Interfacial Nucleation Research Articles

Nucleation Behavior of a Single Al-20Si Particle Rapidly Solidified in a Fast Scanning Calorimeter.

Understanding the rapid solidification behavior characteristics, nucleation undercooling, and nucleation mechanism is important for modifying the microstructures and properties of metal alloys. In order to investigate the rapid solidification behavior in-situ, accurate measurements of nucleation undercooling and cooling rate are required in most rapid solidification processes, e.g., in additive manufacturing (AM). In this study, differential fast scanning calorimetry (DFSC) was applied to investigate the nucleation kinetics in a single micro-sized Al-20Si (mass%) particle under a controlled cooling rate of 5000 K/s. The nucleation rates of primary Si and secondary α-Al phases were calculated by a statistical analysis of 300 identical melting/solidification experiments. Applying a model based on the classical nucleation theory (CNT) together with available thermodynamic data, two different heterogeneous nucleation mechanisms of primary Si and secondary α-Al were proposed, i.e., surface heterogeneous nucleation for primary Si and interface heterogenous nucleation for secondary α-Al. The present study introduces a practical method for a detailed investigation of rapid solidification behavior of metal particles to distinguish surface and interface nucleation.

Density functional theory investigation on the stability, adhesion strength, tensile properties and fracture behavior of γ-Fe/Cu heterogeneous nucleation interface

To theoretically study the stability and the heterogeneous nucleation characteristics of γ-Fe/Cu interface in steel/copper bimetallic, the six surface models and seven interface models were investigated through density functional theory. Besides, the interface stability, adhesion energy, electronic properties, tensile process and fracture behavior of three kinds typical Fe/Cu interface model were calculated by first-principles calculations. Simultaneously, the mechanism on heterogeneous nucleation of pure Fe on Cu-based alloy was revealed. The results indicate that the bramfitt’s lattice mismatches of all the three Fe/Cu interfaces were both 4.11%, and all the Cu surfaces and the Fe surfaces were trends to converge, when the number of layers were 9 and 7, respectively. Among three kinds Fe/Cu interfaces with HCP structure, the Fe (110)/Cu (110) interface shown higher strength of metallic bonds and stable ionic properties. When the strain is 37%, the maximum value of the tensile stress is about 20.3GPa and the electron density between Fe and Cu atoms drop to disappear. The calculated adhesion work of Fe (110)/Cu (110) interface with HCP structure is 1.88 J/m2, is higher than that between Cu/Cu melt (1.78 J/m2), which proved that the Fe particles can promote heterogeneous nucleation of Cu atoms and then account for the grain refinement of Cu-based alloy.

Nitrogen-doped carbonaceous scaffold anchored with cobalt nanoparticles as sulfur host for efficient adsorption and catalytic conversion of polysulfides in lithium-sulfur batteries

The effective inhibition of lithium polysulfides (LiPSs) and promotion of their conversion in the redox processes is indispensable to achieve the long cycle stability and excellent rate performance of lithium-sulfur (Li-S) batteries. Especially, the generally slow electrocatalytic sulfur redox kinetics and large interfacial Li2S nucleation energy barriers have hindered the widespread application of Li-S batteries. Herein, a robust three-dimensional sulfur carrier (denoted as Co-NCNT) is well-constructed using the potassium citrate derived porous carbon sheets as substrate and the catalytic growth nitrogen-doped porous carbon nanotubes as vertical scaffolds. Such a rationally designed structure guarantees efficient electron transfer pathways and ions diffusion channels. More importantly, it is conducive to the adsorption/catalytic conversion of intermediate lithium polysulfides and the nucleation of Li2S. Due to these merits, the S@Co-NCNT cathode achieves an initial discharge capacity up to 1072.7 mAh g−1 at 1.0 C, and it can retain a high capacity of 482.9 mAh g−1 with a capacity attenuation rate of only 0.045% per cycle after 1000 cycles. Upon a high sulfur loading of 5.87 mg cm−2, the S@Co-NCNT electrode can still reach an initial capacity of 739.5 mAh g−1 at 0.3 C. Particular emphasis is that our work broadens the way to prepare well-designed carbonaceous materials sulfur host for long-life Li-S batteries.

