Fig 2
Grain microstructure and precipitates in IN738LC cast material (sample 3). Light optical image (a), SEM backscatter electron (BSE) image (b) and orientation map (c) using the standard IPF color key with respect to an arbitrary reference direction. Black line segments indicate traces of high angle grain boundary (defined by 4151 misorientation between neighbor pixels). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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Nickel-based IN738LC samples were built by selective laser melting (SLM). To evaluate the anisotropic mechanical behavior of IN738LC material due to layer-wise build up, specimens were built with their cylinder axis (loading direction) oriented either parallel to the building direction, or perpendicular to the building direction and at 45° to the l...
Contexts in source publication
Context 1
... the long axis (along the building direction) and about 0.1 mm in the shorter two axes (perpendicular to the building direction), which is much smaller than the grain size in cast material ranging between millimeter and centimeter. The grain and precipitate distribution in IN738LC cast material is characterized by an optical metallographic image ( Fig. 2a), a SEM BSE image (Fig. 2b) and an orientation map (Fig. 2c), all at the same scale with mm-sized field of ...
Context 2
... direction) and about 0.1 mm in the shorter two axes (perpendicular to the building direction), which is much smaller than the grain size in cast material ranging between millimeter and centimeter. The grain and precipitate distribution in IN738LC cast material is characterized by an optical metallographic image ( Fig. 2a), a SEM BSE image (Fig. 2b) and an orientation map (Fig. 2c), all at the same scale with mm-sized field of ...
Context 3
... mm in the shorter two axes (perpendicular to the building direction), which is much smaller than the grain size in cast material ranging between millimeter and centimeter. The grain and precipitate distribution in IN738LC cast material is characterized by an optical metallographic image ( Fig. 2a), a SEM BSE image (Fig. 2b) and an orientation map (Fig. 2c), all at the same scale with mm-sized field of ...
Context 4
... main reason for the inferior creep behavior of SLM specimens compared to cast material is most likely the significantly smaller grain size in SLM specimens, as shown by corresponding orientation maps (Figs. 2 and 4). Additional potential factors for differences in creep behavior are γ 0 precipitate size and morphology as well as decoration of grain boundaries with precipitates. ...
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... Due to its several properties which include but are not limited to microstructural stability, excellent creep properties and corrosion resistance at elevated temperatures, Inconel 738 has been commonly utilized in hot gas path component for high temperature combustion cycles in gas turbines and aerospace engine parts like blades, vanes, heat shields, etc. [3]. Other exceptional mechanical properties of Inconel 738 can include solid-solution strengthening and grain boundary strengthening [4][5]. Using the precipitation of coherent intermetallic c0 -phase with the Ni3(Al,Ti) basic composition and the L12 crystal structure, the precipitation strengthening is achieved [6]. Figure 1 represents a binary phase diagram for Ni-Al alloy system using ThermoCalc TM using TTNi7 database, similarly a multi-component system could be evaluated using thermodynamic modeling. ...
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... Moreover, due to the rapid heating and cooling during PBF-LB, the preferred grain orientation (PGO) of the 316L sample is concentrated in the middle of <001> and <101> orientations, while after the addition of the MF, the grain orientation tends to be more toward <101> and <111>. Compared to grain orientations in the <101> and <111> directions, when the grain orientation is concentrated in <001>, the mechanical performance of the material is typically poorer [56]. This further indicates that the application of the MF can enhance the mechanical properties of the samples. ...
The lightweight nature and superior mechanical properties of the triply periodic minimal surface (TPMS) structure have attracted considerable attention across various fields, including aerospace, automotive, and medicine. Currently, research on TPMS structures primarily focuses on optimizing macro-scale mechanical properties, with the limited investigation into macro/micro dual-scale optimization. This study introduces a novel nonlinear gradient TPMS structural design method, regulating the porosity of the TPMS structure through trigonometric functions, and designs Gyroid sin and Gyroid sin square structures. To fully tune the mechanical properties of the samples on both macro and micro scales, laser powder bed fusion (PBF-LB) and magnetic field (MF) were used to produce the structures. The effects of MF-assisted machining and annealing on the mechanical properties of Gyroid gradient structures were investigated by compression tests. The results show that the gradient specimens along the build direction have high energy absorption capacity and the gradient specimens perpendicular to the build direction have high elastic modulus. Annealing reduces the residual stresses and the MF refines the grains, which improve the mechanical properties of the structure. Additionally, after the addition of MF and subsequent annealing treatment, all structures show higher plateau stresses, and the energy absorption capacity of the structures along the gradient of the build direction is also improved.
