HVOF- and HVAF-sprayed Cr3C2-NiCr coatings deposited from feedstock powders of spherical morphology: Microstructure formation and high-stress abrasive wear resistance up to 800 °C

Chromium carbide based coatings are commonly applied to protect surfaces against wear at high temperatures. This work discusses the influence of spray torch and feedstock powder selection on the microstructure and high-stress abrasion resistance of thermally sprayed Cr3C2-NiCr coatings. Four commercial feedstock powders with spherical morphology were deposited by different high-velocity spray processes, namely third generation gas- and liquid fuelled HVOF-torches and by the latest generation HVAF-torch. The microstructures of the coatings were studied in the as-sprayed state and after various heat treatments. The high-stress abrasion resistance of as-sprayed and heat treated coatings was tested at room temperature and at 800 °C. The study reveals that the selection of the spray torch mainly affects the room temperature abrasion resistance of the as-sprayed coatings, which is due to differences in the embrittlement of the binder phase generated by carbide dissolution. At elevated temperatures, precipitation and growth of secondary carbides yields a fast equalization of the various coatings microstructures and wear properties.