Prediction of thermal stresses and shape deviation of selective laser melted overhanging region with a coupled CFD-FEM model

Selective laser melting (SLM), also known as powder bed fusion (PBF), is a flexible approach to fabricate complex-shaped metal parts layer-by-layer, especially for parts with complex interior shapes that are difficult to be machined conventionally. One of its typical applications is to fabricate molds consisting of conformal cooling system in which cooling channels may have to be printed horizontally without any supports [1]. Moreover, the internal channel surface cannot be further finished after SLM due to structural limitations. Thermal stress-induced deformation and surface roughness of the overhanging region are two major contributors to shape deviation and are thus concerns that must be addressed. The simulation work presented in this abstract investigates the mechanisms of deformation and surface roughness on overhanging region induced by thermo-mechanical behavior of SLM process under different overhanging angles, laser power, and scan velocity. A 3D coupled CFD-FEM model is developed by considering the heat conduction, melting and solidification with latent heat, surface tension, as well as Marangoni convection. A quasi-randomly distributed powder bed is employed. The simulation results are validated with SLM printing experiments. The overhanging region is nonrigid and essentially a cantilever due to the unmelted powder below. The simulation result shows that the stresses in the SLMed overhanging region are much lower than the stresses in the solid region. The stresses in the overhanging region are released, however, leading to unwanted upward deflection. The surface roughness on the overhanging region is largely determined by the shape and size of the molten pool. It increases with increasing overhanging angle and energy input per volume (i.e. increase of laser power or decrease of scan velocity). This simulation work can thus be directly used to compensate for the shape deviation in the design stage, namely design-for-AM guidelines for the additive manufacturing of internal channels. It will also be helpful for process parameter optimization in the overhanging region to minimize surface roughness.<br/

Design and fabrication of conformal cooling channels in molds:Review and progress updates

Conformal cooling (CC) channels are a series of cooling channels that are equidistant from the mold cavity surfaces. CC systems show great promise to substitute conventional straight-drilled cooling systems as the former can provide more uniform and efficient cooling effects and thus improve the production quality and efficiency significantly. Although the design and manufacturing of CC systems are getting increasing attention, a comprehensive and systematic classification, comparison, and evaluation are still missing. The design, manufacturing, and applications of CC channels are reviewed and evaluated systematically and comprehensively in this review paper. To achieve a uniform and rapid cooling, some key design parameters of CC channels related to shape, size, and location of the channel have to be calculated and chosen carefully taking into account the cooling performance, mechanical strength, and coolant pressure drop. CC layouts are classified into eight types. The basic type, more complex types, and hybrid straight-drilled-CC molds are suitable for simply-shaped parts, complex-shaped parts, and locally complex parts, respectively. By using CC channels, the cycle time can be reduced up to 70%, and the shape deviations can be improved significantly. Epoxy casting and L-PBF show the best applicability to Al-epoxy molds and metal molds, respectively, because of the high forming flexibility and fidelity. Meanwhile, LPD has an exclusive advantage to fabricate multi-materials molds although it cannot print overhang regions directly. Hybrid L-PBF/CNC milling pointed out the future direction for the fabrication of high dimensional-accuracy CC molds, although there is still a long way to reduce the cost and raise efficiency. CC molds are expected to substitute straight-drilled cooling molds in the future, as it can significantly improve part quality, raise production rate and reduce production cost. In addition to this, the use of CC channels can be expanded to some advanced products that require high-performance self-cooling, such as gas turbine engines, photoinjectors and gears, improving working conditions and extending lifetime

Experimental and numerical investigation of the origin of surface roughness in laser powder bed fused overhang regions

Surface roughness of laser powder bed fusion (L-PBF) printed overhang regions is a major contributor to deteriorated shape accuracy/surface quality. This study investigates the mechanisms behind the evolution of surface roughness (Ra) in overhang regions. The evolution of surface morphology is the result of a combination of border track contour, powder adhesion, warp deformation, and dross formation, which is strongly related to the overhang angle (θ). When 0° ≤ θ ≤ 15°, the overhang angle does not affect Ra significantly since only a small area of the melt pool boundaries contacts the powder bed resulting in slight powder adhesion. When 15° 50°, large waviness of the overhang contour, adhesion of powder clusters, severe warp deformation and dross formation increase Ra sharply

