Cooling rate effect on microstructure and mechanical properties of AlxCoCrFeNi high entropy alloys

Abstract

The AlxCoCrFeNi alloys were prepared by arc-melting (AMx) and suction-casting (SCx) method. Their microstructure and phase constituents were characterized by scanning electron microscope, X-ray diffractometer and electron backscattered diffraction, and the compressive properties were tested as well. It is found that higher cooling rate during suction-casting process could not only refine microstructure but also change the phase morphology and strengthening mechanism. Microstructure refinement should enhance the strength of SCx alloys, but the strength difference between SCx and AMx alloys increases first when the Al content increase from 0.15 to 0.75 and then decreases. For Al0.15CoCrFeNi alloy, the density of 60°〈111〉 deformation twins in the compressive samples prepared by arc-melting is higher than suction-casting. This will offset the strength contribution of microstructure refinement caused by higher cooling rate. For Al0.75CoCrFeNi alloy, the high strength for SC0.75 alloy can be attributed to not only microstructure refinement but also increase in volume fraction of BCC phase with high strength and lattice strain in FCC phase.