Microstructure, thermodynamics and compressive properties of AlCoCrCuMn-x (x=Fe, Ti) high-entropy alloys

Two equiatomic high-entropy alloys (HEAs), AlCoCrCuMnFe and AlCoCrCuMnTi, were produced by vacuum arc melting. Their microstructure, thermodynamics and mechanical properties were investigated in as-cast condition. The AlCoCrCuMnFe alloy is comprised of a face centered cubic (FCC) phase and two body centered cubic (BCC) phases, while the AlCoCrCuMnTi alloy consists of the intermetallics-base solid solution (AlCu2Mn-like phase) besides a FCC phase and two BCC phases. Through analyzing the thermodynamics of equiatomic multicomponent alloys, two parameters, kn and φ, were proposed. The parameter kn is a function of n (n - the number of the components in an alloy system), while φ is defined as a parameter of Tsum over |Hsum| (Tsum - the sum of every elemental melting point in an alloy system, |Hsum| - the sum of mixing enthalpies of different pairs of alloying elements). φ≥1.1/kn is equivalent to Ω≥1.1 proposed by Yang to predict high entropy stabilized solid solution in equiatomic multicomponent alloys and more convenient to calculate. Compressive properties of the two HEAs together with their hardness have been investigated. Comparing to AlCoCrCuMnFe alloy, AlCoCrCuMnTi alloy has higher Vickers hardness, yield strength and compressive strength, but lower ultimate strain.