Diffusion Of Atoms Research Articles

Laser shock-enabled optical–thermal–mechanical coupled welding method for silver nanowires

Silver nanowires (AgNWs) are recognized as highly promising materials for flexible and transparent electrode applications. However, existing material-processing methods fail to achieve uniform and reliable AgNWs junctions. In this study, we propose a new method using the laser shock effect combined with the laser heating effect, for creating AgNW junctions within thin films. We explored the welding mechanism of AgNWs through optic-thermal welding, laser shock-enabled mechanical welding, and laser-shock-enabled optical-thermal-mechanical (LS-OTM) experiments, as well as numerical simulations, and the results demonstrate that the innovative mechanism of the LS-OTM process lies in its utilization of laser shock to adjust the gap between the nanowire junctions, which in turn achieves a fine control of the thermal effect of the heating laser localised surface plasmon resonance, and the atomic diffusion in the solid state at intermediate temperature under the action of the impact force is the mechanism of the formation of high-quality junctions. We prepared flexible transparent conductive films and studied their transmittance, conductivity, and thermal properties, the results show that the flexible transparent conductive films prepared by LS-OTM welding method have excellent transmittance, conductivity, and thermal properties, this verifies the feasibility and effectiveness of this processing strategy. The LS-OTM method is a viable solution for manufacturing transparent, conductive films from AgNWs for emerging applications such as flexible heated films, flexible displays, and wearable medical devices.

Plasma activated titanium-based bonding for robust and reliable Si–Si and Si-glass integration

The exceptional biocompatibility of Ti/Ti bonding technology makes it highly significant for the sealing of implantable devices. However, achieving highly reliable Ti/Ti bonding at low temperatures is challenging due to the facile formation of a native oxide film, which hinders the diffusion of interfacial atoms. This paper develops a low-temperature Ti/Ti bonding process based on plasma activation, resulting in a remarkable bonding strength of 17.5 MPa at 300 °C, which can be used for Si–Si homogeneous and Si-glass heterogeneous integration. After optimizing the processes, the surface oxides of Ti can be partially reduced through Ar/H2 plasma activation to form unsaturated chemical bonds, thereby overcoming the limitation of film thickness in Ti/Ti bonding. The results indicate that plasma activation can realize high strength Ti/Ti bonding in the film thickness range of 10–50 nm. It is worth noting that the Ti/Ti bonding area and strength remain stable after immersion experiments in DI water and normal saline for 7 days, which proves that Ti/Ti bonding has good corrosion resistance. In addition, the microcavity structures were prepared using photolithography and etching techniques. The Ti/Ti bonding technology enables direct bonding of microcavity structures with plate Ti, and an intact bonding interface near the microcavity was obtained. This low-temperature Ti/Ti bonding technology is suitable for the three-dimensional integration of various substrate materials, and its excellent corrosion resistance makes it promising for application in the sealing of BioMEMS.

Grain size prediction for stainless steel fabricated by material extrusion additive manufacturing

Most traditional powder melting-based additive manufacturing (AM) technologies generally yield high-performance parts at the expense of additional cost and energy consumption. As an economical and efficient alternative method, material extrusion (ME) that deploys polymer-based filaments with highly filled metal particles offers the possibility of scalable, low-cost fabrication of metal components. As a critical step, sintering governs the mechanical strength and geometry of the final parts. The grain growth behavior induced during sintering should be well controlled to achieve the parts with the desired mechanical performance. Due to the nature of AM, grain growth kinetics could also involve extremely complex grain boundary migration and atomic diffusion mechanisms caused by the heterogeneous pore distribution. In this work, an analytical model was developed to predict and understand the grain growth behavior of stainless steel (SS) 316L built by ME-based sintering-assisted AM. Such a model accounts for anisotropic viscosity parameters calibrated through a three-dimensional dilatometry test, enabling the prediction of grain size evolution during sintering. Grain growth kinetic parameters were further identified by the grain size data at the heating and holding stages. To validate and generalize the model, we also conducted the grain size evolution prediction under different sintering temperature profiles for as-built SS 316L specimens. This work will provide scientific insights into the grain growth behavior of metal parts built by this AM technique and its understanding can be readily transferred to other sintering-assisted AM processes like binder jetting and ink writing for metal structure creation.

