The role of nozzle diameter on the microstructure and abrasion wear resistance of plasma sprayed Al2O3/TiO2 composite coatings

Al2O3-50 Wt% TiO2 composite coatings were sprayed on a mild steel substrate by using Bay State Plasma spraying and SG-series plasma systems. Oxygen was used as a carrier gas for the feedstock powder during spraying with a Bay State Plasma gun to reduce the extent of reduction of alumina and titania (extraction of oxygen) in the high plasma jet temperature and provide higher heating energy to the particles in the plasma jet. The powder was injected internally into the plasma jet. The influence of nozzle diameter on the coating properties was studied. The interior diameter of the Bay State plasma gun (PG-series) nozzle (anode) was ϕϕ 7.5 mm and it was increased to 8 mm by a mechanical drilling process. Al2O3/TiO2 composite coatings were deposited with the two different nozzle diameters. The microstructure and mechanical properties of Al2O3/TiO2 composite coatings were evaluated. The results showed that the nozzle diameter greatly affected the microstructure and mechanical properties of the composite coatings. Sprayed coatings with a smaller nozzle showed high hardness, low porosity and high abrasion resistance. Moreover, the Al2O3/TiO2 composite coatings sprayed with the Bay State Plasma system showed better mechanical properties than Al2O3/TiO2 coatings sprayed by a SG-series gun.