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At least 1,099 records · Page 61
All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Influence of microstructure and temperature on impact toughness of H13 steel produced by binder jet additive manufacturing

Binder Jet Additive Manufacturing (BJAM) is a promising manufacturing pathway to produce H13 steel dies and tooling with complex geometries for applications in high pressure aluminum die casting, hot stamping, and injection molding. While fully dense H13 coupons produced using BJAM have been subjected to detailed microstructure characterization, properties which are critical and relevant to the aforementioned applications, such as impact toughness, have not been reported. Here, this work evaluated the influence of microstructural characteristics and test temperature on the impact toughness of H13 produced by BJAM. Coupons were produced from three different powder size distributions (PSDs), with nominal powder size ranges of −22 μm, 10-32 μm, and 15-53 μm. Coupons were printed, sintered, hot isostatically pressed (HIPed), and heat treated by quenching and tempering. After HIPing, the measured porosities of the different PSDs were all less than 0.015 vol%. The −22 μm PSD BJAM material exhibited the best impact toughness of all three PSDs across the entire test temperature range from 25 to 400 °C, and also exhibited an ambient temperature impact toughness of 10.9 J at a hardness of 46 HRC, equivalent to minimum threshold requirements for premium grade H13. However, all three BJAM PSDs exhibited moderately lower impact toughness than premium grade wrought H13 from RT to 400 °C. We attribute this in part due to the very large prior-austenite grain (PAG) sizes near 400 μm and segregation from former liquid channels leading to greater amounts of carbide precipitation on PAG boundaries. Technical pathways for optimizing processing and chemistry of BJAM H13 to further improve impact toughness are discussed.

Binder jet additive manufacturing↗
DOE OSTI2018

Influence of Boron on Austenite to Ferrite Transformation Behavior of Low Carbon Steel Under Continuous Cooling

In the current work, the influence of boron on austenite to ferrite transformation behavior under continuous cooling condition and its associated features, e.g., final microstructure, mechanical properties, etc., in low carbon steel has been studied. The steels (C 0.04 wt.%, B 10-100 ppm) prepared in an open air laboratory furnace showed identical microstructures having ferrite grains of 20-25 µm. However, tensile test data indicate variation of yield strength and ultimate tensile strength with boron content. The yield point elongation and strain aging index both were found to decrease with increase in boron content or boron-to-nitrogen ratio. As the boron nitride precipitates stimulate the nucleation of ferrite phase, the dilation curves show an increase in austenite to ferrite transformation start temperature with boron content. The resulting microstructure and hardness value also corroborate the finding. Transmission electron microscopy findings revealed the presence of ultra-fine boron nitride (BN) precipitates in both grain boundary and grain body of the steel having boron concentration of 30 ppm and beyond. The presence of these precipitates also increased with boron content. Based on austenite decomposition behavior, related microstructure and hardness values it is conjectured that these BN precipitates may act as nucleating agent for polygonal ferrite during austenite decomposition, thereby softening the steel during fast cooling.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Laser Powder Deposition Parametric Optimization and Property Development for Ti-6Al-4V Alloy

In this study, Ti6Al4V alloy was produced via laser powder deposition (LPD). To obtain Ti6Al4V alloy with maximum density, LPD parameters for preparing Ti6Al4V samples were optimized using the Taguchi method. Results were analyzed on the basis of the signal-to-noise (S/N) ratios and analyses of variance. A high energy density should be used to achieve higher levels of densification. The optimal combination of parameters for density was a scanning speed of 550 mm/min, laser power of 160 W, powder feeding rate of 0.99 g/min, and shield gas flow of 8 L/min. An almost fully dense Ti6Al4V sample was prepared using the optimized LPD process, and the relative density was greater than 99%. In addition, the microstructure and properties of Ti6Al4V samples prepared by optimized LPD process were investigated. The microstructure investigation revealed that the LPD-prepared Ti6Al4V sample was predominantly composed of fine acicular α phase and lath-type α phase. Tensile and microhardness tests indicated that the LPD sample had higher mechanical properties than the traditional cast Ti6Al4V alloy because of the acicular martensitic phase and smaller grain size.