Interface Structures and Dislocation Nucleation of Cu/graphene Incoherent Interface Via Molecular Dynamic Simulations

Molecular dynamic simulations have been performed to investigate the effects of Cu {111}/graphene interface structures on the initial dislocation nucleation behavior in Cu/graphene layered composites. The characteristics of interfacial structures, including four possible types of stacking structures, interfacial misfit dislocations and interfacial energy distribution, have been studied based on geometrical analysis Thompson tetrahedron, disregistry analysis and excess potential energy. In addition, interfacial structures are transformed by rotating the graphene layer with various angles, which further changing the morphology of the interface. After relaxation, the equilibrium state of the interface consists of a hexagon unit region arranging in periodicity, which also depicts the periodic energy distribution both on the Cu and graphene side. Under uniaxial X and Y directions loading, the evolution of interface patterns provides a non-Schmid factor for initial interfacial dislocation nucleation which prefer to locate the sites of higher potential energy area. Moreover, the rotation of graphene layer changes the interfacial structures by changing the atoms mismatch on the Cu/graphene interface, which consequently influences the nucleation conditions including sites, morphology and slip system as well. This work provides an understanding on the Cu/graphene interface-dominated dislocation nucleation.

Microstructural Characterizations and Kinetics Model of Isothermal Bainite Formation with the Presence of Prior Martensite in High‐Carbon Nanostructured Bainitic Steel

Quenching and subsequent isothermal bainite transformation (QBT) and direct isothermal transformation (DIT) procedures are performed to comparatively evaluate the impact of the introduced prior martensite on bainite transformation behaviors and microstructural characterizations in a high‐carbon nanostructured bainitic steel. A thermodynamic model under a QBT process based on displacive theory is also developed to expound the bainite formation kinetics. The results indicate that the modified kinetics model, by considering austenite/martensite interface nucleation, austenite grain boundary nucleation, and autocatalytic nucleation, evolved here can be used to accurately describe the bainite formation behavior in the presence of prior martensite. A certain fraction of prior austenite/martensite interface can serve as the preferential nucleation site for the bainite transformation and assist in an acceleration of transformation rate. The bainite nucleation event initially takes place at prior martensite plate boundary in the QBT process instead of austenite grain boundary in the DIT process and subsequently continues through autocatalytic nucleation at austenite/bainite interface generated at either austenite/martensite interface or austenite/austenite interface. The introduced prior martensite slightly refines bainite sheaves and lessens the blocky retained austenite size, presenting a feasible approach to shorten the required time for producing a nanosized bainitic microstructure.

Elucidating the interfacial nucleation of higher-index defect facets in technologically important GaP/Si(0 0 1) by azimuthal angle-resolved polarized Raman spectroscopy

Structural complexities evolving at hetero-polar interface of III-V/Si have been critical obstacles to high-quality and cost-effective epitaxial integration of wide-bandgap GaP on closely lattice-matched Si. Unveiling the nature of interface-originated defect structures is quintessential for efficientintegration of III-V semiconductorson Si. In this work,investigation of surface and interface of technologically important GaP/Si(001)hetero-structuresis presented, through unique implementation of combiningtheinformation onvariation in spatially resolved polarized Raman spectra and surface topography of grown epilayer.The mechanisms responsible for variation in ratio of Raman scattering cross-section of symmetry forbidden to allowed optical phonons of GaP aredelineatedusingazimuthal angle-resolvedpolarizedRaman measurements by allowing for the contribution of energetically favorable higher-index {111} and {112} crystallographic facets, nucleating near the hetero-interface, to light scattering. This is reasserted from polarized Raman spectroscopy performed on cross-sectional surface of GaP/Si(001) hetero-structures.To the best of our knowledge, this is first of it’s kind work wherein angle-dependent polarized Raman measurements are employed for ascertaining the nature and orientations of interfacial defect facets in advanced hetero-structures. Non-invasive and expeditious nature of this optical technique open pathways for fabrication of efficient device structures of III-Vsemiconductors on Si and Geplatforms.

A Calculation Method for the Coupling of Temperature and Concentration during Inconel 718 Alloy Solidification

Due to the temperature and concentration determine the kinetic undercooling of interface growth and nucleation undercooling inside the melt, they play an important role in the solidification microstructure of the alloy. In this paper, the effect of temperature gradient and cooling rate on the dynamic undercooling was studied and the mechanism of the concentration at the solid-liquid interface on the kinetic undercooling during the continuous cooling process was analyzed. A calculation method for the coupling of temperature and concentration during Inconel 718 alloy solidification was developed, which can solve the problem that the concentration and temperature are difficult to be calculated at the same time in the numerical calculation.

