The effect of low melting point phases on the elevated temperature microstructural stability of hot pressed beryllium

The factors governing the growth of BeO particles and beryllium grains in hot-pressed beryllium block have been studied. The size of BeO particles was found to increase as the aluminum, magnesium and silicon contents were raised. Higher processing temperatures during manufacture also increased the size of the oxide. Silicon doping of the beryllium powder before pressing was found to be a particularly effective way of increasing BeO particle size. The pressure-temperature cycle employed during hot pressing was also found to affect the oxide morphology. Cycles that produced full density at the lowest temperature minimized the extent of oxide agglomeration. Diffusion of aluminum and a combination of aluminum, silicon and iron into high purity beryllium at 1366 K produced a grain boundary liquid phase which resulted in an accelerated grain growth rate and BeO agglomeration.