PREPARATION AND HIGH-TEMPERATURE STRENGTHENING OF TETRAGONAL ZIRCONIA MULLITE WHISKER COMPOSITES

Using sol-gel methods for the preparation of mullite whiskers (mullite(w)) and subsequent chemical processing with mixed chemical solutions, mullite(w)-tetragonal zirconia polycrystal (TZP) composites were fabricated by sintering and hot pressing. The effects of mullite(w) content on the microstructures and the mechanical properties of mullite(w)-TZP composites were studied. If the mullite(w) fraction was greater than 15 vol.-% and the hot pressed temperature higher than 1600-degrees-C, the composites cracked as a result of Y2O3 disolution from the TZP into a glassy phase at the interface between the mullite(w) and the TZP grains. The mechanical properties of the composites with 5-20 vol.-% mullite(w) at room temperature were flexural strength sigma(f) 1200 MN m-2 and fracture toughness (K(IC)) 12 MN m-3/2, closely similar to the properties of the TZP matrix. These properties are attributed to the stress induced ZrO2 transformation toughening mechanism. The flexural strengths of the composites at 1000-degrees-C were 1.8-2.1 times that of the TZP matrix. This increase is attributed to a load transfer mechanism.