The effect of particle size and volume fraction on the aging behavior of a liquid-phase sintered SiC/aluminum composite

The aging response of a SiC particulate reinforced powder metallurgy aluminum composite was examined as a function of particle size and volume fraction. The addition of SiC particles ranging in size from 24 to 142 μm at 9 vol pct had no effect on the aging kinetics of the composites. Acceleration of the aging behavior or inhibition of the initial stage of the age-hardening process was observed at 18 and 27 vol pct. The accelerated aging kinetics were consistent with smaller particles creating larger thermal misfit dislocation densities. In addition, it was shown that different combinations of ceramic particle size and volume fraction lead to similar effects on the aging behavior. Loss of the initial hardening response was attributed to the suppression of Guinier-Preston (GP) zone formation due to the annihilation of excess vacancies at the thermal misfit dislocations. © 1995 The Minerals, Metals & Material Society

MICROSTRUCTURAL ANALYSIS OF FRACTURE-TOUGHNESS VARIATION IN 2XXX-SERIES ALUMINUM-ALLOY COMPOSITES REINFORCED WITH SIC WHISKERS

The effects of local microstructure on fracture properties in powder-metallurgy (P/M)-processed 2124/SiC/15w and 2009/SiC/15w composites are analyzed in this study. Ductility and fracture toughness of the 2009/SiC/15w, in which dispersoid-forming elements such as manganese and iron were nearly absent, were greater than in the 2124/SiC/15w, while its tensile and yield strengths were somewhat less. Microstructural examination and fracture parameter analysis revealed that the improved fracture toughness of the 2009/SiC/15w compared to the 2124/SiC/15w was due to the increase in the critical microstructural distance, l*, when manganese-containing particles are absent. 2009/SiC/15w was also heat-treated in T4P and overaged (OA) conditions. The OA 2009 composite showed lower fracture toughness than the 2009-T4P composite and the critical fracture strain of the OA condition was much lower, too. Detailed fractographic analyses indicated that interface precipitates facilitate premature SiC whisker failure in the OA condition.open1118sciescopu