Precipitation During Controlled Cooling of Magnesia-Partially-Stabilized Zirconia

A study has been made of the precipitation and growth processes which occur during cooling from solution treatment and under isothermal hold conditions in a magnesia-partially-stabilized zirconia alloy. Three types of precipitate have been identified which develop during cooling or during isothermal hold treatments just above and below the eutectoid temperature. These precipitate forms are termed (i) primary, (ii) large random, and (iii) secondary. Further precipitation, slow growth of existing precipitates, and subeutectoid decomposition result when an additional 1100°C aging treatment is given to the previously cooled material. It is shown that type (iii) secondary precipitates form rapidly within the temperature range of 1300° to 1375°C. The secondary precipitates are largely responsible for the improved room-temperature strength properties of the heat-treated samples. The formation and effects on mechanical properties of each type of precipitate are discussed.