Optimization of the Post-Process Heat Treatment of Inconel 718 Superalloy Fabricated by Laser Powder Bed Fusion Process

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.

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Performance Characterization of Laser Powder Bed Fusion Fabricated Inconel 718 Treated with Experimental Hot Isostatic Processing Cycles

Journal of Manufacturing and Materials Processing ◽

10.3390/jmmp4030073 ◽

2020 ◽

Vol 4 (3) ◽

pp. 73 ◽

Cited By ~ 1

Author(s):

Jaime Varela ◽

Jorge Merino ◽

Christina Pickett ◽

Ahmad Abu-Issa ◽

Edel Arrieta ◽

...

Keyword(s):

Grain Boundaries ◽

Yield Stress ◽

Inconel 718 ◽

Solution Treatment ◽

Stress Relief ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Post Process ◽

Process Heat

Inconel 718 alloy fabricated by selective laser melting (SLM) (or laser powder-bed fusion (LPBF)) has been post-process heat-treated by stress-relief anneal at 1065 °C; stress-relief anneal (1065 °C) + solution treatment (at 720 °C) + aging (at 620 °C); hot isostatic pressing (HIP) (at 1120–1200 °C); stress-relief anneal + HIP; and stress-relief anneal + HIP + solution treatment + aging. Microstructure analysis utilizing optical metallography revealed primarily equiaxed grain structures (having average diameters ranging from ~30 to 49 microns) containing annealing twins, and a high concentration of carbide precipitates in all HIP-related treatments in the grain boundaries and intragrain regions. However, no precipitates nucleated on the {111} coherent annealing twin boundaries because of their very low interfacial free energy in contrast to regular grain boundaries. The mechanical properties for the as-fabricated Inconel 718 exhibited a yield stress of 0.64 GPa, UTS of 0.98 GPa, and elongation of 26%. Following stress-relief anneal at 1065 °C, the yield stress dropped to 0.60 GPa, while the elongation increased to 43%. The associated grain structure was an irregular, somewhat elongated, recrystallized structure. This structure was preserved at a stress anneal at 1065 °C + solution treatment + aging, but grain boundary and intragrain precipitation resulted in a doubling of the yield stress to 1.3 GPa and a reduced elongation of 12.6%. The results of HIP-related post-process heat treatments involving temperatures above 1060 °C demonstrated that the yield stress and elongations could be varied from 1.07 to 1.17 GPa and 11.4% to 19%, respectively. Corresponding Rockwell C-scale hardness values also varied from 33 for the as-fabricated Inconel 718 to 53 for simple post-process HIP treatment at 1163 °C.

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Microstructure and Residual Stress Evolution of Laser Powder Bed Fused Inconel 718 under Heat Treatments

Journal of Materials Engineering and Performance ◽

10.1007/s11665-020-05338-z ◽

2020 ◽

Author(s):

Giulio Marchese ◽

Eleonora Atzeni ◽

Alessandro Salmi ◽

Sara Biamino

Keyword(s):

Residual Stresses ◽

Inconel 718 ◽

Heat Treatments ◽

Powder Bed Fusion ◽

Stress Evolution ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Melt Pool ◽

Sintering Mechanisms ◽

Dendritic Structures

AbstractThe current work aimed to study the influence of various heat treatments on the microstructure, hardness, and residual stresses of Inconel 718 processed by laser powder bed fusion process. The reduction in residual stresses is crucial to avoid the deformation of the component during its removal from the building platform. Among the different heat treatments, 800 °C kept almost unaltered the original microstructure, reducing the residual stresses. Heat treatments at 900, 980, and 1065 °C gradually triggered the melt pool and dendritic structures dissolution, drastically reducing the residual stresses. Heat treatments at 900 and 980 °C involved the formation of δ phases, whereas 1065 °C generated carbides. These heat treatments were also performed on components with narrow internal channels revealing that heat treatments up to 900 °C did not trigger sintering mechanisms allowing to remove the powder from the inner channels.

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Short Heat Treatments for the F357 Aluminum Alloy Processed by Laser Powder Bed Fusion

Materials ◽

10.3390/ma14206157 ◽

2021 ◽

Vol 14 (20) ◽

pp. 6157

Author(s):

Matteo Vanzetti ◽

Enrico Virgillito ◽

Alberta Aversa ◽

Diego Manfredi ◽

Federica Bondioli ◽

...

