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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.

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At least 559 records · Page 31
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Adhesion, structure, and mechanical properties of Cr HiPIMS and cathodic arc deposited coatings on SiC

Chromium deposited by high-power impulse magnetron sputtering (HIPIMS) versus cathodic arc (CA) processes exhibits very different mechanical properties. Combining the two can result in a single-phase with superior performance that can be tailored for use in coating SiC for advanced nuclear fuel cladding. Coating morphology, residual stress, elemental depth profiles, and mechanical testing by scratch, pull-off adhesion, and microcantilevers are shown for HiPIMS, CA, and combined coatings. CA coatings were likely to spall and had lower adhesion strength due to tensile residual stresses but had desirable material properties. Additionally, by depositing an initial layer of Cr by HiPIMS followed by a layer of Cr by CA, a more adherent coating was achieved and some of the stress issues with CA morphology were resolved. Combined coatings withstood at least 80 MPa in pull-off adhesion tests and had maximum failure stress values of 5GPa in microcantilever tests. These results were better than either individual deposition method and point to a hybrid approach being a path forward for a more robust coating.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tribological behavior of spark plasma sintered Ti 3 SiC 2 MAX phase composites

Ti₃SiC₂ MAX phases are considered promising candidates for tribological applications; but, their low hardness (5-6 GPa) can lead to increased abrasive wear and higher wear rates. This study investigates the effect of incorporating hard SiC particles on microstructure, mechanical, and tribological behavior of Ti₃SiC₂-SiC-based MAX phase composites prepared using spark plasma sintering at 1400 °C, 40 MPa, 15-minute holding time. Phase and microstructural characterization of composites confirmed the formation of Ti₃SiC₂ MAX phase (90%) along with TiC as a minor phase (10%). For Ti₃SiC₂-SiC, homogeneous distribution of SiC grains within Ti₃SiC₂ matrix resulted in increased hardness from ~11.6 GPa to ~14.8 GPa; however, the flexural strength decreased from ~615 MPa to ~597 MPa due to coefficient of thermal expansion mismatch. Tribological behavior of Ti₃SiC₂-SiC MAX phase composites was assessed using unidirectional sliding ball-on-flat tests with a 52100 steel ball at different loads and a constant speed of 0.05 m/s. SiC reinforced composites exhibited a decreased friction coefficient from 0.39 to 0.29 and wear rates comparable to Ti₃SiC₂ (7-10×10⁻³ mm³/N·m). SEM and EDS analysis of the worn surfaces indicated material transfer from the steel ball counter body and its oxidation due to frictional heating, at lower loads (2N and 5N), whereas at higher load (10N), fracture of the transfer layer dominated, with the presence of microcracks, delamination, grain pull-outs, and wear debris. Improved mechanical properties and good adhesion of SiC with Ti₃SiC₂ matrix resulted in reduced microcracks and grain pull-outs, making Ti₃SiC₂-SiC/Steel tribo-pair more suitable for tribological applications.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Experimental evaluation of direct current magnetron sputtered and high-power impulse magnetron sputtered Cr coatings on SiC for light water reactor applications

Two types of physical vapor deposition Cr coatings were deposited on chemical vapor deposited SiC coupons using conventional direct current magnetron sputtering (DCMS) and high-power impulse magnetron sputtering (HiPIMS) to mitigate the corrosion of SiC, an advanced fuel and structural material in light water nuclear reactor cores. Coating microstructure was characterized using scanning electron microscopy and scanning transmission election microscopy. X-ray diffraction analysis was conducted for phase identification and qualitative analysis of residual stresses. The mechanical integrity of the coatings was evaluated using scratch testing, micro-indentation, and nano-indentation tests. Additionally, the microstructure of the DCMS coating consisted of fine columnar grains with nanoscale intercolumnar channels, while the HiPIMS microstructure was denser and free of any columnar defects. The DCMS coating showed a small tensile residual stress, while the HiPIMS coating was under compressive stress. Both types of coatings showed good mechanical integrity in terms of ductility and adhesion to the substrate. Corrosion performance of the coatings was assessed with a 30-day high temperature water autoclave test. Both types of coatings formed a protective Cr 2 O 3 surface layer 20-30 nm thick during the autoclave test. In the DCMS coating, the columnar defects provided permeation pathways for water penetration resulting in oxide formation in the intercolumnar regions in the interior of the coating. Overall, both types of Cr coatings offer promise for the mitigation of hydrothermal corrosion of SiC in light water reactor operating environments.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Tailorable Micelle Morphology in Self-Assembling Block Copolymer Gels for Templating Nanoporous Ceramics

