The interface resistance between cathode and electrolyte in solid oxide fuel cell is the crucial factor for the performance. Although the cathode of (La, Sr) MnO3 (LSM) creates a stable interface with yttria stabilized zirconia (YSZ) electrolyte, the chemical activity of LSM is lower than that of (La, Sr) CoO3 (LSC) or (La, Sr)(Co, Fe)O3 (LSCF). However, at the interface between YSZ and LSC (YSZ/LSC) or YSZ and LSCF (YSZ/LSCF), SrZrO3 and/or La2Zr2O7 are produced, which show high resistance. Therefore, CeO2 material is inserted to the interface as intermediated. However, this insertion of CeO2 material also creates solid layer of (Ce,Zr)O2, which shows high resistance. Therefore, comprehending the oxygen ion conduction phenomena at the interface is important for reducing the resistance.Regarding the structure of membrane and interface, by applying the current nano-engineering technology, the thickness of membrane can be reduced to nanoscale and the interface structure can be manipulated in nanoscale. In other words, if the oxygen ion conduction mechanism is clarified in nanoscale by using molecular dynamics (MD) method, the interface resistance can be reduced based the clarified mechanism and the nano-engineering technology.Therefore, this study performed MD simulations of dual-phase (DP) solid oxide membrane, which consists of fluorite and perovskite structures to elucidate the oxygen ion conduction mechanism at the interface. We constructed MD simulation model of DP membrane including grain boundary (GB) as the interface. The constructed DP membrane model is consistent of fluorite electrolyte (YSZ, GDC) and perovskite cathode (LSM, LSC, LSCF). The GB between the different structure was constructed corresponding oxygen ion position in each membrane by rotating 45° (see the image). The buckingham potential with coulomb potential was applied to the interatomic interactions. Pressure was controlled at 0.1 MPa during the simulations. The dopant and oxygen vacancies were randomly introduced to the DP membrane. The diffusion coefficient of oxygen ion was computed as the indicator of conduction property by changing the membrane temperature. The temperature conditions were 1500, 1650, 1800, 2000 K. At each temperature conditions, MD simulations were performed on five different initial configurations and those results were analyzed.As results, the diffusion coefficient f oxygen ion in DP membrane is lower than that in single phase (SP) membrane. Moreover, the activation energy for diffusion is larger than that in SP membrane. From detailed analysis of diffusivity by dividing the simulation system into tiny regions, the diffusivity of oxygen reduces in the vicinity of GB. From these results, we confirmed that the reduction of diffusivity due to GB is the reason of decreases in diffusion coefficient. In addition, the excess energy produced by introducing GB was computed. The results showed that the energy of cations in DP membrane increases due to GB, while the energy of oxygen ion decreases. These results indicates that the cations in the vicinity of GB produces high potential energy filed around the GB. Hence the diffusivity of oxygen ion reduces in the vicinity of GB and the oxygen ion is hard to across the GB. Consequently, the diffusion coefficient f oxygen ion in DP membrane is lower than that in single phase membrane. Figure 1

Perovskite solar cells have witnessed remarkable progress in recent years, yet several pivotal factors persistently impede their widespread commercial adoption. Among these, the behavior of excess lead iodide (PbI2) during perovskite synthesis is particularly concerning. Excess PbI2 that promotes perovskite growth will accumulate at grain boundaries during annealing, which restricts the device performance and hinders its long-term applicability. In this work, an innovative pretreatment strategy is developed by depositing the Cs3ErCl6 quantum dots (QDs) on the perovskite film during annealing, which is different from the traditional post-treatment strategy by depositing QDs after annealing. It is evident that PbI2 can react with Cs3ErCl6 QDs, enabling its secondary utilization and promoting the secondary growth of perovskite in the vicinity of grain boundaries to inhibit the formation of excess PbI2. The pretreated perovskite layer has a betterfit grain, resulting in higher power conversion efficiency (PCE) and better stability of the device. The (FAPbI3) 0.95(MAPbBr3) 0.05 perovskite solar cell treated using the pretreatment method demonstrates a champion PCE of 26.01%. This work offers new perspectives for inhibiting excessive PbI2 growth and thus holds great promise for advancing the commercial viability of perovskite solar cells and contributing to the future landscape of renewable energy.

