空间用反应烧结碳化硅反射镜坯体制备技术研究

摘要

Silicon Carbide (SiC) is a new type of candidate material for large-scale lightweight space born mirror.Its low thermal distortion, high stiffness, high optical quality, and its dimensional stability are better than other traditional optical substrate materials such as ULE, Zerodure, Beryllium (Be) and so on.In this paper, the lightweight silicon carbide space mirror blank was fabricated by reaction sintering.Lots of large scale SiC green bodies were prepared by a gel-casting method with the lost mould technology.And the size of the largest SiC green body with sandwich structure is 1080 mm × 820 mm now.After drying, burning out the organic elements and reaction sintering, the reaction bonded SiC (RB-SiC) mirror blanks were fabricated.The test results of ground mirrors show that the structure of RB-SiC is fully solid, and the mechanical and thermal properties of RBSiC are excellent in elastic modulus of 330 GPa, bending strength of 340 MPa, fracture toughness of 4.0 MPa·m1/2 and Coefficient of Thermal Expansion (CTE) of 2.6 × 10-6 K-1.The surface roughness (RMS) of the polished mirror is better than 3 nm, which means SiC is a fine candidate material for the spaceborne mirror.%采用凝胶注模(gel-casting)成型工艺并结合一种先进的消失模技术,制备了具有各种不同轻量化结构形式的碳化硅(SiC)陶瓷素坯,目前制备的背部半封闭素坯最大尺寸为1080mm×820 mm;素坯经过脱模、干燥、脱脂和反应烧结等,可得到空间用SiC反射镜坯体.对反应烧结碳化硅(RB-SiC)反射镜坯体的表面进行了光学加工,并且测试了其各项性能.结果表明,所制备的RB-SiC陶瓷内部结构均匀致密;力学性能和热学性能优异,弹性模量、抗弯强度、断裂韧性和热膨胀系数分别达到了330 GPa,340 MPa,4.0 MPa.m1/2和2.6×10-6K-1;镜体经抛光后的表面粗糙度RMS值优于3 nm,可作为空间用反射镜的候选材料.