Diffusion Of Atoms Research Articles

New insights into lamellar and twinning transformations in TiAl/Nb composites with core-shell structure during high temperature annealing

Lamellar and twinning transformations play a crucial role in stabilizing the ordered phases in TiAl based composites for property improvement. In this work, we have systematically investigated the lamellar and twinning transformations in TiAl/Nb composites with core-shell structure and proposed novel insights on γ → α2 and γ → γT processes from an atomistic perspective. The results show that high temperature annealing facilitates the formation of lamellar microstructure including γ + α2 and γT twin lamellae in the vicinity of core/shell interface, due to rapid diffusion of principal atoms followed by atomic shuffling. Specifically, plenty of lenticular γT can nucleate in B2 regime by accidental misalignment of atoms on a 110B2 plane adhering to Kurdjumov-Sachs relationship, and then grow even into α2 lath driven by the release of internal stress via Shockley partial slips on the 111γ plane. The formation of γT mediated by 9R involves γ → 9R and γ ← 9R → γT transformations. Among them, a full period of atomic stacking …ABC|BCA|CAB… (LPSO) can be achieved through three Shockley partials being sequentially activated on the C, A and B atomic layers in the stacking of …ABC|ABC|ABC… (L10) with the total shift of 3δA. Then 9R will change synchronously to γ and γT once the migrating Shockley partials react with Frank partials to yield a full dislocation, i.e., δA + Dδ→DA and δA + δC + δD→BD, which can also be considered as detwinning and twinning behaviors, respectively. Additionally, the transition of bulk γ to α2 or γT lamellae is closely associated with the stacking faults, i.e. whether the activated atomic layer is located at the boundary or periphery of the updated stacking fault region.

Effect of alternating current on the corrosion behavior of Inconel 693 alloy in borosilicate glass

The corrosion behavior of Inconel 693 alloy in borosilicate glass at 1150 °C with different alternating current (AC) densities was investigated. It was found that the samples with AC applied had greater dimensional loss than the samples without AC applied. The corrosion products were all the double-layer film in two cases, with the outer layer of Cr2O3 and the inner layer of Al2O3. In addition, corrosion was more severe with increasing current density. The AC promoted atomic diffusion and induced corrosion holes within the alloy matrix. Besides, the AC enrichment at the tip led to a localized temperature increase that exacerbated the corrosion of the sample coil section based on the simulation results.

Mass Inversion at the Lifshitz Transition in Monolayer Graphene by Diffusive, High-Density, On-Chip Doping.

Experimental setups for charge transport measurements are typically not compatible with the ultrahigh vacuum conditions for chemical doping, limiting the charge carrier density that can be investigated by transport methods. Field-effect methods, including dielectric gating and ionic liquid gating, achieve too low a carrier density to induce electronic phase transitions. To bridge this gap, we developed an integrated flip-chip method to dope graphene by alkali vapor in the diffusive regime, suitable for charge transport measurements at ultrahigh charge carrier density. We introduce a cesium droplet into a sealed cavity filled with inert gas to dope a monolayer graphene sample by the process of cesium atom diffusion, adsorption, and ionization at the graphene surface, with doping beyond an electron density of 4.7 × 1014 cm-2 monitored by operando Hall measurement. The sealed assembly is stable against oxidation, enabling measurement of charge transport versus temperature and magnetic field. Cyclotron mass inversion is observed via the Hall effect, indicative of the change in Fermi surface geometry associated with the Liftshitz transition at the hyperbolic M point of monolayer graphene. The transparent quartz substrate also functions as an optical window, enabling nonresonant Raman scattering. Our findings show that chemical doping, hitherto restricted to ultrahigh vacuum, can be applied in a diffusive regime at ambient pressure in an inert gas environment and thus enable charge transport studies in standard cryogenic environments.

