Research On Fabrication And Properties Of Plasam Sprayed Nanostructural Al₂O₃/TiO₂ Coatings

In this paper, plasma-sprayed nanostructured Al2O3/TiO2 coatings were fabricated by using reconstituted spray-dried powders. The content of the binders of PVA, the sintering temperature and the plasma spray powers all have great impact on the fabrication of the coating. Through series of experiments, the preparation routes of the nanostructued powders and the coatings were optimized by comparative investigations. And the nano-coatings were also made successfully. The conclusions are drown as following:1. The preparation route of nanometer Al2O3/TiO2 powders was determined, prepared using PVA as binder:Preparation of slurry →long time blending→adding binder(PVA) →spray-drying→ sintering of powders→filtering→plasma spraying2. The results show that: the optimized parameters of spray-dried powders include solids content 25wt%, binder content 2.5-3.0wt%, spray-drying temperature 450-550℃, sintering temperature 1100-1200℃, contract air pressure 0.4±0.05MPa.3. The formation of nanostructured Al2O3/TiO2 coating is: The heating difference of the powders in-outer layer during spraying results in that the inner nanoparticles are only partially melted without growing into larger grain, a lot of nanoparticle agglomerates with sintered shape were detected in the coating.4. The properties of the coating depend greatly on plasma spray powers. Through comparative experiments, the best properties can be produced with spray power of 35kw, lower or higher power cannot produce nice properties.5. Compared to the conventional coating, the improvement of the properties of the nanostructured coating is due to the bimodal structure existed in the coating, which has great contribution to the toughness of the coating.6. Comparisons of microstructure, microhardeness, toughness and wear abrasive resistance were also made between nanostructured and conventional coating. And the nanostructured coatings exhibit superior microhardness, toughness and wear abrasive resistance than conventional coating due to the bimodal structure.