IN-SITU FORMATION OF COMPOSITE MICROSTRUCTURES

Microstructural evolution in two in situ reinforced composite systems, one produced by partial reduction and the other by grain growth, has been examined over a range of size scales using light microscopy, scan ning electron microscopy (SEM) and transmission electron microscopy (T EM). Metal-ceramic matrix composites were formed by the partial reduct ion of Al2O3-Cr2O3 solid solutions to form Cr metal particles in an Al 2O3-Cr2O3 matrix which had a lower Cr2O3 concentration. In a second sy stem, grain growth of Si3N4 during liquid phase sintering produced lar ge, whisker-like grains in a fine-grained Si3N4 matrix, bonded by an o xynitride phase. The mechanisms controlling microstructural evolution in these two systems were examined.