Difference in the structure and morphology of CVD diamond films grown on negatively charged and grounded substrate holders: Optical study

Microcrystalline diamond films were grown by plasma-enhanced chemical vapor deposition from a CH4/H2 gas mixture on Si single-crystalline substrates placed on negatively charged and grounded substrate holders. The obtained diamond films had the (100) predominant faceting of microcrystals. The film structure and morphology were analyzed by scanning electron microscopy, photoluminescence, Raman and FTIR spectroscopies. The main physical factor causing the difference in the structure of the diamond films grown on the grounded and charged substrate holders was found to be the flow of low-energy (up to 200 eV) Si+, N2+, H, O ions in the latter holder. These ions predominantly embedded into the structure of the diamond films grown on the charged substrate holder leading to appearance of residual mechanical stress up to 2 GPa. Ion bombardment led to increase in the volume fraction of non-diamond carbon component in the film grain boundaries, decrease in sp3-bonded carbon fraction and reduction of the diamond microcrystals lateral size. Larger amount of grain boundaries in the diamond films grown on the charged substrate holder promoted diffusion of Si atoms from the substrate to the plasma and growing film surface, inducing formation of SiV centers in the diamond microcrystals even in the 150…200 μm thick films. The concentration of Si-related defects was much smaller in the films grown using the grounded substrate holder. These films had substantially smaller volume fraction of graphite-like carbon in the grain boundaries and were more homogeneous.

Vertically Stacked Amorphous Ir/Ru/Ir Oxide Nanosheets for Boosted Acidic Water Splitting.

Integrating multiple functional components into vertically stacked heterostructures offers a prospective approach to manipulating the physicochemical properties of materials. The synthesis of vertically stacked heterogeneous noble metal oxides remains a challenge. Herein, we report a surface segregation approach to create vertically stacked amorphous Ir/Ru/Ir oxide nanosheets (NSs). Cross-sectional high-angle annular darkfield scanning transmission electron microscopy images demonstrate a three-layer heterostructure in the amorphous Ir/Ru/Ir oxide NSs, with IrOx layers located on the upper and lower surfaces, and a layer of RuOx sandwiched between the two IrOx layers. The vertically stacked heterostructure is a result of the diffusion of Ir atoms from the amorphous IrRuOx solid solution to the surface. The obtained A-Ir/Ru/Ir oxide NSs display an ultralow overpotential of 191 mV at 10 mA cm-2 toward acid oxygen evolution reaction and demonstrate excellent performance in a proton exchange membrane water electrolyzer, which requires only 1.63 V to achieve 1 A cm-2 at 60 °C, with virtually no activity decay observed after a 1300 h test.

Effect of adaptive nanocrystalline behaviors on the cavitation erosion performance of Cu47.5Zr45.1Al7.4 bulk metallic glass

Amorphous alloys have attracted much attention in the field of cavitation erosion (CE) due to their good comprehensive properties. However, due to the special amorphous structures that are difficult to characterize, their micro-response behaviors and damage mechanisms during the CE process have not been well elucidated. In this paper, advanced techniques including focused ion beam (FIB) and transmission electron microscope (TEM) were used to comparatively study the microstructure evolution and volume loss rules of Cu47.5Zr45.1Al7.4 and Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glasses (BMG) under the action of cavitation load and cavitation heat to reveal their CE mechanisms. The results showed that the absence of small atoms in Cu47.5Zr45.1Al7.4 led to a large free volume, thereby compromising its hardness, modulus, and yield strength. However, this also made it more susceptible to shear banding, which in turn enhanced its energy absorption capabilities. Although Cu47.5Zr45.1Al7.4 had a higher glass transition temperature (Tg) and onset temperature of crystallization (Tx), as well as a wider supercooled liquid phase region (ΔTx), its exothermic peak was obviously pronounced and the transformation temperature range was significantly narrower. Therefore, it is more likely to adaptively form Cu-rich nanocrystals under the action of cavitation heat. Additionally, the larger free volume in the shear band was conducive to the diffusion of atoms and the occurrence of adaptive nanocrystallization behaviors in Cu47.5Zr45.1Al7.4. These nanocrystals were able to effectively force crack deflection, thereby dissipating impact energy and delaying the fatigue spallation of the material. Consequently, Cu47.5Zr45.1Al7.4 exhibited a far longer incubation period and a noticeably lower cumulative volume loss.

