Fabrication and characterization of stainless steel 308 L / Inconel 625 functionally graded material with continuous change in composition by dual-wire arc additive manufacturing

Abstract

Additive manufacturing (AM) technology can fabricate functionally graded materials (FGMs) with a layered gradient change in chemical composition and microstructure by changing the composition ratio of different filler materials layer by layer, which indeed have uneven and uncontrolled composition gradients between layers. In the present work, FGMs of stainless steel 308 L and Inconel 625, with continuous change in composition, were fabricated by dual-wire arc additive manufacturing (D-WAAM) by changing the speeds of dual wires in each single layer. The chemical composition, microstructure, phases, and mechanical properties of the FGM were investigated. The results showed that the composition gradient was smoothly distributed along the torch-travelling direction in each single layer, and the composition at the same position along the building direction was stable. With the increase in the content of Inconel 625, the austenite dendrites, which was the main microstructure, became finer first and then coarser, but there was no apparent abrupt change in microstructure in the gradient zone, which made the mechanical properties also show a smooth change. The mechanical properties were weak when the content of Inconel 625 was within 10–50 wt% due to the secondary phases (MC, Laves) distributed at the grain boundary. The proposed fabrication approach of FGM also showed advantages and flexibility in the design of gradient path, or the design of structure size if there is a requirement on the size in the building direction.