In situ reinforcement of particulate SiC porous samples with β-Si₃N₄-nanofibers synthesized by the CVI method without catalytic precursors

The aim of this work is to reinforce particulate porous SiC samples by the in situ synthesis of β-Si₃N₄ nanofibers within the porous samples by the chemical vapor infiltration method without catalytic metallic precursors. The experiment considered the variation of the reaction time (1, 2, 3, and 4 h) and the N₂ flow rate (3, 5, and 9 cm³/min); while the inner pressure (10 mbar), the thermal decomposition of the solid precursor Na₂SiF₆ (400°C), and the temperature of the SiC sample (1300°C) remained constant. The mechanical properties of the composites revealed a non-linear behavior due to the arrangement of the particles during the loading process and to the plastic properties of the β-Si₃N₄ nanofibers. The stress and strain energy density magnitudes for different times had a rising behavior up to 3 h (σ = 15.65 MPa and u = 2.41 MJ/m³) due to the increasing diameter (100 to 200 nm) and quantity of β-Si₃N₄ nanofibers; while, at 4 h were significantly decreased (σ = 8.83 MPa and u = 1.44 MJ/m³) based on the reduction of the β-Si₃N₄ nanofiber diameter (30 to 100 nm) and to the presence of a new phase (S_i2N₂O).