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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

Understanding Twinning and Deformation in High Entropy Alloys

On the one hand, multi-principal element alloys (MPEAs) have created a paradigm shift in alloy design due to large compositional space, whereas on the other, they have presented enormous computational challenges for theory-based materials design, especially density functional theory (DFT), which is inherently computationally expensive even for traditional dilute alloys. In this project, we developed a machine learning framework, namely PREDICT ( PR edict properties from E xisting D atabase I n C omplex alloys T erritory), that opens a pathway to predict elastic constants in large compositional space with little computational expense. The framework only relies on the DFT database of binary alloys and predicts Voigt–Reuss–Hill Young’s modulus, shear modulus, bulk modulus, elastic constants, and Poisson’s ratio in MPEAs. We show that the key descriptors of elastic constants are the A–B bond length and cohesive energy. The framework can predict elastic constants in hypothetical compositions as long as the constituent elements are present in the database, thereby enabling property exploration in multi-compositional systems. We illustrate predictions in a FCC Ni-Cu-Au-Pd-Pt system.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Tailoring Mechanical Properties of a Multi-Principle-Element Alloy by a Multi-Length-Scale Approach

A multiscale strengthening approach was employed to tailor the mechanical properties of a NiCoCr-based multi-principal element alloy (MPEA). Initially, the addition of Mo was utilized to strengthen the alloys by achieving grain size refinement, severe lattice distortion, and a reduction in stacking fault energy (SFE). Subsequently, the Suzuki segregation phenomenon was leveraged by carefully controlling stacking fault (SF) density via pre-straining and a subsequent 500°C heat treatment. Consequently, the Mo-added MPE alloys that were pre-strained and subsequently heat-treated exhibited a true yield stress of 2.3 GPa, with a corresponding fracture elongation of 12%. The Mo promotes complex SF interactions and the SFs formed during prior straining serve as sites for Suzuki segregation during subsequent heat treatment, varying the local SFE with Cr segregation, creating a roughened landscape and hindering dislocation dynamics. This multiscale strengthening approach presents a promising route for achieving desired mechanical properties in MPEAs.

mechanical properties↗
DOE OSTI2022

Localized Corrosion of Chromium-Containing Conventional and Multiprincipal Element Alloys in Methanol and Aqueous Chloride Environments

The localized corrosion behavior of Type 304L stainless steel (UNS S30400), Alloy 625 (UNS N06625), and three experimental NiCoCrMo multiprincipal element alloys (MPEA), exposed to methanol/lithium chloride solutions with different water contents, is examined in this paper. Cyclic potentiodynamic polarization tests indicated that water increased the pitting and repassivation potentials and the critical temperature at which localized corrosion occurred in chloride solutions. The effect of water on repassivation potential in methanol-chloride solution depended on the chloride concentration and alloy content. At lower chloride concentration and higher alloy content, water had a greater inhibiting effect on repassivation potential, suggesting a competitive reaction between chloride and water on the metal surface in the pit. The localized corrosion resistance of the MPEAs followed the same trend as that of commercial stainless steels and Ni-base alloys in terms of the effect of alloying elements. The implications of these results on the mechanisms of localized corrosion are discussed.

Materials Science↗
DOE OSTI2026

Mechanical Behavior of Neutron Irradiated Refractory Multi-Principal Element Alloys Processed via Spark Plasma Sintering