36 MATERIALS SCIENCE↗
NASA NTRS1984

Deformation and fracture behavior of Ni-Mo-Al(gamma/gamma prime-alpha) in situ composite

Tensile properties of a directionally solidified (DS) eutectic alloy of the nominal composition Ni-33 Mo-5.7 Al (weight percent) have been investigated both at room temperature and elevated temperatures. The microstructure-mechanical property relationship has been studied for the alloy both in the as-DS and heat-treated conditions. Changes in the yield strength, the work hardening behavior, and the fracture morphology have been explained in terms of the microstructural changes due to the heat treatment. The yield drops observed have been attributed to the microdebonding due to the possible segregation of impurities at the fiber-matrix interface, and partly to the strain aging. The deformation mechanism has been identified to be the cutting of gamma prime particles.

Sriramamurthy, A. M.↗
DOE OSTI2017

Evaluation of Additively Manufactured Materials for Nuclear Plant Components

Powder bed fusion Direct Metal Laser Melting (DMLM) is an evolving additive manufacturing (AM) fabrication technology that is providing high performance parts to many industries. This technology has significant promise for use in building components for nuclear power plants. Implementation of materials produced using this and similar processes offer a potential step change in efficiency for complex parts production and hence a potential for innovative design as well as cost savings for components in the future. Properties of AM Type 316L have been reported in previous work, showing properties that match wrought properties. The fine grain structure may even lead to better environmental resistance. However, there is a need to confirm the behavior of these innovative materials after exposure to radiation if this innovative technology is to be used in current and future nuclear applications. This paper discusses new efforts being explored via a joint program between GE Hitachi (GEH) and INL (Idaho National laboratory) aimed at developing corresponding un-irradiated and irradiated data for AM materials. This paper will present data for both Type 316L stainless steel, a single-phase alloy, and Ni-base Alloy 718, a precipitation hardened alloy, manufactured using AM. This paper, serving as a progress report, will present the mechanical property and microstructural data for both Type 316L and 718 AM alloys to assess their correspondence to wrought alloy data and establish a baseline for future comparison to irradiated properties. The paper will end by discussing the requirements for using these and other additively manufactured materials in future reactor component applications where irradiated data is not available.

316 Stainless Steel↗
DOE OSTI2021

On the interactions between molten aluminum and high entropy alloy particles during aluminum matrix composite processing

The feasibility of adding AlCrTiV high entropy alloy (HEA) particles to molten aluminum to make metal matrix composites was studied. Equiatomic AlCrTiV HEA particles, produced by a solid state reduction process, were dispersed into pure aluminum and 7075 alloy (Al-5.8Zn-2.3Mg-1.4Cu, all weight %) melt and by a ultrasonic dispenser. It was found that the AlCrTiV particles reacted with molten aluminum, leading to the formation of Al 45 (Cr,V) 7 and Al 3 Ti intermetallic phases in the aluminum matrix composites. Although the AlCrTiV HEA particles did not survive in molten aluminum during composite processing, the final composite materials showed significantly improved mechanical properties, due to grain refinement and dispersion strengthening. Finally, the research suggests that the interactions between matrix aluminum alloys and the particles are key in controlling the final microstructure and properties of the composites.

36 MATERIALS SCIENCE↗
NASA NTRS1974

Microscopic investigation of cavitation erosion damage in metals

The results of research to identify the cavitation erosion damage mechanisms at the microscopic level for three metals (aluminum, stainless steel, and titanium) representing a range of properties and microstructure are presented. The metals were exposed to cavitation generated in distilled water by a 20-kHz ultrasonic facility operating at a vibration amplitude of 2 mils. Representative properties of the metals and experimental details are summarized. Replicas of the eroded surfaces of the specimens obtained periodically during exposure were examined with a transmission electron microscope to follow progression of the erosion damage and identify dominant erosion mechanisms as a function of exposure time. Eroded surfaces of selected specimens were also examined with a scanning electron microscope to assist in the interpretation.

Hackworh, J. V.↗
DOE OSTI2018

Evolution of the Fe{sup 3+} Ion Local Environment During the Phase Transition ε-Fe{sub 2}O{sub 3} → α-Fe{sub 2}O{sub 3}

