Microstructure and Properties of Atmospheric Plasma Sprayed (Al,Cr)O-TiO Coatings from Blends.

Coatings prepared from chromia-rich (Al,Cr)O solid solution (ss) feedstock powders are intended to improve the properties of CrO coatings, but are rarely studied so far. In this work, the processability of a commercial (Al,Cr)O solid solution (ss) powder containing 78 wt.% CrO 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 powder. For comparison, plain CrO and TiO 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)O ss showed only a small change of the composition, and the formation of -AlO, as found for alumina-rich (Al,Cr)O ss powders, was avoided. Compared to the plain chromia coating, some improvements of the processability and coating properties for the ss (Al,Cr)O coating were found. The most balanced coating performance was achieved by blending the ss (Al,Cr)O with 2 wt.% TiO, as this coating showed both a high sliding and abrasion wear resistance, in combination with a high corrosion resistance.