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The current work explores the meso-scale deformation behaviour of an additively manufactured CM247 LC at room and high temperatures. In particular, the study focuses on assessing grain boundary sliding (GBS), which can play a crucial role in the high-temperature deformation of superalloys. Specific samples were produced using the Laser Based Powder Bed Fusion technique (PBF-LB), heat treated and tested under monotonic compression in a Gleeble® system. Compression tests were carried out in a wide temperature range at two strain rates and the effect of testing parameters on GBS activity was studied. A thorough microstructural characterization of the PBF-LB material using EBSD and TEM revealed a γ/γ’ microstructure consisting of columnar grains decorated with Hf-rich MC carbides without any segregations of alloying elements. Qualitative and quantitative analysis of GBS was performed using FEG-SEM and AFM, and contribution of GBS into plastic deformation was estimated. It was demonstrated that GBS is activated at 760 °C. A direct correlation between the contribution of GBS into plastic deformation and testing temperature was found, while strain rate has the opposite effect. The highest GBS contribution (∼32%) was recorded at 1093 °C/10−3 s−1. Finally, intergranular microcracking at triple junctions and along grain boundaries was observed when the material was tested at the highest temperatures (871 °C and 1093 °C). The effect of the temperature and the strain rate on the GBS activity in the PBF-LB material is discussed.

During the γ phase–δ phase transition, U-50Zr fuel experiences spinodal decomposition, which has a significant effect on fuel properties. However, little is known about the spinodal decomposition of U-50Zr. The spinodal decomposition behavior in U-50Zr is studied in this research using the phase-field approach. The mechanism of spinodal decomposition from a thermodynamic perspective is studied, and the effects of temperature and grain boundary (GB) on spinodal decomposition are analyzed. It is found that the concentration of U atoms in the U-rich phase formed during spinodal decomposition is as high as 90%. The U-rich phase first appears at the GB position, and precipitation phases appear inside the grain later. Ostwald ripening occurs when larger precipitation phases on the GB absorb isolated smaller precipitation phases inside the grain. The coarsening rate of precipitation phases and the time it takes for spinodal decomposition to achieve equilibrium are both influenced by temperature.

This study explores the effects of Zn addition through micro-alloying on the microstructure and discharge performance of Mg-Al-Mn-Ca alloy anodes for magnesium-air batteries. The results show that the second-phase particles (d > 1 μm) in a Mg-Al-Mn-Ca alloy promote dynamic recrystallization (DRX) via particle-stimulated nucleation (PSN), resulting in a uniform equiaxed grain structure and fiber texture. In contrast, Zn and Ca co-segregation in a Mg-Al-Mn-Ca-Zn alloy facilitates continuous dynamic recrystallization (CDRX) and, combined with the PSN mechanism, forms a unique structure where three types of grains with different grain boundary densities coexist. The addition of Zn and Ca effectively reduces the c/a axis ratio, promoting texture homogenization. The Mg-Al-Mn-Ca alloy exhibits rough discharge surfaces due to simultaneous discharge at numerous grain boundaries and severe hydrogen evolution corrosion from micro-galvanic effects, inducing the chunk effect (CE). Conversely, the structure where three types of grains with different grain boundary densities coexist in the Mg-Al-Mn-Ca-Zn alloy promotes discharge product detachment through stress cracking, achieving uniform discharge and significantly enhancing discharge performance. The uniform texture reduces hydrogen evolution corrosion, improving anode utilization. This study demonstrates that controlling the microstructure, particularly grain boundary density and grain texture, enables the development of high-performance Mg-Al-Mn-Ca-Zn alloy anodes, especially at higher current densities, offering a new strategy for designing efficient magnesium alloy anode materials.

Catalysts involving post‐transition metals have shown almost invincible performance on generating formate in electrochemical CO2 reduction reaction (CO2RR). Conversely, Cu without post‐transition metals has struggled to achieve comparable activity. In this study, a sulfur (S)‐doped‐copper (Cu)‐based catalyst is developed, exhibiting excellent performance in formate generation with a maximum Faradaic efficiency of 92 % and a partial current density of 321 mA cm−2. Ex situ structural elucidations reveal the presence of abundant grain boundaries and high retention of S−S bonds from the covellite phase during CO2RR. Furthermore, thermodynamic calculations demonstrate that S−S bonds can moderate the binding energies with various intermediates, further improving the activity of the formate pathway. This work is significant in modifying a low‐cost catalyst (Cu) with a non‐metallic element (S) to achieve comparable performance to mainstream catalysts for formate generation in industrial grade. [ABSTRACT FROM AUTHOR]

The presence of excess secondary‐phase PbI2 in perovskite films shows a negative impact on their long‐term stability. Herein, an intermediate phase modification (IPM) strategy is proposed to eliminate residual PbI2 for improved quality of all‐inorganic CsPbI3‐type perovskite films, wherein the extrinsic agent is introduced to address the intermediate phase. By transforming residual PbI2 into a novel 1D perovskite phase, the IPM strategy acts as a patch to suture grain boundaries in the inorganic perovskite films. In addition, the IPM strategy not only enhances the quality of perovskite films but also mitigates energy disorder, reduces trap state density, and prolongs carrier lifetime by expediting the intermediate phase conversion process and passivating surface defects. As such, the perovskite solar cells (PSCs) with a high power conversion efficiency (PCE) of ≈20% and a high fill factor of 83.3% are considered to be very efficient, with excellent shelf stability of 3000 h of exposure in air without any encapsulation. This work not only exhibits a novel optimization route for inorganic perovskite but also emphasizes the crucial role of eliminating residual PbI2 in inorganic perovskites. [ABSTRACT FROM AUTHOR]

