Interface Coherency Research Articles

(Invited) Non-Intuitive Failure Mechanics in Solid State Batteries

Solid electrolyte failure can occur through a range of different mechanisms. Electrochemical delamination at electrode and electrolyte interfaces is a prominent failure mechanism during high capacity and low N/P operating conditions, and filament formation is prevalent during high rate and long cycle-life deposition. Interface coherency and solid electrolyte microstructure both impact the ultimate degradation mode. Solid electrolyte microstructure, described in part by the density, periodicity, and interconnected arrangement of pores, plays a role in failure. Herein, we combine modeling, synchrotron imaging, and electrochemical experiments to systematically understand how densification and processing of solid electrolyte influences filament formation. The work reveals that the density of pores does not correlated with failure. Instead, the periodicity, size and arrangement of pores is a driver for failure in amorphous solid electrolytes absent of grain boundaries.

Strength-ductility synergy of a laser welded 7085Al matrix nanocomposite joint: Interaction between ZrB2, Al3(Er, Zr) nanoparticles and MgZn2 precipitates

The dissolution and coarsening of precipitates during welding thermal cycle weakened mechanical properties of 7xxx Al alloy joints. In this work, ZrB2 ceramic nanoparticles and core-shell structured Al3(Er, Zr) (L12) with high thermal stability were introduced to synergistically enhance the mechanical property of laser welded 7085Al nanocomposite joint, and the interaction between ZrB2, Al3(Er, Zr) nanoparticles and MgZn2 precipitates was analyzed. The results showed that grain boundaries were covered by fine precipitates with discrete distribution under the action of ZrB2 and Al3(Er, Zr). The interface coherency of ZrB2/Al and Al3(Er, Zr)/Al was improved by introducing highly coherent MgZn2 precipitates to form coherent multi-interfaces of ZrB2/MgZn2/Al and Al3(Er, Zr)/MgZn2/Al. The ultimate tensile strength and uniform elongation of ZrB2/7085Al-Er nanocomposite joint were 678.9 MPa and 18.5 %, with a 36.6 % and 55.5 % increase as compared to 7085Al counterpart. The reinforced grain boundary can prevent strain localization here and allow the activation of high density of dislocations within grains. The higher interface coherency could effectively promote the dislocation multiplication and dislocation annihilation, relieving stress concentration at semi-coherent interface caused by dislocation pile-up. Finally, the strength-ductility synergy was achieved in ZrB2/7085Al-Er nanocomposite joint by strengthening grain boundary and tailoring interface structure.

Thermal and compositional fields to maneuver Cu6Sn5 intermetallic growth on (111) nanotwinned copper substrate

The microstructure of the Cu6Sn5 phase plays a pivotal role in the functionality of microbumps utilized in 3D packaging. In this study, we present an experimental methodology aimed at maneuvering the orientation and morphology of Cu6Sn5 grains formed on (111) nanotwinned Cu substrate, achieved through variations in reflow temperatures (260∘C and 300∘C) and initial Cu proportion in solder (ranging from 0 to 3.0 wt%). At 300∘C and lower initial Cu concentrations (0 and 0.7 wt%), irregularly arranged roof-type Cu6Sn5 grains exhibiting a pronounced {21¯1¯0} texture were observed. Conversely, typical scallop-type Cu6Sn5 grains displaying a specific preferential {21¯1¯3} texture were identified at this temperature for Cu concentrations of 1.5 and 3.0 wt% At 260∘C, the scallop-type morphology was solely present at all Cu composition variants. The differing rates of solute controlled intermetallic phase clustering mechanism at altered solubility limits and magnitudes of thermodynamic driving force for different temperatures, can decide the relative loss of interface coherency and subsequently change the preferred orientation direction of evolving interfacial structures. Our findings demonstrate that the precise control over soldering temperature, solder Cu composition, and the microstructure of Cu UBM can enable the attainment of Cu6Sn5 microstructure with a designated orientation and morphology.

