SEARCH · Engineering Papers
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Since the discovery of superconducting Nb 3 Sn in 1954, continuous developments have led to a strong improvement of its properties. This chapter describes the evolution of Nb 3 Sn fabrication techniques since the 1960s and the main properties of modern Nb 3 Sn composite wires and Rutherford cables.
Hybrid manufacturing combines the simultaneous benefits of additive manufacturing (complex geometries, part consolidation, and mass customization) with the advantages of subtractive manufacturing (superior surface finish and enhanced dimensional accuracies) by integrating a suite of complementary traditional processes into a base platform of additive manufacturing. The use of hybrid technology has grown in recent years given its capabilities on repairing metallic structures, producing parts with conformal cooling features, and manufacturing functionally graded products. These kinds of capabilities are of great interest to the medical implant, energy, automotive, maritime, and aerospace industry sectors, among many other fields. This work investigated the mechanical properties of stainless steel (SS) 316L as a function of different tool paths strategies using an integrated 5-axis CNC hybrid Mazak system with a laser hot wire deposition system (LHWDS). This study includes the evaluation of different printing parameters and their impact on the quality of the printed bead as well as the incorporation of a structure–property material relationship based on the mechanical performance of the manufactured coupons.
Here, this study systematically investigates the effects of shielding gas, bead spacing, weld mode, and travel speed on the phase balance, porosity, and hardness of wire arc additively manufactured (WAAM) super duplex stainless steel (ER2594). Robotic WAAM was employed to fabricate multilayer walls under systematically varied process conditions, followed by phase transformation simulations, X-ray computed tomography (XCT), electron backscatter diffraction (EBSD), and microhardness evaluation. Thermodynamic simulations predicted rapid cooling of AM process can suppress the potential formation of deleterious precipitates which was later validated via cross-sectional microstructure analyses of printed samples. XCT revealed porosity levels below 0.2% for all deposits, with reduced travel speed significantly lowering defect volume. Microstructural analyses revealed the evolution of various austenite precipitates, including grain boundary austenite (GBA), Widmanstätten austenite (WA), and intergranular austenite (IGA), sequentially upon cooling of the ferrite phase. Among all process parameters, weld transfer mode exhibited the strongest influence on phase balance; pulsed mode promoted higher ferrite retention (~ 36%) compared to RapidX mode. No consistent relationship between stabilized phase fraction and captured microhardness was observed. This work provides critical insights for optimizing WAAM parameters to control phase balance and mechanical performance, which is essential for producing high-integrity super duplex stainless-steel components for nuclear and marine applications.
Recent research has studied the use of low transformation temperature (LTT) martensite steel as feedstock for wire arc additive manufacturing (WAAM) and low tensile residual stresses or compressive residual stresses were detected in the printed walls. These residual stress states help to improve printed product properties such as fatigue strength and corrosion resistance. However, the thermal and mechanical properties of WAAM printed LTT martensite steel walls are largely unknown. In this work, a printed LTT martensite steel was characterized for its thermal, metallurgical, and mechanical behavior at room and elevated temperatures. The temperature-dependent specific heat capacity, thermal expansion, atomic lattice spacing, and tensile properties were measured during both heating and cooling and related to observed microstructural features and computational thermodynamics predictions. These results revealed a large hysteresis in the martensitic transformation, with a martensite start temperature of 240 °C and austenite start temperature of 680 °C. Additional thermal cycles and specimen orientation did not affect the printed specimen austenite and martensite transformations. However, it was observed that the printed metal may exhibit tempering embrittlement at about 350 °C but further studies are needed to confirm that. Further, these results suggest that a temperature control of 250 °C to 350 °C during WAAM is needed to maximize the stress reduction potential of the LTT250 martensite steel. Opportunities for future implementation of LTT martensite steels and optimization of additive manufacturing process conditions are identified.
We report thermoelectric measurements over a temperature range of 80 K to 300 K of heavily boron-doped nanocrystalline silicon films prepared by hot-wire and plasma-enhanced chemical-vapor depositions. The nanocrystalline silicon films were doped by either gaseous deposition precursors or post-deposition ion implantation, resulting in boron concentrations ranging from 1 -2 x 10 20 cm -3 to 3 x 10 21 cm -3 . Reasonable values of the Seebeck coefficient and electrical conductivity were obtained at 300 K, comparable to many other research work. We also report thermal conductivity measurements on these films before doping, which we use to estimate their prospective thermoelectric efficiency. These measurements show values as low as 0.76 W/mK at 300 K which depend highly upon the grain sizes of the nc-Si films. We find that post-deposition doping by ion-implantation is more effective at enhancing the power factor than gaseous doping, and the power factor is only weakly dependent upon doping concentration for the films doped by ion implantation. We conclude that improvements of the thermoelectric efficiency of nc -Si films may depend more on a reduction of their thermal conductivity than doping optimization. The small grain sizes and the low thermal conductivity of the undoped nc -Si films accomplished in this work are therefore encouraging developments.
