On the influence of heat treatment on microstructure and mechanical behavior of laser powder bed fused Inconel 718

Schröder, Jakob; Mishurova, Tatiana; Fritsch, Tobias; Serrano-Muñoz, Itziar; Evans, Alexander; Sprengel, Maximilian; Klaus, Manuela; Genzel, Christoph; Schneider, Judith; Bruno, Giovanni

doi:10.1016/j.msea.2020.140555

Cited by 40 publications

(23 citation statements)

References 71 publications

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“…The explanation for the use of the Reuβ model can be found in other studies. [ 35,36 ] The occurrence of shear stresses (measured only at some reference points) was observed to be negligible. [ 15 ] As advised in the ISO standard 21432, the Ni‐311 reflection was chosen based on it exhibiting low intergranular stress accumulation.…”

Section: Methodsmentioning

confidence: 99%

“…For example, it has been observed that the elastic diffraction constants (DEC, which relates the measured lattice spacing to the macroscopic stress state) calculated by the Reuβ model (as opposed to the conventionally used Kröner model) are more suited for the RS analysis of textured LPBF IN718 microstructures. [ 35,36 ] This counterintuitive result has a very practical impact, as the correct determination of the bulk RS state is also necessary in the validation of computational models of the AM process. Further, the choice of the unstressed reference lattice parameter,

d_{0}

, has proven to be of paramount importance (as for any material), but even more challenging for AM materials.…”

Section: Introductionmentioning

confidence: 99%

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Scanning Manufacturing Parameters Determining the Residual Stress State in LPBF IN718 Small Parts

et al. 2021

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The influence of scan strategy on the residual stress (RS) state of an as-built IN718 alloy produced by means of laser powder bed fusion (LPBF) is investigated. Two scan vector rotations (90 -alternation and 67 -rotation), each produced following two different scan vector lengths (long and short), are used to manufacture four rectangular prisms. Neutron diffraction (ND) and laboratory X-ray diffraction (XRD) techniques are used to map the bulk and surface RS state, respectively. The distortion induced upon removal from the baseplate is measured via profilometry. XRD measurements show that the two long scan vector strategies lead to higher RS when compared with the equivalent short scan vector strategies. Also, the 67 -rotation strategies generate lower RS than their 90 -alternation counterparts. Due to the lack of reliable stress-free d 0 references, the ND results are analyzed using von Mises stress. In general, ND results show significant RS spatial non-uniformity. A comparison between ND and distortion results indicates that the RS component parallel to the building direction (Z-axis) has a predominant role in the Z-displacement. The use of a stress balance scheme allows to discuss the d 0 variability along the length of the specimens, as well as examine the absolute RS state.

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Section: Methodsmentioning

confidence: 99%

d_{0}

, has proven to be of paramount importance (as for any material), but even more challenging for AM materials.…”

Section: Introductionmentioning

confidence: 99%

Scanning Manufacturing Parameters Determining the Residual Stress State in LPBF IN718 Small Parts

et al. 2021

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“…The microstructure consists of face-centered cubic (FCC) supersaturated solution matrix strengthened by ′-Ni3(Nb,Ti,Al) and ″-Ni3Nb. Other undesired phases such as laves phases, δ phases, carbides (Cx), and nitrides (TiN) could be found in their microstructure in the as-built and heat-treated conditions [2,[10][11][12]. The strengthening effect of this alloy is given by the precipitation of ′ and ″ phases.…”

Section: Introductionmentioning

confidence: 99%

“…These phases precipitate from the supersaturated solid solution during the double aging stage heat treatment, ′ in the range of 621 °C to 649 °C, and ″ in the range of 718 °C to 760 °C. The effectiveness of the double aging depends on the Nb concentration and its distribution in the matrix, on the Al/Ti ratio [11] to optimize the mechanical properties, and the relationship between them. Their morphology must be taken into account independent of the manufacturing route of the IN718 alloy [11].…”