Evolution of the local environment of Fe{sup 3+} ions in deposited Fe{sub 2}O{sub 3}/SiO{sub 2} nanoparticles formed in samples with different iron contents was investigated in order to establish the conditions for obtaining the stable ε-Fe{sub 2}O{sub 3}/SiO{sub 2} samples without impurities of other iron oxide polymorphs. Microstructure of the samples with an iron content of up to 16% is studied by high-resolution transmission electron microscopy, X-ray diffraction analysis, and Mössbauer spectroscopy, and their magnetic properties are examined. At iron concentrations below 6%, calcinations of iron-containing precursor nanoparticles in a silica gel matrix lead to the formation of the ε-Fe{sub 2}O{sub 3} iron oxide polymorphic modification without foreign phase impurities, while at the iron concentration in the range of 6–12%, the hematite phase forms in the sample in the fraction of no more than 5%. It is concluded on the basis of the data obtained that the spatial stabilization of iron-containing particles is one of the main factors facilitating the formation of the ε-Fe{sub 2}O{sub 3} phase in a silica gel matrix without other iron oxide polymorphs. It is demonstrated that the increase in the iron content leads to the formation of larger particles in the sample and gradual changes of the Fe{sup 3+} ion local environment during the phase transition ε-Fe{sub 2}O{sub 3} → α-Fe{sub 2}O{sub 3}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effects of Nb on Superelasticity and Low Modulus Properties of Metastable β-Type Ti-Nb-Ta-Zr Biomedical Alloys

In this work, a series of Ti-xNb-2Ta-3Zr (x = 25, 30, 35, 40 wt.%) alloys are designed, and the transformation of β-phase to α″ martensitic, β-phase stability, microstructure, mechanical properties and corrosion performance of these alloys are investigated. The phase analysis shows as the Nb content increases, the α″ phase in these alloys decreases, while the intensity of the two main peaks β(110) and β(211) of Ti-40Nb-2Ta-3Zr alloy is reduced. These results can be attributed to the variation of β-phase stability caused by Nb element of alloy and cold rolling process. The mechanical properties test shows that the elastic modulus (52 GPa) of the Ti-35Nb-2Ta-3Zr alloy is the lowest and the elongation (18.8%) is the maximum. In addition, the alloy is susceptible to β-phase elastic deformation and stress-induced martensitic transformation resulting in the highest recovery strain of the alloy (66.87%). The polarization curves show that the Ti-35Nb-2Ta-3Zr alloy has the highest corrosion potential (− 0.34 V) and the lowest corrosion current density (0.21 μA cm{sup −2}) exhibiting the best corrosion resistance.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Bulk nanocrystalline Al–Mg–Y alloys with amorphous grain boundary complexions display high strength and compressive plasticity

Although nanocrystalline alloys regularly exhibit high strengths, their use in structural applications often face challenges due to sample size limitations, unstable microstructures, and the limited ability to plastically deform. The incorporation of amorphous grain boundary complexions has been proposed to address these issues, by simultaneously stabilizing nanocrystalline grain structures for scale-up processing and improving alloy toughness. In the present study, the mechanical behavior of bulk nanocrystalline Al–Mg–Y is examined with macroscale compression testing, probing a length scale that is relevant to real-world structural applications. Bulk samples were fabricated via a simple powder metallurgy approach, with different hot-pressing temperatures and durations employed for consolidation in order to investigate microstructural and property evolution. All of the specimens contained primary face-centered cubic Al and secondary Al 4 C 3 and Al 3 Y phases, with the Al 3 Y particles exhibiting two populations of small equiaxed and larger elongated particles. Appreciable plasticity was measured along with high ultimate stresses over 800 MPa due to the presence of amorphous grain boundary complexions. Microstructural characterization of fracture surfaces revealed that the area fraction of dimpled regions increased with longer hot-pressing time. Most importantly, the elongated Al 3 Y particles formed regular cellular patterns with increasing hot-pressing time, delaying shear localization and significantly enhancing plasticity. The hierarchy present in the microstructure of the Al–Mg–Y alloy, from amorphous grain boundary complexions to secondary phases, gives rise to excellent bulk mechanical properties, which are attractive for structural applications.

Bulk nanocrystalline alloy↗
DOE OSTI2019

Effect of Tempering Temperature on the Precipitation Behavior and Mechanical Properties of a Martensite Ferritic Steel

In this investigation, the precipitation of boron-containing M{sub 23}C{sub 6} in the CB2 steel during tempering was investigated. Scanning electron microscopy, energy-dispersive x-ray spectroscopy, transmission electron microscopy and differential scanning calorimetry were used to analyze the influence of temperature on the microstructure and properties of CB2-tempered martensite ferritic steel. The steel was normalized at 1100 °C for 2 h and then tempered at six different temperatures between 690 and 790 °C for 2 h. During air-cooling following austenitization, the precipitation of M{sub 3}C particles occurred in flakes forming with their diameter and thickness of 100 and 20 nm, respectively. The boron-containing M{sub 23}C{sub 6} was formed on the lath boundary after the dissolution of M{sub 3}C within the boundary. When the tempering temperature increased from 690 to 790 °C, the average diameter of boron-containing M{sub 23}C{sub 6} increased from 132 to 198 nm. Owing to the rapid growth of the precipitates, the phenomenon of lath widening as well as the recovery of microstructure would take place at high temperature. With an increase in the temperature, the tensile and yield strengths decreased gradually, while the plasticity increased and the boron-containing M{sub 23}C{sub 6} grew rapidly. Furthermore, when the tempering temperature exceeded 750 °C, the plasticity of CB2 steel was significantly improved.

