Dual wire arc additive manufacturing of compositionally graded Al -Co-Cr-Fe-Ni high-entropy alloy

Graded materials are promising alloys due to their improved strength and ductility. In this study, a functionally graded Alx-Co-Cr-Fe-Ni high entropy alloy with a variation of Al concentration along the building direction was produced in-situ by dual wire arc additive manufacturing for the first time, and the microstructure and mechanical properties of the deposited alloy were investigated. The results showed that the FCC + BCC dual-phase gradually transformed to a single BCC phase with increasing Al content, the precipitation temperature of the ordered B2 phase became high, and the precipitation temperature range of the disordered BCC phase became wider, which promoted the formation of the disordered BCC phase. With the change in phase ratio, the hardness gradually increased from 342 HV to 397 HV, and the bottom deposited alloy had an optimal combination with a compressive strength of 827.4 MPa and elongation of 42.3%. Compared to the bottom region, the top region shows much higher sliding wear resistance. The high-density dislocations and grain refinement result in better toughness and strength in the bottom region, while the segregation of Cr elements at the grain boundaries changes the properties of the grain boundaries and makes them more brittle in the top region. This investigation realizes a novel method to fabricate GHEAs, which can produce a more convenient and cost-effective gradient material with a complex composition.