Title

Effect of oxide addition on plasma sprayed alumina-based coatings

Date of Completion

January 2007

Keywords

Engineering, Materials Science

Degree

Ph.D.

Abstract

Plasma spray feed powders of Al2O3, Al2O 3-TiO2, Al2O3-CeO2, and Al2O3-ZrO2 were prepared using a spray-dry and sintering method. Coatings of these powders were deposited onto metal substrates under a same set of plasma spraying parameters. Coating properties such as phase composition, degree of melting, splat thickness, microhardness, indentation fracture resistance, molten region "nanohardness", and abrasive wear resistance were investigated. These results indicate that compared with pure Al2O3 coating, the addition of secondary oxides, such as TiO2, CeO2, and ZrO2, enhances the degree of melting and splat deformability on impact, reduces splat thickness, increases coating microhardness and fracture resistance, and improves coating abrasive wear resistance. The correlation of secondary oxide addition and the resulting changes on coating microstructures and mechanical properties compared with pure alumina coating was theorized. Coatings from three different Al2O3/13TiO2 feed powders were also compared to in detail. It is demonstrated that the degree of mixing of the Al 2O3 and TiO2 ingredients in the feed powder has immense impact on the phase composition, microstructure, hardness, crack growth resistance, and abrasive wear performance of the coatings. A high degree of mixing of Al2O3 and TiO2 in the powder state results in more uniform microstructure, higher hardness, higher crack growth resistance, and consequently better abrasive wear resistance of the coating. ^