Comparative studies on microstructural characteristics and wear behavior of high-speed and low-speed laser cladding graphene/CoCrFeMo0.5NiTi0.5 high-entropy alloy composite layers

To prevent the failure of curved parts due to wear under actual working conditions, a graphene/CoCrFeMo0.5NiTi0.5 high-entropy alloy composite coating was prepared on the surface of a curved part using both high-speed and low-speed laser cladding (LLC). The surface morphology, physical phases, elemental distribution, microstructure, microhardness, and wear behavior of this coating applied via high-speed and LLC were comparatively studied. The results showed that the maximum height difference on the surface of the high-speed laser cladding (HLC) layer was only 44.7 % of that of the LLC layer, and the surface powder was more completely melted. The average microhardness of the HLC layer was about 1.49 times higher than that of the LLC layer and showed a maximum hardness of 666.38 HV0.5, which was about 2.95 times higher than that of the substrate. The internal microstructure of the HLC layer was finer and the diffusion of Fe atoms from the substrate into the coating was significantly reduced. In all three wear environments, abrasive wear occurred in both the low-speed and HLC layers. The total wear rate of the LLC layer was 230.588 μm3 N−1 mm−1, which was about 3.06 times higher than that of the HLC layer (75.395 μm3 N−1 mm−1). The wear surfaces of both cladding layers were oxidized, and the wear rate increased with the oxygen content on the wear surfaces under the same wear conditions. Meanwhile, the oxygen content of the wear surfaces of both cladding layers in sodium chloride solution was significantly higher than that during dry wear.

Effect of Grain Structure of Gold Plating Layer on Environmental Reliability of Sintered Ag-Au Joints.

Gold-plated substrate is widely used in sintering with silver paste because of its high conductivity, stability, and corrosion resistance. However, due to massive interdiffusion between Ag and Au atoms, it is challenging for sintered Ag-Au joints to maintain high reliability. In order to study the effect of grain structure of gold plating layer on the environmental reliability of sintered Ag-Au joints, we prepared four substrates with different gold structures. In addition to the original gold structure (Au substrate), other gold structures were obtained by heat treatment at temperatures of 150 °C (Au-150 substrate), 250 °C (Au-250 substrate), and 350 °C (Au-350 substrate) for 1 h. Compared with the other three gold substrates, the sinter jointed on the Au-350 substrate obtained the highest shear strength. By analyzing the grain structure of the gold plating layer, it is found that the average grain size of the Au-350 substrate is the largest, and the proportion of low-angle grain boundaries is less. Few grain boundaries have a positive impact on inhibiting the excessive diffusion of Ag atoms and improving the bonding performance of the joint. Based on the above study, we further evaluated the environmental reliability of sintered joints. In 150 °C high-thermal storage, the interdiffusion of Ag and Au in the sintered joint on the Au-350 substrate was restricted, retaining stronger bonding until 200 h. In a hygrothermal environment of 85 °C/85% RH, the shear strength of the sintered Ag-Au joint with the Au-350 substrate maintained above 40.2 MPa during 100 h aging. The results indicated that the sintered Ag-Au joint on the Au-350 substrate with the largest grain size has superior high thermal reliability and hygrothermal reliability.

