裂解碳包覆对SiC纳米纤维增强SiC陶瓷基复合材料性能的影响

以SiC纳米纤维(SiC_nf)为增强体,通过化学气相沉积在SiC纳米纤维表面沉积裂解碳(PyC)包覆层,并与SiC粉体、Al₂O₃-Y₂O₃烧结助剂共混制备陶瓷素坯,采用热压烧结工艺制备质量分数为10%的SiC纳米纤维增强SiC陶瓷基(SiC_nf/SiC)复合材料。研究了PyC包覆层沉积时间对SiC_nf/SiC陶瓷基复合材料的致密度、断裂面微观形貌和力学性能的影响。结果表明:在1 100 ℃下沉积60 min制备的PyC包覆层厚度为10 nm,且为结晶度较好的层状石墨结构;相比于纤维表面无包覆层的复合材料,复合材料的断裂韧性提高了35%,达到最大值(19.35±1.17) MPa·m^1/2,抗弯强度为(375.5±8.5) MPa,致密度为96.68%。复合材料的断裂截面可见部分纳米纤维拔出现象,但SiC_nf/SiC陶瓷基复合材料界面结合仍较强,纳米纤维拔出短,表现为脆性断裂。

Effect of PyC Coating on Properties of SiC Nanofiber Reinforced SiC Ceramic Matrix Composites

In this work, SiC nanofiber reinforced SiC (SiC_nf/SiC) ceramic matrix composites with 10% (mass fraction) of nanofiber were fabricated by the hot pressing (HP) using SiC nanofiber as reinforcement, which were coated with pyrolysis carbon (PyC) via chemical vapor deposition, SiC powders as matrix and Al₂O₃-Y₂O₃ as sintering aids. The effects of deposition time of the PyC coating on density, fracture surface morphology and mechanical properties of SiC_nf/SiC ceramic matrix composites were investigated. The results show that PyC layer has a layered graphite structure with good crystallinity, and the coating thickness of PyC prepared by deposition at 1 100 ℃ for 60 min is 10 nm. The fracture toughness of SiC_nf/SiC ceramic matrix composites with the SiC_nf content of 10% is (19.35±1.17) MPa·m^1/2, which is 35% higher than that of composites without PyC coating, with the bending strength of (375.5±8.5) MPa and relative density of 96.68%. In addition, the phenomenon of nanofiber pulling out is observed in the fracture section of the composites. However, the SiC_nf/SiC ceramic matrix composites exhibit brittle fracture due to the strong interfacial bond between the nanofiber and matrix and short pull-out length of nanofiber. This work can be used as a reference for the interface design of SiC_nf/SiC ceramic matix composites.