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At least 631 records · Page 35
All sourcesNASA NTRSDOE OSTI
DOE OSTI2020

Materials Data on Ti3ZnHg4 by Materials Project

Ti3Hg4Zn is Tetraauricupride-derived structured and crystallizes in the tetragonal P4/mmm space group. The structure is three-dimensional. there are two inequivalent Ti sites. In the first Ti site, Ti is bonded in a distorted body-centered cubic geometry to eight Hg atoms. All Ti–Hg bond lengths are 2.95 Å. In the second Ti site, Ti is bonded in a distorted body-centered cubic geometry to eight equivalent Hg atoms. All Ti–Hg bond lengths are 2.96 Å. There are two inequivalent Hg sites. In the first Hg site, Hg is bonded in a distorted body-centered cubic geometry to four equivalent Ti and four equivalent Zn atoms. All Hg–Zn bond lengths are 2.94 Å. In the second Hg site, Hg is bonded in a distorted body-centered cubic geometry to eight Ti atoms. Zn is bonded in a distorted body-centered cubic geometry to eight equivalent Hg atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on ThZr2U2O10 by Materials Project

U2ThZr2O10 is alpha bismuth trifluoride-derived structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are two inequivalent U4+ sites. In the first U4+ site, U4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of U–O bond distances ranging from 2.33–2.35 Å. In the second U4+ site, U4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of U–O bond distances ranging from 2.33–2.43 Å. Th4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Th–O bond distances ranging from 2.36–2.51 Å. There are two inequivalent Zr4+ sites. In the first Zr4+ site, Zr4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Zr–O bond distances ranging from 2.13–2.29 Å. In the second Zr4+ site, Zr4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Zr–O bond distances ranging from 2.13–2.30 Å. There are ten inequivalent O2- sites. In the first O2- site, O2- is bonded to three equivalent U4+ and one Th4+ atom to form OThU3 tetrahedra that share corners with sixteen OThU3 tetrahedra and edges with six OTh3U tetrahedra. In the second O2- site, O2- is bonded to one U4+ and three equivalent Zr4+ atoms to form OZr3U tetrahedra that share corners with sixteen OZr3U tetrahedra and edges with six OZr4 tetrahedra. In the third O2- site, O2- is bonded to four U4+ atoms to form OU4 tetrahedra that share corners with sixteen OThU3 tetrahedra and edges with six OZrU3 tetrahedra. In the fourth O2- site, O2- is bonded to three equivalent Th4+ and one Zr4+ atom to form OTh3Zr tetrahedra that share corners with sixteen OThU3 tetrahedra and edges with six OTh3U tetrahedra. In the fifth O2- site, O2- is bonded to four Zr4+ atoms to form OZr4 tetrahedra that share corners with sixteen OZr3U tetrahedra and edges with six OZr4 tetrahedra. In the sixth O2- site, O2- is bonded to one U4+ and three equivalent Th4+ atoms to form OTh3U tetrahedra that share corners with sixteen OU4 tetrahedra and edges with six OTh3Zr tetrahedra. In the seventh O2- site, O2- is bonded to three equivalent U4+ and one Zr4+ atom to form OZrU3 tetrahedra that share corners with sixteen OU4 tetrahedra and edges with six OZr3U tetrahedra. In the eighth O2- site, O2- is bonded to four U4+ atoms to form OU4 tetrahedra that share corners with sixteen OThU3 tetrahedra and edges with six OU4 tetrahedra. In the ninth O2- site, O2- is bonded to one Th4+ and three equivalent Zr4+ atoms to form OThZr3 tetrahedra that share corners with sixteen OThU3 tetrahedra and edges with six OTh3Zr tetrahedra. In the tenth O2- site, O2- is bonded to four Zr4+ atoms to form a mixture of corner and edge-sharing OZr4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeHfO4 by Materials Project

