V. Guipont, F. Borit, ECOLE DES MINES DE PARIS / C2P, Evry, France; M. JEANDIN, Mines ParisTech, UMR CNRS 7633, EVRY, France; S. Barradas, Ecole des Mines de Paris (ENSMP), Evry Cedex, France; R. Vilar, INSTITUTO SUPERIOR TECNICO, Lisbon, Portugal; T. Tavsanoglu, A. Addemir, ISTANBUL TECHNICAL UNIVERSITY, Istanbul, Turkey; S. Bansard, K. A. Khor, NANYANG TECHNOLOGICAL UNIVERSITY, Singapore, Singapore; Y. Ichikawa, TOHOKU UNIVERSITY, Sendai, Japan; K. Ogawa, Tohoku University, Sendai, Japan; M. Nivart, L. Berthe, LALP (Laboratoire pour l'Application des Lasers de Puissance), Arcueil, France
The coating-substrate adhesion strength is a key factor which does characterize the quality of hydroxyapatite (HAP) coatings such as those for biomedical applications. In the present work, adhesion was studied using the recently-developed advanced Laser Shock Adhesion Test, namely LASAT. Before spraying, spraying conditions were investigated as a function of the type of powder, in particular. Three types of HAP powders, i.e. a commercial powder and two lab-scale-produced powders obtained by mechanical grinding and by spray-drying respectively, were studied. The study involved optical and scanning electron microscopy and X-ray diffraction analysis in addition to direct observation of the sprayed particles in the jet using a "SprayWatch" system. LASATests showed the influence of substrate surface preparation especially. Various grit blasting conditions and the influence of a thin PVD bond-coat prior to HAP spraying. First, adhesion was all the higher because substrate roughness was great. Second, PVD pre-metallization with Au-Pd was shown to improve adhesion dramatically. All the results were discussed in the light of the microstructural study of coating-substrate interface cross-sections before and after LASATesting. These led to the conclusion that further improvements in current HAP coating can still be done and that LASAT can be claimed to be a powerful tool to help in this.
Summary: The coating-substrate adhesion strength is a key factor which does characterize the quality of hydroxyapatite (HAP) coatings such as those for biomedical applications. In the present work, adhesion was studied using the recently-developed advanced Laser Shock Adhesion Test, namely LASAT. Before spraying, spraying conditions were investigated as a function of the type of powder, in particular. Three types of HAP powders, i.e. a commercial powder and two lab-scale-produced powders obtained by mechanical grinding and by spray-drying respectively, were studied. The study involved optical and scanning electron microscopy and X-ray diffraction analysis in addition to direct observation of the sprayed particles in the jet using a "SprayWatch" system. LASATests showed the influence of substrate surface preparation especially. Various grit blasting conditions and the influence of a thin PVD bond-coat prior to HAP spraying. First, adhesion was all the higher because substrate roughness was great. Second, PVD pre-metallization with Au-Pd was shown to improve adhesion dramatically. All the results were discussed in the light of the microstructural study of coating-substrate interface cross-sections before and after LASATesting. These led to the conclusion that further improvements in current HAP coating can still be done and that LASAT can be claimed to be a powerful tool to help in this.
