Triple-wire plasma-arc additive manufacturing of Alx-Cr-Fe-Ni medium-entropy alloys: Microstructure and mechanical properties

High/medium-entropy alloys (HEAs/MEAs) have received significant attention in materials science and engineering owing to their attractive properties. However, their applications are hindered because the production of MEA components is costly and inefficient. In this study, triple-wire plasma arc additive manufacturing (TW-PAAM) method was used to prepare MEAs. Non-equiatomic Alx-Cr-Fe-Ni MEAs (where x is the feeding speed of Al wire) were prepared using three commercial wires (ER1070, ER304L, and Ni80Cr20 wire). The inclusion of the Al element can lead to solid-solution strengthening and phase transformation of the alloy structure, thereby enhancing the strength of the alloys. Three different alloys (x = 0, 0.5 and 1.0 m/min) were chosen for the study, and the corresponding samples were labeled as Al0, Al0.5, and Al1.0. As the feeding speed of the Al wire increased, the structure of the MEAs progressively changed from single-phase FCC to FCC + BCC/B2 and finally to single-phase BCC/B2. MEAs with a higher Al content displayed a higher microhardness and yield strength owing to solid-solution strengthening and the formation of the BCC/B2 phase. Among all the alloys, Al0 exhibited excellent ductility (~48%), with a yield strength of 216 MPa and ultimate tensile strength of 464 MPa. Al1.0 had the highest yield strength (761 MPa) and lowest elongation (0.7%). Further, the Al0.5 alloy exhibited a good combination of strength (855 MPa) and elongation (10%).