Mechanical and Surface Characterization of Titanium–29Niobium–13Tantalum–4.6Zirconium Alloy Coated with Hydroxyapatite using High-Velocity Oxy-Fuel Spraying for Biomaterial Applications

The -titanium alloy Ti-29Nb-13Ta-4.6Zr (TNTZ) is a highly promising orthopedic implant material due to its exceptional biocompatibility, corrosion resistance, and favorable mechanical properties; however, its bioinert nature restricts direct osseointegration. Although hydroxyapatite (HA) coatings can significantly enhance surface bioactivity, optimizing deposition parameters to achieve desirable surface topography and mechanical stability remains a critical challenge. This study investigates the influence of high-velocity oxygen fuel (HVOF) spray distance on the physical and mechanical properties of HA coatings deposited on TNTZ substrates. The coatings were synthesized at varying spray distances (20, 25, and 30 cm) and characterized using surface profilometry and nanoindentation. The results reveal a distinct trade-off between the surface roughness and mechanical properties governed by the spray distance. Specifically, a 25 cm stand-off distance yielded the highest surface roughness (Ra = 5.48 m), which is highly conducive to initial cellular attachment. Conversely, the maximum coating hardness was achieved at a distance of 20 cm, attributed to elevated particle impact energy, whereas Young’s modulus peaked at 187.49 GPa at a distance of 30 cm. A comprehensive analysis identified 25 cm as the optimal deposition distance, providing the most favorable balance between coating morphology and mechanical response derived from nanoindentation. Overall, these findings indicate that the HVOF spray distance is a critical processing parameter influencing the morphological, surface, and nanomechanical characteristics of HA-coated TNTZ coatings, thereby providing valuable guidance for coating optimization.

Coating; High-Velocity oxygen fuel; Hydroxyapatite; Osseointegration; Titanium

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