Hydroxyapatite-carboxymethyl cellulose-graphene composite coating development on AZ31 magnesium alloy: Corrosion behavior and mechanical properties

Abstract In this study, hydroxyapatite (HA) coatings containing carboxymethyl cellulose (CMC) and graphene (Gr) were developed on AZ31 magnesium alloy through two-step electrophoretic deposition method. The morphology and chemical bonding of coatings were characterized and also the phase identification was done using scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction, respectively. Moreover, the corrosion behavior of the applied coatings was compared with the bare AZ31 Mg alloy substrate in the simulated body fluid by the means of potentiodynamic polarization test and electrochemical impedance spectroscopy. Obtained results revealed that the novel HA-CMC-Gr coating possesses the highest corrosion resistance compared to the HA, HA-CMC, and HA-Gr coatings due to its uniform and compact structure. To investigate the mechanical properties and to elucidate the effect of CMC on the adhesion of coating-alloy interface, pull-off test was employed, where results demonstrated that the addition of CMC increases the adhesion force from 1.06 MPa to 1.62 MPa. Besides, the modulus of elasticity and the hardness of HA and HA-Gr composite coatings were compared by applying nanoindentation test. Interestingly, it is detected that the presence of Gr has considerably increased the elastic modulus of the coating by approximately 30% in comparison to the pure HA coating.