Microstructural Characteristics Of Different Cr3C2 Coating Compositions Sprayed with HVAF Process

High coating quality and correct material selection are prerequisite for the high performance and long lifetime of thermally sprayed coatings operating under harsh environments. Coating performance is strongly linked to selected material and spray process. Chromium carbide (Cr3C2) containing powders with ifferent chemical compositions were sprayed with novel high velocity air-fuel (HVAF) and high velocity oxygen-fuel (HVOF) processes to produce dense coatings with promising structures for demanding wear applications. Thorough structural study was carried out to evaluate the powders and sprayed coatings by using scanning electron microscope (SEM) and X-ray diffraction (XRD). The HVOF sprayed coating microstructures showed signs of carbide melting due to excessive heating of the particles. Melting was confirmed by XRD analysis, which showed secondary phase formation in the case of HVOF sprayed Cr3C2-25NiCr. HVAF sprayed coatings, on the other hand, showed similar structure as the feedstock powders. Corrosion products were observed on the surface of HVOF sprayed coatings after open cell potential measurements, which was not the case with HVAF sprayed coatings. This showed the achieved increase in coating density when HVAF spraying was used. Dense structure also increased the microhardness of the HVAF sprayed coatings compared to the HVOF counterparts.