CeHfO4 is alpha bismuth trifluoride-derived structured and crystallizes in the cubic P2_13 space group. The structure is three-dimensional. there are two inequivalent Ce4+ sites. In the first Ce4+ site, Ce4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Ce–O bond distances ranging from 2.29–2.37 Å. In the second Ce4+ site, Ce4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Ce–O bond distances ranging from 2.27–2.39 Å. There are two inequivalent Hf4+ sites. In the first Hf4+ site, Hf4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Hf–O bond distances ranging from 2.21–2.33 Å. In the second Hf4+ site, Hf4+ is bonded in a body-centered cubic geometry to eight O2- atoms. There are a spread of Hf–O bond distances ranging from 2.15–2.48 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded to two Ce4+ and two Hf4+ atoms to form a mixture of edge and corner-sharing OCe2Hf2 tetrahedra. In the second O2- site, O2- is bonded to two Ce4+ and two Hf4+ atoms to form a mixture of edge and corner-sharing OCe2Hf2 tetrahedra. In the third O2- site, O2- is bonded to two equivalent Ce4+ and two equivalent Hf4+ atoms to form a mixture of edge and corner-sharing OCe2Hf2 tetrahedra. In the fourth O2- site, O2- is bonded to four Hf4+ atoms to form a mixture of distorted edge and corner-sharing OHf4 tetrahedra. In the fifth O2- site, O2- is bonded to four Ce4+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra. In the sixth O2- site, O2- is bonded to two equivalent Ce4+ and two equivalent Hf4+ atoms to form a mixture of edge and corner-sharing OCe2Hf2 tetrahedra. In the seventh O2- site, O2- is bonded to four Hf4+ atoms to form a mixture of edge and corner-sharing OHf4 tetrahedra. In the eighth O2- site, O2- is bonded to four Ce4+ atoms to form a mixture of edge and corner-sharing OCe4 tetrahedra.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrFeCoSi by Materials Project

CoFeCrSi is Tungsten-derived structured and crystallizes in the cubic F-43m space group. The structure is three-dimensional. Cr is bonded in a distorted body-centered cubic geometry to four equivalent Fe, four equivalent Co, and six equivalent Si atoms. All Cr–Fe bond lengths are 2.43 Å. All Cr–Co bond lengths are 2.43 Å. All Cr–Si bond lengths are 2.80 Å. Fe is bonded in a distorted body-centered cubic geometry to four equivalent Cr and four equivalent Si atoms. All Fe–Si bond lengths are 2.43 Å. Co is bonded in a distorted body-centered cubic geometry to four equivalent Cr and four equivalent Si atoms. All Co–Si bond lengths are 2.43 Å. Si is bonded in a distorted body-centered cubic geometry to six equivalent Cr, four equivalent Fe, and four equivalent Co atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Fe3Ni3Ge2 by Materials Project

Fe3Ni3Ge2 is Tungsten-derived structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are three inequivalent Fe sites. In the first Fe site, Fe is bonded in a distorted body-centered cubic geometry to seven Ni and four Ge atoms. There are four shorter (2.47 Å) and three longer (2.86 Å) Fe–Ni bond lengths. All Fe–Ge bond lengths are 2.48 Å. In the second Fe site, Fe is bonded in a distorted body-centered cubic geometry to seven Ni and four Ge atoms. There are a spread of Fe–Ni bond distances ranging from 2.48–2.86 Å. There are one shorter (2.47 Å) and three longer (2.48 Å) Fe–Ge bond lengths. In the third Fe site, Fe is bonded in a body-centered cubic geometry to four Ni and four Ge atoms. There are three shorter (2.48 Å) and one longer (2.51 Å) Fe–Ni bond lengths. There are one shorter (2.47 Å) and three longer (2.49 Å) Fe–Ge bond lengths. There are three inequivalent Ni sites. In the first Ni site, Ni is bonded in a 8-coordinate geometry to six Fe, four Ni, and four Ge atoms. There are one shorter (2.46 Å) and three longer (2.48 Å) Ni–Ni bond lengths. There are three shorter (2.48 Å) and one longer (2.49 Å) Ni–Ge bond lengths. In the second Ni site, Ni is bonded in a 8-coordinate geometry to seven Fe, one Ni, and six Ge atoms. There are three shorter (2.86 Å) and three longer (2.87 Å) Ni–Ge bond lengths. In the third Ni site, Ni is bonded in a 8-coordinate geometry to five Fe, three equivalent Ni, and six Ge atoms. There are three shorter (2.85 Å) and three longer (2.87 Å) Ni–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a distorted body-centered cubic geometry to five Fe and nine Ni atoms. In the second Ge site, Ge is bonded in a distorted body-centered cubic geometry to seven Fe and seven Ni atoms.

