A Benchmark Between Conventional and Custom Heat Treaments for Inconel 718 Alloy Processed Through Cold Metal Transfer Technology

Inconel 718, one of the most employed nickel-based superalloys, proved to be efficiently processable through Wire-Arc Additive Manufacturing (WAAM), including Cold Metal Transfer Technology (CMT). Nevertheless, a multi-step heat treatment is still necessary to control the microstructure and the mechanical properties of this complex alloy. This work aimed to compare the effects on microstructure, tensile properties, Vickers microhardness and chemical composition of two heat treatments performed on Inconel 718 parts produced through CMT, namely: i) the heat treatment used for conventionally processed Inconel 718 parts, defined by the AMS5662 and AMS5663 standards; ii) a custom heat treatment that reduces the number of steps included in the previous case. The experiments were performed on prismatic CMT-produced parts, subsequently machined to extract the test specimens, considering both the aforementioned heat treatment conditions as well as the as-deposited material. The results suggested that comparable results were achieved for the selected heat treatments, however, a complete recrystallization of the fine grains never occurred for all the investigated conditions, thus retaining the typical microstructural anisotropy deriving from the CMT process. Moreover, the heat-treated parts showed, in any case, comparable properties to those of the conventionally cast alloy, opening a new scenario in the context of industrial production of semi-finished parts with huge costs and time savings.