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

Abstract

In this work, the sintering of nano- and micro-sized yttrium stabilized zirconia powders, ZrO2-3mol% Y2O3, has been compared. The finer powder exhibited an average particle size of 0.15µm, a crystallit e size of 40nm and a specific surface of 16.2m2/g, while the micro-sized powder had a particle size of 0.68µm, crystallite size of 120nm and a specific surface of 7.0m2/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 16h 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 0.18µm, when sintered at 1250°C without isothermal holding time, to 0.64µm when sintered at 1400°C for 16h. In the case of micro-sized powders the average grain size varied between 0.40µm, when sintered at 1530°C without isothermal holding time, and 1.84µm when sintered at 1600°C for 16h. 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 141.3kJ/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 0.22µm.