Impact of TiO2 additives on the microstructure and properties of plasma sprayed (Al,Cr)2O3 coatings

By using a commercial chromia-rich (Al,Cr)2O3 solid solution feedstock powder microstructures and properties of a plain chromia coatings can be enhanced. As shown in this study, further improvements can be obtained from blended TiO2 additions. In this study the influence of TiO2 additions on the microstructure of the plasma sprayed (Al,Cr)2O3 coatings as well as the resulting coating properties are investigated. The microstructure is analyzed using SEM, EDS and XRD measurements. The oscillating sliding wear was measured with a ball-on-disc test at room temperatures as well as at high temperatures up to 900°C. It has been shown that TiO2 additions reduce porosity and increase deposition efficiency. Due to the enhanced microstructure, the wear resistance is also improved by the TiO2 additions. The coatings reveal an increased wear resistance at high temperatures. Investigations indicate that the high temperatures cause a change in the microstructure. This manifests itself in a reduction of the porosity and the occurrence of reactions between the TiO2 and (Al,Cr)2O3 splats. The electrical properties are significantly influenced by the TiO2 additions. Even small additions of TiO2 lead to a rapid reduction of the specific DC resistivity.