Mechanical and corrosion properties of composite  ZrB2–SiC ceramics with oxide additions

A.D. Panasyuk,

I. M. Frantsevich Institute for Problems of Materials Science of the NAS of Ukraine, Krzhizhanovsky str., 3, Kyiv, 03142, Ukraine
Powder Metallurgy - Kiev: Frantsevich Institute for Problems of Materials Science NASU, 2021, #09/10


Hot pressing was used to produce compact ceramics 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 KIc, tensile strength df, compressive strength Y, grain-boundary strength S, and bending strength s) were studied. Study of the microstructure and elemental composition of the phases revealed that a defect-free structure formed in the ZrB2-based composite through strong Van Der Waals’ adhesive phase interaction at the SiC–Al2O3 interface, which increased the fracture toughness to 9.4 MPa × m1/2. In turn, this increased the grain strength from 0.64 GPa for the base 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 °C for a holding time of 1 h was stabilized by the formation of dense oxide scale on the material, while the weight increment of the ZrB2 + 20 wt.% SiC sample and, consequently, the scale thickness increased monotonically. The scale 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 μm thick with ZrO2 inclusions and a lower ZrO2-based layer up to 80 μm 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.