Influence of the component interactions during APS of microstructurally tailored ternary oxide feedstock powders

The electrical coating properties of the Al2O3-Cr2O3-TiO2 system range from highly insulating to semiconductive, rendering them crucial for energy transition and electromobility applications. Reliable properties are expected from binary or ternary compounds and solid solutions, which require homogeneous, high-quality feedstock powders. The reactivity of the individual oxides influences the formation of these compounds. This study examines the reactivity of three agglomerated and sintered spray powders with a composition of 81.0% Al2O3, 12.5% Cr2O3, and 6.5% TiO2 (wt.-%).The powders differ from the initial oxide grain size (fine and coarse) and their phase composition adjusted by the sintering temperature: an initially fine structured (Al,Cr)2O3 / TiO2, an initially fine structure reacted (Al,Cr)2O3 / Al2TiO5 and a coarse-structured reacted (Al,Cr)2O3 / Al2TiO5. The occurrence of needle-like TiO2 structures was observed in the initially fine structured (Al,Cr)2O3 / TiO2 powder only The influence of spraying parameters on the reactivity of various ternary oxide spray powders was investigated. To determine the reaction location (during flight or upon substrate impact), powders were collected in a trap after passing through the plasma. Chemical and microstructural properties of the feedstock and sprayed powders, along with the coatings, were analyzed, including porosity measurements and phase analysis via XRD.