Effects of synthesis and hot-pressing conditions on ZrB2-ZrC-SiC eutectic ceramics: Structure formation and properties

The paper investigates the macrokinetic combustion features of Zr-B-C, Zr-B-C-Si, and Zr-B-C-SiC mixtures calculated for obtaining eutectic compositions ZrB 2 -40.8 %ZrC and (ZrB 2 -ZrC)-8 %SiC (wt%) and analyzes the structure of the synthesis products . The article also examines the correlation between the method of SiC introduction into ZrB 2 -ZrC boride-carbide ceramics and the mechanical and thermal characteristics of hot-pressed samples. It has been determined that the method of obtaining reaction mixtures has an impact on combustion temperature and rate, as well as the dispersion of ZrB 2 and ZrC eutectic grain colonies in SHS products. The maximum grain size was observed in SHS products derived from the (Zr-B-C-Si) mixture (d ZrB2 ≈1.4 μm, d ZrC ≈1.2 μm), whereas the minimum grain size was observed in products derived from the (Zr-B-C-SiC) mixture (d ZrB2 ≈0.9 μm, d ZrC ≈0.8 μm). The dispersion of SHS powders after grinding the synthesis products ranges from 0.1 to 50 μm, the largest being the Zr-B-C powder with a particle size of D [4.3] = 12.13 μm and the smallest being the Zr-B-C-SiC powder with a particle size of D [4 . 3] = 6.62 μm. The in-situ shrinkage kinetics of SHS powders during hot pressing in the temperature range of 20–1600/1750/1900 °C was also examined. The optimal temperature-time regimes of hot pressing were found, which ensured the complete occurrence of shrinkage processes and allowed for the obtaining of samples with a relative density of 96–98 %. The dense ceramics obtained by combining the SHS and hot pressing methods has a homogeneous structure consisting of bonded grains of ZrB 2 , ZrC, and SiC phases, with the following properties: residual porosity −2.4 %, hardness −18.7 GPa, fracture toughness — 5.3 MPa m 0.5 , bending strength — 360 MPa, heat capacity — 0.44 J/(g·K), thermal diffusivity — 22.22 mm 2 /s, thermal conductivity — 57.9 W/(m·K).