Mid Sweden University

This study introduces the anisotropy effect of Ti6Al4V substrate obtained by electron beam melting (PBF-EB) on the anodizing process, revealing its capacity to induce anisotropic TiO2 nanotubes. Highly organized TiO2 nanotubes are formed on Ti6Al4V substrates produced through PBF-EB or forging, with the PBF-EB cross-orientation displaying superior nanotube growth due to enhanced catalytic activity. Morphological and electrochemical characterizations underscore the significant influence of substrate orientation and anodizing voltage on nanotube growth and corrosion resistance. PBF-EB-cross orientation at 30 V exhibits a thicker and more homogeneous nanotube layer, resulting in improved film resistance and substantially lower corrosion rates compared to forged substrates. The electrochemically calculated nanotube film thickness aligns with microscopic analyses, emphasizing the importance of a homogenous and resistive nanotube coating for effective corrosion control.

This work investigates microstructural and mechanical transitions in multi-material assemblies of American iron and steel institute 316L stainless steel and V4E tool steel, fabricated using a dual-hopper layer alternation strategy via electron beam powder bed fusion (PBF-EB). Two types of layered transitions are produced: alternating transition and alternating incremental transition (AIT). The assemblies are characterized using electron backscattered diffraction and high-speed nanoindentation (HSN), with mechanical phases extracted via Gaussian mixture modeling applied to nanoindentation maps. In the alternating layer sample, localized mechanical features are identified within the elongated austenite grains of 316L, and V4E is observed growing along grain boundaries at the interphase. In the AIT sample, similar interfacial features are observed, but the gradual addition of V4E layers generates a continuous mechanical gradient. Nanoindentation maps reveal increasing hardness and elastic modulus along the transition, ultimately reaching homogenized mechanical behavior in the V4E region. The study demonstrates the feasibility of producing compositionally graded steel assemblies with robust interfaces using PBF-EB. It also emphasizes the value of HSN combined with statistical clustering to resolve micromechanical heterogeneities, enabling more precise design and optimization of advanced multi-material systems.

This study introduces an innovative approach for optimizing process development in electron beam powder bed fusion (PBF-EB) of non-flowing chemically reduced tungsten powder. Both line- and spot melting strategies were employed, with gradient-based variations of key processing parameters—beam current and scanning speed (line melting)/dwell time (spot melting)—applied across the XZ and XY planes on prismatic specimens. This method allowed mapping the transition from porous to swelling material within a single specimen and exposed the effects of changing gradient directions. Scripts were developed to analyze swelling and porosity from stacked backscattered electron data, providing valuable insights into material density and defect distribution. Optimal parameters for line melting (1400 W, 115 mm/s) and spot melting (1400 W, 4.5 ms dwell time) were identified, resulting in high-density samples. Solid samples were achieved with Archimedes densities of 99.8% and 99.9% respectively. Microscopical analysis verified parameter windows with dense, swelling-free material, selected for further builds and detailed characterization. Microstructural and compositional analysis was conducted using SEM and EBSD, while local micromechanical properties were assessed through micro hardness. Scaling up line melting was deemed infeasible due to warping, while spot melting was scaled to a melting area of 50 mm × 50 mm. 

The ability to control process parameters over time and build space in electron beam powder bed fusion (PBF-EB) opens up unprecedented opportunities to tailor the process and use materials of a different nature in the same build. The present investigation explored the various methods used to adapt the PBF-EB process for the production of functionally graded materials (FGMs). In this way, two pre-alloyed powders—a stainless steel (SS) powder and a highly alloyed cold work tool steel (TS) powder—were combined during processing in an S20 Arcam machine. Feasibility experiments were first carried out in a downscaled build setup, in which a single powder container was installed on top of the rake system. In the container, one powder was placed on top of the other (SS/TS) so that the gradient materials were produced as the powders were spread and intermixed during the build. The process was later scaled up to an industrial machine setup, where a similar approach was implemented using two configurations of powder disposal: SS/SS + TS/TS and TS/TS + SS/SS. Each configuration had an intermediate layer of powder blend. The FGMs obtained were characterized in terms of their microstructure and local and macromechanical properties. For the microstructural analysis, optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDX) were performed on the polished cross-sections. This provided evidence of gradual microstructural and compositional transitions in the samples, with a shift from SS to TS and vice versa. Nanoindentation experiments confirmed that there was a consequent gradient in the hardness, stiffness, and wear ratio from the softer and ductile SS to the harder and stiff TS. Scratch experiments revealed gradual evolution in the sliding wear behavior of the printed materials. A “progressive spring” and a “hardness-tailored punching tool” were fabricated as demonstrators. The results obtained demonstrate the great potential to gradually tailor the composition, microstructure, mechanical properties, and wear resistance by combining different powders, and they suggest that any PBF-EB system can be repurposed to build gradient materials without hardware modification. Potential applications include the tooling industry, where hard and wear-resistant materials are needed for the surfaces of tools, with tougher and more ductile materials used in the cores of tools.

