Effects of Al addition on microstructure and mechanical properties of Co-free (Fe40Mn40Ni10Cr10)100−xAlx high-entropy alloys

Abstract The high-entropy alloys (Fe40Mn40Ni10Cr10)100-xAlx (x=0, 5, 8, 10, 15, 20) were obtained by vacuum arc melting. Their microstructure was characterized and the mechanical properties were tested. The Fe40Mn40Ni10Cr10 alloy exhibits a single face centered cubic (FCC) phase. Dual-phase microstructure with body centered cubic (BCC) phase distributing along FCC grain boundaries presents in the alloy with 5 at.% Al. Further addition of Al content results in the formation of triplex-phase microstructure consisting of FCC phase and coherent B2 nano-phase embedded in the BCC phase. At the Al content of 20 at. %, there are only the BCC and B2 phases in this alloy. The BCC/B2 lattice misfit increases sharply with the Al content, resulting in the transformation of B2 nano-phase morphologies from spherical to cuboidal, and ultimately to rod-like. Addition of Al significantly enhances the strength whilst deteriorates the plasticity. With the Al addition of 10 at. %, the alloy exhibits a high strength of 841 MPa along with a ductility of 25%.