Abstract
The AlxCoFeNiCr1−x (0.1 ≤ x ≤ 1)high entropy alloys (HEAs) were prepared by repeated vacuum arc-melting in a Ti-gettered high-purity argon atmosphere to investigate the effects of the different Al/Cr ratio on the microstructure, mechanical properties and corrosion resistance in a 3.5 wt% NaCl solution. The experimental results shows that microstructures shifts from the FCC-dominated phase to BCC-dominated phase, and phase segregation switches from BCC phase rich in (Al,Ni) to FCC phase rich in (Fe,Ni) with the molar ratio of the Al/Cr increase. It was found that, with the FCC-dominated phase HEAs, the crystal phase changes from primarily single FCC phase (Al0.1CoFeNiCr0.9, Al0.2CoFeNiCr0.8, and Al0.3CoFeNiCr0.7) to a duplex FCC and BCC structure (Al0.4CoFeNiCr0.6, Al0.5CoFeNiCr0.5 and Al0.6CoFeNiCr0.4). With the molar ratio of Al/Cr further increase, The microstructures of the BCC-dominated of HEAs transform from the FCC + BCC/B2 phase (Al0.7CoFeNiCr0.3 and Al0.8CoFeNiCr0.2) to FCC + BCC (Al0.9CoFeNiCr0.1) phase, and then to a single BCC structure (Al1.0CoFeNiCr0). The hardness and compression tests analysis reveals that suitable Al/Cr ratio addition to AlxCoFeNiCr1−x HEAs can improve the comprehensive mechanical properties before reaching the highest point at the Al0.8CoFeNiCr0.2 HEAs, while excessive Al/Cr ratio addition will completely sacrifice plasticity, such as Al0.9CoFeNiCr0.1 and Al1.0CoFeNiCr0 HEAs. Moreover, the different Al/Cr molar ratio of the AlxCoFeNiCr1−x HEAs on corrosion resistance were discussed. The results showed that, in the single-FCC phase, the corrosion resistance of Al0.1CoFeNiCr0.9, Al0.2CoFeNiCr0.8 and Al0.3CoFeNiCr0.7 HEA have gradually decreases, while, in a dual phase of AlxCoFeNiCr1−x HEAs, the tendency of corrosion resistance is consistent with the volume fraction of segregation phase. The less the volume fraction of segregation phase of alloys have, the larger the corrosion resistance of it retain, such as Al0.4CoFeNiCr0.6 andAl0.9CoFeNiCr0.1. When the volume fraction of segregation phase is close to the matrix phase, it has the worst the corrosion resistance, like Al0.7CoFeNiCr0.3 HEAs.
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