36 MATERIALS SCIENCE↗
NASA NTRS1987

Quantitative analysis of the reconstruction performance of interpolants

The analysis presented provides a quantitative measure of the reconstruction or interpolation performance of linear, shift-invariant interpolants. The performance criterion is the mean square error of the difference between the sampled and reconstructed functions. The analysis is applicable to reconstruction algorithms used in image processing and to many types of splines used in numerical analysis and computer graphics. When formulated in the frequency domain, the mean square error clearly separates the contribution of the interpolation method from the contribution of the sampled data. The equations provide a rational basis for selecting an optimal interpolant; that is, one which minimizes the mean square error. The analysis has been applied to a selection of frequently used data splines and reconstruction algorithms: parametric cubic and quintic Hermite splines, exponential and nu splines (including the special case of the cubic spline), parametric cubic convolution, Keys' fourth-order cubic, and a cubic with a discontinuous first derivative. The emphasis in this paper is on the image-dependent case in which no a priori knowledge of the frequency spectrum of the sampled function is assumed.

Lansing, Donald L.↗
NASA NTRS1986

Efficient inverse solution of Kepler's equation

A bicubic polynomial approximation to Kepler's equation for elliptic orbits is shown to provide accurate starting values for efficient numerical solution of this equation for eccentric anomaly. In the approximate equation, a cubic in mean anomaly is set equal to a cubic in eccentric anomaly. The coefficients in the two cubics are obtained as functions of eccentricity by specifying values of function and slope at the midpoint and the endpoint of the complete interval (0 to pi). The initial estimate of eccentric anomaly to use in an iteration formula is obtained by evaluating the cubic in mean anomaly and finding the single real root of the cubic in eccentric anomaly. Numerical results are presented which indicate that the estimate accuracy of this method is roughly an order of magnitude better than that of other recently-reported formulas.

Boltz, Frederick W.↗
NASA NTRS2002

Cloud Condensation Nuclei Measurements in Tropical Cyclones

The first measurements of cloud condensation nuclei (CCN) within and around tropical cyclones were made with the Desert Research Institute (DRI) CCN spectrometer (Hudson 1909) from a NOAA P-3 Hurricane Hunter aircraft throughout the 2001 season. Two penetrations of the closed eye of Hurricane Erin off the northeast US coast on Sept. 10 showed concentrations consistently well in excess of 1000 per cubic cm at approximately 1.4% supersaturation. Simultaneous condensation nuclei (CN--total particle) concentrations were consistently well in excess of 2000 per cubic cm throughout these closed eye penetrations. These within eye measurements at 4 km altitude for exceeded CCN and CN measurements just outside of the storm at similar altitudes--300 and 600 per cubic cm respectively. These CCN and CN concentrations within this closed eye were far above concentrations in maritime air masses; they are characteristic of continental or polluted air masses. Although there was a possibility that Saharan duct may have gotten into this storm these sub tenth micrometer particles are much too small and much too numerous to be dust. Such high concentrations may have originated from European air pollution, which may have been transported by similar airflow patterns to those that carry Saharan dust across the Atlantic. These high concentrations may be a manifestation of descending air that brings higher concentrations that are often characteristic of the upper troposphere (Clarke and Kapustin 2002). Later in the month measurements in Humberto showed highly variable CCN and CN concentrations that ranged from lots than 5 per cubic cm to more than 1000 per Cubic cm over km scale distances within and around the open eye of this tropical storm/hurricane. These very low concentrations suggest strong cloud scavenging.

