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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 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

New insights on the effects of chemistry and temperature on α’ precipitation during aging of FeCrAl alloys

Here, the effect of Al on α' precipitation in FeCrAl alloys was studied through thermal aging of several model binary FeCr and FeCrAl alloys with Cr content of 13 wt.%, 17 wt.%, and 25 wt.% with and without 5.5 wt.% Al. Aging was performed up to 1,000h at varying temperatures from 400-500°C. At 400°C no age hardening was observed due to slow kinetics at this temperature. For both the 17Cr and 25Cr alloys, the addition of Al shows a lowering of the miscibility gap, consistent with other reports in literature. Interestingly, however, for the 25Cr alloys the addition of Al in the FeCrAl ternary alloy accelerated α' precipitation below the miscibility gap. Such enhanced precipitation has also been predicted by our atomistic kinetic Monte Carlo (AKMC) simulations. While previous literature has often focused on Al suppressing α', here we show that while Al can lower the miscibility gap in the Fe-Cr ferritic system thermodynamically, it may also enhance the kinetics of precipitation.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Effects of helium on irradiation response of reduced-activation ferritic-martensitic steels: Using nickel isotopes to simulate fusion neutron response

Understanding the effects of helium on microstructures and mechanical properties of reduced-activation ferritic-martensitic steels is important to use of these steels in fusion reactor structures. The 9Cr-2WVTa steels were doped with 58Ni and 60Ni isotopes at 2 weight percent to control the rate of transmutation helium generation. The samples were irradiated in the High Flux Isotope Reactor to ~24 displacements per atom at nominal temperatures of 300, 400, and 500°C, producing 228 and 7 atomic parts-per-million helium in the 58 Ni- and 60 Ni-doped samples, respectively. Transmission electron microscopy revealed a variety of precipitates and the radiation-induced dislocation loops and cavities (voids or helium bubbles). Tensile tests of the irradiated samples at the irradiation temperatures showed radiation-induced hardening at 300°C and radiation-induced softening at 400°C. Analysis indicates that the hardening primarily originated from the loops and cavities. The 58 Ni-doped samples had greater strengthening contributions from loops and cavities, leading to higher hardening with lower ductility than the 60 Ni-doped samples. The greater helium production of 58 Ni did not show pronounced reductions in ductility of the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2020

The correlation between microstructure and nanoindentation property of neutron-irradiated austenitic alloy D9

The microstructure and nanomechanical properties of three samples of the modified stainless steel (referred as the alloy D9) were systematically characterized after neutron irradiation in the Advanced Test Reactor. The samples were irradiated to 5.0, 8.2, and 9.2 displacements per atom at 448, 430, and 683°C, respectively. The evolutions of dislocation loops, cavities, and radiation-induced precipitates were quantitatively studied to reveal their dose and temperature dependencies. Nanohardness and nanoindentation creep tests were conducted at room temperature on the irradiated samples. Unexpected radiation hardening was observed in the highest-temperature-irradiated sample due to the formation of an unknown type of Ni- and Si-rich precipitates whose contributions to the radiation and mechanical performances of the alloy were discussed. We provide the radiation-microstructure-property correlations of alloy D9 with new insights, which can benefit the development and optimization of advanced austenitic alloys for future nuclear applications.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Improved irradiation resistance of accident-tolerant high-strength FeCrAl alloys with heterogeneous structures