Keyword(s):

Heat Treatment ◽

Precipitation Hardening ◽

Solution Treatment ◽

Heat Treatments ◽

Point Of View ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Heat Treated ◽

Direct Aging

Conventionally processed precipitation hardening aluminum alloys are generally treated with T6 heat treatments which are time-consuming and generally optimized for conventionally processed microstructures. Alternatively, parts produced by laser powder bed fusion (L-PBF) are characterized by unique microstructures made of very fine and metastable phases. These peculiar features require specifically optimized heat treatments. This work evaluates the effects of a short T6 heat treatment on L-PBF AlSi7Mg samples. The samples underwent a solution step of 15 min at 540 °C followed by water quenching and subsequently by an artificial aging at 170 °C for 2–8 h. The heat treated samples were characterized from a microstructural and mechanical point of view and compared with both as-built and direct aging (DA) treated samples. The results show that a 15 min solution treatment at 540 °C allows the dissolution of the very fine phases obtained during the L-PBF process; the subsequent heat treatment at 170 °C for 6 h makes it possible to obtain slightly lower tensile properties compared to those of the standard T6. With respect to the DA samples, higher elongation was achieved. These results show that this heat treatment can be of great benefit for the industry.

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Creep-rupture Performance of a Recrystallizing Solution Treatment for Inconel 718 Fabricated by Laser Powder-bed Fusion

AIAA Scitech 2020 Forum ◽

10.2514/6.2020-1123 ◽

2020 ◽

Author(s):

David Newell ◽

Anthony N. Palazotto ◽

Ryan P. O'Hara

Keyword(s):

Inconel 718 ◽

Solution Treatment ◽

Creep Rupture ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed

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Knowledge of process-structure-property relationships to engineer better heat treatments for laser powder bed fusion additive manufactured Inconel 718

Additive Manufacturing ◽

10.1016/j.addma.2019.100977 ◽

2020 ◽

Vol 31 ◽

pp. 100977 ◽

Cited By ~ 8

Author(s):

Thomas G. Gallmeyer ◽

Senthamilaruvi Moorthy ◽

Branden B. Kappes ◽

Michael J. Mills ◽

Behnam Amin-Ahmadi ◽

...

Keyword(s):

Inconel 718 ◽

Heat Treatments ◽

Powder Bed Fusion ◽

Structure Property ◽

Laser Powder Bed Fusion ◽

Powder Bed ◽

Structure Property Relationships ◽

Process Structure

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Effect of homogenization and solution treatments time on the elevated-temperature mechanical behavior of Inconel 718 fabricated by laser powder bed fusion

Scientific Reports ◽

10.1038/s41598-021-81618-5 ◽

2021 ◽

Vol 11 (1) ◽

Author(s):

Eslam M. Fayed ◽

Mohammad Saadati ◽

Davood Shahriari ◽

Vladimir Brailovski ◽

Mohammad Jahazi ◽

...

Keyword(s):

Mechanical Properties ◽

Heat Treatment ◽

Elevated Temperature ◽

Mechanical Behavior ◽

Inconel 718 ◽

Treatment Time ◽

Solution Treatment ◽

Powder Bed Fusion ◽

Laser Powder Bed Fusion ◽

Powder Bed

AbstractIn the present study, the effect of homogenization and solution treatment times on the elevated-temperature (650 °C) mechanical properties and the fracture mechanisms of Inconel 718 (IN718) superalloy fabricated by laser powder bed fusion (LPBF) was investigated. Homogenization times between 1 and 7 h at 1080 °C were used, while solution treatments at 980 °C were performed in the range from 15 to 60 min. The as-printed condition showed the lowest strength but the highest elongation to failure at 650 °C, compared to the heat-treated conditions. After heat treatments, the strength of the IN718 alloy increased by 20.3–31% in relation to the as-printed condition, depending on the treatment time, whereas the ductility decreased significantly, by 67.4–80%. Among the heat treatment conditions, the 1 h homogenized conditions at 1080 °C (HSA1 and HSA2) exhibited the highest strength and ductility due to the combined effects of the precipitation hardening and sub-structural changes. Further increases in the homogenization time to 4 and 7 h led to a decrease in the strength and significant ductility loss of the LPBF IN718 due to the considerable annihilation of the dislocation tangles and a greater precipitation of coarse MC carbide particles. Furthermore, it was found that the solution treatment duration had a crucial influence on the mechanical properties at 650 °C due to the increase in the grain boundary strength through the pinning effect of the intergranular δ-phase. In addition, the fracture mechanism of the LPBF IN718 was found to be dependent on the heat treatment time. Finally, this investigation provides a map that summarizes the effect of homogenization and solution treatment times on the high-temperature mechanical behavior of LPBF IN718 by relating it to the corresponding microstructural evolution. This effort strives to assist in tailoring the mechanical properties of LPBF IN718 based on the design requirements for some specific applications.

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