Precipitation behavior in boundaries and its influence on impact toughness in 22Cr25Ni3W3CuCoNbN steel during short-term ageing

The 22Cr25Ni3W3CuCoNbN steel is a new kind of heat-resistant steel and is developed as super-heater and reheater materials used in the A-USC boilers at 700 °C. Its impact toughness directly affects the safety of boilers in the process of startup and shutdown. The microstructure evolution and second phase precipitation behavior are accounted for the change of mechanical properties. In the present study, the 22Cr25Ni3W3CuCoNbN steel was aged at 700 °C for up to 1000 h. Using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD), the twin structure evolution and the precipitation of M23C6 carbides on grain boundaries and twin boundaries were analyzed, and their influence on the toughness was discussed. The grain size of the investigated steel was stable and numerous coherent and incoherent twins which were formed during solution heat-treatment still retained after ageing. The M23C6 carbides precipitated on both grain boundaries and twin boundaries. The amount of M23C6 carbides on grain boundaries was higher than that on incoherent boundaries, which in turn was higher than that on coherent boundaries. On grain boundaries, the critical interfacial nucleation energy was the lowest compare to the coherent and incoherent boundaries, thus the nucleation of M23C6 carbides on grain boundaries was the easiest. The M23C6 carbides formed a network on grain boundaries, but precipitated as parallel plates on incoherent boundaries and kept as dispersed particles on coherent boundaries. The impact toughness decreased obviously at the early ageing stage, which is the result of rapid precipitation of M23C6 carbides at grain boundary. The twin structure is beneficial to increase the impact toughness, because the coherent twin can disperse the impact force, and the incoherent twin can reduce the precipitation of M23C6 carbides at grain boundary by promoting the precipitation of M23C6 carbides at the incoherent twin boundary.

Lattice Matching Growth of Conductive Hierarchical Porous MOF/LDH Heteronanotube Arrays for Highly Efficient Water Oxidation.

The conjugation of metal-organic frameworks (MOFs) into different multicomponent materials to precisely construct aligned heterostructures is fascinating but elusive owing to the disparate interfacial energy and nucleation kinetics. Herein, a promising lattice-matching growth strategy is demonstrated for conductive MOF/layered double hydroxide (cMOF/LDH) heteronanotube arrays with highly ordered hierarchical porous structures enabling an ultraefficient oxygen evolution reaction (OER). CoNiFe-LDH nanowires are used as interior template to engineer an interface by inlaying cMOF and matching two crystal lattice systems, thus conducting a graft growth of cMOF/LDH heterostructures along the LDH nanowire. A class of hierarchical porous cMOF/LDH heteronanotube arrays is produced through continuously regulating the transformation degree. The synergistic effects of the cMOF and LDH components significantly promote the chemical and electronic structures of the heteronanotube arrays and their electroactive surface area. Optimized heteronanotube arrays exhibit extraordinary OER activity with ultralow overpotentials of 216 and 227mV to deliver current densities of 50 and 100 mA cm-2 with a small Tafel slope of 34.1 mV dec-1 , ranking it among the best MOF and non-noble-metal-based catalysts for OER. The robust performance under high current density and vigorous gas bubble conditions enable such hierarchical MOF/LDH heteronanotube arrays as promising materials for practical water electrolysis.

The nucleation sequence of α-Al on TiB2 particles in Al-Cu alloys

The refinement of Al alloys by TiB2 has been extensively investigated for decades, both in industry and academia. In order to achieve higher grain refinement potency, it is known that other solutes must be added alongside TiB2, thus tailoring the heterogeneous nucleation at the interface between the TiB2 particles and the Al matrix. Here, we report results from an atomic-scale experimental investigation of the heterogeneous nucleation interface of TiB2 in Al-Cu based alloys as well as in an Al-5Ti-1B grain refiner employed in these Al-Cu based alloys. We focus on the effect of segregation of the main solute elements (Ti, Cu) to the interface of TiB2 and attempt to disentangle this effect from other factors affecting the nucleation and growth. Significant Ti segregation in the form of a Ti-rich layer, identified as an Al3Ti two-dimensional compound, was unambiguously observed on the basal plane of TiB2 particles in the Al-5Ti-1B grain refiner, in agreement with prior literature. In the Al-Cu alloy system, prevalent Ti segregation was also observed on the basal plane of TiB2, accompanied in cases when the Cu concentration is high by the presence of a further atomic-scale Cu-rich layer. Based on these observations, a possible nucleation sequence for the Al-Cu based alloys with the addition of Al-5Ti-1B grain refiner is proposed whereby Al nucleation occurs on an Ti-rich layer on the surface of TiB2, which can then be preserved from a subsequent peritectic transformation by a surrounding eutectic reaction that forms a Cu-rich layer when sufficient Cu is present. This proposed nucleation sequence should help to link the absence or presence of Al3Ti layers on the basal plane of TiB2 to processing conditions in post-solidification studies. Although it is difficult to know with absolute certainty if a TiB2 particle observed in the post-solidification microstructure was active or inactive for heterogeneous nucleation during the solidification process, this experimental study highlights the possible role of Cu segregation on grain refinement of Al-Cu alloys by the Al-5Ti-1B grain refiner.

