Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “PINS”

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.

At least 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Landau level splitting in nitrogen-seeded epitaxial graphene

We present a new form of semiconducting graphene grown on C-face silicon carbide, SiC(0001), seeded with a sub-monolayer of nitrogen. This graphene exhibits a gap of 0.3-0.7 eV from the Fermi level to the valence band dependent on lm thickness as measured via angle resolved photo-emission spectroscopy (ARPES). Scanning tunneling microscopy (STM) images imply that the bandgap may be the result of strain-induced confinement. STM indicates that much of the graphene consists of wide at hexagonal plateaus, 8-20 nm2 on average, surrounded by both smooth and disordered folds of length scales from 0.5-2 nm tall, 1-4 nm thick, and 1-20 nm long. The remainder of the surface is covered in smooth or disordered ripples and folds intermixed. Scanning tunneling spectroscopy (STS) measurements on all features show peaks suggestive of Landau levels, and have been analyzed to give pseudo-magnetic field magnitudes. The magnetic lengths associated with these fields are less than the average plateau diameter but comparable to typical fold widths. We consider a growth process whereby the graphene grows pinned to the substrate by the interface nitrogen. The graphene experiences compressive strain as a result of both this pinning as well as competing thermal expansion forces between the substrate and lm. As a result, graphene on nitrogen-seeded SiC has a more concentrated network of strained ripples and folds than seen on C-face SiC graphene without nitrogen.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Mechanical characterization of fine-grain dispersion-strengthened tungsten as a plasma facing material

Field-Assisted Sintering Technology (FAST) was used to produce fine-grained, dispersion-strengthened tungsten (W) materials. Investigated materials 4138, 4353, and 4355 composed of 3 wt% ZrC sintered at 1800 °C, 5 wt% ZrC sintered at 1800 °C, and 3 wt% ZrC sintered at 2000 °C, respectively. They were compared against ITER-grade W. A series of mechanical and thermal property testing and microstructure studies were conducted to study them as a potential plasma facing material (PFM) for fusion reactors. Hardness testing showed that manufacturing conditions substantially altered hardness. Material 4355 had an average HV10 value of 497.2 ± 16.8, slightly higher than ITER-grade at 378.5 ± 40.3. However, material 4353 was substantially higher with an HV10 value of 738.9 ± 31.7 over the investigated temperature range. Electron Backscatter Diffraction (EBSD) analysis showed that FAST produced substantially smaller grains than the hot-rolled ITER-grade W material, offering notable control over grain size. Materials 4353 and 4355 had grain sizes of 0.44 ± 0.20 µm and 3.67 ± 0.89 µm, respectively, whereas ITER-grade 27.14 ± 19.76 µm at room temperature. The fine grain structures showed no net coarsening after 1 hr. anneals up to 1800 °C, several hundred degrees above the 1100 – 1500 °C recrystallization range reported for conventional W. Inverse application of the Zener pinning relationship to the measured grain sizes indicates that these two FAST sintering conditions produce markedly different effective dispersoid populations, with effective particle diameters of approximately 90 nm at a peak sintering temperature of 1800 °C and approximately 460 nm at 2000 °C, respectively. This result demonstrates that the FAST thermal condition itself, and not the nominal ZrC content alone, governs the pinning effectiveness of the dispersion. Thermal diffusivity measurements support this finding independently. Materials of identical composition sintered at different temperatures differ by approximately 19% in measured thermal diffusivity with statistically indistinguishable density, while materials of different composition and sintering temperature converge to within approximately 2%. At a representative divertor heat flux of 10 MW/m², the lower thermal conductivity of the fine-grained materials corresponds to approximately 28 to 33 °C per millimeter of armor thickness relative to ITER-grade W, traded against a substantially larger margin to recrystallization-driven degradation. While high temperature tensile testing revealed likely contamination that motivates refinement of the manufacturing process, FAST-produced, fine-grained, dispersion-strengthened W offers process-controlled microstructural stability well above the operating temperatures of conventional W and supports its continued development as a PFM for economically viable commercial fusion power.

