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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

The role of ternary alloying elements in eutectoid transformation of U-10Mo alloy part II. In and Ex-situ Neutron diffraction-based assessment of eutectoid phase transformation kinetics in U-9.8Mo-0.2X alloy (X = Cr, Ni or Co)

HExploring the effects of minor ternary alloying additions, typically impurity elements, on the phase stability of U-10Mo is important for preventing undesirable phase decomposition during processing or during service. This work examines the influence small ternary additions of Cr, Ni, and Co. Both in-situ and ex-situ neutron diffraction measurements made during and after high temperature (450 – 525°C) exposures were used to better define the influence of these elements on the time-temperature-transformation (TTT) behavior of U-10Mo, providing information which is complementary to electron microscopy investigations of the same alloy systems performed in the first part of this work. Minor additions of Ni and Co decrease the ?-phase stability at all temperatures investigated. Signatures of U6X (X = Ni or Co) compounds were shown to be present in amounts of up to 6 wt% in the heat treated alloys, suggesting that the initial precipitation of this phase may catalyze further ?-phase decomposition. On the other hand, the Cr containing alloys were observed to have nearly the same, and in some cases slower, phase transformation kinetics when compared to the binary U-10Mo control samples. The results of the study have enabled preliminary estimates of the TTT curves for the ternary alloys.

phase transformation, kinetics, discontinuous prec↗
DOE OSTI2020

Progress in Understanding the Origins of Excellent Corrosion Resistance in Metallic Alloys: From Binary Polycrystalline Alloys to Metallic Glasses and High Entropy Alloys

Some of the factors responsible for good corrosion resistance of select polycrystalline and emerging alloys in chloride solutions are discussed with a goal of providing some perspectives on the current status and future directions. Traditional metallic glass alloys, single phase high entropy alloys (HEAs), early metallic glasses, and high entropy metallic glasses are all emerging corrosion-resistant alloys (CRAs) that utilize traditional strategies for improved corrosion resistance as well as take advantage of some other novel beneficial attributes. These materials enjoy many degrees of freedom as far as choice of both composition and structure, providing great flexibility in the pursuit of superior corrosion resistance. The new materials depart from classical solvent-solute type polycrystalline binary or ternary alloys. Thus, such emerging materials provide significant opportunities to achieve even greater improvements in corrosion resistance in harsh environments. Several examples of the unique corrosion properties of selected materials in the context of modern theories of corrosion are discussed herein. Discussion is restricted to solid-solution binary or ternary polycrystalline alloys, several metallic glass alloys, and single phase HEAs. A common feature of many CRAs is that composition and microstructure often affect both passivity and resistance to localized corrosion that can be divided into initiation, stabilization, and propagation stages. Enormous complexities in protective oxide structures and chemistries and the large number of combinatorial possibilities in newer materials such as HEAs preclude trial-and-error approaches and perhaps even combinatorial experimental design. Computational materials methodologies will be required in the search for new corrosion-resistant alloys in these material classes. The search must consider the best scientific insights available regarding how major and minor alloy additions, as well as various microstructural attributes, contribute to corrosion mitigation. Additional scientific insights, as they emerge, will enable choices beyond the reliance on high concentrations of alloying elements that are known to affect passivity breakdown and pit stabilization. A challenge is to connect the “basic attributes” of an alloy with its properties. The strength of this connection will likely require new scientific principles enabling deep multiphysics insights in order to link feature(s) such as composition and metallurgical phases to the desired corrosion properties. Application of data informatics will likely also play a role given the plethora of variables that are important in corrosion and the difficulty in assessing all relationships. Here, the opportunity exists to accelerate the design of emerging materials for high corrosion resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Enhancing fatigue life by ductile-transformable multicomponent B2 precipitates in a high-entropy alloy

