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Wire and arc additive manufacturing (WAAM) is a promising technology for the preparation of refractory metal functional gradient materials (FGMs) due to its high material utilization, high deposition efficiency and ability to create large-sized parts. In the present work, 316L/IN625 FGM with chemical composition gradients of 25 wt% and 100 wt% were fabricated using dual-wire plasma arc additive manufacturing (DW-PAAM) by changing the wire feeding speeds (WFSs) layer by layer. The phase evolution, microstructure, chemical composition and mechanical properties of the FGM were analyzed. The results demonstrated that the microstructure in all regions was predominantly the austenite phase, and no cracks or defects were observed. The microstructure of the 100 wt% 316L zone was composed of the austenite phase (face-centered cubic, FCC) and a small amount of ferrite phase (body-centered cubic, BCC), whereas mainly FCC structure was observed in the other chemical composition regions. There was a certain error between the actual composition gradient and the designed gradient. The microhardness transition of S1 was smoother and wider, while the tensile test results of S2 were better. In addition, the position of the tensile fracture was different for S1 and S2. In conclusion, the DW-PAAM process shows great potential for manufacturing FGM with desirable properties for various industrial applications. Further studies are warranted to optimize process parameters and develop new design strategies to enhance the performance of FGM in various industrial applications. • 316L/IN625 FGM with composition gradients of 25 wt% and 100 wt% were prepared by the DW-PAAM process. • The microstructure in all regions was predominantly the FCC structure, no cracks or defects were observed. • A certain error existed between the chemical composition curve of the actual gradient and the design gradient. • Sample S1 has the lowest microhardness and tensile strength in the zone of 75 wt% 316L. [ABSTRACT FROM AUTHOR]

Powder plasma arc additive manufacturing (PPA-AM) is a promising method for fabricating high-entropy alloys (HEAs). However, the characteristics of thermal cycling during the PPA-AM process and the mechanism of subsequent heat treatment on the microstructure and mechanical properties are unclear. In this study, an Al 1.2 CoCrFeNi 2.1 HEA with dual-phase (FCC + B2) was fabricated via PPA-AM. The microstructure and mechanical properties of the as-built and heat-treated samples were explored. The crystallographic orientations of the FCC and B2 phases were also determined. Because the alloy in the bottom region was affected by thermal cycling, B2 particles precipitated in the FCC phase, and FCC particles precipitated in the B2 phase. During the tensile test, the phase boundary between B2 matrix and FCC particles produced cracks preferentially. These cracks reduced the strength and elongation of the alloy. After heat treatment at 1200 °C, the FCC and B2 precipitates formed globular shapes inside the B2 and FCC grain matrix, respectively. The alloy showed a uniform structure and the ductility of the alloy was improved significantly. This work elucidates the mechanisms of thermal cycling and heat treatment on the microstructure and mechanical properties of the alloy. [ABSTRACT FROM AUTHOR]