Toughness enhancement in TiN/Zr0.37Al0.63N1.09 multilayer films

The hardness and fracture toughness of high-temperature wear-resistant transition metal aluminum nitride multilayer films depend largely on the constituting layer's structure, compositional modulation, morphology, and interface coherency. We present a study on 1-micron thick multilayered films consisting of stacked layers of TiN and Zr0.37Al0.63N1.09, each layer being 10 nm thick. The films were grown using ion-assisted reactive magnetron sputtering on MgO(001) and Si(001) at substrate temperatures ranging from ambient to 900°C. By increasing growth temperature, we found that the ZrAlN layers transition from near amorphous to nanocrystalline wurtzite to decomposed c-ZrN and w-AlN domains. Concurrently, the TiN layers exhibit strong fiber texture, polycrystallinity, and epitaxial growth carried by the ZrN domains. Both hardness and fracture stress, evaluated by nanoindentation and micromechanical tests, increase with temperature from H=24 GPaMgO, 23 GPaSi to 36 GPaMgO, 30 GPaSi, and σFSi= 6.1-7.7 GPa, respectively. An improved fracture toughness of KIC=2.4-2.8 MPa√m is related to different toughening mechanisms for the various microstructures. The difference in hardness between the substrates is related to compressive stress due to the deposition conditions and thermal contraction. The superior fracture stress is attributed to dense multilayers, free from macroscopic defects due to ion-assisted growth. After being deposited at 200°C, the multilayers remained thermally stable when vacuum annealed for 15 hours at 900°C, with no significant change in phase composition or hardness. The improved hardness, toughness, and temperature stability of the otherwise brittle nitrides are promising for industrial applications.

Influence of interfacial dislocation network on strain-rate sensitivity in Ni-based single crystal superalloys

The excellent mechanical properties of Ni-based superalloys rely on their unique two-phase microstructure. Here we probe the influence of interfacial dislocation network on strain-rate sensitivity in Ni-based single crystal superalloys. The interfacial dislocation could generate a weak long-range interaction to the matrix dislocations at low stress, and react with the incoming dislocation to form junctions at high stress. The weak interaction results in the dislocation pile-up around the interphase boundary, while the strong dislocation reaction makes the gradual loss of interface coherency. With the activation energies, we predict the dependence of strain-rate sensitivity on temperature in a regime with two bounds correlated with these two kinds of interactions. The predicted values match well with that measured in experiments at elevated temperatures.

Evolution of residual stress and interface coherency and their impact on deformation mechanisms in Al/Ti multilayers

Evolution of residual stress and interface coherency and their impact on deformation mechanisms in Al/Ti multilayers

Atomistic Understanding of the Coherent Interface Between Lead Iodide Perovskite and Lead Iodide

AbstractMetal halide perovskite semiconductors have shown great performance in solar cells, and including an excess of lead iodide (PbI2) in the thin films, either as mesoscopic particles or embedded domains, often leads to improved solar cell performance. Atomic resolution scanning transmission electron microscope micrographs of formamidinium lead iodide (FAPbI3) perovskite films reveal the FAPbI3:PbI2 interface to be remarkably coherent. It is demonstrated that such interface coherence is achieved by the PbI2 deviating from its common 2H hexagonal phase to form a trigonal 3R polytype through minor shifts in the stacking of the weakly van‐der‐Waals‐bonded layers containing the near‐octahedral units. The exact crystallographic interfacial relationship and lattice misfit are revealed. It is further shown that this 3R polytype of PbI2 has similar X‐ray diffraction (XRD) peaks to that of the perovskite, making XRD‐based quantification of the presence of PbI2 unreliable. Density functional theory demonstrates that this interface does not introduce additional electronic states in the bandgap, making it electronically benign. These findings explain why a slight PbI2 excess during perovskite film growth can help template perovskite crystal growth and passivate interfacial defects, improving solar cell performance.

