A major goal in printing soft magnetic Fe-Si steels using additive manufacturing is to take advantage of the potential for complex geometric designs and site-specific grain control. One major step in the processing of these alloys is understanding how processing parameters might impact how the as-built microstructure responds to annealing (i.e. the annealing response). The impact of scan strategy on the annealing response for thin wall geometries is specifically explored. Two scan strategies were explored for a thin wall geometry that produced a strongly columnar grain structure and equiaxed grain structure. Samples from both scan strategies annealed at 1200 degrees C showed a marked difference in annealing response with the more equiaxed sample seeing full recrystallization and grain growth, while the more columnar grain structure saw little change in microstructure. After analysis through characterization techniques and thermal-mechanical simulations Differences in internal energy within the grains were ruled out because calculated GND density values were similar for both samples. The formation of secondary particles was ruled out as a contributing factor due to the type of oxide formations and their size. It was concluded that the contributing factor to the difference in the annealing response were a difference in the resulting grain size and the density of high angle grain boundaries. These two differences were largely attributed to differences in the thermal gradient conditions due to grains preferentially growing in the direction of the steepest thermal gradient.

Fabrication of nuclear reactor components using additive manufacturing (AM) methods is now a practical option since the AM technologies have advanced to allow for building of complex parts with high quality materials. To assess the mechanical performance of printed components in reactor-relevant conditions and to build a property database for the AM 316L stainless steel (SS), mechanical testing and characterization were performed before and after neutron irradiation. Miniature tensile specimens were irradiated at the High Flux Isotope Reactor (HFIR) to 0.2 and 2 displacements per atom (dpa) at 300 and 600°C. The AM 316L SS was tested in the as-built, stress-relieved, and solution-annealed conditions, and the wrought (WT) 316L SS in solution-annealed condition as a reference alloy. The baseline test result showed that the AM 316L SS, regardless of the post-build heat treatment, had higher strength than the WT 316L SS, but similar ductility. Post-irradiation tensile testing was conducted at RT, 300°C, and 500°C for selected irradiation conditions. Neutron irradiation induced significant changes in the mechanical behavior of the AM stainless steels, including both hardening and softening. Although the as-built 316L steel after 300°C irradiation showed necking just after yielding, the overall property changes of the as-printed alloy became less significant after 600°C irradiation. Irradiation-induced ductilization was also observed after the higher temperature irradiation. In general, the strength change was smaller in the relatively stronger as-built and stress-relieved AM SSs than in the solution-annealed AM and WT SSs. These relatively lower strength 316L SSs overall retained higher ductility in the irradiation conditions tested, but the stronger 316L SSs demonstrated a similar level of ductility after the higher temperature (600°C) irradiation. It is a positive assessment for the AM 316L materials that no embrittlement was observed within the test and irradiation conditions of the experiment.

This research paper evaluated three pathways for qualification of 316 L stainless steel components made by laser powder bed fusion additive manufacturing (AM). Comprehensive and consistent process flows with computational modeling, in-situ measurements, ex-situ characterization and mechanical testing with simple-and complex-geometries were explored. The role of post-process hot isostatic pressing (HIP), and solution anneal treatment were evaluated. By using HIP, the scatter in 316 L steel AM properties within single and complex components was minimized to meet the requirement of existing industry standards. For applications where HIP may not be feasible and with some extent of defect tolerance, alternative qualification methodologies of deploying L-PBF AM parts were also explored with samples made with and without engineered porosities. The data generated in this research will be relevant to deployment of AM components for emerging nuclear energy applications. (c) 2021 Elsevier B.V. All rights reserved.

The power losses associated with the electrical resistance of copper (Cu) have generated considerable interest in the development of advanced conductors that incorporate carbon nanotubes (CNTs) int...

Additive manufacturing (AM) of functional alloys has become a promising area of research for the development of novel devices with complex geometric features that cannot be manufactured using conventional methods. In this work, we investigate the additive manufacturing of Fe3Si and Fe6Si benchtop scale transformer cores. A novel design inspired by a Hilbert curve was developed to exploit the geometric complexity of AM, and cores of each alloy were successfully printed, heat treated, machined, pickled, and assembled. The microstructure and magnetic performance of the cores were characterized and compared to additively manufactured components with simpler square cross-sections as well as to conventionally laminated non-oriented electrical steel sheet. The AM cores showed performance roughly comparable or better than the conventional non-oriented sheet, but higher power losses than Goss oriented steel. The increased Si content of the Fe6Si alloy resulted in a significant reduction in core losses. The transformer cores had higher losses than the similarly manufactured simple cross-sections, which was attributed to defects in fabrication and assembly that resulted in air gaps between the transformer legs. The performance was also rationalized relative to nanoscale carbide and oxide inclusions.