Hudson, J. G.↗
NASA NTRS2005

Neutron Diffraction Study Oxygen Dissolution Alpha(sub 2)-Ti3Al

Rietveld refinements of neutron powder diffraction data on alpha(sub 2)-Ti3Al have been performed to determine the crystal structure as a function of interstitial oxygen (O) concentration for three alloys with a Ti/Al ratio of approximately equal to 2.34 and O concentrations of 0.25%, 3.99% and 7.71%. The structures of the allows are hexagonal in space group P6(sub 3)/mmc where Ti and Al atoms populate unique sites with excess Al at the Ti site and O atoms occupy octahedral interstitial sites surrounded by six Ti sites. The length of the c-axis was found to increase linearly as the O occupancy of the interstitial sites increased; this lattice lengthening effect was much less pronounced along the alpha axis. Correspondingly, the increases in the lengths of Ti-Al and Ti-Ti bonds with a major component of their direction parallel to the c-axis were roughly an order of magnitude greater than the increases in the lengths of Ti-al and Ti-Ti bonds more closely aligned with the alpha-axis. Densities calculated form the lattice parameters and occupancy factors fall in the range (4.118 plus or minus 0.004) grams per cubic centimeter to (4.194 plus or minus 0.004) grams per cubic centimeter, and exhibit a nearly linear increase with oxygen concentration. Measured densities of (4.113 plus or minus 0.001) grams per cubic centimeter, (4.146 plus or minus 0.009) grams per cubic centimeter, and (4.191 plus or minus 0.002) grams per cubic centimeter for these alloys agree with the results of the refinements.

Jones, Camille Y.↗
NASA NTRS2009

Lattice-Matched Semiconductor Layers on Single Crystalline Sapphire Substrate

SiGe is an important semiconductor alloy for high-speed field effect transistors (FETs), high-temperature thermoelectric devices, photovoltaic solar cells, and photon detectors. The growth of SiGe layer is difficult because SiGe alloys have different lattice constants from those of the common Si wafers, which leads to a high density of defects, including dislocations, micro-twins, cracks, and delaminations. This innovation utilizes newly developed rhombohedral epitaxy of cubic semiconductors on trigonal substrates in order to solve the lattice mismatch problem of SiGe by using trigonal single crystals like sapphire (Al2O3) as substrate to give a unique growth-orientation to the SiGe layer, which is automatically controlled at the interface upon sapphire (0001). This technology is different from previous silicon on insulator (SOI) or SGOI (SiGe on insulator) technologies that use amorphous SiO2 as the growth plane. A cubic semiconductor crystal is a special case of a rhombohedron with the inter-planar angle, alpha = 90 deg. With a mathematical transformation, all rhombohedrons can be described by trigonal crystal lattice structures. Therefore, all cubic lattice constants and crystal planes (hkl) s can be transformed into those of trigonal crystal parameters. These unique alignments enable a new opportunity of perfect lattice matching conditions, which can eliminate misfit dislocations. Previously, these atomic alignments were thought to be impossible or very difficult. With the invention of a new x-ray diffraction measurement method here, growth of cubic semiconductors on trigonal crystals became possible. This epitaxy and lattice-matching condition can be applied not only to SiGe (111)/sapphire (0001) substrate relations, but also to other crystal structures and other materials, including similar crystal structures which have pointgroup rotational symmetries by 120 because the cubic (111) direction has 120 rotational symmetry. The use of slightly miscut (less than plus or minus 10 deg.) sapphire (0001) substrate can be used to improve epitaxial relationships better by providing attractive atomic steps in the epitaxial process.

Choi, Sang↗
DOE OSTI2024

Advanced EXAFS analysis techniques applied to the L -edges of the lanthanide oxides

The unique properties of the lanthanide (Ln) elements make them critical components of modern technologies, such as lasers, anti-corrosive films and catalysts. Thus, there is significant interest in establishing structure–property relationships for Ln-containing materials to advance these technologies. Extended X-ray absorption fine structure (EXAFS) is an excellent technique for this task considering its ability to determine the average local structure around the Ln atoms for both crystalline and amorphous materials. However, the limited availability of EXAFS reference spectra of the Ln oxides and challenges in the EXAFS analysis have hindered the application of this technique to these elements. The challenges include the limited k-range available for the analysis due to the superposition of L-edges on the EXAFS, multielectron excitations (MEEs) creating erroneous peaks in the EXAFS and the presence of inequivalent absorption sites. Herein, we removed MEEs to model the local atomic environment more accurately for light Ln oxides. Further, we investigated the use of cubic and non-cubic lattice expansion to minimize the fitting parameters needed and connect the fitting parameters to physically meaningful crystal parameters. The cubic expansion reduced the number of fitting parameters but resulted in a statistically worse fit. The non-cubic expansion resulted in a similar quality fit and showed non-isotropic expansion in the crystal lattice of Nd 2 O 3 . In total, the EXAFS spectra and the fits for the entire set of Ln oxides (excluding promethium) are included. The knowledge developed here can assist in the structural determination of a wide variety of Ln compounds and can further studies on their structure–property relationships.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Observations of phase changes in monoolein during high viscous injection

