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DOE OSTI2017

Misfit dislocation patterns of Mg-Nb interfaces

The role of heterogeneous interfaces in improving mechanical properties of polycrystalline aggregates and laminated composites has been well recognized with interface structure being of fundamental importance in designing composites containing multiple interfaces. In this paper, taking the Mg (hexagonal close-packed (hcp))/Nb (body-centered cubic (bcc)) interface as an example, we develop Mg-Nb interatomic potentials for predicting atomic configurations of Mg/Nb interfaces. We systematically characterize interface dislocations of Mg/Nb interfaces with Nishiyama-Wassermann (NW) and Kurdjumov-Sachs (KS) orientation relationships and propose a generalized procedure of characterizing interface structure by combining atomistic simulation and interface dislocation theory, which is applicable for not only hcp/bcc interfaces, but also other systems with complicated interface dislocation configurations.Here, in Mg/Nb, interface dislocation networks of two types of interfaces are significantly different although they originate from partial dislocations of similar character: the NW interface is composed of three sets of partial dislocations, while the KS interface is composed of four sets of interface dislocations - three sets of partial dislocations and one set of full dislocations that forms from the reaction of two close partial dislocations.

36 MATERIALS SCIENCE↗

DOE OSTI2017

Effects of LPSO/α-Mg interfaces on dynamic recrystallization behavior of Mg96.5Gd2.5Zn1 alloy

Highlights: • The effects of LPSO/α-Mg interfaces on the dynamic recrystallization (DRX) behavior of Mg{sub 96.5}Gd{sub 2.5}Zn{sub 1} (at.%) alloy during indirect extrusion at 350 °C were investigated. • The LPSO/α-Mg interfaces in Mg{sub 96.5}Gd{sub 2.5}Zn{sub 1} alloy appeared as two groups, including the basal and non-basal LPSO/α-Mg interfaces, which have various effects on the DRX behavior of Mg{sub 96.5}Gd{sub 2.5}Zn{sub 1} alloy. • Compared with the basal LPSO/α-Mg interfaces, DRX grains are preferentially nucleated near the non-basal LPSO/α-Mg interfaces where there is higher V{sub GROD} and lower required energy E{sub s} for the DRX nucleation. - Abstract: Mg-Gd-Zn alloy, which contains a long period stacking ordered (LPSO) structure, has the potential to become a high-strength Mg alloy within the automotive and aerospace industries. Two types of LPSO/α-Mg interfaces in Mg{sub 96.5}Gd{sub 2.5}Zn{sub 1} (at.%) alloy were characterized, namely, basal and non-basal LPSO/α-Mg interfaces. The effects of LPSO/α-Mg interfaces on the dynamic recrystallization (DRX) behavior during indirect extrusion at 350 °C were investigated. The grain reference orientation deviation (GROD) value (V{sub GROD}), derived from EBSD, could qualitatively characterize the dislocation density within a grain and determine the presence of DRX grain nucleation. The results suggested that the areas around non-basal LPSO/α-Mg interfaces always have higher V{sub GROD} than do basal LPSO/α-Mg interfaces. In addition, the stored energy (E{sub s}) required for DRX nucleation on the non-basal LPSO/α-Mg interface is lower than that on the basal LPSO/α-Mg interface. This is a result of the flat, sharp basal LPSO/α-Mg interface compared to the faceted non-basal LPSO/α-Mg interface. Regardless of whether the LPSO structure/α-Mg matrix interface is coherent or not, non-basal LPSO/α-Mg interfaces are favorable nucleation sites for DRX grains due to the higher V{sub GROD} and lower required energy E{sub s}.

