Abstract
In the present study, multi-objective optimization is employed to develop the optimum heat treatments that can achieve both high-mechanical performance and non-distinctive crystallographic texture of 3D printed Inconel 718 (IN718) fabricated by laser powder bed fusion (LPBF). Heat treatments including homogenization at different soaking times (2, 2.5, 3, 3.5 and 4 h) at 1080 °C, followed by a 1 h solution treatment at 980 °C and the standard aging have been employed. 2.5 h is found to be the homogenization treatment threshold after which there is a depletion of hardening precipitate constituents (Nb and Ti) from the γ-matrix. However, a significant number of columnar grains with a high fraction (37.8%) of low-angle grain boundaries (LAGBs) have still been retained after the 2.5 h homogenization treatment. After a 4 h homogenization treatment, a fully recrystallized IN718 with a high fraction of annealing twins (87.1%) is obtained. 2.5 and 4 h homogenization treatments result in tensile properties exceeding those of the wrought IN718 at both RT and 650 °C. However, considering the texture requirements, it is found that the 4 h homogenization treatment offers the optimum treatment, which can be used to produce IN718 components offering a balanced combination of high mechanical properties and adequate microstructural isotropy.
Highlights
Inconel 718 (IN718) is the most widely nickel-based superalloy used in different industrial spheres such as the petrochemical, aeronautics, energy, and aerospace sectors [1,2].Thanks to its outstanding combination of superior strength, high creep performance, and high resistance to wear, oxidation and corrosion, even at cryogenic and elevated temperatures, IN718 is a suitable candidate for numerous applications
The soaking times for both the homogenization and solution treatments were defined as factors, whereas the TS, YS, El, HV and f values of the heattreated laser powder bed fusion (LPBF) IN718 were defined as responses
The degree of the material texture in the heat-treated conditions is defined by the intensity ratio f as reported in [27,28], which can be defined as: I(111)
Summary
Thanks to its outstanding combination of superior strength, high creep performance, and high resistance to wear, oxidation and corrosion, even at cryogenic and elevated temperatures (up to 650 ◦ C), IN718 is a suitable candidate for numerous applications. It is typically used in critical components subjected to aggressive environments in jet and gas turbine engines, nuclear plants and cryogenic tanks, which are produced using conventional manufacturing processes such as forging and casting [2]. The widespread use and implementation of this technique in some specific applications, that demand isotropic mechanical properties, are only just beginning due to the vertically
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