Fcc vs. hcp competition in colloidal hard-sphere nucleation: on their relative stability, interfacial free energy and nucleation rate

In this work, we provide a detailed computational characterization of the polymorphic crystallization scenario between fcc, hcp and a random stacking mixture of both crystal phases in colloidal hard-spheres.

Kinetics on Formation, Growth and Removal of Alumina Inclusions in Molten Steel

A series of Al deoxidation mechanisms from the nucleation and growth of Al2O3 nuclei immediately after the addition of Al to the growth, agglomeration, and removal of Al2O3 inclusions after the deoxidation equilibrium has been analyzed in light of the kinetics taking into consideration the influences of the interfacial properties on the basis of Al deoxidation experiments of molten steel. The nucleation number density of Al2O3 is (0.72 to 1.62) × 1014 m−3 and increases as the degree of supersaturation increases and the interfacial tension between the nuclei and molten steel decreases. These tendencies can be explained by the homogeneous nucleation theory, and the average interfacial tension, frequency factor, nucleation time, and average nucleation rate are respectively estimated to be 1.43 N·m−1, 4.27 × 1035 m−3·s−1, 0.01 s, and 1.96 × 1016 m−3·s−1 for the nucleation of Al2O3. Al2O3 nuclei rapidly grow to Al2O3 single inclusions having diameters of 2.0 to 2.6 µm through diffusion growth of supersaturated O in molten steel within 2.2 to 3.7 s after the addition of Al, and the molten steel reaches the deoxidation equilibrium. In the subsequent deoxidation equilibrium, the growth rate of Al2O3 single inclusions increases as the O concentration in molten steel increases, and their growth mechanism can be explained by Ostwald ripening. Meanwhile, Al2O3 cluster inclusions grow with the increase in the agglomeration force while agglomerating not only with single inclusions dispersed in molten steel but also with other cluster inclusions existing in the floating paths.

First-principles calculation on γ-Fe/La2O3 interface properties and austenite refinement mechanism by La2O3

In this paper, the interface properties and interfacial interaction were calculated by the first principle method, and the growth of γ-Fe boundary was inhibited by La2O3 so as to refine the austenite grain was also analyzed. The calculated results show that the two-dimensional lattice mismatch between γ-Fe(110) plane and La2O3(001) plane is 8.7%. Therefore, the nucleation interface between γ-Fe and La2O3 is most likely γ-Fe(110)/La2O3(001). Meanwhile, there are three kinds of interface models, which are Fe–La-OT, Fe–La-OM and Fe–La-Bridge, respectively. The interface adhesion work of Fe–La-OT interface is smallest, which is −0.10 J/m2, while, that of Fe–La-OM interface is largest, which is −0.02 J/m2. The ideal interface adhesion work of the three interfaces is negative, which indicates that they cannot be existed stably. The three kinds of interfacial chemical bonds are composed of ionic bonds and metallic bonds. The chemical bond polarity of Fe–La-OT interface is the strongest, and the metallic property of Fe–La-OM interface and Fe–La-Bridge interface is stronger than that of Fe–La-OT one. In addition, most interfacial interaction forces of the three interface models are repulsive, which indicates that La2O3 has a good inhibitory effect on the growth interface of γ-Fe. Therefore, La2O3 can inhibit the growth of γ-Fe boundaries so as to refine the austenite grains.