Wire and arc additive manufacture (WAAM), as an emerging and promising technology of metal additive manufacturing, it lacks of experimental works to clarify the feature of geometrical configuration, microstructure and tensile properties, which can be used for further evaluating whether the as-deposited part can be used directly, and providing design reference for structure optimization. Taking 5A06 aluminum alloy additive manufacturing for example, in this paper, the geometric limitation and tensile property criteria are characterized using experimental method. The minimum angle and curvature radius that can be made by WAAM are 20° and 10 mm when the layer width is 7.2 mm. It shows isotropy when loading in build direction and perpendicular one. When loading in the direction of parallel and perpendicular to texture orientation, the tensile properties are anisotropic. The difference between them is 22 MPa.
The extensive usage of P91 steel in certain reactor components requires its precision fabrication by wire electrical discharge machining (WEDM). The WEDM cut surfaces consist of primarily re-melted and solidified layer (recast layer) of 2-8 µm. The recast layer is a result of fast removal of heat by unaffected metallic substrate and dielectric medium leading to rapid cooling. The WEDM surface is expected to affect the component performance in terms of its corrosion properties. The microstructural changes taking place due to EDM cutting of P91 steel bring about a drastic change in the electrochemical response of surface as compared to that for bulk P91 steel. The surface microstructure is shown to alter the passivation behavior and resistance to localized corrosion. Electrochemical polarization studies were done to evaluate passivation, pitting and intergranular corrosion (IGC) behavior and field emission gun—scanning electron microscopy was used for microstructural characterization of P91 steel surfaces. The passivation behavior for P91 steel WEDM cut surfaces was better than that for diamond polished surface. But pitting corrosion resistance decreased for the P91 steel WEDM surface which is a result of inhomogeneities in the microstructure of recast layer. The IGC resistance though increased due to the decreased grain size in the surface layer.
A new type of cobalt-containing iron-based slag-free self-shielded flux-cored wire was developed for hardfacing. The influence of cobalt additions on the microstructure and wear performance of the hardfacing was investigated. The cobalt-containing iron-based hardfacing alloy has a typical hypereutectic microstructure consisting of primary M{sub 7}(C, B){sub 3} carbide, and a eutectic of M{sub 3}(C, B) carbide and austenite (part of which subsequently transformed into martensite). Cobalt promoted the formation of austenite and changed the morphology of the primary carbide and eutectic colonies. The morphology of primary carbide became fragmented with increasing cobalt due to the possible impeding effect of cobalt to the movement of the M{sub 7}(C, B){sub 3}/liquid interface. Different structures of the eutectic carbides were observed—the chrysanthemum structure for 1.42 wt.% cobalt, the skeleton form for 2.88 wt.% cobalt, the radial stripe 4.37 wt.% cobalt and the discrete stripe for 5.75 wt.% cobalt. Wear loss of the hardfacing alloy containing 2.88 wt.% cobalt was the smallest among all the alloys, owing to the large primary large carbide and skeleton-shaped eutectic carbides, the proper amount of austenite phase separating the M{sub 7}(C, B){sub 3} and M{sub 3}(C, B) carbides, the solid solution strengthening by cobalt in the matrix, and the high hardness of the alloy. Moreover, the wear resistance has a tendency to decrease with the increase in velocity as well as load.
In this paper, superelastic behavior of nickel-titanium thin wires is characterized using the method of dynamic mechanical analysis. Nominal dynamic storage modulus E{sup ′} is measured as function of nominal strain and stress during isothermal superelastic tensile tests at three testing temperatures above the reverse martensitic transformation finish temperature. The method brings new information on deformation mechanisms compared to the consideration of only tensile stress–strain curves. It is shown that determination of the elastic moduli E, especially at high strain, requires to calculate the true storage modulus E{sub t}{sup ′}. Using E{sub t}{sup ′} and not E{sup ′}, elastic modulus of oriented martensite E{sub M} is determined equal to 73 GPa of the same order than the elastic modulus of austenite E{sub A} equal to 70 GPa. Two models are then proposed to simulate experimental storage moduli evolution during the tests. A first model explains the E{sup ′} evolution during stress plateau by the localization phenomenon; it leads to express E{sup ′} as function of the nominal strain. A second model describes the evolution of E{sub t}{sup ′} after the stress plateau as function of true stress and test temperature. This model permits to determine the Clausius–Clapeyron coefficient of the forward transformation.
