Mechanical and Corrosion Properties of ZrB2-SiC Composite Ceramics with Oxide Additions

Hot pressing was used to produce compact ceramic samples with the following composition (wt.%): 60 ZrB2 + 20 SiC + 20 (Al2O3 + 32 t-ZrO2). The tetragonal modification of zirconium oxide in the eutectic was stabilized by yttrium oxide. The porosity of the samples was 3-5%. The mechanical properties of the ceramics (hardness HV, fracture toughness K-Ic, tensile strength delta(f), compressive strength Y, grain-boundary strength S, and bending strength sigma) were studied. Analysis of the microstructure and elemental composition of the phases revealed that a defect-free structure developed in the ZrB2-based composite through strong Van Der Waals adhesive interaction at the SiC-Al2O3 interface, which increased the fracture toughness to 9.4 MPa center dot m(1/2). In turn, this increased the grain strength from 0.64 GPa for the basic composite to 3.46 GPa for the ZrB2-SiC composite with an oxide addition. An addition of Al2O3 + 32 wt.% t-ZrO2 was introduced in sufficient quantities not only to reduce the fracture stress but also to promote plastic deformation of the material for high-temperature bending strength. Study of the oxidation process showed that the weight increment of the 60 wt.% ZrB2 + 20 wt.% SiC + 20 wt.% (Al2O3 + 32 wt.% t-ZrO2) sample at 1600 degrees C for a holding time of 1 h was stabilized by dense oxide scale formed on the material, while the weight increment of the ZrB2 + 20 wt.% SiC sample and, consequently, the scale thickness increased monotonically. The scale that formed on the ZrB2 + 20 wt.% SiC samples with an addition of Al2O3 + 32 wt.% t-ZrO2 consisted of an upper Al2SiO5-based layer 50 mu m thick with ZrO2 inclusions and a lower ZrO2-based layer up to 80 mu m thick with Al2SiO5 inclusions. The eutectic Al2O3 + 32 wt.% t-ZrO2 oxide addition to the basic ZrB2-SiC system had higher oxidation resistance and thus prevented the diffusion of oxygen into the material.