Microstructure control and acid corrosion resistance of additively manufactured CoCrFeMnNi high-entropy alloy

The as-printed CoCrFeMnNi high-entropy alloy (HEA) possesses a hierarchical microstructure,which undergoes significant transformation with the increase of annealing temperature from 700℃ to 1100℃. The as-printed state consists of melt pools,columnar grains,and cellular sub-grain structure. The melt pool boundaries and cellular sub-grain structure gradually disappear after annealing,while the grain size gradually increases. The corrosion of HEAs in acidic solutions is mainly intergranular corrosion,and the corrosion current density gradually decreases with the increase of annealing temperature. Compared with the as-printed sample,the corrosion current density of the 1100℃ annealed sample decreased by 58%,and the corrosion potential increased by 61%. The proportion of corrosion-resistant elements in the passive film was 55.4% and 63.2% for the as-printed and 1100℃-annealed samples,respectively,and the intrinsic Cr oxide layer thickness increased to 2.7 nm and 3.1 nm. The disappearance of the highly reactive melt pool boundaries and cellular sub-grains,in conjunction with enhanced acid resistance of the passive film,collectively contributes to the superior corrosion resistance exhibited by the sample annealed at 1100℃.