Carbide-Based Cermet Plasma Coatings TiC–Cr 3 C 2 –WC

Five cermet coatings based on carbides 45TiC–10Cr 3 C 2 –5WC with different contents of additional carbon (0, 1.4, 2, and 2.8 wt %) were formed by plasma spraying with local protection. In four cermets, the matrix was based on Ni–20Cr. In one cermet, the alloy used was 38.5Co–32Ni–21Cr–8Al–0.5Y. All matrices were supplemented with Mo. Powders for spraying were obtained by crushing cakes. In the particles of the obtained powders, carbides were distributed relatively uniformly; in coatings, this was noticeable to a lesser extent. After liquid-phase sintering, WC and Mo were not fixed in cermets; part of the Cr 3 C 2 carbide transformed into another structural state. The initial carbides in the cake and coating partially dissolved and, upon solidification and together with matrix elements and additional carbon, formed an annular zone around the initial TiC carbide, decreasing its lattice period. XRD fixed TiMoC 2 carbide in annular zone, the content of which was higher than the content of TiC carbide in the initial mixture. The content of the initial carbides in the coatings, measured by optical microscopy, decreased from 71 vol % in the powder to 48 vol % at the minimum plasma power and to 36 vol % at the maximum power. The average total TiMoC 2 content of carbides in coatings according to X-ray data in four cermets was 76 wt %, higher than their content in spraying powders (72 wt %) owing to higher spray hardening rates. The average microhardness for all coatings was 22.01 GPa at an indenter load of 20 gf, which was lower than the average microhardness for all powders (23.51 GPa). At an indenter load of 200 gf; the average microhardness for all coatings of 15.88 GPa corresponded to the average microhardness for all powders (15.17 GPa).