... It is worth noting that during the LPBF process, the columnar grains growing along the build direction are significantly influenced by the direction of heat conduction. This unique growth mechanism enables the Cu-10Sn alloy to exhibit excellent properties in its microstructure [27][28][29]. ...
... It is worth noting that during the LPBF process, the columnar grains growing along the build direction are significantly influenced by the direction of heat conduction. This unique growth mechanism enables the Cu-10Sn alloy to exhibit excellent properties in its microstructure [27][28][29]. The columnar crystals form on the melt pool layer and grow epitaxially along the stacking direction. ...
This article focuses on investigating the effect of printing direction on the mechanical properties of Cu–10Sn alloys prepared by laser powder bed fusion (LPBF) technology. Specimens with different forming angles (0°, 15°, 30°, 45°, 60°, 75°, and 90°) were fabricated using LPBF technology, and their mechanical properties were systematically tested. During the testing process, we used an Instron 5985 electronic universal material testing machine to accurately evaluate the mechanical properties of the material at a constant strain rate of 10−3/s. The experimental results showed that the mechanical properties of the specimens were the best when the test direction was perpendicular to the growth direction (i.e., the 0° direction). As the angle between the test direction and the growth direction increased, the mechanical properties of the material exhibited a trend of first decreasing, then increasing, and then decreasing again, which was consistent with the direction of the microtexture of the specimens. The root cause of this trend lies in the significant change in the stress direction borne by the columnar crystals under different load directions. Specifically, as the load direction gradually transitions from being parallel to the columnar crystals to perpendicular to them, the stress direction of the columnar crystals also shifts from the radial direction to the axial direction. Due to the differences in the number and strength of grain boundaries in different stress directions, this directly leads to changes in mechanical properties. In particular, when the specimen is loaded in the radial direction of the columnar crystals, the grain boundary density is higher, and these grain boundaries provide greater resistance during dislocation migration, thus significantly hindering tensile deformation and enabling the material to exhibit superior tensile properties. Among all the tested angles, the laser powder bed fusion specimen with a forming angle of 0° exhibited the best mechanical properties, with a tensile strength of 723 MPa, a yield strength of 386 MPa, and an elongation of 33%. In contrast, the specimen with a forming angle of 90° performed the worst in terms of tensile properties. These findings provide important insights for us to deeply understand the mechanical properties of Cu–10Sn alloys prepared by LPBF.
... Furthermore, the mechanical properties of the AM Ni-based alloys are strongly influenced by these microstructure heterogeneities. Previous studies suggested that AM Ni-based alloys exhibit inferior creep behavior compared to their CM counterparts due to anisotropy [26], the presence of inter-metallic phases [27] and accelerated cavity nucleation kinetics [28][29][30], resulting from rapid solidification during LPBF as well as pronounced segregation [31] and the formation of fine-grained structures [25]. Davies et al. [36] observed that cast C-263 alloy displayed better creep resistance than AM C-263 due to a higher volume fraction of grain-boundary carbides. ...
... Davies et al. [36] observed that cast C-263 alloy displayed better creep resistance than AM C-263 due to a higher volume fraction of grain-boundary carbides. Kunze et al. [26] reported inferior creep properties of AM alloy 738LC compared to the cast alloy due to smaller grain size correlated to a higher fraction of more finely dispersed carbides in the LPBF-processed material. Furthermore, AM-specific heterogeneities have a significant influence on creep fracture modes. ...
... However, due to time-consuming experiments and long research cycles, there is limited literature on the creep properties of LPBF-processed Ni-based alloys [32]. Creep behavior has been investigated for LPBF-processed, common superalloys such as alloy 625 [33], alloy 718 [27], alloy 738LC [26,34], CM247LC [35], C-263 [36,37] and alloy X [38]. While creep behavior has been studied in conventional manufacturing of single-crystalline γ'-strengthened Ni-based alloys [39][40][41], for γ'-strengthened polycrystalline materials, the focus has primarily been on dislocation activity and interaction with γ' precipitates, lacking consideration of grain microstructures or heterogeneities in AM [42,43]. ...
... Anisotropy concentrates the mechanical properties of the material in a certain direction, while exhibiting poorer mechanical properties in other directions, making the material prone to phenomena such as stress concentration and local failure under external loads [46]. Furthermore, compared to <101> and <111>, when grain orientation is concentrated in <001>, it usually results in poorer mechanical properties [28,47,48]. Therefore, when KAM ave , grain size, and texture index are small, and the grain orientation is less concentrated in the <001> direction, the sample will exhibit better tensile properties. ...
