Laser-induced damage in cold-sprayed composite coatings

Ag-Ni composite coatings were achieved using the cold spray process. In this work, two blends were sprayed to lead to coatings with different mechanical properties, which corresponded to either a fine or a coarse microstructure. These coatings were studied using SEM and X-ray microtomography (XMT) to determine the best coating quality through characterization of particle-to-particle bonding. The fine microstructure showed better properties than the coarse microstructure. To avoid time-consuming characterization techniques such as SEM and XMT, an innovative laser characterization test was developed. The principle of this test is based on the thermal shock-induced by a laser pulse at the surface of the coating. Thus, particle interfaces were stressed and cracking damage could occur. SEM observation of cross-sections and top views was carried out to rank the coatings as a function of the generated damage. The influence of heat treatments was also studied. To enhance the approach, thermomechanical simulations have been performed on a real meshed microstructure. The influence of layering effect in the cold spray was shown to be detrimental due to local concentrated stresses.