Understanding In-Situ Programming for Smart Home Automation

Programming a smart home is an iterative process in which users configure and test the automation during the in-situ experience with IoT space. However, current end-user programming mechanisms are primarily preset configurations on GUI and fail to leverage in-situ behaviors and context. This paper proposed in-situ programming (ISP) as a novel programming paradigm for AIoT automation that extensively leverages users' natural in-situ interaction with the smart environment. We built a Wizard-of-Oz system and conducted a user-enactment study to explore users' behavior models in this paradigm. We identified a dynamic programming flow in which participants iteratively configure and confirm through query, control, edit, and test. We especially identified a novel method "snapshot" for automation configuration and a novel method "simulation" for automation testing, in which participants leverage ambient responses and in-situ interaction. Based on our findings, we proposed design spaces on dynamic programming flow, coherency and clarity of interface, and state and scene management to build an ideal in-situ programming experience.

Mechanical properties of an Al10Nb20Ta15Ti30V5Zr20 A2/B2 refractory superalloy and its constituent phases

Refractory superalloys (RSAs) are a new class of high-temperature structural materials consisting of a nanometer-sized mixture of two coherent A2 (disordered BCC) and B2 (ordered) phases. While these RSAs typically exhibit superior mechanical properties at elevated temperatures, they suffer from limited plasticity at lower temperatures, often attributed to the continuous ordered B2 matrix in these two-phase alloys. To knowledgably control the microstructure and mechanical properties of these alloys, the properties of the constitutive phases in RSAs should be known. Currently this information is absent. In the present work, the microstructure and mechanical properties (at 20–1200 °C) of a candidate Al0.5NbTa0.8Ti1.5V0.2Zr RSA and two single-phase alloys, which compositions correspond to the compositions of the A2 and B2 phases in the selected RSA, are reported. Interestingly, and quite unexpectedly, the intrinsic mechanical behavior of the constituent A2 and B2 phases, deciphered for the first time in the present study, revealed that they are softer and substantially more ductile than the parent two-phase RSA. Furthermore, the ordered B2 phase exhibits a deformation twinning mechanism leading to twinning induced plasticity (TWIP) coupled with a low APB energy and activity of 1/2<111> dislocations. These mechanisms are thought to be responsible for the high plasticity of the ordered B2 phase. The results presented here question the current assumption that the ordered B2 phase in these RSAs has limited plasticity and strongly indicate that the nature of the B2/A2 interface boundaries and coherency strengthening play an important role in controlling the mechanical properties of the two-phase RSA.

Effect of heat treatment regime on microstructure and phase evolution of AlMo0.5NbTa0.5TiZr refractory high entropy alloy

This paper reports the effect of heat treatment process on the ensuing microstructure evolution, and hardness variation of a cast and homogenized AlMo0.5NbTa0.5TiZr refractory high-entropy alloy (RHEA). Heat treatments were carried out on the homogenized samples at 1000, 1100, and 1200 °C for 10, 24, and 48 h. It was revealed that the phase decomposition in the alloy took place in a much shorter time than that reported in the literature. The significant tendency of Zr and Ti in respect of separation from the solid solution was found as the main reason for the formation of multi-phase structure and causing thermal instability. The phase decomposition occurred though the formation of Zr-rich needle-like phase constituents and Ti-rich globular ones. The semi-stable Zr-rich phase constituents are believed to form on B2 lamellas, and during their growth, the crystal structure gradually transforms from body-centered cubic (BCC) to a hexagonal close-packed (HCP) configuration. The electron back-scattered diffraction (EBSD) analyses confirmed that the HCP phase fraction increased significantly with increase in annealing temperature and/or time. A remarkable increase of 78% in Vickers hardness was measured for the sample heat treated at 1100 °C for 24 h compared to that of the homogenized state. It turned out that the morphology, size, interface coherency, and volume fraction of the needle-like precipitates played the leading role in influencing the alloy’s hardness. A comprehensive mechanism has been proposed for the phase decomposition of the alloy, based on the microstructure and chemical composition variations.

