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In this study,coatings of zirconia alloyed with8wt% yttria were prepared by plasma spraying.A comprehensivesequence of annealing experiments comprising time from 1 to 100hours at temperatures between 1100 and 1500℃ were carried out.It is shown that the T′phase in coatings decomposes into low yttriatetragonal phase(T_1′)and high yttria tetragonal phase(T_2′)following high temperature annealing.The content of YO_(1.5)in T_1′decreases with the increasement of annealing time.Both T_1′andT_2′phases are also “non-transformable”tetragonal phases.Andfurther annealing causes a cubic phase (C) to precipitate fromT_2′.The increasement of C phase is accompanied by the decrease-ment of T_2′phase.The probable mechanism of T′→T_1′+T_2′phase transformation is of spinodal decomposition and that of T_2′→C is of precipitation.
In this study, coatings of zirconia alloyed with 8 wt% yttria were prepared by plasma spraying. A comprehensive sequence of annealing experiments includes time from 1 to 100 hours at temperatures between 1100 and 1500 ° C were carried out. It is shown that the T’phase in layer decomposes into low yttriatetragonal phase (T_1 ’) and high yttria tetragonal phase (T_2’) following high temperature annealing. content of YO_ (1.5) in T_1’decreases with the increasement of annealing time. Both T_1’and T_2’phases are also “non -transformable ”tetragonal phases. Additional annealing causes a cubic phase (C) to precipitate from T 2 ’. The increasement of C phase is accompanied by the decrease-ment of T_2’phase.The probable mechanism of T’ → T_1 ’+ T_2’phase transformation is of spinodal decomposition and that of T_2 ’→ C is of precipitation.