Phase boundary propagation mode in nano-sized electrode materials evidenced by potentiostatic current transients analysis: Li-rich LiFePO4 case study

Phase boundary propagation dynamics in phase-transforming battery nanomaterials is widely studied due to high practical relevance of the boundary propagation patterns to the rate performance and degradation of metal-ion batteries. In this work, we decipher the complex interplay between the kinetic limitations in the course of phase boundary movement, which can be controlled by slow diffusion, interfacial charge transfer and nucleation. Employing nanosized Li-rich LiFePO4 materials as model systems, we consistently analyze the effect of each of the possible limiting factors on the evolution of potentiostatic current transients’ shape. Our results conclusively demonstrate that under the experimental conditions all three rate-controlling factors contribute to the rate-limitations of an intercalation material. We used numerical modeling to provide illustrative examples of current transients under different limiting regimes, which can be employed for the rapid and accurate diagnostics of the control factors during phase transformations. The derived conclusions allow rationalizing both the phase-transformation pathways in multiparticle electrodes (particle-by-particle or concurrent intercalation) and phase-growth morphologies (intercalation wave or shrinking core) based on easily accessible experimental estimates of kinetic parameters. These results are of high diagnostic value for the development of physically adequate battery models.

Development and validation of a semi-analytical framework for droplet freezing with heterogeneous nucleation and non-linear interface kinetics

We present a novel, semi-analytical framework which accurately predicts every stage of droplet freezing. Supercooling degree of the freezing droplet is computed by coupling the 1-D transient heat conduction equation in spherical coordinates with a modified heterogeneous nucleation model. The coupling connects atomic-scale thermodynamic properties with bulk thermophysical properties and yields interesting insights into the freezing process. The study also develops a novel dendritic growth model for crystal propagation that takes into account the effects of non-linear interface kinetics and surface curvature. This non-equilibrium phase-change formulation during the recalescence stage is coupled with quasi-steady phase change approximation using perturbation series for equilibrium freezing stage to yield an accurate closed form solution of freezing dynamics. The temperature curves, nucleation rates, dendritic growth velocities and mass fraction evolution from the model are validated or verified with the available experimental or numerical data in the literature. The analytical framework developed is a reduced-order freezing model that is fast to compute and yields accurate results. The framework presented can be useful as a subgrid model for high-fidelity crystal growth and spray freezing simulations.

Determining the origin of inclusions in garnet: Challenges and new diagnostic criteria

ABSTRACT Permian metapegmatite garnets from the Koralpe region (Eastern Alps, Austria) contain abundant submicrometer- to micrometer-sized inclusions of rutile, corundum, Fe-Mn phosphate, ilmenite, xenotime, zircon, and apatite. Variations in inclusion abundance, phase assemblage, habit, and size define sector and concentric zones in the garnets, tracing low-indexed garnet facets. Zoning resulted from a process occurring at the garnet-melt interface, homogeneous along each facet, but sensitive to its crystallographic plane. Furthermore, inclusion and host lattices interacted, generating host-inclusion crystallographic orientation relationships (CORs). These phenomena exclude inclusion formation via overgrowth of pre-existing phases, infiltration of fluids/melts, or dissolution-reprecipitation. Magmatic garnet rims contain rutile needles up to 100 μm long, showing an interface-dependent shape-preferred orientation (SPO) that cannot be explained by exsolution models. Furthermore, the COR distribution for needles is unique, and implies large 3D lattice mismatches. These phenomena suggest that needles originated via oriented heterogeneous nucleation at the garnet interface and subsequent simultaneous growth of both phases. The origin of equant inclusions in core domains is less clear. With some assumptions, integrated compositions remain compatible with closed system exsolution or open system precipitation (OSP) involving divalent cation loss. Still, the oriented interface nucleation hypothesis seems to better explain the fact that the frequency of rutile-garnet CORs varies strongly not only between cores and rims but also between garnet core domains. Inclusion formation by oriented interface nucleation and simultaneous growth can explain many observations commonly attributed to exsolution, making distinguishing between these two mechanisms a challenge. We suggest interface-dependence of SPOs and COR frequencies as criteria for identifying inclusion formation via oriented nucleation at an interface and subsequent simultaneous growth.

