Sintering of nanocrystalline ZrO2 and zirconia toughened alumina (ZTA)

Abstract

Abstract Ultrafine oxide powders of ZrO 2 and MgO were produced by laser ablation. The pure atomised powders and mixtures thereof were heated up to temperatures between 600 and 1600°C. The tetragonal phase in pure ZrO 2 powder transformed continuously between approximately 400 and 1000°C to the monoclinic phase. On addition of 5 vol.% MgO the transformation temperature could be increased by about 400 K and grain growth suppressed. Dilatometer measurements on compressed powder specimens showed that the shrinkage curve for nanocrystalline ZrO 2 was depressed by 300 K relative to a microcrystalline ZrO 2 specimen. The ZrO 2 specimen with 5 vol.% MgO was isostatically pressed and sintered in the temperature range 1000–1500°C. Sintered specimens contained 20–50% of the tetragonal phase. The specimen sintered at 1250°C for 1 h achieved a relative density of 95%. Small increases above this were observed in specimens sintered between 1250 and 1500°C. The 90 vol.% Al 2 O 3 + 10 vol.% ZrO 2 (with 5 vol.% MgO) specimens were also sintered in the temperature range 1400–1600°C. The specimens achieved high density (98%), microhardness (17·8 GPa) and toughness (7·2 MPa m ) .