Laser surface remelting of plasma sprayed nanostructured Al_2o_3-13wt%TiO_2 coatings on titanium alloy

摘要

Plasma sprayed nanostructured coatings were successfully fabricated on a titanium alloy (Ti-6A1-4V) substrate using the as-prepared nanostructured Al_2O_3-13wt%TiO_2 feedstock. A CO_2 laser was used to remelt the plasma sprayed coatings. The effects of laser remelting on the phase constituents, microstructure and properties of the ceramic coatings were investigated. The laser remelted coatings (LRmC) possessed a much denser and more homogenous structure and excellent metallurgical bonding to the substrate. The average porosity of the LRmC was reduced to 0.9%, compared with 6.2% of the as-sprayed coatings. The net-like structure in the as-prepared feedstock remained in the coatings before and after laser remelting. The metastable γ-Al_2O_3 phase in the as-sprayed coatings transformed to stable αa-Al_2O_3 during laser remelting. The LRmC could remain nanostructure. The microhardness of the coatings was enhanced to 1000-1400 HV_(0.3) after laser remelting, which was much higher than that of the plasma sprayed coatings and 2-3 times higher that of the substrate. Significant decreases in surface roughness were also found in the LRmC.