Grain Boundary Evolution in Hot‐Pressed ABC‐SiC

Abstract

Silicon carbide with aluminum, boron, and carbon additions (ABC‐SiC) was hot‐pressed to full density. The samples were examined by transmission electron microscopy (TEM), with an emphasis on high‐resolution electron microscopy (HREM). Amorphous grain boundary interlayers, typically less than 2 nm wide, were formed between SiC grains. Heat‐treating the ABC‐SiC at temperatures as low as 1100°C in Ar crystallized the grain boundary interlayers completely without significantly changing the dominant chemical constituents. Chemical microanalyses demonstrated Al and O enrichment for all examined grain boundaries in both as‐prepared and annealed samples. Quantitative EDS analyses revealed Al2OC‐ and Al2O3‐related species (with Si, C, B, or S substitutions) as two of the most likely grain boundary interlayer materials, both before and after heat treatment. Al2O3, and (Al1−xSix)2OC with a 2H‐type wurtzite structure, were identified as grain boundary films by HREM images. The structural evolution in the grain boundary phases during the hot pressing and postannealing is discussed.