Electrochemical Al2O3–Cr2O3 alloy coatings on non-oxide ceramic substrates

Aqueous solutions of xAl(NO₃)₃ + (1−x)Cr(NO₃)₃ were used for electrodeposition of ceramic Al₂O₃–Cr₂O₃ alloy coatings on TiC, TiB₂ and SiC substrates. Cell voltage and deposit weight were studied as function of deposition duration, current density and electrolyte composition. It was shown that the electrochemical parameters permit simple control of the deposition process. Optimal current densities and deposition durations were determined to obtain maximal deposit weights for different solutions and substrates. Deposits with thicknesses up to 10 μm were formed. The green deposits revealed a crystalline nature for compositions of x < 0.3, and an amorphous nature for x ≥ 0.3, independent of the substrate material. Voltage–electrolyte composition dependencies exhibited an ubiquitous minimum at x ≈ 0.3 to 0.4 independent of substrate type and deposition duration. These minima were attributed to the change in the electrical resistance of the deposit with composition and degree of crystallinity. This revised version was published online in November 2006 with corrections to the Cover Date.