The search for advanced materials capable of withstanding the extreme conditions of Generation IV reactors is a critical area in materials science research. These reactors operate under severe environments, including high temperatures, corrosion, stress, and irradiation damage. Consequently, there is a need for innovative alloy systems to ensure the reliability and longevity of proposed Generation IV reactor components. Refractory multi-principal-element alloys (RMPEA) have emerged as a promising candidate due to their exceptional properties. These alloys, characterized by their composition of multiple principal elements in near-equiatomic ratios, exhibit superior resistance to irradiation damage, reduced void swelling, enhanced microstructural stability, and minimal irradiation-induced hardening. While initial studies on RMPEAs have shown promising results, most research has been limited to thin films, nanocrystalline microstructures, and ion irradiation, which do not accurately represent the behavior of bulk materials. To address this gap, our research focused on the neutron irradiation of bulk RMPEAs. We aim to conduct comprehensive post-irradiation examinations (PIE) of RMPEAs irradiated at the Advanced Test Reactor at Idaho National Laboratory. The RMPEAs were synthesized using spark plasma sintering (SPS) with mechanically alloyed metallurgical powder. The RMPEA specimens are a MoNbTi alloy system with additions of -Zr, and -ZrV. Furthermore, PIE consisted of mechanical testing and advanced materials characterization. The mechanical testing consisted of sub-sized tensile testing, micro- and nano- indentation. Microstructural characterization included scanning electron microscopy and transmission electron microscopy. Mechanical testing coupled with advanced microscopy techniques provides insight into phase morphology and its effects on the mechanical properties of the RMPEA specimens. The results indicate that both pristine and irradiated RMPEA specimens exhibited brittle behavior during tensile testing, which can be attributed to their heterogeneous microstructure. The SPS manufacturing process did not include any post treatment, which resulted in a heterogeneous microstructure. Energy-dispersive X-ray spectroscopy revealed the presence of intermetallic such as laves phases within the microstructure. Specifically, Ti-rich precipitates were observed in the MoNbTi specimen, while Mo-rich precipitates were found in the MoNbTiZrV specimen. Nano-hardness testing of pristine samples showed that the laves phases exhibited higher hardness values compared to the matrix phase, suggesting that precipitate hardening is likely the dominant hardening mechanism in these specimens. The results from this work will be used to build a finite element model to predict mechanical behavior of future MPEA compositions. Thus, enabling for a streamlined approach to developing novel MPEAs for the nuclear industry.

36 - MATERIALS SCIENCE↗
DOE OSTI2022

Effect of dose rate on the phase stability of a CrFeNiMn alloy

We report CrFeNi-based multi-principal element alloys (MPEAs) are being considered for nuclear applications because of their potentially superior mechanical properties and irradiation resistance. While the alloys appear stable against phase decomposition during ion irradiation performed at high dose rate, previous electron irradiation and thermal annealing studies suggested that some of them may be susceptible to phase decomposition. Therefore, to clarify the role of dose rate during ion irradiation on phase decomposition, a CrFeNiMn alloy was irradiated using Fe ions at 500 °C with an intermediate dose rate of 10 -4 dpa/s. Transmission electron microscopy and atom probe tomography observations revealed a high number density of NiMn precipitates, cavities, and dislocation loops, which had not previously been observed after ion irradiation at higher dose rates.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Microstructure and corrosion of CrFeMnV multi-principal element alloy

In this study, a multi-principal element alloy consisting of equiatomic concentrations of Cr, Fe, Mn, and V was produced by arc melting. The combination of X-ray diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy indicated that the CrFeMnV MPEA was comprised of a BCC matrix with a dispersion of a secondary phase. Cyclic potentiodynamic polarization tests in 0.6M NaCl revealed high corrosion resistance – superior to that of stainless steel 304L, as evident from high breakdown and repassivation potentials. X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry provided insight into the formed multi-layer surface film after constant immersion and potentiostatic conditioning.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Characterization data of an (AlFeNiTiVZr) 1-x Cr x multi-principal element alloy continuous composition spread library

The data provided in this article is related to the research article entitled “Phase stabilization and oxidation of a continuous composition spread multi-principal element (AlFeNiTiVZr) 1-x Cr x alloy”. This data article describes the high-throughput synthesis and characterization processes of an (AlFeNiTiVZr) 1-x Cr x alloy system. Continuous composition spread (CCS) thin-film libraries were synthesized by co-depositing an AlFeNiTiVZr metal alloy target and Cr target via magnetron sputtering. Post-processing was performed on the sample libraries with a vacuum anneal at 873 K and an air anneal at 873 K. Compositional data was determined via WDS in order to verify parameters provided by an in-house sputter model. Crystallographic data was captured via synchrotron diffraction and diffractograms were compared as a function of the change in Cr concentration. These measurements were taken in order to observe phase behavior after oxidation throughout the composition library. Furthermore, vibrational spectrographic data is provided of the oxidized library to show surface speciation along the composition gradient of the alloy system. The structural and oxidative behavior of the (AlFeNiTiVZr) 1-x Cr x alloy can be analysed using the data provided in this article. Additionally, this characterization dataset can be utilized in machine learning algorithms for determining important features and parameters for future hypothesis generation of functional multi-principal element alloys (MPEAs).

