Керметные плазменные покрытия на основе карбидов TiC – Cr3C2 – WC

Abstract

Five cermet coatings based on carbides 45TiC – 10Cr3C2 – 5WC with different contents of additional carbon were formed by plasma spraying with local protection: 0; 1.4; 2 and 2.8 %. 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 additionally introduced Mo. Powders for spraying were obtained by crushing cakes. In the particles of the obtained powders, carbides are distributed relatively uniformly; in coatings, this is noticeable to a lesser extent. After liquid-phase sintering, WC and Mo are not fixed in cermets; part of the Cr3C2 carbide passes to another structural state. The initial carbides in the cake and coating partially dissolve and, upon solidification and together with matrix elements and additional carbon, form an annular zone around the initial TiC carbide, decreasing its lattice period, X-ray fixes TiMoC2 carbide, the content of which is higher than the content of TiC carbide in the initial mixture. The content of the initial carbides in the coatings, measured by optical microscopy, decreases from 71 vol.% In the powder to 48 vol.% At the minimum plasma power and up to 36 vol.% At the maximum power. The average total TiMoC2 content of carbides in coatings according to x-ray data for four cermets is 76 %, higher than their content in spraying powders, 72 %, due to higher spray hardening rates. The average microhardness for all coatings is 22.01 GPa with an indenter load of 20 gf, which is lower than the average microhardness for all powders, 23.51 GPa. With an indenter load of 200 gf, the average microhardness for all coatings of 15.88 GPa corresponds to the average microhardness for all powders, 15.17 GPa.