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In this paper, alumina-zirconia ceramics with different contents of strontium hexaaluminate are investigated. Materials were obtained by pressing granulated powder and following free sintering. An XRD analysis was carried out. The structure was studied using a scanning electron microscope. Vickers hardness was determined at a load of 10 kg. Fracture toughness was evaluated using the indentation method. The change of composites structure at different temperatures was analyzed. The growth of SrAl 12 O 19 platelet length proceeds predominantly up to 1400 °C. The platelet length range from 0.30 μm to 1 μm. At a temperature of 1500 °C the platelets thickness increases. In materials sintered at 1520 °C for 5 h with an increase in the SrAl 12 O 19 content, the relative density decreases, and the porosity of the materials increases. Increasing the strontium hexaaluminate content in sintered materials decreases the alumina grain size. With strontium hexaaluminate content of 15 wt %, the average grain size of the alumina component decreases by 19% compared to unaided alumina ceramics (from 0.74 ± 0.06 to 0.60 ± 0.04 μm). With increasing SrAl 12 O 19 content, the length of the platelets increased one and a half times from 0.80 μm to 1.20 μm. The width of the platelets remained essentially unchanged. Formation of strontium hexaaluminate platelets in materials and increase of its content contribute to increasing of fracture toughness of alumina-zirconia ceramics. The maximum level of fracture toughness is recorded at 15 wt % strontium hexaaluminate and is 7.7 ± 0.3 MPa*m1/2. The hardness of the composite with 15 wt % SrAl 12 O 19 is 18% lower than alumina zirconia ceramics and is ∼1400 HV. Mechanisms for increasing the fracture toughness of alumina-zirconia ceramics depend on the strontium hexaaluminate content. At hexaaluminate strontium content up to 6 wt %, bending, platelet fracture, and bridging mechanisms are observed. At 9 and 12 wt % SrAl 12 O 19 deflection mechanisms, crack branching and platelets fracture were detected. At 15 wt % SrAl 12 O 19 the crack deflection is observed. • An increase in SrAl 12 O 19 content in sintered materials decreases alumina grain size. • The platelets size ratio increases with an increase in its content in materials. • The maximum level of fracture toughness is recorded at 15 wt% strontium. [ABSTRACT FROM AUTHOR]

In this study, the effect of a small amount of strontium hexaaluminate (3 wt %) additives on the properties of alumina- and zirconia-based ceramics is discussed. α-Al 2 O 3 , 3Y-ZrO 2 and SrO submicron powders are used as the starting materials. Specimens are prepared by water suspension dispersion in a bead mill, spray drying granulation, isostatic pressing and pressureless sintering. Structural studies are conducted using a scanning electron microscope. The Archimedes approach is employed to determine the density and porosity of the specimens. Microhardness, flexural strength at three-point bending and fracture toughness are determined by the single-edge V-notch beam (SEVNB) method and indentation. A material containing 50-wt. % Al 2 O 3 and 50-wt. % ZrO 2 exhibited the most rational combination of characteristics such as strength (950 ± 50 MPa), microhardness (1800 HV) and fracture toughness (6.5 MPa m1/2). The SEVNB fracture toughness tests showed that the highest recorded value of a critical stress intensity factor was 9 MPa m1/2 for specimens containing 47-wt. % Al 2 O 3 , 3-wt. % SrAl 12 O 19 and 50-wt. % ZrO 2. The length of strontium hexaaluminate platelets decreased with an increase in the zirconia content in the materials and reached 0.8–2.6 μm. A pronounced fragmentary structure is characteristic of the strontium hexaaluminate platelets. The platelets under study comprised one or two boundary-separated blocks with a thickness of ~150–200 nm. Each block is divided into smaller fragments. The structure of strontium hexaaluminate platelets affects the crack propagation trajectory. The identified mechanisms of crack propagation are as follows: transcrystalline and intercrystalline fractures of alumina grains, crack deflection from the propagation trajectory, crack branching and failure of SrAl 12 O 19 platelets. • 3 wt% SrAl 12 O 19 improves the fracture toughness of alumina–zirconia ceramics. • Fragmentary structure is characteristic of the strontium hexaaluminate platelets. • The structure of SrAl 12 O 19 platelets affects the crack propagation trajectory. [ABSTRACT FROM AUTHOR]