Laser remelting of plasma-sprayed conventional and nanostructured Al ₂O₃-13 wt.%TiO₂ coatings on titanium alloy

Plasma-sprayed microstructured and nanostructured Al₂O ₃-13 wt.%TiO₂ coatings were successfully deposited on Ti-6Al-4V titanium alloy substrates with commercial Metco 130 powder and as-prepared nanostructured feedstock, respectively. The as-sprayed coatings were remelted by a CO₂ laser to further enhance their compactness and bonding strength. The effects of laser remelting on the microstructure, phase constituents and mechanical properties of the ceramic coatings were investigated by scanning electron microscope, X-ray diffractometer and Vickers microhardness tester. The results indicate that the laser-remelted coatings exhibit more compact and homogenous structure as well as strong metallurgical bonding to the substrates. The dominating metastable γ-Al₂O₃ phase in the as-sprayed coatings transforms to stable α-Al₂O ₃ during laser remelting. The microhardness value of the as-sprayed Metco 130 and nanostructured Al₂O₃-13 wt.%TiO₂ coatings is in the range of 700-1000 HV_0.3, while the microhardness values of the corresponding remelted coatings are enhanced to 1000-1350 HV _0.3 and 1100-1800 HV_0.3, respectively. With the decrease of laser scanning velocity, the microhardness is increased.