Enhanced Electrical Properties of Bi2−xSbxTe3 Nanoflake Thin Films Through Interface Engineering

The structure–property relationship at interfaces is difficult to probe for thermoelectric materials with a complex interfacial microstructure. Designing thermoelectric materials with a simple, structurally‐uniform interface provides a facile way to understand how these interfaces influence the transport properties. Here, we synthesized Bi2−xSbxTe3 (x = 0, 0.1, 0.2, 0.4) nanoflakes using a hydrothermal method, and prepared Bi2−xSbxTe3 thin films with predominantly (0001) interfaces by stacking the nanoflakes through spin coating. The influence of the annealing temperature and Sb content on the (0001) interface structure was systematically investigated at atomic scale using aberration‐corrected scanning transmission electron microscopy. Annealing and Sb doping facilitate atom diffusion and migration between adjacent nanoflakes along the (0001) interface. As such it enhances interfacial connectivity and improves the electrical transport properties. Interfac reactions create new interfaces that increase the scattering and the Seebeck coefficient. Due to the simultaneous optimization of electrical conductivity and Seebeck coefficient, the maximum power factor of the Bi1.8Sb0.2Te3 nanoflake films reaches 1.72 mW m−1 K−2, which is 43% higher than that of a pure Bi2Te3 thin film.

The nucleation and growth mechanism of solid-state amorphization and diffusion behavior at the W–Cu interface

The W–Cu materials hold vast potential for applications in electronic information, nuclear energy, and aerospace sectors. Here, we report a new occurrence of solid-state amorphization on the Cu side near W–Cu interface. A potential function with accuracy close to density functional theory (DFT) is constructed using machine learning, while the atomic mechanism of solid amorphous nucleation and growth is unveiled through a combination of in-situ transmission electron microscopy (TEM) and molecular dynamics (MD) simulations. Our findings indicate that the Cu near W–Cu interface experiences an amorphous phase transition at 400 °C. This amorphous nucleation is linked to the stress coupling between the W–Cu interface and dislocations within Cu. The lattice distortion arising from dislocations, combined with interfacial stress, results in lattice twisting, leading to the formation of dislocation pileup, HCP and disordered structures. The results of the in-situ TEM show that the dislocation stacking and HCP structures exist for a short period of time, and these structures quickly turn into disordered structures, eventually forming an amorphous band with a width of about 8 nm at the W–Cu interface. However, the amorphous structure is unstable. As temperature rises, the amorphous structure undergoes recrystallization into an ordered structure. Furthermore, we investigated the atomic diffusion behavior of W–Cu. Simulation results reveal that the defect in W significantly impacts diffusion. In summary, our study provides theoretical support for the nucleation mechanism of solid-state amorphization, the understanding of interfacial stress-strain, and the application of W–Cu materials.

Pressureless sintered high-entropy transition metal diboride ceramics doped with yttrium tetraboride

High entropy diborides (HEBs) are new candidates of ultra-high temperature ceramics. However, it is difficult to obtain dense HEB ceramics via pressureless sintering. In this study, yttrium tetraboride (YB4) was introduced to consolidate (Ti0.25Zr0.25Hf0.25Ta0.25)B2 (4TMB2) ceramics and its effects on the microstructures and mechanical properties were studied. YB4 addition facilitates the densification and grain elongation of 4TMB2 ceramics by forming eutectic liquid phases and eliminating oxide impurities. Relative density of 4TMB2 ceramics containing 5 vol% YB4 reaches to 94.4 % after pressureless sintered at 2000 °C for 3 h. The hardness and toughness determined by indention method are 26.9±1.5 GPa and 5.73±1.65 MPa∙m1/2. This ceramics also exhibit excellent four-point bending creep resistance with the strain rate of 1.48×10−7 s−1 at 1900 °C under 20 MPa. The observed creep behavior is attributed to grain boundary sliding, plastic deformation, grain refinement and enhanced atomic diffusion of Y element, all driven by high-temperature stresses.

Luminescence-Monitored Progressive Chemical Pressure Implementation Realized through Successive Y3+ and Mg2+ Doping into Ca10.5(PO4)7:Eu2.

