Fabrication and microstructure of ZrB2-ZrC-SiC coatings on C/C composites by reactive melt infiltration using ZrSi2 alloy

ZrB2-ZrC-SiC ternary coatings on C/C composites are investigated by reactive melt infiltration of ZrSi2 alloy into pre-coatings. Two different pre-coating structures, including porous B4C-C and dense C/B, are designed by slurry dip and chemical vapor deposition (CVD) process respectively. The coating prepared by reactive melt infiltration (RMI) into B4C-C presents a flat and smooth surface with a three-layer cross-sectional structure, namely interior SiC transition layer, gradient ZrB2-ZrC-SiC layer, and ZrB2-ZrC exterior layer. In comparison, the coating prepared by RMI into C/B shows a more granular surface with a different three-layer cross-sectional structure, interior unreacted B-C pre-coating layer, middle SiC layer, and exterior ZrB2-ZrC-ZrSi2 layer. The forming mechanisms of the specific microstructures in two coatings are also investigated and discussed in detail.