The advantages of field-assisted laser additive manufacturing in optimizing microstructure and performance are increasingly recognized. Recently, we investigated the effects of acoustic field (AF) assisted laser powder bed fusion (LPBF) on the mechanical properties of 316L stainless steel (SS) and 316L SS/WC composite materials. Due to the effects of acoustic streaming and cavitation, acoustic field-assisted LPBF achieved optimized mechanical properties. Building on our previous research on AF-assisted LPBF, we introduced magnetic field (MF) and compound field (MF+AF) to study their effects on the microstructure and mechanical properties of 316L SS, 1 wt% and 3 wt% WC/316L SS. Application of the MF induces induced currents in the melt pool due to the Thomson-Seebek effect. The interaction between the MF and induced currents generates thermoelectric magnetic force (TEMF) and thermoelectric magnetic convection (TEMC), which inhibit the growth of columnar grains and enhance mass and heat transfer in the melt pool. Compound field-assisted LPBF reduced the dislocation density of 316L SS, refined grain size, alleviated the concentration distribution of grain orientation, and the ultimate tensile strength of the samples reached 777 MPa and the elongation at break reached 57.5%. Interestingly, for WC/316L SS, both MF and compound field resulted in a decrease in tensile performance, with ultimate tensile strengths as low as 677 MPa and elongations at break as low as 25.1%. This is because the MF affects the uniform distribution of WC particles, causing significant agglomeration and severe unmelted defects in the composite material, leading to a decrease in tensile performance.
... While the elongated grains are due to the strong temperature gradients, the low texture results from the alternating laser scanning pattern (67 • ), which assists with producing more homogeneous temperature fields and the subsequent heat treatment. The effect of laser scanning strategies and heat treatment on the AMed IN738LC's microstructure was previously studied [14,81] where a {001} -fiber texture and a cube texture were observed in the case of 67 • rotating scanning pattern and 90 • rotating scanning, respectively. The PBF-EB/M manufactured microstructure reported in [33] also exhibits a {001}-fiber texture in the BD. ...
The current lack of quantitative knowledge on processing-microstructure–property relationships is one of the major bottlenecks in today’s rapidly expanding field of additive manufacturing. This is centrally rooted in the nature of the processing, leading to complex microstructural features. Experimentally-guided modeling can offer reliable solutions for the safe application of additively manufactured materials. In this work, we combine a set of systematic experiments and modeling to address creep anisotropy and its correlation with microstructural characteristics in laser-based powder bed fusion (PBF-LB/M) additively manufactured Inconel-738LC (IN738LC). Three sample orientations (with the tensile axis parallel, perpendicular, and 45° tilted, relative to the building direction) are crept at 850 °C, accompanied by electron backscatter secondary diffraction (EBSD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations. A crystal plasticity (CP) model for Ni-base superalloys, capable of modeling different types of slip systems, is developed and combined with various polycrystalline representative volume elements (RVEs) built on the experimental measurements. Besides our experiments, we verify our modeling framework on electron beam powder bed fusion (PBF-EB/M) additively manufactured Inconel-738LC. The results of our simulations show that while the crystallographic texture alone cannot explain the observed creep anisotropy, the superlattice extrinsic stacking faults (SESF) and related microtwinning slip systems play major roles as active deformation mechanisms. We confirm this using TEM investigations, revealing evidence of SESFs in crept specimens. We also show that the elongated grain morphology can result in higher creep rates, especially in the specimens with a tilted tensile axis.
... This contributes to a stronger creep resistance but induces a higher susceptibility to cracks. Recent studies concluded that such defects such as voids and cracks can be eliminated by an appropriate printing strategy and post heat treatments, and thus mechanical properties have resulted superior than those from traditionally cast [4,9,[18][19][20]. However, L-PBFed IN738LC have showed a strong anisotropic behavior regardless of the testing temperature [9,18,21]. ...
... Recent studies concluded that such defects such as voids and cracks can be eliminated by an appropriate printing strategy and post heat treatments, and thus mechanical properties have resulted superior than those from traditionally cast [4,9,[18][19][20]. However, L-PBFed IN738LC have showed a strong anisotropic behavior regardless of the testing temperature [9,18,21]. The main factor for this anisotropy stems from the microstructure evolution due to the BD, which is similar to that from liquid metal cooling process [22]. ...
... The main factor for this anisotropy stems from the microstructure evolution due to the BD, which is similar to that from liquid metal cooling process [22]. The BD also plays a role at elevated temperature regarding creep and fatigue [9,23]. ...