Effect of ionic liquids on the corrosion behaviour of X80 pipeline steel

The study encompasses the synthesis of an ionic liquid corrosion inhibitor using the ion exchange method. Its impact on the corrosion and hydrogen permeation behaviour of X80 pipeline steel in a CO2 environment is thoroughly investigated. The findings reveal that the corrosion resistance and hydrogen atom diffusion of X80 pipeline steel exhibit an initial decline, followed by an increase with escalating inhibitor concentration. The nadir values are recorded at an inhibitor concentration of 500 mg·L−1, attaining a remarkable maximum inhibition efficiency of 97%. Following the addition of corrosion inhibitors, the formation of corrosion products notably decreases, indicating a positive inhibition effect on both corrosion and hydrogen permeation. Additionally, a correlation is successfully established between hydrogen permeation parameters and inhibitor concentration.

Field-free switching in perpendicular Ta/CoFeB/MgO multilayers achieved by annealing temperature gradient

Current flowing through heavy metals generates spin current by the spin Hall effect (SHE), and spin current exerts a torque on the adjacent magnetic layer, thereby switching the magnetization direction of the magnetic layer. Normally, an external magnetic field must be used to break symmetry in the response to the SHE torque, to realize deterministic switching. However, the presence of magnetic fields increases the difficulty in integrating spintronic devices with complementary metal-oxide-semiconductor. Thus, field-free spin–orbit torque switching has been a research hotspot. Here, symmetry-breaking has been realized by tilting the sample during the annealing process, resulting in a non-uniform diffusion of Ta atoms in the samples along the temperature gradient (x-direction), which was confirmed by transmission electron microscope mapping. As a result, the sample has demonstrated deterministic switching, in the absence of an external magnetic field, with a switching ratio of up to 88% and the critical current density of 1.5 × 107 A/cm2. Tilting annealing is a simple approach to achieve field-free switching.

Unveiling the oxidation mechanism of CrTaTiMo refractory medium-entropy alloys: A synergy of density functional theory and ab initio molecular dynamics

The demand for advanced materials capable of withstanding extreme high-temperature conditions has led to the development of novel High-Entropy Alloys (HEAs). Recent works indicate that forming a CrTaO4 protection layer gives HEAs excellent long-term oxidation resistance. In this study, the high-temperature oxidation resistance properties of CrTaTiMo Refractory Medium-Entropy Alloys (RMEAs) were assessed by Density Functional Theory (DFT) and ab initio Molecular Dynamics (AIMD). Through the oxygen adsorption and diffusion calculations, we demonstrated the preferential oxygen adsorption sequence on the surface of the RMEA as Ti, Ta, Cr, and Mo. Furthermore, our analysis identified the sites featuring Ta as subsurface atoms were the weakest locations for oxygen atom diffusion. The dynamic oxidation mechanism of oxygen molecules on CrTaTiMo RMEA was investigated by AIMD simulations. The results confirmed that the adsorption and dissociation of O2 molecules on the alloy surface. Additionally, the diffusion of the O atom took place at temperatures greater than 873 K and confirmed the O-attracting feature of Ta atoms. Moreover, electronic structure calculations confirmed the bonding of oxygen atoms with those four metal elements. This study could serve as a valuable reference for the strategic development of the CrTaTiMo-based RMEAs or RHEAs for high-temperature, long-term oxidation resistance applications.

Fast Li Replenishment Channels-Assisted Recycling of Degraded Layered Cathodes with Enhanced Cycling Performance and Thermal Stability.

The direct recycling of cathode materials in lithium-ion batteries is important for environmental protection and resource conservation. The key regeneration processes are composition replenishment and atom rearrangement, both of which depend on the migration and diffusion of atoms. However, for the direct recycling of degraded LiNi0.5 Co0.2 Mn0.3 O2 (D-NCM523) cathode, the irreversible phase transitions that accumulate during the long-term cycles block the Li diffusion channels with a high diffusion energy barrier, making it difficult to fully repair the layered structure and resulting in rapid capacity decay. To address the challenge, fast Li replenishment channels are rebuilt to regulate the surface phase and effectively assist the regeneration process with a reduced energy barrier. This method reduces the amount of Li supplement by >75% and shortens the sintering time (only 2h) to fully regenerate D-NCM523, compared to general direct recycling methods. The regenerated NCM523 (LCMB-NCM523) exhibits a satisfactory repaired specific capacity of 160mAhg-1 and excellent cycling stability, retaining 78% of its capacity after 300 cycles. In addition, LCMB-NCM523 is recycled with improved thermal decomposition peak temperature and enables 200 cycles even at 60°C, greatly improving safety. This work proposes a promising way for the large-scale direct regeneration of layered cathodes.

