Residual stresses and heat treatments of Inconel 718 parts manufactured via metal laser beam powder bed fusion: an overview

Additive manufacturing (AM) is a unique manufacturing process that disrupted completely the way which components are made, since this process is capable of producing complex parts layer after layer. As a matter of fact, one of its distinct technologies is metal laser beam powder bed fusion (mLB-PBF), also known as selective laser melting (SLM) or direct metal laser sintering (DMLS), which creates metallic parts with the aid of a high-energy laser beam. One of the most employed superalloys in this technology is the Inconel 718 (IN718), a precipitation-hardened alloy that is used in the marine, nuclear power plants, gas turbines, and aerospace field due to its capacity of retaining good mechanical properties at high temperatures. The research novelty of this review manuscript is the compilation of all kinds of information from the last 15 years of investigation about IN718 parts produced via mLB-PBF, namely, information related to distinct heat treatments and the influence they have in increasing mechanical properties of the manufactured components, as well as reducing residual stresses (RS) and part porosity. Throughout the review, it can be seen that the expected microstructure in the as-built state is characterized by fine columnar grains and a saturated γ matrix with the presence of the Laves phase and carbides. However, distinct heat treatments can be employed which lead to the dissolution of the undesired phases (Laves and carbides), the precipitation of the strengthening phases (γ’ and γ”), and the porosity decrease. Furthermore, it was also shown that heat treatments as well as optimized process parameters can be held accountable for lowering the RS of the IN718 manufactured parts. Nevertheless, there are still some problems to overcome, namely, the mechanical properties variability when subjecting IN718 powder to different process parameters. Moreover, the RS evolution under different heat treatments needs to be further investigated.