Investigations on composition and morphology of electrochemical alumina and alumina-yttria stabilised zirconia deposits

Conversion coatings modified by deposits of electrolytic alumina added or n ot with yttria and/or zirconia, have been studied which are well known for their resistance to chemical. attack and high temperature. Conversion coati ng, characterised by a particular morphology and strong interfacial adhesio n with the substrate, facilitate the electrochemical deposition of ceramic layers and enhance their adhesion to the substrate. Zirconia-alumina coatin g behaviour at 1000 degreesC is similar to that of alumina coating; from 80 0 degreesC, the chromium diffuses from the stainless steel through the elec trolytic refractory coating up to the external interface, provokes disconti nuities and can modify its protective character. Yttrium stabilises the cub ic and the tetragonal form of the zirconia; so, during cooling, the phase t ransformation near 1000 degreesC of tetragonal zirconia to monoclinic form cannot take place. (C) 2001 Elsevier Science B.V. All rights reserved.