Effect of molybdenum additives on corrosion behavior of (CoCrFeNi)_100-xMo_x high-entropy alloys

The present work investigates the influence of micro-alloyed Mo on the corrosion behavior of (CoCrFeNi)_100-xMo_x high-entropy alloys. All of the (CoCrFeNi)_100-xMo_x alloys exhibit a single face-centered cubic (FCC) solid solution. However, the (CoCrFeNi)₉₇Mo₃ alloy exhibits an ordered sigma (σ) phase enriched in Cr and Mo. With the increase of x (the Mo content) from 1 to 3, the hardness of the (CoCrFeNi)_100-xMo_x alloys increases from 124.8 to 133.6 Vickers hardness (HV), and the compressive yield strength increases from 113.6 MPa to 141.1 MPa, without fracture under about a 60% compressive strain. The potentiodynamic polarization curve in a 3.5% NaCl solution indicates that the addition of Mo has a beneficial effect on the corrosion resistance to some certain extent, opposed to the s phase. Furthermore, the alloys tend to form a passivation film in the 0.5 M H₂SO₄ solution in order to inhibit the progress of the corrosion reaction as the Mo content increases.