A Study of Electroplated Nanoporous Copper Using Aberration-Corrected Transmission Electron Microscopy.

Nanoporous Cu foam is widely applied in many fields such as the packaging of electronic power devices. In this study, a sandwich-structured Cu-Zn eutectic alloy precursor composed of Cu0.53Zn0.47/Cu5Zn8/Cu0.53Zn0.47 is prepared through electroplating. The surface layer of the precursor, Cu0.53Zn0.47, has a flat surface with numerous grain boundaries, which effectively promotes its dealloying behavior. By contrast, Cu5Zn8 has a porous structure, which promotes the dealloying behavior at the center of the precursor. The dealloying of Cu0.53Zn0.47 is dominated by the coherent surface diffusion of Cu atoms, and the crystal lattice and orientation show no changes before and after dealloying. By contrast, the dealloying behavior of Cu5Zn8 requires the renucleation of Cu crystals; in this process, Cu atoms are transported to the surface of the layer by capillary forces to form clusters, which nucleate and grow.

A Coherent Pd–Pd16B3 Core–Shell Electrocatalyst for Controlled Hydrogenation in Nitrogen Reduction Reaction

AbstractThe manipulation of surface catalytic sites has rarely been explored for metal borides, and the subsurface effects on the electrocatalytic activity of the nitrogen reduction reaction (NRR) remain unknown. Herein, this work develops a core–shell nanoparticle catalyst with a Pd core that ensures high electron transfer rates and an Pd16B3 atomical shell that possess tunable active sites for regulating the NRR. The atomic structural evolution from Pd to Pd16B3 is investigated by precisely controlling the B atom diffusion, molecular rearrangement, and d–sp orbital hybridization. Pd/Pd16B3 core–shell nanocrystals exhibit an exceptional NRR performance with a high NH3 Faradaic efficiency of 30.8%, which is superior to those of pristine Pd (1.2%) and B‐doped Pd (4.8%) under identical conditions, and a yield rate of 0.81 µmol h−1 cm−2. This work discovers that the Pd16B3 shell could promote the NRR selectivity by separating the separating the hydrogen evolution reaction proceeded on hole sites and NRR proceeded on bridge sites, and the Pd core could provide the excellent conductivity to Pd16B3 shell through regulated electron interactions. Consequently, the controlled chemical ordering of palladium boride on palladium surfaces provides insight into the synthesis of advanced NRR electrocatalysts.

Coverage-Dependent Site-Specific Placement and Correlated Diffusion of Atomic Oxygen on Moiré-Patterned Graphene on Ru(0001).

Nano-periodic arrays of atomic oxygen are visualized on epitaxial graphene on Ru(0001) via STM following supersonic beam exposure to non-equilibrium fluxes of atomic oxygen. Self-organization of atomic oxygen on graphene is directed by the intrinsic moiré pattern of the ruthenium-graphene interface. Atom-resolved STM imaging reveals the richness of multiparticle interactions, leading to correlated atomic diffusion and placement. Pair-distribution functions demonstrate that repulsive oxygen-oxygen interactions play an increasingly important role in the site specificity and diffusivity of atomic oxygen on the moiré lattice with increasing coverage. Atomic visualization shows the number of oxygen atoms in a local region changes overall diffusion rates and promotes the correlated motion of oxygen atoms. Understanding the site specificity of oxygen adsorption and diffusive behavior of atomic oxygen on epitaxial graphene on Ru(0001) provides insight for both the synthesis and stability of moiré-templated two-dimensional materials which show promise as platforms for next-generation quantum materials and catalysts.

Deformation Behavior of an Extruded 7075 Aluminum Alloy at Elevated Temperatures.

