A good adhesion of plasma sprayed hydroxyapatite (HA) coating on Ti-based alloy is crucial for ensuring highly-reliable non cemented implants in the biomedical industry. In the present work, the laser shock adhesion test, namely LASAT, has been applied to investigate the interface strength of plasma sprayed HA coatings. This contact less method allowed a rapid assessment of the HA coating adhesion on simple coated plates. Varying the laser energy to impact the substrate and to generate the interface decohesion, a LASAT adhesion threshold can be determined for the highest laser fluence (J/m²) for which no debonding of the coating occurred. This qualitative and discerning LASAT procedure has been carried out on HA coatings to investigate the role of various interfaces on the adhesive property of the HA/Ti bond. According to the LASAT analysis, a surface roughness prepared with medium or coarse grit-blasting did not influence drastically the adhesion threshold while smooth pre-oxidized specimens LASAT threshold were near to those obtained with a Ti bond-coat. These thresholds also corresponded with the highest adhesion measured in this study. In addition, pre-heating treatment of substrates just prior to spraying up to 270°C did not exhibit a significant difference with grit-blasted HA/Ti interface. Further investigations (SEM, XRD) was also achieved to investigate the interface characteristics before and after the laser treatment. Sample cross-sections of laser shocked specimens were examined in detail, right at the impact location and within the debonding area to assess the fracture feature. This complementary materials analysis permitted to establish the relevance of the LASAT test as a fast and easy-to-use method devoted to the design or the control of highly adhesive HA coatings. Preliminary experiments to apply the LASAT method in liquid environment is described. Further work is on progress to implement an in situ adhesion testing of HA coating in simulated body fluid.

The adhesion strength of a ceramic coating deposited through direct spraying on a roughened substrate is a key issue in the manufacture of high-quality coatings on industrial components. The purpose of this work was to develop a rapid and discerning procedure for establishing adhesion level of a ceramic coating on a metallic substrate. The Laser Shock Adhesion Test, namely LASAT, was successfully applied to ceramic coatings with irradiation impact on the metallic side. Suitable parameters were found to determine the LASAT adhesion threshold using a standard Nd:YAG laser source. With a laser-irradiated area of several millimetres in diameter, it allowed assessment of the coating threshold on several areas of a coated plate sample. A control procedure for a qualitative assessment of coating adhesion was developed. This testing procedure could be easily used in industry, with possible location of the LASAT unit near to the spraying booth, for a direct production control on coated sample to improve the tracability of manufactured parts. Additional work was carried out to investigate a quantitative approach of the LASAT test to ceramic coating. The purpose was to simulate the shock wave propagation with the RADIOSS® code (a 3D software originally developed for car crash simulation). This code was implemented to calculate the velocity of the material and corresponding pressure throughout the substrate and the coating during the shock wave release (less than 2 ms). Experimental VISAR profiles ('Velocity Interferometer System for Any Reflector') were monitored in the straight direction of the laser-irradiated area on the rear side. These experimental signals (velocity measures) of the ceramic coating could be fitted and compared with a fairly good agreement with simulated profiles obtained by RADIOSS®. This modelling work was the first step towards a more comprehensive coating adhesion strength calculation in the future.