The effect of heat treatment on the grain size, phase assemblage, and mechanical properties of a 3 mol% Y‐TZP ceramic was investigated. Specimens were initially sintered for 2 h at 1450°C to near theoretical density; some specimens were then heat‐treated at 1550°, 1650°, 1750°, or 1850°C to coarsen the microstructure. The average grain size increased with heat treatment from <0.5 to ∼10 μ‐m. Phase analyses revealed predominantly tetragonal and cubic phases below 1750°C, with a significant decrease in tetragonal content and increase in monoclinic content for temperatures >1750°C. The maximum fraction of tetragonal phase that transformed during fracture corresponded with the largest tetragonal grain size of ∼5–6 μm. Strength was on the order of 1 GPa, and was surprisingly insensitive to heat‐treatment temperature and grain size, contrary to previous studies. The fracture toughness increased from 4 to 10 MPa.m1/2 with increasing grain size, owing to an increasing transformation zone size. Grain sizes larger than 5–6 μm spontaneously transformed to monoclinic phase during cooling. Such critical grain sizes are much larger than those found in past investigations, and may be due to the greater fraction of cubic phase present which decreases the strain energy arising from crystallographic thermal expansion anisotropy of the tetragonal phase.

Chemical coprecipitation was used to prod~~ce ultrafine and easily sinterrMc MsogcpbiliVa and (Mg0,Y203)stabilized Zr02 porrders. The sintering behavior is very sensitive to post-precipitation washing because Yhard" agglomerates form when the precipitated gels are washed with water, whereas "soft" agglomerates form when they are washed with ethanol. The soft agglomerates pack oniformly, resnlting in hshrinkage of powder compacts to neartheoretical density. The hard agglomerates result in compacts which have regions of l d i z e d densification and a signifiint fraction of residual porosity. [

Pure zirconia fired in HCI shows greatly reduced shrinkage compared to the same material fired in air. One of the main microstructural differences is the much more rapid grain growth in the porous zirconia fired in HCI. The observed grain growth does not follow any simple growth law over the temperature range investigated. The grains grow up to a limiting particle size close to the initial agglomerate size and appear to stop.