Strength and toughness of laser-remelted Al₂O₃-TiO₂ coatings

Laser-remelted Al₂O₃-TiO₂ coatings were prepared on Ti-6Al-4V alloy substrates by plasma spraying and laser remelting. X-ray diffraction (XRD), scanning electron microscopy (SEM), micro-hardness and indentation tests were carried out to investigate the effects of laser remelting on the microstructure and properties of the coatings. The results showed that the major phase in the as-sprayed Al₂O₃-TiO₂ coatings was γ-Al₂O₃, while that in the remelted coatings was α-Al₂O₃. After laser remelting, pores, micro-cracks, lamella structure and other defects in the as-sprayed coatings could be eliminated to form compact microstructure as well as good metallurgical bonding between the coating and substrate. The hardness and crack propagation resistance of the remelted coatings were approximately 50%, which were twice higher than those of the corresponding as-sprayed coatings, respectively. The unmelted particles and nanostructure in the laser-remelted nanostructured coatings contributed to the strength and toughness.