Microstructure and Properties of Atmospheric Plasma Sprayed (Al,Cr)₂O₃-TiO₂ Coatings from Blends

Coatings prepared from chromia-rich (Al,Cr)₂O₃ solid solution (ss) feedstock powders are intended to improve the properties of Cr₂O₃ coatings, but are rarely studied so far. In this work, the processability of a commercial (Al,Cr)₂O₃ solid solution (ss) powder containing 78 wt.% Cr₂O₃ by atmospheric plasma spraying (APS), the corresponding coating microstructures and properties were investigated. Possible further improvements were expected by blending with 2, 23 and 54 wt.% TiO_x powder. For comparison, plain Cr₂O₃ and TiO_x coatings were studied as well. The microstructures were analyzed using SEM, EDS and XRD measurements. Hardness (HV0.3) was measured, as well as the dry unidirectional sliding wear resistance and the abrasion wear resistance (ASTM G65). Moreover, the corrosion and electrical insulating properties were measured. The (Al,Cr)₂O₃ ss showed only a small change of the composition, and the formation of γ-Al₂O₃, as found for alumina-rich (Al,Cr)₂O₃ ss powders, was avoided. Compared to the plain chromia coating, some improvements of the processability and coating properties for the ss (Al,Cr)₂O₃ coating were found. The most balanced coating performance was achieved by blending the ss (Al,Cr)₂O₃ with 2 wt.% TiO_x, as this coating showed both a high sliding and abrasion wear resistance, in combination with a high corrosion resistance.