Historically seen as a limitation, grain boundaries (GBs) within polycrystalline metal halide perovskite (MHP) films are thought to impede charge transport, adversely impacting the efficiency of perovskite solar cells (PSCs). In this study, we employ home-built confocal photoluminescence microscopy, combined with photocurrent detection modules, to directly visualize the carrier dynamics in the MHP film of PSCs under real operating conditions. Our findings suggest that GBs in high-efficiency PSCs function as carrier transport channels, where a notable enhancement in photocurrent is observed. Femtosecond transient absorption and Kelvin probe force microscopy measurements further validate the existence of a built-in electric field in the vicinity of GBs, offering additional driving force for charge separation and establishing channels for swift carrier transport along the GBs, thereby expediting subsequent charge collection processes. This study elucidates the pivotal role of GBs in operational PSCs and provides valuable insights for the fabrication of high-efficiency PSCs.

Studies have shown that the corrosion resistance of stainless steels in passive environments is enhanced by grain refinement into the order of submicron or nanoscale via various methods, including severe plastic deformation (SPD). This beneficial effect has been attributed to the enhanced protective nature of the passive film due to a greater Cr enrichment in the film. Two independent mechanisms for the greater Cr enrichment in passive films have been proposed: enhanced selective dissolution of Fe and faster Cr diffusion. Both mechanisms originate from high density grain boundaries. However, recent studies have used high-resolution scanning transmission or in-situ atomic force microscopy to visualize the near atomic-scale passivation process and suggest that the increased protectiveness of passive films caused by the Cr enrichment is limited to a zone in the vicinity of grain boundaries. This finding suggests that both these mechanisms, facilitated by grain refinement, might be capable of the homogeneous passive film formation over the entire surface if the grain size is extremely small (＜100 nm), which most classical SPD methods, represented here by equal channel angular pressing, cannot achieve. Therefore, for the formation of a uniform and homogeneous passive film inside all the grains, the role of factors other than that of grain size might be involved. A fresh review of the literature on the corrosion behavior of ultrafine grained (UFG) stainless steels with grain size smaller than 1 μm and nanocrystalline ones smaller than 100 nm, generated by classical SPD, surface SPD, and other physical methods, was undertaken in light of the uniformity of the passive film. The possible role of high internal stress and residual dislocations, which are common constituents of UFG materials obtained by SPD, on the formation of the protective passive film was discussed.

In a quest to vet UNS S32205 as a potential structural material to serve moderate-to-high temperature operations of NPP auxiliary components, the DL-EPR test was exploited. A bifronted scheme comprised of 650 and 850 °C discrete treatments intended to explore progressive eutectoid decomposition and degree-of-sensitization (DoS) scenarios was adopted. The nuance witnessed with yet another dual approach—the Cihal- and image processing (IP)-normalized signal landscape—was rationalized through its attribution to culprit microstructures. This was sought, inter alia, in the vicinity of grain boundaries and σ-phase inclusions by virtue of postmortem FESEM, STEM-EDX, HRTEM SAED and XRD ascertainment. Discernable reactivation-kinetics resurgence was believed to mark the onset of deleterious σ-phase dissolution. This only came into fruition with longer ageing times (8–17 h) at 650 °C and succumbed to prematurely (1 h), and at DC biases more cathodic than −0.25 VAg/AgCl with the 850 °C counterpart. Opportune corroboration was offered in ir/ia breakaway for the respective conditions, which was unveiled to be particularly pre-emptive (5 h) with IP- vs. Cihal-normalized peers (8 h) related to the 650 °C condition. Meanwhile, the 850 °C condition endured a similar surge after as little as 1 h of ageing across the board, which hints at concomitant sigma-phase culpability.

