Post-treatment of Plasma-Sprayed Cr2O3 with Methane-Containing Gas for Conversion to Binder-Free Cr3C2

In most applications, the performance of thermally sprayed Cr3C2-NiCr cermet coatings is known to be adversely affected by the presence of the NiCr binder phase. A processing technique for the rapid synthesis of Cr3C2 on industrial-scale components could improve the functionality of these coatings by eliminating the metallic binder phase. To form a thick, continuous surface layer of adherent, binder-free Cr3C2, the reduction of plasma-sprayed Cr2O3 with methane-containing gas was investigated. Conversion of the plasma-sprayed Cr2O3 to carbide resulted in a significant increase in coating porosity, yielding a highly microporous Cr3C2 surface layer. The physical characteristics of the reduction process appear to be dependent on the coating defect structure at the reduction temperature. Phase morphology and porosity evolution throughout the reduction process were qualitatively examined using x-ray diffraction and scanning electron microscopy. The utility of the resultant Cr3C2 coating is discussed with respect to these microstructural characterizations and microindentation hardness measurements.