There is a synergy between welding and additive manufacturing with reference to spatial and temporal variations of heat transfer. In this research,in-situmeasurements of heat transfer conditions are considered as a viable qualification methodology for additive manufacturing (AM). Infrared imaging (IR) was performed within a laser powder bed fusion (L-PBF) AM machine equipped with an IR camera. Infrared thermal signatures as a function of space and time, while processing Ti6Al4V and 316L stainless steel powders, were extracted and analysed. The analyses correlated the defect evolution at low- and high-heat input conditions to thermal decay and integrated intensities. The IR based results were validated by processing a 316L cylinder with engineered porosities and detecting the same with ground truth data from computed tomography.

The influence of geometry and scan pattern on the microstructure evolution and magnetic performance of additively manufactured Fe-3Si components was investigated. To reduce eddy current losses, novel geometries were designed and built and the microstructure and properties of these samples were characterized. The laser scan pattern was shown to strongly influence both the as-built grain structure and strength of the crystallographic texture, resulting in measurable changes in the as-built magnetic performance. In thin wall samples, heat treatment resulted in an increase in the maximum relative magnetic permeability and decrease in power losses in most samples, consistent with grain growth. However, decreases in the spacing between thin walls to increase the stacking factor of the cross-section was shown to result in unwanted electrical shorting between walls and an increase in eddy current losses. Compared to simple parallel plate construction and a mesh structure, a novel cross-section design based on the Hilbert space filling curve was found to produce the lowest power losses. The mechanisms behind these results were explored using a combination of heat conduction and electromagnetic simulations, providing a route for future component and process optimization.

In laser powder bed additive manufacturing processes, feedstock materials are often recycled after each build. Currently, a knowledge gap exists regarding powder reuse effects on powder size distribution, morphology, and chemistry as a function of part geometry and processing conditions. It was found during selective laser melting (SLM) of 316 stainless steel that a significant amount of (0.100 wt pct) oxygen pickup can occur in molten material (spatter) ejected from the powder bed surface. This value was significantly larger than the oxygen content of the as-received powder feedstock (0.033 wt pct). Furthermore, the powders in the heat-affected-zone regions, adjacent to molten pool, also exhibit oxygen pickup (≥ 0.043 wt pct). The oxygen content in unmelted 316L powder was found to vary as a function of its spatial position in the powder bed, relative to the heat source. Interestingly, the volume of melted material (i.e., thin vs thick walls) did not correlate well with the extent of oxygen pickup. Possible mechanisms for oxygen pickup in the powder during SLM, such as adsorption and breakdown of water, oxygen solubility, spatter re-introduction, and solid-state oxide growth, are discussed.

Additive manufacturing (AM) of the complex devices for energy application remains an almost unexplored area, and the harsh acidic environment also limits the application of AM parts in water splitting for hydrogen production. Here, bipolar plates (BPs), which are used to transport reactants/products and conduct electrons in proton exchange membrane electrolyzer cells (PEMECs), are printed from stainless steel (SS) with selective laser melting (SLM). Then surface treatments are employed on those BPs by thin film electroplating with Au, and the protective thin layer enables the utilization of AM SS parts to both cathode and anode sides of water electrolyzer cells and exhibits superior corrosion resistances and electronic conductivities. The Au-coated AM SS BPs deliver a low interfacial contact resistance (6.4 m Omega cm(2) under 1.45 MPa) and an excellent performance in PEMECs (1.71 Vat 2 A/cm(2)), and maintain a remarkable durability in the simulated anode environment compared with the uncoated AM SS BPs and conventional graphite BPs. This approach demonstrates the possibility of 3-dimensional printing fully integrated water electrolyzer cells at both anode and cathode sides.