... Laser powder bed fusion (LPBF) is one of the metal additive manufacturing technologies that produces metal parts by laser melting metal powders and repeatedly stacking them according to a 3D model [6,7]. Metal powders applied to LPBF include stainless steel [8][9][10], titaniumbased alloys [11,12], nickel-based alloys [13][14][15], and aluminum-based alloys [16,17]. ...
A new approach is proposed that identifies three different zones of the Si-rich network structure (the cellular structure) in laser powder bed fused (LPBF) AlSi10Mg alloy, based on the variation in morphology, grain growth transition, and melt pool solidification conditions. The three identified zones are denoted in the present work as the liquid solidification zone (LSZ), the mushy solidification zone (MSZ), and the heat affected zone (HAZ). The LSZ is the result of liquid–solid transformation, showing small planar growth at the boundary and large cellular growth in the center, while the MSZ is related to a semisolid reaction, and the HAZ arises from a short-time aging process. The boundary between the LSZ and MSZ is identified by the change of grain growth direction and the Si-rich network advancing direction. The boundary between MSZ and HAZ is identified by the start of the breakdown of the Si-rich network. In addition, it is found that the fracture is generated in and propagates along the HAZ during tensile tests.
... In existing research, it has been found that there are different variations of anisotropy between the plane perpendicular to the construction direction and the plane parallel to the construction direction in AM technology. Researchers attribute the anisotropy of mechanical properties to manufacturing defects [21], textures [15,18,[22][23][24][25], dislocations [15], and grain size and shape (columnar crystals) [26][27][28], among other factors. ...
Selective laser melting (SLM) forms specimens that often exhibit anisotropic mechanical properties. Most existing research only explains that the mechanical properties of specimens perpendicular to the build direction are superior to those parallel to the build direction. In this paper, the mechanical properties of SLM 316L SS specimens with different surfaces and different directions are compared. Finally, it was found that the mechanical properties of specimens on Face 3 are stronger than those on Face 1 and Face 2, while the mechanical properties of specimens on Face 1 and Face 2 are similar. For specimens in different directions on the same surface, the mechanical properties of Face 1 and Face 2 exhibit clear anisotropy, while the mechanical properties of Face 3 tend to be isotropic. In this paper, the EBSD technique was used to analyze the specimens. It was found that the anisotropy of the mechanical properties of Face 1 and Face 2 are attributed to the presence of texture and columnar crystals in the sample. This paper can provide accurate and reliable material performance data for the practical application of SLM 316L SS, thereby guiding the optimization of engineering design and manufacturing processes.
... The slightly elongated grain structure along the build direction has an almost random texture (Fig. 1c). The grain length along the BD (~30 µm) is more refined than in LPBF IN738 [35] and in EPBF IN738 printed via linear scan (~50 µm) [27]. This is due to the lower cooling rate and relatively more complex thermal profile during solidification compared to a linear scan. ...
Electron-beam powder bed fusion (EPBF) has been demonstrated to enable crack-free additive manufacturing of the traditionally non-weldable IN738 Ni-based superalloy. This is related to grain boundary (GB) segregation and precipitation phenomena during EPBF thermal cycling. We investigate such GB microstructures around typical interphase boundaries in IN738. Cyclic reheating results in γʹ dissolution, reprecipitation, and formation of layers enriched in refractory elements at γʹ-γʹ interfaces. Interfacial excess shows that >10 atomic layers of Cr and 3.5 of Co at the GB suppress the segregation of W, B, and C. GBs around heterogeneously nucleated γ grains are decorated with less Cr and Co. This is linked to microsegregation of carbide and boride-forming elements, facilitating diffusion of minor elements during cooling. A heterogeneous interfacial excess profile at a γʹ-γʹ interface is reported. These findings improve the current understanding of interphase boundaries and segregation in EPBF-manufactured IN738, possibly contributing to crack-free additive manufacturing. The Ni-based superalloy IN738 is widely used in modern gas turbines due to its excellent high-temperature strength [1,2]. It is considered a non-weldable alloy due to its high Ti and Al contents and a high-volume fraction of γ', which promote cracking [3,4]. This has made additive manufacturing (AM) of this alloy a challenge. 3D printing crack-free parts requires careful control of the solidification conditions and microstructure evolution. Electron-beam powder bed fusion (EPBF) has seen the most success in fabricating crack-free IN738 builds. The pre-heated substrate and precise control over the scanning strategy contribute to lower thermal gradients and minimum residual stress in the final builds. In addition, unique thermal cycles lead to in-situ γ' precipitation, solute segregation, and secondary phase formation at the grain boundaries (GBs) [5-7].