Transition metal elements are necessary dopants in ZnO ceramics to improve electrical properties by defects engineering. In the present study, the tweaking effect of MnCO 3 on the intrinsic point defects, i.e., the zinc interstitial and the oxygen vacancy, are investigated to optimize electrical properties of ZnO ceramics. After analyzing microstructure and dielectric response, it was found that Mn2+ was further oxidized to Mn4+ during sintering and Mn4+ solved into ZnO grains and inhibited the formation of the intrinsic point defects. On the other hand, due to the increase of the interface states contributed by Mn separation at grain boundaries, the barrier width broadened to keep charge neutrality. As a result, although the barrier height decreased from 0.68 eV to 0.54 eV as MnCO 3 content increased from 0 mol% to 0.63 mol%, the nonlinear electrical properties were enhanced, that is, the breakdown field increased from 188.47 V/mm to 234.82 V/mm, the nonlinear coefficient increased from 12.87 to 74.76, and the leakage current density decreased from 22.08 μA/cm2 to 0.04 μA/cm2. Combined with the stability during DC aging tests, it is suggested that the optimal content of MnCO 3 is 0.38 mol%. The study also indicates that the barrier width is a sensitive parameter in optimizing electrical properties of ZnO ceramics, instead of the sole focus on higher barrier height. • MnCO 3 is doped in ZnO ceramics to tweak point defects, the zinc interstitial and the oxygen vacancy, and therefore enhance electrical properties, where the optimal content is 0.38 mol%. • Mn2+ can be further oxidized to Mn4+ during sintering and Mn4+ solves into ZnO grains and inhibits the formation of the intrinsic point defects. • Although the barrier height decreases from 0.68 eV to 0.54 eV with increasing MnCO 3 content, electrical properties are enhanced due to the barrier width increasing from 4.50 nm to 11.59 nm. [ABSTRACT FROM AUTHOR]

Even though grain boundaries (GBs) have been previously employed to increase the number of active catalytic sites or tune the binding energies of reaction intermediates for promoting electrocatalytic reactions, the effect of GBs on the tailoring of the local chemical environment on the catalyst surface has not been clarified thus far. In this study, a GBs‐enriched iridium (GB−Ir) was synthesized and examined for the alkaline hydrogen evolution reaction (HER). Operando Raman spectroscopy and density functional theory (DFT) calculations revealed that a local acid‐like environment with H3O+ intermediates was created in the GBs region owing to the electron‐enriched surface Ir atoms at the GBs. The H3O+ intermediates lowered the energy barrier for water dissociation and provided enough hydrogen proton to promote the generation of hydrogen spillover from the sites at the GBs to the sites away from the GBs, thus synergistically enhancing the hydrogen evolution activity. Notably, the GB−Ir catalyst exhibited a high alkaline HER activity (10 mV @ 10 mA cm−2, 20 mV dec−1). We believe that our findings will promote further research on GBs and the surface science of electrochemical reactions. [ABSTRACT FROM AUTHOR]

Some lead‐free complex compounds containing the two perovskite compounds BaTiO3 and Bi0.5Na0.5TiO3 of chemical composition (Ba1–xBix/2Nax/2)TiO3 (x = 0, 0.05, 0.1, 0.15) are fabricated using a cost‐effective mixed oxide method. Synthesis and characterization (electrical, ferroelectric, and optical) of the above‐defined complex ferroelectrics are reported in this article. Analysis of the X‐ray diffraction data/pattern reveals the formation of phase pure compounds with tetragonal symmetry. Determination of particle size is done using the Scherrer formula. A morphology study of sintered (at 1100 °C) pellets indicates that average grain size decreases with an increase in Bi/Na content of Bi0.5Na0.5TiO3. Studies of Fourier transform infrared spectroscopy and ultraviolet–visible–near‐infrared spectroscopy reveal the type of chemical bonds present in the materials. The energy bandgaps of the compounds are found to be suitable for optical device applications. The frequency and temperature dependence of the dielectric study reveals that the dielectric constant increases and loss tangent decreases with an increase in Bi/Na content of Bi0.5Na0.5TiO3. The analysis of the I–V plot and the field‐dependent polarization (P–E hysteresis loop) provide the low leakage current and existence of ferroelectricity at room temperature, respectively. [ABSTRACT FROM AUTHOR]

This paper reviews quantitative characterization via transmission electron microscopy (TEM) and its application to interfacial phenomena based on the results obtained through the studies. Several signals generated by the interaction between the specimen and the electron beam with a probe size of less than 1 nm are utilized for a quantitative analysis, which yields considerable chemical and physical information. This review describes several phenomena near the interfaces, e.g., clear solid–vapor interface (surface) segregation of yttria in the zirconia nanoparticles by an energy-dispersive X-ray spectroscopy analysis, the evaluation of the local magnetic moment at the grain boundary in terms of electron energy loss spectroscopy equipped with TEM, and grain boundary character dependence of the magnetism. The direct measurement of the stress to the dislocation transferred across the grain boundary and the microstructure evolution focused on the grain boundary formation caused by plastic deformation are discussed as examples of material dynamics associated with the grain boundary. Finally, the outlook for future investigations of interface studies, including the recent progress, is also discussed. [ABSTRACT FROM AUTHOR]