Parker, Gabe [ORNL] (ORCID:0000000190394100)↗
DOE OSTI2021

Structural and magnetic properties of hard magnetic system Ce(Co 1 -Fe ) 4.4 Cu 0.6 (0 ≤ x ≤ 0.19)

The Ce(Co 1 -Fe ) 4.4 Cu 0.6 (0 ≤ x ≤ 0.19) is a composite, hard magnetic system that is based on the CaCu 5 -type structure (1:5). It shows both, unique magnetic and microstructural features that are essential for permanent magnets, e.g., exceptional squareness of the 2nd. quadrant of the magnetization loops and microstructural features typically needed for pinning. Samples solidified in alumina crucibles are coarse-grained and often clearly faceted and readily align in a magnetic field. X-ray, SEM, and TEM analyses show a 1:5-type single-phase material when quenched from high temperature, which, after heat treatment, transforms into a laminar coherent nanostructure through the formation of a dense array of extended intercalated regions. Furthermore, these extended intercalated regions are comprised of segments of the Ce 2 Ni 7 –type structure (2:7) which segregate into various closely related precipitates forming a nanostructure similar to the SmCo 5 - Sm 2 Co 17 composites seen in Sm-Co permanent magnets. Based on TEM and Lorentz microscopy of well-aligned single grain particles, the magnetic domains’ reversal mechanism is regulated by anisotropy fluctuations occurring along the easy direction of magnetization and strong exchange interactions between the matrix and defects (e.g.: stacking faults). Lorentz microscopy suggests the domain wall is not physically pinned by the defect, but rather is offset/deflected when it interacts with the defect. The Lorentz and magnetization data suggest that defects cause a bending of the moment away from the c axis inside the grains.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Hot zero power reactor calculations using the Insilico code

In this paper we describe the reactor physics simulation capabilities of the Insilico code. A description of the various capabilities of the code is provided, including detailed discussion of the geometry, meshing, cross section processing, and neutron transport options. Numerical results demonstrate that Insilico using an SP{sub N} solver with pin-homogenized cross section generation is capable of delivering highly accurate full-core simulation of various pressurized water reactor problems. Comparison to both Monte Carlo calculations and measured plant data is provided.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

A new approach to three-dimensional neutron transport solution based on the method of characteristics and linear axial approximation

A new approach based on the method of characteristics (MOC) is proposed to solve the neutron transport equation. A new three-dimensional (3D) spatial discretization is applied to avoid the instability issue of the transverse leakage iteration of the traditional 2D/1D approach. In this new approach, the axial and radial variables are discretized in two different ways: the linear expansion is performed in the axial direction, then, the 3D solution of the angular flux is transformed to be the planar solution of 2D angular expansion moments, which are solved by the planar MOC sweeping. Based on the boundary and interface continuity conditions, the 2D expansion moment solution is equivalently transformed to be the solution of the axially averaged angular flux. Using the piecewise averaged angular flux at the top and bottom surfaces of 3D meshes, the planes are coupled to give the 3D angular flux distribution. The 3D CMFD linear system is established from the surface net current of every 3D pin-mesh to accelerate the convergence of power iteration. The STREAM code is extended to be capable of handling 3D problems based on the new approach. Several benchmarks are tested to verify its feasibility and accuracy, including the 3D homogeneous benchmarks and heterogeneous benchmarks. The computational sensitivity is discussed. The results show good accuracy in all tests. With the CMFD acceleration, the convergence is stable. In addition, a pin-cell problem with void gap is calculated. This shows the advantage compared to the traditional 2D/1D MOC methods.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2022

Features of relaxation modes in soft magnetic metallic glasses and their correlation with magnetic ordering

Although the anneal-induced relaxation process of Fe-based metallic glasses has been widely reported, there is a lack of a systematic description of the relaxation modes of atoms. Here, in this work, the relaxation modes of FeSiBPC metallic glasses and their relationship with magnetic ordering have been investigated. A two-stage relaxation behavior has been observed, and the pinning effect of Curie temperature is found in the first stage. The short-range ordering involved in the β relaxation in the first stage is confined and facilitated by magnetic ordering. It causes a smaller E β compared to that of non-magnetic metallic glasses. In the second stage, the pinning effect disappears. It is mainly the medium-range rearrangements involved in α relaxation that begins to yield the influence on magnetic ordering. This work uncovers the inner magnet-influenced β relaxation in Fe-based metallic glasses and provides insights into the interaction between structural arrangement during relaxation and magnetic ordering.

