High manganese steels offer an excellent combination of high strength and good ductility, making them ideal for lightweight and energy absorbing applications such as open cellular structures. Additive manufacturing is often used to produce metallic open cellular structures since it allows a high complexity of the geometry and high material efficiency, but the structures often exhibit anisotropic behavior and processing requires specific powder sizes with correspondingly high prices. This study therefore addresses the feasibility of investment casting to produce open cellular structures. A high manganese X30Mn22 base alloy with different contents of aluminum (0, 1 and 5 wt %) was used for the manufacturing of a newly designed cell structure. Processing parameters and mold materials needed to be adjusted due to pronounced chemical reactions with the commercial SiO2-based mold material. Using an Al2O3-based mold material and increasing the mold temperature during casting to 1000 °C allowed for the successful casting of high manganese steel structures with different designs regarding the strut diameter. Quasi-static compression tests of the structures confirm the cast quality and illustrate the effect of increasing alloying contents of Al on the deformation behavior, building the foundation for the development of programmable cellular structures for energy absorbing applications.

The assessment of the environmental impact of additively manufactured parts is difficult due to the hard-to-compare system boundaries. This study proposes a novel property-dependent option for the comparison of additively to conventionally produced parts based on the life cycle assessment (LCA) of two different designs of structural components for energy-absorption applications. While the optimized additive manufacturing (AM) lattice structure led to significant reduction of global warming potential (GWP), cumulative energy demand (CED), and material footprint (MF) (−45%, −51% and −56%, respectively), additively manufacturing the standard design led to an increase of those environmental indicators (+33.9%, +33.1% and +34.6%, respectively) as compared to the conventionally manufactured standard design. It is demonstrated that the environmental impact of metallic components is only reduced by AM if the freedom of design offered by these techniques is utilized to realize weight reduction and, more importantly, that this design must be based on critical part properties. Especially, argon consumption during atomization was found to drastically increase the environmental impact. Consequently, the material yield during powder atomization and AM, combined with minimized gas consumption, can pave the way towards more sustainable AM.

Incorporating nano-scaled ceramic particles into additively manufactured Al-alloys is a validated strategy to simultaneously enhance the elevated-temperature mechanical properties and laser powder bed fusion (PBF-LB/ M) processability. While B4C exhibits outstanding thermal stability and interfacial compatibility with Al, the integration of nano-B4C into Al alloys through PBF-LB/M remains insufficiently investigated. In particular, the underlying mechanisms governing laser-particle interaction, processability, and the consequent microstructural formation have not been comprehensively explored. This study aims to address this gap by investigating the effect of nano-B4C additions (1, 3, and 5 wt%) to AlSi10Mg on PBF-LB/M processability and the alloy behavior. The results demonstrated excellent PBF-LB/M processability of the B4C/AlSi10Mg composites at all weight fractions of B4C. The as-built B4C/AlSi10Mg revealed a remarkable columnar-to-equiaxed transition, featuring an ultrafine grain structure (as small as 1.23 mu m) with almost random crystallographic texture. This grain refinement was attributed to a reactive nucleation process, where the interfacial reaction between B4C and the matrix results in the coherent AlB2 core-shell structured phase. Furthermore, this interfacial reaction induced a novel morphological transition, characterized by the spheroidization of irregularly shaped nanoparticles as a consequence of partial reactive melting. The B4C nanocomposites exhibited superior elevated-temperature mechanical properties, increasing tensile strength by up to 60 % compared to their AlSi10Mg counterparts. This study provides fundamental insights into the design and PBF-LB/M processing of Al-based metal-matrix nano-composites (AMMNCs) for high-temperature applications.

