基于纳米结构团聚颗粒包覆的碳化硅镜坯激光快速成形方法研究

Large aperture mirrors in long focal length space borne telescope require high strengthen,high stiffness and high thermal dimensional stability. With the rapid development of the remote sensing technique, more and more requirements are needed in improving the ground resolution of the space optics. Many efforts focus on the research of high performance, low cost, very lightmass reflective telescope systems. SiC is a promising material available for space optics mirrors because of its outstanding advantages, including high specific stiffness, high thermal conductivity and high thermal dimensional stability. But the high hardness and brittleness can bring some difficulties for the machining of SiC mirror. Because of the limitation of equipment and technology, the traditional methods are not suitable for preparation of SiC mirror with large aperture, lightweight and complicated structure. Following closely internationally advanced development, this project searched a new approach and mechanism for preparing the SiC mirror. After detailed analyzing the critical factors for space using, a method of laser rapid forming based on coating nano-particles aggregation for preparing SiC mirror was proposed. This method was combined with the coating nano-particles aggregation, selective laser melting and sintering. Firstly, nano-particles aggregation was obtained by granulation of “SiC/sintering aids” particles. Then, these particles with nanostructure were coated for SLM. A biscuit was formed by SLM. Finally, a high quality SiC mirror was prepared by sintering under high temperature. A new method for preparing SiC mirror with large aperture will be proposed. There will be important theoretical significance and extensive applied value to improve the efficiency and cost.

碳化硅凭借其比刚度大、热导率高、热稳定性好等综合品质，已成为空间反射镜的理想材料。但由于碳化硅的硬度和脆性较大，导致毛坯加工难度大、成本高、周期长。而且，受到设备、工艺等方面的限制，利用传统方法制备大尺寸、轻量化、结构复杂的高品质镜坯时遇到了很大障碍，制约了其发展程度。本项目紧跟国际前沿发展，探索碳化硅镜坯制备的新方法与新机理。在对碳化硅反射镜的空间应用关键因素分析基础上，将纳米粒子团聚颗粒包覆、选区激光熔化成形与传统烧结工艺相结合，提出基于纳米结构团聚颗粒包覆的碳化硅镜坯激光快速成形方法研究，即通过对“碳化硅/烧结助剂”纳米粒子的造粒及其包覆预处理，形成包覆颗粒，利用选区激光熔化成形制备碳化硅素坯，再结合传统烧结工艺实现高品质碳化硅镜坯的制备。能够为未来中大尺寸碳化硅（SiC）镜坯及支撑结构的成形成性一体化制造探索新的解决途径，将对提高研制效率、降低加工成本具有重要的科学及工程意义。

碳化硅凭借其比刚度大、热导率高、热稳定性好等综合品质，已成为空间反射镜的理想材料，但同时，由于碳化硅高硬度、高熔点、强吸波性能的特点，导致毛坯加工难度大、成本高、周期长，使其成为典型的难加工材料，严重制约其发展。本项目紧跟国际前沿发展，在碳化硅加工中引入增材制造的思想，探索碳化硅镜坯制备的新方法与新机理，为了更好的完成坯体的制备，在成形前对碳化硅颗粒进行包覆，提出了利用沉淀反应在颗粒表面生成一定厚度的氧化铝包覆层，在扫描电镜下可以观测到包覆层均匀，在宏观上可以观测到碳化硅粉末颜色有明显变化，包覆层可以明显增加材料对光的反射率。对于碳化硅的加工工艺，本项目主要探讨了以下四类：.（1）碳化硅选区激光烧结技术：对激光选区烧结设备进行改造，以聚苯乙烯作为粘结剂，探究激光功率以及扫描速度对成形质量的影响，结果表明SiC包覆体的工艺窗口极窄，很难获得连续稳定地烧结道。此外，对烧结层的形貌和金相进行研究发现，球化、开裂、熔合不全等现象经常发生，使用高温预热可以在一定程度上减少缺陷的产生。.（2）碳化硅光固化技术：以丙烯酸酯作为主要粘结材料，聚丙烯酸钠作为分散剂，配制粘度合适的陶瓷浆料，在自研的面曝光成形设备上探究曝光参数的影响，使用光固化成形碳化硅坯体时，层与层之间结合力较小，需采用小的成形层厚。.（3）碳化硅三维印刷技术：以碳化硅和糊精粉末按一定比例混合，在蒸馏水中加入微量PVP粉末，在成形过程中控制液滴，获得典型形状的碳化硅坯体，在扫描电镜下可以观测到碳化硅粉末间距减小，颗粒堆叠更为紧密。.（4）碳化硅熔融堆积技术：利用碳化硅、水与微量聚丙烯酸钠的胶体作为原材料，成形了具有一定精度的坯体。.此外，针对典型碳化硅坯体，探究其脱脂与烧结工艺，提出减少坯体在后处理过程中产生缺陷的方法。碳化硅的增材制造工艺，是中大尺寸碳化硅（SiC）镜坯的成形的新的解决途径，将对提高研制效率、降低加工成本具有重要的科学及工程意义。