Structure and fracture toughness of ceramics based on Al2O3 and ZrO2 with SrAl12O19 additive

The formation of second phases with a high aspect ratio (whiskers, fibers, platelets) in the structure of the material is an effective method of increasing the fracture toughness of ceramic materials. The paper presents the results of determination of the fracture toughness of ceramics based on Al2O3 and ZrO2 with the addition of 3 wt.% SrAl12O19 (SrA6). Experimental samples were prepared according to the following technology: dispersion of water suspensions in a bead mill, spray drying granulation, hydrostatic pressing and free sintering. Submicron powders of alpha-Al2O3 (CT3000 SG), 3Y-TZP (Stanford Materials) and SrO were used as raw materials. X-ray diffraction analysis revealed the presence of three phases in sintered ceramics: a-Al2O3, t-ZrO2 and SrAl12O19. Structural investigations were carried out using scanning electron microscopy. It has been determined that the size of SrAl12O19 platelets in alumina ceramics is 1.2 x 0.2 mu m. The addition of 20 wt.% ZrO2 leads to an increase in platelet sizes up to 2.5 x 0.5 mu m. However, this also leads to a decrease in the number of SrAl12O19 grains. The dimensions of the platelets are 0.8 x 0.2 mu m in the material with 85 wt.% ZrO2. Therefore, it has been determined that an increase in the content of ZrO2 affects the platelets sizes. The fracture toughness by indentation under a load of 5 kg is calculated by the Niihara formula. It has been found that the presence of SrAl12O19 leads to an increase in the fracture toughness by 1.2 -1.6 times. The maximum value has been obtained for material 80(Al2O3-3SrA6)-20ZrO(2). The study of the propagation of crack growth allows revealing inter-and transgranular fractures. The crack propagation path changes upon collision with a perpendicular oriented platelet of SrAl12O19. At the same time, there is a realization of the mechanism for increasing crack resistance due to the deviation of the path of the propagating crack. Another mechanism is associated with the dissipation of energy due to the destruction of the platelets.