36 MATERIALS SCIENCE↗

DOE OSTI2026

Non-conformal interface-cohesive modeling with the shifted boundary method

The accurate simulation of boundary- and interface-dominated problems on complex geometries remains challenging when boundary- or interface-fitted meshes are difficult to generate, particularly for curved boundaries, polycrystalline microstructures, and dense interface networks. The Shifted Boundary Method (SBM) alleviates this meshing burden by shifting the enforcement of boundary conditions from the true boundary to a nearby surrogate boundary and recovering the effect of the true boundary through geometric correction terms, thereby enabling standard finite element spaces on non-boundary-fitted meshes. In this report, we develop a general shiftedboundary and shifted-interface framework within the open-source MOOSE framework. We first present a general SBM implementation for complex geometries on non-boundary-fitted meshes. We then adopt the Shifted Interface Method (SIM) for internal interfaces and develop a unified shifted-interface treatment in which the interface law is enforced on a surrogate interface and the effect of the true interface is recovered through shifted jumps, fluxes, and tractions. This perspective brings scalar thermal-contact and vector-valued cohesive-zone mechanics into a single framework, the latter realized as the Shifted Cohesive Zone Method (SCZM) and coupled with history-dependent constitutive models from NEML2. We further extend the MOOSE mesh infrastructure to support cohesive-zone calculations on distributed meshes. The framework is verified and demonstrated through three progressive studies: Poisson’s equation on a smoothed starshaped domain, a manufactured thermal-contact problem on a non-interface-fitted mesh, and a two-dimensional polycrystalline representative volume element combining crystal plasticity with cohesive grain-boundary interfaces. Across these studies, the shifted formulations reproduce boundary- and interface-fitted reference solutions with high fidelity, indicating that the proposed framework provides an accurate and efficient route to boundary- and interface-dominated simulations on arbitrary geometries without requiring fitted meshes.

Yang, Cheng-Hau↗

DOE OSTI2017

Interfaces in Heterogeneous Catalysts: Advancing Mechanistic Understanding through Atomic-Scale Measurements

Developing novel catalysts with high efficiency and selectivity is critical for enabling future clean energy conversion technologies. Interfaces in catalyst systems have long been considered the most critical factor in controlling catalytic reaction mechanisms. Interfaces include not only the catalyst surface but also interfaces within catalyst particles and those formed by constructing heterogeneous catalysts. The atomic and electronic structures of catalytic surfaces govern the kinetics of binding and release of reactant molecules from surface atoms. Interfaces within catalysts are introduced to enhance the intrinsic activity and stability of the catalyst by tuning the surface atomic and chemical structures. Examples include interfaces between the core and shell, twin or domain boundaries, or phase boundaries within single catalyst particles. In supported catalyst nanoparticles (NPs), the interface between the metallic NP and support serves as a critical tuning factor for enhancing catalytic activity. Surface electronic structure can be indirectly tuned and catalytically active sites can be increased through the use of supporting oxides. Additionally, tuning interfaces in catalyst systems has been identified as an important strategy in the design of novel catalysts. However, the governing principle of how interfaces contribute to catalyst behavior, especially in terms of interactions with intermediates and their stability during electrochemical operation, are largely unknown. This is mainly due to the evolving nature of such interfaces. Small changes in the structural and chemical configuration of these interfaces may result in altering the catalytic performance. These interfacial arrangements evolve continuously during synthesis, processing, use, and even static operation. A technique that can probe the local atomic and electronic interfacial structures with high precision while monitoring the dynamic interfacial behavior in situ is essential for elucidating the role of interfaces and providing deeper insight for fine-tuning and optimizing catalyst properties.Scanning transmission electron microscopy (STEM) has long been a primary characterization technique used for studying nanomaterials because of its exceptional imaging resolution and simultaneous chemical analysis. Over the past decade, advances in STEM, that is, the commercialization of both aberration correctors and monochromators, have significantly improved the spatial and energy resolution. Imaging atomic structures with subangstrom resolution and identifying chemical species with single-atom sensitivity are now routine for STEM. These advancements have greatly benefitted catalytic research. For example, the roles of lattice strain and surface elemental distribution and their effect on catalytic stability and reactivity have been well documented in bimetallic catalysts. In addition, three-dimensional atomic structures revealed by STEM tomography have been integrated in theoretical modeling for predictive catalyst NP design. Recent developments in stable electronic and mechanical devices have opened opportunities to monitor the evolution of catalysts in operando under synthesis and reaction conditions; high-speed direct electron detectors have achieved sub-millisecond time resolutions and allow for rapid structural and chemical changes to be captured. Investigations of catalysts using these latest microscopy techniques have provided new insights into atomic-level catalytic mechanisms. Further integration of new microscopy methods is expected to provide multidimensional descriptions of interfaces under relevant synthesis and reaction conditions.In this Account, we discuss recent insights on understanding catalyst activity, selectivity, and stability using advanced STEM techniques, with an emphasis on how critical interfaces dictate the performance of precious metal-based heterogeneous catalysts. The role of extended interfacial structures, including those between core and shell, between separate phases and twinned grains, between the catalyst surface and gas, and between metal and support are discussed. We also provide an outlook on how emerging electron microscopy techniques, such as vibrational spectroscopy and electron ptychography, will impact future catalysis research.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2020