Cold rolling can be used in-process or post-process to improve microstructure, mechanical properties and residual stress in directed-energy-deposition techniques, such as the high deposition rate wire + arc additive manufacturing (WAAM) process. Finite element simulations of the rolling process are employed to investigate the effect of rolling parameters, in particular rolling load and roller profile radius on the residual stress field as well as plastic strain distribution for the profiled roller. The results show the response to rolling of commonly used structural metals in WAAM, i.e., AA2319, S335JR steel and Ti-6Al-4V, taking into account the presence of residual stresses. The rolling load leads to changes in the location and the maximum value of the compressive residual stresses, as well as the depth of the compressive residual stresses. However, the roller profile radius only changes the maximum value of these compressive residual stresses. Changing the rolling load influences the equivalent plastic strain close to the top surface of the wall as well as in deeper areas, whereas the influence of the roller profile radius is negligible. The plastic strain distribution is virtually unaffected by the initial residual stresses prior to rolling. Finally, design curves were generated from the simulations for different materials, suggesting ideal rolling load and roller profile combinations for microstructural improvement requiring certain plastic strains at a specific depth of the additive structure.
Residual stresses cause geometric distortion and affect mechanical performance of additively manufactured structures, yet they are notoriously difficult to assess and predict. Distortion (warpage) can drive parts outside dimensional tolerance limits, leading to part rejection or rework. For parts that meet tolerance, locked-in residual stress fields can affect structural integrity during operation, particularly subcritical cracking by fatigue, creep, or corrosion. This work develops benchmark data for a common additive manufacturing process (Wire Arc Additive Manufacturing) that can be applied for calibration and validation of physical process models that predict residual stress fields. The work includes design of two different samples of differing geometry, detailed manufacturing records for a set of physical samples, and an extensive set of residual stress measurement data developed using two diverse techniques (the contour method and neutron diffraction). An initial application of the work is also reported, where a modeling challenge was issued to secure residual stress model predictions from two independent laboratories that were blind to residual stress measurement data. These initial blind residual stress predictions show significant discrepancies relative to the measurement data, illustrating the potential value of the underlying validation data. An open repository for this work, including the sample designs, manufacturing process records, and the residual stress data, is also provided for future application in non-blind validation efforts.
Multi-electrode technique named as wire beam electrode (WBE) was used to study pitting corrosion of rebar under concrete cover. When WBE embedded mortar sample was immersed in NaCl solution, uneven distributions of galvanic current and open circuit potential (OCP) on the WBE were observed due to the initiation of pitting corrosion. The following oxygen depletion in mortar facilitated the negative shift of the OCP and the smoothing of the current and potential distributions. Wetting–drying cycle experiments showed that corrosion products instead of oxygen in wet mortar specimen sustained the propagation of pitting corrosion due to Fe (III) taking part in cathodic depolarization during oxygen-deficient wet period, which was confirmed by micro-Raman spectroscopy. In addition, new pitting corrosion occurred mainly near the corrosion products, leading to preferentially horizontal propagation of rust layer on the WBE. A localized corrosion factor was further presented to quantify the localised corrosion based on galvanic current maps.
Molecular weaving is the interlacing of covalently linked threads to make extended structures. Although weaving based on 3D networks has been reported, the 2D forms remain largely unexplored. Reticular chemistry uses mutually embracing tetrahedral metal complexes as crossing points, which, when linked, typically lead to 3D woven structures. Realizing 2D weaving patterns requires crossing points with an overall planar geometry. We show that polynuclear helicates composed of multiple metal-complex units, and therefore multiple turns, are well suited in this regard. By reticulating helicate units, we successfully obtained 2D weaving structures based on the familiar chicken-wire pattern.
