Effects of Mo element on microstructure , mechanical properties and corrosion behavior of Al0.3CrFeCoNiMox high-entropy alloys

In order to improve the mechanical properties and corrosion resistance of Al-Cr-Fe-Co-Ni system high-entropy alloys (HEAs), the effects of Mo on the microstructure, mechanical properties and corrosion behavior of the Al0.3CrFeCoNiMox (x=0. 2, 0. 4, 0. 6, 0. 8, molar ratio, the same below) HEAs were studied. The results show that the microstructures of the HEAs evolve from the FCC phase (x=0. 2) to the FCC+ sigma phases (x=0. 4-0. 8) with the increase of Mo content. The compressive yield strength and hardness of the HEAs are enhanced from 304 MPa and 214HV (x=0. 2) to 1192 MPa and 513HV (x=0. 8), respectively, while the plastic strain decreases from >50% to 5. 2%, mainly due to the solution strengthening and the increase in sigma phase of the alloys. Among the present alloys system, the Al0.3CrFeCoNiMo0.4 and Al0.3CrFeCoNiMo0.6 alloys show relatively high yield strength (571-776 MPa) combined with good plasticity (plastic strain of 10. 3%-23. 8%). In 3. 5% (mass fraction) NaCl solution, the Al0.3CrFeCoNiMox HEAs are spontaneously passivated and exhibited low corrosion rates of 3. 6X10(-4)-5. 9X 10(-4) mm/a, and the addition of Mo effectively suppresses pitting corrosion. The corrosion resistance of the Al0.3CrFeCoNiMox HEAs could be improved with the increase of Mo content, which is related to the increment in the electrochemical impedance and the thicknesses of the passive films on the alloys. Appropriate addition of Mo to the Al-Cr-Fe-Co-Ni system HEAs can lead to a combination of good mechanical properties and corrosion resistance.