粒间界面明显,表面更加致密;但温度达到900℃时,晶粒变大,晶粒之间的界面变得模糊;温度达到1050℃时,只能看到连续的大颗粒,并且没有明显的界面。同时,随着热处理温度的升高,涂层的表面粗糙度、硬度和弹性模量都增加。在300℃、500℃和700℃温度下测试了SiC涂层的辐射率,其辐射率为整体结构的宏观辐射率,并且其辐射率随着温度的升高而逐渐增大。热处理后的SiC涂层,其辐射率较制备态的有所提高,并且随着热处理温度的升高,辐射率也在升高。在700℃下涂层辐射率达到0.90左右,该结构有很好辐射性能。随着热处理温度的变化,涂层的成分和表面粗糙度等有相应的变化,对涂层的辐射率有一定的影响。更多还原

【Abstract】 In recent years, many countries have given their attention to explor near space vehiles. In this paper, we designed a high thermal emittance structure based on three dimensional photonic crystal for near space vehile to proctect the equipment inside. In the structure designed, three dimensional nickel structure which was also called three-dimensionally ordered macroporous (3DOM) Ni films was prepared on the nickel alloy substrate, which would reflect the light to the top SiC coating to enhance the thermal emittance of the structure. The phase composite, microstructure,suface roughness were investigated by SEM, AFM, XPS, FTIR, Raman spectroscropy and PL spectroscropy. The mechanical properties were ananlyzed by nano-indentation and nano-scratch. The optical properties were studied by UV-Vis-NIR Spectrophotometers. The emissivity of SiC coating was measured by Fourier tranform infrared spectrometer. The influnce of composition, surface roughness and thickness on the emissivity were analyzed.The polystyrene (PS) colloidal crystals have been formed by self-assembly of PS particles using vertical deposition method, in which the PS particles displayed a hexagonal array which indicated the most stable state of thermodynamics. 2D nickle films were get in the plating time shorter than 1min,and 3DOM nickel films were finally obtained in the time longer than 3min, in whcih the pores possesses a face-centred cubic (fcc) crystal structure and no structure shrinkage relative to PS particles during the fabrication process. The pore wall of 3DOM nickel films was smooth which was deposited at 40℃. When the plating temperature above 50℃, the pore wall became rough. The gain size changed with the different plating current density.No abscission and desquamation were observed in the 3DOM Ni films under 10% tensile strains and after nano-scratch test, which suggested that the combination between the nickel PCs and substrate is very stable. And the deformation of the pores less than 10% showed the excellent plasticity. The hardness and Young’s modulus of 3DOM Ni films without strain are 0.99 GPa and 23.52 GPa, respectively. And the hardness (0.88 GPa) and Young’s modulus (22.68 GPa) of 3DOM nickel PCs with 10% strain are also little smaller than that of 3DOM Ni films without strain. These results imply that the 3DOM nickel PCs on nickel alloy substrate have good mechanical properties. The reflectance of 3DOM Ni films increased as the wavelength increased. And it varied with different current density, in which the reflence of the 3DOM Ni films obtained under 30mA·cm-2 was highest 78%. Cubic YSZ coating was prepared in the 3DOM Ni skeleton when the YSZ precursor was calcined at 600℃for 2h. And the surface of YSZ coating was smooth and compact, which showed us the sizes of particles was similar.SiC coatings were prepared on the Ni alloy substrates by radio frequency magnetron sputtering at low temperature. SiC films were thermal annealed at 300℃,600℃,900℃and 1050℃for 30 min in the vacuum ambient. There were mainly C-Si bonds, C-C bonds, and a small quantity of Si-O bonds, Si-Si bonds on the surfaces of the SiC films. The Si-C bonds were from mainly amorphous SiC and 6H-SiC in small part. And the C-C bonds (sp2) were from amorphous graphite. The surface of SiC coating were smooth and copact. But as the samples were thermal annealed at differernt temperture, the percentages of different bonds were respectively calculated from the peak area and sensitivity factors. The results showed that chemical composition the SiC increased as annealing temperature increased, which suggested the annealing in vacuum was beneficial to the formation of SiC. From the PL spectra, the 6H-SiC were comfired in SiC the films. After annealing, the sizes of particle on the surface SiC coating became larger, and the interface between particles became illegibility. Meanwhile, the surface roughness, hardness and Young’s modulus increased.The 3DOM Ni films, YSZ coating and SiC coating was one integrated mass in the thermal protection structure. And the spectral emissivity of SiC films was investigated at 300℃, 500℃, 700℃. The results showed the spectral emissivity of SiC coating increased as the test temperture increased. And at the same test temperture, it increased as the thermal annealing temperture increased. The emissivity of SiC coating were about 0.90 at 700℃. With wavelength, the variations of SiC coatings annealed at the same temperature were different. From all the reasults, The emissivity of the structure was in the relationship of test temperature, chemical composition, surface roughness,and so on.更多还原