Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “antiphase boundaries”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

The Effect of Antiphase Boundary Tubes on the Hardness of FeAl

The high work hardening rate unique to ordered intermetallic alloys has long been attributed to antiphase boundary (APB) tubes. In this work, APB tubes are introduced in Fe–40 at. pct Al and Fe–43 at. pct Al by cold-rolling and then removed by annealing. The presence and absence of APB tubes is verified with magnetic measurements. When APB tubes are annealed out the hardness does not change, thus indicating that APB tubes do not contribute to strengthening.

36 MATERIALS SCIENCE↗
DOE OSTI2022

The annihilation of antiphase boundary tubes and their effect on strengthening in Ni 3 Al

The temperature at which antiphase boundary (APB) tubes anneal out of lightly-strained Ni-rich Ni 3 Al thin foils has been measured via in-situ heating in a transmission electron microscope to be ~530 °C. Given this new information, the wealth of literature on the mechanical properties of Ni 3 Al across the entire temperature regime of the yield stress anomaly, ~25–800 °C, is re-evaluated to consider the impact of APB tubes. Contrary to previous theoretical predications, APB tubes do not appear to affect the strength of Ni 3 Al.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Metastable antiphase boundary ordering in CaFe 2 O 4

CaFe 2 O 4 is an $\textit{S}$ = 5/2 antiferromagnet exhibiting two magnetic orders that shows regions of coexistence at some temperatures. Using a Green’s function formalism, we model neutron scattering data of the spin wave excitations in this material, elucidating the microscopic spin Hamiltonian. In doing so, we suggest that the low-temperature A phase order (↑↑↓↓) finds its origins in the freezing of antiphase boundaries created by thermal fluctuations in a parent B phase order (↑↓↑↓). In this work, the low-temperature magnetic order observed in CaFe 2 O 4 is thus the result of a competition between the exchange coupling along $\textit{c}$, which favors the B phase, and the single-ion anisotropy, which stabilizes thermally generated antiphase boundaries, leading to static metastable A phase order at low temperatures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of alloying elements on the $γ$’ antiphase boundary energy in Ni-base superalloys

Mechanical and fatigue performance of γ-γ' Ni-base superalloys are strongly affected by the antiphase boundary energy (APBE) of the γ' precipitates which, in turn, is dictated by the alloy's composition. Due to the multicomponent character of these alloys, establishing composition-APBE relationships are challenging, even though the qualitative effect of individual solutes on the APBE may be known. This work attempts to utilize density functional theory-based cluster expansion calculations to systematically assess the effect of composition on the APBE of the γ' phases in Ni-base superalloys. We aim to elucidate the influence of not only one single element but also multiple coexisting alloying elements on the γ' APBE. By explicit consideration of configurational disorder via Monte Carlo sampling, the effect of temperature on the APBE has also been analyzed. Overall, this work reveals that (1) effects of individual solute element M on the APBE energy obtained in an isolated, ternary condition (i.e. in Ni 3-x Al 1-y M x+y ) does not directly translate to a multi-solute case and that (2) the mutual synergistic interactions among different solute elements are not negligible. Based on the present results, an empirical master equation that predicts the APBE based on the composition of the γ' phases has been obtained.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Modeling antiphase boundary energies of Ni 3 Al-based alloys using automated density functional theory and machine learning

Antiphase boundaries (APBs) are planar defects that play a critical role in strengthening Ni-based superalloys, and their sensitivity to alloy composition offers a flexible tuning parameter for alloy design. Here, we report a computational workflow to enable the development of sufficient data to train machine-learning (ML) models to automate the study of the effect of composition on the (111) APB energy in Ni 3 Al-based alloys. We employ ML to leverage this wealth of data and identify several physical properties that are used to build predictive models for the APB energy that achieve a cross-validation error of 0.033 J m –2 . We demonstrate the transferability of these models by predicting APB energies in commercial superalloys. Moreover, our use of physically motivated features such as the ordering energy and stoichiometry-based features opens the way to using existing materials properties databases to guide superalloy design strategies to maximize the APB energy.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Antiphase-Boundary-Engineered Domain Switching in a (110)-Oriented BiFeO 3 Film

