Many components in the mobility sector are subjected to elevated temperatures and tribological demands while requiring light weight construction at the same time. Laser powder bed fusion (PBF-LB) enables the formation of unique microstructures through process-related high cooling rates, resulting in desirable component properties. In this study, an Al80Mn11Ce9 (wt.%) alloy was fabricated by PBF-LB, achieving a microstructure consisting of a supersaturated Al-matrix and fine-sized, metastable, high-strength Al20Mn2Ce particles. The mechanical performance and wear rate of this alloy were benchmarked against the industrially employed, heat-treated Al-7075 alloy. Both alloys reach high hardness and compressive strength, while Al80Mn11Ce9 outperforms the reference material in terms of wear resistance and strength retention at 300 degrees C. Under dry sliding against steel, Al80Mn11Ce9 forms an iron-oxide-rich, protective, mechanically mixed layer across all tested conditions, including loads up to 30 N and sliding times up to 5 h. The primary limitation of this alloy is the ductility-limited strength at room temperature. Nevertheless, this study estimates the potential of Al80Mn11Ce9 for lightweight applications requiring durability at elevated temperatures and high tribological performance.

The microstructure, physical, and mechanical characteristics of 3D-printed metal products can be improved with high-energy heat treatment included in the manufacturing process. In the present study, Ti-6Al-4V titanium alloy products were 3D-printed with electron beam melting of wire of appropriate composition, while surface laser treatment of 3D-printed material was studied to determine the potential of microstructure modification and characteristics improvement. It was found that certain laser processing modes make it possible to eliminate micro defects (pores) in the samples that are harmful to structural materials. The obtained results also open the prospect of creating 3D-printed metal parts with specified profiles of physical and chemical properties, including gradients, as they model the change in material properties depending on the depth of the deposited layer during high-energy processing of each layer during its application. As demonstrated, both the condition of 3D printing as the velocity of deposition and thickness of each layer, the chemical composition and amount of impurities added to the matrix material during deposition, and the high-energy processing (heating or remelting) parameters are important to form the phase composition and mechanical properties of the final products. The high-energy processing also can be used to control the physicochemical properties of the product’s surface.

Biodegradable medical implants promise to benefit patients by eliminating risks and discomfort associated with permanent implantation or surgical removal. The time until full resorption is largely determined by the implant's material composition, geometric design, and surface properties. Implants with a fixed residence time, however, cannot account for the needs of individual patients, thereby imposing limits on personalization. Here, an active Fe-based implant system is reported whose biodegradation is controlled remotely and in situ. This is achieved by incorporating a galvanic cell within the implant. An external and wireless signal is used to activate the on-board electronic circuit that controls the corrosion current between the implant body and an integrated counter electrode. This configuration leads to the accelerated degradation of the implant and allows to harvest electrochemical energy that is naturally released by corrosion. In this study, the electrochemical properties of the Fe-30Mn-1C/Pt galvanic cell model system is first investigated and high-resolution X-ray microcomputed tomography is used to evaluate the galvanic degradation of stent structures. Subsequently, a centimeter-sized active implant prototype is assembled with conventional electronic components and the remotely controlled corrosion is tested in vitro. Furthermore, strategies toward the miniaturization and full biodegradability of this system are presented.

Iron is an abundant and non-toxic element that holds great potential as energy carrier for large-scale and long-term energy storage. While from a general viewpoint iron oxidation is well-known, the detailed kinetics of oxidation for micrometer sized particles are missing, but required to enable large-scale utilization for energy production. In this work, iron particles are subjected to temperature-programmed oxidation. By dilution with boron nitride a sintering of the particles is prevented enabling to follow single particle effects. The mass fractions of iron and its oxides are determined for different oxidation times using Mössbauer spectroscopy. On the basis of the extracted phase compositions obtained at different times and temperatures (600-700 °C), it can be concluded that also for particles the oxidation follows a parabolic rate law. The parabolic rate constants are determined in this transition region. Knowledge of the particle size distribution and its consideration in modeling the oxidation kinetics of iron powder has proven to be crucial.

