Influence of the interface layer deposited hydroxyapatite on the adhesion of pulsed laser coatings on titanium alloy

Hydroxyapatite (HA) coatings were deposited on Ti-6Al-4V substrates by laser ablation with a KrF excimer laser. Depositions were performed at 45 Pa of water vapour and at a substrate temperature of 575 C. After 7 min of deposition, coatings were left at this temperature for different times before cooling down. The samples morphology and structure were characterised by scanning electron microscopy, X-ray diffractometry and Raman spectroscopy. The mechanical performance of the coatings was evaluated through the scratch-test technique. The coatings do not present important differences between them. However, there is an interface layer between the coating and the substrate that indeed presents an evolution with the heating time. This interface layer is constituted by two different species: titanium oxide and Ti-6Al-4V with oxygen diffused in its lattice. Its thickness increases during the first minutes of heating after deposition. An evolution of the titanium oxide phases with the time of heating has been detected by Raman spectroscopy. The samples fail at lower loads in the scratch-test as longer is the time that they remained at high temperature. The mode of failure of the samples suggests that failure occurs at the interface. (C) 2002 Elsevier Science B.V All rights reserved.