Catastrophic accidents caused by fatigue failures often occur in engineering structures. Thus, a fundamental understanding of cyclic-deformation and fatigue-failure mechanisms is critical for the development of fatigue-resistant structural materials. Here we report a high-entropy alloy with enhanced fatigue life by ductile-transformable multicomponent B2 precipitates. Its cyclic-deformation mechanisms are revealed by real-time in-situ neutron diffraction, transmission-electron microscopy, crystal-plasticity modeling, and Monte-Carlo simulations. Multiple cyclic-deformation mechanisms, including dislocation slips, precipitation strengthening, deformation twinning, and reversible martensitic phase transformation, are observed in the studied high-entropy alloy. Its improved fatigue performance at low strain amplitudes, i.e., the high fatigue-crack-initiation resistance, is attributed to the high elasticity, plastic deformability, and martensitic transformation of the B2-strengthening phase. This study shows that fatigue-resistant alloys can be developed by incorporating strengthening ductile-transformable multicomponent intermetallic phases.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The role of ternary alloying elements in eutectoid transformation of U10Mo alloy part I. Microstructure evolution during arc melting and subsequent homogenization annealing in U9.8Mo0.2 X alloy ( X = Cr, Ni, Co)

This paper describes the microstructural evolution in an alloy of uranium with 10 wt.% molybdenum (U10Mo), with minor addition of a third alloying element, namely, Cr, Ni, or Co, at 0.2 wt.%. The microstructures of arc-melted buttons in the as-cast condition show significant Mo segregation. The segregation behavior of Cr, Ni, and Co was investigated through detailed scanning electron microscope imaging. A homogenization heat treatment at 900°C for 48 h results in uniform Mo distribution and associated grain growth in all of the four alloys that were fabricated. Further, formation of multiple phases was noted in U-9.8 wt.% Mo-0.2 wt.% Ni and U-9.8 wt.% Mo-0.2 wt.% Co alloys after the homogenization annealing step. The greatest grain-boundary-initiated eutectoid transformation as measured by % volume fraction was observed when the homogenized U-9.8 wt.% Mo-0.2 wt.% Ni alloy was aged at 500°C for 20 h. The least eutectoid transformation occurred in U10Mo.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2017

Thermal reliability of Al-Si eutectic alloy for thermal energy storage

Highlights: • Thermal reliability of material is investigated after long time vacuum thermal cycling. • The latent heat of fusion show almost no change after 1000 thermal cycles. • The thermal conductivity exhibit a good stability after 1000 cycles. • Al-Si eutectic alloy is a potentially good candidate for thermal energy storage applications. - Abstract: The thermal reliability of Al-Si eutectic alloy as phase change materials (PCMs) was investigated through vacuum thermal cycling 250, 500, 750, and 1000 times going through the solid-liquid phase change. The changes in thermal properties of Al-Si eutectic alloy, including melting point, latent heat, specific heat, thermal diffusivity and thermal conductivity, were investigated using differential scanning calorimetric (DSC) and laser flash apparatus. The results revealed that, with increasing the number of cycles, the melting point and latent heat of fusion of the Al-Si eutectic alloy showed almost no changes. Moreover, the thermal conductivity showed an outstanding stability after 1000 thermal cycles. Therefore, it is concluded that the thermal reliability of Al-Si eutectic alloy is more than adequate for long-term performance as a phase change material for thermal energy storage (TES) applications.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Friction and wear of titanium alloys and copper alloys sliding against titanium 6-percent-aluminum - 4-percent-vanadium alloy in air at 430 C

Experiments were conducted to determine the friction and wear characteristics of aluminum bronzes and copper-tin, titanium-tin, and copper-silver alloys sliding against a titanium-6% aluminum-4% vanadium alloy (Ti-6Al-4V). Hemispherically tipped riders of aluminum bronze and the titanium and copper alloys were run against Ti-6Al-4V disks in air at 430 C. The sliding velocity was 13 cm/sec, and the load was 250 g. Results revealed that high tin content titanium and copper alloys underwent significantly less wear and galling than commonly used aluminum bronzes. Also friction force was less erratic than with the aluminum bronzes.

Wisander, D. W.↗
DOE OSTI2019

Local structure of Ni 80 X 20 (X: Cr, Mn, Pd) solid-solution alloys and its response to ion irradiation

In this work, the local structure of Ni 80 X 20 (X: Cr, Mn, Pd) solid-solution alloys was investigated with x-ray absorption and total scattering x-ray diffraction methods. Atomic pair distribution function (PDF) analysis indicated that the local lattice distortion is strongly relevant to the atomic size mismatch, and the local lattice distortion in Ni80Pd20 alloy is obviously larger than that in other solid-solution alloys. The bond length of different atomic pairs was derived from the fitting of extended x-ray absorption fine structure spectra. Quantitative analysis of the local bonding environment in Ni 80 Cr 20 during Ni ion irradiation suggested that Cr atoms tend to form clusters in Ni 80 Cr 20 with the increase of ion dose.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Correlation between microstructures and mechanical properties of cryorolled CuNiSi alloys with Cr and Zr alloying