In this study, the damage-integrated thermo-micro-mechanical (D-TMM) model was advanced to simulate the deformation and damage behavior of high-strength steels under complex multiaxial loading. The original D-TMM model combined a thermo-micro-mechanical (TMM) framework, based on dislocation dynamics, with the Gurson-Tvergaard-Needleman (GTN) damage model to describe material behavior across cold and warm regimes. By treating dislocation densities and void fraction as averaged microstructural state variables (MSVs) defined at each integration point, the framework links macroscopic responses directly to the evolving internal material state. A key strength of the D-TMM approach is its ability to transfer evolved MSVs between steps in a multi-step process chain, embedding the material’s deformation history into subsequent simulations. However, the original implementation was limited to uniaxial loading, restricting its use in manufacturing processes with complex multiaxial stress states. This work extends the D-TMM model to handle such conditions, enhancing its capacity to simulate multi-step manufacturing scenarios involving shear and fracture. To achieve this, normalized functions of stress triaxiality and the Lode parameter were incorporated, and the enhanced model was calibrated using notch tensile and shear tests. Its predictive capability was validated by successfully reproducing the forming limit curves (FLCs) of S700 steels under different loading conditions. The refined D-TMM model was then applied to simulate two key steps within the laser-assisted flange-forming process — shear cutting and flange forming — with experimental validations conducted at extreme processing conditions. This study demonstrates the D-TMM model’s ability not only to capture geometrical and mechanical aspects of the components but also to accurately track the evolution of microstructure-informed state variables and damage, providing a powerful tool for optimizing multi-step manufacturing processes based on the material’s deformation and damage history.

Since its conception in the early 1990s, additive manufacturing of metallic materials has evolved into a staple manufacturing technique in various industries. Among other process-specific advantages, such as sustainability and geometric freedom, the unique thermal conditions of extremely fast heating and cooling cycles can allow for the manufacturing of alloy systems facing challenges in conventional processing or eliminate the need for further heat treatments. This holds true for Fe-Mn-Al-C steels, which exhibit extraordinary strength and ductility due to x-carbide precipitation but encounter challenges during casting and demand extensive heat treatments. In this study, we set out to achieve in situ x-carbide precipitation within an X110MnAl30-8 steel by manipulating the thermal history of the laser-based directed energy deposition process. Using CALPHAD calculations to determine suitable heat treatment temperatures, a preheating setup was developed, which allowed for the precise adjustment and measurement of the temperature development within the samples. Subsequently, different preheating temperatures were evaluated for potential in situ x-carbide precipitation. Preheating the substrate plate to 500 degrees C resulted in x-carbide formation in the as-built material. Simultaneously, the formation of grain boundary cracking was observed. Similar to the strain-age cracking phenomenon in Ni-base alloys, the rapid formation of x-carbides at grain boundaries leads to the weakening of grain boundaries.

Solute enrichment at lattice defects is a well-established phenomenon for promoting phase transformations. Metal additive manufacturing (AM) inherently enables this by promoting cellular structures during solidification and thermal cycling. Cellular structures exhibit compositional and lattice defect density variations between cell cores and boundaries, leading to site-specific phase-transformation (e.g., precipitation) behavior that can be selectively activated by post-AM heat treatments. Despite this potential, cellular structures have largely been treated as byproducts rather than intentionally exploited alloy design features. Guided by these insights, we designed a model Al10.5Co25Fe39.5Ni25 multi-principal element alloy to intentionally control composition and thus, precipitation driving forces across cellular structures. The alloy composition was computationally selected to promote segregation of a fast-diffusing, precipitate-forming element into the interdendritic regions during solidification in the laser powder bed fusion (PBF-LB/M) process. This segregation aligned with dislocation walls at cell boundaries, creating a "pre-conditioned" state with enhanced chemical driving force and reduced nucleation barrier for precipitation. This targeted design enabled site-specific nucleation and growth of precipitates at cell boundaries during aging. Comprehensive multiscale characterization complemented by in situ synchrotron X-ray diffraction confirmed that cellular structures accelerated precipitation, increased precipitate volume fraction and refined the precipitate size compared to the reference state where cellular structures were removed via solution annealing before aging. As a result, the alloy achieved enhanced yield strength (122.2 % increase), and improved tensile properties compared to the reference state. These findings demonstrate the potential of harnessing cellular structures as functional components to control microstructure evolution in precipitation strengthened AM alloys.