A ferroelectric domain wall memory device exploits the presence (or absence) of domain walls as the basis for information storage. Although structural defects strongly influence ferroelectric domain wall nucleation and growth, this correlation is far from being fully understood. For example, a single defect can play opposing roles: it can act as a nucleation site to initiate domain switching or, conversely, serve as a pinning center inhibiting domain wall motion. This is particularly the case for antiphase boundaries (APBs), whose influence on switching remains relatively unexplored despite being ubiquitous in oxide perovskite ferroelectrics. Here, we use aberration-corrected scanning transmission microscopy and in situ transmission electron microscopy under an applied bias to extensively characterize the influence of an APB on the switching behavior in a (110)-oriented BiFeO 3 thin film. We demonstrate that deterministic nucleation occurs in the proximity of a vertically oriented APB, following which domain growth occurs laterally in a symmetric fashion. Atomic-scale structural analysis reveals that the shear operation vector for the APB is 1/2[110]; this half-unit-cell shift extends over a few nanometers, implying that the APB plane is inclined toward the imaging direction. The symmetric switching observation is attributed to local inhomogeneous lattice strain and a reduction of polarization caused by the APB. These results demonstrate that an extended structural defect can be used as an active switching element rather than a stumbling block in reprogrammable domain-wall-based devices. Ultimately, this will expand the capabilities of ferroelectric thin films for future electronic devices based on ferroelectric domain walls.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Antiphase boundary migration as a diffusion mechanism in a P3 sodium layered oxide

The electrode materials of Na-ion batteries must exhibit fast ion transport, a property that is often negatively impacted when mobile cations order. Many layered Na (and K) intercalation compounds adopt the P3 crystal structure, which tends to stabilize cation-vacancy orderings over a wide range of Na concentrations. The ordered phases have been predicted to consist of domains that are periodically separated by antiphase boundaries (APBs) to accommodate variations in Na concentration. The mechanisms and rates with which Na diffuses within such ordered phases of P3 are not understood. We have conducted a first-principles study of Na diffusion in the P3 structure, using Na x CoO 2 as a model system. We find that most simple nearest-neighbor hops in Na-vacancy ordered phases in P3 result in unstable configurations and are therefore forbidden. We identify an alternative mechanism of Na transport that is mediated by APB migration via the formation and expansion of kinks along domain boundaries. The limiting kinetic barriers for this mechanism are quite low (0.03 to 0.30 eV). Vacancy defects are not required, and furthermore have formation energies that are higher than those of the APB kink defects. Furthermore, our results suggest that APB migration is a fundamental diffusion mechanism in the P3 structure.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Structural complexity of γ-Al 2 O 3 : The nature of vacancy ordering and the structure of complex antiphase boundaries

The structure of γ-Al2O3 remains largely undetermined despite decades of research. This is due to the high degree of disorder, which poses significant challenges for structural analysis using conventional crystallographic approaches. Herein, we study the structure of γ-Al2O3 with Scanning Transmission Electron Microscopy (STEM) and ab-initio calculations to provide a complete structural description. We show that the microstructure can be understood in terms of two key structural features of nanoscale spinel domains and finite thickness segments termed as complex antiphase boundaries (cAPB) that provide the domain interconnectivity. The spinel domains have a distinctive preference for vacancy ordering, which can be rationalized in terms of a structure with a stacking disorder. Tetragonal P4 1 2 1 2 or monoclinic P2 1 models, all based on the identical motif, can be considered as representative ordered forms. Individual spinel domains are interconnected via cAPBs, which adopt a distinct non-spinel bonding environment of δ-Al 2 O 3 . The most common cAPB consists of a single delta motif with thickness of just 0.6 nm on (001), with the resulting displacement a/4 [101]. Remarkably, the cAPBs are shown to energetically stabilize the spinel domains of γ-Al 2 O 3 explaining their high abundance. We demonstrate how the tetragonal distortions naturally arise in this intricate microstructure and place the proposed model in the context of phase transformations to high temperature transition aluminas.

36 MATERIALS SCIENCE↗
NASA NTRS2019

Investigation of Stacking Fault and Antiphase Boundary Segregation in Ni-Based Superalloys Using Density Functional Theory

