Transformation‐Toughened ZrO ₂ : Correlations between Grain Size Control and Composition in the System ZrO ₂ ‐Y ₂ O ₃

Abstract

The average grain size of ZrO 2 (+Y, o,) materials sintered at 1400°C was observed to depend significantly on the Y 2 O 3 content. The average grain size decreased by a factor of 4 to 5 for Y 2 O 3 contents between 0.8 and 1.4 mol% and increased at Y 2 O 3 contents of 6.6 mol%. Grain growth control by a second phase is the concept used to interpret these data; compositions with a small grain size lie within the two‐phase tetragonal + cubic phase field, and the size of the tetragonal grains is believed to be controlled by the cubic grains. This interpretation suggests that the Y 2 O 3 ‐rich boundary of the two‐phase field lies between 0.8 and 1.4 mol% Y 2 O 3 . Transformation toughened materials fabricated in this binary system must have a composition that lies within the two‐phase field to obtain the small grain size required, in part, to retain the tetragonal toughening agent.