RAPID RATE SINTERING OF NANOCRYSTALLINE ZRO2-3MOL-PERCENT Y2O3

Conventional ramp-and-hold sintering with a wide range of heating rate s was conducted on submicrometer and nanocrystalline ZrO2-3 mol% Y2O3 powder compacts. Although rapid heating rates have been reported to pr oduce 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, f ast heating rates severely retarded densification and had a minimal ef fect on grain growth, The large adverse effect of fast heating rates o n the densification of the nanocrystalline powder was traced to a ther mal gradient/differential densification effect. Microstructural eviden ce suggests that the rate of densification greatly exceeded the rate o f heat transfer in this material; consequently, the sample interior wa s not able to densify before being geometrically constrained by a full y dense shell which formed at the sample exterior. This finding implie s that rapid rate sintering will meet severe practical constraints in the manufacture of bulk nanocrystalline ZrO2-3 mol% Y2O3 specimens.