In the thermoanalytical analyses till 1500 °C, conducted on two of the experimental powders, was shown that no loss of Cr2O3 occurred under these conditions that could limit the application of these powders in thermal spraying. After process optimization, it was possible to obtain, by both APS and HVOF, homogenous and dense coatings. By means of the spraying process, significant phase transformations occurred, and some phases present in the powders (like E-Phase or TiCr2O5) where no longer present in the coating.
The eskolaite structure (Cr2O3) is the only phase present in the coatings composed of powder rich in Cr2O3. In the APS sprayed coatings, escolaite is found as a secondary phase for compositions up to 76,5% TiO2 – 23,5 % Cr2O3. As principal constituents of the coatings rich in TiO2, high temperature Magneli-Phase (n-phase) and rutile mix crystal are detected.
Regarding the electrical resistivity of the coatings, a dependence on the Cr2O3 content is observed. Figure 1 demonstrates this relationship for APS and HVOF coatings. The electrical resistivity of the HVOF coatings is, when both values can be compared, slightly higher than the one measured for the APS coatings. The already expected low electrical resistivity and its dependence on the phase composition for the coatings rich in TiO2 were confirmed. Due to their high temperature stability, electrically conductive ceramic coatings have high application potential.