36 MATERIALS SCIENCE↗
DOE OSTI2016

On the irradiation creep by climb-enabled glide of dislocations

The plastic deformation is defined by the proportional to stress elastic deflections of pinned dislocations in climb-enabled glide models of irradiation creep. Here, we argue that this relation is incorrect; instead, as in other pinning-unpinning-type models, the dislocations move from one set of obstacles to another, so that the inter-obstacle spacing determines creep rate, whereas the dependence on the applied stress is only implicit in the unpinning time.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2018

Postirradiation examination on metallic fuel in the AFC-2 irradiation test series

In this paper, irradiation experiments on metallic fuel alloys containing rare earth additions to simulate potential carry-over from pyro-metallurgical reprocessing and minor actinide additions were performed in the Idaho National Laboratory Advanced Test Reactor. These tests were designated AFC-2A and AFC-2B. Additionally irradiation experiments were also performed on metallic fuel alloys containing minor actinide additions that were fabricated by different techniques. These tests were designated AFC-2E. These pins were removed from the reactor after achieving burnups between 6 and 11% fission per initial heave metal atom. Examination of these pins revealed that they were unintentionally operated beyond their desired power and temperature conditions. Highlights from the postirradiation examination of these experiments is discussed. A variety of issue contributed to the poor performance of these irradiation tests including capsule design, reactor power variations and fabrication issues. While all the issues contributed, the major issue was determined to be unanticipated variations in reactor power. Through comparisons between these experiments and historical off-normal experiments, it was possible to conclude bound the operating temperatures of these experiments. There likely was some in-pile melting in the rare earth addition experiments (AFC-2A, AFC-2B), but it is not likely that there was in-pile melting in the fabrication technique experiments (AFC-2E).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2020

Irradiation performance of nonfertile (Pu-MA-Zr) fast reactor metal fuels

This work was part of a program begun in 2001 to develop advanced nuclear fuels, originally as carriers for plutonium and minor actinides (neptunium, curium, and americium) taken from spent commercial light-water reactors (LWR) so that the plutonium and minor actinides could be ‘burned’ or transmuted in an accelerator or a fast nuclear reactor. A central part of these experiment programs has been the development of advanced fast reactor fuels, because a fast reactor was considered the most efficient vehicle to transmute the actinide waste products, and metallic fuels is a central focus of these tests. An experiment design was developed in which a thermal test reactor, the Advanced Test Reactor (ATR), was used to test small fuel pin prototypes, by creating areas in the core shielded by cadmium filters to produce a largely epithermal and fast neutron spectrum environment in which the pins could be irradiated. The results of non-fertile metallic fuel (no uranium) tests are presented here. Pu-Am-Np-Zr fuels were irradiated to fission densities up to 33 × 10 20 fission/cm 3 and Pu-239 depletions of up to 39%. The depletions were created by roughly 2/3 by fission and 1/3 by transmutation neutron capture. Up to five fuel ‘rodlets’ were irradiated in three sealed capsules stacked axially in the core, and the peak cladding temperatures ranged from 300°C to 500°C, depending on axial location as those near the core centerline are operating hotter and to higher fission densities. Several post-irradiation examinations (precision gamma scanning and fission gas release) were similar to other historical metal fuel experiments in fast reactors. However, optical metallography indicated that two of the rodlets had breached. The exact reasons are unclear. Due to the design of this irradiation experiment a rodlet breach could have increased the temperature in others in the same capsule by contaminating the thermal gap helium with heavier and less conductive fission product gases. Finally, some of those rodlets showed high amounts of fuel/cladding chemical interaction (FCCI).

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2021

Automatic information extraction from neutron radiography imaging to estimate axial fuel expansion in $\mathrm{EBR-II}$

