Hydroxyapatite (HA) coatings with strong (002) preferred orientation were successfully prepared on Ti-6Al-4V substrates with conventional atmospheric plasma spraying (APS). The intensity changes of (002) preferred orientation along the coating depth were investigated and the mechanical properties of these coatings were analyzed. Results indicated that the intensity of (002) preferred orientation at a distance of longer than ~90 mm from the interface showed a high value, where uniformly distributed columnar grains in a direction perpendicular to the coating surface were observed. The results obtained from experiments on the mechanical properties revealed that the (002) oriented coatings prepared by conventional APS technique exhibited excellent mechanical properties. Meanwhile, this study provided a simple and rapid method for the preparation of HA coatings with (002) preferred orientation.

In this study, hydroxyapatite (HA) coatings were deposited on Ti-6Al-4V by micro-plasma spraying (MPS). The influence of the process parameters on the microstructure of HA coatings was investigated. The splat morphology and spreading behavior were examined to understand the influence of process parameters on the coating. The texture strength of HA coatings was characterized by X-ray diffraction (XRD). The texture coefficients were all applied to characterize the variation in texture. The morphology of splats and coatings were characterized by scanning electron microscopy (SEM). XRD pattern shows that the texture intensity of the c-axis of HA was greatly influenced by spraying distance and spraying current. SEM reveals the different texture strength of HA coatings with different ratios of columnar grains. The strongest c-axis texture was found in the coating by 60 mm spraying distance with a spraying current of 40 A. In the cross-section SEM images of the coating with the strongest c-axis texture, uniform distribution columnar grains were observed in the upper part (~100 μm). The investigation of splats indicates that columnar grain growth occurs after fully melted particles impact the heated substrate. By controlling the melting state prior to in-flight particle impacts, columnar grain growth can be achieved during slow solidification of the disk shape splat during MPS.