Bond strength determination of hydroxyapatite coatings on Ti-6Al-4V substrates using the LAser Shock Adhesion Test (LASAT)

An adhesion test procedure applied to plasma- sprayed hydroxyapatite (HA) coatings to measure the ''LASAT threshold'' (LAser Shock Adhesion test) is described. The good repeatability and minimal discrepancy of the laser-driven ad- hesion test data were ascertained for conventional plasma sprayed HA coatings. As a further demonstration, the proce- dure was applied to HA coatings with diverse characteristics on the ceramic/metal interface. Different preheating and grit blasting conditions and the presence of a thick plasma-sprayed Ti sublayer or a thin TiO2 layer prepared by oxidation were investigated through LASAT. It was assessed that a rough sur- face can significantly improve the coating's bond strength. However, it was also demonstrated that a thin TiO2 layer on a smooth Ti-6Al-4V substrate can have a major influence on ad- hesion as well. Preheating up to 270� C just prior to the first HA spraying pass had no effect on the adhesion strength. Further development of the procedure was done to achieve an in situ LASAT with in vitro conditions applied on HA coatings. To that end, different crystalline HA contents were soaked in simulated body fluid (SBF). Beyond the demonstration of the capability of this laser-driven adhesion test devoted to HA coatings in dry or liquid environment, the present study provided empirical in- formation on pertinent processing characteristics that could strengthen or weaken the HA/Ti-6Al-4V bond. V C 2010 Wiley Peri-