Enhanced pitting resistance for high-entropy alloys by precipitating nano-sized L12-strengthened phase

Precipitation-strengthened HEAs exhibit outstanding integration of strength and toughness at ambient temperature. Nevertheless, precipitates generally reduce the localized corrosion resistance in aggressive solution environments. To solve this problem, a strategy of introducing nano-sized L12 precipitates in CoCrFeNiAlTi HEAs has been proposed in this work. Results demonstrate the pitting corrosion potential can be elevated from 258 mVSCE to 603 mVSCE by increasing the precipitate content to 38 wt.%. Such an improvement in localized corrosion resistance can be attributed to two aspects. Firstly, L12 precipitates tend to be dissolved during the corrosion process, which promotes the heterogeneous nucleation of protective Cr2O3 due to the rapid deposition of oxides/hydroxides of Al/Ti, and improves the passive film stability due to the Cr-rich FCC matrix. Secondly, the dissolution kinetic inside the pits can be suppressed on account of the enrichment of Cr element in the FCC matrix, thus inhibiting the pitting growth. In summary, the current work not only reveals the mechanisms of the nano-sized L12 precipitates upon the corrosion behavior, but also provides a strategy for designing corrosion-resistant HEA.