Laser powder bed fusion (LPBF) constitutes a promising alternative to directly produce Cu-based shape memory parts with high superelasticity due to the fact that the grain size and morphology as well as the texture can be tailored during processing. It is known that immediate laser remelting of previously processed layers during LPBF can serve as an important and complementary method to improve part density and to adjust the microstructure and mechanical behavior. As a consequence, this study focuses on the effects of an additional remelting step on the material properties of an additively fabricated Cu 71.6 Al 17 Mn 11.4 (at.%) shape memory alloy (SMA). Firstly, the effects of different remelting parameters, obtained via systematically changing the hatching distance and scanning speed, on the sample density and transformation temperatures were analyzed. Secondly, microstructural observations as well as incremental compression tests were performed to establish the relationships between the applied remelting process parameters, the microstructure, and the superelastic properties. The comparison of the results for remelted and non-remelted counterparts clearly proves that a subsequent exposure of already solidified layers can serve as an adaptive tool to improve the performance of Cu-based SMAs and to allow the fabrication of locally adapted shape memory parts for application-oriented scenarios.

Laser powder bed fusion (LPBF) for the fabrication of dense components used for tooling applications, is highly challenging. Residual stresses, which evolve in the additively manufactured part, are inherent to LPBF processing. An additional stress contribution in high-carbon steels arises from the austenite-to-martensite phase transformation, which may eventually lead to cracking or even delamination. As an alternative to pre-heating the base plate, which is not striven by industry, lowering the martensite con-tent which forms in the part, is essential for the fabrication of dense parts by LPBF of high-carbon tool steels which are then adapted to LPBF. In this study, a successful strategy demonstrates the process-ing of the Fe85Cr4Mo1V1W8C1 (wt%) high-carbon steel by LPBF into dense parts (99.8%). The hierarchi-cal microstructure consists of austenitic and martensitic grains separated by elemental segregations in which nanoscopic carbide particles form a network. A high density of microsegregation was observed at the molten pool boundary ultimately forming a superstructure. The LPBF-fabricated steel shows a yield strength, ultimate compressive stress, and total strain of 1210 MPa, 3556 MPa, and 27.4%, respectively. The mechanical and wear performance is rated against the industrially employed and highly wear-resistant 1.2379 tool steel taken as the reference. Despite its lower macro-hardness, the LPBF steel (58.6 HRC, 0.0061 mm3 Nm-1) shows a higher wear resistance than the reference steel (62.6 HRC, 0.0078 mm3 Nm-1). This behavior results from the wear-induced formation of martensite in a microscale thick layer directly at the worn surface, as it was proven via high-energy X-ray diffraction mapping. (c) 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

The effects of the scan vector rotation angle in adjacent layers during laser powder bed fusion of a Cu71.6Al17Mn11.4 (at.%) shape memory alloy on the porosity, microstructure, transformation temperatures, as well as superelastic properties, were investigated. To explore the influence of the applied scanning strategy, a bidirectional stripe hatching was employed by utilizing 0°, 25°, 50°, 79° and 90° rotation of the scanning direction in adjacent layers. Changing the scan vector rotation had no apparent effect on the characteristics of porosity. The scan vector rotation allowed a manipulation of the microstructure (grain size, texture) to some extent which was evaluated via electron backscattered diffraction (EBSD) analysis. While the size and distribution of grains only showed negligible differences, a more pronounced change in the texture as well as in the grain misorientation has been observed. A significant recoverable strain difference for the applied scan vector rotations was observed as a result of compressive loading-unloading tests. The samples produced with 90° scan vector rotation exhibited 6.05% recoverable strain under 8% applied strain, whereas only minor recoverable strain values (around 1.4%) were obtained in the specimens produced without a shift in the scan vector rotation (0°). Other vector rotations (25°, 50°, 79°) resulted in a moderate superelastic performance with respect to the 90°-samples. These findings clearly show that polycrystalline Cu–Al–Mn shape memory parts with high shape-recovery rates can be directly fabricated using laser powder bed fusion and an adjusted scanning strategy. Thus, this approach can serve as a general tool to optimize or control superelasticity in additively manufactured Cu-based SMAs.