Highlights: • Annihilation of dislocations was suppressed by Cr alloying to CuNiSi alloys. • Cr alloying to CuNiSi alloys hinders the kinetics and refines precipitates. • Zr alloying to CuNiSi alloys promotes the growth and kinetics of precipitates. • The mechanical properties were quantitatively related to the microstructures. - Abstract: Due to their high strength and high electrical conductivity, CuNiSi system alloys are widely used as lead frames and connectors. In this work, CuNiSi alloys alloyed with Cr and Zr were rolled at liquid nitrogen temperature and subjected to various aging treatments. High-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) analysis showed that in addition to forming Cr{sub 3}Si and Ni{sub 2}SiZr particles, elemental Cr and Zr distributed evenly in the matrix. Ni and Si segregated at the interface between the particles and matrix to form Ni{sub 2}Si precipitates. During the aging process, Cr alloying increased the hardness while slightly reducing the electrical conductivity of the alloy. This was ascribed to the refined precipitates and hindered precipitation kinetics. Zr alloying promoted both the precipitate growth and the precipitation kinetics of the CuNiSi alloys, while decreasing their hardness and enhancing their electrical conductivity. According to the results of the synchrotron X-ray diffraction (XRD) analysis, Cr alloying increased the dislocation density of CuNiSi alloys and suppressed the annihilation of dislocations during aging. This promoted strength through work hardening. Compared to CuNiSi alloys aged at 723 K for 2 h, the ultimate tensile strength of the alloys obtained after Cr alloying using a two-step rolling aging process was increased by 154 MPa and their electrical conductivity was increased by 4.8% International Annealed Copper Standard (IACS).

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation of structural and magnetic properties of rapidly-solidified iron-silicon alloys at ambient and elevated temperatures

In this work, we investigated the ambient temperature structural properties (~300 K) and the ambient and high temperature (up to 900 K) direct current (DC) magnetic properties of melt-spun Fe-x wt.% Si (x = 3, 5, & 8) alloys. The wheel surface speeds selected for the study were 30 m/s and 40 m/s. The thickness, width, lattice parameter, saturation magnetization (MS), and intrinsic coercivity (HCI) of the melt spun ribbons are presented and compared with data in the literature. The ribbons produced at the lower wheel surface speed (30 m/s) were continuous having relatively uniform edges compared to the ribbons produced at the higher wheel surface speed. The thickness and the width of the melt-spun ribbons ranged between ~15-60 μm and 500-800 μm, respectively. The x-ray diffraction spectra of the melt-spun ribbons indicated the presence of disordered α-phase, irrespective of the composition, and the wheel-surface speed. The lattice parameter decreased gradually as a function of increasing silicon content from ~0.2862 nm (Fe-3 wt.% Si) to ~0.2847 nm (Fe-8 wt.% Si). Wheel surface speed was not shown to have a significant effect on the magnetization, but primarily impacted the ribbon structure. A decreasing trend in the saturation magnetization was observed as a function of increased silicon content. The intrinsic coercivity of the melt-spun alloys ranged between ~50 to 200 A/m. Elevated temperature evaluation of the magnetization in the case of Fe-3 & 5 wt.% Si alloy ribbons was distinctly different from the Fe-8 wt.% Si alloy ribbons. The curves of the as-prepared Fe-3 wt.% Si and Fe-5 wt.% Si alloy ribbons were irreversible while that of Fe-8 wt.% Si was reversible. The MS for any of the combinations of wheel surface speed and composition decreased monotonically with the increase in temperature (from 300 – 900 K). The percentage decrease in MS from 300 K to 900 K for the Fe-3 wt.% Si and Fe-5 wt.% Si alloys was ~19-22 %, while the percentage decrease in the same temperature range for Fe-8 wt.% Si alloy was ~26-30 %. It appears that Fe-3 wt.% Si and Fe-5 wt.% Si alloys ribbons are primarily comprised of the α phase (disordered phase) with any minor constituents being beyond the detection limits of the studies performed, while the Fe-8 wt.% Si alloy ribbons are comprised of disordered and regions of short-range ordering.

Elevated Temperature↗