Inertial dynamics of an interface with interfacial mass flux: Stability and flow fields’ structure, inertial stabilization mechanism, degeneracy of Landau’s solution, effect of energy fluctuations, and chemistry-induced instabilities

This work focuses on the long-standing problem of inertial dynamics of an interface with interfacial mass flux and reports new mechanisms for the interface stabilization and destabilization. The interface is a phase boundary separating fluids of different densities and having interfacial mass flux. To analyze the interface dynamics from a far field, we develop and apply the general matrix method to rigorously solve the boundary value problem involving the governing equations in the fluid bulk and the boundary conditions at the interface and at the outside boundaries of the domain. We find the fundamental solutions for the linearized system of equations and analyze the interplay of interface stability with flow fields’ structure by directly linking rigorous mathematical attributes to physical observables. We find that the interface is stable when the dynamics conserves the fluxes of mass, momentum, and energy; the stabilization is due to an inertial mechanism causing small oscillations of the interface velocity. In the classic Landau’s dynamics, the postulate of perfect constancy of the interface velocity leads to the development of Landau–Darrieus instability. This destabilization is also linked to the imbalance of the perturbed energy at the interface. The classic Landau’s solution is found to have degeneracy; lifting of the degeneracy may lead to singularity and self-similar dynamics. Our results compare well with traditional theories of combustion and propose new experiments to study the dynamics of the interface and the flow fields in combustible systems. We further conduct reactive molecular dynamics simulations to elucidate the complexity of chemical processes, to study the destabilizing effect of energy fluctuations on the interface stability, and to illustrate the chemistry-induced instabilities. In summary, we identify the extreme sensitivity of the interface dynamics to the interfacial boundary conditions, including the formal properties of fundamental solutions and the qualitative and quantitative properties of the flow fields. This provides new opportunities for studies, diagnostics, and control of multiphase flows in a broad range of processes in nature and technology.

42 ENGINEERING↗

DOE OSTI2022

Revisiting W–ZrC interfaces: A first principles study

We investigate W–ZrC interfaces using first-principles calculations based on the density functional theory. There have been theoretical and experimental studies exploring W–ZrC interfaces, however, the debate regarding the most stable interface continues to persist. In this study, we systematically simulated various W–ZrC interfaces merging W and ZrC surfaces with different orientations. Subsequently, we evaluated their stabilities and explained the corresponding stabilities in terms of the nature of bonding and charge-transfer processes at the interface. We find ZrC(111)–W(110) is the most stable interface with higher adhesive energy than the other interfaces. The additional stability associated with the ZrC(111)–W(110) results from significant interface reconstruction. Three layers of W and ZrC adjacent to the interface are involved in the charge-transfer process leading to stronger ionic bonds in ZrC(111)–W(110) as compared to the other potential candidate: ZrC(100)–W(100). The C and W atoms are found to be displaced from their symmetric position during the reconstruction process at the interface to facilitate stronger bonds with shorter W–C and W–Zr bonds in ZrC(111)–W(110) as compared to ZrC(100)–W(100). This leads to stronger covalent bonds in ZrC(111)–W(110) than that in ZrC(100)–W(100). Therefore, we conclude that the stronger covalent and ionic forces in ZrC(111)–W(110) than those in ZrC(100)–W(100) are responsible for making ZrC(111)–W(110) to be the most stable interface. In conclusion, this study addresses the long-standing question of the most stable W–ZrC interface and derives a number of implications for other W-transition metal carbide interfaces which are potential candidates for improving the mechanical properties of plasma facing materials.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2026

