The effect of particle size on microstructure, relative density and indentation load of Mg-B4C composites fabricated at different loading rates

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 × 103 s−1, 8 × 102 s−1 and 8×103 s−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.