The formation of the α-Al2O3 scale on reactive element (RE)-doped FeCrAl alloys is commonly believed to be primarily caused by inward oxygen transport along grain boundaries. However, this study suggests that metal ion outward diffusion also plays a role in the development of the oxide scales and their microstructural characteristics. The study examines the oxidation behavior and grain boundary outward diffusion of iron-chromium alloys containing ~ 10 at% aluminum and ~ 22 at% chromium, doped with an over-critical concentration of REs, i.e., Zr and Hf. All samples were investigated after thermal exposure at 1100 °C by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atom probe tomography (APT). As a result of the overdoping, a considerable increase in oxide growth, an increase in the depth of internal oxidation, and RE-oxide formation near and at oxide grain boundaries (GBs) were observed as a consequence of increased inward and outward diffusion. The effect of overdoping manifests itself differently depending on the RE type and amount due to different solubility, ionic size, and electronic structure of alumina. The sample with Zr retained the adhesion of alumina to the alloy after the first and second thermal exposure, while Hf overdoping resulted in severe spallation after the second thermal exposure. [ABSTRACT FROM AUTHOR]

The Hall-Petch and inverse Hall-Petch behaviors in nanocrystalline ceramics are not well understood because dislocation activities, which are important in metals, are usually limited in these materials. In this study, we use molecular dynamics simulations with a machine-learning force field to investigate the shear deformation behaviors of nanocrystalline Al-doped boron carbide (n -B 12 -CAlC) as the grain size varies. We find a transition from the Hall-Petch to inverse Hall-Petch behavior in n -B 12 -CAlC when the grain size reaches its critical value of 6.09 nm, with a maximum shear strength of 14.93 GPa. Interestingly, mobile dislocation nucleated from grain boundaries (GBs) is activated in n -B 12 -CAlC due to the breakage of weakened C-Al chain bonds, which plays a significant role in its Hall-Petch behaviors. As the grain size decreases, the increasing GB regions homogenize the shear stress, which suppresses dislocation nucleation from GBs and strengthens the material, as observed in the conventional Hall-Petch relationship. However, with a further decrease in the grain size (< ∼ 6 nm), the increasing GB regions provide more favorable sites and a higher possibility for dislocation nucleation, reducing the shear strength and triggering a transition into the inverse Hall-Petch behavior. These findings shed light on deformation behaviors and mechanisms of nanocrystalline ceramics and provide an explanation for the transition from Hall-Petch to inverse Hall-Petch behaviors. [ABSTRACT FROM AUTHOR]

Mass transfer along grain boundaries (GBs) in two kinds of polycrystalline Yb 3 Al 5 O 12 (YbAG) wafers with chemical compositions that deviated slightly in both directions from the stoichiometric composition was investigated at high temperatures by the oxygen permeation technique with 18O 2. Oxygen permeation through both wafers proceeded with mutual diffusion of oxide ions from the higher oxygen partial pressure P O2 (hi) surface side to the lower P O2 (lo) surface side and with the diffusion of ytterbium ions in the opposite direction. The apparent activation energies for oxygen permeation due to GB diffusion of oxide ions and ytterbium ions were 420–440 and 260–300 kJ mol−1, respectively, and almost no difference in the activation energies due to the different chemical compositions was observed. However, the oxygen permeability constants, which were divided by the GB density, for the aluminum-rich YbAG were clearly lower than those for the ytterbium-rich YbAG. [ABSTRACT FROM AUTHOR]

Although single-band emission upconversion fluorescence, which is particularly important in sensors, biomedical and imaging applications, has been extensively investigated in nanoparticles using energy transfer engineering, it is still difficult to be achieved in transparent ceramics. Herein, the MgAlON: Er3+/Yb3+ transparent ceramics with functionalized grain boundaries were successfully fabricated. Lanthanide ions were investigated to highly enrich at the MgAlON grain boundaries, resulting in novel fluorescent properties. Upon 980 nm laser excitation, the sample emitted temperature and excitation power-independent single-band red upconverted fluorescence with a red-to-green fluorescence intensity ratio of ∼25. The new mechanism of Yb3+-Yb3+ cooperative fluorescence-assisted energy transfer, which is responsible for the single-band feature, was elucidated. Moreover, the upconverted fluorescence chromaticity can be modified by the excitation wavelength, relying on the existence of the cooperative fluorescence level and its related energy transfer mechanism. This work reveals the potential of grain boundary functionalization of transparent ceramics in energy transfer engineering. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The elemental segregation behaviors and interactions between point defects and symmetrical tilt grain boundaries (GBs) in TiVTa concentrated solid–solution alloys (CSAs) have been studied through hybrid Monte Carlo/molecular dynamics (MC/MD) simulations. A pure V model, a random TiVTa CSA with randomly distributed elements, and an equilibrated TiVTa CSA with Ti segregation were constructed to investigate the influence of chemical disorder and local elemental segregation on defect–GB interactions. For defect–GB interactions, GBs interact more strongly with interstitials than with vacancies. Compared with the pure V, the vacancy absorption length scale of GBs is greater, whereas the interstitial absorption length scale of GBs is shorter in TiVTa CSAs due to the chemical fluctuation and local lattice distortion. This means a higher recombination efficiency of point defects in TiVTa CSAs. The elemental (Ti) segregation in TiVTa CSAs can further enhance the sink strength of GBs towards interstitials, while simultaneously reducing their sink strength towards vacancies. Consequently, the preference effects of GBs towards interstitials and vacancies are amplified in the equilibrated CSA due to local ordering, thereby reducing efficient defect annihilation around GBs. These results provide fundamental insights into the irradiation defect dynamics of CSAs with body-centered cubic (bcc) structure. [ABSTRACT FROM AUTHOR]