Approximately 130,000 metal fuel pins were irradiated in the Experimental Breeder Reactor II (EBR-II) during its 30 years of operation to develop and characterize existing and prospective fuels. For many of the metal fuel irradiation experiments, neutron radiography imaging was performed to characterize fuel behavior, like fuel swelling. However, due to the lack of technology or resources, many of the images have not been processed or were processed manually through visual examination. This paper represents first-attempt to develop an image processing algorithm capable of automatically extracting information regarding the degree of fuel swelling from neutron radiography imaging. The algorithm was applied to 120 images of three different metallic fuel pin compositions—U-10Zr, U-8Pu-10Zr, and U-19Pu-10Zr. The algorithm performs operations of image intensity adjustment, image binarization, region finding, and labeling to extract information about fuel swelling. The average growth for U-10Zr was found to be 8.49% with 95% Confidence Interval (CI) [8.33 –8.66%], for U-8Pu-10Zr — 7.50% with 95% CI [7.23 – 7.78%], and for U-19Pu-10Zr — 3.15%, with 95% CI [2.40 – 3.91%]. The results obtained by applying this automatic image processing algorithm are consistent with previously reported studies of the same types of fuels. The automatic image processing algorithm will be expanded to include thousands of available neutron radiography images and different types of fuels to investigate empirical dependencies of fuel swelling, which can be subsequently applied to advanced fuel modeling. Results from this study can later be compared to BISON simulations to further benchmark modeling efforts and develop assessment cases.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2025

In-situ ion irradiation induced nanograin growth in a spent UO 2 fuel

This study investigates the irradiation-driven evolution of nanograins in the early-stage restructured rim region of medium burnup spent uranium dioxide (UO 2 ) fuel. Transmission electron microscopy (TEM) lamellas prepared from Belgium Reactor 3 (BR-3) fuel were subjected to in-situ 300 keV Xe ion irradiations under varying doses, fluxes, and temperatures to evaluate their effect on the evolution of the nanograins. Our results reveal that the nanograins grow during ion irradiation. Additionally, the growth is most pronounced at elevated temperatures (300 °C), moderate at room temperature, and negligible at cryogenic temperature (−223 °C). This behavior indicates that thermal activation, alongside irradiation effects, is essential to overcome grain boundary pinning by fission gas bubbles, metallic precipitates, and porosity. Furthermore, while nanograins (<200 nm) consistently coarsened under irradiation, larger grains did not undergo further restructuring, which can be attributed to the strong defect annihilation at TEM lamella surfaces combined with the limited electronic stopping power of low energy Xe ions used in this work. These findings highlight the roles of thermal spike effects, defect mobility, and impurity pinning in governing grain evolution in the rim region of spent UO 2 fuel during ion irradiation, providing key insights for predictive models of restructuring and performance of the high burnup nuclear fuel.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Plutonium migration and phase evolution in irradiated U-Pu-Zr metallic fuels: An integrated EPMA-SEM-TEM study

Constituent redistribution is a defining feature of irradiated U-Pu-Zr metallic fuels, yet its mechanisms and effects on fuel performance are not sufficiently resolved to guide model development. Although decades of irradiation testing have established broad trends, a true mechanistic understanding of constituent redistribution has not been achieved. Here, in this study, we use electron probe microanalysis (EPMA), scanning electron microscopy (SEM), and transmission electron microscopy-based (TEM) selective area electron diffraction (SAED) on a EBR-II irradiated U-19 wt.% Pu-6 wt.% Zr fuel pin cross-section to correlate the composition, porosity, and crystallographic phases formed after irradiation. Constituent redistribution is thought to consist of three distinct zones, in which uranium and zirconium migrate while plutonium remains relatively unchanged. Our EPMA results resolve eight distinct compositional regions, and more importantly, show that plutonium redistributes alongside zirconium, contrary to historical assumptions. The distribution of fission products was highly asymmetric with a few large lanthanide precipitates observed at isolated sites on the pin periphery instead of a uniform distribution of smaller precipitates around the periphery. Using thermodynamic data from TAF-ID and the measured EPMA compositions, matrix phase fractions were predicted across the fuel radius. Phase predictions based on composition did not match TEM/SAED results, which revealed a much higher fraction of α−U phase than would be expected if phases were retained from reactor temperatures. These findings highlight the need for expanded SAED phase identification to capture post-irradiation and storage effects, as well as rigorous uncertainty quantification in fuel performance and phase diagram modeling to better constrain predictions from compositional data.

