Tailoring oxidation resistance of Fe2CoCrNi0.5 based high entropy alloys by addition of alloying elements (Si, Cu and Si-Cu co-added)

Abstract

Investigations about how to improve the properties of high entropy alloys (HEAs) play a key role in growing their potential for use in future industrial applications. Accordingly, this study aims to shed light on the effects of alloying elements (Si, Cu and Si-Cu co-added) on the microstructure and oxidation performance of the Fe 2 CoCrNi 0.5 based high entropy alloys. To this end, a series of high entropy alloys containing Fe 2 CoCrNi 0.5 , Fe 2 CoCrNi 0.5 Si 0.25 , Fe 2 CoCrNi 0.5 Cu 0.25 and Fe 2 CoCrNi 0.5 Si 0.25 Cu 0.25 were produced by electric current assisted sintering (ECAS) method, which is founded on the principle of simultaneous application of high-density electric current flowing through the powder mixture and uniaxial pressure within a short span of time. The oxidation test was carried out in air at 1123 K for 1200 h under cyclic conditions. The X-ray diffraction results showed that all HEAs have simple FCC solid solution phases. Among all HEAs, the oxidation resistance of the alloy exhibited an increasing trend with the Si addition and the best oxidation behavior at 1123 K for 1200 h was noted with Fe 2 CoCrNi 0.5 Si 0.25 , which experienced the least mass change of 4.72 mg cm −2 . Cu addition caused the highest mass change of 15.92 mg cm −2 and the thickest oxide scale of 38.2 µm after oxidation for 1200 h. Si addition is observed to enhance the amount of Cr-rich oxide in the scale. The oxide scale formed on HEA with Cu-added and HEA with Si-Cu co-added contained two oxide layers, including an outer layer of Fe-rich oxide and an inner layer of Cr-rich oxide, which showed continuous structure. However, the alloying elements did not play a favorable role in relieving the formation of internal oxidation. Additionally, it has been reported that Fe 2 CoCrNi 0.5 Si 0.25 HEA can exhibit high resistance to cyclic oxidation, which can be reasoned as an optimum material for structural and high-temperature applications. • Alloying element behavior has been shown to have a significant influence on the investigated properties of HEAs. • Si has proved to be effective in enhancing oxidation resistance. • Cu addition produced the thickest oxide scale. • One of the encouraging results of this investigation was the synergic effect of Si-Cu co-added.