ELECTROCHEMICAL AL2O3-CR2O3 ALLOY COATINGS ON NONOXIDE CERAMIC SUBSTRATES

Aqueous solutions of xAl(NO3)(3) + (1-x)Cr(NO3)(3) were used for elect rodeposition of ceramic Al2O3-Cr2O3 alloy coatings on TiC, TiB2 and Si C 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 d urations were determined to obtain maximal deposit weights for differe nt solutions and substrates. Deposits with thicknesses up to 10 mu m w ere formed. The green deposits revealed a crystalline nature for compo sitions of x < 0.3, and an amorphous nature for x greater than or equa l to 0.3, independent of the substrate material. Voltage-electrolyte c omposition dependencies exhibited an ubiquitous minimum at x approxima te to 0.3 to 0.4 independent of substrate type and deposition duration . These minima were attributed to the change in the electrical resista nce of the deposit with composition and degree of crystallinity.