In this work, post–neutron irradiation examination is performed on advanced accident-tolerant fuel (ATF) cladding iron-chromium-aluminum (FeCrAl) alloys with ~10–13at. % Cr, ~10–12 at. % Al, ~1 at. % Mo, and minor alloying elements including Y irradiated to a damage level of 7 displacements per atom (dpa) at irradiation temperatures of 267–282 °C. A compositional dependency of the Cr and Al content is observed on the ratio of sessile and glissile dislocation loops, where the density of a$\langle$100$\rangle$ type loops is somewhat higher than the a/2$\langle$111$\rangle$ type loops. The α' precipitate number density is inversely correlated to the starting Cr concentration of the alloys of interest. The irradiation to a higher dose of 7 dpa results in a higher density of dislocation loops and α' precipitates for the same alloys at a lower irradiation dose, such as 1.8 dpa. In this work, the effect of α' precipitates on the dislocation loop density is discussed, and the presence of α' appears to inhibit the nucleation of loops. Compared with first-generation FeCrAl alloys, these advanced alloys with heterogeneous structure exhibit a lower Cr concentration in α' precipitation at the same dose level; they act as weaker obstacles deviating from the primary hardening contribution from the mature α'. Hence, the overall irradiation-induced hardening decreases; our alloys show improved radiation resistance because of their stronger sink strengths. The results presented in this paper could provide insights for the design and optimization of ATF cladding materials for future fission and space applications.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Data-Driven Surrogate Modeling with Microstructure-Sensitivity of Viscoplastic Creep in Grade 91 Steel

Abstract To support the development of advanced steel alloys tailored to withstand extreme conditions, it is imperative to account for the mechanical performance of components, while considering the influence of local microstructure on the macroscopic response. To this end, this study focuses on the development of microstructure-sensitive constitutive models for the mechanical response of Grade 91 steel exposed to extreme thermo-mechanical environments. Polynomial chaos expansion (PCE) surrogates are used to emulate high-fidelity polycrystal simulations of the viscoplastic response of Grade 91 steel as a function of the microstructure fingerprint (e.g., dislocations and precipitates). To cover a wide temperature–stress domain, two separate PCE surrogates—one that captures softening and the other that captures hardening behavior—are combined using another (sparse) Gaussian process regression model. The resulting constitutive creep surrogate model is integrated within the MOOSE finite element framework to simulate the intricate effects of microstructure, in particular MX-phase precipitates, on a component with a graded microstructure. Surrogate sensitivity analysis is applied to quantify the relevant impact of spatially varying microstructure on the creep response in a test-case involving a Grade 91 alloy with a prototypical weld.

36 MATERIALS SCIENCE↗
NASA NTRS2006

Development of a Thin Gauge Metallic Seal for Gas Turbine Engine Applications to 1700 F

The goal of doubling thrust-to-weight ratio for gas turbine engines has placed significant demands on engine component materials. Operating temperatures for static seals in the transition duct and turbine sections for instance, may well reach 2000 F within the next ten years. At these temperatures conventional age-hardenable superalloys lose their high strength via overaging and eventual dissolution of the gamma precipitate, and are well above their oxidation stability limit. Conventional solid-solution-strengthened alloys offer metallurgical stability, but suffer from rapid oxidation and little useful load bearing strength. Ceramic materials can theoretically be used at these temperatures, but manufacturing processes are in the developmental stages.

England, Raymond O.↗
DOE OSTI2025

Flux effects in precipitation under irradiation simulation of Fe-Cr alloys

Radiation-enhanced precipitation of Cr-rich α’ in irradiated Fe-Cr alloys, which results in hardening and embrittlement, depends on the irradiating particle and the displacement per atom (dpa) rate. Here, we utilize a Cahn-Hilliard phase-field based approach, that includes simple models for nucleation, irradiating particle and rate dependent radiation-enhanced diffusion and cascade mixing to simulate α’ evolution under neutrons, heavy ions, and electron irradiations. Different irradiating particles manifest very different cascade mixing efficiencies. The model was calibrated using neutron data. For cascade inducing neutron/heavy-ion dpa rates at 300 °C between 10-8 and 10-6 dpa/s the model predicts approximately constant number density, decreasing radius, decreasing α’ Cr composition, and lower α’ volume fraction. The model then predicts a dramatic transition to no α’ formation above approximately 10-5 dpa/s, while electron irradiation, with weak mixing, had little effect at dpa rates up to 10-3 dpa/s. These model predictions are consistent with experiments. We explain the results in terms of the flux dependence of the radiation enhanced diffusion, cascade mixing, and their ratio, which all vary significantly in relevant flux ranges for neutron and cascade inducing ion irradiations. These results show that both cascade mixing and radiation enhanced diffusion must be accounted for when attempting to emulate neutron-irradiation effects using accelerated ion irradiations.

