Grain Boundaries Research Articles

Intelligent Classification and Segmentation of Sandstone Thin Section Image Using a Semi-Supervised Framework and GL-SLIC

This study presents the development and validation of a robust semi-supervised learning framework specifically designed for the automated segmentation and classification of sandstone thin section images from the Yanchang Formation in the Ordos Basin. Traditional geological image analysis methods encounter significant challenges due to the labor-intensive and error-prone nature of manual labeling, compounded by the diversity and complexity of rock thin sections. Our approach addresses these challenges by integrating the GL-SLIC algorithm, which combines Gabor filters and Local Binary Patterns for effective superpixel segmentation, laying the groundwork for advanced component identification. The primary innovation of this research is the semi-supervised learning model that utilizes a limited set of manually labeled samples to generate high-confidence pseudo labels, thereby significantly expanding the training dataset. This methodology effectively tackles the critical challenge of insufficient labeled data in geological image analysis, enhancing the model’s generalization capability from minimal initial input. Our framework improves segmentation accuracy by closely aligning superpixels with the intricate boundaries of mineral grains and pores. Additionally, it achieves substantial improvements in classification accuracy across various rock types, reaching up to 96.3% in testing scenarios. This semi-supervised approach represents a significant advancement in computational geology, providing a scalable and efficient solution for detailed petrographic analysis. It not only enhances the accuracy and efficiency of geological interpretations but also supports broader hydrocarbon exploration efforts.

Dynamic recrystallisation: A quantitative study on grain boundary characteristics and dependence on temperature and strain rate in an aluminium alloy

Dynamic recrystallisation (DRX) usually occurs during hot forming of metallic materials, significantly impacting the mechanical properties of the final parts. Although DRX has been studied for decades, the types of DRX that occurs in high stacking fault energy (SFE) materials like aluminium alloys are still controversial, and their dependence on both temperature and strain rate is surprisingly missing. To fill these gaps, in the present study, uniaxial compression tests on an aluminium alloy AA6061 were carried out at different temperatures from 250 to 475 °C and strain rates from 0.01 to 1 s-1. The grain orientation and misorientation before and after the hot deformation were quantitively characterised using high-resolution Electron Backscatter Diffraction (EBSD) with a misorientation resolution of 0.05°, enabling high-angle grain boundaries (HAGBs), low-angle grain boundaries (LAGBs) and geometrically necessary dislocations (GNDs) to be accurately quantified and correlated against temperature and strain rate. Results reveal that both continuous dynamic recrystallisation (CDRX) and geometric dynamic recrystallisation (GDRX) occurred concurrently, resulting in the formation of discontinuous HAGBs and fine equiaxed grains, respectively. The misorientation angle distributions of the discontinuous HAGBs exhibit an opposite trend compared to those of the fine grains’ HAGBs. Both temperature and strain rate significantly affect the density of HAGBs formed by DRX, but have little effect on their misorientation angle distributions. This study sheds light on the fundamental understanding of DRX and provides comprehensive experimental data for future modelling of DRX processes in high SFE materials.

Probing the micro-mechanism of precipitate-strengthened alloys with precipitate free zone: An experimental and theoretical study

Precipitate free zone (PFZ) consistently forms near the grain boundaries (GBs) in precipitate-strengthened alloys, significantly weakening the materials because of their intrinsic softness compared to the bulk. However, the influence of PFZ near GBs on deformation mechanism remains largely unrevealed. Here, we systematically investigate the effects of PFZ on the macroscopic mechanical behavior and the microstructure deformation mechanism of the modelled precipitate-strengthened Al-Zn-Mg-Cu alloy, using a combination approach of experiments, molecular dynamics (MD) simulations, and theoretical modeling. Four Al-Zn-Mg-Cu alloys with highly different PFZ widths are prepared by tailoring the quenching media and applying the new deformation heat- treatment process proposed by us. Experimental characterizations demonstrate that severe dislocation accumulation occurs at the interface between PFZ and bulk. Meanwhile, MD simulations further reveal that PFZ is prone to plastic deformation during tensile process, contributing to the softening of materials. The PFZ exhibits significant strain concentration, leading to the preferential formation of dislocations within PFZ rather than at GBs. It is found that the level of strain concentration and the degree of dislocation accumulation are not sensitive to the PFZ width. Based on these mechanisms, a PFZ-dependent strength model is developed to quantitatively evaluate the influence of PFZ on tensile strength by considering dynamic strengthening of PFZ. It is predicted that an increase in PFZ width greatly reduces the tensile strength, with a 21 % reduction observed when PFZ width reaches 268 nm, emphasizing the important impact of PFZ width on materials strength.

