Microstructures and property profiles of atmospheric plasma sprayed (Al,Cr,Ti)2O3 solid solution coatings

Ternary compositions of the Al2O3-Cr2O3-TiO2 system are expected to improve the coating properties of the binary compositions, such as Al2O3-Cr2O3. Previous studies have shown that mechanical blends of all three components are not suitable for the formation of solid solutions. Thus, experimental ternary agglomerated and sintered feedstock powders were prepared in this study, which had different Al2O3/Cr2O3 ratios but a similar content of TiO2 (about 8.5 mol%). Atmospheric plasma spraying (APS) was used to prepare coatings from these powders, as well as from commercial powders of the Al2O3-Cr2O3 system. In the experimental feedstock powders, an (Al,Cr)2O3 solid solution was formed, while significant amounts of TiO2 were found to exist separately. During spraying a ternary (Al,Cr,Ti)2O3 solid solution was formed. The deposition efficiency is positively influenced by the use of agglomeration and sintering for feedstock powder preparation and Al2O3-rich solid solutions connected with some porosity in the powder. The coatings were characterized by their microstructure, phase composition, hardness, abrasion and sliding wear resistance, corrosion against H2SO4 and specific DC resistivity. The coating properties depend on the Al/Cr-ratio. All ternary solid solution coatings show a high corrosion resistance. The addition of TiO2 creates the possibility to tailor the electrical resistance.