High-power laser power bed fusion (HP-LPBF) with a large flat-top laser beam allows additive manufacturing of components at much higher build-up rates than conventional LPBF, since thicker powder layers can be processed. This makes this technology attractive for industry due to the augmented productivity. Here, we have utilized HPLPBF to fabricate Al-33Cu (wt%) specimens at differing layer thickness and laser power. Based on the average spacing of the lamellae of the eutectic microstructure, the cooling rate inherent to HP-LPBF was experimentally determined as a function of the processing conditions. At the lowest layer thickness (50 & mu;m) and laser power (500 W), the cooling rate amounts to about 90000 K/s, whereas it drops to about 15000 K/s for HP-LPBF with the largest layer thickness (200 & mu;m) and highest laser power (1000 W). When the base plate is additionally preheated, the cooling rate prevailing during solidification decreased to about 5000 K/s. Our findings demonstrate that relatively low cooling rates are effective during HP-LPBF at high build-up rates being tantamount to high productivity. It should be considered that such drastic changes in cooling rate may strongly affect the microstructure formation, the properties and hence performance of the corresponding additively manufactured component.

Metals can serve as carbon-free energy carriers, e. g. in innovative metal-metal oxide cycles as proposed by Bergthorson (Prog. Energy Combust. Sci., 2018). Iron powder is a suitable candidate since it can be oxidized with air. Nevertheless, the combustion of iron powder in air is challenging especially with respect to flame stabilization which depends on the particle size distribution among other factors. Models for the prediction of reaction front speed in iron-air suspensions can contribute to overcoming this challenge. To this end, three different models for iron particle oxidation are integrated into a laminar flame solver for simulating reaction fronts. The scientific objective of this work is to elucidate the influence of polydispersity on the reaction front speed, which is still not satisfactorily understood. In a systematic approach, cases with successively increasing complexity are considered: From single particle combustion to iron-air suspensions prescribing binary particle size distributions (PSDs), generic PSDs, and a PSD measured for a real iron powder sample. The simulations show that, dependent on the PSD, particles undergo thermochemical conversion in a sequential manner according to their size and every particle fraction exhibits an individual combustion environment. The local environment can be leaner or richer than the overall iron-to-air ratio would suggest and can be very different from single particle experiments. The contribution of individual particle fractions to the overall reaction front speed depends on its ranking within the PSD. The study further demonstrates, that although the three particle models show good agreement for single particle combustion, they lead to very different reaction front speeds. This is due to the different ignition behavior predicted by the particle models, which is shown to strongly influence the reaction front characteristics.

This study focuses on the influence of additive manufacturing process strategies on the specimen geometry, porosity, microstructure and mechanical properties as well as their impacts on the design of metamaterials. Filigree additively manufactured NiTi specimens with diameters between 180 and 350 µm and a nominal composition of Ni50.9Ti49.1 (at %) were processed by laser powder bed fusion in a first step. Secondly, they structures were characterized by optical and electron microscopy as well as micro tomography to investigate the interrelations between the process parameters, specimen diameters and microstructure. Each specimen was finally tested in a micro tensile machine to acquire the mechanical performance. The process strategy had, besides the resulting specimen diameter, an impact on the microstructure (grain size) without negatively influencing its quality (porosity). All specimens revealed a superelastic response while the critical martensitic phase transition stress decreased with the applied vector length. As a conclusion, and since the design of programmable metamaterials relies on the accuracy of FEM simulations, precise and resource-efficient testing of filigree and complex structures remains an important part of creating a new type of metamaterials with locally adjusted material behavior.

