Improvement of toughness of reaction bonded silicon carbide composites reinforced by surface-modified SiC whiskers

To improve the reliability, especially the toughness, of the reaction bonded silicon carbide (RBSC) ceramics, silicon carbide whiskers coated with pyrolytic carbon layer (PyC-SiC_w) by chemical vapor deposition (CVD) were introduced into the RBSC ceramics to fabricate the SiC_w/RBSC composites in this study. The microstructures and properties of the PyC-SiC_w/RBSC composites under different mass fraction of nano carbon black and PyC-SiC_w were investigated methodically. As a result, a bending strength of 550 MPa was achieved for the composites with 25 wt% nano carbon black, and the residual silicon decreased to 11.01 vol% from 26.58 vol% compared with the composite of 15 vol% nano carbon black. The fracture toughness of the composites reinforced with 10 wt% PyC-SiC_w, reached a high value of 5.28 MPa m^1/2, which increased by 39% compared to the RBSC composites with 10 wt% SiC_w. The residual Si in the composites deceased below to 7 vol%, resulting from the combined actively reaction of nano carbon black and PyC with more Si. SEM and TEM results illustrated that the SiC_w were protected by PyC coating. A thin SiC layer formed of outer surface of whiskers can provide a suitable whisker-matrix interface, which is in favor of crack deflection, SiC_w bridging and pullout to improve the bending strength and toughness of the SiC_w/RBSC composites.