36 MATERIALS SCIENCE↗
DOE OSTI2025

Utilizing machine learning to predict tensile ductility and yield strength of CoNiV-based multi-principal elements alloys

This study explores the use of machine learning (ML) as a computational tool to accelerate the design of multi-principal element alloys (MPEAs) with improved tensile elongation. An ML model was trained using available experimental data from the literature along with theoretically derived features to predict yield strength (YS) and ductility. A subset of ML-predicted compositions—CoNiVFe, CoNiVTi, CoNiVTiFe, and CoCrNiVTi—was synthesized and evaluated through tensile testing. The ML model underpredicted YS by approximately 20–30 % and overpredicted ductility by 60–70 % for Ti-containing alloys. Microstructural analysis revealed that Ti segregation at interdendritic regions contributed to early fracture, leading to discrepancies in ductility predictions. Ti segregation at these regions likely drives the increased YS due to segregation strengthening. In contrast, the CoNiVFe alloy showed good agreement with both experimental YS and elongation, with prediction errors of ∼10.2 % and ∼20.7 %, respectively. Microstructural characterization revealed minimal segregation in this alloy, suggesting that the ML model can reliably predict the properties of alloys with little to no segregation. These findings highlight the capability of ML in predicting YS with good accuracy but underscore its limitations in capturing defect-driven failure mechanisms such as segregation-induced embrittlement.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Bayesian optimization with active learning of design constraints using an entropy-based approach

Abstract The design of alloys for use in gas turbine engine blades is a complex task that involves balancing multiple objectives and constraints. Candidate alloys must be ductile at room temperature and retain their yield strength at high temperatures, as well as possess low density, high thermal conductivity, narrow solidification range, high solidus temperature, and a small linear thermal expansion coefficient. Traditional Integrated Computational Materials Engineering (ICME) methods are not sufficient for exploring combinatorially-vast alloy design spaces, optimizing for multiple objectives, nor ensuring that multiple constraints are met. In this work, we propose an approach for solving a constrained multi-objective materials design problem over a large composition space, specifically focusing on the Mo-Nb-Ti-V-W system as a representative Multi-Principal Element Alloy (MPEA) for potential use in next-generation gas turbine blades. Our approach is able to learn and adapt to unknown constraints in the design space, making decisions about the best course of action at each stage of the process. As a result, we identify 21 Pareto-optimal alloys that satisfy all constraints. Our proposed framework is significantly more efficient and faster than a brute force approach.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Electrochemical corrosion of multiphase stainless steel-based alloy nuclear waste forms

Abstract The electrochemical corrosion behaviors of two multiphase alloys representing waste forms made with 316 L stainless steel and different amounts of surrogate metallic fuel wastes were measured and related to the microstructures. Potentiodynamic (PD) scans were performed in an acid brine solution and the corroded surfaces were characterized with scanning electron microscopy (SEM) to compare the electrochemical responses to the corrosion of specific phases. PD scans for the two multiphase alloys, 316 L stainless steel, and pure palladium were compared to understand the complex corrosion behavior of these multiphase alloys also recently classified as multi principle element alloys (MPEAs) and to determine the effects of alloying elements and noble metals present in constituent phases on the corrosion behavior.

Gattu, Vineeth Kumar (ORCID:0000000307265813)↗
DOE OSTI2024

Metal-to-Ceramic Joining Methods to Support Development of Advanced Ceramic-Based CSP Components

The National Renewable Energy Laboratory, Missouri University of Science and Technology (MS&T), Massachusetts Institute of Technology (MIT), and Colorado School of Mines (CSM) collaborated to design, develop, and test a material concept at bench scale which will be used to achieve a ceramic-to-metal (C2M) joint between a selected metal HTF loop material and a selected ceramic material used by the Gen3 CSP technology pathway. The final joint assembly will need to possess sufficient mechanical properties to withstand static high-temperature (650 degrees-700 degrees C) and high-pressure (20 MPa) and thermal cycling (between 650 degrees C and 100 degrees C) conditions. The material concept consists of three key components: (1) a ceramic matrix composite (CMC) that serves as a compliant transition material aiming to mitigate the stresses due to the mismatch of coefficient of thermal expansion (CTE) from a direct ceramic-to-metal joint, (2) a metal-end joint utilizing a multi-principal element alloy (MPEA) with changing percentage of particle loading to bond the candidate metal to the CMC, and (3) a ceramic-end joint utilizing a glass ceramic to bond the candidate ceramic to the CMC.