Grain boundaries are widely recognized as line defect sinks. During reactor operation, vacancies and fission gas atoms within UO2 fuel grains migrate to the grain boundaries, forming bubbles at these locations. In order to better understand the effect of grain boundaries on the migration of fission gas atoms, this study employed a phase-field model to simulate the nucleation and growth process of fission gas bubbles within the UO2 fuel grains and in the vicinity of grain boundaries. This study also investigated the degree to which grain boundaries affect fission gas atoms under different temperature conditions. The results indicated that in models containing grain boundaries, the nucleation of fission gas bubbles occurred earlier, as compared to models without grain boundaries. A noticeable bubble denuded zone was also observed adjacent to grain boundary interfaces. Furthermore, with increasing temperature, the bubble denuded zone becomes thicker. The effects of irradiation, vacancy diffusion, Ostwald ripening, as well as grain boundary trapping were discussed.

To investigate the effect of the microstructure adjacent to the grain boundaries on the mechanical properties and hydrogen embrittlement susceptibilities in the Al–Cu base 2219 alloy, alloy specimens were solution-treated and then aged at 100°C, 130°C, and the usual aging temperature of 190°C, to control the alloy microstructure in the vicinity of grain boundaries. The slow strain rate technique was conducted on the specimens in humid air and dry nitrogen gas environments to evaluate the effect of environmental hydrogen on them. Transmission electron microscopy was used to measure the grain boundary precipitate size and precipitate-free zone width of the specimens. Thermal desorption analysis was conducted on the gauge sections of the fractured specimens to evaluate the trapping sites and amount of hydrogen desorbed. The specimens aged below 190°C had finer grain boundary precipitates than those aged at 190°C. The test environment did not affect the specimen strength under any of the aging conditions 100°C, 130°C, and 190°C. Some samples had intergranular fractures on their entire fracture surfaces, irrespective of the test environment. The thermal desorption analysis results showed no significant difference between the hydrogen emission spectrum and the amount of hydrogen released within each temperature range. Thus, hydrogen embrittlement does not occur in the 2219 alloy, irrespective of the characteristics of its microstructure adjacent to the grain boundaries.

Controllable precipitation behavior near grain boundaries enabled by artificial strain concentration in age-hardening aluminum alloys

Fracture mode transition from intergranular to transgranular in (TiZrNbTaCr)C: The grain boundary purification effect of Cr carbide

In this study, the 2024 Al powder with different weight fractions of graphite is mechanically milled using a high-energy ball mill for 3 hours each in the nitrogen environment. The milled powder is compacted at an elevated temperature. X-ray diffraction is used to phase analysis of milled powder as well as compacted specimens. Optical microscopy is used for microstructural analysis and hardness measurements are done for the evaluation of mechanical properties. The hot compacted specimens are also tested for their wear properties. Results show that there is no new phase formed during mechanical milling. But, after hot compaction of the milled powder, Al2Cu formed due to precipitation. No reaction is observed between the aluminum and the carbon (graphite) after milling as well as hot compaction. Microstructures of all hot compacted specimens are not showing pores, which, signifies full density after compaction. The formation of Al4C3 is not observed at any stage of processing. Therefore, graphite is uniformly distributed in all specimens, and the same is observed at grain boundaries of α-Al grains in the microstructures. Hardness increases with the addition of 1 wt.% graphite but it decreases with a further increase in graphite. The wear resistance of 2024 Al with 1 wt% graphite is the highest among all the compositions. The high hardness and wear resistance of 2024Al with 1 wt% graphite is the consequence of precipitation of Al2Cu during hot compaction and the presence of graphite which creates hindrances in the metal matrix. The presence of free graphite in the vicinity of grain boundaries acts as a solid lubricant which improves wear resistance of 2024 Al.

