Microstructural development of Y-alpha/(beta)-sialons after post heat-treatment and its effect on mechanical properties

Dense Y-alpha and duplex Y-alpha/beta-sialon ceramics were fabricated
by hot isostatic pressing (HIP) using the compositions with the formula
Ym/3Si12-(m+n)Alm+nOnN16-n, and extra addition of 2 wt-%Y2O3. The
sintered materials were subsequently heat-treated at 1300-1700degreesC
to investigate the thermal stability of Y-sialons. The results show
that alpha-sialon stabilized by yttrium has high thermal stability. An
adjustment of alpha-sialon phase composition is the dominating reaction
during annealing. Post heat-treatment has a little effect on the
microstructure and properties of the Y-alpha/beta-sialons, but
significantly changes the morphology of alpha-phase grains in
Y-alpha-sialons from elongated to equiaxed after heat-treatment at
1500degreesC for extended time, hence decreasing its toughness.