36 MATERIALS SCIENCE↗
DOE OSTI2018

A review on the fatigue behavior of Ti-6Al-4V fabricated by electron beam melting additive manufacturing

Electron beam melting (EBM) is a swiftyly-developing metal additive manufacturing process that holds significant interest in the aerospace and biomedical industries for the high-strength titanium alloy, Ti-6Al-4V. These industries have fatigue-limited applications, yet a lack of understanding of the EBM process-microstructure-fatigue relationships limit widespread use and presents challenges for certification. In this review, uniaxial fatigue data was collected and the effects of build orientation, surface roughness, and hot-isostatic pressing are linked to the fatigue properties highlighting microstructure, defects, and failure mechanisms. The observations and conclusions are supported by statistical analysis using the mean fatigue life obtained by the Statistical Fatigue-Limit Model. Both EBM-process and post-process structure relationships are discussed in order to identify the best-practice for fatigue-resistant design. The performance of the EBM material is compared to conventionally manufactured Ti-6Al-4V and possible methods to increase the fatigue resistance are discussed. Anisotropic fatigue behavior was observed in as-fabricated parts and no statistical distinction was found in the fatigue performance of HIPed and as-fabricated material provided the same as-fabricated rough surface condition. However, comparable fatigue life to traditionally manufactured lamellar Ti-6Al-4V is achieved when both post-process HIP and machining are applied to EBM-fabricated parts.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructural evolution in shear-punch tests: A comparative study of pure Cu and Cu-Cr alloy

Understanding the mechanisms behind microstructural evolution during shear deformation has been a long-standing area of interest. However, establishing a connection between microstructure, mechanical properties, and extent of shear deformation is challenging and requires refined experimental approaches. Shear-punch testing (SPT) provides a controlled method to introduce shear into small volumes of material that later can be subjected to detailed microstructural characterization. In this study, we utilize an SPT device to induce shear deformation to pure copper and a binary copper-chromium alloy. Electron backscatter diffraction and transmission electron microscopy were used to study the mechanisms of plastic deformation after SPT. Our results indicate that shear deformation of pure Cu produces a dense network of intercepting microshear bands upon sustained deformation. Twin boundaries undergo degradation into high angle grain boundaries due to simultaneous deviation from the axis-angle pair condition of 60° misorientation on [111] direction. The presence of 50% volume Cr particles in the soft Cu matrix fundamentally altered the shear deformation mechanism. Preferential deformation of the Cu matrix led to accelerated shear-induced formation of low and high angle grain boundaries, and subsequent grain refinement. Comparatively, no grain refinement occurred in pure Cu at a strain ~10 times larger (ϵ = 4.73) than that of the copper-chromium case (ϵ = 0.42). Overall, our study sheds light on the microstructural evolution during shear deformation and highlights the significant influence of particle reinforcements on the shear deformation mechanisms of metals.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Bridging multimodal microscopy for advanced characterization on nuclear fuel using machine learning

Uranium dioxide (UO 2 ), widely used as driver fuel in light water reactors, experiences microstructure and property change by nuclear fission reactions. This paper bridges the characterization of fresh UO 2 fuel at different length scales, serving as a baseline for future post irradiation examination of irradiated UO 2 fuel. To characterize the microstructural change of nuclear fuel, modern approaches cover a wide range of length scales through different characterization techniques, such as mm scale for Synchrotron-based X-ray computed tomography (SXCT) and microscale for focused ion beam (FIB) and scanning electron microscopy (SEM). It is challenging to bridge the data and knowledge of the same sample in different length scales. This paper proposed a deep learning framework leveraging transfer learning to detect microstructural defects, trained from a sparse FIB, SEM, and SXCT images. The proposed model achieved superior performance in defect segmentation on multiscale microscopic data compared to four of the latest deep learning models.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Correlating energy density induced residual stress, porosity, and mechanical property variations in directed energy deposition using neutron diffraction and imaging techniques