Ke, Jia-Hong↗
DOE OSTI2023

Deformation mechanisms in an additively manufactured dual-phase eutectic high-entropy alloy

Nanostructured metals and alloys often exhibit high strengths but at the expense of reduced ductility. Through harnessing the far-from-equilibrium processing conditions of laser powder-bed fusion (L-PBF) additive manufacturing, we develop a dual-phase nanolamellar structure comprised of FCC/L1 2 and BCC/B2 phases in a Ni 40 Co 20 Fe 10 Cr 10 Al 18 W 2 eutectic high-entropy alloy (EHEA), which exhibits a combination of ultrahigh yield strength (>1.4 GPa) and large tensile ductility (~17%). The deformation mechanisms of the additively manufactured EHEA are studied via in-situ synchrotron X-ray diffraction and high-resolution transmission electron microscopy. The high yield strength mainly results from effective blockage of dislocation motion by the high density of lamellar interfaces. The refined nanolamellar structures and low stacking fault energy (SFE) promote stacking fault (SF)-mediated deformation in FCC/L1 2 nanolamellae. The accumulation of abundant dislocations and SFs at lamellar interfaces can effectively elevate local stresses to promote dislocation multiplication and martensitic transformation in BCC/B2 nanolamellae. The cooperative deformation of the dual phases, assisted by the semi-coherent lamellar interfaces, gives rise to the large ductility of the as-printed EHEA. In addition, here we also demonstrate that post-printing heat treatment allows us to tune the non-equilibrium microstructures and deformation mechanisms. After annealing, the significantly reduced SFE and thicknesses of the FCC nanolamellae facilitate the formation of massive SFs. The dissolution of nano-precipitates in the BCC/B2 nanolamellae reduces spatial confinement and further promotes martensitic transformation to enhance work hardening. Our work provides fundamental insights into the rich variety of deformation mechanisms underlying the exceptional mechanical properties of the additively manufactured dual-phase nanolamellar EHEAs.

36 MATERIALS SCIENCE↗
DOE OSTI2024

A FFT-based mesoscale continuum dislocation mechanics with defect energy: Applications to composites and polycrystals

A crystal plasticity elastoviscoplastic FFT (fast Fourier transform) formulation with a mesoscale continuum field dislocation mechanics model is presented, which incorporates a defect energy density that depends on GND densities and an associated material length scale. This allows to thermodynamically derive internal length scale dependent intra-crystalline backstress and Peach–Koehler force acting on GND densities. The model considers GND density evolution through a filtered numerical spectral approach, which is coupled with stress equilibrium through the elastoviscoplastic FFT algorithm. The discrete Fourier transform (DFT) method together with finite difference (FD) schemes is applied to solve both the backstress tensor and the Fourier–Green operator. Numerical results are first reported for two-phase laminate composites with plastic single crystal channels and elastic precipitates for shear loadings. Channel size effects are simulated and analyzed on the overall and local hardening behaviors during monotonous loadings. In addition, the evolutions of GND densities and the role of their associated backstress on size effects are examined during reversible shear loading. In a second part, the role of the defect energy internal length scale on polycrystal’s hardening during tension–compression is discussed. The results are compared to those obtained using FFT-based continuum field dislocation mechanics without defect energy.

36 MATERIALS SCIENCE↗
NASA NTRS2002

Method of producing superplastic alloys and superplastic alloys produced by the method

A method for producing new superplastic alloys by inducing in an alloy the formation of precipitates having a sufficient size and homogeneous distribution that a sufficiently refined grain structure to produce superplasticity is obtained after subsequent PSN processing. An age-hardenable alloy having at least one dispersoid phase is selected for processing. The alloy is solution heat-treated and cooled to form a supersaturated solid solution. The alloy is plastically deformed sufficiently to form a high-energy defect structure useful for the subsequent heterogeneous nucleation of precipitates. The alloy is then aged, preferably by a multi-stage low and high temperature process, and precipitates are formed at the defect sites. The alloy then is subjected to a PSN process comprising plastically deforming the alloy to provide sufficient strain energy in the alloy to ensure recrystallization, and statically recrystallizing the alloy. A grain structure exhibiting new, fine, equiaxed and uniform grains is produced in the alloy. An exemplary 6xxx alloy of the type capable of being produced by the present invention, and which is useful for aerospace, automotive and other applications, is disclosed and claimed. The process is also suitable for processing any age-hardenable aluminum or other alloy.

