Effects of rare earth elements on AlCoCrFeNi 2.1 eutectic high-entropy alloy

Abstract

In order to explore the effect of rare earth elements (REEs) on the eutectic high-entropy alloys (EHEAs), 0.2 atomic per cent of Sc, Y, and La elements were added to the AlCoCrFeNi_2.1(REE0) EHEA in this work. The phase composition, element distribution, electrochemical properties and mechanical properties of the alloys were analysed. The results showed that the AlCoCrFeNi_2.1-based HEAs are still composed of Co, Cr, Fe (face-centred cubic)-rich phase and Al, Ni (face-centred cubic)-rich phase. After Sc, Y, La were added, Ni₂Sc, Al₂Y, Al₂La and other intermetallics were formed in the AlCoCrFeNi_2.1 alloy. In addition, it was proved that Y element can promote the formation of hexagonal close-packed (HCP) phase. AlCoCrFeNi_2.1Y_0.2(Y0.2) alloy has excellent corrosion resistance. AlCoCrFeNi_2.1Sc_0.2(Sc0.2) alloy has the best mechanical properties.

HIGHLIGHTS

With the addition of rare earth elements, the face-centred cubic phase and the B2 phase still exist in the alloy. In addition, there are intermetallics in the alloys. Combined with first-principles calculations, it was determined that the Laves phases in AlCoCrFeNi_2.1Y_0.2 alloy may be Al₂Y, Al₃Y or AlY. The Laves phase in the AlCoCrFeNi_2.1La_0.2 alloy may be Al₂La, Al₃La or LaNi₅.

The addition of Y element can promote the formation of HCP phase in AlCoCrFeNi_2.1 alloy. The generated HCP phase occupies the position of the original B2 phase. Y element can also improve corrosion resistance.

The Vickers hardness of AlCoCrFeNi_2.1Sc_0.2 alloy is 20% higher than that of AlCoCrFeNi_2.1 alloy, while the compressive strength of 1897 MPa and the compressive deformation of 26% are retained.