Laser Shock Adhesion Test (LASAT) applied to bioceramic coatings involving two-dimensional shock wave propagation

Biomedical orthopaedic implants are often coated with plasma-sprayed hydroxyapatite (HA) coatings to enhance bone anchorage. The adhesion strength on substrate of HA coating is usually measured according to standardized pull-out test with glued specimens. Nevertheless, there is a need for alternative adhesion tests that would be more reliable and suitable for thin coatings. The LASAT (LAser Shock Adhesion Test) has been applied on several porous ceramic coatings to determine their debonding threshold in GW/cm² using the ‘white-spot’ phenomenon. This threshold can also be determined in MPa with calculated stress charts. In this work, the LASAT is investigated on HA coatings varying 2D effects on laser shockwave temporal and spatial propagations. These 2D effects were induced thanks to various HA coatings (60 and 150µm) and TA6V or CoCr substrates (2, 3 and 6mm) thicknesses and also through different laser spot diameters (3, 6 and 10mm). Moreover, HA coatings exhibiting two different adhesion levels (4 and 8 MPa following the ISO 13779-4) were LASATested. Thus, different LASAT procedures are compared using non-destructive techniques (Interferometry, optical, IR) to detect the debonded area. Finally, the opportunity to develop a robust LASAT method in comparison to the standard method is discussed.