De-alloying of rapidly solidified amorphous and crystalline alloys

De-alloying occurs when a less noble metal is selectively removed from an alloy either by chemical or electrochemical means. Under appropriate experimental conditions and for suitable alloy composition, the resulting material is constituted by crystalline ligaments rich in the noble element and pores. The literature reports a substantial amount of information on de-alloying crystalline homogeneous solid solutions, mostly based on noble metals, whereas the process has been attempted in a limited number of cases with amorphous alloys. The latter case is reviewed here and new results are given for an Au-based metallic glass evidencing the role of the critical potential and surface roughness. It can be also of interest to remove selectively from the alloy a single phase leaving a sieve-like matrix. which might itself be porous. The size of the pores and of the remaining solid can be tailored by controlling the grain size of the phases. Examples are given for this second process and experiments are reported on successful selective etching of rapidly solidified Fe–C eutectics.