大尺寸碳化硅基空间反射镜制备工艺及性能

Large ceramic mirror for space optical applications

采用轻量化的硅/碳化硅复合材料制造大尺寸摆镜或高分辨率相机的主镜.该材料的组织构成是双峰分布的碳化硅晶粒和游离硅.利用碳化硅、碳注浆成型制备复杂轻量化结构的的素坯.在硅气相渗透过程中,碳与硅反应形成新的碳化硅,过量硅填充坯体孔隙.由于干燥和反应过程中收缩量小,可用来制备形状复杂且无缺陷的大尺寸样品.硅/碳化硅复合材料可用作空间光学镜面基板,利用电子束物理气相沉积,在基板上沉积硅膜,同时检测硅/碳化硅复合材料和硅膜的性能.制备了各种尺寸的空间用反射镜,直径为120 mm的六角形镜面重0.23 kg,厚度15 mm,表面抛光并镀硅膜,后开式蜂窝状结构的面密度为24.3 kg/m2,面形精度为0.1λ@632.8 nm p-v,表面粗糙度<3nm rms.利用有限元分析方法估计实际条件下的应力和变形.

Lightweight ceramic composite mirrors were prepared for the large pointer mirror or the primary mirror of the high resolution camera. The Si/SiC composite was a ceramic matrix of free silicon containing a bimodal distribution of silicon carbide grains. The green body of silicon carbide grains and free carbon was fabricated by slip casting. Inserts were used to form the complex lightweight structure. During silicon vapor infiltration process, silicon reacted with carbon to form new silicon carbide phase and the pores of green body disappeared Because there are very little shrinkage during drying and reaction process, the large scale production with complex shape has no crackles and distortions. The results indicated that Si/SiC composite could be used as space optical mirror substrates. Using electron beam physical vapor deposition, we prepared a silicon film on the mirror substrate. The properties and microstructure of Si/SiC composite and Si film were measured. We fabricated some space mirrors with various scales. A 120 mm hexagonal mirror with 15 mm thickness and 0. 23 kg weight was polished and coated with Si film. Open back honeycomb lightweight structure was produced to gain 24. 3 kg/m^2 areal density. Polishing technique different from optical glass polishing was introduced to achieve less than 0. 1 λ@ 632. 8 nm p - v surface error and less than 3 nm rms surface roughness. The stress and displacement under factual condition were estimated using finite element analysis method.