Si3N4-ZrO2 composites with small Al2O3 and Y2O3 additions prepared by HIP |
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Authors: | T. Ekström L. K. L. Falk E. M. Knutson-Wedel |
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Affiliation: | (1) AB Sandvik Hard Materials, S-126 80 Stockholm, Sweden;(2) Department of Physics, Chalmers University of Technology, S-41296 Gothenburg, Sweden |
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Abstract: | Si3N4-ZrO2 composites have been prepared by hot isostatic pressing at 1550 and 1750 °C, using both unstabilized ZrO2 and ZrO2 stabilized with 3 mol% Y2O3. The composites were formed with a zirconia addition of 0, 5, 10, 15 and 20 wt%, with respect to the silicon nitride, together with 0–4 wt% Al2O3 and 0–6 wt% Y2O3. Composites prepared at 1550 °C contained substantial amounts of unreacted -Si3N4, and full density was achieved only when 1 wt% Al2O3 or 4 wt % Y2O3 had been added. These materials were generally harder and more brittle than those densified at the higher temperature. When the ZrO2 starting powder was stabilized by Y2O3, fully dense Si3N4-ZrO2 composites could be prepared at 1750 °C even without other oxide additives. Densification at 1750 °C resulted in the highest fracture toughness values. Several groups of materials densified at 1750 °C showed a good combination of Vickers hardness (HV10) and indentation fracture toughness; around 1450 kg mm–2 and 4.5 MPam1/2, respectively. Examples of such materials were either Si3N4 formed with an addition of 2–6 wt% Y2O3 or Si3N4-ZrO2 composites with a simultaneous addition of 2–6 wt%Y2O3 and 2–4 wt% Al2O3. |
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