Some lead‐free complex compounds containing the two perovskite compounds BaTiO3 and Bi0.5Na0.5TiO3 of chemical composition (Ba1–xBix/2Nax/2)TiO3 (x = 0, 0.05, 0.1, 0.15) are fabricated using a cost‐effective mixed oxide method. Synthesis and characterization (electrical, ferroelectric, and optical) of the above‐defined complex ferroelectrics are reported in this article. Analysis of the X‐ray diffraction data/pattern reveals the formation of phase pure compounds with tetragonal symmetry. Determination of particle size is done using the Scherrer formula. A morphology study of sintered (at 1100 °C) pellets indicates that average grain size decreases with an increase in Bi/Na content of Bi0.5Na0.5TiO3. Studies of Fourier transform infrared spectroscopy and ultraviolet–visible–near‐infrared spectroscopy reveal the type of chemical bonds present in the materials. The energy bandgaps of the compounds are found to be suitable for optical device applications. The frequency and temperature dependence of the dielectric study reveals that the dielectric constant increases and loss tangent decreases with an increase in Bi/Na content of Bi0.5Na0.5TiO3. The analysis of the I–V plot and the field‐dependent polarization (P–E hysteresis loop) provide the low leakage current and existence of ferroelectricity at room temperature, respectively. [ABSTRACT FROM AUTHOR]

BaZr 0.1 Ce 0.7 Y 0.1 Yb 0.1 O 3-δ (BZCYYb) as a potential candidate for protonic ceramic fuel cells (PCFCs) electrolytes, often suffers from its high sintering temperature, making it deviate from the stoichiometric ratio and present a poor electrochemical performance than expected. Here, we reported a Ba evaporation inhibition strategy to fabricate stoichiometric BZCYYb electrolyte. By using this strategy, Ba evaporation and Y 2 O 3 /Yb 2 O 3 segregation can be effectively suppressed. The electrolyte's average grain size is ∼5.29 μm, significantly promoting grain growth. An improvement of 60 % in total conductivity is accomplished at 700 °C in humid air, approaching 2.7 × 10−2 S cm−1. By constructing the proton transport model, the reasons for the enhanced electrochemical performance are explained from both bulk and grain boundary. Finally, at 700 °C, an anode-supported single cell with stoichiometric BZCYYb electrolyte demonstrates a maximum power density of 0.65 W cm−2, showing that the barium evaporation inhibition strategy is a powerful tool to fabricate PCFCs with high performance. • Stoichiometric BZCYYb electrolyte is obtained by a Ba evaporation inhibition strategy. • Large grain size (∼5.29 μm) of BZCYYb electrolyte is obtained. • Enhanced electrical conductivity reaches to 2.7 × 10−2 S cm−1 at 700 °C in humid air. [ABSTRACT FROM AUTHOR]

In this work, the one-dimensional (1D) Ni–Co–Se nanowire arrays with rich grain-boundaries were prepared through the solvothermal method and gas-phase selenizaiton. The results showed that the structure and crystallization of the Ni–Co–Se nanowire arrays could be modulated through the optimization of selenizaiton time. The optimal Ni–Co–Se electrode sample displayed an area specific capacitance of 242.6 μ Ah cm−2 at 30 mA cm−2 with a current retention rate of 68.34%. The assembled Ni–Co–Se/Active carbon (AC) electrode-based asymmetric supercapacitor (ASC) showed the area specific capacitances of 329.2 μ Ah cm−2 and 225.8 μ Ah cm−2 at 3 mA cm−2 and 30 mA cm−2, respectively. A 73.33% retention rate of capacitance was observed after 8000 charge/discharge cycles. Besides, the further fabricated all-solid ASC delivered the power densities of 342.94 W kg−1 and 3441.33 W kg−1 at the energy densities of 37.62 Wh kg−1 and 25.81 Wh kg−1, respectively. Those results suggested the potentials of the obtained Ni–Co–Se nanowire arrays as electrode material for the high-performance pseudocapacitors. [ABSTRACT FROM AUTHOR]

The grain boundary characteristics of oxide scales affect the surface quality and fracture behavior of steel plates during hot rolling. In the present work, the electron backscatter diffraction technique was used to investigate the texture evolution behavior of magnetite (Fe3O4) and hematite (Fe2O3) in the deformed oxide layer of high-strength steel. The results show that Fe3O4 formed a γ texture parallel to the oxide growth direction, whereas Fe2O3 formed a component with {0001}<10 1 ¯ 0> texture. High thickness reduction rates of > 27% reduced the wedge of Fe2O3 into Fe3O4 grains through cracks and hindered the formation of internal cracks. In comparison with Fe3O4 and Σ3a, when Σ13b and Σ19b grain boundaries existed in Fe2O3, the scale was more likely to crack. Therefore, appropriate grain boundary engineering methods must be used to improve the required grain boundary type and suppress crack propagation. Finally, avoiding the growth of Fe2O3 along the <111> grain direction of Fe3O4 grains at an angle of 55° can greatly reduce the disturbance from Fe2O3 during hot rolling. [ABSTRACT FROM AUTHOR]