11 - NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2015

Microstructural evolution of nanocrystalline Fe–Zr alloys upon annealing treatment

Nanocrystalline Fe–Zr alloys exhibit an extraordinary thermal stability at elevated temperatures, which enables their potential applications in various fields. However, there remain concerns regarding the controlling stabilization mechanisms responsible for their thermal stability. In this work, two nanocrystalline Fe–Zr alloys containing 1 at.% Zr and 5 at.% Zr were annealed at various temperatures (T{sub ann}) up to 900 °C. Microstructural evolution of the alloys upon annealing was investigated by means of an X-ray diffractometer equipped with a 2-dimensional detector and transmission electron microscopy. Below 600 °C, microstructures of the two alloys consist of single nanocrystalline ferrite whose grain size is rather stable upon annealing treatments. Above 600 °C, accompanying the precipitation of Fe{sub 3}Zr phase, an apparent grain coarsening of ferrite is observed, whereas the thermal stability of the alloys is still considerably higher than that of nanocrystalline pure Fe. Based on the experimental results, it was claimed that stabilization of the nanocrystalline Fe–Zr alloys should not be totally ascribed to the thermodynamic stabilization mechanism due to the reduction in grain boundary energy as suggested in earlier investigations [K.A. Darling et al., Scr. Mater. 59 (2008) 530 and K.A. Darling et al., Mater. Sci. Eng. A527 (2010) 3572]; when T{sub ann} is higher than 600 °C, along with the precipitation of Fe{sub 3}Zr, the effect of thermodynamic stabilization is weakened, the kinetic effect arising from Zener pinning of Fe{sub 3}Zr precipitates turns to be an important mechanism contributing to the stabilization of the nanoscale grain size. - Highlights: • We show clear evidence of precipitation of Fe{sub 3}Zr phase above 600 °C. • Stabilization of nanostructure is not solely controlled by thermodynamic mechanism. • Above 600 °C, Zener pinning plays an important role in stabilizing nanostructure.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Feasibility of formation of nanocrystalline Fe-Cr-Y alloys: Mechanical properties and thermal stability

Aim of the present study is to investigate the feasibility of formation of Fe-Cr-Y disordered solid solutions by mechanical alloying and effect of Y on the thermal stability and mechanical properties of such nanocrystalline alloys. Thermodynamic analysis by Miedema's and Toop's models confirms that the energy barrier required to form the disordered solid solutions has been overcome by the stored energy due to strain dislocations and grain boundary defects. Although limited grain growth was observed during annealing of metastable Fe-15Cr-1Y alloy, the grains size found to stabilize at ~ 53 nm after annealing at 1000 °C; and the corresponding hardness value measured to be also quite high (8 GPa). The grain size analysis by TEM and AFM is well-corroborated with the XRD crystallite size. The high thermal stability and large strengthening effect have been discussed in the light of grain boundary pinning by solute segregation, solute drag effect and Zener pinning due to intermetallic phase(s). - Highlights: • Metastable Fe-Cr-Y alloys were developed by mechanical alloying for nuclear applications. • Formation of Fe-Cr-Y solid solutions was explained from the Gibbs free energy change using Toop's model. • 1 at.% Y found to be very effective in the stabilization of Fe-Cr alloys at high temperatures. • Solute drag effect and/or segregation of Y atoms played a pivotal role in the stabilization.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Effect of vanadium carbide on dry sliding wear behavior of powder metallurgy AISI M2 high speed steel processed by concentrated solar energy

Mixtures of AISI M2 high speed steel and vanadium carbide (3, 6 or 10 wt.%) were prepared by powder metallurgy and sintered by concentrated solar energy (CSE). Two different powerful solar furnaces were employed to sinter the parts and the results were compared with those obtained by conventional powder metallurgy using a tubular electric furnace. CSE allowed significant reduction of processing times and high heating rates. The wear resistance of compacts was studied by using rotating pin-on-disk and linearly reciprocating ball-on-flat methods. Wear mechanisms were investigated by means of scanning electron microscopy (SEM) observations and chemical inspections of the microstructures of the samples. Better wear properties than those obtained by conventional powder metallurgy were achieved. The refinement of the microstructure and the formation of carbonitrides were the reasons for this. - Highlights: •Powder metallurgy of mixtures of M2 high speed steel and VC are studied. •Some sintering is done by concentrated solar energy. •Rotating pin-on-disk and linearly reciprocating ball-on-flat methods are used. •The tribological properties and wear mechanisms, under dry sliding, are studied.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Development of nano-Y2O3 dispersed Zr alloys synthesized by mechanical alloying and consolidated by pulse plasma sintering