Chemical pressure generated through ion doping into crystal lattices has been proven to be conducive to exploration of new matter, development of novel functionalities, and realization of unprecedented performances. However, studies are focusing on one-time doping, and there is a lack of both advanced investigations for multiple doping and sophisticated strategies to precisely and quantitatively track the gradual functionality evolution along with progressive chemical pressure implementation. Herein, high-valent Y3+ and equal-valent Mg2+ is successively doped to replace multiple Ca sites in Ca10.5(PO4)7:Eu2+. The luminescence evolution of Eu2+ serves as an optical probe, allowing step-by-step and atomic-level tracking of the site occupation of Y3+ and Mg2+, interassociation of Ca sites, and ultimately functionality improvement. The resulting Ca8MgY(PO4)7:Eu2+ displays a record-high relative sensitivity for optical thermometry. Utilization of the environment-sensitive emission of Eu2+ as a luminescent probe has offered a unique approach to monitoring structure-functionality evolution in vivo with atomic precision, which shall also be extended to optimization of other functionalities such as ferroelectricity, conductivity, thermoelectricity, and catalytic activity through precise control over atomic diffusion in other types of substances.

Enhancement in interfacial bonding quality of CoCrFeMnNi high-entropy alloy vacuum hot-compression bonding via surface shot peening

Vacuum hot-compression bonding (VHCB) is an advanced solid-state bonding technique. To expand its application in high-entropy alloys (HEAs), a new strategy to enhance the interfacial bonding quality of CoCrFeMnNi HEA VHCB joints by surface shot peening (SP) was proposed, and the effects of SP treatment on the interfacial bonding behavior and mechanical properties of VHCB joints were investigated. The results revealed that SP treatment introduced a nanocrystalline layer and plastic deformation layer with non-uniform strain on the specimen bonding surface, and a hierarchical grain size gradient fine microstructure was formed by a static recrystallization process under the thermal activation condition before VHCB. During the bonding process, the fine microstructure of the SP-treated layer was retained and provided a large number of grain boundaries and dislocations, which facilitated atomic diffusion and plastic flow in the interfacial region and promoted the closure of interfacial voids and the dissolution of interfacial oxide particles. Additionally, interfacial crystallographic and tensile test analyses indicated that the SP treatment induced a multiple interfacial grain boundary (IGB) migration mechanism in the VHCB joints, which dramatically improved the IGB migration level and ultimately led to a complete recovery of the mechanical properties of the CoCrFeMnNi HEA VHCB joints.

Atomistic Simulation Study of Grain Boundary Segregation and Grain Boundary Migration in Ni-Cr Alloys

Using Molecular Dynamics (MD) and Monte Carlo (MC) simulations, we studied the grain boundary (GB) segregation under different temperatures and Cr concentrations in Ni-Cr alloys with two distinct grain-boundary structures, i.e., Σ5(310)[010] and Σ101(200)[100]. Temperature plays a minor influence on Cr segregation for Σ5(310)[010] GB, but Cr segregation rapidly diminishes with elevating temperatures for Σ101(200)[100] GB. We also used the synthetic driving force and corresponding identification methods to investigate the effect of Cr solute segregation on grain boundary stability. All Σ5(310)[010] models have multi-stage grain boundary migration at 800 K. In the first stage, the grain boundary’s slow acceleration time is related to solute concentration. The migration temperature can influence this phenomenon. As temperatures rise, the duration of this slow acceleration phase diminishes. No similar phenomenon was observed in the process of the grain boundary movement of Σ101(200)[100]. The influence of solute concentration on grain boundary migration is complicated. The segregation concentration at the grain boundary cannot be regarded as the only factor affecting the migration of the grain boundary because the Cr atom on the grain boundary does not move with the grain boundary. This work will also discuss the grain boundary migration‘s relationship with lattice distortion and grain boundary atom diffusion. The results and findings of this study provide further insights into the segregation-increase GB stabilization of NC Ni-Cr alloys.

