Abstract Scope |
Functionally graded materials (FGMs) are innovative whose chemical composition and microstructure change gradually from side to the other side according to the design requirements, resulting in continuous or quasi-continuous gradient changes in physical and chemical properties. The double-wire arc additive manufacturing (D-WAAM) technology based on TIG welding can not only accurately control the composition due to few spatters, but also build component with few limitation on the size. It improves the utilization of materials and working efficiency. In the present work, a D-WAAM system was designed to manufacture FGMs with a smooth transition from 100 wt.% Inconel 625 to 100 wt. % stainless steel 308L, whose composition transition is in the torch-travelling direction. The microstructure, phase composition, microhardness, and tensile properties of the FGM were carefully examined with the change in position. With the increase in content of Inconel 625, the dendrites gradually became coarser and the secondary phase changed from Nb and Mo carbides to γ' phase. The microhardness showed a trend of decreasing first and then increasing, with the minimum 140 HV<sub>0.5</sub> at the position with Inconel 625 of 10 wt.%. The tensile strength in the building direction decrease first, with the minimum of 432 MPa which located in the position with Inconel 625 of 34 wt.%, and the increased significantly after the position with Inconel 625 of 50 wt.%, with the maximum of 624 MPa which located in the position with Inconel 625 of 100 wt.%; and the elongation presents an oscillating upward trend from 26% to 62%. The tensile strength in the torch-travelling direction was 492 MPa and the elongation was 17%. The fracture for the tensile test in the torch-travelling direction showed that it was the ductile fracture, and the fracture location was in the zone with Inconel 625 of 0-10 wt.% because of the stress concentration. The experimental results showed the FGMs prepared by D-WAAM in the torch-travelling direction was with smoother composition and performance transition, and provided greater flexibility for gradient path design. |