Here, this study investigated the deformation behavior in Nb nanoparticle-martensitic NiTi composite wire during tensile loading by means of in-situ high-energy X-ray diffraction. Compared to Nb nanowires, the dispersedly distributed Nb nanoparticles have little effect on the transformation and deformation behaviors of NiTi matrix, causing the absence of R phase transformation and the occurrence of deformation twinning in NiTi matrix. Meanwhile, the occurrence of deformation twinning in NiTi matrix can reduce the shape strain to be coordinated by the unfavorable orientated martensite variants, and thus decreases the internal stress among NiTi martensite variants generated during martensite reorientation process. In addition, TEM result proved that Nb nanoparticles can achieve exceptionally large elastic strain in B19'-NiTi matrix (~4%), just as Nb nanowires. However, this large elastic strain (stress) will be released with the occurrence of NiTi deformation twinning.
Residual resistance ratio (RRR) of superconducting strands is an important parameter for magnet electrical stability. RRR serves as a measure of the low-temperature electrical conductivity of the copper within a conductor that has a copper stabilization matrix. For Nb 3 Sn, due to the need of a reaction heat treatment, the technical requirements for high quality measurements of strands extracted from Rutherford cables are particularly demanding. Quality of wire, cabling deformation, heat treatment temperature, heat treatment atmosphere, sample handling, and measurement methods can all affect the RRR. Therefore, as an integral part of the electrical quality control (QC) of Nb 3 Sn Rutherford cables manufactured at the Lawrence Berkeley National Laboratory, it was prudent that we established a RRR measurement system that can isolate the assessment of cable-fabrication-related impacts from sample preparation and measurement factors. Here we describe a bespoke cryocooler-based measurement system, capable of measuring RRR of over 80 samples in a single cooldown. The samples are mounted on custom-designed printed circuit boards that accommodate the shape of strands extracted from a Rutherford cable without added deformation, which we will show is critical in ensuring that the measurements accurately represent the RRR values of the conductor within the cable. Using this sample mounting solution, we routinely measure the overall RRR of the strand as well as individual intra-strand sections corresponding to both cable edges and cable broad faces with high reproducibility. Such measurements provide valuable information on the variation of RRR along the length of the strands as well as across strand productions and cable runs over time.
Transcription factors (TFs) bind combinatorially to cis-regulatory elements, orchestrating transcriptional programs. Although studies of chromatin state and chromosomal interactions have demonstrated dynamic neurodevelopmental cis-regulatory landscapes, parallel understanding of TF interactions lags. To elucidate combinatorial TF binding driving mouse basal ganglia development, we integrated chromatin immunoprecipitation sequencing (ChIP-seq) for twelve TFs, H3K4me3-associated enhancer-promoter interactions, chromatin and gene expression data, and functional enhancer assays. We identified sets of putative regulatory elements with shared TF binding (TF-pRE modules) that orchestrate distinct processes of GABAergic neurogenesis and suppress other cell fates. The majority of pREs were bound by one or two TFs; however, a small proportion were extensively bound. These sequences had exceptional evolutionary conservation and motif density, complex chromosomal interactions, and activity as in vivo enhancers. Our results provide insights into the combinatorial TF-pRE interactions that activate and repress expression programs during telencephalon neurogenesis and demonstrate the value of TF binding toward modeling developmental transcriptional wiring.
In this paper, a simple electrospinning methodology is described for generating novel fiber configurations of sulfur with the potential of yielding high performance sulfur electrodes for use in lithium-sulfur batteries. The unique fiber morphology derived by electrospinning has the capability of generating flexible sulfur yarns for the first time rendering them a highly attractive platform for small-scale mobile device applications such as textile-batteries. The electrospinning methodology reported herein also allows for the formation of a polymer-sulfur interface which acts as a physical barrier to liquid lithium electrolyte facilitating the reduction of polysulfide dissolution, a primary barrier to the progress of Li-S systems. Such flexible sulfur wire materials when converted into pellet sulfur electrodes, exhibit very stable capacities over 135 cycles with high areal capacities (~2.5 mAh cm -2 ). Finally, coating the electrodes with an inorganic lithium ion conductor coating results in further improvement of cycling behavior with electrodes of ~650 mAh g -1 capacity and an impressive low fade rate of ~0.003% fade cycle -1 demonstrating the promise of this unique platform.
Here, to better understand the complex interplay of speed and environment on metals commonly used in implants, rotary bend fatigue tests were conducted on stainless steel and nitinol wires. A range of alternating strains was tested to create ε-N curves at two speeds (physiologic and accelerated) and in three environments (deionized water at body temperature, phosphate buffered saline at body temperature, and laboratory air at ambient room temperature). Results indicate that speed and environment can affect the observed fatigue life in nuanced ways. An electropotential monitoring technique was demonstrated to characterize fatigue crack growth which may be useful in future investigations.