Development of HA-CNTs composite coating on AZ31 magnesium alloy by cathodic electrodeposition. Part 1: Microstructural and mechanical characterization

Magnesium alloys are considered as a new class of biodegradable alloys having many favorable properties to overcome the problems of currently used biomedical materials. Hydroxyapatite (HA) containing carbon nano tubes (CNTs), with concentration ranging from 0 to 1.5 wt.%, coated on AZ31 magnesium alloy by direct and pulse cathodic electrodeposition methods. The coating properties including phase analysis, chemical bonding, morphology, and thickness were characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), and field emission scanning electron microscopy (FESEM), respectively. Nano-indentation, micro-hardness and adhesion tests were also used to evaluate the mechanical properties of the coatings. The results showed that a dense and fine coating structure was obtained by pulse deposition method. Moreover, the presence of carbon nanotubes in composite coating increased crystallization, presumably due to the increase in nucleation sites affecting the growth direction of hydroxyapatite crystals. The optimum condition having high crystallinity (71.2%) along with an uniform structure was the pulse deposited hydroxyapatite coating containing 1 wt.% CNTs. The elastic modulus and hardness of this sample increased by approximately 42% and 130% compared to the pure HA coating, respectively. Furthermore, the fracture toughness of pulse deposited HA-1 wt % CNTs on AZ31 alloy reaches 1.96 +/- 0.72MPa/m(0.5) which is in the range of compact bone.