Rapid Rate Sintering of Nanocrystalline ZrO2−3 mol% Y2O3

Abstract

Conventional ramp‐and‐hold sintering with a wide range of heating rates was conducted on submicrometer and nanocrystalline ZrO2–3 mol% Y2O3 powder compacts. Although rapid heating rates have been reported to produce high density/fine grain size products for many submicrometer and smaller starting powders, the application of this technique to ZrO2–3 mol% Y2O3 produced mixed results. In the case of submicrometer ZrO2–3 mol% Y2O3, neither densification nor grain growth was affected by the heating rate used. In the case of nanocrystalline ZrO2–3 mol% Y2O3, fast heating rates severely retarded densiflcation and had a minimal effect on grain growth. The large adverse effect of fast heating rates on the densification of the nanocrystalline powder was traced to a thermal gradient/differential densification effect. Microstructural evidence suggests that the rate of densification greatly exceeded the rate of heat transfer in this material; consequently, the sample interior was not able to densify before being geometrically constrained by a fully dense shell which formed at the sample exterior. This finding implies that rapid rate sintering will meet severe practical constraints in the manufacture of bulk nanocrystalline ZrO2–3 mol% Y2O3 specimens.