Multi-principal element alloys (MPEA) have gathered significant attention in the scientific community due to their versatility and design concepts. The Fe30Mn10Co10Cr (at.-%) MPEA system revealed outstanding mechanical properties, owing to the activation of multiple strengthening mechanisms. In this MPEA system, the formation of vanadium carbides was found to be efficient to enhance the strength and to provide further design flexibility. However, the low-cycle fatigue behavior has not yet been investigated. To address this, a fully recrystallized, single-phase face-centered cubic (fcc) structure and a recrystallized and aged state that was strengthened by a uniform distribution of 6.5 % nanosized vanadium carbides were evaluated. It was revealed that the aged samples exhibited a notable improvement in cyclic fatigue performance. The precipitation of vanadium carbides led to a reduction in solute carbon content in the fcc matrix, which in turn resulted in the transformation-induced plasticity effect becoming the dominant deformation mechanism in the aged samples. This was coupled with a decrease in plastic strain amplitude and an increase in slip reversibility. As a result, the number of cycles to failure in the low-cycle fatigue regime increased by 40.8 % to 62.1 %, facilitating the concurrent optimization of both tensile and fatigue properties.

The design flexibility offered by powder bed fusion using a laser beam enables the production of parts with complex geometries, such as topologically ordered, strut-based lattice structures. Research on lattice structures has predominantly focused on tailoring the macroscopic mechanical response through geometrical design rather than material characteristics. This study, on the other hand, aims for a synergistic approach focusing on both geometry and alloy design to enhance the energy absorption performance of high-manganese steel (HMnS) lattice structures. In HMnS, different deformation mechanisms, such as transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), can be activated in addition to dislocation slip, depending on the stacking fault energy of the alloy. When effectively activated, these mechanisms, particularly TRIP, lead to pronounced strain hardening that contributes to the energy-absorption capacity of a lattice structure. For this purpose, an f2ccz lattice structure was selected as the reference design, and the unit cell geometry was modified to effectively leverage TRIP and/or TWIP effects. Thereby, the mechanical stability was significantly improved, and the energy-absorption capacity was increased by 22 %. Furthermore, the findings highlight the potential for extending the alloy-geometry synergy to chemically or functionally graded structures, enabling precise control over local behaviour and enhancing global performance.

Developing novel alloys for 3D printing of metals is a time- and resource-intensive challenge. High-throughput 3D printing and material characterization protocols are used in this work to rapidly screen a wide range of chemical compositions and processing conditions. In situ, alloying of high-strength steel with pure Al in the targeted range of 0-10 wt.% and flexible adjustment of the volumetric energy input is performed to derive 20 individual alloy combinations. These conditions are characterized using large-area crystallographic analysis combined with chemistry and nanoindentation protocols. The significant influence of Al content and processing conditions on the constitutive material behavior of the metastable base alloy allowed for efficient exploration of the underlying process-structure-properties (PSP) relationships. The extracted PSP relations are discussed based on the dominant physical mechanisms observed in the samples. Furthermore, the microstructure-property relationship based on limited experimental data is supported by an explainable machine-learning approach.

The efficiency of gas turbines plays an important role for a sustainable energy transition resulting in high requirements for turbine blade materials. Nickel‐based superalloys, such as CM247LC, are often used for this application. Using additive manufacturing (AM), the major subtractive processing steps after conventional casting of turbine blades can be avoided and complex lightweight structures achieved. However, the nickel‐based superalloys withstanding the highest temperatures are prone to cracking during the AM process. This study presents a method to mitigate the cracking tendency of the non‐processable nickel‐based superalloy CM247LC in powder bed fusion laser beam of metals (PBF–LB/M) by adding reinforcing TiC particles resulting in a metal matrix composite (MMC). The focus of the investigation is put on the influence of the incorporated particles on the selection of PBF–LB/M process parameters and the evolution of the microstructure. The results show a reduction in crack length and density in the new MMC by grain refinement and a homogeneous distribution of local strains. Heat‐treatment and hardness testing reveal a transformation of the TiC to (Hf,Ta,W)C and γ′ as well as excessive grain coarsening.

