Oxidation Behavior of HfB2-SiC-Nd2O3 Ultra-High Temperature Composite Sintered through SPS Process

The current study aims to fabricate HfB2-30 vol. % SiC and HfB2-30 vol. % SiC-2 vol. % Nd2O3 composites through Spark Plasma Sintering (SPS) method at 1950 °C for 10 min. The oxidation behavior of the prepared composites was investigated at 1400 °C and different times namely 4, 8, 12, and 16 hours. The relative density, hardness, toughness, and strength of the HfB2-30 vol. % SiC composite increased from 98.5 %, 20.19 GPa, 414.9 MPa, and 4.36 MPa.m0.5 up to 99.1 % , 24.47 GPa, 485 .5 MPa, and 4.93MPa.m0.5 for HfB2-30 vol. % SiC-2 vol. % Nd2O3 composite, respectively. After 16 hours of oxidation, SiO2 layer, which was extremely thick, was produced locally on the oxidized HfB2-30 vol. % SiC composite surface. The thinckness of the SiO2 layer was calculated to be around 25 μm. The thickness measurement revealed the SiO2 produced layer on the surface of the HfB2-30 vol. % SiC-2 vol. % Nd2O3 composite to be 5 μm. The oxidation kinetic results of the composite exhibited linear-parabolic behavior. The chemical reaction during the oxidation process controlled the oxidation rate after eight hours. After 16 hours of performing the oxidation procedure at 1400 °C, HfB2-30 vol. % SiC-2 vol. % Nd2O3 composite exhibited parabolic behavior, while HfB2-30 SiC exhibited linear behavior. This composite's improved oxidation resistance was attributed to Nd(Hf,Si)OxCy phases and decreased porosity, resulting in the generation of thin, dense, adherent, and protective layers. Therefore, it was concluded that the oxygen diffusion rate could control the oxidation process in HfB2-30 vol. % SiC-2 vol. % Nd2O3 composite.