Serial crystallography of membrane proteins often employs high-viscosity injectors (HVIs) to deliver micrometre-sized crystals to the X-ray beam. Typically, the carrier medium is a lipidic cubic phase (LCP) media, which can also be used to nucleate and grow the crystals. However, despite the fact that the LCP is widely used with HVIs, the potential impact of the injection process on the LCP structure has not been reported and hence is not yet well understood. The self-assembled structure of the LCP can be affected by pressure, dehydration and temperature changes, all of which occur during continuous flow injection. These changes to the LCP structure may in turn impact the results of X-ray diffraction measurements from membrane protein crystals. To investigate the influence of HVIs on the structure of the LCP we conducted a study of the phase changes in monoolein/water and monoolein/buffer mixtures during continuous flow injection, at both atmospheric pressure and under vacuum. The reservoir pressure in the HVI was tracked to determine if there is any correlation with the phase behaviour of the LCP. The results indicated that, even though the reservoir pressure underwent (at times) significant variation, this did not appear to correlate with observed phase changes in the sample stream or correspond to shifts in the LCP lattice parameter. During vacuum injection, there was a three-way coexistence of the gyroid cubic phase, diamond cubic phase and lamellar phase. During injection at atmospheric pressure, the coexistence of a cubic phase and lamellar phase in the monoolein/water mixtures was also observed. The degree to which the lamellar phase is formed was found to be strongly dependent on the co-flowing gas conditions used to stabilize the LCP stream. A combination of laboratory-based optical polarization microscopy and simulation studies was used to investigate these observations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2023

Structural Explanation of the Dielectric Enhancement of Barium Titanate Nanoparticles Grown under Hydrothermal Conditions

Abstract When synthesized under certain conditions, barium titanate (BaTiO 3 , BTO) nanoparticles are found to have the non‐thermodynamic cubic structure at room temperature. These particles also have a several‐fold enhanced dielectric constant, sometimes exceeding 6000, and are widely used in thin‐layer capacitors. A hydrothermal approach is used to synthesize BTO nanocrystals, which are characterized by a range of methods, including X‐ray Rietveld refinement and the Williamson–Hall approach, revealing the presence of significant inhomogeneous strain associated with the cubic phase. However, X‐ray pair distribution function measurements clearly show the local structure is lower symmetry than cubic. This apparent inconsistency is resolved by examining 3D Bragg coherent diffraction images of selected nanocrystals, which show the existence of ≈50 nm‐sized domains, which are interpreted as tetragonal twins, and yet cause the average crystalline structure to appear cubic. The ability of these twin boundaries to migrate under the influence of electric fields explains the dielectric anomaly for the nanocrystalline phase.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Flux Synthesis of A-site Disordered Perovskite La 0.5 M 0.5 TiO 3 (M$=$Li, Na, K) Nanorods Tailored for Solid Composite Electrolytes

Inorganic fillers play an important role in improving the ionic conductivity of solid composite electrolytes (SCEs) for Li-ion batteries. Among inorganic fillers, perovskite-type lithium lanthanum titanate (LLTO) stands out for its high bulk Li + conductivity on the order of 10 -3 S cm -1 at room temperature. According to a literature survey, the optimal LLTO filler should possess the following characteristics: i) a single-crystal structure to minimize grain boundaries; ii) a small particle size to increase the filler/polymer interface area; iii) a 1D morphology for efficient interface channels; and iv) cubic symmetry to facilitate rapid bulk Li + diffusion within the filler. However, the synthesis of single crystal, 1D LLTO nanomaterials with cubic symmetry is challenging. Herein, a flux strategy is developed to synthesize La 0.5 M 0.5 TiO 3 (LMTO, M$=$Li, Na, and K) single-crystal nanorods with an A-site-disordered, cubic perovskite phase. The flux media promotes the oriented growth of nanorods, prevents nanorods from sintering, and provides multiple alkali metal ion doping at M sites to stabilize the cubic phase. SCEs compositing the Li + -conducting LMTO nanorods as fillers and poly[vinylene carbonate- co -lithium sulfonyl(trifluoromethane sulfonyl)imide methacrylate] matrix exhibit more than twice the conductivity of the neat polymer electrolyte (30.6 vs 14.0 µS cm -1 at 303 K).