Ni-base superalloys have a long history of use in jet turbine engines, and efforts to improve their performance in that application are ongoing. It is known that the precipitation of the Ni3Al γ' phase within the disordered FCCγ phase strengthens the overall material. However, in the high-temperature environment found inside a turbine engine during operation, creep can cause the γ' phase to transform to different, weaker phases along stacking faults, leading to a deterioration of performance. In the γ' phase one mode of creep deformation is the formation of stacking fault ribbons, which consist of intrinsic stacking faults further shearing into antiphase boundaries (APBs). It is also known that certain alloying additions exhibit segregation to stacking faults. If segregating elements could be identified which segregate to the intrinsic stacking fault, but not to the APB, the inclusion of such elements could lead to improved creep strength in these alloys. To investigate this possibility, a density functional investigation of the segregation of W, Mo and Cr to both a superlattice intrinsic stacking fault (SISF) and an APB was performed. It was found that W, Mo and Cr all exhibit segregation to the SISF. In contrast, for the APB, Cr was either energy-neutral, or segregates, depending on the presence of additional nearby Cr, or on the specific lattice site upon which it was placed, while Mo and W did not segregate. Because W and Mo segregate to the SISF but not to the APB, the inclusion of these elements could provide a degree of protection against creep-related deterioration.

Good, Brian S.↗
NASA NTRS1987

Antiphase boundaries in epitaxially grown beta-SiC

When the surface of beta-SiC, grown epitaxially on (001) silicon by chemical vapor deposition, is chemically etched, boundaries appear which may be observed by optical or scanning electron microscopy. Examination by plan-view and cross-sectional transmission electron microscopy shows boundaries in the film which exhibit line or fringe contrast. Convergent beam electron diffraction has been used to show that these boundaries separate domains that are in an antiphase relationship to each other. A model is presented which discusses the formation of these domains from independent nucleation on a stepped substrate surface.

Pirouz, P.↗
DOE OSTI2021

Robust long-range magnetic correlation across antiphase domain boundaries in Sr 2 CrReO 6

Here, we report a resonant elastic x-ray scattering study of a thin-film sample of Sr 2 CrReO 6 , which has one of the highest ferrimagnetic transition temperatures among ordered double perovskites.We found resonantly enhanced magnetic Bragg peaks at Q = (odd, odd, odd) at both the rhenium L 2 and L 3 edges, which coincide with the structural Bragg peaks of Sr 2 CrReO 6 . By analyzing the widths of these Bragg peaks, we extracted very different structural and magnetic correlation lengths. The former is about 15 nm, while the latter is constrained by the instrumental resolution to be at least 90 nm. We argue that a finite structural correlation length is consistent with the existence of antiphase nanodomains in our sample. On the other hand, a much larger magnetic correlation length indicates that the magnetic correlation extends far beyond the boundaries of individual domains and is consistent with strong antiferromagnetic coupling between different antiphase domains. Last, from the azimuthal dependence of the magnetic intensity, we show that the magnetic moments lie perpendicular to the c axis, which explains the earlier bulk magnetization data.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Competing magnetic interactions and emergent phase diagrams in double perovskite Y 2 Ni x Co 1–x MnO 6

We present a comparative study of double perovskites Y 2 Ni x Co 1–x MnO 6 for x = 1, 0.5, and 0. The polycrystalline samples of Y 2 Ni x Co 1–x MnO 6 with space group P2 1 /n were synthesized via sol-gel technique. X-ray photoelectron spectroscopy (XPS) confirms the presence of majority Ni 2+ /Mn 4+ in Y 2 NiMnO 6 (YNMO) and a mixed valence state Ni 2+/3+ /Co 2+/3+ /Mn 4+/3+ in co-doped Y 2 Ni 0.5 Co 0.5 MnO 6 (YNCMO). The temperature dependent magnetization results suggest homogeneous substitution of Ni ions with Co ions with minimal contribution of 3+ cationic magnetic interactions in YNCMO. The superexchange ferromagnetic (FM) interaction has a major contribution to the magnetism of YNMO. The strength of antiferromagnetic (AFM) coupling resulting from the antiphase boundaries in Y 2 Ni x Co 1–x MnO 6 increases with the increase in the Co concentration. The AC susceptibility (AC-χ) study further validates the presence of higher density of antiphase boundaries, which is reflected by the dynamics of domain walls in YNCMO. The isothermal magnetic entropy change (ΔS M ) as functions of temperature and magnetic field is exploited to assess the stabilization of different magnetic phases. Finally, the findings of ΔS M (T,µ 0 H) lead to the proposed new magnetic phase diagrams for Y 2 Ni x Co 1–x MnO 6 for x = 1 and 0.5, in comparison with the previously established phase diagram of Y 2 CoMnO 6 .

