Characterization, wear behavior and biocompatibility of HA/Ti composite and functionally graded coatings deposited on Ti-6Al-4V substrate by mechanical coating technique

Characterization, wear behavior, and biocompatibility of hydroxyapatite (HA)/Ti composite coating and functionally graded coatings (FGCs) deposited on a Ti-6Al-4V substrate by a mechanical coating technique were compared. The composite coating was produced using the initial powder mixture of 50 wt.% Ti + 50 wt.% HA, while the FGC was deposited by two separate layers containing 75 wt.% Ti + 25 wt.% HA and 25 wt.% Ti + 75 wt.% HA, respectively. The XRD results exhibited that no phase changed during the deposition process. Moreover, due to the presence of Ti particles in the primary powder mixtures, a continuous interface with a superior bond was formed between the coating and the substrate, especially in the samples coated by the FGCs. The wear test results of the non-graded composite coating showed a coefficient of friction (COF) of about 0.37 with an abrupt change at the interface, while the COF of the FGCs increased from 0.32 to 0.5 with a gentle change at the interface. The SEM images of the worn surfaces indicated the dominance of the abrasive wear mechanism. The biocompatibility evaluations revealed better cell attachment and proliferation of the FGC-coated samples.