SiC Nanowire-Toughened Si-Based Ceramic Coating for Oxidation Protection of Large-Scale C/C Composites

摘要

A dense oxidation protective Si-based ceramic coating with homogeneously dispersed SiC nanowires was prepared on the large-scale carbon/carbon (C/C) composites using a two-step technique consisting of chemical vapor deposition and hot-pressing reactive sintering. After incorporating SiC nanowires, the results of indentation test showed that the fracture toughness of the coating was enhanced from 4.02±0.28 to 7.03±0.35 MPa?m~(1/2) due to their toughening effects including nanowire pullout, nanowire bridging, microcrack deflection and two special energy dissipation mechanisms involving the plastic fracture at the interface of the nanowire-matrix and the super-plasticity deformation of SiC nanowires. This result was confirmed by an additional thermal shock experiment, which demonstrated that the mass loss of the coated C/C samples was decreased from 4.14% to 2.41% after 30-time thermal cycles between 1773 Κ and room temperature in air. The results of isothermal oxidation test showed that the mass loss of the coated C/C samples was only 0.51% after isothermal oxidation at 1773 Κ in air for 70 h. This result was also confirmed by an additional mechanical experiment conducted using a three-point bending test, which demonstrated that the remaining flexural strength of the coated C/C samples was still up to 94.6% after isothermal oxidation test.