In this study, nanoporous high-entropy alloys (HEAs) were fabricated by chemically de-alloying aluminium atoms in mechanically alloyed HEAs. In addition, the effect of alloy composition, compositional uniformity, and porosity of the HEA precursors on the pore structures of the final HEA foams was investigated. Aluminium was successfully de-alloyed only for Ni-free HEAs because of the low mixing enthalpy of Ni and Al. For HEAs containing pre-existing microscale pores, aluminium atoms were readily de-alloyed because the pores opened pathways for NaOH, thereby resulting in hierarchical micro-nanoporous structures in the final foams. For denser HEAs with better compositional uniformity, homogeneous nanoporous structures were revealed in the final foams.
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