The ss-type Ti-42Nb alloy was processed by laser powder bed fusion (LPBF) with an infrared top hat laser configuration aiming to control the Young's modulus by creating an adapted crystallographic texture. Utilizing a top hat laser, a microstructure with a strong (0 0 1) texture parallel to the building direction and highly elongated grains was generated. This microstructure results in a strong anisotropy of the Young's modulus that was modeled based on the single crystal elastic tensor and the experimental texture data. Tensile tests along selected loading directions were conducted to study the mechanical anisotropy and showed a good correlation with the modeled data. A Young's modulus as low as 44 GPa was measured parallel to the building direction, which corresponds to a significant reduction of over 30% compared to the Young's modulus of the Gaussian reference samples (67-69 GPa). At the same time a high 0.2% yield strength of 674 MPa was retained. The results reveal the high potential of LPBF processing utilizing a top hat laser configuration to fabricate patient-specific implants with an adapted low Young's modulus along the main loading direction and a tailored mechanical biofunctionality. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Shape memory alloys (SMAs), such as Ni–Ti, are promising candidates for actuation and damping applications. Although processing of Ni–Ti bulk materials is challenging, well-established processing routes (i.e. casting, forging, wire drawing, laser cutting) enabled application in several niche applications, e.g. in the medical sector. Additive manufacturing, also referred to as 4D-printing in this case, is known to be highly interesting for the fabrication of SMAs in order to produce near-net-shaped actuators and dampers. The present study investigated the impact of electron beam powder bed fusion (PBF-EB/M) on the functional properties of C-rich Ni 50.9 Ti 49.1 alloy. The results revealed a significant loss of Ni during PBF-EB/M processing. Process microstructure property relationships are discussed in view of the applied master alloy and powder processing route, i.e. vacuum induction-melting inert gas atomization (VIGA). Relatively high amounts of TiC, being already present in the master alloy and powder feedstock, are finely dispersed in the matrix upon PBF-EB/M. This leads to a local change in the chemical composition (depletion of Ti) and a pronounced shift of the transformation temperatures. Despite the high TiC content, superelastic testing revealed a good shape recovery and, thus, a negligible degradation in both, the as-built and the heat-treated state.

Additive manufacturing overcomes the restrictions of classical manufacturing methods and enables the production of near-net-shaped, complex geometries. In that context, lattice structures are of high interest due to their superior weight reduction potential. AlSi10Mg is a well-known alloy for additive manufacturing and well suited for such applications due to its high strength to material density ratio. It has been selected in this study for producing bulk material and complex geometries of a strut-based lattice type (rhombic dodecahedron). A detailed characterisation of as-built and heat-treated specimens has been conducted including microstructural analyses, identification of imperfections and rigorous mechanical testing under different load conditions. An isotropic elastic–plastic material model is deduced on the basis of tension test results of bulk material test specimens. Performed experiments under compression, shear, torsion and tension load are compared to their virtual equivalents. With the help of numerical modelling, the overall structural behaviour was simulated using the detailed lattice geometry and was successfully predicted by the presented numerical models. The discussion of the limits of this approach aims to evaluate the potential of the numerical assessment in the modelling of the properties for novel lightweight structures.

Additive manufacturing of near β-type Ti-13Nb-13Zr alloys using the laser powder bed fusion process (LPBF) opens up new avenues to tailor the microstructure and subsequent macro-scale properties that aids in developing new generation patient-specific, load-bearing orthopedic implants. In this work, we investigate a wide range of LPBF parameter space to optimize the volumetric energy density, surface characteristics and melt track widths to achieve a stable process and part density of greater than 99 %. Further, optimized sample states were achieved via thermal post-processing using standard capability aging, super-transus (900 °C) and sub-transus (660 °C) heat treatment strategies with varying quenching mediums (air, water and ice). The applied heat treatment strategies induce various fractions of α, martensite (α', α'') in combination with the β phase and strongly correlated with the observed enhanced mechanical properties and a relatively low elastic modulus. In summary, our work highlights a practical strategy for optimizing the mechanical and corrosion properties of a LPBF produced near β-type Ti-13Nb-13Zr alloy via careful evaluation of processing and post-processing steps and the interrelation to the corresponding microstructures. Corrosion studies revealed excellent corrosion resistances of the heat-treated LPBF samples comparable to wrought Ti-13Nb-13Zr alloys.

Despite rapid development of laser powder bed fusion (L-PBF) and its monitoring techniques, there is still a lack of in situ crack detection methods, among which acoustic emission (AE) is one of the most sensitive. To elaborate on this topic, in situ AE monitoring was applied to L-PBF manufacturing of a high-strength Al92Mn6Ce2 (at. %) alloy and combined with subsequent X-ray computed tomography. By using a structure borne high-frequency sensor, even a simple threshold-based monitoring was able to detect AE activity associated with cracking, which occurred not only during L-PBF itself, but also after the build job was completed, i.e. in the cooling phase. AE data analysis revealed that crack-related signals can easily be separated from the background noise (e.g. inert gas circulation pump) through their specific shape of a waveform, as well as their energy, skewness and kurtosis. Thus, AE was verified to be a promising method for L-PBF monitoring, enabling to detect formation of cracks regardless of their spatial and temporal occurrence.

