Laser remelting of plasma-sprayed conventional and nanostructured Al2O3-13 wt.%TiO2 coatings on titanium alloy

Research highlights: → Both of the laser-remelted conventional and nanostructured coatings possess a strong metallurgical bonding to the substrates without interface porosity. More compact and homogenous structure is observed in the LRmC, with the elimination of pre-existing defects and lamellae structure of the as-sprayed coatings. → The conventional LRmC exhibit randomly distributed strip-like microstructure, while the nanostructured LRmC possess actinomorphic microstructure. → The microhardness value of both of the as-sprayed microstructured Metco 130 and nanostructured Al2O3-13 wt.%TiO2 coatings is significantly increased. - Abstract: Plasma-sprayed microstructured and nanostructured Al2O3-13 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-Al2O3 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 HV0.3, while the microhardness values of the corresponding remelted coatings are enhanced to 1000-1350 HV0.3 and 1100-1800 HV0.3, respectively. With the decrease of laser scanning velocity, the microhardness is increased.