α-Graphyne nanotubes as a promising material for Li-ion battery anodes

Developing high storage capacity of lithium-ion batteries (LIBs) by applying novel anodes based on nanostructures has been allocated to extensive research. Although, SP2-hybrid carbon nanostructures exhibit a low storage capacity, a two-dimensional (2D) graphyne (Gy) monolayer is proved to be an efficient electrode material due to its large surface area and significant mechanical and chemical properties. Herein, a derivative of Gy called α-graphyne nanotube (αGyNT) is proposed as the anode material of LIBs, in which the adsorption of lithium (Li) on Gy nanobelt (GyNB) (one-segment) and short open-ended GyNTs with different lengths are modeled by implementing of ab initio first-principles calculations. Lithium diffusion behaviors inside and outside of GyNTs has been investigated by ab initio molecular dynamics (ABMD) to calculate open-circuit voltage. The results reveal that Li adsorption energies of short αGyNTs have no regular oscillatory dependence on the number of segments along the tube axis (length of the tubes). Furthermore, the largest storage capacity of C4Li4 (1273.75 mAh/g) was obtained for (4, 4) αGyNTs, which demonstrate better storage capacity compared to single/multiple graphyne nanostructures. The curvature of αGyNTs can enhance the diffusion of Li atoms and leads to promote storage capacities, which suggest these anode materials improve LIBs's performance.

Reconstructing brittle hydrides using pulsed electric current to restore the degraded performance of zirconium alloys

When zirconium alloy undergoes water corrosion reaction during the service process, it absorbs hydrogen to form brittle hydrides, which is one of the main reasons for the deterioration of the mechanical properties of zirconium alloy. There is an urgent need to find an effective method to regulate brittle hydrides to restore the properties of hydrogen-containing zirconium alloys. This study conducted electropulsing treatment on the hydrogen-charged nuclear grade Zr-4 alloy, and the results showed that the electropulsing process caused the hydrides to transform from large-sized brittle stripe-shaped δ-phase to the small-sized ζ-phase. The hydrogen content in the alloy is significantly reduced, which basically restores the mechanical properties of the alloy. However, in the comparative experiment of isothermal heat treatment at 400 °C, brittle hydrides did not dissolve and their mechanical properties did not recover. A mathematical model was established for the characteristics and morphological changes of strip hydrides, and the current density distribution and introduced free energy during the microstructure evolution process were calculated and analyzed. The calculation results indicate that the pulsed current promotes the decomposition of hydrides through the introduction of free energy, reduces the activation energy of hydrogen atom diffusion, accelerates the diffusion and desorption of hydrogen atoms, and realizes the repair of mechanical properties of hydrogen-charged zirconium alloy.

Effect of the Post‐Annealing Temperature on the Interfacial Reaction Between a High TC Superconductor and Topological Insulator

AbstractThis work reports the formation of a heterojunction composed of Tl2Ba2CaCu2O8 (Tl‐2212) and Bi2Se3 as the high critical temperature superconductor and topological insulator, respectively. The Bi2Se3 film is deposited on the Tl‐2212 by a chemical mechanical polishing process. Due to the rough surface of Tl‐2212, the treated Tl‐2212 is then subjected to post‐annealing at various temperatures. This temperature does not affect the formation of the interfacial layer at the heterojunction; however, an improved layered crystal structure of the Bi2Se3 film is observed at 500 °C. The in‐depth profile of the relative atomic concentration indicates the diffusion of Cu and Tl into the Bi2Se3 film with the Ba diffusion being closer to the interfacial layer. At 500 °C, Cu atoms are more actively diffused into the Bi2Se3 film, thus blocking Tl diffusion, and improving the layered crystal structure of the film. The density functional theory calculations reveal that the lowest formation energy of the Cu vacancy is when Bi2Se3 is in contact with Tl‐2212, which results in the diffusion of Cu atoms from Tl‐2212, thus transforming the interstitial Cu atoms into the film. These atoms have an n‐type doping effect and prefer intercalating at a vdW gap deep inside the layered Bi2Se3.