Controlling Deformation in Al/Ti: How Interface Roughness and Orientation Drive Bimetal Mechanics

The microstructural characteristics and morphology of interfaces in metals can be crucial in governing the initiation of plasticity and early deformation mechanisms under extreme conditions. During high-strain-rate deformation, these interfaces significantly affect dislocation nucleation, twinning, and other mechanisms that directly impact material strength and failure. Despite their importance, a substantial knowledge gap remains between the observed macroscopic material behavior and the underlying role of bimetal interfaces in plasticity initiation. Here, to address this gap, large-scale molecular dynamics simulations are performed on Al/Ti bimetal structures to examine the effect of interface characteristics on the onset of plasticity under uniaxial compression. Specifically, this study investigates how interface roughness (flat vs waveform interfaces) modifies the initiation of plastic events in the microstructure. Atomistic simulations indicate that interface roughness (a microscopic behavior) reduces the stress required for dislocation nucleation, thereby reducing the peak stress relative to a flat interface. For the square interface, the step height strongly influences plasticity initiation by setting the separation of locally flat regions. Varying the interface rotation relative to the loading direction (macroscopic behavior) reveals that the peak stress for both flat and waveform interfaces initially decreases and then increases with rotation, accompanied by a shift in dominant mechanisms—from Al twinning (flat) to interface sliding and Ti-dominated phase transformation and twinning at lower angles. The change in the stress-strain slope during initial compression reflects how rotation alters the resolved shear stress and activates different slip systems. Overall, the study provides valuable insights into the role of bimetal interfaces in controlling plasticity initiation and early deformation pathways for Al/Ti under extreme loading conditions.

36 MATERIALS SCIENCE↗

DOE OSTI2020

First-principles study of hydrogen behavior near W/WC interfaces

Hydrogen (H) solution, migration, and binding to vacancies near the tungsten/tungsten carbide (W/WC) interfaces based on hcp WC or bcc W (W/WCb and Wb/WC) have been studied by first-principles simulations to provide insights into the effect of C on H behavior in W exposed to C deposition in fusion reactors. The H behavior near the W/WC interfaces is related to the tensile or compressive strain due to the lattice match and interfacial effects. Near the W/WCb interface, the H solution energy in hcp WC increases approaching the interface, while it decreases from the W side to the interface. The configuration change of the W slab significantly decreases the H solution energy but has only a modest effect on the H migration energy barrier in comparison with the values in bcc W. The interface enhances the H binding to vacancies in WC layers. Both the interface and configuration adjustment of the W slab reduce the H binding to vacancies on the W side of the interface. Near the Wb/WC interface, H solution energies in both WC and W slabs weakly decrease approaching the interface. The configuration change of the WC slab significantly increases the H solution energy and binding energy to vacancies but decreases the H migration energy barrier in comparison with the values in hcp WC. The H energetics near the W/WC interfaces indicate the likelihood of H localization and diffusion in the W side of the interface, rather than diffusing through the interface into WC layers.

