DENSIFICATION OF LARGE PORES .1. EXPERIMENTS

Three different diameters (0.50, 1, and 2-mu-m) of monosized spherical pores were introduced, at different volume percents up to 15%, into two submicrometer commercial Zr(Y)O2 powders which exhibited either sluggish (ZrO2-3 mol% Y2O3) or rapid (ZrO2-8 mol% Y2O3) grain growth kinetics. Densification and grain growth behavior was studied as a function of heat-treatment period at 1400-degrees-C and/or 1500-degrees-C. Pores in the finer-grain Zr(3Y)O2 densified more rapidly. The grain growth kinetics of the Zr(3Y)O2 material were unaffected by porosity, because the pores were always larger than the grains. Consistent with the Zener concept applied to mobile pores on grain junctions, the spherical pores influenced the grain growth kinetics of Zr(8Y)O2 once the grain size was greater than the pore size. Measurements indicated that the number of pores per unit volume decreased dramatically during densification, whereas their average size remained approximately constant.