Bioactive surface modification of carbon/carbon composites with multilayer SiC-SiC nanowire-Si doped hydroxyapatite coating

Multilayer SiC-SiC nanowire-Si doped hydroxyapatite (S-SN-SiH) coatings were applied on carbon/carbon composites (CC) for bone implant applications. The SiC, SiC nanowire(SN) and Si doped hydroxyapatite(SiH) were prepared using pack cementation, electrophoretic deposition(EPD) and electrochemical deposition(ECD), respectively. The morphology and composition of the S-SN-SiH coatings were investigated by scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectrometer and X-ray photoelectron spectroscopy. The formation process of the coating was proposed. The bonding strength between S-SN-SiH coating and CC substrate was studied by testing the shear strength. The in-vitro bioactivity was evaluated by simulated body fluid(SBF) immersion test. The results showed that the SiC layer was in-situ formed on CC and exhibited dense and rough morphology. The SN layer was composed of random orientated SN and showed a porous structure on the surface of SiC modified CC. The amount of SN increased with increasing EPD voltages and EPD time. SiH coating demonstrated blade morphology with a width of 1–3 μm and a thickness of 30–50 nm. Moreover, SN could keep their random orientation and form uniform distribution inside the SiH layer. The formation process of SiH was affected by not only the nucleation points provided by both SiC layer and SN but also the OH⁻ concentration near the nucleation points. The shear strength test showed the bonding strength between S-SN-SiH coating and CC reached to 17.20 MPa. The in-vitro bioactivity test showed that the morphology of S-SN-SiH coating transformed from blade shape to grainy shape, suggesting that S-SN-SiH coating had the ability of inducing apatite formation in SBF and exhibited good in-vitro bioactivity.