Formation of heterogeneous microstructure and its effect on corrosion properties of high-silicon stainless steel S38815 weldment

This study aims to clarify the formation of heterogeneous microstructure and its effect on corrosion properties of high-silicon stainless steel (high-Si SS) S38815 weldment. A series of tests about microstructure and electrochemical characteristics were performed, including the electron backscatter diffraction (EBSD) analysis, Mott-Schottky tests, electrochemical impedance spectroscopy (EIS) tests, potentiodynamic and potentiostatic polarization tests. The formation mechanism of heterogeneous microstructure related to high-silicon and its correlation on corrosion was discussed extensively. The results show that the significantly deformed and recrystallised grains were observed at the low temperature heat affected zone (LT-HAZ) and high temperature heat affected zone (HT-HAZ) respectively. The metastable pitting and low impedance values were formed in the above region, despite their low donor density. The deterioration in corrosion resistance of S38815 weldment as a result of high-angle grain boundaries (HAGBs) and carbides is more pronounced than the beneficial impact of Cr and Si oxidation. This study provides valuable references to the manufacturing and enhancing the anti-corrosion properties of this high-Si SS.

Influence of scanning strategies on microstructure and mechanical properties of laser powder bed fusion 2195 Al-Li alloy

Optimizing the scanning strategy is considered as an effective approach to address the challenges of laser powder bed fusion(LPBF). However, the impact of the scanning strategy on lightweight Al-Li alloys remains unclear. In this study, various scanning strategies LPBF were employed to process 2195 Al-Li alloy specimens, and a systematic investigation was conducted on the effects of the laser path on the defects, microstructure, and mechanical properties of 2195 Al-Li alloy. The results revealed that the specimens processed with the linear strategy exhibited the lowest gas pores and crack density, achieving a densification rate of 98.6 %. Furthermore, adjusting the scanning strategy led to changes in grain morphology among specimens; those processed with linear scanning demonstrated smaller average grain size (19.7 μm), a lower percentage of high-angle grain boundaries (HAGBs) (57.4 %), and a higher texture index compared to other strategies tested. When employing linear strategy for processing, tensile performance reached 315.03 MPa with 5.03 % elongation due to concise thermal history and fast cooling conditions associated with this particular scanning method. This study provides valuable insights into optimizing scanning strategies for LPBF 2195 Al-Li alloy.

Mechanism of grain boundary angle on solidification cracking in directed energy deposition Hastelloy X superalloys

Solidification cracking occurs only when the grain boundary (GB) angle (θ) exceeds a critical value. This value, known as the critical cracked GB angle (θ*), can be predicted from the grain coalescence theory based on GB-angle-dependent GB energy. However, the calculated value (θc*) is always less than the measured value in experiments (θe*), which is also confirmed in our directed energy deposition Hastelloy X superalloys. In addition to GB energy, there are evidences showing that GB angle can affect cracking by changing dendrite spacings. We show by experiments and phase field simulations that, same as GB energy, the dendrite spacings at GBs increase with GB angle, but its effect on solidification cracking sensitivity (SCS) is opposite to GB energy. Depending on their relative contributions, three ranges can be identified. In the first range of θ<θc*, both dendrite spacings and GB energy have negligible effects on dendrite coalescence, compared to the case inside a grain. In the second range of θc*<θ<θe*, dendrite spacings counteract the effect of high GB energy on SCS. It is exactly this effect that induces the gap in θ* between theory and experiments. In the third range of θ>θe*, GB energy plays a dominant role and leads to severe solidification cracking. After including the effect of dendrite spacings on SCS, we predict θ*=15° in directed energy deposition Hastelloy X superalloys, close to the experimental value of 18°. These new findings provide new insights for suppressing cracking by controlling the dendrite spacings near GBs.