Deformation processes of additively manufactured interstitial-strengthened high entropy alloy:In-situ high-energy synchrotron X-ray diffraction and microstructural appraisal

Additively manufactured components often exhibit pronounced anisotropy due to the heterogeneous microstructure generated by the complex and repetitive thermal cycling history. Grain orientation is one of the determinant microstructural features that influences the activation of different deformation mechanisms. In this work, laser powder-bed fusion (LPBF) was applied to fabricate Fe49.5Mn30Co10Cr10C0.5 interstitial-strengthened high entropy alloy (iHEA). Fabrication was performed at angles of 0° and 90° relative to the main laser scanning direction, and the plastic deformation behavior of these two oriented specimens was studied. The initial microstructure of the LPBF-built iHEA was composed of a complex heterogeneous columnar grains containing high-density dislocation network and a large number of stacking faults, as well as nano-precipitates and elemental segregation of Mn at subgrain boundaries. During uniaxial tension in-situ high-energy synchrotron X-ray diffraction (HE-SXRD) was performed to track the deformation processes and mechanisms of this metastable iHEA. The influence of different deformation mechanisms on the mechanical responses of the current LPBF-built iHEA was scrutinized combining in-situ HE-SXRD with electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) analyses, which not only gives insights into the macrostructural evolution but also provides comprehensive characterization on microstructural responses and the orientation-dependent effects imposed by the fabrication constraints originally imposed. The implemented multiscale characterization revealed the presence of a strain-induced fcc to hcp phase transformation, which is influenced by the growth texture close to &lt;110&gt; along the building direction. Moreover, EBSD and TEM analysis of the fracture regions uncovered the formation of nanosized deformation twins, confirming the simultaneous activation of phase transformation- and twinning-induced plasticity (TRIP and TWIP) effects. The results obtained in this work gain new insights into orientation-dependent deformation behavior of additively manufactured iHEA, which facilitates the microstructural design when exploiting the TRIP/TWIP effects.</p

Ultra-strong and ductile precipitation-strengthened high entropy alloy with 0.5 % Nb addition produced by laser additive manufacturing

Funding Information: This research was carried out under project number S17024o in the framework of the Partnership Program of the Materials Innovation Institute M2i ( www.m2i.nl ) and the Netherlands Organization for Scientific Research ( www.nwo.nl ). Funding Information: WZ acknowledges the China Scholarship Council for her PhD grant (CSC No. 201906250212 ). YP acknowledges financial support by Samenwerkingsverband Noord-Nederland (SNN) within the program “3D Print Kompas”. JPO and JS acknowledge Fundação para a Ciência e a Tecnologia (FCT-MCTES) for its financial support via the project UID/00667/2020 (UNIDEMI). JPO acknowledges funding by national funds from FCT - Fundação para a Ciência e a Tecnologia, I.P., in the scope of the projects Nos. LA/P/0037/2020, UIDP/50025/2020, and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N. JS acknowledges the China Scholarship Council for her PhD grant (CSC No. 201808320394). The authors acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Beamtime was allocated for proposal I-20210899 EC. The research leading to this result has been supported by the project CALIPSOplus under Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. SF acknowledges financial support from the National Natural Science Foundation of China (No. 52105318 and 52311530340 ) and "Chunhui Plan" Collaborative Research Project of the Ministry of Education, China (HZKY20220023). Funding Information: WZ acknowledges the China Scholarship Council for her PhD grant (CSC No. 201906250212). YP acknowledges financial support by Samenwerkingsverband Noord-Nederland (SNN) within the program “3D Print Kompas”. JPO and JS acknowledge Fundação para a Ciência e a Tecnologia (FCT-MCTES) for its financial support via the project UID/00667/2020 (UNIDEMI). JPO acknowledges funding by national funds from FCT - Fundação para a Ciência e a Tecnologia, I.P. in the scope of the projects Nos. LA/P/0037/2020, UIDP/50025/2020, and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N. JS acknowledges the China Scholarship Council for her PhD grant (CSC No. 201808320394). The authors acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Beamtime was allocated for proposal I-20210899 EC. The research leading to this result has been supported by the project CALIPSOplus under Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. SF acknowledges financial support from the National Natural Science Foundation of China (No. 52105318 and 52311530340) and "Chunhui Plan" Collaborative Research Project of the Ministry of Education, China (HZKY20220023). This research was carried out under project number S17024o in the framework of the Partnership Program of the Materials Innovation Institute M2i (www.m2i.nl) and the Netherlands Organization for Scientific Research (www.nwo.nl). Publisher Copyright: © 2024Achieving a superior strength-ductility combination for fcc single-phase high entropy alloys (HEAs) is challenging. The present work investigates the in-situ synthesis of Fe49.5Mn30Co10Cr10C0.5 interstitial solute-strengthened HEA containing 0.5 wt.% Nb (hereafter referred to as iHEA-Nb) using laser melting deposition (LMD), aiming at simultaneously activating multiple strengthening mechanisms. The effect of Nb addition on the microstructure evolution, mechanical properties, strengthening and deformation mechanisms of the as-deposited iHEA-Nb samples was comprehensively evaluated. Multiple levels of heterogeneity were observed in the LMD-deposited microstructure, including different grain sizes, cellular subgrain structures, various carbide precipitates, as well as elemental segregation. The incorporation of Nb atoms with a large radius leads to lattice distortion, reduces the average grain size, and increases the types and fractions of carbides, aiding in promoting solid solution strengthening, grain boundary strengthening, and precipitation strengthening. Tensile test results show that the Nb addition significantly increases the yield strength and ultimate tensile strength of the iHEA to 1140 and 1450 MPa, respectively, while maintaining the elongation over 30 %. Deformation twins were generated in the tensile deformed samples, contributing to the occurrence of twinning-induced plasticity. This outstanding combination of strength and ductility exceeds that for most additively manufactured HEAs reported to date, demonstrating that the present in situ alloying strategy could provide significant advantages for developing and tailoring microstructures and balancing the mechanical properties of HEAs while avoiding conventional complex thermomechanical treatments. In addition, single-crystal micropillar compression tests revealed that although the twining activity is reduced by the Nb addition to the iHEA, the micromechanical properties of grains with different orientations were significantly enhanced.publishersversionpublishe