Surface roughness of the additively manufactured (AM) parts can reduce the service life, especially under dynamic loadings, due to promoting fatigue by providing initiation sites for fatigue cracks. Therefore, improving the surface condition of AM specimens can be a solution to increase the fatigue strength. The stiffness method is a rapid fatigue test method that allows to obtain reliable fatigue limit values in a cheaper and easier way than traditional methods. Consequently, this work aims to investigate the effect of surface roughness on the fatigue behavior of stainless steel AISI 316L specimens using the stiffness method. These specimens were printed with both laser and electron beam powder bed fusion techniques, and different contour parameters were produced to obtain different surface roughness values. The competitional effect of the internal defects, which become surface defects after machining, and the surface roughness of the as-built specimens, is also addressed by the stiffness method results.

Electron beam powder bed fusion (PBF-EB) is a known metal additive manufacturing (AM) technology. Processing non-conducting powders such as ceramics has so far been considered as not feasible because of the inherent problems with Coulomb repulsion due to insufficient electrical conductivity. In this study, a method for functionalizing ceramic powder is proposed where particles are electroless coated by a ~ 1 µm Ni layer to decrease the surface resistivity. The feasibility of the suggested approach is tested on Al2O3 powder, and the results show that the coated ceramic powder has a decreased surface resistivity, which enables processing by PBF-EB. Heating and melting parameters were investigated and samples were manufactured at ~ 1600 °C. Sintered and melted powders were analyzed by microscopy and micromechanically tested by nanoindentation. Calculations, visual observation and SEM–EDX suggest that the Ni coating is evaporated during the process, which suggests that the process could be feasible for the manufacturing of pure ceramic parts.

En el presente estudio, se han analizado una serie de muestras de metales producidos mediante PBF-EB (Powder Bed Fusion – Electron Beam) usando diferentes parámetros de manufactura mediante ensayos de nanoindentación con el objetivo de conocer los cambios que se producen en las propiedades mecánicas (concretamente, la dureza y el módulo elástico), y correlacionarlos con la microestructura. Paralelamente, se han llevado a cabo análisis estadísticos de los datos obtenidos en los ensayos mediante algoritmos de aprendizaje automático (Machine Learning). Concretamente, se han aplicado métodos de agrupación (clustering), con la intención de crear un método robusto que sea capaz de, a partir de los datos de los ensayos de nanoindentación, identificar determinadas características del material, como por ejemplo qué fases contiene, cómo están distribuidas y sus orientaciones cristalinas.

Metal additive manufacturing technologies, such as electron beam powder bed fusion (PBF-EB), rely on layer heating to overcome the so-called “smoke” phenomenon. When scaled up for industrial manufacturing, PBF-EB becomes less productive due to the lengthy preheating process. Currently, only the electron beam (EB) is used for preheating in PBF-EB, resulting in increased manufacturing times, energy consumption, and in some cases limiting the applicability of the technology. In this study, a new preheating approach is suggested that incorporates a near-infrared radiation (NIR) emitter inside an PBF-EB system. The NIR unit eliminates the need for EB heating, reducing build time and powder charging. Successful builds using 316 L and Ti6Al4V precursor powders validate the feasibility of the proposed approach. The produced samples exhibit similar properties to those obtained by the standard PBF-EB process. The introduction of NIR technology also reduced build cost and increased the service intervals of the electron gun. 

The use of an electron beam (EB) as a heating source in EB-based powder bed fusion (PBF-EB) has several limitations, such as reduced powder recyclability, short machine service intervals, difficulties with heating large areas and the limited processability of charge-sensitive powders. Near-infrared (NIR) heating was recently introduced as a feasible replacement and/or complement to EB heating in PBF-EB. This work further investigates the feasibility of using NIR to eliminate the need for a build platform as well as to enable easier repairing of parts in PBF-EB. NIR-assisted Ti-6Al-4V builds were successfully carried out by starting from a loose powder bed without using a build platform. The results do not only confirm that it is possible to eliminate the build platform by the aid of NIR, but also that it can be beneficial for the process cleanliness and improve the surface quality of built parts. Furthermore, a 430 stainless-steel (SS) component could be repaired by positioning it in a loose 316L SS powder bed using a fully NIR-heated PBF-EB process.

This study investigates the use of Electron Beam Powder Bed Fusion (PBF-EB) spot melting on SDSS 2507, a material known for its high tensile strength, corrosion resistance, and welding properties. Spot melting, a localized melting technique, utilize a stationary beam to create melt pools before rapidly repositioning to form new ones, offering precise control over material properties in additive manufacturing. We conducted a design of experiments with 32 samples and analysed them using SEM, XRD, EBSD, optical microscopy, nanoindentation and statistical modelling. Elevated PBF-EB processing temperatures significantly influence microstructure and phase composition. XRD analysis identified the presence of the detrimental sigma phase. EBSD analysis revealed a composition primarily consisting of austenite (63 %) and sigma phase (33.5 %), with residual ferrite (3.5 %). Statistical modelling demonstrated that a combination of spot-time, spot distance, focus offset, and layer thickness was the most reliable predictor for density while area energy proved to be the most accurate predictor for hardness, with R2adj values of 0.766 and 0.802, respectively. Our study confirms that PBF-EB is capable of processing SDSS 2507 through spot melting, resulting in high-density samples at high productivity rates. The presence of sigma phase shows a need for post build heat treatment to achieve the desired phase distribution. This research enhances the understanding of the process and also holds promise for industrial applications.