Understanding the isothermal compression behavior of Al-Mg-Si alloy based on hot deformation parameters and instability criteria

This work comprehensively studied the microstructure evolution and thermodynamic behavior of homogenized cast Al-Mg-Si alloy by using the dynamic materials model (DMM) of hot deformation activation energy (Q) and power dissipation efficiency (η), which were influenced by Zener-Holomon (Z) parameters of temperature-compensated strain rate. The Q varies with the material constitutive parameters n(T) and sε̇ and leads to a non-monotonic trend in the Z parameter. These coupling relationships have profound significance for revealing plastic deformation. The microstructure and microtexture evolution under four representatively Z parameters had been characterized, and it was found that the deformation mechanism under higher lnZ was mainly dynamic recovery (DRV) and a typical <101>//TD texture with a maximum strength of 14.41 was exhibited. As lnZ decreased, the volume fraction of high angle grain boundaries (HAGBs) and recrystallized grains increased from 20.89 % and 1.5 % to 49.47 % and 40.9 %, the geometrically necessary dislocation (GNDs) density dropped from 1.55 × 1014/m2 to 0.40 × 1014/m2, and the softening mechanism gradually shifted to dynamic recrystallization (DRX), with the volume fraction of Cube texture {001} <100> increasing and Goss texture {011} <110> decreasing. Hot processing maps were established based on the Prasad and Murty instability criterion. The results showed that the instable and stable zones had a strong correlation with η. Lower η often implies microcracks, deformation bands and flow localization, as well as extremely uneven grain distribution and a low recrystallization volume fraction, and the stable zone mainly exhibited the phenomenon of DRX dominated recrystallization behavior improving microstructure homogenization. By comparing the specific hot processing map and microstructure evolution, the prediction ability for determining Murty instability criterion is stronger than Prasad for homogenized cast Al-Mg-Si alloy.

Grain boundary-mediated strain response mechanism of AZ31 gradient- structure Mg alloy plate under uniaxial tensile loading

The changes in strain gradient induced by grain boundaries are crucial for enhancing the plasticity of gradient magnesium (Mg) alloys. The change of strain distribution influence by grain boundaries during plastic deformation of the gradient structure was examined. In this paper, the gradient structure AZ31 Mg-alloy plate with the surface fine grain (FG) to the center coarse grain (CG) was fabricated using hard plate rolling (HPR). The microstructure and strain distribution of Mg-alloy with a gradient structure were analyzed by electron backscatter diffraction (EBSD) and Digital image correlation (DIC) during uniaxial tensile. The findings indicate that the gradient structure sample (GS sample) displays a uniform strain distribution during the tensile process. Coarse-grain sample (CG sample) have obvious strain concentration, which leads to premature fracture. Based on EBSD characterization, low-angle grain boundaries (LAGBs) accumulates in the CG during plastic deformation. Orientation of CG tends to the (0001) basal. At the same time, the density of geometrically necessary dislocations (GNDs) inside CG has changed, which improves the Heterogeneous deformation induced (HDI) stress of gradient structure. During the uniaxial tensile, LAGBs accumulates in CG and changes the strain distribution of the gradient structure, which induces the accumulation of GNDs, and hence improving the properties of the GS Mg-alloy. These findings unveil the mechanism of strength-plasticity synergism of GS alloys from a new perspective and offer insights into the application of GS in Mg-alloys.

Effect of the cooling behavior on phase transformation and mechanical property of RAFM steel

The phase transition behavior of RAFM steel during Hot Isostatic Pressing (HIP) diffusion bonding process would extensively impact the service performance of blanket component in the future fusion reactor. In this paper, the influence of cooling behavior on phase transformation and mechanical property of RAFM steel was studied using a combination of Electron Backscatter Diffraction (EBSD) and a thermal dilatometer. The results show that as the cooling rate decreases after austenitizing, the phase category transitions from a single-phase of martensite to the dual-phase of martensite and ferrite, along with an increase in the rate of ferrite, minor martensite packets and high-angle grain boundaries (HAGB). As the cooling rate decreases, the initial temperature for martensite transformation significantly increases, and the transformation driving force slowdown. Moreover, specimens processed with HIP cooling show lower strength, higher elongation, and a greater standard deviation of hardness compared to air cooling. These differences can be attributed to the formation of ferrite and the diffusion of carbon atoms within martensite. The research findings reveal the phase transition and microstructural evolution of martensite under varying cooling conditions, providing a reference for the controlling the cooling process after HIP bonding of blanket steel components in the future fusion reactor.