Grain rotation is commonly observed during the evolution of microstructures in polycrystalline materials of different kinds, including metals, ceramics, and colloidal crystals. It is widely accepted that interface migration in these systems is mediated by the motion of line defects with step and dislocation character, i.e., disconnections. We propose a crystallography-respecting continuum model for arbitrarily curved grain boundaries or heterophase interfaces, accounting for the disconnections' role in grain rotation. Numerical simulations demonstrate that changes in grain orientations, as well as interface morphology and internal stress field, are associated with disconnection flow. Our predictions agree with molecular dynamics simulation results for pure capillarity-driven evolution of grain boundaries and are interpreted through an extended Cahn-Taylor model. [ABSTRACT FROM AUTHOR]

The effect of displacement cascade on the mechanical properties of symmetrical grain boundaries in BCC tungsten has been studied by molecular dynamics method. At first, results show that the point defects induced by displacement cascade are absorbed by the grain boundary, in which the number of absorbed interstitials is more than that of vacancies. Then, displacement cascade can decrease both the ultimate strength in tensile simulation and the critical stress in shear simulation. The change of microstructure and mechanism during deformation has been investigated. During tensile deformation, vacancy clusters promote the formation of micro-cracks and interstitial clusters accelerate the nucleation of 1/2 < 111 > dislocation loops. In terms of shear loading, the migration of grain boundary could be significantly enhanced by displacement cascade. [ABSTRACT FROM AUTHOR]

Graphene is a two-dimensional carbon allotrope which exhibits exceptional properties, making it highly suitable for a wide range of applications. Practical graphene fabrication often yields a polycrystalline structure with many inherent defects, which significantly influence its performance. In this study, we utilize a Monte Carlo approach based on the optimized Wooten, Winer and Weaire (WWW) algorithm to simulate the crystalline domain coarsening process of polycrystalline graphene. Our sample configurations show excellent agreement with experimental data. We conduct statistical analyses of the bond and angle distribution, temporal evolution of the defect distribution, and spatial correlation of the lattice orientation that follows a stretched exponential distribution. Furthermore, we thoroughly investigate the diffusion behavior of defects and find that the changes in domain size follow a power-law distribution. We briefly discuss the possible connections of these results to (and differences from) domain growth processes in other statistical models, such as the Ising dynamics. We also examine the impact of buckling of polycrystalline graphene on the crystallization rate under substrate effects. Our findings may offer valuable guidance and insights for both theoretical investigations and experimental advancements. [ABSTRACT FROM AUTHOR]

The interactions between displacement cascades and three types of structures, dislocations, dislocation loops and grain boundaries, in BCC-Fe are investigated through molecular dynamics simulations. Wigner–Seitz analysis is used to calculate the number of point defects induced in order to illustrate the effects of three special structures on the displacement cascade. The displacement cascades in systems interacting with all three types of structure tend to generate more total defects compared to bulk Fe. The surviving number of point defects in the grain boundary case is the largest of the three types of structures. The changes in the atomic structures of dislocations, dislocation loops and grain boundaries after displacement cascades are analyzed to understand how irradiation damage affects them. These results could reveal irradiation damage at the microscale. Varied defect production numbers and efficiencies are investigated, which could be used as the input parameters for higher scale simulation. [ABSTRACT FROM AUTHOR]

The phase and grain boundary characteristics of recently developed fine-grained dual-phase high-entropy (Ti-Zr-Nb-Hf-Ta)C/(Ti-Zr-Nb-Hf-Ta)B 2 was investigated throughout all the accessible length scales using scanning electron microscopy (SEM), aberration-corrected scanning transmission electron microscopy (STEM), energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS). The system exhibits relatively homogeneous grain size distribution where the average size is approximately 0.97 µm, with chemical composition (Ti 0.14 Zr 0.2 Nb 0.2 Hf 0.2 Ta 0.26)C + (Ti 0.38 Zr 0.18 Nb 0.22 Hf 0. 115 Ta 0.105)B 2. SEM analyses revealed no micro-crack formation and second – phase segregation at the boundaries or micro-pores at the triple – points. Investigation down to the sub-nanometer scale revealed that the phase and grain boundaries were typically clean and sharp with an indistinct 1 – 1.5 nm thin gradient of metallic elements at boride/boride and carbide/carbide interfaces. The sharp phase and grain boundaries do exhibit elemental enrichment from a trace amount of Fe being incorporated in interstitial positions of carbide and boride grains locally at boride/carbide boundaries or are present in boride and carbide grains in the form of continuous thin layer at boride/boride and carbide/carbide interfaces with the probably origin from starting powders. [ABSTRACT FROM AUTHOR]

The influence of material micro-defects on the main crack growth under pure shear loading is studied theoretically. The mechanism behind the initiation of micro-cracks and crack propagation induced by dislocation accumulation near the grain boundary (GB) is mainly considered, and the influence of dislocation accumulation on the main crack propagation is analyzed. The research results reveal that the initiation of micro-cracks near the GB is prior to the propagation of the main crack. In a hydrogen environment, hydrogen can cause serious embrittlement of the crack tip and promote crack growth. The energy release rate in the main crack growth direction in the dislocation emission direction is the highest. Therefore, the main crack will eventually merge with the micro-cracks at the GB along the direction of the slip band, resulting in fracture of the crystal material. The research presented in this paper provides some new information for the first stage of crack propagation and contributes to the analysis of the mechanism of crystal metal fracture. [ABSTRACT FROM AUTHOR]