The self-assembly of block copolymers offers opportunities for the facile organization and templating of inorganic nanomaterials. Here, we describe a morphology map for a poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) (PMMA-b-PnBA-b-PMMA) block copolymer/polycarbosilane system that allows for tunable control over nanoscale micelle geometry via manipulation of the preceramic polymer content. We produced gels with spherical, wormlike, and bicontinuous morphologies, which were processed to create silicon carbide-based ceramic structures with tunable nanoscale porosities. The role of the constituent polymers in influencing the structure and rheology of this system is discussed. The PMMA-b-PnBA-b-PMMA block copolymer/preceramic polymer system offers a number of advantages including: (i) commercial availability, (ii) rapid self-assembly kinetics, and (iii) successful conversion of the self-assembled nanostructure to ceramic via pyrolysis. Finally, this system may be useful for catalytic, structural, or thermal applications in both industrial and academic settings because of its ease of use and relatively inexpensive reagents.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Thermophysical Properties of Ti3SiC2 MAX Phase Composites with SiC Reinforcement

In the present work, dense (∼100%) Ti 3 SiC 2 composites (TSC) are processed along with 20 vol% of SiC reinforcement (TSC20) via spark plasma sintering at 1400°C, 40 MPa, 15 min, and dynamic vacuum environment. Thermal expansion of both the composites increases from RT to 1273 K and linear fitting of data yields coefficient of thermal expansion (CTE) of 9.4 × 10 −6 K −1 for TSC which decreases to 8.3 × 10 −6 K −1 for TSC20. With increase in temperature from RT to 773 K, specific heat for both TSC and TSC20 composites is observed to increase from 598-850 J.kg −1 .K −1 , whereas thermal diffusivity and thermal conductivity values decrease with testing temperature. SiC reinforcement in Ti 3 SiC 2 resulted in improved thermal diffusivity from 12.7 to 18.7 mm 2 .s −1 and thermal conductivity from ∼57 to ∼79 W.m −1 .K −1 at RT. However, with increase in temperature (773 K), thermal diffusivity and conductivity decrease, and values get closer for both TSC and TSC20 composites. Further extrapolation of thermal conductivity data showed cross-over at ∼973 K due to domination of phonon-phonon scattering and thus lower values of thermal conductivity for TSC20 than TSC. Therefore, reduced CTE and higher thermal conductivity of TSC20 make it a viable choice for applications in high temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Quantitative analysis of dislocations in 4H-SiC wafers using synchrotron X-ray topography with ultra-high angular resolution

Utilization of an Si(331) beam conditioner together with an Si(111) double-crystal monochromator (DCM) enables the angular resolution of synchrotron X-ray topography to be increased by an order of magnitude compared with grazing-incidence topography or back-reflection topography conducted with the DCM alone. This improved technique with extremely small beam divergence is referred to as synchrotron X-ray plane-wave topography (SXPWT). This study demonstrates that the rocking curve width of 4H-SiC 0008 in PWT is only 2.5" and thus the lattice distortion at the scale of 1" will significantly affect the diffracted intensity. This work reports the ultra-high angular resolution in SXPWT which enables detailed probing of the lattice distortion outside the dislocation core in 4H-SiC, where the sign of the Burgers vector can be readily determined through comparison with ray-tracing simulations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Switching Characteristics of a 1.2 kV, 50 mΩ SiC Monolithic Bidirectional Field Effect Transistor (BiDFET) with Integrated JBS Diodes