The role of symmetric tilt grain boundaries on the precipitation of hydrides in zirconium: A molecular dynamics study

Zirconium (Zr) alloys are widely used as structural materials in the core of nuclear reactors. However, the absorption of hydrogen by these alloys during the reactor operation may lead to the precipitation of hydrides. Such hydrides have considerable effects on the microstructure and mechanical properties of the alloys, thus significantly impacting their overall performance. In this work, we investigate the behavior of hydrogen in the presence of symmetric tilt grain boundaries in Zr using molecular dynamics simulations. To systematically explore the conditions for the formation of hydrides, we consider hydrogen concentration levels of up to 50 at.%. We find that hydrogen concentrations of 30 at.% or lower are below the threshold for the precipitation of hydrides, while fcc coordinated hydrides precipitate at 50 at.%, which is very close to the solubility limit of hydrogen in Zr at 800 K. We find that the grain boundaries (GBs) play a pivotal role in the behavior of hydrogen, as well as the formation of hydrides in Zr systems. In most cases, large amounts of hydrogen are found to accumulate at GBs. However, both homogeneous and heterogeneous nucleation are observed during the formation of hydrides at the grain interiors and GBs, respectively. Nonetheless, in some cases the GB inhibit the formation of hydrides.

Mechanical Impact of Heterogeneously Distributed H2O on Quartz Deformation

AbstractIn order to identify relations between mechanical behavior, deformation mechanisms, microstructural properties, and H2O distribution, Tana‐quartzite samples with added H2O ranging from 0 to 0.5 wt.% were deformed by axial shortening at constant displacement rates, at 900°C and 1 GPa, reaching up to ∼30% bulk strain. Samples with lower quantities of added H2O (0.1 and 0.2 wt.%) were in average ∼30 MPa weaker than the as‐is samples with no added H2O. In contrast, samples with more than 0.2 wt.% added H2O revealed more variable mechanical behavior, showing either weaker or stronger trend. The weaker samples showed strain localization in their central parts in the vicinity of the thermocouple, that is, the hottest parts of the samples, whereas the stronger samples showed localization in their upper, slightly colder parts. Bulk deformation is accommodated by crystal plasticity and dissolution‐precipitation processes. Distribution of H2O in our samples revealed systematic decrease of H2O content in the interiors of original grains, caused by increasing strain and H2O draining into grain boundary regions. With increasing content of added H2O, the quartz recrystallization gradually changes from subgrain‐rotation‐dominated to crack‐induced nucleation, along with increasing quantity of melt/fluid pockets. The unexpected strain localization in the upper parts of stronger samples most likely results from mode‐1‐cracking that led to drainage of grain boundaries (GB) due to the crack dilatancy effect, and inhibited dissolution‐precipitation in the hottest part of the samples next to the thermocouple. The locus of deformation is then shifted to colder regions where more H2O is available along GB.

A model for predicting grain-boundary energy of refractory high-entropy alloys based on local element concentration

Refractory high-entropy alloys (RHEAs) exhibit exceptional high-temperature mechanical properties, and their structural stability is primarily influenced by grain boundaries (GBs). However, it remains challenging to accurately quantify the grain boundary energy (GBE) in RHEAs. Herein, we introduce a quantitative descriptor for point-to-point prediction of GBEs in RHEAs based on local element concentration and valence-electron numbers. Our results demonstrate that the role of the constituent elements on GBEs is primarily determined by their valence-electron numbers in RHEAs. These findings are derived from the cohesive energy and atomic structure of the elements within the framework of the broken-bond model, as well as the differential contributions of s-electrons and d-electrons. The model establishes a structure-property relationship between local element concentration and GBEs, with the prediction consistent with experimental and theoretical results, which is crucial for evaluating the GB stability of RHEAs and facilitating the development of high-performance alloys.