Hot compression tests were conducted to explore the deformation behavior of an extruded 7075 aluminum alloy bar at elevated temperatures. Specimens with 0°, 45°, and 90° angles along the extrusion direction were prepared. The compression temperatures were 300 and 400 °C, and the strain rates ranged from 0.001 to 0.1 s-1. The corresponding microstructures were characterized via OM and TEM, and the macroscopic texture was tested using XRD. The results indicated that the strength of the 7075 alloy decreases with higher compression temperatures and is in a proportional relationship with respect to the strain rate. During high-temperature compression, it is easier to stimulate atomic diffusion in the matrix, which can improve thermal activation abilities and facilitate dynamic recovery and dynamic recrystallization. In addition, the coarsening of precipitates also contributed to dynamic softening. When compressed at 300 °C, the stress levels of the 0° specimens ranked first, and those for the 45° specimens were the lowest. When compressed at 400 °C, the flow stresses of the specimens along three directions were comparable. The anisotropic mechanical behavior can be explained by the fiber grains and brass {011} <211> texture component. However, higher temperature deformation leads to recrystallization, which can weaken the anisotropy of mechanical properties.

Effect of sodium atom adsorption on the electronic structure of a thin gold film

The effect of sodium adsorption on a gold film deposited on a tungsten substrate was studied. The deposition of Na atoms onto a thin film of gold on tungsten leads to a change in the spectra of the valence band and the core levels of gold and tungsten. An analysis of the spectra showed that the sodium atoms in the surface layer are in a neutral state, and the diffusion of sodium atoms deep into the gold film leads to the formation of the NaxAuy intermetallic compound. Heating a gold film with the formed NaxAuy intermetallic compound at a temperature 640 K leads to partial desorption of sodium and gold atoms from the surface layer of the NaxAuy intermetallic compound.

Fitness-for-Service assessment of a Hydrogen-Induced crack in an inlet gas separator pressure vessel using computational modelling

Hydrogen-induced cracking is the cracking of carbon steel or low-alloy steel in a wet H2S environment, driven by the diffusion of hydrogen atoms into the steel due to corrosion reaction. The formation of blisters and hydrogen-induced cracks in pressurized components in the oil and gas or petrochemical industries imposes a serious risk to personnel safety and production continuity. In this study, a fitness-for-service assessment of a gas separator pressure vessel containing 3.76 % H2S and 3.47 % CO2 was analyzed using finite element analysis as required by level III assessment in API 579–1/ASME FFS-1 2021. Different load scenarios, including internal pressure, static head from liquid, dead weight, and wind loads, were considered using elastic-perfectly plastic stress analysis. The hydrogen-induced affected area, with dimensions of 2650 mm × 900 mm, was shown to sustain an internal pressure of 14.8 MPa, which is above 1.35 times the design pressure (i.e., 12.1 MPa). The assessment of API 579–1/ASME FFS-1 in level I and II failed due to the presence of a hydrogen-induced crack near the weldment. However, the evaluation in level III assessment considered the influence of residual welding stresses on both longitudinal and circumferential cracks in their as-welded state. The findings indicated that the affected area fell within the acceptable region of the failure assessment diagram, thereby confirming the continued safe operation of the HIC damaged pressure vessel while accounting for welding residual stresses.

The role of interlayers in the flash joining of Y2O3 transparent ceramic to titanium alloy

The application of soft metal interlayers in the joining process is an efficient strategy for enhancing the joint strength. In this study, we select the Ni interlayer from among three soft metals, meticulously adjusting various parameters to achieve optimal joint performance. These parameters include the interlayer thickness, temperature, current density and joining time. When the thickness of the Ni interlayer is 600 nm, the Y2O3/Ni/Ti–6Al–4V joint strength reaches a maximum of 65 ± 4 MPa at 900 °C with a current density of 1.5 mA/mm2 for 30 s, improved by 81.6% than Y2O3/Ti–6Al–4V direct flash joining. During the flash joining process, the presence of a threshold electric field induces the formation of oxygen vacancies. These vacancies tend to accumulate at the interface, thereby facilitating rapid material transfer and reaction. Notably, the role of interlayers here is not for traditional stress relieving, but to enhance the metallurgical bonding and promote the defect reaction. Wherein, the latter includes an increase in oxygen vacancies and acceleration of atomic diffusion. Hence, it is anticipated that a wider variety of interlayers will be explored for application in flash joining technologies.