Troeger, Lillianne P.↗
DOE OSTI2024

Comparison of hardening and microstructures of ferritic/martensitic steels irradiated with fast neutrons and dual ions

Ferritic/martensitic steels T91 and HT9 were irradiated with neutrons (BOR-60 reactor) and dual ions (9 MeV Fe 3+ and 3.42 MeV energy degraded He 2+ ) from 369 to 520 °C and damage levels of 16.6 to 72 dpa to quantify the possibility of using ion irradiation to simulate neutron irradiation in terms of microstructures and mechanical properties. Nanoindentation testing was performed to obtain the bulk equivalent hardness of the dual-ion irradiated samples. For the neutron irradiated samples, both nanoindentation and Vickers hardness testing were conducted. Transmission Electron Microscopy (TEM) characterizations of the cavities, dislocation loops and precipitates were conducted to account for the strengthening contribution of each microstructure element. The good agreement between the microstructure-predicted (dispersed barrier hardening) and measured strength of the irradiated specimens demonstrated the accuracy of the strengthening model and the nanoindentation tests. Furthermore, the comparison of mechanical property and microstructure changes in ion and neutron irradiated structural materials indicated that ion irradiation replicated many neutron irradiation features. However, a single 70 °C temperature shift is insufficient to match all complex microstructures of neutron vs. ion irradiation over the irradiation temperature range of 369–520 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Optimization of direct aging temperature of Ti free grade 300 maraging steel manufactured using laser powder bed fusion (LPBF)

Maraging steels are of interest to the tool and die industry owing to their high strength, toughness and machinability. Additive manufacturing technologies like laser powder bed fusion (LPBF) can result in a paradigm shift in the design of maraging steel tools. Here, the lack of precipitates, in combination with solute segregation and non-equilibrium microstructure in Grade 300 maraging steel fabricated via LPBF makes the steel amenable to strengthening via direct aging post fabrication instead of the conventional solution treatment and aging. In this study we have focused on optimizing the direct aging temperature for a Ti-free Grade 300 maraging steel fabricated via LPBF for two different aging times. Through strain hardening analysis and detailed microstructural characterization, we show that direct aging at a temperature of 440 °C for 6 h resulted in the best strength-ductility combination. Aging samples at a lower temperature or shorter time resulted in no strain hardening prior to necking as a result of lower fraction of reverted austenite, whereas aging samples at a higher temperature resulted in extensive recrystallization of martensite, coarsening of precipitates, and extensive austenite reversion, resulting in softening of the fabricated parts.

36 MATERIALS SCIENCE↗
DOE OSTI2023

In-situ investigation of strengthening and strain hardening mechanisms of Cu-added medium-Mn steels by synchrotron-based high-energy X-ray diffraction

A novel Cu-added medium-Mn steel with a chemical composition of Fe–0.27C–9.1Mn–1.86Al–3.3Cu (wt.%) was designed and subjected to intercritical annealing (IA) temperature range from 620 °C to 680 °C for 1 h. The ultimate tensile strength (UTS) increases and the yielding strength (YS) decreases with the IA temperature increasing. The YS of 824 MPa, UTS of 1222 MPa, total elongation (TE) of 55%, and product of strength and elongation (PSE) of 67.2 GPa·% are achieved after IA at 660 °C. Transmission electron microscopy confirmed that Cu-rich nanoparticles precipitate in the ferrite. The in-situ high-energy X-ray diffraction (HE-XRD) experiments show that at the beginning of plastic deformation, both austenite and ferrite bear the applied load. The load is mainly undertaken by martensite with effective transformation-induced plasticity (TRIP) effect triggered. The YS of ferrite is significantly higher than that of austenite. The individual contribution of solid solution strengthening, grain refinement strengthening, dislocation strengthening, and precipitation strengthening in ferrite and austenite is analyzed. The discrepancy between the YS of ferrite and austenite is mainly attributed to the precipitation strengthening due to the Cu-rich nanoparticles precipitation. The moderate mechanical stability and the collaboration of TRIP and twinning-induced plasticity (TWIP) effects of austenite contributed to the enhanced strain hardening capability and resulted in large ductility.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Irradiated Microstructure of Zorita Materials