Section: Introductionmentioning

confidence: 99%

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Analysis of Microstructure and Mechanical Properties in As-Built/As-Cast and Heat-Treated Conditions for IN718 Alloy Obtained by Selective Laser Melting and Investment Casting Processes

et al. 2021

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In this work, new customized heat treatments for selective laser melted (SLM) parts in IN718 alloy were analyzed. This was done through the evaluation of the mechanical properties and advanced characterization of the phases and microstructure obtained in as-built condition and after the application of standard and tailored heat treatments. The microstructure and mechanical properties were compared and discussed with results reported in the literature. Finally, strengthening mechanisms of IN718 alloy processed by SLM and its differences with mechanisms that occur in investment casting were analyzed. Both processes generate quite different microstructures, investment casting is composed mainly by a dendritic structure, and SLM is characterized by columnar and cellular structures with very thin cells. Due to the fine and homogeneous microstructure obtained from SLM processing and its specific strengthening mechanisms, it is not necessary to apply homogenization and solution stages as in standard heat treatment used for this type of alloy in casting or wrought. The pre-heating and process parameters selected, in combination with a direct stepped aging (at 720 °C/620 °C), provide the material with its best mechanical properties, which are superior to those obtained by standard heat treatment (AMS 5383F) applied to investment casting of IN718 alloy.

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A Novel Approach to Robustly Determine Residual Stress in Additively Manufactured Microstructures Using Synchrotron Radiation

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Introduction 1.1. Microstructure of Additively Manufactured MaterialsAdditive manufacturing (AM) is the subject of many recent publications. [1][2][3] Typical representatives of AM methods for the processing of metallic metals are mainly divided into three categories: wire feeding, powder feeding, and powder bed fusion systems. [3] The latter technique enables the production of metallic structures by layer-wise melting of a thin metal powder bed only using AM equipment and a sliced model generated by a computeraided design (CAD) program. The application of a powder bed in powder-based AM technology facilitates the selective processing of individual layers in complex geometry. The most commonly used powder bed fusion techniques are selective electron beam powder bed fusion (EPBF) and laser powder bed fusion (LPBF). [3,4] EPBF structures are produced in a vacuum atmosphere and at a high temperature, eventually leading to a relatively low residual stress level. In contrast, LPBF processes usually take place at temperatures up to 200 C. The localized energy input and the small melt pool sizes, respectively, in combination with low build chamber temperatures result in high temperature gradients, whereby residual stresses are favored. [5] Generally, the influence of scan vectors and related strategies is a complex topic, which crucially has to be dealt with. Scan vector lengths, orientations, the order of rotation within a specific layer, and its subsequent layers are variables in every building process. Only a very limited number of comprehensive studies have reported on the effect of the scan strategy on the density, microstructure, mechanical properties, and residual stresses of LPBF parts, as clearly stated in previous studies. [5][6][7][8] Already an increased scan path length, e.g., due to a change of cross-section of a part, can result in a severely decreased relative density as well as fundamentally changed microstructure. [9,10] The influence of parameters on the evolution of residual stresses was already numerously studied. [11,12] The authors showed that the residual stresses are mainly influenced by cooling rates, temperature gradients, and melt pool sizes. Also, a minimization of the temperature gradient by powder bed preheating is an option to reduce process-induced stresses. [1,13] The high influence of the laser power and the effect of scan strategies have been characterized.

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On the influence of heat treatment on microstructure and mechanical behavior of laser powder bed fused Inconel 718

Cited by 40 publications

References 71 publications

Scanning Manufacturing Parameters Determining the Residual Stress State in LPBF IN718 Small Parts

Scanning Manufacturing Parameters Determining the Residual Stress State in LPBF IN718 Small Parts

Analysis of Microstructure and Mechanical Properties in As-Built/As-Cast and Heat-Treated Conditions for IN718 Alloy Obtained by Selective Laser Melting and Investment Casting Processes

A Novel Approach to Robustly Determine Residual Stress in Additively Manufactured Microstructures Using Synchrotron Radiation

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