This study presents an alloy design perspective guided by elemental segregation during solidification to determine the site-specific chemistry and related local thermodynamic properties of dendritic microstructures. This was accomplished via manipulation of the microsegregation behavior by means of nominal alloy composition and thermal conditions of the solidification processes, including modified cooling rates spanning over six orders of magnitudes using ingot casting, directed energy deposition (DED-LB/M) additive manufacturing (AM) and laser powder bed fusion (PBF-LB/M) AM processes. Our approach was demonstrated by computationally designing a novel AlxCo25Fe(50-x)Ni25 multi-principal element alloy (MPEA) as a model system, employing a combination of CALPHAD, Scheil, and multiphase-field simulations, and by experimentally validating the resulting microstructure evolution. The lower Al content (x = 10.5) was designated to generate a supersaturated single-phase fcc matrix suitable for heat-treatments to trigger local phase transformations. The higher Al content (x = 14.5) was selected to define the size and morphology of dual-phase microstructures by controlling phase nucleation and growth through segregation during solidification. Our results showcased how selective enrichment of the desired elements in interdendritic regions can be employed to induce local phase transformations during solidification or post heat-treatments, while their size can be flexibly controlled by the degree of undercooling during solidification. The suggested segregation-guided design approach can be transferred to other alloy systems, enabling effective tuning of local functional, structural, kinetic, and, as shown in this study, thermodynamic properties of dendritic microstructures by predetermining the nature of the alloy matrix through tailored solidification behavior.

Controlling microstructure evolution in metastable steels like medium-manganese steel (MMnS) during additive manufacturing (AM) is complex due to the dependence of the phase transformation behavior on AM conditions. The present study investigates the phase evolution of a X21Mn13 MMnS produced via laser-based powder bed fusion of metals (PBF-LB/M), utilizing both experimental analysis (microscopy and X-ray diffraction) and computer-aided simulations (finite element analysis and phase field method) focusing on the impact of varying laser scanning speeds on microstructure evolution during solidification and subsequent cooling. This comprehensive analysis allowed for a thorough investigation, separating the distinct influences of chemical composition, grain morphology and mechanical factors on the austenite stability. Additionally, a crystallographic examination, comparing primary austenite grains (PAG) and retained austenite grains (gamma(R)) was conducted to elucidate phase evolution. The findings reveal that increased scanning speed leads to less Mn evaporation, decreased PAG size, lower density of geometrically necessary dislocations (GND) and compressive residual stress in gamma(R); influencing the austenite stability. The martensite formation due to austenite-to-martensite transformation was found to occur predominantly within non-<100>-oriented gamma(R) grains, eventually weakening the contribution of this component to the crystallographic texture, whereas <100>-oriented gamma(R) grains were retained and thus, dominate austenite texture.

Medium‐manganese steels (MMnS) represent novel third‐generation advanced high‐strength steels, which are characterized by Mn content between 3 and 12 wt% as well as a multiphase microstructure. These steels are well‐known for outstanding combinations of high to ultrahigh strength at relatively high total elongation. Strength and ductility are significantly affected by the amount of retained austenite, its stability, and the related transformation‐induced plasticity. Due to the possibility of microstructure design, laser‐based powder bed fusion of metals (PBF‐LB/M) is a promising processing method to tailor the mechanical performance of MMnS. In the present study, a Fe–12Mn–0.2C MMnS is manufactured by PBF‐LB/M using blended powder as well as pre‐alloyed powder to investigate the applicability of rapid alloy development. Various scanning speeds are used to determine the influence of energy deposition rate on microstructure and mechanical properties. Microstructural analysis of the different as‐built conditions is carried out by optical and scanning electron microscopy, X‐ray diffraction, and electron backscatter diffraction. The feasibility of using blended powder instead of atomized powder for preliminary experiments on PBF‐LB/M‐produced MMnS is discussed. In addition, a significant influence of process parameters on the resulting austenite fraction as well as strength and ductility for the investigated material is revealed.

