Effect of microwave heating time on bonding strength and corrosion resistance of Ca-P composite layers for carbon/carbon composites

Three coated Ca-P composite layers were fabricated by microwave-assisted hydrothermal (MH) and supersonic atmospheric plasma spray (SAPS) method. This multilayer coating aims to promote the bonding strength as well as the corrosion property against stimulated body fluid (SBF) on carbon/carbon (C/C) composites. The morphologies and the chemical composition of the Ca-P composite layers were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The bonding strength was evaluated by scratch test and the bioactivity was measured using SBF. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) were investigated for the corrosion resistance. The results reveal that Ca-P composite layers exhibit excellent bonding strength which reaches to the loading force of 39.5 N. In SBF solution, the Ca-P composite layers can induce a new and uniform apatite layer. Additionally, potentiodynamic polarization and EIS results indicate that adding MH influences the corrosion resistance of the Ca-P composite layers. The above conclusion illustrate that MH approach could become a very useful route to enhance the long-term protection and corrosion resistance of the layers on C/C substrates for orthopedic application.