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At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Tailoring Cu-Zr gradient nanoglass structures: Influence of nanoparticle size and cooling rates on glass-glass interfaces

The study of gradient nanoglasses (GNGs) has gained attention due to their unique mechanical properties and potential applications in advanced materials. This study employs molecular dynamics simulations to synthesize a GNG using Cu-Zr metallic glass nanoparticles (NPs) sized from 3 to 15 nm. The NPs were produced by melting and quenching metallic clusters at a relatively slow quench rate of 10 9 K/s. The synthesis of GNG is elucidated along with the characterization of its heterogeneous metallic glass nanostructure. A seamless GNG structure is formed through cold compression of Cu 64 Zr 36 amorphous NPs of varying sizes. The influence of NP size on the GNG structure is investigated, utilizing deeply relaxed NPs, which exhibit a characteristic Cu segregation pattern on their surfaces. The results highlight an increase in structural heterogeneity due to heterogeneous mass transport and the development of local composition and density variations caused by Cu segregation at glass-glass interfaces (GGIs). A reduction in NP size is correlated with decreased Cu atomic displacements and local density at GGIs, suggesting that larger NPs may produce stronger GGIs. This research presents a novel methodology for synthesizing heterogeneous metallic glasses, demonstrating the capacity to control and customize nanostructure heterogeneity through the manipulation of NP sizes and cooling rates. Furthermore, these findings enhance our understanding of structural evolution during nanoglass synthesis and lay the foundation for further exploration in nanomaterial synthesis and characterization.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Amorphous complexions alter the tensile failure of nanocrystalline Cu-Zr alloys

Grain boundary-based mechanisms are known to control the plastic deformation and failure of nanocrystalline metals, with manipulation of the boundary structure a promising path for tuning this response. In this study, the role of interfacial structural disorder on plasticity and failure of nanocrystalline Cu-Zr alloys is investigated with in situ scanning electron microscopy tensile deformation experiments. Two model materials are created, one with only the typical ordered grain boundaries and another with amorphous intergranular films interspersed into the boundary network, while the microstructures are otherwise identical. Hence, the importance of complexion type on plasticity and failure is isolated by only varying complexion structure. Here, the tensile experiments show that failure of the samples containing amorphous films is significantly retarded, as evidenced by an increase in the cross-sectional area reduction, a decrease in the occurrence of shear-dominated failure, a decrease in strain localization, and fracture surfaces with more elongated dimple features. As a whole, this study provides direct evidence that structural disorder at the grain boundaries can be beneficial for improving the ductility of nanocrystalline metals.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Amorphous complexion-aided sintering enables scalable processing of bulk nanocrystalline Cu-Zr with high strength and compressive plasticity

Nanocrystalline alloys can have exceptional strengths, yet due to limited microstructural stability it is difficult to fabricate bulk pieces through traditional processing routes that retain nanosized grains. In this study, centimeter-sized Cu-Zr alloy pellets were fabricated via a simple and improved powder metallurgy processing route. Different consolidation temperatures and times were employed to investigate the effect of amorphous grain boundary complexions on densification and the resulting mechanical properties. Bulk compression tests were carried out, with the samples that were hot pressed at 900 °C for 10 h exhibiting an excellent combination of average yield strength of 722 ± 45 MPa and average failure strain of 25.3 ± 2.4 %. Furthermore, we find that a powder processing route which enables amorphous complexion-assisted sintering leads to samples that (1) reach full density without requiring quenching treatments or other complex processing, (2) demonstrate appreciable plasticity, and (3) have strength that competes with commercially available high-strength Cu alloys.

Bulk nanocrystalline alloy↗
DOE OSTI2021

Critical cooling rates for amorphous-to-ordered complexion transitions in Cu-rich nanocrystalline alloys

Amorphous complexions in nanocrystalline metals have the potential to improve mechanical properties and radiation tolerance, as well as resistance to grain growth. In this study, the stability of amorphous complexions in binary and ternary Cu-based alloys is investigated by observing the effect of cooling rate from high temperature on the occurrence of amorphous-to-ordered complexion transitions. Bulk Cu-Zr and Cu-Zr-Hf alloy samples were annealed to induce boundary premelting and then quenched through a procedure that induces a gradient of local cooling rate through the sample height. Amorphous complexion thickness distributions were found to be invariant to local cooling rate in the Cu-Zr-Hf alloy, demonstrating enhanced stability of the amorphous complexion structure compared to the Cu-Zr alloy, which had thinner amorphous complexions in the regions that were slowly cooled. The experimental results are used to construct time-temperature-transformation diagrams for the amorphous-to-ordered complexion transition in both the binary and ternary alloys, enabling a deeper understanding of the influence of cooling rate and grain boundary chemistry on complexion transitions. In conclusion, the critical cooling rate necessary to avoid complexion transitions in the ternary alloy is found to be at least three orders of magnitude slower than that for the binary alloy.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Enhanced Radiation Damage Tolerance of Amorphous Interphase and Grain Boundary Complexions in Cu-Ta