Reactor baffle plate materials were harvested from the decommissioned Zorita nuclear power reactor after 38 years of service and were characterized with transmission electron microscope. The samples were Type 304 stainless steels and had been irradiated to 0.05, 16.9, ad 48.6 dpa. Faulted dislocation loops, voids, and irradiation-induced precipitates were observed in this material. While dislocation loops were the dominant irradiation defects for all samples, small voids and precipitates were also observed at 16.9 and 48.6 dpa, but not at 0.05 dpa. The size of dislocation loops increased with irradiation dose and saturated below 16.9 dpa. The loop density continued to increase between 16.9 and 48.6 dpa. For voids, both the density and mean size were small, and the volume swelling was negligibly small even at 48.6 dpa. In addition, carbides or G-phase precipitates were detected at 16.9 and 48.6 dpa, and a complex dose dependence was observed. A range of irradiation hardening was estimated at each dose, and the resulting yield strengths were consistent with the previous tensile results measured from the Halden and BOR-60 specimens.

22 GENERAL STUDIES OF NUCLEAR REACTORS↗
NASA NTRS1981

Effect of mechanical surface and heat treatments on erosion resistance

The effect of erosion by glass beads and crushed glass and by heat treatments on the erosional resistance of 6061 aluminum alloy and 1045 steel were studied. The aluminum alloy's erosion resistance was found to be insensitive to mechanical surface treatment applied before testing, and was determined to depend on the properties of the work-hardened surface layer; this was also demonstrated for aluminum alloy single crystals. The aluminum alloy heat treatments included annealing, solution, and precipitation. Solution was found to increase erosion resistance but precipitation had the opposite effect. Hardness showed no correlation with erosion resistance for either aluminum alloy steel. The steel tests showed that crushed glass provides an order of magnitude more erosion than glass beads.

Salik, J.↗
NASA NTRS1983

Development of tough, strong, iron-base alloy for cryogenic applications

The development of an iron-base alloy that combines the normally divergent properties of high toughness and high strength at cryogenic temperatures is discussed. Specifically, alloy properties were sought which at -196 C would exhibit a fracture toughness of 220 MPa-m(1/2) with a corresponding yield strength of 1.4 GPa (200 ksi). Early work showed that high toughness could be achieved in Fe-12Ni alloys containing reactive metal additions such as Al, Nb, Ti, and V. Further research emphasized strengthening of these tough alloys by thermomechanical processing and the addition of Cu. Results showed that high strength and high toughness could be achieved in a single alloy at temperatures as low as -196 C. An alloy with composition Fe-12Ni-9.5Al-2Cu exhibited a yield strength of 1.65 GPa with a corresponding fracture toughness of 220 MPa-m(1/2) at -196 C. Strengthening due to Cu additions to the Fe-12Ni base alloys results primarily from precipitation of Cu-rich epsilon particles approximately 20 nm in diameter. Strengthening mechanisms are discussed in terms of an elastic modulus hardening model and are supported by transimission electron microscopy examinations of selected test specimens.

Stephens, J. R.↗
DOE OSTI2020

Exploiting Commonly-Reported Age-Hardening Data and Discovering Systematics Across Metallic Alloys and Alloy Systems to Identify Corrosion’s Most Influential Factors

This work explored ways to data mine legacy literature and predict solid-solid precipitation in support of simpler assessment of corrosion propensity in metallic alloys. Of interest was locating the peak age watershed (maximum hardness or strength), beyond which lies the regime termed “overaging.” A diligent search of literature and reference books, discussions with SMEs, and application of various algorithms showed that none of the premises going in held up to scrutiny.

36 MATERIALS SCIENCE↗