Bonding pressure effects on characteristics of microstructure, mechanical properties, and mass diffusivity of Ti-6Al-4V and TiAlNb diffusion-bonded joints

This research highlights the influence of bonding pressure on the features of diffusion-bonded joints (DBJs) between Ti6Al4V alloy and TiAlNb alloy investigated at 900 °C for 120 minutes in vacuum with variable pressures of 0.5, 1, 2, 3, and 4 MPa. Characterization of the bonded interfaces was conducted using optical microscopy and scanning electron microscopy in backscattered mode. A molecular dynamics (MD) model was developed with the commercial Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) package utilizing second nearest neighbor modified embedded atom method (2NN MEAM) potentials to predict the diffusion mechanism with variable compressive pressures along the TiAlNb|Ti6Al4V joint interface. Microstructural characterization with light microscopy and scanning electron microscopy in back-scattered mode (SEM-BSE) along the TiAlNb|Ti6Al4V DBJs revealed no interfacial intermetallic phase nucleation. Energy dispersive spectroscopy (EDS) maps and line profiles helped to understand composition variation across the interface. The maximum joint tensile strength of ~ 875 MPa, ~ 13.1% elongation, and mass diffusivity on both sides were obtained at 4 MPa processing pressures with a significant tendency of diffusivity improvement in the TiAlNb side.

The mechanism of the crystalline characteristics of spinel-induced epitaxial growth of diopside in CMAS glass-ceramics

The edge-to-edge matching model (E2EM) is used to predict and analyze the epitaxial growth mechanism of spinel and diopside in CaO-MgO-Al2O3-SiO2 (CMAS) glass-ceramics. At the same time, the prepared glass-ceramics were characterized by X-ray diffraction (XRD) and electron backscatter diffraction (EBSD). It is found that the theoretically predicted phase interface where epitaxial growth can occur is consistent with the conclusion measured by characterization. In the crystallization zone: <1-12 >spinel//<001>diopside (1-11-)spinel at an angle 1.06° (200)diopside, <1-12 >spinel//<101>diopside (311)spinel at an angle 1.26° (1- 31)diopside. Through models and experiments, it was found that spinel with a lattice constant of 7.632–8.597 Å (Fd-3 m) can provide a special nucleation interface for diopside, which can effectively induce the precipitation of diopside. This study provides good theoretical guidance for the preparation of diopside. Meanwhile, the model has strong potential to be used to develop new crystal nucleating agents in glass-ceramics.

Morphology Regulation of Monosodium Urate Monohydrate Crystals via Fabricated Uniform Hydrogel Slices

AbstractCrystal morphology control is a common concern for the crystal engineering and relevant applications. For example, urate crystallization is important for the study of the hyperuricemia induced gout. Herein, biomimetic hydrogel material with uniform surface and vertical structure is fabricated, which possesses hybrid pH‐temperature responsibility for high‐efficiency interfacial nucleation and concentration regulation functions. The developed hydrogel layers are prepared to slice type as a functional microplatform and then added into the uric acid dihydrate (UAD) crystal solution to induce monosodium urate monohydrate (MSUM) crystallization. With different dosage of the hydrogel slices (HGS) in the solution, diverse crystal morphologies can be obtained in an efficient manner, such as “flower,” “sphere,” “sticky spheres,” which entirely distinguishes from the one prepared via no‐HGS. This work explores a new path for revealing the relevant crystallization mechanism and developing crystal morphology control technology with hydrogel interfacial materials.

Effect of Twin Boundary Motion and Dislocation-Twin Interaction on Mechanical Behavior in Fcc Metals.

The interplay of interface and bulk dislocation nucleation and glide in determining the motion of twin boundaries, slip-twin interaction, and the mechanical (i.e., stress-strain) behavior of fcc metals is investigated in the current work with the help of molecular dynamics simulations. To this end, simulation cells containing twin boundaries are subject to loading in different directions relative to the twin boundary orientation. In particular, shear loading of the twin boundary results in significantly different behavior than in the other loading cases, and in particular to jerky stress flow. For example, twin boundary shear loading along results in translational normal twin boundary motion, twinning or detwinning, and net hardening. On the other hand, such loading along results in oscillatory normal twin boundary motion and no hardening. As shown here, this difference results from the different effect each type of loading has on lattice stacking order perpendicular to the twin boundary, and so on interface partial dislocation nucleation. In both cases, however, the observed stress fluctuation and “jerky flow” is due to fast partial dislocation nucleation and glide on the twin boundary. This is supported by the determination of the velocity and energy barriers to glide for twin boundary partials. In particular, twin boundary partial edge dislocations are significantly faster than corresponding screws as well as their bulk counterparts. In the last part of the work, the effect of variable twin boundary orientation in relation to the loading direction is investigated. In particular, a change away from pure normal loading to the twin plane toward mixed shear-normal loading results in a transition of dominant deformation mechanism from bulk dislocation nucleation/slip, to twin boundary motion.