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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 Fe 3Si and Fe 6Si 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 Fe 6Si 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.

Additive manufacturing (AM) is being considered as a primary manufacturing process for heat pipes. The Savannah River National Laboratory is researching AM to fabricate a hydrogen isotope separation unit for a thermal cycling absorption process that cycles from cryogenic to moderate temperatures and is a pressure boundary. AM is being explored as a replacement technology to improve heat transfer. Simple test samples with three internal geometries were designed and built from type 316L stainless steel using the powder bed fusion laser process. Nine test article geometries were prepared and subjected to tensile and burst testing and were interrogated using x-ray computed tomography and metallography. The parameters selected for processing the tubes produced a consistent product with acceptable tensile properties and microstructures; however, the process parameters used did not produce full density and minor modifications are needed to achieve full density.

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 µs) and point spacings (80 to 110 µm). 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.

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.

While continuous stabilization in filamentary Y-Ba-Cu-O (YBCO) coated conductors can generate additional heating due to coupling loss, a balance between low ac loss and conductor stability can be found through the introduction of interfacial resistance between the stabilizer and the filaments. The impact of interfacial resistance with respect to ac loss as a function of field was studied for YBCO filaments with a continuous silver cap layer. Starting with uncoated YBCO filaments on standard ion beam assisted deposition (IBAD) templates, an interfacial resistance between filaments was introduced through the exposure of filaments to air at room temperature and followed by the deposition of a continuous, 3 mum thick silver cap layer. The interfacial resistance between silver and the YBCO was controlled by oxygen annealing at different temperatures between 200degC and 450degC. Measurements of the ac loss as a function of applied perpendicular field and frequency and the interfacial resistance revealed a correlation between the coupling loss and the oxygen annealing temperature, where the coupling loss was lowest at an oxygen annealing temperature of 200degC.

To achieve low ac losses in applied ac fields, YBa2Cu3Ox (YBCO) filaments were created on a RABiTS buffered substrate through solution inkjet deposition. A metal organic decomposition (MOD) solution was placed into an inkjet dispenser and filaments of widths of 100 mum and 0.8 mm were deposited on the substrate at a spacing of 50 to 100 mum. Each sample, which had a width of 1 cm and a nominal length of 4 cm, was placed in a perpendicular ac field and the ac losses were measured thermally as a function of the field strengths up to 100 mT and at frequencies between 60 Hz and 120 Hz. Samples with inkjet filaments had a high coupling loss. This coupling between filaments may extend along the entire sample length because removal of the conductor ends did not reduce the coupling loss contribution. Reduction in ac loss was observed in samples with laser-scribed filaments that were made from the same MOD solution.

Use of many Ni-based and Cu-based alloys requires deposition of a Ni overlayer prior to the deposition of the seed layer in order to obtain better epitaxy. In this work, Ni overlayers have been deposited by DC sputtering on biaxially textured NiW and Cu substrates. Films were characterized by x-ray diffraction and atomic force microscopy as a function of temperature, film thickness and deposition rate. The optimum temperature range for deposition was found to be around 400?500??C, which results in relatively smooth films with a good cube texture on both substrates.

Fabrication of a biaxially textured, strengthened Ni substrate with small alloying additions of W and Fe is reported. The substrates have significantly improved mechanical properties compared to 99.99% Ni and surface characteristics which are similar to that of 99.99% Ni substrates. High quality oxide buffer layers can be deposited on these substrates without the need for any additional surface modification steps. Grain boundary misorientation distributions obtained from the substrate show a predominant fraction of low-angle grain boundaries. A high critical current density, J c , of 1.9 MA/cm 2 at 77 K, self-field is demonstrated on this substrate using a multilayer configuration of YBCO/CeO 2 /YSZ/Y 2 O 3 / Ni–3at.%W–1.7at.%Fe. This translates to a I c /width of 59 A/cm at 77 K and self-field. J c at 0.5 T is reduced by only 21% indicating strongly-linked grain boundaries in the YBCO film on this substrate.

Transmission electron microscopy was used to study the microstructure of pulsed laser deposited YBa 2 Cu 3 O 7− δ (YBCO) layers on four different biaxially textured Ni-substrates with epitaxial oxide buffer layers. The oxide layer sequence, YBCO/YSZ/CeO 2 /Ni (YSZ signifies yttria-stabilized zirconia) was the same in each sample, but different deposition techniques were used to deposit the buffer layers. The thicknesses of all three oxide layers varied from sample to sample. A columnar sub-grain structure composed of equiaxed sub-grains in the plane of the film was observed in the YBCO layer of each sample. The sub-grain shape and local mosaic spread (∼3°) appeared to be largely insensitive to the surface topography, density, or method of depositing the YSZ layer immediately below. The sub-grain size (0.2–1.2 μm) increased with film thickness (0.2–2.3 μm), but showed no obvious correlation with the microstructure of the underlying YSZ. The measured misorientation angles ( θ ) at individual sub-grain boundaries suggested that a large fraction of the boundaries in the sub-grain boundary network have θ in the range of 2–3°. For most boundaries, the measured θ was below the 5° “threshold” angle for weak link behavior. Thus, a representative picture of the sub-grain boundary network above a single grain of nickel in a film of sub-micron thickness might be a honeycomb shaped arrangement of 2.5° [0 0 1] tilt boundaries spaced 0.25 μm apart and containing dislocations at a spacing of 10 nm. This structure probably has consequences for the structure of grain boundaries in the YBCO that are replicated from the Ni template below. The superposition of the Ni grain boundary network with the grain boundary network due to mosaic spread almost certainly introduces substantial variations of θ along such boundaries on the sub-micron to micron length scale.

