The adhesion of plasma sprayed hydroxyapatite (HA) coating on Ti-based alloy is crucial for ensuring highly-reliable implants for 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 some interface characteristics on the adhesive property of the HA/Ti-6Al-4V bond. Therefore, to vary the roughness of the substrate, different grit blasting conditions were operated and a Ti bond-coat was also prepared prior to HA. Moreover, to vary the thermal conditions during the coating build-up, various controlled pre-heating temperatures up to 250°C were applied to grit-blasted substrates. Further modification of the interface was achieved operating a pre-oxidizing treatment of the substrate in a furnace (500°C, 700°C) to allow the formation of a thin and rough oxide layer.

According to the LASAT analysis, the roughness does not influence drastically the adhesion threshold while the pre-oxidized specimens were with the highest interface strength similar to those obtains with the Ti bond-coat. Moreover, the pre-heating treatment did not exhibit a significant influence on the adhesion threshold. Further analysis (SEM, XRD,…) were also achieved to discuss the interface strengthening. 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 material analysis permitted to establish the relevance of the rapid LASAT method applied to the design of highly adhesive HA coatings. Further works are in progress to develop the in-vitro LASATesting of HA coatings in simulated body fluids (SBF).