In a directed energy deposition (DED) process, the energy density deposited into the materials drives the structure and properties. The energy density is influenced by several printing parameters, such as laser power, hatch spacing, scanning speed, etc. In this study, 316L stainless steels samples were fabricated with varying hatch spacing aiming to induce variations in sample microstructure and properties. A combination of techniques including engineering neutron diffraction, neutron computed tomography, and tensile testing, were employed to correlate the structure and macroscopic properties. Porosity was predominantly observed at the bottom of the deposited materials and was effectively reduced by decreased hatch spacing. Correlatively, compressive residual stress was observed at the bottom of the specimens, while internal stress is largely determined by the hatch spacing. The residual stress in general decreases as the hatch spacing decreases. The maximum ultimate tensile strength (UTS) was found to increase from 517.4 to 528.6 MPa with a strain increased from 0.847 to 0.897 as the hatch spacing decreased from 0.45 to 0.42 mm. However, further increase in energy density by reducing the hatch spacing resulted in a significant decrease in UTS (as low as 452 MPa). This work provides new insights from bulk non-destructive techniques into correlating energy density induced residual stress, porosity, and mechanical property variations in directed energy deposition.

316L stainless steel↗
DOE OSTI2018

The effect of cell-size dispersity on the mechanical properties of closed-cell aluminum foam

Highlights: • The effect of cell-size dispersity on the Young’s modulus of foam was investigated through experiments and simulations • Crushing experiments were conducted on 27 foam specimens in order measure the relative Young’s modulus • Three types of numerical models, including monodispersed, bidispersed and polydispersed models were studied • The numerical convergence on the model size for different models was also studied • The difference among numerical results obtained from the three models was insignificant - Abstract: The mechanical properties of open-celled and closed-celled metallic foam are strongly influenced by the cellular microstructure and material properties of the base material from which the foam is made. The present study investigated the microstructure and mechanical properties of ALPORAS closed-cell Al foam. In particular, the effect of cell-size dispersity on the Young's modulus of foam was investigated through crushing experiments and numerical simulations. Crushing experiments were first conducted on two mutually perpendicular directions. Numerical models of varying cell-size dispersity and complexity were subsequently developed, including the monodispersed model that is based on the Kelvin structure, the bidispersed model, and the polydispersed model that is based on the random Laguerre tessellation algorithm. The numerical models were discretized using shell elements, and the simulations were conducted using the ABAQUS finite element method software. Relative Young's moduli with various relative densities were predicted, and the numerical convergence on the model size was studied accordingly. Numerical results obtained from all three numerical models developed were found to overestimate the experimental results by a factor of approximately 3. The difference between the numerical and experimental results can be attributed to the difference in detailed microstructural characteristics. Furthermore, the difference among numerical results obtained from the three models was insignificant.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Spark plasma sintering (SPS) densified U 3 Si 2 pellets: Microstructure control and enhanced mechanical and oxidation properties

Dense U 3 Si 2 pellets with controlled grain structure and enhanced thermal-mechanical and oxidation properties are synthesized with spark plasma sintering (SPS). Microstructure and phase composition of the SPS densified pellets are characterized systematically using SEM, EDS, and XRD. Thermal-mechanical properties and oxidation behavior of the sintered silicide fuel pellets are analyzed by laser flash, indentation, and dynamic thermogravimetric analysis. Dense U 3 Si 2 pellets are consolidated by combining high energy ball milling and rapid sintering by SPS, and the microstructure structures are controlled from micron-sized (~5.7 μm grain size) for conventional silicide to a nanocrystalline matrix with an average grain size of ~280 nm. A dominant phase of distorted U 3 Si 2 was identified with lattice expansion due to residual thermal stress upon SPS consolidation and rapid cooling processes. Both micron-sized and nano-sized pellets show exceptional thermal transport properties, consistent with monolithic silicides reported in literature. The SPS-densified pellets possess simultaneously high hardness and fracture toughness. The SPS-densified silicide pellets also demonstrate exceptional oxidation performance with extended onset oxidation temperature above 500 °C and reduced oxidation kinetics, particularly for nano-sized pellets. A strong strain effect was proposed in which compressive stress in nano-sized pellets enhances the oxidation resistance of silicide fuels, as evidenced by the degradation of oxidation performance upon strain relaxation by isothermal annealing. The correlation among the sintering process – microstructure control – physical properties and fuel behavior is established. A new concept of strain engineering is proposed further properties optimization, enabling the development of potential oxidation and corrosion-resistant silicides with extended performance, the key technological challenge of U 3 Si 2 as the leading concept of accident tolerant fuels.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