Bonding state and scratch failure behavior of laser remelted Al₂O₃-TiO₂ coatings

Conventional Metco 130 and nanostructured Al₂O₃-13%TiO₂ feedstock powders were plasma sprayed to form as-sprayed coatings on Ti-6Al-4V substrates. A CO₂ was employed to remelt the as-sprayed coatings to get denser hard coatings. The microstructures of the coatings before and after laser remelting were investigated by optical microscope (OM) and scanning electron microscope (SEM). The bonding state of the coatings was evaluated by a Vickers Microindentor. The scratch tests of the coatings were performed on a coating scratch tester. The results of destructive indentation tests near the interfaces show that cracks are found at the interfaces between both as-sprayed coatings and their substrates, while the interfaces between the laser-remelted coatings and their substrates could maintain intact. The results of scratch tests show that the degree of damage of the laser-remelted coatings is significantly lower than that of the as-sprayed coatings. The scratch damage mode of the as-sprayed coatings is severe brittle fracture and delamination damage, while that of the laser-remelted coatings is mainly local brittle fracture.