Multilayer coatings with improved reliability produced by aqueous electrophoretic deposition

Laminates in the system Al2O3/Y-TZP have been produced by an aqueous electrophoretic deposition (EPD) process combined with the use of thermogelling polysaccharides. Mixtures with relative volume ratios of Al2O3 to Y-TZP of 95/5, 60/40 and 0/100 have been studied in terms of colloidal stability, gelation behaviour and EPD kinetics. A graded symmetrical architecture, with external layers of A95Z5, and intermediate layers of A60Z40 sandwiching a layer of A0Z100 has been designed by controlling the sequential EPD kinetics of each suspension. The fracture strength of monoliths and laminates has been studied by three point bending and Weibull analysis. Even though the multilayer does not present strength values significantly higher than those of the A95Z5 monolith it presents enhanced reliability, as demonstrated by a higher Weibull modulus. Reliability of the laminate, under critical fracture conditions such as those involved in strength testing, is mostly due to a strong effect of the reduced thickness of the A95Z5 layers as compared to total thickness of the A95Z5 monolith.