PHASE-STABILITY OF ZIRCONIA-BASED THERMAL BARRIER COATINGS .2. ZIRCONIA CERIA ALLOYS

Coatings consisting of zirconia alloyed with 12, 15, 20 and 25 wt.% ceria were prepared by plasma spraying. Samples of these coatings were annealed at temperatures ranging from 1200 to 1600-degrees-C for times up to 100 h and the phase structures were compared with those in the as-sprayed coatings. In the coatings containing 12, 15 and 20 wt.% ceria the monoclinic content increased although at 1600-degrees-C the presence of an orthorhombic phase was detected in the coatings containing 12 and 15 wt.% ceria. The coating with 25 wt.% ceria was wholly tetragonal after annealing except after the 100 h anneal at 1600-degrees-C when monoclinic structure was detected. Results of thermal expansion tests on selected samples containing 20 and 25 wt.% ceria are presented.