In situ studies of non-equilibrium crystallization of AlxCoCrFeNi (x = 0.3, 1) high-entropy alloys

Abstract

To understand the effect of aluminum addition on the non-equilibrium solidification of the equiatomic CoCrFeNi alloy, the Al0.3CoCrFeNi and AlCoCrFeNi high-entropy alloys (HEAs) have been investigated in situ using electromagnetic levitation and high-energy synchrotron X-ray diffraction (XRD). Because the five-component alloys could not be deeply undercooled, the studies were confined to the low undercooling regime. The in situ XRD revealed that a fcc single-phase solid solution is the primary crystalline phase nucleating in Al0.3CoCrFeNi melt undercooled up to 80 K. In contrast, the B2 ordered phase appears as the primary phase in the AlCoCrFeNi melt, at least at a low undercooling of about 30 K. These results correlate with the equilibrium phase diagrams available. Crystal growth velocities of the Al0.3CoCrFeNi alloy are shown to be smaller than for CrFeNi and CoCrNi equiatomic alloys; nonetheless, they are in the same order of magnitude. Spontaneous grain refinement was observed in the Al0.3CoCrFeNi alloy solidified at a low undercooling of ΔT = 70 K.