Laser remelting of plasma sprayed nanostructured Al₂O₃-TiO₂ coatings at different laser power

Plasma sprayed nanostructured Al₂O₃-13wt.% TiO₂ coatings were fabricated on a Ti-6Al-4V alloy using as-prepared feedstock. The as-sprayed coatings were remelted by a CO₂ laser. The coatings before and after laser remelting were characterized by using X-ray diffractometer (XRD), scanning electron microscope (SEM), energy-dispersive spectrometer (EDS) and Vickers microhardness tester. The effects of laser power on microstructure and properties of the laser remelted Al₂O₃-13wt.% TiO₂ coatings (LRmC) were investigated. The metastable γ-Al₂O₃ phase in the as-sprayed coatings was transformed to stable α-Al₂O₃ during laser remelting. The LRmC possessed much denser and more homogenous structure as well as an excellent metallurgical bonding to the substrate. Microstructural correlation was found in the coatings before and after laser remelting. The microhardness of the LRmC was enhanced to 1200-1800 HV_0.3, which was much higher than that of the as-sprayed coatings and 3-5 times that of the substrate. The microhardness values were increased with increasing laser power.