One significant maintenance problem and cost associated with solar energy conversion systems is the soiling due to the accumulation of dust and other pollutants. In this work, we describe a scalable approach for applying antisoiling coatings based on superhydrophobic (SH) silica particles using a spray coating process. A large water contact angle (WCA) is one of the characteristics of excellent SH surfaces and because of the low surface energy and low adhesion forces the soiling rate is reduced. Our findings indicate that the WCA depends strongly on the ratio of the polymer binder and the nanoparticles. The nanoparticle surface coverage of the spray coated samples was substantially improved after rinsing with solvent. This process tended to remove large aggregates and excess polymer binder and further increased the WCA by allowing exposure of the functionalized nanoparticles. The durability of the SH coatings was enhanced when the substrate was pretreated with polymer binder and an optimal curing time between 30 and 60 min. The abrasion tests of the SH coatings we report in this study showed that the WCA decreased from ~ 166° to ~ 157° after exposure to 2.6 g of sand. Such coatings will help reduce costs of periodic cleaning of solar energy conversion systems (photovoltaic panels and concentrated solar mirrors).

Using additive manufacturing (AM) technology, a fundamental material and structure innovation was proposed to significantly increase the energy efficiency, and to reduce the weight, volume and component quantity of proton exchange membrane electrolyzer cells (PEMECs). Four conventional parts (liquid/gas diffusion layer, bipolar plate, gasket, and current distributor) in a PEMEC were integrated into one multifunctional AM plate without committing to tools or molds for the first time. In addition, since the interfacial contact resistances between those parts were eliminated, the comprehensive in-situ characterizations of AM cells showed that an excellent energy efficiency of up to 86.48% was achieved at 2 A/cm(2) and 80 degrees C, and the hydrogen generation rate was increased by 61.81% compared to the conventional cell. More importantly, the highly complex inner structures of the AM integrated multifunctional plates also exhibit the potential to break limitations of conventional manufacture methods for hydrogen generation and to open a door for the development of other energy conversion devices, including fuel cells, solar cells and batteries.

Components made by laser powder bed fusion (L-PBF) additive processes require extensive trial and error optimization to minimize defects and arrive at targeted microstructure and properties. In this work, in situ infrared thermography and ex situ surface roughness measurements were explored as methodologies to ensure Inconel ® 718-part quality. For a given laser energy of 200 Watts, prismatic samples were produced with different exposure times (80 to 110 µ s) and point spacings (80 to 110 µ m). The infrared intensities from laser–material interaction zones were measured spatially and temporally. The conditions leading to higher IR intensity and lowest surface roughness values correlated well with less porosity and coarse solidification grain structure. The transition from highly columnar to misoriented growth is attributed to changes in thermal gradients and liquid–solid interface velocities. Hardness measurements and electron microscopy of the as-processed and post-processed heat-treated samples show complex transitions in microstructural states including the heavily dislocated FCC matrix, reduction of dislocation density, and copious precipitation, respectively. These results show that the geometry-process-structure-property correlations are dynamic, and they cascade depending on the transitions of phase states from powder to liquid to solid, as well as phase decompositions and deformations within the solid FCC phase. Validity of using analytical weld process models to describe the above phenomena is also highlighted.

There is a demand for the manufacture of two-dimensional (2D) materials with high-quality single crystals of large size. Usually, epitaxial growth is considered the method of choice(1) in preparing single-crystalline thin films, but it requires single-crystal substrates for deposition. Here we present a different approach and report the synthesis of single-crystal-like monolayer graphene films on polycrystalline substrates. The technological realization of the proposed method resembles the Czochralski process and is based on the evolutionary selection(2) approach, which is now realized in 2D geometry. The method relies on 'self-selection' of the fastest-growing domain orientation, which eventually overwhelms the slower-growing domains and yields a single-crystal continuous 2D film. Here we have used it to synthesize foot-long graphene films at rates up to 2.5 cm h(-1) that possess the quality of a single crystal. We anticipate that the proposed approach could be readily adopted for the synthesis of other 2D materials and heterostructures.

