功能梯度连续纤维增韧碳化硅基复合材料可控制备与数字成形机制

Continuous fiber reinforced silicon carbide ceramic matrix composites (CFCC) possess superior properties such as high-temperature resistant, high specific strength, and high specific modulus, demonstrating great potential in aerospace application. However, precision manufacturing of functional graded CFCC parts with complex structure continues to be a challenge. For this reason, this project proposes a novel additive manufacturing method for forming of functional graded CMC parts with complex structure and their microstructure control. Specifically, fused deposition modeling principle would be applied to control fibers transfer, deposition of fibers and coaxial ceramic slurries could be synchronously controlled by employing directed writing additive manufacturing method and light curing technology; and porous green body after freeze drying and vacuum pyrolysis would be treated by chemical vapor infiltration (CVI) to acquire dense functional graded CFCC parts. In order to support rapid manufacturing of functional graded CFCC parts, interactions between slurries and fibers in forming process, multiphase flow regularity of slurries in pressure field and their cure behavior, would be explored to establish additive manufacturing mechanism of functional graded CFCCs; formation characteristics of micro pores in CFCCs during vacuum pyrolysis and effects of CVI on formation of interfacial layers and matrix densification would be investigated; influence of graded microstructure (fibers, interfacial layers and ceramic matrices) on high temperature mechanical performance of CFCCs would be studied to discover relationship between process, structure and performance.

连续纤维增韧碳化硅基复合材料(简称CFCC)具有耐高温、高比强、高比模等优异性能，在航空航天等领域具有巨大应用潜力，而功能梯度CFCC复杂结构零件快速制造一直是难题。为此，本项目提出一种增材制造新思路：以熔融沉积成型原理控制连续纤维传输，以直写增材制造原理和光固化方法同步控制纤维及其同轴陶瓷浆料成形，然后冷冻干燥，以真空热解获得多孔结构CFCC，以化学气相渗透方法控制界面层生长和陶瓷致密化，实现功能梯度CFCC微观组织(连续纤维、界面层、陶瓷)控制及其复杂结构数字成形。拟研究纤维和陶瓷浆料交互作用力，探索压力场下陶瓷浆料多相流动规律及其光固化行为，揭示功能梯度CFCC增材制造机理；研究真空热解CFCC内部微观孔隙形成规律，探索化学气相渗透对界面层形成和陶瓷致密化作用机制；研究功能梯度CFCC微观组织对其高温力学性能影响，探明工艺-组织-性能关系，为功能梯度CFCC零件增材制造提供理论依据。

针对航空航天关键碳化硅基零部件的快速高性能制造，重点研究了基于直写成型工艺的碳化硅基复合材料零件的强韧化制造方法，实现了针对典型多孔及致密Cf/SiC零件的制造；分析探讨了直写成型工艺对成型性能的影响规律，对比研究了浸渍裂解与液相渗硅两种致密化处理方法的工艺适用性；研究了碳纤维在挤出过程的取向性控制方法；提出了一种具有芯壳结构多孔碳纤维增强SiC陶瓷复合材料的制备方法；提出了3D直写成型CFR-CMC零件的新思路，采用同轴挤出方式实现了一种连续碳纤维/短碳纤维芯壳结构。研究表明：（1）喷嘴直径小于0.5mm时，短碳纤维在挤出过程中受剪切力作用呈高度取向，带有界面层的纤维在渗硅致密后得到有效保留。（2）纤维断裂显著提高了零件的断裂韧性，纤维含量为17.5vol%，界面层厚度为0.63μm的制件弯曲强度为274±13MPa，断裂韧性为5.82MPa m1/2。（3）共挤出可以有效控制碳纤维（核）与碳化硅（壳）的比值（d/D），高度定向排列的短纤维壳核结构在断裂过程中的脱粘，断裂现象，提高了零件的断裂韧性，实验成功制备出开气孔率为31%，强度为123MPa，韧性为2.71MPa m1/2（d/D=0.6）的试样。（4）扫描速度与挤出流量是一对协同参数，二者比值应在一个合理范围。最佳层高为喷嘴直径的0.8倍，最佳打印间隙为1600 μm。当填充率由32%下降至10%时，成型件将由致密结构转变为多孔支架结构。建立了梯度功能碳化硅陶瓷基复合材料3D打印的控形控性机制，为高性能碳化硅陶瓷基复合材料零部件的快速制造提供了试验基础和理论依据。