Phase evolution and mechanical properties of AlxCoCrFeNi high-entropy alloys by directed energy deposition

Directed energy deposition (DED), as an important branch of additive manufacturing (AM), has been widely used in the design and fabrication of high-entropy alloys (HEAs). Al is a common alloying element, it is critical to understand the effect of Al content on the phase evolution and mechanical properties of AlxCoCrFeNi HEAs. Here, a series of AlxCoCrFeNi (x = 0.2, 0.6 and 1.0) HEAs were manufactured by DED to investigate the alloying effect of Al on the phase evolution and mechanical properties. The phase transformation process was explored in conjunction with thermodynamic calculations. The results showed that the AlxCoCrFeNi HEAs transformed from single FCC phase (Al0.2) to FCC + BCC duplex phases (Al0.6), and then to single BCC phase (Al1.0) with the increase of Al content. Moreover, BCC phase further decomposed into the nanoscale two-phase structure containing ordered B2 phase and disordered A2 phase, which is beneficial to improve microhardness, yield strength and tensile strength. This work provides useful guidelines for the preparation and research of HEA systems with desirable properties.