14 SOLAR ENERGY↗
NASA NTRS2020

Producing Next Generation Superalloys Through Advanced Characterization and Manufacturing Techniques

NASA is currently working towards developing the next generation high temperature alloys for various aerospace and energy applications. Through advanced microscopy and computational insights, a novel atomic scale strengthening mechanism was discovered in Ni-base superalloys. This new local phase transformation strengthening technique has been successfully implemented resulting in new disk alloys with substantial improvements in creep strength over current state-of-the-art. Furthermore, additive manufacturing has been leveraged to produce dispersion strengthened (DS), multi-principal element alloys (MPEA) without the use of traditional mechanical alloying or chemical reactions. This new processing technique has successfully resulted in 99.9% dense oxide dispersion strengthened NiCoCr alloy parts. High temperature mechanical testing of the DS alloys showed significant improvements in strength and ductility over the baseline NiCoCr. As a result, this recently discovered processing route opens a new alloy design and production path that is synergistic between additive manufacturing and dispersion strengthening, possibly enabling a new generation of high-performance alloys.

Smith, Timothy M.↗
NASA NTRS2020

Efficient production of a high-performance dispersion strengthened, multi-principal element alloy

Additive manufacturing currently facilitates new avenues for materials discovery that have not been fully explored. In this study we reveal how additive manufacturing can be leveraged to produce dispersion strengthened (DS), multi-principal element alloys (MPEA) without the use of traditional mechanical alloying or chemical reactions. This new processing technique employed resonant acoustic mixing to coat an equiatomic NiCoCr powder with nano-scale yttrium oxides. Then, through laser powder bed fusion (L-PBF), the coated powder was successfully consolidated into 99.9% dense parts. Microstructural analysis confirmed the successful incorporation and dispersion of nano-scale oxides throughout the build volume. Furthermore, high temperature mechanical testing of the DS alloys showed significant improvements in strength and ductility over the baseline NiCoCr. As a result, this recently discovered processing route opens a new alloy design and production path that is synergistic between additive manufacturing and dispersion strengthening, possibly enabling a new generation of high-performance alloys.

T.M. Smith↗
NASA NTRS2023

Superior Tensile Creep Behavior of A Novel Oxide Dispersion Strengthened Crconi Multi-Principal Element Alloy

The creep behavior of an additively manufactured (AM) yttrium oxide dispersion strengthened (ODS) CrCoNi multi-principal element alloy (MPEA) is investigated in this study. Tests were conducted over a constant tensile stress range of 40–200 MPa and a temperature range of 973–1173 K. A stress exponent of 6.5 ± 0.1 and activation energies in the range of 335–367 kJ/mol were measured. Compared to its non-ODS counterpart and its parent alloy (CrMnFeCoNi), AM ODS CrCoNi has superior creep resistance at all tested stresses and temperatures. The mechanism contributing to the excellent creep resistance of AM ODS CrCoNi is attributed to the interaction of mixed character dislocations with oxide particles. The creep ductility of AM ODS CrCoNi is higher than its nonODS counterpart due to a large percentage of low angle grain boundaries associated with its columnar grain structure. It was also found that creep ductility is significantly greater at the highest applied stress of 200 MPa compared to lower stresses. The steady state dislocation structure of AM ODS CrCoNi consists of long arrays of dislocations, which is different from that observed in non-ODS CrCoNi which consists of individual curved dislocations.

Seyed Gianmarco Sahragard-Monfared↗
DOE OSTI2024

Enhancing Mechanical Properties of a Medium-Entropy Alloy by Regulating Mo Addition

Some multi-principal element alloys (MPEAs), including equiatomic, single-phase CrCoNi and CrCoFeMnNi are now widely recognized for their remarkable combinations of pronounced hardening rates, high ductility, and exceptional fracture toughness at room and cryogenic temperatures. To push the limit of hardenability of the medium-entropy alloy, the strategies associated with local lattice distortion or stacking fault energy (SFE) reduction that promote complex heterogeneity and defect dynamics require further investigation. The purposes of this study are to (1) further enhance the mechanical properties of a typical medium-entropy NiCoCr with alloying Mo, and (2) understand the strengthening mechanism of a Mo-added medium-entropy alloys.

