Analysis of the interface between a pulsed laser deposited calcium phosphate coating and a titanium alloy substrate

Calcium phosphate coatings deposited on titanium alloy are intended to add a bioactive surface to medical implants. This work presents the characterisation of the interface between Ti-6Al-4V and a crystalline calcium phosphate coating obtained by pulsed laser deposition, with a KrF excimer laser, at 575 °C and under a 45 Pa water-vapour atmosphere. The coating–substrate system was studied by secondary-ion mass spectrometry, scanning electron microscopy, X-ray diffractometry, Raman spectroscopy and X-ray photoelectron spectroscopy. The results show that the deposition process promotes the interdiffusion of substrate elements into the coating and coating elements into the substrate oxide layer. Thus, a graded layer of mixed calcium phosphate and amorphous titanium oxide is formed. For the substrate, a hydroxyapatite coating acts more as a barrier for oxygen incoming from a gas than as an oxygen source during deposition. Moreover, oxygen diffusion into the substrate occurs. Thus, the content of oxygen of this oxide layer diminishes with depth. When the oxygen concentration is low enough it is incorporated in solid solution in the titanium alloy . PACS 81.15.Fg; 68.55.-a; 87.68.+z