Variation of BCC/B2 coherent microstructure and resultant improvement in strength of Al0.7CrxFe3_xCoNi high-entropy alloys

The effects of Cr and Fe contents on the microstructure and mechanical properties of B2 nanoparticle-enhanced BCC-based Al0.7CrxFe3_xCoNi (x = 1.5-3.0) high-entropy alloys (HEAs) were studied. It was indicated that the addition of Cr and reduction of Fe in the alloys can increase the lattice misfits between the BCC and B2 phases, inducing the variations of BCC/B2 coherent microstructure and the significant improvements of the compressive yield strengths from 1485 MPa to 2252 MPa. The calculations of the yield strengths based on the microstructure of the alloys suggested that the improvements of the strengths were mainly due to the enhancements of the precipitation-strengthening effects. The interactions between dislocations and B2 particles with various shapes and sizes were also discussed on the basis of the calculations. It is demonstrated that adjusting the contents of Cr and Fe is an effective way to control BCC/B2 coherent microstructure and improve the mechanical properties of Al-Cr-Fe-Co-Ni HEAs.