—The switching performance of large area (1cm x 1cm) monolithic 1.2 kV 50 mΩ 4H-SiC bidirectional field effect transistor (BiDFET) with integrated JBS diodes is reported for the first time. The devices were fabricated in a 6-inch commercial foundry and then packaged in a custom-designed four-terminal module. The switching performance of the BiDFET has been observed to be 1.4x better than that of its internal JBSFETs. Dynamic characterization was performed at 800 V with different gate resistances, current levels and case temperatures. An increase in switching losses was observed for the BiDFET with increasing gate resistance and current level as observed for SiC power MOSFETs. The BiDFET showed a 9% reduction in total switching loss from 25 °C to 150 °C with a current of 10 A.

Silicon Carbide, Monolithic, Bidirectional, FourQu↗
DOE OSTI2020

Grid Application and Controls Development for Medium-Voltage SiC-Based Grid Interconnects

This paper studies, the grid-interconnection requirements of directly connected medium-voltage (MV) Silicon Carbide-based (SiC-based) converters and details the necessary control implementations. These power electronic converters follow the interconnection standard IEEE 1547-2018, but can also have additional controls supported by the microgrid standards in IEEE 2030.7, which is demonstrated in this work. Additionally, this paper defines the grid applications realized by these directly connected medium-voltage power electronic converters at the distribution scale and demonstrates results. The controls for the studied grid applications are then developed and implemented on the controller. The paper also includes details of the control algorithm development and validations of the control algorithm through hardware-in-the-loop results.

28 EE - Advanced Manufacturing Office (EE-5A)↗
DOE OSTI2022

Design Considerations for Developing 1.2 kV 4H-SiC BiDFET-enabled Power Conversion Systems

Bidirectional switches are essential for cycloconverter and matrix converter applications to facilitate single-stage AC-AC conversion without intermediate energy storage elements. The 1.2 kV 4H-SiC BiDFET was developed as the first monolithic bidirectional SiC power transistor. This paper describes the design considerations taken into account while creating the BiDFET device and developing custom packages for housing the switch in discrete form for low power applications and in module form for high-power applications. The realized switches are characterized for their on-state and switching performance. The versatility of the BiDFET device is demonstrated by operating a single BiDFET H-bridge in voltage-source-inverter and current-source-inverter topologies only by varying the gate bias on the individual BiDFETs and reversing the input-output connections.

Bidirectional, Silicon Carbide, Half-Bridge Module↗
DOE OSTI2023

Comprehensive Efficiency Analysis of Seven-Switch Current-Source Inverter Based on Voltage-Boost Function and Genetic Algorithm

This paper investigates the voltage-boost features of the emerging seven-switch current-source inverter (H7-CSI) to improve the efficiency of the CSI-based motor drive system. The switching transient and power loss model of the H7-CSI topology during voltage-boost operation are analyzed in detail. The effects of the boost function on the switching and conduction loss of the H7-CSI topology are investigated. A genetic algorithm has been introduced that makes it possible to optimize the H7-CSI’s modulation index to minimize its power loss. Experimental results for the H7-CSI unit show that this optimization can reduce the power loss by 10.6%.

42 ENGINEERING↗
DOE OSTI2020

Packaging Development for a 1200V SiC BiDFET Switch Using Highly Thermally Conductive Organic Epoxy Laminate

A novel 1.2 kV/10A, 4H-SiC monolithic, bidirectional switch has been developed for use in cycloconverter applications to facilitate high-frequency direct AC-to-AC power conversion and enables new power converter topologies. A new packaging solution, utilizing a 100 µm flexible polyimide organic laminate substrate is developed to mitigate thermo-mechanical stress during power cycling and enable smaller form factor and lower cost. Multiphysics simulations and static tests were conducted to show performance characterization of the module and compare it against metallic substrates. A new organic laminate epoxy resin composite dielectric (ERCD) is also evaluated for superior thermal performance and shows 63% reduction in junction to case resistance compared to DBC substrates.