Additive manufacturing (AM) technology is capable of fast and low-cost prototyping from complex 3D digital models. To take advantage of this technology, a stainless steel (SS) plate with parallel flow field served as a combination of a cathode bipolar plate and a current distributor; it was fabricated using selective laser melting (SLM) techniques and investigated in a proton exchange membrane electrolyzer cell (PEMEC) in-situ for the first time. The experimental results show that the PEMEC with an AM SS cathode bipolar plate can achieve an excellent performance for hydrogen production for a voltage of 1.779 V and a current density of 2.0 A/cm(2). The AM SS cathode bipolar plate was also characterized by SEM and EDS, and the results show a uniform elemental distribution across the plate with very limited oxidization. This research demonstrates that AM method could be a route to aid cost-effective and rapid development of PEMECs. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Additive Manufacturing brings unique opportunities to the fabrication world, especially for complex, high value added components that are challenging if not impossible to fabricate using traditional technologies. There are several different technologies that can be used for making metal additive manufactured parts. In this study, selective laser melting (SLM) was used to fabricate conceptual process tubing. Through an evolutionary design and build process coupled with thermal and mechanical modeling, tubing with a unique additive manufacturing compatible geometry has been fabricated. This paper will briefly describe the application, which has a thermal swing from nominally 140°C to −40°C, the evolution of the design, and the characterization conducted to date. Finally, the challenges of designing and printing a coiled segment of this tubing that is 150 cm long will be described. The results will include non-destructive and destructive testing and evaluation. The data from tensile testing the first and second generations of the tubing will be compared. The properties and characterization of the surrogate coil will be described and discussed. Future component development and testing will be discussed for this unique AM process tubing.

The new series of commercially produced high temperature superconducting (HTS) tapes based on the YBa2Cu3O7 (YBCO) structure have attracted renewed attention for their performance under applied magnetic fields without significant loss in supercurrent compared to the earlier generation of conductors. This adaptability is achieved through rare earth substitution and dopants resulting in the formation of nanoparticles and extended defects within the superconducting film matrix. The electrical performance of Zr-(Gdx,Y1−x)Ba2Cu3O7 and (Y1−x,Dyx)Ba2Cu3O7 coated conductor tapes were tested prior to and after neutron exposures between 6.54×1017 and 7.00×1018 n/cm2 (E > 0.1MeV). Results showed a decrease in superconducting current with neutron irradiation for the range of fluences tested, with losses in the Zr-(Gdx,Y1−x)Ba2Cu3O7 conductor being more rapid. Post-irradiation testing was limited to evaluation at 77K and applied fields of up to 0.5Tesla, and therefore testing at lower temperatures and higher applied fields may result in improved superconducting properties as shown in previous ion irradiation work. Under the conditions tested, the doped conductors showed a loss in critical current at fluences lower than that of undoped YBa2Cu3O7 tapes reported on in literature.

Additive manufacturing (AM), widely known as 3D printing, is a method of manufacturing that forms parts from powder, wire or sheets in a process that proceeds layer by layer. Many techniques (using many different names) have been developed to accomplish this via melting or solid-state joining. In this review, these techniques for producing metal parts are explored, with a focus on the science of metal AM: processing defects, heat transfer, solidification, solid-state precipitation, mechanical properties and post-processing metallurgy. The various metal AM techniques are compared, with analysis of the strengths and limitations of each. Only a few alloys have been developed for commercial production, but recent efforts are presented as a path for the ongoing development of new materials for AM processes.

This paper focuses on sintering kinetics of inkjet-printed lines containing silver nanoparticles deposited on a plastic substrate. Upon heat treatment, the change of resistance in the printed lines was measured as a function of time and sintering temperatures from 423 K to 473 K (150 °C to 200 °C). A new phenomenon was observed that a critical temperature existed for the sintering process, beyond which there was no further reduction in resistance. Experimental evidence and analysis show the critical temperature is associated with the boiling point of the solvent. New sintering mechanisms have been proposed to explain the observed phenomenon, including accelerated diffusion facilitated by the existence of liquid solution based on the theory of liquid phase sintering, and particle collision and coalescence caused by the induced liquid flows in the solution. The proposed theory suggest new means can be devised to improve the sintering results for inkjet-printed lines and other applications.

We report the magnetic field and temperature dependence of the critical current density {Jc(H) and Jc(T)} flowing in a 5 μm thick sample of SmBa2Cu3O7−δ (SmBCO) film. The film is a coated conductor (CC) deposited on an IBAD-MgO textured metallic template. For a range of intermediate fields, we find JcαH-α with values of α between 0.44 and 0.49. These values are lower than those reported for other CC in the literature. The sample has a Jc of 13.6 MA/cm2 at 5 K and self-field. Such high-Jc wires should find applications in large-scale energy applications of high-temperature superconductors. The temperature dependence of Jc at self-field and different applied fields is also analyzed.