  The relationship between matrix phase composition and microstructure yielding
in phase separated calcium aluminosilicate glasses is investigated. Varying the
treatment temperature of a phase separated glass results in glasses with
different microstructures and matrix compositions. The impact of matrix
composition on hardness depends on the mode of microstructural deformation. In
glasses that deform via the droplet-densification mechanism, decreasing the
matrix silica content results in a decrease in hardness due to the weakest-link
effect and greater amounts of incongruent yielding of the phases. This
relationship may act as an additional source of the indentation size effect in
phase separated glasses. In glasses that deform via droplet-coalescence,
decreasing the matrix silica content results in increasing hardness due to
increased coalescence of the droplet phase during yielding.
