2006 Volume 47 Issue 5 Pages 1374-1379
The instrumented pulse electric discharge consolidation method is used to provide a way of in process nanocrystalline control densification of the amorphous ZrO2-20 mol%Al2O3 powder as prepared by rotating-arm reaction ball milling. The cylindrical compact height (hf) of the amorphous ZrO2-20 mol%Al2O3 powder is found to be a dominant process variable; at 1 mm, it leads to the densification prior to major crystallization after a high relative density of roughly 0.86 at 800 K, and significant decreases down to 1284 K in temperature necessary to obtain the full densification under 100 MPa. The rapid densification for amorphous and nanocrystalline supersaturated cubic ZrO2-20 mol%Al2O3 is fairly well expressed by an Arrhenius-type equation of Newtonian viscous flow: ηp=ηpoexp(Q⁄kT) having greatly decreasing apparent activation energy Q from 300 to 72 kJ mol−1 and process viscosity ηp at 1200 K with decreasing hf from 14.6 to 1 mm. The Berkovich indentation testing permits us to derive a relatively low level of 4.4 GPa for the value of the yield stress at room temperature in the full-density nanocrystalline ZrO2-20 mol%Al2O3 sample having the Vickers hardness number of approximately 800 DPN.
