Electrochemical Chromium(III) Oxide Coatings on Non‐oxide Ceramic Substrates

SiC and TiB 2 were electrochemically coated with Cr 2 O 3 from a 0.1 M aqueous solution of chromium nitrate hydrate with ethanol additives. On both substrate materials poly‐crystalline Cr 2 O 3 was formed at current densities from 5 to 50 mA/cm 2 and deposition durations of 5 to 30 min. The coating weight increased with current density and with deposition time. The as‐deposited coatings contained microcracks due to drying shrinkage. Microstructural observations indicate that sintering of the Cr 2 O 3 coatings on TiB 2 at 1100°C for 1 n in a reducing atmosphere in a closed graphite crucible causes the densification of the coating via a liquid phase, which forms by oxidation of TiB 2 . Under similar conditions, the Cr 2 O 3 coatings on SiC may be sintered via an evaporation–condensation mechanism.