Yang, L. (ORCID:0000000322166071)↗

DOE OSTI2012

Experimental and Theoretical Studies of Liquid-Solid and Liquid-Vapor Interfaces of Metals and Alloys

The research supported by ER46321 was designed to understand in microscopic detail the structures of the interfaces between liquid metals and alloys and solid media. The system chosen for study, because of detailed knowledge of the structure of the corresponding liquid alloy-vapor interface, was the interface between a Si crystal and a dilute alloy of Pb in Ga. Experimental study of the Si:PbGa interface was anticipated to be very difficult; it requires preparation of an interface between a liquid metal and a solid surface that is flat to better than a nanometer on the scale length of the x-ray coherence, alignment of the x-ray beam and the surface in the sub-micro radian regime, and the use of high energy x-rays to penetrate the window and reach the interface without disastrous loss of intensity. The experimental design was subject to compromises forced by the limit to the highest x-ray energy available at the ChemMatCARS beam-line, namely 30 keV, which reduced the scattered signal relative to what can be obtained with higher x-ray energy. Although considerable progress was achieved during the support period and its no-cost extension, the difficulties encountered prevented completion of the studies and the data collected are incomplete. These data hint at the existence of unexpected structural features of the interface, in particular that Pb dimers play an important role in the interfacial structure. These data provide a different picture of the interface from the pentagonal structure inferred to be present in the interface between pure Pb and Si 001 (Nature 408, 839 (2000)), but much like the Ga dimers in the interface between liquid Ga and the 100 face of diamond (Nature 390, 379 (1997), J. Chem. Phys. 123, 104703 (2005)). However, during the latter part of the support period significant progress was made in the theoretical description of the liquid metal-crystal interface. In particular, stimulated by the results of an experimental study of the interface between liquid Hg and the reconstructed (0001) face of sapphire, we developed an extension of the self-consistent quantum Monte Carlo scheme previously used to study the structure of the liquid metal-vapor interface.

36 MATERIALS SCIENCE↗

DOE OSTI2023

Star Block Copolymers at Homopolymer Interfaces: Conformation and Compatibilization

Star block copolymers (s-BCPs), comprised of multiple linear diblock copolymers joined at a central point, are shown to segregate to the interface between two immiscible homopolymers that are identical to the blocks of the s-BCPs. The s-BCPs undergo a configurational transition at the interface, with different blocks of copolymers being embedded in their respective homopolymers, thereby bridging the interface and promoting adhesion. A series of 4-arm s-BCPs were synthesized with hydrogenated or deuterated polystyrene (PS/dPS) as the core block and poly(2-vinylpyridine) (P2VP) as the corona block, which was directly placed at the interface between the two homopolymers. Neutron reflectivity (NR) was used to determine the concentration profiles of the PS homopolymer, s-BCP core blocks, and P2VP total segments under equilibrium. The investigation varies the molecular weight (MW) and the total number of s-BCPs at the interface. Self-consistent-field theory (SCFT) was also employed to calculate the concentration profiles of the components at the interface, which were in excellent agreement with experimental results. The NR showed that the interfacial width between the homopolymers increased with the increasing number of s-BCPs at the interface up to a saturation limit. Beyond this limit, additional s-BCPs were released into the corona-miscible phase as unimolecular micelles. For a comparable interlayer thickness of s-BCPs at the interface, lower MW s-BCPs generated a broader interface. SCFT analysis suggested that, at the same packing density, the arms of the low MW s-BCPs align more parallel to the interface, while the arms of high MW s-BCPs adopt a more normal orientation, like their linear BCP counterparts. Furthermore, it was also observed that the core blocks, constrained by the junction points, were oriented more parallel and closer to the interface than the corona blocks. The phase behavior of the polymer blends revealed that s-BCP additives can efficiently reduce the domain size, with the low MW yielding smaller domain sizes due to the greater reduction in the interfacial energy and the high MW arresting phase separation due to their higher binding energy and a jamming of the interfacial assemblies. Asymmetric double cantilever beam (ADCB) tests demonstrated that s-BCPs promoted adhesion more efficiently than their linear BCP counterparts due to stronger binding energy per molecule, suggesting a more efficient compatibilizer for polymer upcycling. In conclusion, the results from these studies provide fundamental insights into the assembly of s-BCPs at homopolymer interfaces, the reduction of domain size, and promotion of adhesion, providing a strategy for the use of s-BCPs as stealth surfactants and universal compatibilizers.

