Effect of B content on microstructure and mechanical properties of (Co 30 Cr 25 Fe 40 Ni 5 ) 100-x B x high-entropy alloys

(Co 30 Cr 25 Fe 40 Ni 5 ) 100-x B x ( x = 0, 1, 2, 4, 6, 8, 10 and 12 , x values in molar ratio) high-entropy alloys (HEAs) were prepared by vacuum arc melting, and the effect of B content on crystal structure, microstructure and mechanical properties of (Co 30 Cr 25 Fe 40 Ni 5 ) 100-x B x HEAs were systematically studied. In this present work, the results showed that Co 30 Cr 25 Fe 40 Ni 5 HEA was mainly composed of FCC and BCC solid solutions. With the addition of B element, the microstructure of the studied alloy first changed to hypoeutectic microstructure ( x = 1, 2, 4, 6 and 8), then to fully eutectic microstructure with a mixture of FCC, BCC and boride phases ( x = 10), and finally to hypereutectic microstructure ( x = 12). With the increased of B content, the hardness of (Co 30 Cr 25 Fe 40 Ni 5 ) 100-x B x HEAs show overall upward trend; The strength firstly increases and then decreases. The strengthening and toughening mechanisms of the studied alloys were second phase strengthening, fine grain strengthening and solid solution strengthening. Graphical abstract