Fabrication of silicon carbide composites with carbon nanofiber addition and their fracture toughness

Abstract

The authors have examined the fabrication conditions of SiC composites containing carbon nanofiber, i.e., vapor-grown carbon nanofiber (VGCF), to enhance the fracture toughness. Commercially available ultrafine SiC powder (specific surface area: 47.5 m² g⁻¹) was mixed with VGCF and sintering aid in the Al₄C₃–B₄C system. Approximately 1.5 g of the mixture was uniaxially pressed at 50 MPa to obtain a compact with a diameter of 20 mm and a thickness of approximately 1.5 mm. The resulting compact was hot-pressed at 1800 °C for 1 h in Ar atmosphere under a pressure of 62 MPa. The relative density of hot-pressed SiC composite decreased from 98.0 to 96.3%, whereas the fracture toughness was enhanced from 3.8 to 5.2 MPa m^1/2, as the amount of VGCF increased from 0 to 6 mass%. Furthermore, an acid treatment of VGCF was conducted to enhance its dispersibility within the SiC matrix, owing to the formation of COO⁻ groups on the VGCF surface. As a result of this treatment, the relative density and fracture toughness of hot-pressed SiC composite with 6 mass% acid-treated VGCF addition increased to 99.0% and 5.7 MPa m^1/2, respectively.