Microstructural characterization of pulsed laser–deposited hydroxyapatite thin films on Ti-6Al-4V

Hydroxyapatite (HA), Ca₁₀(PO₄)₆(OH)₂, the main mineral component of natural bone (∼ 70%), shows the most desirable bone response among the bioactive materials. In the present study, HA coatings of approximately 2–3 µm thickness were deposited on Ti–6Al–4V substrate by KrF excimer laser (λ=248 nm, pulse repetition rate = 10Hz, pulse duration = 20 ns, Laser fluence = 3 J cm⁻²) ablation of HA targets. The deposition process was carried at room temperature under different chamber pressures (10⁻¹–10⁻⁴ Torr of oxygen). The morphology and structure of the deposited layers were studied by scanning electron microscopy and X–ray diffraction analysis. Mechanical and adhesive properties of the coatings were evaluated through the Nanoindentation and scratch test, respectively. The XRD analysis revealed that as-deposited HA film is amorphous. However, for biomedical applications HA coatings should be crystalline, because amorphous HA films easily dissolve in body fluids. The initially amorphous pulsed laser deposited thin films were annealed at 300 °C for 4 h in ambient air in order to restore the crystalline structure. This study reveals that the pulsed-laser deposition followed by post deposition annealing is a promising technique to produce ideal crystalline adherent HA thin films.