Break through the strength-ductility trade-off dilemma in aluminum matrix composites via precipitation-assisted interface tailoring

Strength-ductility trade-off is usually an inevitable scenario in most engineering materials, including metal matrix composites (MMCs) where reinforcement particles significantly degrade ductility. The decrease of ductility is mainly attributed to dislocation pile-ups at the high mismatch interface between reinforcement particles and matrix, which can not lead to effective dislocation multiplication and annihilation, finally leading to a low work hardening rate. To address this challenge, herein we propose a precipitation-assisted interface tailoring (PAIT) mechanism to improve the coherency of interface between reinforcement particles and matrix by introducing an interphase (IP). To achieve this PAIT mechanism, we design a manufacturing process combining the conventional casting, friction stir processing (FSP), hot extrusion with heat treatment. A TiB2/Al-Zn-Mg-Cu composite fabricated with this process shows higher strength and ductility, which stand out from most available Al-based materials. In this composite, a Mg(Zn1.5Cu0.5) IP is introduced to improve the coherency and strength of the TiB2/Al interface by transforming the high mismatch TiB2/Al interface into the low mismatch TiB2/IP/Al multi-interfaces (i.e. sandwich structure). This effectively promotes dislocation multiplication and subsequent dislocation annihilation to increase the work hardening rate by restricting the dislocation pile-ups surrounding the interface, thus leading to a higher ductility. Our study aims to overcome the strength-ductility trade-off of MMCs by tailoring interface structure, which can provide insight into the production of high-performance MMCs.

Tuning the Carrier Transfer Behavior of Coaxial ZnO/ZnS/ZnIn2 S4 Nanorods with a Coherent Lattice Heterojunction Structure for Photoelectrochemical Water Oxidation.

Serious degradation and the short photogenerated carrier lifetime for the wide-bandgap semiconductor ZnO have become prominent issues that negatively affect photoelectrochemical (PEC) water splitting. Herein, a novel electron transport pathway was constructed by simple but effective coaxial growth of ZnO/ZnS/ZnIn2 S4 heterostructure nanoarrays to increase the carrier separation efficiency. This new photoanode fulfilled the requirements of both favorable band alignment and stability, achieving a stable photocurrent density of 1.146 mA cm-2 at 1.2 VRHE , which was approximately twice that of pristine ZnO. Detailed experimental studies revealed that the improved PEC activity was due to the lattice-matching interface coherency that activated the carrier transport pathway, giving rise to an optimized interfacial electronic structure for promoted charge separation by the built-in electric field and strengthened water oxidation activity. This design may provide a new approach to fabricating various efficient lattice-matching coherent interface photoanodes for PEC water splitting.

Определение когерентности интерфейса твердорастворной и интерметаллидной фазыв монокристаллических литейных сплавах на основе интерметаллида Ni3Al рентгенодифрактометрическим методом

The paper considers splitting of the solid solution gamma phase diffraction peaks in the nickel heat-resistant alloys, including alloys based on the Ni3Al intermetallic compound with the heterophase structure. It is shown that the effect of splitting the solid solution gamma phase diffraction peaks is missing in the alloys based on the Ni3Al intermetallic compound with heterophase structure, in contrast to the nickel heat-resistant alloys. It was established that splitting of the solid solution gamma phase diffraction peaks in the diffraction pattern was caused by tetragonal distortion of the gamma phase crystal lattice (solid solution) exposed to the interphase stresses. Only under condition of the interphase boundary coherence exposed to the interfacial stresses the tetragonal distortion of the gamma phase crystal lattice (solid solution) appeared. Therefore, a conclusion could be made based on the absence of splitting the gamma phase diffraction peaks that the interphase boundary (interface) coherence was missing in alloys based on the Ni3Al intermetallic compound with the heterophase structure.

