Microstructure evolution and mechanical properties improvement of Ni0.6CoFe1.4Nb0.05 medium-entropy alloys via addition of Al

The influence of Al additions on the phase composition, microstructural evolution, and mechanical properties of AlxNi0.6CoFe1.4Nb0.05 medium-entropy alloys (MEAs) was investigated in this work. The results showed that AlxNi0.6CoFe1.4Nb0.05 (x = 0, 0.1, 0.2, and 0.3, in molar ratio) MEAs exhibited a typical cellular substructure, where the main phase was body-centered cubic structure and the intermetallic compound with face-centered cubic structure distributed at cellular boundary. The mechanical results showed that both the hardness and the ultimate tensile strength (sigma(UTS)) increased along with the increase of Al content. The hardness and sigma(UTS) of Al0.3Ni0.6CoFe1.4Nb0.05 MEA were about 108% and 83% higher than those of the Ni0.6CoFe1.4Nb0.05 MEA, respectively. The enhancement of mechanical properties of AlxNi0.6CoFe1.4Nb0.05 MEAs was ascribed to the increase of Al content that aggravated distortion of the crystalline lattice and enhanced the dispersion strengthening.