Enhancing hardness of Inconel 718 deposits using the aging effects of cold metal transfer-based additive manufacturing

Abstract

The effects of successive deposition using continuous heat from a plasma arc on a multi-layer Inconel 718 deposit was investigated using a wire-arc additive manufacturing (WAAM) process with cold metal transfer (CMT). Deposits consisting of 10 layers were manufactured, where interpass time was the only process parameter varied. The shape of the deposits was determined by the interpass time, while microstructural characteristics (growth of dendrite, segregation of chemical component, formation of various phases, etc.) developed due to successive deposition. An aging effect was observed, which caused precipitation of the γ″ and γ′ strengthening phases and the δ phase. The highest hardness value was measured in the middle section of each deposit due to precipitation of the strengthening phases. The cooling rate was calculated using the thermal profile of the deposition process and was found to be slower using the CMT-based WAAM process than that of other additive manufacturing (AM) processes that use laser or electron beams. The results presented here also demonstrated that in-situ heat treatment during deposition is possible using this CMT-based WAAM approach.