Effects of HA-Coating on the Surface Morphology and Corrosion Behavior of a Co-Cr-Based Implant in Different Conditions

The corrosion behavior and surface morphology of a Co-Cr-based implant after HA-coating using the sol-gel method were investigated. Sintering was performed at four different conditions. Surfaces of the samples were characterized and evaluated using field emission scanning electron microscopy. Atomic force microscope was used to measure the surface roughness and to collect the micrographs of the HA-coating layer. The x-ray diffraction results confirmed the formation of a crystalline phase of HA on the surface of the substrates. To measure the corrosion resistance, the samples were dip-coated with two different thicknesses (78 and 142 µm), and then tested by potentiodynamic polarization and spectroscopy (EIS) in SBF at 37 °C after sintering process. This study revealed that the thickness of the HA-coating layer affects the corrosion rate of the substrate, but the sintering condition of the HA-coating layer plays a remarkably more significant role in improving the corrosion resistance of Co-Cr-based implants. Moreover, the sample sintered at 600 °C for 20 min with thickness of 142 µm showed considerably enhanced surface morphology and superior corrosion resistance compared with the bare material and other treated samples

Evaluation of mechanical and electrochemical properties of FHA-coated Co–Cr implant

In this study, hydroxyapatite (HA) and fluoridated hydroxyapatite (FHA) as a comparison were deposited electrophoretically on a cobalt (Co)–chromium (Cr)-based implant to increase its surface bioactivity and reduce ion release. The coated substrates were then sintered at 650°C for 1 h. Typical apatite structures were obtained for both coatings after electrophoretic deposition and subsequent post-treatment. The morphology of the coated layers was characterised using field emission scanning electron microscopy and energy-dispersive spectroscopy. Mechanical properties of the coated layers including adhesion strength and Vickers microhardness were examined. In addition, the electrochemical corrosion behaviour of the FHA-coated substrate was evaluated in simulated body fluid solution and compared to uncoated as well as HA-coated samples. The results indicate that FHA coating has a denser structure compared to the HA-coated layer, resulting in the improvement of mechanical properties as well as corrosion resistance. Furthermore, immersion test findings reveal that FHA coated Co–Cr shows lower Cr ion release after 1, 7, 14 and 21 d of immersion as compared to the HA-coated implant