The structure formation in reaction sintering of cubic boron nitride submicron and nanosized powders with aluminum at the stage of high-pressure infiltration

Abstract

Porosity, phase composition, and structure of samples produced from submicron and nano-metric cBN powders high-pressure infiltrated with aluminum (at a pressure of 2.5 GPa and a temperature of 1300 K) have been studied. It has been found that a special feature of the nanopowder consolidation under these p, T parameters is the formation of local volumes of different densities, which is responsible for the complexity of the infiltration, causes an increase of the closed porosity and gradients of stresses by volume, and thus, the cBN → hBN deformation phase transformation and the crack initiation as the temperature and pressure decrease. It has been shown that to obtain a homogeneous infiltration structure, the initial cBN powders with a small concentration of nanosized fractions, when nanoparticles do not form aggregates of different densities but are distributed on the surfaces of larger particles, can be promising.