The aerospace alloy AA8090 T87 was friction stir welded with varying traverse speeds of 30 and 70 mm/min at rotation speeds of 900 and 1100 r/min to realize the effect of traverse speed and rotation speed on the joint strength. This variation in the rotation and traverse speeds produced variation in the thermal cycle in the weld joint that altered the microstructure of the stir zone and morphology of the grains. The increase in the rotational speed from 900 to 1100 r/min at 30 mm/min increased the grain size from 4.1 µm to 7.8 µm in the stir zone which was evident from the microscopy images and Schmid factor maps and contributed to the mechanical property changes. The increase in traverse speed from 30 to 70 mm/min has led to the hardness improvement and reduction in grain size in the stir zone. The nature of the fracture observed in the stir zone is ductile fracture having more dimples. An effective joint was produced at 900 r/min rotational speed and 30 mm/min traverse speed. [ABSTRACT FROM AUTHOR]

Electrical characteristics with various program temperatures (TPGM) in three-dimensional (3-D) NAND flash memory are investigated. The cross-temperature conditions of the TPGM up to 120 °C and the read temperature (TREAD) at 30 °C are used to analyze the influence of grain boundaries (GB) on the bit line current (IBL) and threshold voltage (VT). The VT shift in the E-P-E pattern is successfully decomposed into the charge loss (ΔVT,CL) component and the poly-Si GB (ΔVT,GB) component. The extracted ΔVT,GB increases at higher TPGM due to the reduced GB potential barrier. Additionally, the ΔVT,GB is evaluated using the Technology Computer Aided Design (TCAD) simulation, depending on the GB position (XGB) and the bit line voltage (VBL). [ABSTRACT FROM AUTHOR]

The Ca12Al14O33 ceramic (C12A7) and reduced graphene oxide (rGO) composite which an ultra-high amount (i.e., 40, 50, 60, and 70 wt%) of rGO (ultra-high amount C12A7/rGO composite) were synthesized by a solid-state reaction process. After the hydraulic press, the heat treatment in the temperature range of 773 K under the argon environment had been performed with the composite pellets for 30 min. XRD results of the C12A7 and all the ultra-high amount C12A7/rGO composites indicated a pure phase of C12A7 ceramic. Raman spectra confirmed the existence of rGO content in all the ultra-high amount C12A7/rGO composites. Raman peaks also suggested reduction of the free O22− and O2− ions from the framework of the ultra-high amount C12A7/rGO composites. SEM image presented the homogeneous grain boundary interface after the heat treatment at 773 K of the C12A7 wrapped by the rGO sheet, the agglomerated rGO sheet, and the rough interface stack of rGO sheets. UV-VIS spectroscopy presented the absorption behavior, direct energy gap, and indirect energy gap modifications of the ultra-high amount C12A7/rGO composites. Electrical conductivity of the ultra-high amount C12A7/rGO composites illustrated larger than 108 times improvement with temperature independence. Range of −5 to −17 μV/K , temperature dependence, and increased with rGO content increasing Seebeck coefficient were reported. Thermal conductivity of the ultra-high amount C12A7/rGO composites was increased with the rGO content increasing. Both the Power factor (PF) and the figure of merit (ZT) of the ultra-high amount C12A7/rGO composites were temperature dependent and were increased with the rGO content increasing, within the range of 0.4 μW/m.K2 of PF and the range of 3x10−4 of ZT, respectively. These experimental results verified grain boundary, modified energy band, electrical transport properties and thermoelectric properties of C12A7/rGO composites loading with ultra-high content rGO

Purposes Owing to the serious segregation of Cr and Mo in super austenitic stainless steel, a large number of Mo- and Cr-rich second phases precipitate during the hot rolling process, which leads to rolling cracking and delamination. Boron microalloying is helpful for preventing the σ phase precipitation. Methods The matrices and precipitate structures of boron-free and boron-containing S31254 super austenitic stainless steels and the distribution of elements such as Cr and Mo were analyzed experimentally. Combined with the experimental results, two grain boundary structure models of γ-Fe ∑9(22-1) and γ-Fe ∑11(113) were taken as the research objects. The segregation tendency of Cr, Ni, Mn, Mo, Cu, and Si at grain boundaries was analyzed, and the influence of B on the segregation behavior of these elements at grain boundaries was discussed. Findings It was found that all of these alloying elements can be solid soluble in the grain boundary structure model of γ-Fe ∑9 and γ-Fe ∑11. Both Cr and Mo tend to segregate at the grain boundary of γ-Fe ∑9 and γ-Fe ∑11, and Mo tends to segregate most seriously at the grain boundary. When B is at the grain boundary, the segregation of Cr and Mo at the γ-Fe ∑11 boundary is inhibited, but the segregation of Mo at γ-Fe ∑9 boundary is weakly inhibited. Conclusions The essential reason why the precipitated phase can be inhibited by the addition of super austenitic stainless steel to B is explained from the atomic level, which lays a foundation for the composition optimization of super austenitic stainless steel in the future.

