Degradation and Crystallinity of PLD HA Films on Ternary Ti-Alloy

Failure of hydroxyapatite films on titanium dental implants can occur at the HA/bone interface, between lamellae in the coatings, and at the HA/alloy interface. To obtain improved coatings, pulsed laser deposition (PLD) has been used, along with a new ternary titanium alloy. PLD is a physical vapor deposition process that uses a pulsed laser such as KrF to ablate the target material. Objective: To investigate the crystallinity and degradation of HA coatings deposited by PLD on the new titanium alloy.

Methods: HA (tooth ash) films were grown on titanium alloy (Ti-Ta-Nb) substrates at 350^oC, 400^oC, 500^oC, and 600^oC for 60 min under different O₂ pressures ranging from 5 X 10^-3 to 5 X 10^-1 torr. The growth chamber was pumped to a base pressure of 5 X 10^-6 torr prior to backfilling with the O₂ ambient. A pulsed KrF excimer laser (248 nm, 30 ns duration) was operated with a repetition rate of 5 Hz. The beam energy was typically set at 130 mJ/pulse. Degradation of the HA film surface was investigated using electrochemical methods, and its crystallinity was determined using scanning electron microscopy, energy dispersive x-ray spectroscopy, and x-ray diffraction (XRD).

Results: HA films deposited at 350^oC showed (210), (211), (300), and (202) peaks from XRD analysis. HA films deposited at 600^oC showed two additional peaks from atomic planes: (210), (211), (112), (300), (202) and (310) peaks were observed. From electrochemical tests, the polarization resistance of HA films deposited on the ternary Ti alloy at 600^oC and 350^oC were 4.0 X 10⁶ Ωcm² and 5.5 X 10⁴ Ωcm², respectively.

Conclusions: At 600^oC deposition temperature the HA film on the ternary titanium alloy had more XRD peaks, possibly suggesting superior crystallinity. Polarization resistance measurements showed very small film degradation at this deposition temperature.