激光熔覆叠层增材制造SiCf/Ti复合材料的界面产物生成机理及工艺研究

The additive manufacturing technology of continuous fiber reinforced titanium matrix composites for missile rudder and spacecraft skin has the advantages of short manufacturing cycle, die-less, and high complexity of the parts. .This project combines the laser cladding deposition and the laminated object manufacturing, using silicon carbide fiber as reinforcement and titanium alloy as the matrix, focusing on scientific research in the following five aspects. First, the interaction mechanism of laser and fiber is studied so as to ensure the metal powder melting while avoiding fiber burned by laser. Second, studying the interfacial reaction kinetics and thermodynamics of metal droplet and fiber to ensure that thickness of interfacial reaction layer is uniform and high bonding strength between metal and fiber under the condition of rapid laser heating and cooling. Third, the stress and deformation regulation mechanism of the forming process are researched to reduce the internal stress in the forming parts. Fourth, the arrange of Ultrasonic head array and the suitable frequency of different layer, which reduce the pore in the forming part, will optimized by finite element analysis and microstructure observation. Fifth, the performance of SiCf/Ti composites manufacturing by laser cladding and laminated object hybrid additive manufacturing are tested and optimized by technology parameters..In the basis of analyzing the theories and experimental results, continuous fiber reinforced titanium alloy matrix composite can be prepared whose fiber volume fraction is 30-40% and the distance of the fiber layer is 0.2-0.3mm, the yield strength is about 1000MPa, the ultimate strength is about 1400MPa, to meet the requirements of high-speed aircraft.

采用增材制造技术制造导弹尾翼和航天器蒙皮所需的SiCf/Ti复合材料具有周期短、不需工模具、零件复杂程度高等优点。.本项目将激光熔覆沉积与叠层实体制造两种技术相结合，以SiC纤维为增强相，以钛合金为基体，进行五个方面的科学研究：第一，研究激光与纤维的相互作用机理，保证金属粉末熔化的同时避免纤维被激光烧损；第二，在激光快速加热和冷却条件下，研究金属与纤维的界面反应动力学和热力学，保证界面反应层厚度薄而均匀；第三，研究零件成形过程中应力和变形调控机制，降低成形零件内应力；第四，优化阵列超声的布置及频率的选择，促进零件内部气体逸出；第五，针对应用前景广的高性能SiCf/Ti复合材料进行材料选择、工艺研究及性能检测与优化。.通过理论和实验研究，制备出纤维体积分数在30-40%之间的SiCf/Ti复合材料，屈服强度达到1000MPa左右，极限强度达到1400MPa左右，满足高速飞行器要求。

连续SiC纤维增强钛基复合材料在航空航天领域有着极大的应用前景，本项目提出的激光熔覆叠层复合增材制造技术结合了纤维自动铺设与激光熔覆技术，具有工艺流程短、成形零件形状复杂等特点，可以用于SiCf/Ti基复合材料的大面积制备。.项目围绕SiCf/Ti基复合材料激光熔覆叠层增材制造技术中纤维分解、界面反应、微缺陷控制等科学问题,研究了激光与不同涂层纤维之间的纤维分解行为、金属液滴与纤维之间的界面反应动力学和热力学、激光熔覆过程中的应力和变形控制机制、阵列超声辅助气体逸出机制。主要研究成果如下：.（1）分别对无涂层、C涂层、Cu涂层和Ti-6Al-4V涂层SiC纤维在激光作用下的分解情况进行研究。结果表明不同涂层对纤维的保护情况是：Ti-6Al-4V涂层＞Cu涂层＞C涂层＞无涂层。.（2）开发了一套高精度激光熔覆叠层复合增材制造系统，设计的铺拉丝装置实现了将SiC纤维精准铺放到成形平面的功能，成形尺寸为300mm×300mm×20mm，成形精度达±0.2mm，设计的惰性气氛成形室为SiCf/Ti基复合材料LCLD成形提供所需氩气环境。.（3）针对影响SiCf/TC4复合材料成形性的纤维铺设因素和工艺因素进行了优化研究。当激光熔覆头行进方向与纤维夹角为90°且纤维铺设密度为75%时，纤维铺设效果最优；优化的工艺参数为：激光功率250 W、扫描速度6-10 mm/s、送粉量2.5 g/min、离焦量+1 mm、保护气流量11 L/min，上述优化条件下纤维烧损率最低。.（4）采用激光熔覆叠层技术制备SiCf/Ti-6Al-4V复合材料虽成形时间短，但SiC纤维、C涂层、基体之间也会发生界面反应，界面反应产物主要为TiC。经短时真空高温热暴露，SiC纤维、C涂层、基体及界面反应层的硬度值和弹性模量没有发生明显的变化，表明该材料在900℃及以下温度具有良好的短时热稳定性。.（5）超声辅助能有效逸出气体，减少孔洞，保证制备的复合材料性能不下降。.项目研究结果表明激光熔覆叠层技术制备SiCf/Ti基复合材料的方法可行，掌握的基本理论和实验结果为该技术进一步研究奠定了基础。