Effect of pyrolytic carbon interface thickness on microstructure and mechanical properties of lightweight zirconium boride modified carbon-bonded carbon fiber composites

To improve the mechanical properties of carbon-bonded carbon fiber (CBCF) composites, they are firstly fabricated by chemical vapor deposited (CVD) pyrolytic carbon (PyC) coating layer on the carbon fiber surface, and then modified by zirconium boride (ZrB₂) using three cycles of precursor infiltration and pyrolysis (PIP) process. The effects of different PyC interface thickness on the microstructure and mechanical properties of ZrB₂ modified PyC coated CBCF (PyC-CBCF/ZrB₂) composites were studied and characterized. As the PyC thickness increased from 0.5 to 3.6 μm, the flexural properties of PyC-CBCF/ZrB₂ composites are noticeably enhanced in x/y and z direction, respectively. Mechanical enhancements for PyC-CBCF/ZrB₂ composites are mainly attributed to the effective interface bonding between carbon fiber and PyC, crack deflection and branching within the laminar PyC layer and carbon fiber pullout from PyC interface coating.