Silicon Carbide, Bi-directional switch, BiDFET, MO↗
DOE OSTI2020

Estimation, Minimization, and Validation of Commutation Loop Inductance for a 135-kW SiC EV Traction Inverter

With growing interests in low inductance SiC based power module packaging, it is vital to focus on system level design aspects to facilitate easy integration of the modules and reap system level benefits. To effectively utilize the low inductance modules, busbar and interconnects should also be designed with low stray inductances. A wholistic investigation of the flux path and flux cancellations in the module-busbar assembly which as differentially coupled series inductors is thus mandatory for a system level design. This work presents a busbar design which can be adopted to effectively integrate the CREE’s low inductance 1.2 kV/1.7 kV SiC power modules. The paper also proposes a novel measurement technique to measure the inductance of the modulebusbar assembly as a whole rather than deducing it from individual components. The inductance of the overall commutation loop of the inverter which encompasses the SiC power module, interconnects and PCB busbar have been estimated using finite element analysis (FEA). Furthermore, insights gained from FEA provided the guidelines to decide on the placement of the decoupling capacitors in the busbar to minimize the overall commutation loop inductance from 12.8 nH to 7.4 nH which resulted in significant reduction in the device voltage overshoot. The simulation results have been validated through measurements using an impedance analyzer with less than 5% difference between extracted loop inductance from FEA and measurements. The bus bar design study and the measurement technique discussed in this paper, can be easily extended to other power module packages. Finally, the 135 kW inverter has been compared to a similar highpower inverter utilizing a laminated busbar to highlight the performance of the former.

42 ENGINEERING↗
DOE OSTI2020

Methodology of Low Inductance Busbar Design for Three-Level Converters

Three-level (3L) converters are more susceptible to parasitics compared with two-level converters because of their complicated structure with multiple switching loops. In this article, the methodology of busbar layout design for 3L converters based on the magnetic cancellation effect is presented. The methodology can fit for 3L converters with symmetric and asymmetric configurations. A detailed design example is provided for a high-power 3L-active neutral point clamped (ANPC) converter, which includes the module selection, busbar layout, and dc-link capacitor placement. The loop inductance of the busbar is verified with simulation, impedance measurements, and converter experiments. Furthermore, the results match with each other, and the inductances of short and long loops are 6.5 and 17.5 nH, respectively, which are significantly lower than the busbars of NPC-type converters in other references.

42 ENGINEERING↗
DOE OSTI2023

Power Conversion Systems Enabled by SiC BiDFET Device

The BiDirectional Field-Effect Transistor (BiDFET) can enable circuit topologies requiring four quadrant switches, that were earlier designed using discrete combinations of MOSFETs, IGBTs, GaN HEMTs and PiN diodes. The monolithic nature of the BiDFET allows lower device count, smaller switch volume, lower inductance, and simpler packaging, and hence more reliable and commercially viable implementation in power electronics converters. Furthermore, the matrix converter topologies, now feasible using BiDFETs, can eliminate the bulky and unreliable dc link capacitors or inductors required for conventional voltage-source or current-source converters in ac-ac and ac dc applications. The 1.2 kV BiDFET has the potential to disrupt all the applications utilizing 1.2 kV switches, including electric vehicle (EV) drivetrain, bidirectional EV chargers, industrial motor drives, solid-state transformers, datacenter power supplies, elevator drives, dc microgrids, energy storage grid integration, solid-state breakers, etc.

42 ENGINEERING↗
DOE OSTI2021

Varistors: A Useful Tool for Superconducting Magnet Quench Protection

A perfect varistor is a constant voltage resistor as a function of current through the resistor. A perfect varistor can't exist, because its resistance would be infinite at zero current. In electronic devices, varistors are often used as surge protectors. A varistor can be used in place of an ordinary resistor as the discharge resistance across superconducting coil sections. When used this way, the integral of I 2 dt during the discharge can be reduced by almost one third. When a varistor is used for quench protection of coils that are coupled to shorted secondary circuits the integral of I 2 dt can be reduced much more. Furthermore, this can be a key factor when coil current densities and stored energies are high as in many potential HTS magnet systems. This paper discusses the types of varistors that are commercially available and their characteristics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