interface↗

DOE OSTI2024

In Situ Monitoring the Nucleation and Growth of Nanoscale CaCO 3 at the Oil–Water Interface

Interfaces can actively control the nucleation kinetics, orientations, and polymorphs of calcium carbonate (CaCO 3 ). Prior studies have revealed that CaCO 3 formation can be affected by the interplay between chemical functional moieties on solid–liquid or air–liquid interfaces as well as CaCO 3 ’s precursors and facets. Yet little is known about the roles of a liquid–liquid interface, specifically an oil–liquid interface, in directing CaCO 3 mineralization which are common in natural and engineered systems. Here, in this study, by using in situ X-ray scattering techniques to locate a meniscus formed between water and a representative oil, isooctane, we successfully monitored CaCO 3 formation at the pliable isooctane–water interface and systematically investigated the pivotal roles of the interface in the formation of CaCO 3 (i.e., particle size, its spatial distribution with respect to the interface, and its mineral phase). Different from bulk solution, ∼5 nm CaCO 3 nanoparticles form at the isooctane–water interface. They stably exist for a long time (36 h), which can result from interface-stabilized dehydrated prenucleation clusters of CaCO 3 . There is a clear tendency for enhanced amounts and faster crystallization of CaCO 3 at locations closer to isooctane, which is attributed to a higher pH and an easier dehydration environment created by the interface and oil. Our study provides insights into CaCO 3 nucleation at an oil–water interface, which can deepen our understanding of pliable interfaces interacting with CaCO 3 and benefit mineral scaling control during energy-related subsurface operation.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

First-principles calculation on β-SiC(111)/α-WC(0001) interface

The α-WC(0001) surface and β-SiC(111)/α-WC(0001) interface were studied by first-principles calculation based on density functional theory. It is demonstrated that the α-WC(0001) surface models with more than nine atom-layers exhibit bulk-like interior, wherein the surface relaxations localized within the top three layers are well converged. Twenty-four specific geometry models of SiC/WC interface structures with different terminations and stacking sites were chosen. The calculated work of adhesion and interface energy suggest that the most stable interface structure has the C-C bonding across the interface, yielding the largest work of adhesion and the lowest interface energy. Moreover, the top-site stacking sequence is preferable for the C/C-terminated interface. The effects of the interface on the electronic structures of the C/C-terminated interfaces are mainly localized within the first and second layers of the interface. Calculations of the work of adhesion and interface energy provide theoretical evidence that the mechanical failure may initiate at the interface or in SiC but not in WC.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2021

Non-Diffusive Volume Advection with A High Order Interface Reconstruction Method

We show that non-diffusive volume advection in two-dimensions is achieved with several benchmark problems using a newly developed high-order volume of fluids (VOF) interface reconstruction method. (1) A new VOF interface reconstruction method using circular/corner facets (linear facets are a degenerate case of arcs). We create a circular interface facet in each mixed zone by matching neighbor volume with a hybrid Newton’s-bisection method and the local solution is final. In the general case, the new VOF interface reconstruction has 3rd order accuracy and can be easily made seamless. The new method addresses intrinsic issues with Young’s method such as gaps between interface facets in the case of a curved interface, and inability to define curvature nor identify corners. (2) A non-diffusive volume advection scheme. In an ALE advection step, a well-defined interface can be carried over through a Lagrange step and used to compute volume distribution into a relaxed mesh. Then, an interface reconstruction step is performed to redefine the interface in the relaxed mesh. We must point out that the interface carried over is also a solution of interface reconstruction because all the volume fractions in the relaxed mesh are naturally matched. We provide an interface tracking method compatible with our reconstruction scheme, where it is granted to use the prior info as an initial guess to capture sub-mesh resolution features. As a result, we are able to treat multiple facets inside a single mixed cell and obtain highly accurate, non-diffusive solution for advection problems with rather coarse meshes. We show our solutions for two-dimensional incompressible flows with two materials with a) the X + O diagonal translation; b) the Zalesak rotational test; and c) the single vortex spiral test.

