Corrosion Behavior of Nanostructured Bioactive Apatite Coating on TiVAl Alloys

摘要

Bioinert Ti-6Al-4V alloys have been used for the past decades on total bone replacement applications. However, due to possible corrosion of these alloys, biomaterial scientists have been working on modifying surfaces of these alloys to minimize their corrosion in body media and enhance their bioactivity. In the current study, the corrosion behavior of coated and uncoated bioinert Ti-6Al-4V alloy with different surface roughness has been investigated in a phosphate buffered saline (PBS) solution at 37oC. A sputtering technique has been used to develop a 300 μm thick continuous bone-like apatite (calcium phosphate hydroxide) layer on the surfaces of the alloy of different degrees of surface roughness. Coatings were evaluated for their structure, morphology ad durability in simulated body fluid (SBF) media using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) techniques. Corrosion techniques that have been employed included cyclic polarization measurements, polarization resistance (Rp) vs. time measurements, and EIS measurements. Surface analysis shows the formation of a stable, homogeneous, and nanostructured apatite layer with interconnected porosity. In SBF media, apatite coatings were underwent remodeling into bone-like apatite structure and morphology. Corrosion tests showed the coated samples have corrosion rates 2 to 3 orders of magnitude lower than the uncoated samples while the Rp values were 3 orders of magnitudes higher. Both the uncoated and coated samples showed no hysteresis in the reverse polarization scans signifying the absence of pitting. Finally, the current densities in the passive range were 2-3 orders of magnitude lower for the coated samples than the uncoated ones indicating the enhancement of the already existing protective film in the presence of coatings. These results, therefore, indicate the potential of bioactive apatite-coated Ti-6Al-4V alloys to be further evaluated as total bone replacement in load-bearing sites.