Fabrication of Dense Composite Ceramics Utilizing Pulsed Electric Current and Pressure

抄録

Aluminum oxide (Al₂O₃)-based composite ceramics consisting of vapor-grown carbon nanofiber (CNF) and titanium nitride (TiN) with the compositions of (Al₂O₃/CNF)/TiN=(100-y)[(100-x)/x] /y vol%, (x=0, 1, 3, 5, 10, y=0, 1, 3, 5, 10), have been fabricated utilizing both pulsed electric current and pressure to meet the demand for electric discharge processing for engineering ceramics. Mixtures of fine Al₂O₃ powder (particle size P_s: 0.1×10^-6 m), CNF (150 ×10^-9 m in diameter and ~6 ×10^-6 m in length), and nanoparticle TiN (P_s: 20×10^-9 m) were sintered at 1623 K (1350°C) under 50 MPa for 6.0×10³ s (10 min) in Ar to produce electrically conductive aluminum oxide ceramics (alumina) with high mechanical properties at the same time. The relative densities of Al₂O₃/CNF/TiN composites decreased from 99.9% to 96.1% as the content of TiN increased to 10 vol%, and their electrical resistivity Ρ was much reduced from ~10¹³ (insulator) to less than ~1.0×10^-2 Ω・m by the addition of a small amount of 3~5vol% CNF and TiN simultaneously. High bending strength σ_b and high fracture toughness K_IC have been achieved in the compositions of Al₂O₃/CNF/TiN=95[(97/3)]/5 vol% (x=3, y=5) and 95[(95/5)]/5 vol% (x=5, y=5), respectively. The former revealed the following values: σ_b: 511 MPa, Vickers hardness H_v: 20.4 GPa,K_IC: 6.08 MPa・m^1/2, and Ρ: 6.5×10^-3 Ω・m. The latter showed σ_b: 562 MPa, H_v: 19.9 GPa, K_IC: 6.08 MPa・m^1/2, and Ρ: 2.0×10^-4 Ω・m. These data suggested that these composites could be candidates for electric discharge processing for engineering ceramics.