Parameter study on the electrical resistivity of plasma sprayed TiOx/Cr2O3 coatings

Abstract

Thermally sprayed coatings based on TiOx/Cr2O3 gain increased attention for the application as resistive heating elements. The higher resistivity of ceramic compared to metallic coatings improves the geometric flexibility of the coating as no long or complex conductor paths are required to achieve sufficient resistances. The main objective of this work is to understand the influence of the process parameters on plasma sprayed TiOx/Cr2O3 coatings. Therefore, a design of experiment method is conducted to investigate the effects on the coatings’ resistivity. Initially, the feedstock of TiOx with a weight proportion of 20 % Cr2O3 is characterized. A three cathode-plasma spray gun with an Ar/H2 plasma gas mixture is used to apply the coatings. The current, the amount of H2 in the plasma gas mixture as well as the stand-off distance of the spray gun are varied according to a circumscribed central composite (CCC) design. These three factors are found to be significant in terms of influencing the coatings’ resistivity and a corresponding regression model is established. Furthermore, a significant phase change of the powder due to the spraying process is detected by means of XRD.