Precipitation and coarsening kinetics of H-phase in NiTiHf high temperature shape memory alloy

Precipitate hardening is the most easiest and effective way to enhance strain recovery properties in NiTiHf high-temperature shape memory alloys. This paper discusses the precipitation, coarsening and age hardening of H-phase precipitates in Ni50Ti30Hf20 alloy during isothermal aging at temperatures between 450 °C and 650 °C for time to 75 h. The H-phase mean size and volume fraction were determined using transmission electron microscopy. Precipitation kinetics was analyzed using the Johnson-Mehl-Avrami-Kolmogorov equation and an Arrhenius type law. From these analyses, a Time-Temperature-Transformation diagram was constructed. The evolution of H-phase size suggests classical matrix diffusion limited Lifshitz-Slyozov-Wagner coarsening for all considered temperatures. The coarsening rate constants of H-phase precipitation have been determined using a modified coarsening rate equation for non-dilute solutions. Critical size of H-phase precipitates for breaking down the precipitate/matrix interface coherency was estimated through a combination of age hardening and precipitate size evolution data. Moreover, time-temperature-hardness diagram was constructed from the precipitation and coarsening kinetics and age hardening of H-phase precipitates in Ni50Ti30Hf20 alloy.

Atomistic mechanisms underlying plasticity and crack growth in ceramics: a case study of AlN/TiN superlattices

Interfaces between components of a material govern its mechanical strength and fracture resistance. While a great number of interfaces is present in nanolayered materials, such as superlattices, their fundamental role during mechanical loading lacks understanding. Here we combine ab initio and classical molecular dynamics simulations, nanoindentation, and transmission electron microscopy to reveal atomistic mechanisms underlying plasticity and crack growth in B1 AlN(001)/TiN(001) superlattices under loading. The system is a model for modern refractory ceramics used as protective coatings. The simulations demonstrate an anisotropic response to uniaxial tensile deformation in principal crystallographic directions due to different strain-activated plastic deformation mechanisms. Superlattices strained orthogonal to (001) interfaces show modest plasticity and cleave parallel to AlN/TiN layers. Contrarily, B1-to-B3 or B1-to-B4(Bk) phase transformations in AlN facilitate a remarkable toughness enhancement upon in-plane [110] and [100] tensile elongation, respectively. We verify the predictions experimentally and conclude that strain-induced crack growth—via loss of interface coherency, dislocation-pinning at interfaces, or layer interpenetration followed by formation of slip bands—can be hindered by controlling the thicknesses of the superlattice nanolayered components.

Interfacial engineering of lattice coherency at ZnO-ZnS photocatalytic heterojunctions

Heterogeneous semiconductor interfaces with built-in electric fields are central to promoting directional carrier migration and separation for charge-induced redox reactions. Unfortunately, most heterointerfaces are structurally incoherent due to large lattice mismatch accompanied with multiple dangling bonds, imposing high energy barriers for charge transport. Here, we report the atomic engineering of ZnO-ZnS heterogeneous interfaces, transforming from incoherent characters to semi-coherent counterparts through annealing-induced spontaneous assembly of ZnS nanoparticles on single-crystalline ZnO nanowires, which is substantiated by aberration-corrected scanning transmission electron microscopy. Theoretical calculations reveal that semi-coherent interfaces are beneficial in annihilating deep local gap states and thus, remarkably reducing carrier transport barrier height by 1.25 eV. This contributes to a 5.8-fold enhanced photocatalytic hydrogen production rate with an improved stability. The study provides physical insights into interfacial lattice engineering of photocatalytic heterojunctions and offers a convenient strategy to convert incoherent interfaces to photocatalytically favorable semi-coherent phase boundaries for solar energy utilization. • The coherency of ZnO-ZnS interfaces was atomically engineered by thermal annealing • Creation of semi-coherent interfaces by grain rotation facilitates carrier transfer • Semi-coherent interfaces endow the composites with enhanced photocatalytic property Interfacial interaction in heterogeneous systems has a profound effect on photocatalytic performance. However, the intrinsic phase boundaries between two dissimilar photocatalytic materials are more prone to establish randomly incoherent interfaces containing multiple dangling bonds, due to the large discrepancy in their lattice parameters. This work opens up a convenient scenario to convert incoherent interfaces into plane-matched semi-coherent counterparts through annealing-induced grain rotation. These lattice-matching semi-coherent interfaces are conducive to annihilating deep gap states, resulting in a substantially reduced barrier height for carrier transport, which contributes to strengthened photocatalytic property and improved photostability. Overall, our report provides a practical paradigm for the atomic engineering of interface coherency of advanced photocatalysts, opening a promising avenue for the construction of heterojunctions. The incoherent ZnO-ZnS photocatalytic heterojunctions could be atomically engineered into semi-coherent phase boundaries by the spontaneous assembly of ZnS nanoparticles on ZnO nanowires via a convenient annealing strategy. The lattice-matching interface coherency reduces carrier transport barrier height by removing interfacial dangling bonds, giving rise to optimized interfacial electronic structure for promoted charge separation and strengthened photocatalytic activity.