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Thermoelectric performance in disordered Cu 2 ZnSnSe 4 nanostructures driven by ultra-low thermal conductivity

Here, high-energy reactive mechanical alloying (ball milling) was used to synthesize tetragonal and cubic polymorphs of Cu 2 ZnSnSe 4 . The ordered tetragonal (I-4) polymorph undergoes a phase transition above 400 K into a Cu-Zn disordered tetragonal (I-42 m) polymorph, while the cubic (F-43 m) polymorph with full cation disorder is stabilized at room temperature. Both polymorphs show ultra-low thermal conductivities, 0.42 W m -1 K -1 at 722 K and 0.21 W m -1 K -1 at 523 K for the disordered tetragonal and cubic phases respectively. The cubic polymorph has a higher zT in the low-temperature range, peaking at 0.26 (523 K), while the disordered tetragonal has a maximum zT of 0.46 at 712 K. The latter is the highest reported zT for stoichiometric Cu 2 ZnSnSe 4 , comparable to the best-performing doped materials in the literature. A combination of experimental results and ab-initio calculations point to a coupling between structural disorder and microstructure as the mechanism behind the reported performance.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Structure Sensitive Reaction Kinetics of Chiral Molecules on Intrinsically Chiral Surfaces

Enantiospecific heterogeneous catalysis utilizes chiral surfaces to resolve enantiomers via structure sensitive surface chemistry. The catalyst design challenge is the identification of chiral surface structures that maximize enantiospecificity. Herein, we develop data driven models for the enantiospecificity of tartaric acid reactions on chiral Cu(hkl) R&S surfaces. Measurements of enantiospecific rate constants were obtained by using curved Cu(hkl) R&S surfaces that enable kinetic measurements on hundreds of chiral surface orientations. One model uses feature vectors derived from generalized coordination numbers to capture the local structure around Cu atoms exposed by the Cu(hkl) R&S surfaces. The second model introduces the use of chiral cubic harmonic functions to capture the symmetry constraints of the face-centered cubic Cu structure. The model using 58 generalized coordination numbers has a fitting error similar to that of the model using only 5 cubic harmonic functions. The two models predict maxima in the enantiospecificity on surfaces with very similar surface orientations. The models developed in this work are applicable for any enantiospecific reaction happening on any chiral material with a cubic lattice structure, opening the way to understanding the surface structure sensitivity of the enantiospecific reaction kinetics.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Strong yet ductile nanolamellar high-entropy alloys by additive manufacturing

Additive manufacturing produces net-shaped components layer by layer for engineering applications. The additive manufacture of metal alloys by laser powder bed fusion (L-PBF) involves large temperature gradients and rapid cooling, which enables microstructural refinement at the nanoscale to achieve high strength. However, high-strength nanostructured alloys produced by laser additive manufacturing often have limited ductility. In this work, we use L-PBF to print dual-phase nanolamellar high-entropy alloys (HEAs) of AlCoCrFeNi 2.1 that exhibit a combination of a high yield strength of about 1.3 gigapascals and a large uniform elongation of about 14 percent, which surpasses those of other state-of-the-art additively manufactured metal alloys. The high yield strength stems from the strong strengthening effects of the dual-phase structures that consist of alternating face-centred cubic and body-centred cubic nanolamellae; the body-centred cubic nanolamellae exhibit higher strengths and higher hardening rates than the face-centred cubic nanolamellae. The large tensile ductility arises owing to the high work-hardening capability of the as-printed hierarchical microstructures in the form of dual-phase nanolamellae embedded in microscale eutectic colonies, which have nearly random orientations to promote isotropic mechanical properties. The mechanistic insights into the deformation behaviour of additively manufactured HEAs have broad implications for the development of hierarchical, dual- and multi-phase, nanostructured alloys with exceptional mechanical properties.

36 MATERIALS SCIENCE↗