36 MATERIALS SCIENCE↗
NASA NTRS1989

Center for the development of commercial crystal growth in space

The second year of operation of the Center for Commercial Crystal Growth in Space is described. This center is a consortium of businesses, universities and national laboratories. The primary goal of the Center's research is the development of commercial crystal growth in space. A secondary goal is to develop scientific understanding and technology which will improve commercial crystal growth on earth. In order to achieve these goals the Center's research is organized into teams by growth technique; melt growth, solution growth, and vapor growth. The melt growth team is working on solidification and characterization of bulk crystals of gallium arsenide and cadmium telluride. They used high resolution X-ray topography performed at the National Synchrotron Light Source at Brookhaven National Laboratory. Streak-like features were found in the diffraction images of semi-insulating undoped LEC GaAs. These were shown to be (110) antiphase boundaries, which have not been reported before but appear to be pervasive and responsible for features seen via less-sensitive characterization methods. The results on CdTe were not as definitive, but indicate that antiphase boundaries may also be responsible for the double peaks often seen in X-ray rocking curves of this material. A liquid encapsulated melt zone system for GaAs has been assembled and techniques for casting feed rods developed. It was found that scratching the inside of the quartz ampoules with silicon carbide abrasive minimized sticking of the GaAs to the quartz. Twelve floating zone experiments were done.

Wilcox, William R.↗
DOE OSTI2025

V‐Groove Si Nanopatterning for the Direct Epitaxy of Orientation‐Patterned III–V Nonlinear Optical Crystals

Orientation‐patterned (OP) III–V semiconductors—used as quasi‐phase‐matched crystals for nonlinear optics applications—are typically epitaxially grown on expensive III–V substrates using a complex process requiring three separate epitaxy steps. In this work, a method is demonstrated for growing orientation‐patterned III–V crystals on Si substrates through V‐groove nanopatterning and a single epitaxial growth. V‐groove Si allows for suppression of random antiphase domain formation that is typical of III–V growth on (001)‐oriented Si through the use of (111)‐faceted trenches patterned on (001)‐oriented Si substrates. By alternating the directions of the V‐groove trenches between [110] and [10], antiphase boundaries can be selectively induced at the boundaries between the two directions of trenches due to the difference in symmetry between the III–V material and Si. This approach allows for a greatly simplified process for growing OP‐III‐Vs and more broadly is a new, robust approach for precisely patterning antiphase boundaries of arbitrary shape and length scales down to 50 nm.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
DOE OSTI2022

Quantifying the Role of APB Tubes on the Work-hardening of Ordered Phases

For sixty years, it has been theorized that antiphase boundary (APB) tubes, which are defects produced by deformation, contribute to the high strength of ordered alloys or intermetallic compounds. The concept of an APB tube was originally proposed by Vidoz and Brown [A.E. Vidoz, L.M. Brown, "On work-hardening in ordered alloys", Philosophical Magazine, 7 (1962) 1167–1175] in 1962 to explain the ~50% increase in strength observed when an alloy, such as Ni 3 Fe, is chemically ordered compared to when it is disordered. The existence of APB tubes was only definitively confirmed by Chou and Hirsch in 1981 [C.T. Chou, P.B. Hirsch Antiphase domain boundary tubes in plastically deformed ordered Fe 30.5 at.% Al alloy, Philosophical Magazine, A. 44 (1981) 1415–1419] using a transmission electron microscope (TEM). Prior to the current work, there had been no studies trying to correlate the presence of APB tubes with their effect on the mechanical properties. The main finding of this project was that APB tubes do not contribute to the strength of the strongly-ordered intermetallic compounds FeAl and Ni 3 Al. This was shown by removing the APB tubes by heating the materials and showing that the mechanical properties were unaffected. In addition, in-situ deformation experiments were undertaken in a TEM on both disordered and ordered Ni 3 Fe, in which it was shown that defects (superdislocations) in the ordered alloy underwent many more interaction events than defect (dislocations) in the disordered alloy. This difference can explain the increase in the increase in strength observed when this material is ordered. The project supported a PhD student, Rachel Osmundsen, who successfully defended her thesis in April, 2022. It also supported the principal investigator, Ian Baker, two PhD exchange students and an undergraduate researcher. The work involved collaborations with the following people and use of the following facilities: Dr. Si Chen, Advanced Photon Source at Argonne National Laboratory, for synchrotron X-ray diffraction; and Dr. Katherine Shanks and Dr. Kelly Nygren, Cornell High Energy Synchrotron Source (CHESS), for synchrotron X-ray diffraction. The work led to 12 papers published in refereed journals with two papers currently submitted to journals. There were also 16 presentation made at conferences and universities on the work, ten of which were invited.

36 MATERIALS SCIENCE↗