First developed in 2012, perovskite solar cells (PSC) have been attracting enormous attention for their high-power conversion efficiency, low manufacturing cost, easy annealing and fabricating techniques, good stability in ambient environments, and excellent overall performance. Skyrocketing from a PCE of 2.8% to 25.2%, PSCs are deemed as one of the most promising solar energy harvesters in the near future. However, due to the grain boundaries and some poor interface connections, there appear several defects that affect the efficiency and stability of PSCs. In this case, two primary methods are discussed in this review to minimize such limitations: the introduction of (1) PbI2 and (2) organic halide salts as additives to the perovskite film. By filling the vacancies at the grain boundary, promoting spatial electron–hole separation, generating Lewis acid–base reaction, and forming intermolecular interactions like hydrogen bonding, sulfide bonds, pi-conjunctions, etc., these additives serve as promising candidates for reducing the surface recombination of PSCs. Moreover, because of the hydrophobic characteristics of organic halide-based compounds and the thermal annealing process, the stability of PSCs can also be improved in both high-temperature and -humidity environments. Through presenting and compiling the results of recent studies on various additives, this review also proposes further development and next-generation strategies for minimizing the limitations and challenges in the future.

Hastelloy G30 is a typical representative of Ni–Cr–Fe–Mo–Cu alloys, which have excellent corrosion resistance and mechanical properties. High alloying-element content induces a risk of intermetallic precipitation, which is poorly eliminated in steel/nickel bimetallic composite manufactured by hot forming or welding. In this study, aged material was observed using transmission electron microscopy, electron backscatter diffraction, and scanning electron microscopy. The results show that the precipitates formed in Hastelloy G30 after aging at 800 °C comprised Cr- and Mo-rich σ phase. More than 95% of Σ1 and Σ3 boundaries were free from σ phase, and about half of the other low-Σ boundaries were immune to the formation of σ phase. All Σ9, Σ27, and random high-angle grain boundaries exhibited low intergranular precipitation resistance of approximately 5%–10%. The (301) planes of the σ phase and the (−220) planes of the matrix showed semicoherent lattice matching. Higher grain-boundary energy and serrated grain boundaries provided opportunities for σ phase precipitation to occur.

The stability and strength of the grain boundary (GB) structure are critical for the practical application of nanocrystals. This study systematically calculates the impact of the segregation of 26 transitional alloy elements on Cu Σ11 [110](113) GB using the first-principle theoretical calculation method. The research findings demonstrate that there is a parabolic connection between atomic number and segregation energy of TM elements in the same period. In addition to Fe, Co, and Ni, all other 23 elements have the potential to segregate to Cu GB, with Zr exhibiting the strongest segregation tendency. The difference in atomic radius and electronegativity between solute atoms and copper atoms strongly affects the segregation tendency, the greater the difference, the greater the tendency for segregation. The segregation energy of solute segregation has strong linear correlation with its GB energy, and the stronger the segregation ability, the more stable the GB. Except for Zn, Ag, Cd, and Au, other 19 alloying elements can increase the strength of GB. Electronic analysis indicates that the strengthening and embrittlement of solutes are primarily related to the accumulation and consumption of electrons near GB and the bonding between atoms.

In this study, the effects of differences in grain size, grain boundary type and misorientation on the initiation of discontinuous precipitates are investigated for the Cu–5Ni–1.25Si alloy. Samples with different grain sizes are obtained by thermomechanical treatment, and the smaller the grain size, the higher the percentage of discontinuous precipitate at the same aging time, while there is no significant difference in the growth rate of the reaction front of discontinuous precipitates. EBSD is used to study the effect of grain boundary misorientation on discontinuous precipitates, the characteristics of discontinuous precipitates initiation on different grain boundaries are investigated by multivariate statistical analysis. It is found that discontinuous precipitates only initiate from random grain boundaries instead of coincident site lattice boundaries, where random grain boundaries with misorientation angles of 30–50° are more prone to discontinuous precipitates. And the initiation of DPs at different misorientation axes is different. There is a clear borderline for the axes such as , , and . The grain boundaries below this borderline do not initiate DP, while all grain boundaries below this angle initiate DPs. The cases for axes such as , , and are more complicated. On these misorientation axes, grain boundaries with lower or higher misorientation angles do not initiate DPs, while grain boundaries at intermediate range misorientation angles do initiate DPs.

By employing high-throughput first-principles calculations, the segregation capacity of fifteen widely used metallic alloying elements (viz., Be, Mn, Co, Cr, Ni, Al, Mo, W, Mg, Ta, Nb, Sb, Sn, Zr, and Bi) at ∑3 grain boundary in low alloy ferritic steel, as well as their impact on grain boundary stability, interfacial separation work, and other properties, were systematically investigated. The findings reveal that, for alloying atoms Sb, Sn, Bi, Nb, and Zr, whose size is notably larger than that of the matrix Fe atoms, the effect of strain energy minimization in segregation is comparable to that of chemical energy minimization. Furthermore, the impact of strain energy minimization is closely related to the volume of the alloying atoms both at the solid solution sites in the crystal and at the segregation sites at the grain boundary. Thus, the segregation of large alloy atoms on the grain boundaries can be predicted by atomic volume of each segregation site, which can provide valuable insights for the development of new alloys and for grain boundary engineering.

The effect of grain boundaries on the strength and electrical conductivity of annealed copper wires was studied. After annealing at 100 °C for 30 min, the copper wires retained a fiber-like structure. The increase in electrical conductivity is believed to stem from the decrease of crystallographic defects introduced by drawing. Recrystallization occurred when the annealing temperature reached 150 °C. The formation of small recrystallized grains led to the introduction of additional grain boundaries perpendicular to the drawing direction, resulting in a slight decrease in electrical conductivity. When the annealing temperature rose up to 200 °C, complete recrystallization took place in the copper wires. The grain boundaries parallel to the drawing direction play an important role in boundary strengthening, while the grain boundaries perpendicular to the drawing direction play an important role in both boundary strengthening and electron scattering. The electrical resistivity of grain boundaries in fully recrystallized copper wires at room temperature was determined experimentally, and an empirical relation is proposed to quickly determine the electric conductivity of copper wires at room temperature based on the boundary spacing along the drawing direction.