Amorphous interfacial complexions are particularly resistant to radiation damage and have been primarily studied in alloys with good glass-forming ability, yet recent reports suggest that these features can form even in immiscible alloys such as Cu-Ta under irradiation. In this work, the mechanisms of damage production and annihilation due to primary knock-on atom collisions are investigated for amorphous interphase and grain boundaries in a Cu-Ta alloy using atomistic simulations. Amorphous complexions, in particular amorphous interphase complexions that separate Cu and Ta grains, result in less residual defect damage than their ordered counterparts. Stemming from the nanophase chemical separation in this alloy, the amorphous complexions exhibit a highly heterogeneous distribution of atomic excess volume, as compared to a good glass former like Cu-Zr. Complexion thickness, a tunable structural descriptor, plays a vital role in damage resistance. Thicker interfacial films are more damage-tolerant because they alter the defect production rate due to differences in intrinsic displacement threshold energies during the collision cascade. Overall, the findings of this work highlight the importance of interfacial engineering in enhancing the properties of materials operating in radiation-prone environments and the promise of amorphous complexions as particularly radiation damage-tolerant microstructural features.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Segregation competition and complexion coexistence within a polycrystalline grain boundary network

Interfacial segregation can stabilize grain structures and even lead to grain boundary complexion transitions. However, understanding of the complexity of such phenomena in polycrystalline materials is limited, as most studies focus on bicrystal geometries. In this work, we investigate interfacial segregation and subsequent complexion transitions in polycrystalline Cu-Zr alloys using hybrid Monte Carlo/molecular dynamics simulations. No significant change in the grain size or structure is observed upon Zr dopant addition to a pure Cu polycrystal at moderate temperature, where grain boundary segregation is the dominant behavior. Segregation within the boundary network is inhomogeneous, with some boundaries having local concentrations that are an order of magnitude larger than the global value and others having almost no segregation, and changes to physical parameters such as boundary free volume and energy are found to correlate with dopant concentration. Further, another alloy sample is investigated at a higher temperature to probe the occurrence of widespread transitions in interfacial structure, where a significant fraction of the originally ordered boundaries transition to amorphous complexions, demonstrating the coexistence of multiple complexion types, each with their own distribution of boundary chemical composition. Overall, this work highlights that interfacial segregation and complexion structure can be diverse in a polycrystalline network. Here, the findings shown here complement existing computational and experimental studies of individual interfaces and help pave the way for unraveling the complexity of interfacial structure in realistic microstructures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Grain incompatibility determines the local structure of amorphous grain boundary complexions

Amorphous grain boundary complexions lack long-range crystalline order but are not featureless, as distinct gradients in structural short-range order have been reported through their thickness. In this work, we test the hypothesis that the distribution of short-range order is determined by the confining crystals using atomistic simulations of both Cu-Zr bicrystals and a random polycrystal. Voronoi polyhedra with structures similar to that of perfect face-centered cubic serve as signatures of high structural order and are only found at the amorphous-crystalline transition regions. The density of the ordered structural motifs within a specific amorphous-crystalline transition region is found to not be directly determined by the orientation and symmetry of the grain which touches it, but rather by the incompatibility between the two confining grains. Further, ordered polyhedra density is found to be inversely related to grain incompatibility, meaning that large incompatibilities between the confining crystals lead to less order in the amorphous-crystalline transition region. The finding that the entire grain-film-grain system must be considered to understand local structure unequivocally demonstrates that amorphous complexions are not simply a collection of independent phases which happen to nucleate at a grain boundary. Rather, an amorphous grain boundary complexion is a single entity that finds a local equilibrium configuration.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Predicting the propensity for thermally activated β events in metallic glasses via interpretable machine learning

Abstract The elementary excitations in metallic glasses (MGs), i.e., β processes that involve hopping between nearby sub-basins, underlie many unusual properties of the amorphous alloys. A high-efficacy prediction of the propensity for those activated processes from solely the atomic positions, however, has remained a daunting challenge. Recently, employing well-designed site environment descriptors and machine learning (ML), notable progress has been made in predicting the propensity for stress-activated β processes (i.e., shear transformations) from the static structure. However, the complex tensorial stress field and direction-dependent activation could induce non-trivial noises in the data, limiting the accuracy of the structure-property mapping learned. Here, we focus on the thermally activated elementary excitations and generate high-quality data in several Cu-Zr MGs, allowing quantitative mapping of the potential energy landscape. After fingerprinting the atomic environment with short- and medium-range interstice distribution, ML can identify the atoms with strong resistance or high compliance to thermal activation, at a high accuracy over ML models for stress-driven activation events. Interestingly, a quantitative “between-task” transferring test reveals that our learnt model can also generalize to predict the propensity of shear transformation. Our dataset is potentially useful for benchmarking future ML models on structure-property relationships in MGs.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr2Cu by Materials Project

