Fabrication and Characterization of Carbon Nanofiber (CNF)-Dispersed SiAlON Ceramics via Spark Plasma Sintering (SPS)

Abstract

Carbon nanofibers (CNFs: ∼150 nm^φ and 4∼5 μm^l) added SiAlON (Si₄Al₂O₂N₆) composites were fabricated directly from mixtures of Si₃N₄, Al₂O₃, AlN, and CNF by spark plasma sintering (SPS) at 1700°C for 10 min under 30 MPa in a vacuum. Dispersion of CNFs up to ∼5 vol% into SiAlON matrix introduced the enhancement of densification and diminution of matrix grains, resulted in improvement of mechanical properties, such as bending strength σ_b (450→600 MPa) and fracture toughness K_IC (4.1→4.5 MPa·m^1/2); however, Vickers hardness H_v decreased monotonously from 17.7 to 12.2 GPa with increasing CNF content. In addition, homogeneous CNFs dispersion brought a drastic change in electric conductivity; insulative SiAlON ceramics changed into conductive materials with improved mechanical properties by a small amount of CNFs with more than ∼3 vol%.