Advanced Nanocrystalline Ceramic Matrix Composites with Improved Toughness

摘要

Alumina-based nanocomposites reinforced with niobium and/or carbon nanotubes were fabricated by advanced powder processing techniques and consolidated by spark plasma sintering. Raman spectroscopy revealed that single-walled carbon nanotubes (SWCNT) begin to break down at sintering temperatures above 1150 deg C. Nuclear magnetic resonance (NMR) showed that, although thermodynamically unlikely, no Al4C3 formed in the CNT-alumina nanocomposites. Thus, the nanocomposite is purely a physical mixture and no chemical bond was formed between the nanotubes and matrix. In addition, insitu 3-pt and standard 4-pt bend tests were conducted on niobium and/or carbon nanotube-reinforced alumina nanocomposites to assess their toughness. Although no subcritical crack growth was detected, average fracture toughness values of 6.1 and 3.3 MPa.m1/2 were measured for 10 vol%Nb and 10 vol%Nb-5 vol%SWCNT-alumina, respectively. Corresponding tests for the alumina nanocomposites containing 5 vol%SWCNT, 10 vol%SWCNT, 5 vol%double-walled-CNT and 10 vol% Nb yielded average fracture toughnesses of 2.95, 2.76, 3.33 and 3.95 MPa.m1/2, respectively.