Formation, characterization, and hot isostatic pressing of Cr2O3-doped ZrO2 (0,3 mol% Y2O3) prepared by hydrazine method

In the ZrO2-Cr2O3 system, metastable t-ZrO2 solid solutions containing up to 11 mol% Cr2O3 crystallize at low temperatures from amorphous materials prepared by the hydrazine method. The lattice parameter c decreases linearly from 0.5149 to 0.5077 nm with increased Cr2O3 content, whereas the lattice parameter a is a constant value (a = 0.5077 nm) regardless of the starting composition. At higher temperatures, transformation (decomposition) of the solid solutions proceeds in the following way: t(ss) --> t(ss) + m + Cr2O3 --> m + Cr2O3. Above 11 mol% Cr2O3 addition, c-ZrO2 phases are formed in the presence of Cr2O3. The t-ZrO2 solid solution powders have been characterized for particle size, shape, and surface area. They consist of very fine particles (15-30 nm) showing thin plate-like morphology, Dense ZrO2(3Y)-Cr2O3 composite ceramics (approximate to 99.7% of theoretical) with an average grain size of 0.3 mu m have been fabricated by hot isostatic pressing for 2 h at 1400 degrees C and 196 MPa. Their fracture toughness increases with increased Cr2O3 content. The highest K-Ic value of 9.5 MPa-m(1/2) is achieved in the composite ceramics containing 10 mol% Cr2O3.