Laser Shock Adhesion Test (LASAT) Applied to Bioceramic Coatings Involving Two-Dimensional Shock Wave Propagation
Résumé
Metallic implants for orthopedic or dental are often coated with a plasma-sprayed hydroxyapatite (HA) coating. Such bioactive ceramic coating promotes new bone ingrowth and results in a strong bonding of the prosthesis. The adhesion level of as-sprayed HA coating is usually controlled on coated disks applying the ASTM C633 pull-out test to glued specimens. In this context of quality control, there is a need for alternative adhesion tests that could be more reliable and reproducible, especially in case of thin HA coatings. The LASAT (LAser Shock Adhesion Test) has been developed with qualitative or quantitative procedures for various ceramic coatings. Due to the specific optical and radiative properties of such ceramic coatings, these methods can be implemented rather simply using the so-called “white-spot” diagnostic to detect and/or to measure the debonded area after laser shock. In this work, the LASAT is investigated on different HA/Ti-6Al-4V coatings with various coatings and substrates thicknesses and also with different laser spot diameters. The main purpose is to vary drastically the shockwave features in order to assess their influences on the resulting interfacial debonding and their consequences on the application of LASAT. Therefore, two types of HA coatings exhibiting two different adhesion levels controlled according the ASTM C633 procedure were submitted to these LASAT experiments. Moreover, different non-destructive techniques (Interferometry, optical, IR) are also compared. Finally, the opportunity to develop a robust LASAT method in comparison to the standard test is discussed.