Additive manufacturing techniques, such as laser-based powder bed fusion of metals (PBF-LB/M), have now gained high industrial and academic interest. Despite its design flexibility and the ability to fabricate intricate components, LPBF has not yet reached its full potential, partly due to the challenges associated with microstructure control. The precise manipulation of the microstructure in LPBF is a formidable yet highly rewarding endeavor, offering the capability to engineer components at a local level. This work introduces an innovative parallelized Cellular Automaton (CA) framework for modeling the evolution of the microstructure during the LPBF process. LPBF involves remelting and subsequent nucleation followed by crystal growth during solidification, which complicates and burdens microstructure simulations. In this research, a novel approach to nucleation seeding and crystal growth is implemented, focusing exclusively on the final stages of melting and solidification, enhancing the computational efficiency by 30%. This approach streamlines the simulation process, making it more efficient and effective. The developed model was employed to simulate the microstructure of an austenitic advanced high-strength steel (AHSS). The model was validated by comparing the simulation results qualitatively and quantitatively with the experimental data obtained under the same process parameters. The predicted microstructure closely aligned with the experimental findings. Simulations were also conducted at varying resolutions of CA cells, enabling a comprehensive study of their impact on microstructure evolution. Furthermore, the computational efficiency was critically evaluated.

In this study, a Thermo-micro-mechanical (TMM) model to describe the viscoplastic flow of polycrystalline metallic materials was extended by integration of micromechanical damage. The original TMM model [1] incorporated the fundamentals of dislocation motions during metal deformation, using microstructural state variables (MSVs) for the statistical quantification of dislocations, represented through the dislocation density. These MSVs track dislocation evolution throughout deformation, allowing for the material behavior and mechanical properties in cold and warm regimes (up to 500 degrees C) to be derived as functions of these state variables. A key advantage of the TMM model is its ability to transfer MSVs across multi-step process chain simulations, thereby accounting for the deformation history of materials in subsequent processes. However, the previous model was limited to the plastic regime and cannot be applied to processes involving damage and fracture. The primary objective of the current study is to extend the TMM model to predict fracture and damage. Therefore, the Gurson-Tveergard-Needleman (GTN) model, a widely recognized micromechanical damage model, was integrated into the TMM model to describe the material behavior comprising plasticity, damage and fracture (D-TMM model). This integration introduces void fraction from the damage model as an additional state variable alongside the existing MSVs, thus enabling the transfer of both deformation history and damage accumulation across the process chain. The constitutive equations from both models are numerically integrated, and their parameters are calibrated for a commonly used micro-alloyed high strength construction steel - S700. The model is subsequently tested under isothermal conditions up to 500 degrees C, non-isothermal conditions, and across a range of strain rates.

For many high-performance alloys originally developed for the casting route, hot cracking is a serious problem in the Laser Powder Bed Fusion (PBF-LB/M) process and limits the use of e.g. high-gamma ' nickel-based alloys such as CM247LC in additive manufacturing. In this work, we investigate the relationship between PBF-LB/M processing parameters and the solidification path, i.e. phase formation and microsegregation, and its potential impact on hot cracking for the high-gamma ' alloy CM247LC. We combined experimental microstructural analysis using scanning and transmission electron microscopy, atom probe tomography and diffraction techniques with multiphase-field simulations on mu m scale. Process simulations at mesoscale of the melt pool provide the link between the process conditions and the thermal boundary conditions for the microstructural simulations. The study confirms the appearance of carbides, borides and gamma '-precipitates in the as-solidified microstructure. The quantity and particle size of these phases as observed in the experimental samples, are in qualitative agreement with the simulation results. Therefore, the simulations can be used to elucidate and quantify the differences in the solidification path for different thermal process conditions. Although the comparison of samples processed with high energy density (cooling rate 65,000 K/s) with those processed with low energy density (cooling rate: 570,000 K/s) show large differences in the crack density observed in the experiments, the microstructural differences and the phase formation at the dendritic scale do not show any remarkable qualitative or quantitative differences. The correlation between processing conditions, microstructure evolution and crack formation is critically discussed and differences to the current understanding presented in existing literature are identified.

