Densification and grain growth of nano- and micro-sized Y-TZP powders

In this work, the sintering of nano- and micro-sized yttrium stabilized zirconia powders, ZrO2-3 mol% Y2O3, has been compared. The finer powder exhibited an average particle size of 0.15 µm, a crystallit e size of 40 nm and a specific surface of 16.2 m2/g, while the micro-sized powder had a particle size of 0.68 µm, crystallite size of 120 nm and a specific surface of 7.0 m2/g. Cold uniaxially pressed samples of the nano-sized powders were sintered at temperatures between 1250 and 1400 °C, while samples of the micro-sized powders were sintered at temperatures up to 1600 °C. Furthermore, the influence of isothermal holding times varying between 2 and 16 h has been studied. The nano-sized ZrO2 powders achieved almost complete densification at a temperature as low as 1350 °C, while the micro-sized powders reached similar densification only after sintering at 1530 °C. The average grain size of samples prepared from the nano-sized powders increased from 0.18 µm, when sintered at 1250 °C without isothermal holding time, to 0.64 µm when sintered at 1400 °C for 16 h. In the case of micro-sized powders the average grain size varied between 0.40 µm, when sintered at 1530 °C without isothermal holding time, and 1.84 µm when sintered at 1600 °C for 16 h. From the results of the quantitative microstructural analysis, grain growth exponents of 2.8 and 2.3 were calculated for the nano- and micro-sized starting powders, respectively. The value of the activation energy was determined to be 141.3 kJ/mol for the nano-sized powders. Moreover, the much smaller initial particle size of the nano-sized powders results in a significant reduction of the sintering temperature of approximately 160 °C. Samples prepared from these powders reached almost full density at 1400 °C without further isothermal holding treatment, exhibiting an extremely fine grained and homogeneous microstructure, with an average grain size of 0.22 µm.