Insight into the influence of Cu6Sn5/Cu micro-interface configuration on growth behavior of Cu-Sn interfacial intermetallic compounds in Sn/Cu solder joint

Herein, the behavior and mechanism of Cu atom diffusing across Cu6Sn5/Cu interface was researched for analyzing the influence of Cu6Sn5/Cu micro-interface configuration on growth behavior of Cu-Sn interfacial intermetallic compounds (IMCs) in Sn/Cu solder joint. The results indicate that, during Cu atoms diffusing across Cu6Sn5 (001)/Cu (110), Cu6Sn5 (110)/Cu (001), Cu6Sn5 (110)/Cu (111) interfaces, VA2→VA3 stage, VA2→VA3 stage and IA→VA1 stage are the decisive stages, respectively. At those diffusion decisive stages, the difference of average Mulliken population between Cu atom at saddle point and initial state with the surrounding atoms for Cu6Sn5 (110)/Cu (111) interface is 0.62, much greater than that for Cu6Sn5 (001)/Cu (110) and Cu6Sn5 (110)/Cu (001) interfaces with average Mulliken population difference of 0.29 and 0.20. Therefore, when Cu atom diffusing across Cu6Sn5 (110)/Cu (111) interface, the magnitude of increase in bonding strength between Cu atoms and the surrounding atoms is the largest, leading that the diffusion rate of Cu atom across Cu6Sn5 (110)/Cu (111) interface is several orders of magnitude smaller than the Cu6Sn5 (001)/Cu (110) and Cu6Sn5 (110)/Cu (001) interfaces. As a result, Cu6Sn5 (110)/Cu (111) interface shows the strongest ability for inhibiting Cu atom diffusion, and has the smallest IMC growth rate.

Spontaneously formed dense Cu nanoislands and superior SERS properties of Cu nanoislands/Cu-Ta-Mo films

The co-sputtering method was utilized for preparing Cu-Ta-Mo films. The results indicate that the micromorphology of Cu-Ta-Mo films depends on the composition and annealing temperature. It is worth that the deposited Cu-Ta-Mo films surface was without nanoislands, and substantial quantities of Cu nanoislands are self-formed on the film's surface after annealing. The analysis indicates that the main reason for the Cu nanoislands formation is phase separation, due to atomic diffusion. Notably, the Cu grains in Ta-Cu-Mo films are surrounded by Ta- and Mo-rich amorphous areas, inhibiting the Cu grains’ growth and leading to the formation of nanoislands. In addition, annealing could promote atomic diffusion, thus facilitating Cu nanoislands’ formation and growth. The size and quantity of nanoislands influence the surface-enhanced Raman scattering (SERS) properties of Cu-Ta-Mo films. Furthermore, covering 10 nm Ag film on Cu nanoislands/Cu-Ta-Mo films’ surface could significantly enhance the SERS property, attributed to a synergistic enhancement of the electric field between Ag film and Cu nanoislands. The Ag film/Cu nanoislands/ Cu-16.34 at% Ta-13.05 at% Mo film applied to SERS substrate has high stability and sensitivity, and the limiting concentration for detecting the Raman characteristic spectra of Rhodamine 6G (R6G) solution can reach 5 × 10−14 M.

Interfacial bonding mechanisms of sintered Cu nanoparticles on different metallization surfaces

Cu nanoparticle sintering bonding is a low-cost die-attach method compared with Ag nanoparticles for power electronic packaging. The joint strength highly depends on the surface metallization of the devices. In present study, the interfacial sintering behavior of copper nanoparticle film (CNF) on different metallizations (Au, Ag, and Cu) was studied. The CNF exhibited a superior shear strength (115 MPa) on Cu substrates when sintered at 250 °C-15 MPa, much higher than that on Ag and Au metallized substrates. The interface connection ratio of bondline-substrate showed the same trend as the shear strength. The neck formation at the bonding interfaces showed no orientation preference. The lateral diffusion of Cu atoms on substrates dominated the sintering bonding, rather than the longitudinal diffusion. The Cu metallization showed much faster lateral diffusion than the Ag and Au metallization, which was confirmed by the neck growth of monolayer nanoparticle sintering and the molecular dynamics (MD) simulation.