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 mu m, a crystallit e size of 40 nm and a specific surface of 16.2 m(2)/g, while the micro-sized powder had a particle size of 0.68 mu m, crystallite size of 120 nm and a specific surface of 7.0 m(2)/g. Cold uniaxially pressed samples of the nano-sized powders were sintered at temperatures between 1250 and 1400 degrees C, while samples of the micro-sized powders were sintered at temperatures up to 1600 degrees 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 degrees C, while the micro-sized powders reached similar densification only after sintering at 1530 degrees C. The average grain size of samples prepared from the nano-sized powders increased from 0.18 mu m, when sintered at 1250 degrees C without isothermal holding time, to 0.64 mu m when sintered at 1400 degrees C for 16 h. In the case of micro-sized powders the average grain size varied between 0.40 mu m, when sintered at 1530 degrees C without isothermal holding time, and 1.84 mu m when sintered at 1600 degrees 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 degrees C. Samples prepared from these powders reached almost full density at 1400 degrees C without further isothermal holding treatment, exhibiting an extremely fine grained and homogeneous microstructure, with an average grain size of 0.22 mu m. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.