The effect of particle size on microstructure,relative density and indentation load of Mg-B 4 C composites fabricated at different loading rates

Abstract

The effect of reinforcing particle size on microstructure, relative density and indentation of Mg reinforced by 0, 1.5, 3, 5 and 10% volume fractions of nano- and micro-sized B₄C was investigated. The composites were fabricated through powder compaction technique at strain rates of 1.6 × 10³s⁻¹, 8 × 10²s⁻¹ and 8×10³s⁻¹ using split Hopkinson bar, drop hammer and Instron, respectively. The results indicated that the size of B₄C and loading rate had significant effect on relative density. For example, the relative density of Mg-10 vol.% B₄C nanocomposite was around 2.5% higher than that of its corresponding microcomposites. The relative density of the samples produced at high rate of loading was in average 1.2% higher than that of the samples fabricated quasi-statically. The results of indentation tests on the produced nanocomposite and microcomposite samples also revealed that loading rate and B₄C particle size had significant effect on strength of specimens. For example, for Mg-5 vol.% B₄C, the maximum load in load–depth curve of the specimens produced by split Hopkinson bar increased from 530 N for micron-sized B₄C to 780 N for nano-sized B₄C, around 45% improvement. Moreover, nanocomposites had better indentation resistance compared to similar micro composites fabricated using the three methods.