Abstract
This paper aims at surface characterization, chemical composition, and mechanical properties of Hydroxyapatite/ZnO (HA/ZnO) nanocomposite coatings on NiTi biomedical alloy. Morphological observations by FESEM and AFM techniques showed that ZnO NPs were responsible for a uniform, porous HA matrix. XRD analysis proved the pure HA phase synthesis in the presence of ZnO NPs; without them, there were other secondary CaP phases. XPS chemical state investigations firmly confirmed the presence of ZnO NPs by showing peaks at 531.05 eV (O ─ Zn bond) and 1021.82 eV (Zn ─ O bond). Nano-hardness test highlighted a significant enhancement in hardness of composite coating (0.37 GPa) compared to pure HA coating (0.19 GPa). The notable point was that HA/ZnO nanocomposite exhibited more plasticity than HA simple coating. This is beneficial as it provides a comfortable spot for cellular activities. Last but not least, the nano-scratch analysis revealed a great effect of ZnO inclusion on reducing friction coefficient by around 40%. The critical load was also much higher for HA/ZnO composite coating (91.4 mN) than HA coating (58.5 mN). Owing to higher plasticity and lower friction coefficient, HA/ZnO composite managed to ease the movement of the indenter tip on its surface, thereby suffering less shear stress.
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