MICROSTRUCTURAL CHARACTERIZATION OF AL2O3-SIC

Al2O3 composite ceramics containing 10 vol% SiC nanoparticles were pre pared by pressureless sintering. SiC particles < 150 nm detach from th e matrix grain boundaries during grain growth and are predominantly ob served in intragranular positions, whereas larger SiC particles retain intergranular positions. Thermal expansion mismatch causes local resi dual tensile stresses in the matrix grains, giving rise to strain cont rasts in TEM imaging, occasionally microcracking around intragranular inclusions greater than or equal to 100 nm is observed in thin TEM foi ls. It appears that the volume fraction of intragranular SiC particles in the size range 100 < d < 150 nm should not exceed approximate to 0 .5% in high strength/high toughness Al2O3-SiC nanocomposites. The inte raction between propagating cracks and internal stress fields around i ntragranular inclusions forces a transgranular fracture mode. Grain bo undary pinning by large intergranular SiC particles, in combination wi th solute drag inhibits matrix grain growth, while the presence of an amorphous phase at Al2O3 grain boundaries and Al2O3-SiC phase boundari es assists in densification. Excess liquid phase is exuded from the in terfaces during consolidation and accumulates in large pores, stabiliz ed by the accidental agglomeration of large SiC particles. Published b y Elsevier Science Limited.