The casting of metal alloys followed by hot forging is a widely used manufacturing technology to produce a homogeneous microstructure. The combination of mechanical and thermal energy envisages the microstructural properties of metal alloys. In the present investigation, a metal alloy of composition 0.05C-1.52Cu-1.51Mn (in weight %) was cast in an induction furnace using a zirconia crucible. The melt pool was monitored using optical emission spectroscopy (OES) to maintain the desired composition. The as-cast block was then subjected to forging under a pneumatic hammer of 0.5 t capacity so that any casting defects were eliminated. The as-cast block was reheated to a temperature of 1050 °C and held at that temperature for 6 h to homogenize, followed by hammering with a 50% strain using a pneumatic hammer. The microhardness was calculated using a Vickers microhardness testing apparatus. The microstructure characterization of the processed alloy was carried out using an optical microscope, electron backscattered diffraction (EBSD), energy-dispersive X-ray spectroscopy (EDXA), and a transmission electron microscope (TEM). The sample for optical microscopy was cut using a diamond cutter grinding machine and surface polishing was carried out using emery paper. Further, mechanical polishing was performed to prepare the samples for EBSD using a TEGRAPOL polishing machine. The EBSD apparatus was operated at a 20 kV accelerating voltage, 25 mm from the gun, and with a 60 µ aperture size. HKL Technology Channel 5 Software was used for the post-processing of EBSD maps. The procedure of standard polishing for OES and TEM sample preparation was followed. Recrystallization envisages equiaxed grain formation in hot forging; hence, the strain-free grains were observed in the strained matrix. The lower distribution of recrystallized grains indicated that the driving force for recrystallization was not abundant enough to generate a fully recrystallized microstructure. The fractional distribution of the misorientation angle between 15 and 60° confirms the formation of grain boundaries (having a misorientation angle greater than 15°) and dislocations/subgrain/substructures (having a misorientation angle less than 15°). The fraction of misorientation angle distribution was higher between the angles 0.5 and 6.5°; afterwards, it decreased for higher angles. The substructure was observed in the vicinity of grain boundaries. The softening process released certain strains, but still, the dislocation was observed to be deposited mostly in the vicinity of grain boundaries and at the grain interior. The fine precipitates of the microalloying element copper were observed in the range of size in nanometers. However, the densities of these precipitates were limited and most of these precipitates were deposited at the grain interior. The microhardness of 210.8 Hv and mean subgrain size of 1.61 µ were observed the enhanced microhardness was due to the limited recrystallized grains and accumulation of dislocations/subgrain/substructures.

Inhibiting segregation enabled outstanding combination of mechanical and corrosion properties in precipitation-strengthened aluminum alloys

Room temperature deformation mechanisms of a Fe–Mn–Al–C steel

Temperature damping capacity and microstructure evolution of Mg–Al–Zn–Sn alloy

Molecular dynamic study of oxygen ion diffusion and grain boundary in SrSc0.1Co0.9O3-δ perovskite solid oxide membrane

Enhanced strength and ductility in sand-cast Al-Li-Cu-Mg-Zr alloy via synergistic microalloying with Sc and Ti

Machine learning-enabled identification of micromechanical stress and strain hotspots predicted via dislocation density-based crystal plasticity simulations

Unsupervised clustering of nanoindentation data for microstructural reconstruction: Challenges in phase discrimination

Within the emerging field of proton-conducting fuel cells, BaZr0.9Y0.1O3-δ (BZY10) is an attractive material due to its high conductivity and stability. The fundamentals of conduction in sintered pellets and thin films heterostructures have been explored in several studies; however, the role of crystallographic orientation, grains, and grain boundaries is poorly understood for proton conduction. This article reports proton conduction in a self-assembled multi-oriented BZY10 thin film grown on top of a (110) NdGaO3 substrate. The multiple orientations are composed of different lattices, which provide a platform to study the lattice-dependent conductivity through different orientations in the vicinity of grain boundary between them and the substrate. The crystalline stacking of each orientation is confirmed by X-ray diffraction analysis and scanning transmission electron microscopy. The transport measurements are carried out under different gas atmospheres. The highest conductivity of 3.08 × 10-3 S cm-1 at 400 °C is found under a wet H2 environment together with an increased lattice parameter of 4.208 Å, while under O2 and Ar environments, the film shows lower conductivity and lattice parameter. Our findings not only demonstrate the role of crystal lattice for conduction properties but also illustrate the importance of self-assembled strategies to achieve high proton conduction in BZY10 thin films.

Anisotropy in cyclic behavior and fatigue crack growth of IN718 processed by laser powder bed fusion