Highlights: • Zr-Fe-Cr-Cu-Ti-1.0wt% nano-Y{sub 2}O{sub 3} dispersed alloys are fabricated by mechanical alloying and pulse plasma sintering. • These alloys record extremely high compressive strength, Young’s modulus, and hardness. • These mechanical properties are superior as compared to other commercially available Zr based alloys. • Dispersion of nanometric FeZr{sub 2}, Y{sub 2}Ti{sub 2}O{sub 7}, Fe{sub 2}Ti, ZrCu, Cr{sub 2}Zr, Y{sub 2}O{sub 3} leads to grain boundary pinning at elevated temperature. - Abstract: In this paper, Zr alloys are synthesized with nominal compositions: 50Zr-30Fe-10Cr-5Cu-5Ti (alloy A), and 49Zr-30Fe-10Cr-5Cu-5Ti-1Y{sub 2}O{sub 3} (alloy B), 45Zr-30Fe-10Cr-10Cu-5Ti (alloy C), 44Zr-30Fe-10Cr-10Cu-5Ti-1Y{sub 2}O{sub 3} (alloy D) (all in wt%) by mechanical alloying and consolidated by pulse plasma sintering at 1173 K (900 °C), 1223 K (950 °C) and 1273 K (1000 °C) using 75 MPa uniaxial pressure applied for 5 min and 70 kA pulsed current at 3 Hz pulse frequency. The microstructure and phase evolution during mechanical alloying and sintering has been characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM & TEM) and energy dispersive spectroscopy (EDS). Mechanical properties i.e. hardness and compressive strength were determined by using nano-indentation unit and universal testing machine. The produced alloys recorded very high levels of compressive strength (1359–2456 MPa), and hardness (7.05–10.05 GPa) which measures 1.5–2.0 times more than that of other Zr alloys (2 O{sub 3}) particles which can contribute to grain boundary pinning, and improved creep and oxidation resistance at elevated temperature.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Evaluation of microstructure stability at the interfaces of Al-6061 welds fabricated using ultrasonic additive manufacturing

Ultrasonic additive manufacturing (UAM) is a solid-state additive manufacturing process that uses fundamental principles of ultrasonic welding and sequential layering of tapes to fabricate complex three-dimensional (3-D) components. One of the factors limiting the use of this technology is the poor tensile strength along the z-axis. Recent work has demonstrated the improvement of the z-axis properties after post-processing treatments. The abnormally high stability of the grains at the interface during post-weld heat treatments is, however, not yet well understood. In this work we use multiscale characterization to understand the stability of the grains during post-weld heat treatments. Aluminum alloy (6061) builds, fabricated using ultrasonic additive manufacturing, were post-weld heat treated at 180, 330 and 580 °C. The grains close to the tape interfaces are stable during post-weld heat treatments at high temperatures (i.e., 580 °C). This is in contrast to rapid grain growth that takes place in the bulk. Transmission electron microscopy and atom-probe tomography display a significant enrichment of oxygen and magnesium near the stable interfaces. Based on the detailed characterization, two mechanisms are proposed and evaluated: nonequilibrium nano-dispersed oxides impeding the grain growth due to grain boundary pinning, or grain boundary segregation of magnesium and oxygen reducing the grain boundary energy.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Temperature-dependent cyclic response and microstructure of AlSi10Mg(Cu) alloy

Highlights: • The cyclic behavior of AlSi10Mg(Cu) alloy in LCF regime is temperature-dependent. • The transition temperature of the cyclic behavior is about 180 °C. • Microstructure transitions were observed with increasing temperature. - Abstract: In the present work, the cyclic stress response and microstructure evolution of AlSi10Mg(Cu) alloy at high temperature were investigated. Samples were tested at high temperature, under total strain control and tensile-compression loading (R = −1) until failure. The cyclic stress response was analyzed, as well as the microstructures were examined by TEM. The results demonstrated that the cycle stress response of the studied alloy is experimental temperature dependence. Microstructure analysis indicated the precipitated phase was disruptive changed by high temperature compared to the as-received alloy. A lot of coherent β″-Mg{sub 2}Si precipitates and GP zones were observed in the as-received alloy, resulting in sustaining cyclic hardening by pinning effect. At high temperature, the vast majority of the tiny coherency precipitates and clusters transformed to the large semi-coherency Q′ and β′-Mg{sub 2}Si precipitates, leading to the sharp decrease of pinning number and the change of dislocation interaction mechanism, which is believed to be one of the reasons for softening. Another reason is that high temperatures can promote dislocations movement.

36 MATERIALS SCIENCE↗