Neutron diffraction measurements of residual stresses in alumina/SiC nanocomposites

Abstract

The addition of 200 nm SiC particles to alumina improves its room temperature mechanical and tribological properties. A number of explanations have been proposed, all of which stem from the residual stresses caused by the expansion mismatch between alumina and SiC during cooling from processing temperatures. This paper describes neutron diffraction measurements of these stresses. The hydrostatic stresses were in accord with a simple elastic model and showed that stress relaxation ceased at ∼ 1300°C. Pressures of almost 2 GPa were present in the SiC particles. The average strains in the alumina grains also had a deviatoric component, which was tentatively interpreted in terms of anisotropic stress relaxation at high temperature. This mechanism reduces the thermal expansion anisotropy of the matrix grains. Possible explanations for nanocomposite properties are discussed in the light of the results. Although each mechanism is weak considered in isolation, the possibility for cooperative action exists.