Anisotropic bulk magnets of ThMn12-type SmFe10V2 with a high coercivity (Hc) were successfully fabricated. Powders with varying particle sizes were prepared using the ball milling process, where the particle size was controlled with milling time. A decrease in Hc occurred in the heat-treated bulk pressed from large-sized powders, while heavy oxidation excessively occurred in small powders, leading to the decomposition of the SmFe10V2 (1–12) phase. The highest Hc of 8.9 kOe was achieved with powders ball-milled for 5 h due to the formation of the grain boundary phase. To improve the maximum energy product ((BH)max), which is only 2.15 MGOe in the isotropic bulk, anisotropic bulks were prepared using the same powders. The easy alignment direction, confirmed by XRD and EBSD measurements, was . Significant enhancements were observed, with saturation magnetization (Ms) increasing from 59 to 79 emu/g and a remanence ratio (Mr/Ms) of 83.7%. (BH)max reaching 7.85 MGOe. For further improvement of magnetic properties, controlling oxidation is essential to form a uniform grain boundary phase and achieve perfect alignment with small grain size.

Uranium silicide (U3Si2) is regarded as a viable fuel option for improving the safety of nuclear power plants. In the present work, phase-field simulations were employed to investigate grain growth phenomena, encompassing both isotropic and anisotropic grain growth. In simulations of isotropic grain growth, it is commonly assumed that the energy and mobility of the grain boundaries (GBs) remain constant, represented by average values. The calculated grain growth kinetic rate constant, K, exhibits a close correspondence with the experimental measurements, indicating a strong agreement between the two. In simulations of anisotropic grain growth, the values of GB energy and mobility are correlated with the angular disparity between GBs. The simulation results demonstrated that the growth rate of U3Si2 can be influenced by both the energy anisotropy and mobility anisotropy of GBs. Furthermore, the anisotropy in mobility results in a greater prevalence of low-angle GB distribution in comparison to high-angle GBs. However, the energy anisotropy of GBs does not impact the frequency distribution of the angle difference between GBs.

A phase-field model for the precipitation of Fe-Cr-Al alloy is established incorporating grain boundary (GB) effects and irradiation-accelerated diffusion. The radiation source and grain boundary effect are incorporated to broaden the applicability of the Fe-Cr-Al precipitated phase-field model. The model is firstly employed to simulate the precipitation of the Cr-rich α’ phase in a single-crystal alloy. The precipitation rate and the size distribution of the precipitated phase were analyzed. Subsequently, the model is utilized to simulate segregation at GBs in a double-crystal system, analyzing the enrichment of Cr and depletion of Al near these boundaries. The simulation results are consistent with experimental observations reported in the references. Finally, the model is applied to simulate the precipitation in a polycrystalline Fe-Cr-Al system. The simulated results revealed that the presence of GBs induces the formation of localized regions with enhanced Cr and Al content as well as depleted zones adjacent to these boundaries. GBs also diminish both the quantity and precipitation rate of the formed phase within the grains.

The last two decades have witnessed significant progress in the development of severe plastic deformation techniques to produce ultrafine-grained materials with new and superior properties. This review examines works and achievements related to the low-temperature superplasticity of ultrafine-grained aluminum alloys. The examples are provided of the possibility to observe low-temperature superplasticity in aluminum alloys at temperatures less than 0.5 Tmelt and even at room temperature, and herein, we demonstrate the cases of achieving high ductility and high strength in aluminum alloys from processing utilizing severe plastic deformation. Special emphasis is placed on recent studies of the formation of segregations of alloying elements at grain boundaries in UFG Al alloys and their influence on the development of grain boundary sliding and manifestation of low-temperature superplasticity. In addition, the current status and innovative potential of low-temperature superplasticity in aluminum alloys are observed.

Aluminum-incorporated medium-manganese steel (MMnS) has potential for lightweight transport applications owing to its impressive mechanical properties. Increasing the austenite volume fraction and making microstructural changes are key to manufacturing MMnS. However, the grain boundary character and strain distribution of intercritically annealed low-density MMnS have not been extensively scrutinized, and the effects of crystallographic texture orientation on tensile properties remain ambiguous. Therefore, in this study, the microstructure, microtexture, strain distribution, and grain boundary characteristics of a hot-rolled medium-Mn steel (Fe–0.2 C–4.3 Al–9.4 Mn (wt%)) were investigated after intercritical annealing (IA) at 750, 800, or 850 °C for 1 h. The results show that the 800 °C annealed sample exhibited the highest austenite volume fraction among the specimens (60%). The duplex microstructure comprised lath-type γ-austenite, fine α-ferrite, and coarse δ-ferrite. As the IA temperature increased, the body-centered cubic phase orientation shifted from to . At higher temperatures, the face-centered cubic phase was oriented in directions ranging from to , and the sums of the fractions of high-angle grain boundaries and coincidence–site–lattice special boundaries were significantly increased. The 800 °C annealed sample with a high austenite content and strong γ-fiber {111}//RD orientation demonstrated a noteworthy tensile strength (1095 MPa) and tensile elongation (30%).