An unblocked Li transport pathway for all-solid-state batteries enabled by boosting bulk diffusion kinetic and interfacial ion conduction

The high interfacial resistance and dendrite growth associated with the high Li concentration gradient at the Li/solid-state electrolytes (SSEs) interface significantly hinder the cycle life of solid-state lithium metal batteries (SSLMBs). This limitation is primarily attributed to the slow diffusion of Li atoms in the bulk and the sluggish conduction of Li ions at the interface. Merely focusing on enhancing either aspect is typically not sufficient to fully address this challenge. Herein, we utilize AgNO3 molten salt to in-situ generate LixAg anode and nitrided interphase to simultaneously boost the bulk Li atom diffusion kinetics and the interfacial ion conduction, effectively constructing a fast-continuous ion/atom transport pathway and significantly reducing the concentration gradient of Li. The in-situ formed LixAg alloy, with a Li diffusion coefficient of approximately 10−8 cm2 s−1, demonstrates a diffusion rate three orders of magnitude higher than bulk Li (∼ 10−11 cm2 s−1), alleviating vacancy accumulation and contact loss at the anode/SSE interface. While the in-situ formed ionic conductive nitrided interphase promotes ion transport through the interface to reduce the Li concentration gradient and boost charge transfer kinetics. Benefiting from the high Li ion/atom transport rate in both bulk and interface, ultrahigh critical current density/areal capacity (1.2 mA cm−2;1.2 mAh cm−2) and cyclability (1.0 mA cm−2;0.5 mAh cm−2) are achieved for solid-state Li||Li symmetric cells. Impressively, an SSLMB assembled with a LiFePO4 electrode shows excellent cycling stability for as long as 1600 cycles at 0.5 C with a high capacity retention of 82.6 %.

A promising strategy of multicomponent alloy intermedium for enhancing the mechanical performance of inertia friction welding joints of Inconel 718 alloys

A strategy of using multicomponent alloy (MCA) intermedium for inertia friction welding of IN718 alloys was proposed in this work. Exceptional metallurgic bonding was attained between the IN718 and non-equiatomic CoCrNi–AlTa MCA layer, and the as-received weld joint was absent of any defects like micro-cracks or voids. Compared with the counterpart without an intermedium layer (∼530 MPa), the yield strength of the IN718-MCA weld joint was increased to ∼610 MPa. Moreover, by conducting a two-step ageing treatment, the yield strength of the weld joint was further improved to over 1360 MPa with prominent strain hardening behavior. Noteworthily, the fracture along the interface boundary between the two materials initially observed in the unaged weld joint was fully eliminated, indicating that the ageing treatment efficiently improved the bonding of the interfacial region and further enhanced the reliability of the weld zone. Moreover, the significant strengthening effect of the aged dissimilar weld joint was found to originate from the enhanced atomic diffusion and extra back-stress hardening from geometric necessary dislocations (GNDs) produced within the interfacial regions, as well as the high density of nano-sized dispersive precipitates (for IN718) and ordered structures (for MCA) generated in the alloy matrix at elevated temperatures. The result verifies that the present strategy of adding an MCA intermedium layer can efficiently improve the mechanical performance of the weld joint for IN718 alloys, which is promising for real applications in aerospace engineering.

Phase-change heterostructure with HfTe2 confinement sublayers for enhanced thermal efficiency and low-power operation through Joule heating localization

Although phase-change random-access memory (PCRAM) is a promising next-generation nonvolatile memory technology, challenges remain in terms of reducing energy consumption. This is primarily because the high thermal conductivities of phase-change materials (PCMs) promote Joule heating dissipation. Repeated phase transitions also induce long-range atomic diffusion, limiting the durability. To address these challenges, phase-change heterostructure (PCH) devices that incorporate confinement sublayers based on transition-metal dichalcogenide materials have been developed. In this study, we engineered a PCH device by integrating HfTe2, which has low thermal conductivity and excellent stability, into the PCM to realize PCRAM with enhanced thermal efficiency and structural stability. HEAT simulations were conducted to validate the superior heat confinement in the programming region of the HfTe2-based PCH device. Moreover, electrical measurements of the device demonstrated its outstanding performance, which was characterized by a low RESET current (∼1.6 mA), stable two-order ON/OFF ratio, and exceptional cycling endurance (∼2 × 107). The structural integrity of the HfTe2 confinement sublayer was confirmed using X-ray photoelectron spectroscopy and transmission electron microscopy. The material properties, including electrical conductivity, cohesive energy, and electronegativity, substantiated these findings. Collectively, these results revealed that the HfTe2-based PCH device can achieve significant improvements in performance and reliability compared with conventional PCRAM devices.

