Effect of bi- and trimodal size distribution on the superficial hardness of Al/SiCp composites prepared by pressureless infiltration

The effect of particle size distribution on the superficial hardness of Al/SiCp composites prepared by pressureless infiltration, as well as on the microhardness and fracture toughness (KIC) of particulate silicon carbide (SiCp) was investigated. Preforms with 0.6 volume fraction of SiC powders (10, 68 and 140 μm) with monomodal, bimodal and trimodal distribution were infiltrated with the alloy Al–15.52 Mg–13.62 Si (wt.%) in argon followed by nitrogen at 1100 °C for 60 min. Results show that density behaves linearly with increase in particle-size-distribution whilst superficial hardness, microhardness and fracture toughness exhibit all a parabolic behavior. Superficial hardness behavior can be explained by the combined effect of work-hardening in the alloy matrix and particle-to-particle impingement. Due to the highly covalent nature of SiC, the parabolic response shown by microhardness and KIC cannot be attributed to a dislocation mechanism as in strain-hardening.