Aluminum oxide fracture toughness

Microstructurc. Crystal size, porosity, and impurity phases play a major role in fixing the fracture characteristics and toughness of an abrasive grain. As an example, rapidly cooled fused aluminum oxide has a microcrystalline stmcture promoting toughness for heavy-duty grinding appHcations, whereas the same composition cooled slowly has a macrocrystalline stmcture more suitable for medium-duty grinding. 

Sialons, as ceramic alloys of silicon nitride and aluminum oxide, were developed as an economically and fimctionally superior alternative to H PSN (see above). This alloying imposes increased high-temperature mechanical (flexural and tensile strengths, fracture toughness, hardness, wear resistance), thermal (thermal shock resistance) and chemical properties (corrosion and oxidation resistance) compared to unalloyed silicon nitride (see Table 11.13). 

---