Water-assisted oxidative redispersion of Cu particles through formation of Cu hydroxide at room temperature

Sintering of active metal species often happens during catalytic reactions, which requires redispersion in a reactive atmosphere at elevated temperatures to recover the activity. Herein, we report a simple method to redisperse sintered Cu catalysts via O2-H2O treatment at room temperature. In-situ spectroscopic characterizations reveal that H2O induces the formation of hydroxylated Cu species in humid O2, pushing surface diffusion of Cu atoms at room temperature. Further, surface OH groups formed on most hydroxylable support surfaces such as γ-Al2O3, SiO2, and CeO2 in the humid atmosphere help to pull the mobile Cu species and enhance Cu redispersion. Both pushing and pulling effects of gaseous H2O promote the structural transformation of Cu aggregates into highly dispersed Cu species at room temperature, which exhibit enhanced activity in reverse water gas shift and preferential oxidation of carbon monoxide reactions. These findings highlight the important role of H2O in the dynamic structure evolution of supported metal nanocatalysts and lay the foundation for the regeneration of sintered catalysts under mild conditions.

Accelerated structural ordering during liquid metal dealloying and its effect on thermal coarsening of nanoporous refractory alloys

Nanoporous non-noble metals with attractive properties can be fabricated by liquid metal dealloying (LMD). However, further refinement of the ligament size of nanoporous metals produced by LMD is desired because this high-temperature process induces rapid ligament coarsening. Herein, we fabricate nanoporous refractory metals and alloys by LMD. The molybdenum (Mo)-tantalum (Ta) alloy with the smallest ligament size of the specimens contains a B2 ordered structure, whereas the other specimens possess disordered structures. It is proposed that the B2 ordering of the Mo-Ta alloy suppresses ligament coarsening by restricting the surface diffusion of atoms during LMD. The Mo-Ta alloy with B2 ordered structure exists in a previously inaccessible low-temperature region of the related phase diagram, illustrating that LMD can enable access to new materials. Our results indicate that materials with refined ligaments may be obtained by LMD promoting the formation of ordered structures.

Hydrogen diffusion dynamics on [formula omitted] surface: A mechanism of hydrogen-induced failure

Hydrogen-induced failure (embrittlement as the primary source) is a significant concern for retrofitting existing pipelines to transport hydrogen. One of the major factors associated with hydrogen embrittlement of metals is hydrogen diffusion. Therefore, understanding the modes and dynamics of hydrogen diffusion into metals is critical for understanding better and acting to limit hydrogen-induced damage to metals. It is well established that transition metals catalyze the dissociation of molecular hydrogen into atomic hydrogen even at room temperature. The atomic hydrogen diffuses through the metal surface, and this causes degradation. Understanding atomic hydrogen diffusion dynamics is critical to reducing hydrogen embrittlement. This work presents atomic hydrogen diffusion dynamics along and into Fe(100) surfaces. The results indicated that diffusion of atomic hydrogen along the surface is favored over surface-to-subsurface diffusion. Once hydrogen diffuses to the subsurface layer, the barrier for further hydrogen diffusion into the subsequent layers is relatively lower. The methodology presented here of atomic hydrogen diffusion under dynamic relaxation into metal surface can be used to study the effect of the metal's chemical composition and structure on the hydrogen diffusion rate. This allows for screening various strategies to reduce hydrogen diffusion into metals and guide the design of degradation prevention strategies.