A wide range of additive manufacturing (AM) processing conditions can be rapidly realized within a single specimen via high-speed direct energy deposition laser based (DED-LB), due to a variety of cooling conditions and in-situ powder mixing. Since existing approaches are inefficient in exploring the vast material and process design space in AM, high-speed DED-LB can be employed as a novel technology for high-throughput alloy design tool. However, an evaluation of the process transferability of the high-speed DED-LB process with respect to the currently dominating metal AM technologies, namely laser powder bed fusion (PBF LB/M) and conventional DED-LB, is required. In this study, high-speed DED-LB is applied for the high-throughput sample production, using the nickel alloy IN718 as reference material as well as the AM processes PBF LB/M and DED-LB as reference processes. The resulting microstructures are characterized and compared using optical microscopy and large-area scanning electron microscopy (SEM) analysis combined with energy-dispersive X-ray spectroscopy (EDS). Furthermore, a model for calculation of the volumetric energy density is developed to compare the applied AM processes. The significant influence of the processing conditions on the solidification behavior of the investigated material allows for efficient exploration of the microstructure and phase composition. Specific high-speed DED-LB-process conditions achieved the average solidification cell size and laves phase content as observed in the PBF LB/M- and DED-LB -produced counterparts. The applicability of the high-speed DED-LB process for rapid alloy and process development, i.e., process transferability, is critically evaluated. The results show that high-speed DED-LB can be used to emulate cooling conditions of PBF-LB/M and DED-LB and, therefore, be used as tool for rapid alloy development.

Multi-principal element alloys represent a compelling avenue for the development of innovative alloys that have the potential to surpass conventional alloys in various applications, owing to the extensive compositional space they offer. For structural application though, this potential has not yet been realized, mostly because of hardly superior mechanical properties and elevated alloying costs. To overcome this hurdle, efforts have been made to increase mechanical properties using individual strengthening mechanisms, such as grain refinement, prior plastic deformation, precipitation hardening, and solid solution strengthening. In this study, we aim to combine multiple of these mechanisms into a singular alloy by adding V and C to the Fe30Mn10Co10Cr (at.-%) alloy. Using a custom calphad database, thermodynamic calculations were carried out to determine a suitable chemical composition which was subsequently cast and thermo-mechanically processed. Aging treatments above 700 °C for 4–24 h led to vanadium carbide precipitation, increasing the yield strength by up to 450 MPa to nearly 1 GPa. Extensive aging times were necessary to facilitate precipitation, thereby indicating slow diffusion processes. A transition from twinning-induced to transformation-induced plasticity by vanadium carbide precipitation was observed and attributed to the reduction of C-content and stacking fault energy in the matrix as well as twin-precipitate interactions.

Additive manufacturing (AM) of metallic materials yields distinctive hierarchical and heterogeneous microstructures owing to the complex thermal conditions during the build-up process. Consequently, the knowledge gained from creep properties of conventionally manufactured (CM) Ni-based alloys cannot be directly applied to AMprocessed alloys. Furthermore, insufficient creep life has posed a significant challenge in the development of Ni-based superalloys fabricated by laser powder bed fusion (LPBF), one of the most important AM techniques. Nevertheless, limited research has been conducted to understand their creep behavior due to the time-consuming nature of creep testing and extended research cycles. This study delves into investigating the creep behavior of an additively manufactured, precipitation-strengthened Ni-based alloy (NiCrAl) in comparison to its CM counterpart, focusing on the structure-property relationships. Constant-load creep tests were conducted at temperatures of 750 °C and 950 °C up to a maximum duration of nearly 1500 h. Although both the AM and CM states demonstrated high creep activation energy and creep exponents, indicative of a dislocation climb mechanism, the AM state demonstrated inferior creep life and ductility compared to the CM state for creep times below 500 h. To gain deeper insights into the underlying mechanisms, multi-scale microstructural characterization was performed to understand the effect of the AM-inherent microstructure. Overall, this study provides a comprehensive understanding of the creep behavior of Alloy 699XA after AM and CM processes, emphasizing the significance of AM-specific microstructural heterogeneities.