Microstructure and bond strength of HA(+ ZrO2 + Y2O3)/Ti6Al4V composite coatings fabricated by RF magnetron sputtering

Novel HA(+ ZrO2 + Y2O3)/Ti6Al4V composite coatings have been developed successfully by radio-frequency magnetron sputtering technique (RF-MS). The surface morphology, phase composition and Ca / P ratio analysis of the HA(+ ZrO2 + Y2O3) composite coatings were investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR). Results showed that the average thickness of HA(+ ZrO2 + Y2O3) composite coatings was in the range of 3∼4 μm. The surface morphology of HA(+ ZrO2 + Y2O3) composite coating was rough and uneven with the well-distributed concaves. The average diameter of these concaves was in the range of 0.5∼2 μm, and the surface area of these concaves was about 30∼40%. The XRD and EDS analysis of the sputtered coatings indicated that the n(Ca) / n(P) ratios in the as-sputtered and post-annealing coatings were both in the range of 1.77∼1.79. The pull-out test results showed that the ultimate bond strength of sputtered HA(+ ZrO2 + Y2O3)/Ti6Al4V composite coatings was 59.6 MPa. Furthermore, the bonding strength of HA(+ ZrO2 + Y2O3)/Ti6Al4V composite coatings was enhanced with the increasing of sputtering power and the addition of YSZ. SEM interface morphology on the cross-section of HA(+ ZrO2 + Y2O3)/Ti6Al4V composite coatings showed that there wasn't any pore or crackle in the coating/substrate interface. The diffusion distribution of elements in interfacial zone indicated that there was a diffusion layer between HA film and Ti–6Al–4V substrate. The thickness of the diffusion layer for different elements was about 1.5 μm∼2.0 μm. The high bond strength of the sputtered HA(+ ZrO2 + Y2O3)/Ti6Al4V composite coatings was attributed to the formation of diffusion layer in interfacial zone, the sputter cleaning and ion bombarding processes, and the mechanical interlocking effect resulting from the rougher surface of Ti–6Al–4V substrate treated by sandblasting and etching.