97 MATHEMATICS AND COMPUTING↗

DOE OSTI2013

Effect of re-melting on particle distribution and interface formation in SiC reinforced 2124Al matrix composite

The interface between metal matrix and ceramic reinforcement particles plays an important role in improving properties of the metal matrix composites. Hence, it is important to find out the interface structure of composite after re-melting. In the present investigation, the 2124Al matrix with 10 wt.% SiC particle reinforced composite was re-melted at 800 °C and 900 °C for 10 min followed by pouring into a permanent mould. The microstructures reveal that the SiC particles are distributed throughout the Al-matrix. The volume fraction of SiC particles varies from top to bottom of the composite plate and the difference increases with the decrease of re-melting temperature. The interfacial structure of re-melted 2124Al–10 wt.%SiC composite was investigated using scanning electron microscopy, an electron probe micro-analyzer, a scanning transmission electron detector fitted with scanning electron microscopy and an X-ray energy dispersive spectrometer. It is found that a thick layer of reaction product is formed at the interface of composite after re-melting. The experimental results show that the reaction products at the interface are associated with high concentration of Cu, Mg, Si and C. At re-melting temperature, liquid Al reacts with SiC to form Al{sub 4}C{sub 3} and Al–Si eutectic phase or elemental Si at the interface. High concentration of Si at the interface indicates that SiC is dissociated during re-melting. The X-ray energy dispersive spectrometer analyses confirm that Mg- and Cu-enrich phases are formed at the interface region. The Mg is segregated at the interface region and formed MgAl{sub 2}O{sub 4} in the presence of oxygen. The several elements identified at the interface region indicate that different types of interfaces are formed in between Al matrix and SiC particles. The Al–Si eutectic phase is formed around SiC particles during re-melting which restricts the SiC dissolution. - Highlights: • Re-melted composite shows homogeneous particle distribution • Thick reaction products are observed at the interface • Carbide is identified at interface due to SiC dissolution at high temperature • Reaction products are also Si enrich phase • Mg and Cu segregated and formed MgAl{sub 2}O{sub 4}, CuMgAl{sub 2} phase at grain boundary.

36 MATERIALS SCIENCE↗

DOE OSTI2020

Equilibrium solute segregation to matrix- θ' precipitate interfaces in Al-Cu alloys from first principles

Particular combinations of solute atoms segregated to the interface of the Al and θ ' - Al 2 Cu in Al-Cu alloys can help stabilize θ ' precipitates at high temperatures. Stabilization of such precipitates is determined by a combination of thermodynamics (including driving forces for coarsening and transformation and solute segregation tendencies) and kinetic effects (including solute diffusion and interfacial mobility in the presence of interfacial solute segregation). For some alloys such as recent Al-Cu-based alloys, multiple solutes segregate in significant quantities to interfaces, and solute-solute interactions at the interface are important, with multiple types of solutes competing for similar interfacial sites. To treat this situation, we develop and apply a statistical mechanics approach to calculate the temperature-dependent equilibrium solute atoms distribution near the coherent and semicoherent interfaces between the Al matrix and the θ ' - Al 2 Cu precipitates. The developed approach is applied to the investigation of Si, Mn, and Zr segregation at the interface, as particular combinations of these elements affect the thermal stability of the θ ' precipitates. We demonstrate that because Si and Mn atoms segregate on the same semicoherent interface, the presence of Si reduces the concentration of Mn solutes at the interface. Si atoms preferably occupy the first layer of the interface and compete with Mn atoms for one type of particular sites in the layer. Mn atoms preferably occupy the second layer of the semicoherent interface, and the Mn-Mn interaction plays an important role in their distribution. Zr atoms mostly segregate on one of the two nonequivalent sites of the second layer of the coherent interface. Due to symmetry properties of the coherent interface, the calculations show that the segregation Zr of atoms to this interface will likely lead to the formation of L 1 2 ordered Al 3 Zr layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