Hung, Chang-Yu↗
DOE OSTI2024

Theory-guided design of duplex-phase multi-principal-element alloys

Density-functional theory (DFT) is used to identify phase-equilibria in multi-principal-element and high-entropy alloys (MPEAs/HEAs), including duplex-phase and eutectic microstructures. Here, a combination of composition-dependent formation energy and electronic-structure-based ordering parameters were used to identify a transition from FCC to BCC favoring mixtures, and these predictions experimentally validated in the Al-Co-Cr-Cu-Fe-Ni system. A sharp crossover in lattice structure and dual-phase stability as a function of composition were predicted via DFT and validated experimentally. The impact of solidification kinetics and thermodynamic stability was explored experimentally using a range of techniques, from slow (castings) to rapid (laser remelting), which showed a decoupling of phase fraction from thermal history, i.e., phase fraction was found to be solidification rate-independent, enabling tuning of a multi-modal cell and grain size ranging from nanoscale through macroscale. Strength and ductility tradeoffs for select processing parameters were investigated via uniaxial tension and small-punch testing on specimens manufactured via powder-based additive manufacturing (directed-energy deposition). This work establishes a pathway for design and optimization of next-generation multiphase superalloys via tailoring of structural and chemical ordering in concentrated solid solutions.

36 MATERIALS SCIENCE↗
DOE OSTI2025

An energetic link between order and strength in metals: A nanocrystalline strength limit in high-entropy alloys and intermetallic compounds

The metallurgy and materials communities have long understood and exploited fundamental links between chemical and structural ordering in metallic solids to tailor their mechanical properties. We extend these ideas to include prediction of the nanocrystalline strength limit in high-entropy alloys and intermetallic compounds, where a breakdown occurs in the classical Hall-Petch strengthening behavior. The highest reported strength achievable through alloying has rapidly climbed and given rise to new classifications of materials with extraordinary properties, with a notable case being nanocrystalline metals. High-entropy alloys (chemically disordered, concentrated solid solutions) and intermetallic compounds are two boundary cases of how tailored order can be used to manipulate mechanical behavior. Here, we show that the complex electronic-structure mechanisms governing the peak strength of alloys and pure metals can be reduced to a few physically meaningful parameters based on their atomic arrangements and used – with no fitting parameters – to predict the maximum strength of these materials. This includes a generalized energy-based accounting for the degree of structural and chemical ordering that allows for rapid and reasonably accurate prediction of peak strength (validated in the nanocrystalline limit) as a function of temperature. Predictions of maximum strength based on the activation energy (with all materials properties derived from DFT calculations or experiments) for a stress-driven transition to an amorphous state is shown to accurately describe the breakdown in Hall-Petch behavior at the smallest crystallite sizes for pure metals, intermetallic compounds, high-entropy alloys, and metallic glasses. Further, this activation energy is also shown to be directly proportional to interstitial electronic charge density, which is a good predictor of ductility, stiffness (moduli), and phase stability in high-entropy alloys and solid metals generally. The proposed framework suggests the possibility of coupling ordering and intrinsic strength to mechanisms like dislocation nucleation, hydrogen embrittlement, and transport properties, such as through correlations between the activation energies for amorphization with stacking-fault and grain boundary energies. It additionally opens the prospect for greatly accelerated structural materials design and development to address materials challenges limiting more sustainable and efficient use of energy.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Selective depolymerization of polyolefin copolymer via high-entropy alloy catalyzed pyrolysis in a double-layered ultrafast heating reactor

Chemical recycling of polyolefin copolymers (PCPs) is essential for mitigating plastic pollution, yet achieving selective depolymerization into C 2 –C 3 monomers at high productivity remains challenging. Here, we introduce a double-layered ultrafast heating reactor (DUHR) that integrates Joule heating with a high-entropy alloy (HEA) catalyst composed of near-equimolar Co, Cu, Fe, Mn, and Ni. We achieve highly selective depolymerization of PCP into ethylene and propylene, yielding a 70% non-condensable fraction. Significant aromatic fractions form via radical-driven pathways—a behavior distinct from conventional externally heated pyrolyzers—highlighting DUHR's ability to generate reactive species and modulate reaction pathways. Furthermore, these findings demonstrate an effective strategy for chemical recycling of real-world plastic waste for polyolefin circularity and sustainable resource recovery.

Chemical recycling↗