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 mu m were formed. The green deposits revealed a crystalline nature for compositions of x < 0.3, and an amorphous nature for x greater than or equal to 0.3, independent of the substrate material. Voltage-electrolyte composition dependencies exhibited an ubiquitous minimum at x approximate to 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.