Fluorine-containing hydroxyapatite bioactive coating on the surface of C/C composites

A fluorine-containing hydroxyapatite (FHA) coating was prepared on the surface of carbon/carbon composites (C/C) using the two-step method of sonoelectrodeposition and ion exchange. The effects of ion exchange time and concentration of NaF on the morphology, microstructure and composition of the as-received coating were investigated. The results show that after the ion exchange, the coating is composed of hydroxyapatite (HA) and F-rich apatite (FHA). The coating possesses a similar structure of plate-like crystal before and after ion exchange. With increasing of ion exchange time and concentration of NaF, the content of HA in the coating decreases while F-rich apatite (FHA) increases, and the size of the crystals changes. The bonding strength between the coating and C/C matrix increases slightly after ion exchange, which can be attributed to the good matching of the thermal expansion coefficient between FHA and C/C.