Abstract: High-strength metallic foams have a wide range of applications in engineering as lightweight structural and energy-absorbing materials. However, it is challenging to obtain metallic foam with both good energy absorption performance and high strength. Here, we developed a novel metal matrix syntactic foam fabricated with AlCoCrFeNi_2.1 eutectic high entropy alloy and alumina cenospheres that exhibits a remarkable combination of high strength and energy absorption performance under both quasi-static and dynamic compression. The porous structure of syntactic foam fully exploits the properties of the AlCoCrFeNi_2.1 alloy matrix with a unique FCC/B2 dual-phase eutectic microstructure and thus yields exceptional performance. We discovered that this dual-phase microstructure not only provides high strength but also allows the pores to collapse in a progressive and diffusive way, which enables the formation of a high and smooth energy absorption platform. It is found that the heterogeneity between the two phases in the matrix can provide back stress strengthening, and it also induces multiple micro shear bands and microcracks as additional energy dissipation modes as the deformation proceeds. This unique mechanism ensures the strength of microstructures and makes them fracture promptly, which causes the balance of strengthening and softening on the macro scale. This work opens the avenue for developing advanced high-strength lightweight structural and energy-absorbing materials.

Key words: Eutectic high entropy alloy, Foams, Metal matrix composites (MMCs), Energy absorption