Zr2Cu crystallizes in the tetragonal I4/mmm space group. The structure is two-dimensional and consists of two Zr2Cu sheets oriented in the (0, 0, 1) direction. Zr is bonded in a 4-coordinate geometry to four equivalent Cu atoms. All Zr–Cu bond lengths are 2.87 Å. Cu is bonded in a body-centered cubic geometry to eight equivalent Zr atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrCu by Materials Project

CuZr is Tetraauricupride structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Zr is bonded in a body-centered cubic geometry to eight equivalent Cu atoms. All Zr–Cu bond lengths are 2.83 Å. Cu is bonded in a body-centered cubic geometry to eight equivalent Zr atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrCu5 by Materials Project

Cu5Zr crystallizes in the cubic F-43m space group. The structure is three-dimensional. Zr is bonded in a 12-coordinate geometry to sixteen Cu atoms. There are twelve shorter (2.84 Å) and four longer (2.96 Å) Zr–Cu bond lengths. There are two inequivalent Cu sites. In the first Cu site, Cu is bonded in a 4-coordinate geometry to four equivalent Zr and twelve equivalent Cu atoms. All Cu–Cu bond lengths are 2.83 Å. In the second Cu site, Cu is bonded to three equivalent Zr and nine Cu atoms to form a mixture of distorted face, edge, and corner-sharing CuZr3Cu9 cuboctahedra. There are three shorter (2.41 Å) and three longer (2.43 Å) Cu–Cu bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr2Cu by Materials Project

Zr2Cu crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. there are two inequivalent Zr sites. In the first Zr site, Zr is bonded in a 2-coordinate geometry to four equivalent Cu atoms. There are two shorter (2.90 Å) and two longer (3.20 Å) Zr–Cu bond lengths. In the second Zr site, Zr is bonded in a 6-coordinate geometry to six equivalent Cu atoms. All Zr–Cu bond lengths are 2.67 Å. Cu is bonded in a 12-coordinate geometry to nine Zr and three equivalent Cu atoms. All Cu–Cu bond lengths are 2.92 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr3Cu by Materials Project

Zr3Cu is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Zr is bonded to eight equivalent Zr and four equivalent Cu atoms to form distorted ZrZr8Cu4 cuboctahedra that share corners with twelve equivalent ZrZr8Cu4 cuboctahedra, edges with eight equivalent CuZr12 cuboctahedra, edges with sixteen equivalent ZrZr8Cu4 cuboctahedra, faces with four equivalent CuZr12 cuboctahedra, and faces with fourteen equivalent ZrZr8Cu4 cuboctahedra. All Zr–Zr bond lengths are 3.05 Å. All Zr–Cu bond lengths are 3.05 Å. Cu is bonded to twelve equivalent Zr atoms to form CuZr12 cuboctahedra that share corners with twelve equivalent CuZr12 cuboctahedra, edges with twenty-four equivalent ZrZr8Cu4 cuboctahedra, faces with six equivalent CuZr12 cuboctahedra, and faces with twelve equivalent ZrZr8Cu4 cuboctahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrCu3 by Materials Project

ZrCu3 crystallizes in the hexagonal P6_3/mmc space group. The structure is three-dimensional. Zr is bonded to twelve equivalent Cu atoms to form a mixture of face and corner-sharing ZrCu12 cuboctahedra. There are six shorter (2.77 Å) and six longer (2.83 Å) Zr–Cu bond lengths. Cu is bonded in a 12-coordinate geometry to four equivalent Zr and eight equivalent Cu atoms. There are a spread of Cu–Cu bond distances ranging from 2.57–3.09 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrCu2 by Materials Project

Cu2Zr crystallizes in the orthorhombic Cmcm space group. The structure is three-dimensional. Zr is bonded in a distorted q6 geometry to ten equivalent Cu atoms. There are a spread of Zr–Cu bond distances ranging from 2.73–2.88 Å. Cu is bonded in a 12-coordinate geometry to five equivalent Zr and four equivalent Cu atoms. There are two shorter (2.62 Å) and two longer (2.63 Å) Cu–Cu bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zr2Cu by Materials Project

Zr2Cu crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. there are two inequivalent Zr sites. In the first Zr site, Zr is bonded in a 5-coordinate geometry to five equivalent Cu atoms. There are a spread of Zr–Cu bond distances ranging from 2.78–3.12 Å. In the second Zr site, Zr is bonded in a 12-coordinate geometry to three equivalent Cu atoms. There are two shorter (2.70 Å) and one longer (3.08 Å) Zr–Cu bond lengths. Cu is bonded in a 9-coordinate geometry to eight Zr and one Cu atom. The Cu–Cu bond length is 2.50 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ZrCu by Materials Project

CuZr is delta Molybdenum Boride-like structured and crystallizes in the monoclinic P2_1/m space group. The structure is three-dimensional. Zr is bonded in a 7-coordinate geometry to seven equivalent Cu atoms. There are a spread of Zr–Cu bond distances ranging from 2.76–2.95 Å. Cu is bonded in a 9-coordinate geometry to seven equivalent Zr and two equivalent Cu atoms. Both Cu–Cu bond lengths are 2.53 Å.

36 MATERIALS SCIENCE↗