Effects of HfC/PyC core-shell structure nanowires on the microstructure and mechanical properties of Hf1-xZrxC coating

To elevate the mechanical and anti-ablation properties of Hf1-xZrxC coating on C/C composites, HfC/PyC core-shell structure nanowires (HfCnw/PyC) with different PyC layer thickness were synthesized by two steps of CVD. Influences of HfCnw/PyC on the microstructure and mechanical properties of Hf1-xZrxC coating were researched. Toughening mechanism of HfCnw/PyC was also investigated. PyC layer exhibited a lamellar structure and combined well with HfCnw. After incorporating HfCnw/PyC, Hf1-xZrxC coating structure converted from columnar crystal to isometric crystal. HfCnw improved H, E, Kc and bonding strength of Hf1-xZrxC coating, which is ascribed to the nanowire pullout, debonding, bridging and crack deflection mechanism. With the PyC layer thickness increasing, H and E of the coating reduced, Kc and bonding strength of the coating increased. Because of the moderate bonding strength between HfCnw/PyC and coating matrix, lamellar structure of PyC layer and higher Kc of PyC, toughening effectiveness of the core-shell structures gradually enhanced with the PyC layer thickness increasing.