Synergetic and alone influence of graphite platelet and SiC on the oxidation resistance of ZrB2 ceramics

This study investigates how adding graphite platelets (GP), with and without SiC, affects the oxidation resistance of ZrB₂ ceramics. The specimens-ZrB₂-10GP, ZrB₂-15GP, ZrB₂-15SiC, ZrB₂-30SiC, ZrB₂-30SiC-10GP, and ZrB₂-30SiC-15GP-were sintered at 1850 °C for 8 min via spark plasma sintering (SPS). For oxidation evaluation, the samples were exposed to air in the furnace at a temperature of 1450 °C for different times (30, 60, 90, 120, 180, 300 min). Also, the simultaneous thermogravimetric analysis (TGA) and differential thermal analysis (DTA) up to 1200 °C were applied to investigate the in situ oxidation. FESEM and EDS were utilized to perform microstructural and elemental analyses on the cross-sections of various oxide layers. It was disclosed that the GP and SiC both improve the oxidation resistance. The best oxidation resistances were obtained in the ZrB₂-30SiC and ZrB₂-30SiC-10GP with the lowest oxidation layer thicknesses of 38 ± 3 µm and 40 ± 4 µm, respectively. Also, the lowest oxidation resistance was obtained in pure ZrB₂ with the highest oxide layer thickness of 129 ± 5 µm. The formation of an adherent oxide layer is the dominant factor for improving the oxidation resistance. The oxidation mechanism of all samples except ZrB₂ was diffusion oxygen-controlled with a parabolic behavior. Also, TGA and DTA analysis showed a mass loss at the initial stage (∼ 200°C ), followed by mass gain at 709 °C and 1065°C.