Thermal-shock resistance of in-situ SiC nanowire-toughened SiC ceramics

The brittleness and insufficient thermal-shock resistance are the critical problems for the extensive applications of SiC ceramics. Low-density SiC ceramics decorated with in-situ SiC nanowires were fabricated via the pyrolysis of polycarbosilane assisted by ferrocene. They were further densified by the technique of precursor infiltration and pyrolysis to prepare in-situ SiC nanowire-toughened SiC ceramics. The experimental results showed that, compared with the SiC ceramics without nanowires, the thermal shock resistance of the in-situ SiC nanowire-toughened SiC ceramics was improved significantly, whose oxidation mass gain was only 2.53% and decreased by 59% after 30 thermal cycles between room temperature and 1500 ℃. The corresponding microstructural analysis indicated that the synthesized SiC nanowires were β-SiC and contained some stacking faults. The β-SiC nanowires grew along the preferential orientation of <111> and its growth was governed by a vapor-liquid-solid mechanism. The in-situ SiC nanowires could effectively alleviate the stress concentration due to the ceramic preparation and the thermal cycles between high and low temperatures. The improved fracture toughness and thermal-shock resistance could be attributed to the toughening mechanism including nanowire bridging and pull-out, as well as the decrease of crack number and size in SiC ceramics. After the introduction of SiC nanowires, the average crack length of SiC ceramics decreased from 27.7 μm to 18.2 μm, and the fracture toughness increased from 3.76 MPa·m^1/2 to 7.83 MPa·m^1/2.