Investigation into novel multipass friction stir vibration brazing of carbon steels

ABSTRACT In this examination, an advanced version of friction stir brazing (FSB) entitled friction stir vibration brazing (FSVB) was implemented to produce a joint between low carbon steels. %67 wt Sn-%33 wt Pb alloy was used as brazing metal. This article aims to study the effect of mechanical vibration and brazing pass number on the structure and mechanical behaviors of the brazed samples. In addition, the thermal analysis, the characteristics of intermetallic compounds (IMCs) layers, and void volume percentage at the bond interface were investigated. It was found that the coherency of the joint interface increased as the brazing pass number increased. Additionally, the mechanical performance, namely, shear strength and hardness of brazed samples enhanced as the vibration was applied during FSB, and brazing was done in two passes. The results showed that the metallurgical reaction between the parent metal and the filler enhanced as FSB was replaced by FSVB. Two passes of FSVB decreased the thickness of the IMC layer, void volume percentage, and the formation of micro-cracks in the brazed sample.

Effect of grain orientation and interface coherency on the hydrogen trapping ability of TiC precipitates in a ferritic steel

The way of capturing hydrogen has always been the focus of research in steels. Through the in-situ SKPFM study, a great Volta potential difference has been found between the TiC precipitates (∼0.82 μm) and the matrix after hydrogen charging, especially at the phase interface, which is demonstrated as an effective hydrogen trapping site. Moreover, the TiC carbides precipitated in the ferrite (111) plane show a higher average potential increase than that in the (110) plane. The difference of hydrogen trapping ability can be attributed to the deviation of Baker-Nutting orientation relationship of the precipitate/matrix interface, since the interface coherency on the (111) plane is destroyed more severely due to a lower Schmid factor of (111) orientation during the coiling process.

Carrier Localization by a Quantum Dot in a Quantum Well

We show that a self-organized quantum dot (QD) embedded in a quantum well (QW) can provide better carrier localization compared to the bare QD due to a complex action of three processes, namely, an increase in the QD volume, a change of the QD aspect ratio, and strain redistribution provided by the QW. For an $\mathrm{In}\mathrm{As}$ QD and an ($\mathrm{In}$,$\mathrm{Ga}$)As QW, we calculate the possible energy benefits of these three contributions and examine the optimal dot-in-well configuration sustaining the interface coherency.

Temperature dependence of precipitation mechanism of intragranular χ phase in super duplex stainless steel S32750

Two types of precipitation mechanisms of intragranular χ phase were investigated using scanning electron microscopy (SEM) and high resolution transmission electron microscopy (HRTEM) in super duplex stainless steel S32750 at different aging temperatures. Results showed that lenticular χ phase homogeneously nucleated within ferrite grains after aging at 650 °C. On the other hand, Cr2N provided heterogeneous nucleation sites for intragranular χ phase when aging at 800 °C, and displayed a granular morphology. The lenticular and granular χ phase have different interface coherency and orientation relationships with ferrite matrix, respectively. The difference in driving force for nucleation of χ phase at different temperatures was responsible for the different precipitation mechanisms.