Evolution of Microstructures and Properties of the AlxCrCuFeNi2 High-Entropy Alloys

The microstructure and Vickers hardness of the AlxCrCuFeNi2(x=0.5, 1.0, and 2.0 in molar ratio) high-entropy alloys with as-cast and heat-treated states were investigated. X-ray diffraction (XRD) patterns suggested that for the Al0.5 alloy annealed at 900,an incomplete phase transformation from FCC to BCC occurred, while for the Al2.0 alloy as heated at 500 and 700, a converse phase transformation from BCC to FCC was obtained. Compared with the as-cast dendrites, after heat treatment, the microstructure of the alloys was obviously coarsened or spheroidized or homogenized, whereas the resultant hardness has almost not decreased even at high heating temperatures, which indicated the probability of ordering for this alloy system and thus effectively compensating the stress and structural relaxations. The Al2.0 alloy reached the maximum hardness value of 610 HV by annealing at 1100, which might be ascribed to the worm-like nanoprecipitations and the enhanced fraction of B2-ordered precipitations. By cold rolling, the Al0.5 alloy is able to reach the yield strength of 1055 MPa and the fracture strength of 1179 MPa, which was a significant improvement in comparison with the as-cast alloy.

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