Fabrication of machinable AlN–BN composites with high thermal conductivity by pressureless sintering turbostatic BN-coated AlN nanocomposite powders

Abstract

To impart machinability to hard and brittle AlN ceramics without losing their high thermal conductivity, a homogeneous dispersion of fine BN particles in an AlN matrix was investigated. A homogeneous dispersion of BN particles was obtained by pressureless sintering of turbostatic BN-coated AlN nanocomposite powder (AlN–BN nanocomposite powder), which was prepared by reducing and heating AlN particles containing a mixture of boric acid, urea, and carbon. Though AlN is slightly oxidized by boric acid during the reduction, the addition of carbon reduced the oxygen content of the AlN–BN composite powder by carbothermal reduction of the oxidized AlN particles. As a result, the thermal conductivity of the sintered material increased with decreasing oxygen content of the nanocomposite powder. AlN–BN nanocomposites containing more than 20 vol% BN showed high strength, machinability, and relatively high thermal conductivity in comparison with the conventional microcomposites.