Coating of ti6al4v/ti6al7nb alloys with graphene doped hydroxyapatite biomaterial

The aim of this study is to obtain Graphene Nano Sheets (GNS) and Nano-Hydroxyapatite (nHA) hybrid composite structure on Ti6Al4V / Ti6Al7Nb alloys and to investigate morphological, chemical and mechanical properties of coatings. In this study, the nano-hydroxyapatite(nHA)/GNS hybrid nanocomposites were coated on the surface of Ti6Al4V / Ti6Al7Nb alloys with two different one-step methods which are the hydrothermal (HT) method and plasma electrolytic oxidation (PEO). Samples were cut 25x25x3 mm3 for the Ti6Al4V alloy and 25x25x4.1 mm3 for the Ti6Al7Nb alloy, and the surfaces of the Ti6Al4V / Ti6Al7Nb alloys were firstly polished using 240-1200 mesh SiC emery to remove the natural oxide layers on the surfaces. The hydrothermal reaction was carried out at 200 °C under a pressure of 220 bar for 24 hours, with five diffrent ratios 0%, 1%, 3%, 5% and wt. 7%GNS addition in HA . On the other hand, PEO was carried out by using bipolar mode at 10% Duty Cycle, 500 positive Voltage and -100 negative Voltage for 10 minutes at 1000, 1500 and 2000 Hz frequencies with no additive HA, 0.5%, 1% and wt. 1.5%GNS. The crystallographic properties of the surfaces coatings were determined by XRD analysis, functional groups with ATR-IR and elemental analysis EDS analysis. Surface morphological properties were examined using AFM and SEM analysis. Corrosion resistance of the coatings were examined by in vitro corrosion tests. The coatings obtained by both methods are examined in detail and the changes in the coating properties depending on the parameters and coating methods are compared. The results of the analysis showed that nHA-GNS composites were successfully coated on the surface of Ti6Al4V / Ti6Al7Nb samples in both methods. XRD and ART-IR analysis proved the presence of HA and GNS on surfaces. Porous and rough surface coatings obtained on the surfaces were seen by SEM analysis and AFM analysis. Coating thickness increased due to the increasing frequency and GNS addition rate in PEO. Also the thickness of the coatings increased with increasing of GNS addition in HT. When the results are analyzed, the mechanical and chemical properties of the coatings have been improved with the addition of GNS, and the surface hardness of the coatings produced with the PEO method has increased significantly compared to the undoped-GNS coatings. Corrosion resistance and surface roughness were also increased with GNS additives in coatings. In addition, bone-like apatite formation was observed on the surfaces kept at 36.5 ° C in SBF during the corrosion experiments and a bioactive surface was obtained. When the results are evaluated, significant results have been obtained in the use of GNS doped nHA hybrid composite coatings in biomedical fields.