A NiTi shape memory alloy with the nominal composition Ni 50.9 Ti 49.1 (at%) was processed by laser beam melting/laser powder bed fusion and the process parameters as well as the type of scanning strategy (point-like exposure) were optimized in a first step to obtain delicate lattice structures (strut diameters below 200 µm). In the second step, the lattice structures were analyzed by means of optical and electron microscopy as well as computer tomography to obtain the interrelation between the process parameters, strut diameter and the uniformity of the corresponding struts. The processing, especially the laser power and the type of point-like exposure, has a strong influence on the resulting strut diameter and, therefore, on the haptic stiffness of lattice structures and the mechanical properties (deformability, superelasticity). Unlike other approaches, our findings imply that filigree NiTi lattices with high uniformity can be manufactured on a standard industry laser powder bed fusion machine without modifying its hard- or software configuration.

In order to overcome constraints related to crack formation during additive processing (laser powder bed fusion, L-BPF) of Fe-Mn-Al-Ni, the potential of high-temperature L-PBF processing was investigated in the present study. The effect of the process parameters on crack formation, grain structure, and phase distribution in the as-built condition, as well as in the course of cyclic heat treatment was examined by microstructural analysis. Optimized processing parameters were applied to fabricate cylindrical samples featuring a crack-free and columnar grained microstructure. In the course of cyclic heat treatment, abnormal grain growth (AGG) sets in, eventually promoting the evolution of a bamboo like microstructure. Testing under tensile load revealed a well-defined stress plateau and reversible strains of up to 4%.

Dense and crack-free specimens of the shape memory alloy Cu71.6Al17Mn11.4 (at.%) were produced via laser powder bed fusion across a wide range of process parameters. The microstructure, viz. grain size, can be directly tailored within the process and with it the transformation temperatures (TTs) shifted to higher values by raising the energy input. The microstructure, and the superelastic behavior of additively manufactured samples were assessed by a detailed comparison with induction melted material. The precipitation of the α phase, which inhibit the martensitic transformation, were not observed in the additively manufactured samples owing to the high intrinsic cooling rates during the fabrication process. Fine columnar grains with a strong [001]-texture along the building direction lead to an enhanced yield strength compared to the coarse-grained cast samples. A maximum recoverable strain of 2.86% was observed after 5% compressive loading. The first results of our approach imply that laser powder bed fusion is a promising technique to directly produce individually designed Cu-Al-Mn shape memory parts with a pronounced superelasticity at room temperature.

Lattice structures and their characterization are much discussed in current research. The complex manufacturing process of laser powder bed fusion with its repeated melting and remelting of metallic powder influences the resulting material properties. Within this contribution the influence of process parameters on the overall behaviour of lattice structure compression test specimens is inherently described within the material model which is derived from tensile tests of additively manufactured material test specimens. The simulation of the lattice structures is performed with an isotropic elastic-plastic material model on the as-designed geometry, neglecting all geometric deviations caused by the manufacturing process. The comparison to compression experiments on the same, additively manufactured geometry, shows surprisingly good agreement. The potential of this approach is evaluated on compression tests with as-built test specimens as well as test specimens which were heat treated after manufacturing.

Laser powder bed fusion (LPBF) can help to overcome two challenges occurring by casting of metastable Al alloys: (1) the high amount of casting defects and (2) the limited part size while maintaining rapid solidification of the whole cross-section. In this study, an Al92Mn6Ce2 alloy was processed crack-free without baseplate heating by LPBF. The high cooling rate during fabrication has a significant impact on the microstructure, which was characterized by SEM, TEM and XRD. The processing through LPBF causes a high amount and a strong refinement of the intermetallic Al20Mn2Ce precipitates. This leads, compared to suction-cast specimens, to a higher hardness (180 HV 5) and a higher tolerable compressive stress (>1200 MPa) associated with a pronounced plasticity without failure up to a strain of 40%. The extraordinary mechanical properties of additively manufactured Al92Mn6Ce2 can extend the possibilities of producing novel LPBF lightweight structures for potential applications under harsh conditions.