Surface tension and long range corrections of cylindrical interfaces

The calculation of the surface tension of curved interfaces has been deeply investigated from molecular simulation during this last past decade. Recently, the thermodynamic Test-Area (TA) approach has been extended to the calculation of surface tension of curved interfaces. In the case of the cylindrical vapour-liquid interfaces of water and Lennard-Jones fluids, it was shown that the surface tension was independent of the curvature of the interface. In addition, the surface tension of the cylindrical interface is higher than that of the planar interface. Molecular simulations of cylindrical interfaces have been so far performed (i) by using a shifted potential, (ii) by means of large cutoff without periodic boundary conditions, or (iii) by ignoring the long range corrections to the surface tension due to the difficulty to estimate them. Indeed, unlike the planar interfaces there are no available operational expressions to consider the tail corrections to the surface tension of cylindrical interfaces. We propose here to develop the long range corrections of the surface tension for cylindrical interfaces by using the non-exponential TA (TA2) method. We also extend the formulation of the Mecke-Winkelmann corrections initially developed for planar surfaces to cylindrical interfaces. We complete this study by the calculation of the surface tension of cylindrical surfaces of liquid tin and copper using the embedded atom model potentials.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2014

Computational Studies of [Bmim][PF6]/n-Alcohol Interfaces with Many-Body Potentials

In this paper, we present the results from molecular-dynamics simulations of the equilibrium properties of liquid/liquid interfaces of room temperature ionic liquid [bmim][PF6] and simple alcohols (i.e., methanol, 1-butanol, and 1-hexanol) at room temperature. Polarizable potential models are employed to describe the interactions among species. Results from our simulations show stable interfaces between the ionic liquid and n-alcohols, and we found that the interfacial widths decrease from methanol to 1-butanol systems, and then increase for 1-hexanol interfaces. Angular distribution analysis reveals that the interface induces a strong orientational order of [bmim] and n-alcohol molecules near the interface, with [bmim] extending its butyl group into the alcohol phase while the alcohol has the OH group pointing into the ion liquid region, which is consistent with the recent sum-frequency-generation experiments. We found the interface to have a significant influence on the dynamics of ionic liquids and n-alcohols. The orientational autocorrelation functions illustrate that [bmim] rotate more freely near the interface than in the bulk, while the rotation of n-alcohol is hindered at the interface. Additionally, the time scale associated with the diffusion along the interfacial direction is found to be faster for [bmim] but slowed down for n-alcohols approaching the interface. We also calculate the dipole moment of n-alcohols as a function of the distance normal to the interface. We found that, even though methanol and 1-butanol have different dipole moments in bulk phase, they reach a similar value at the interface. This work was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. Pacific Northwest National Laboratory is a multiprogram national laboratory operated for the Department of Energy by Battelle. The calculations were carried out using computer resources provided by the Office of Basic Energy Sciences.

Chang, Tsun-Mei↗

DOE OSTI2022

Inelastic phonon transport across atomically sharp metal/semiconductor interfaces

Understanding thermal transport across metal/semiconductor interfaces is crucial for the heat dissipation of electronics. The dominant heat carriers in non-metals, phonons, are thought to transport elastically across most interfaces, except for a few extreme cases where the two materials that formed the interface are highly dissimilar with a large difference in Debye temperature. In this work, we show that even for two materials with similar Debye temperatures (Al/Si, Al/GaN), a substantial portion of phonons will transport inelastically across their interfaces at high temperatures, significantly enhancing interface thermal conductance. Moreover, we find that interface sharpness strongly affects phonon transport process. For atomically sharp interfaces, phonons are allowed to transport inelastically and interface thermal conductance linearly increases at high temperatures. With a diffuse interface, inelastic phonon transport diminishes. Our results provide new insights on phonon transport across interfaces and open up opportunities for engineering interface thermal conductance specifically for materials of relevance to microelectronics.

42 ENGINEERING↗