Phase formation and mechanical properties of Al1.2CoxCrFeNi high entropy alloys

Abstract

To obtain Al-Co-Cr-Fe-Ni high entropy alloys (HEAs) with high strength and high ductility, Al1.2CoxCrFeNi(x=1, 1.6, 2.2, 2.8) HEAs were successfully prepared by arc melting method and its microstructure and mechanical properties were systematically studied. The results show that in Al1.2CoxCrFeNi alloy, Co element can induce the transformation from BCC to FCC phase. With the increase of the atomic ratio of Co from 1 to 2.8, the volume fraction of FCC phase increases from 0% to 59%, and the volume fraction of BCC phase decreases from 100% to 41%. The results of compression experiment show that the addition of Co plays an important role in improving the plasticity of Al1.2CoxCrFeNi high entropy alloys but has no obvious effect on the strength of the high entropy alloys. With the increase of Co content, the fracture strain of Al1.2CoxCrFeNi HEAs increases from 16.9% to 30%. The ultimate compressive strength decreases from 2128 MPa to 1913 MPa, and the maximum compressive strength is 2361 MPa, and the average hardness decreases from 513.7HV to 323.4HV. The increase of Co content decreases the atomic size difference of the alloys, which weakens the lattice distortion effect and solid solution strengthening effect caused by the large atomic radius of Al element. At the same time, the increase of Co content also increases the valence electron concentration (VEC) of the alloys. The changes of the above two parameters are the main factors for the increase of FCC phase volume fraction in the alloy. The increase of the volume fraction of FCC phase is the main reason for the improvement of the plasticity of the alloy.

Keywords

• high entropy alloy
• phase transition
• microstructure
• mechanical property
• atomic size difference
• valence electron concentration