The main objective of this research is to find a suitable alternate solution based seed layer for the standard RABiTS three-layer architecture of physical vapor deposited CeO2 cap/YSZ barrier/Y2O3 seed on Ni-5%W metal tape. In the present work, we have identified CeO2 buffer layer as a potential replacement for Y2O3 seeds. Using a metal-organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of CeO2 (pure and Zr, Cu and Gd-doped) directly on biaxially textured Ni-5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial CeO2 phase with slightly improved out-of-plane texture compared to the texture of the underlying Ni-W substrates can be achieved in pure, undoped CeO2 samples. We have also demonstrated the growth of YSZ barrier layers on pure CeO2 seeds using sputtering. Both sputtered CeO2 cap layers and MOD-YBCO films were grown epitaxially on these YSZ-buffered MOD-CeO2/Ni-5W substrates. High critical currents per unit width, Ic of 264 A/cm (critical current density, Jc of 3.3 MA/cm2) at 77 K and 0.01 T was achieved for 0.8 μm thick MOD-YBCO films grown on MOD-CeO2 seeds. These results indicate that CeO2 films can be grown directly on Ni-5W substrates and still support high performance YBCO coated conductors. This work holds promise for a route for producing low-cost buffer architecture for RABiTS based YBCO coated conductors.

The electromagnetic connectivity and microstructure of three YBa 2 Cu 3 O 7− δ (YBCO) films grown on biaxially textured substrates were investigated by magneto optic (MO) imaging and scanning electron microscopy (SEM). The films were deposited by pulsed laser deposition (PLD) on yttria-stabilized zirconia (YSZ) and CeO 2 -buffered, biaxially textured Ni tapes. The transport critical current density ( J c ) values of the films were 0.3, 0.6 and 0.7 MA/cm 2 (77 K, 0 T). MO imaging revealed clearly granular electromagnetic behavior in the lowest J c and one of the higher J c samples, but considerably better connectivity in the sample with a J c value of 0.6 MA/cm 2 . High resolution SEM showed a dense and rather featureless microstructure in the YBCO of the most highly electromagnetically connected sample, whereas pores and/or second phase particles cluttered the YBCO layers of the granular samples. Thus, the granular behavior in these samples appears to be caused by pores and second phase particles that locally obstruct the superconducting current in the YBCO layer. Control of these types of defects clearly is important for raising the J c value.

A reel-to-reel, electron beam evaporation system has been developed to continuously deposit epitaxial CeO/sub 2/ and other oxide buffer layers on meter-long lengths of biaxially textured Ni tapes. The deposition system includes two interconnected electron beam evaporation chambers and a chamber in which as-rolled Ni tape is in situ annealed to develop biaxial texture. An integral reel-to-reel system with tension control enables motion of the tape with little or no plastic deformation. When depositing epitaxial oxides on Ni, the formation of unfavorably oriented NiO is difficult to avoid. Oxide free, {100} oriented Ni tapes are prepared by control of the partial pressures of H/sub 2/, H/sub 2/O and O/sub 2/ during Ni annealing. X-ray /spl phi/-scans have been performed as a function of length to determine the crystallographic consistency of the epitaxial CeO/sub 2/ over length. Results of SEM examinations of the CeO/sub 2/ buffer layer microstructure are presented. Results for YBCO films deposited on short segments of these buffered substrates are summarized.

The biaxial textures created in metals by rolling and annealing make them useful substrates for the growth of long lengths of biaxially textured material. The growth of overlayers such as high-temperature superconductors requires flat substrates with a single, sharp texture. A sharp cube texture is produced in high-purity Ni by rolling and annealing. We report the effect of rolling reduction and annealing conditions on the sharpness of the cube texture, the incidence of other orientations, the grain size and the surface topography. A combination of high reduction and high-temperature annealing in a reducing atmosphere leads to >99% cube texture, with a mosaic of about the rolling direction, about the transverse direction, and about the normal direction.

React-before-wind surface-coated BSCCO-2212 is being established as a relatively low cost HTS conductor for practical applications. Quality tape is presently being manufactured in lengths of 450 to 500 m at a cost estimated to be 1/3 to 1/5 of the industry costs of BSCCO-2223 powder-in-tube tape. Robust, mechanically sound coils for applications ranging from NMR insert magnets to transformer windings are being made from this BSCCO-2212 tape. The coils have performed consistently through test and thermal cycling without degradation and operate as projected from short sample measurements. A hybrid approach, which uses mainly BSCCO-2212 augmented by BSCCO-2223 conductor in the high radial field end regions, is expected to halve the overall superconductor cost for magnet systems.

We describe a simple experimental apparatus capable of simultaneous measurements of elastic and anelastic properties of film/substrate composites in controlled atmospheres (10-6-104 Pa) from 25 to 1000°C. The apparatus employs the technique of dynamic resonance in which the mechanical response of a material can be determined over a wide range of frequency (0.1–100 kHz) with a resolution of ±1 μHz. We present experimental results for thin films (approximately 100 nm) of nickel and gold on sapphire substrates. These results demonstrate the sensitivity of the apparatus to both the adhesion and the elasticity of the supported film.