On the orientation-dependent mechanical properties of interstitial solute-strengthened Fe49.5Mn30Co10Cr10C0.5 high entropy alloy produced by directed energy deposition

This research was carried out under project number S17024o ( P16-46 project 6) in the framework of the Partnership Program of the Materials innovation institute M2i ( www.m2i.nl ) and the Netherlands Organization for Scientific Research ( www.nwo.nl ). WZ acknowledges the China Scholarship Council for her PhD grant (CSC No. 201906250212 ). YP acknowledges financial support by Samenwerkingsverband Noord-Nederland (SNN) within the program “3D Print Kompas”. JPO and JS acknowledge Fundação para a Ciência e a Tecnologia ( FCT - MCTES ) for its financial support via the project UID/00667/2020 (UNIDEMI). JPO acknowledges funding by national funds from FCT - Fundação para a Ciência e a Tecnologia, I.P., in the scope of the projects LA/P/0037/2020 , UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N. JS acknowledges the China Scholarship Council for her PhD grant (CSC No. 201808320394 ). The authors acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Beamtime was allocated for proposal I-20210899 EC. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020 . SF acknowledges financial support by the National Natural Science Foundation of China (No. 52105318 and 52311530340 ) and "Chunhui Plan" Collaborative Research Project of the Ministry of Education , China ( HZKY20220023 ). Publisher Copyright: © 2023 The AuthorsInterstitial solute-strengthened Fe49.5Mn30Cr10Co10C0.5 (at%) high entropy alloy was additively manufactured by directed energy deposition (DED) process in this work. While the as-deposited material exhibits an excellent combination of strength and ductility, the effect of anisotropy on the mechanical performance of the DED processed component was studied in detail. The ultimate tensile strength (UTS) of the horizontal tensile sample with a main fiber texture of // tensile direction (TD) went up to 1 GPa while maintaining a superb failure elongation of 36%. The vertical tensile sample, with a dominant // TD texture, failed at an UTS of 750 MPa with an enhanced failure elongation of 52%. Microstructural analysis of the deformed samples showed that the horizontal samples were mainly deformed via the formation of mechanical twins, whereas the twining activity was less profound in the vertical samples. Single crystal micro-pillar compression testing revealed that the deformation mechanism complies well with the Schmid's factor. In addition, a higher critical resolved shear stress for twining compared to slip was also confirmed in the micro-pillar compression testing.publishersversionpublishe