Abstract ▼ AI-Helper

The microstructures and mechanical properties of zirconia toughened alumina (ZTA) ceramics prepared from two kinds of 3Y-TZP powders were investigated. ZTA composites were prepared by adding two kinds of 3Y-TZP powders, 3YEH(BET=7m2/g) and 3YEM(BET=16m2/g), to α-alumina in the range of 5–25 wt% . Po...

The microstructures and mechanical properties of zirconia toughened alumina (ZTA) ceramics prepared from two kinds of 3Y-TZP powders were investigated. ZTA composites were prepared by adding two kinds of 3Y-TZP powders, 3YEH(BET=7m2/g) and 3YEM(BET=16m2/g), to α-alumina in the range of 5–25 wt% . Powder mixture with desired composition were put into a 250ml jar and ball-milled for 20hrs. Water as dispersion medium, Cerasperse 5468CF (Sannopco, Japan) as dispersant, PVA # 500 (10wt% aqueous solution) as binder, ethylene glycol(Duksan, Korea) as a plasticizer and SN-defoamer 485 (Sannopco, Japan) as defoamer were used. Volume ratio of powder mixtures: water and slurry : ball was 1:1 and 1:1.2. Additives for powder mixtures were fixed; dispersant 0.8wt%, binder 1wt%, plasticizer 0.1wt% and defoamer 0.04wt% were added. In this experiment, slip casting method was adopted rather than general uniaxial compression-molding in order to guarantee uniformity of the mixed slurry. Obtained slurry respectively after ball milling for 20hours were injected into plaster mold and green compacts were fabricated. In order to obtain a specimen thickness more than 5mm, injection hold time was more than two hours and obtained compacts were dried for three days. The green body was sintered in an electric furnace with kantal as heating element. Sintering temperature was reached with a heating rate of 10 ℃/min up to 1000℃, 5℃/min to 1300℃ and 1.6 ℃ to final temperature. The rate of densification in both 3YEH and 3YEM zirconia were increased beyond 1500℃ and saturation density were achieved. The maximum density of 99.8% were achieved with addition of 5 wt% zirconia at 1600℃ for 2h. Density of sintered body were decreased with increasing zirconia content due to zirconia particle with drag force. The microstructure photographs of ZTA composites shows that the average grain size of alumina decreased as the content of zirconia increased. Specimens adding 3YEM zirconia exhibited smaller grain size compared to 3YEH zirconia. Vickers hardness of ZTA composties sintered at 1600℃ for 2hrs was smoothly decreased with increasing zirconia content because of low Young modulus in zirconia. Vickers hardness of ZTA adding 3YEH zirconia was greater than 3YEM zirconia. Fracture toughness(K1c) of ZTA composites increased as the content of zirconia increased. The main toughening mechanism was stress-induced transformation toughening. The maximum fracture toughness was 10.42MPam½ in pure 3YEH zirconia and 12.05MPam½ in pure 3YEM zircoina.

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