Effect of individual and synergistic alloying of In and Ni on microstructure, phase stability and thermal properties of lead-free Sn-0.7Cu solder

ABSTRACT The study explores the individual and synergistic effect of alloying indium (In) and nickel (Ni) with Sn-0.7 wt.% Cu solder on microstructure and thermal properties. Solders consist of β-Sn phase matrix and Cu6Sn5 intermetallic phase. In dissolves within β-Sn, while Ni substitutes Cu atoms of Cu6Sn5 forming (Cu,Ni)6Sn5. Alloying either In or Ni with Sn-0.7Cu lowers solidus and liquidus temperatures of the alloys, with a greater reduction in the case of In. Synergistic alloying of In and Ni with Sn-0.7Cu leads to a widening of 93%. Smaller fraction and localised presence of Cu6Sn5 in In-containing alloys resulted in dual-peaked grain size distribution. In the case of Ni, a fraction of (Cu,Ni)6Sn5 increased, generating more interfaces for nucleating β-Sn grains and eventually causing grain refinement. An increment in the fraction of low-angle grain boundaries (LAGBs) was observed in both alloying cases. The synergistic effect of In and Ni yields a more uniform grain size and lesser LAGBs.

Impact of Permanent Magnet Stirring on Inclusion Evolution, Solidification Structure and Mechanical Properties of AH32 Shipbuilding Steel

An experimental investigation has been conducted with respect to the effect of permanent magnet stirring (PMS) under different rotation speeds (0, 60, 180 rpm) on the solidification of AH32 shipbuilding steel by analyzing the inclusion evolution, solidification structure, and mechanical properties. As the rotation speed increased from 0 to 180 rpm, the mean size of inclusions (Al2O3, MnS, and Al2O3–MnS) reduced significantly from 6.23 to 2.92 μm, their number increased from 49 to 82 n mm−2 and the ratio of complex inclusions increased from 30.6% to 75.6% in the AH32 steel ingot. Besides, the increasing number of small complex inclusion promotes the formation of acicular ferrite in steel, resulting in an elevation of the area ratio from 10.5% to 27.8%. Furthermore, under a rotation speed of 180 rpm, the mean grain size decreased to 99.4 μm and the frequency of high‐angle grain boundaries (HAGBs) increased to 86.1%. In addition, the as‐cast AH32 steel exhibited an optimized ultimate tensile strength of 532.0 MPa and an improved elongation of 24.2% after an enhanced PMS, which was attributed to more acicular ferrite, higher HAGBs ratio, and refined grain size.

Constructing Slip Stacking Diversity in Van der Waals Homobilayers.

The van der Waals (vdW) interface provides two important degrees of freedom-twist and slip-to tune interlayer structures and inspire unique physics. However, constructing diversified high-quality slip stackings (i.e., lattice orientations between layers are parallel with only interlayer sliding) is more challenging than twisted stackings due to angstrom-scale structural discrepancies between different slip stackings, sparsity of thermodynamically stable candidates and insufficient mechanism understanding. Here, using transition metal dichalcogenide (TMD) homobilayers as a model system, this work theoretically elucidates that vdW materials with low lattice symmetry and weak interlayer coupling allow the creation of multifarious thermodynamically advantageous slip stackings, and experimentally achieves13 and 9 slip stackings in 1T″-ReS2 and 1T″-ReSe2 bilayers via direct growth, which are systematically revealed by atomic-resolution scanning transmission electron microscopy (STEM), angle-resolved polarization Raman spectroscopy, and second harmonic generation (SHG) measurements. This work also develops modulation strategies to switch the stacking via grain boundaries (GBs) and to expand the slip stacking library from thermodynamic to kinetically favored structures via in situ thermal treatment. Finally, density functional theory (DFT) calculations suggest a prominent dependence of the pressure-induced electronic band structure transition on stacking configurations. These studies unveil a unique vdW epitaxy and offer a viable means for manipulating interlayer atomic registries.

Gradient microstructures and mechanical properties of WAAMed and aged Al–Cu alloy after laser shock peening

The integration of wire-arc additive manufacture (WAAM) and laser shock peening (LSP) facilitated the study of the gradient microstructure in T6-treated WAAM Al–Cu alloy and the synergistic strengthening mechanisms involving the precipitation phase and LSP parameters. The results indicate that pore closures, increases in kernel average misorientation (KAM), and low angle grain boundary (LAGB) are positively associated with LSP energy density. Residual stress positively correlates with LSP energy density and inversely with spot diameter, where larger spots exacerbate non-uniformity. The values of dislocation density, microhardness and residual stress of the post-LSP specimen gradually increase with the increase of depth, and reach the maximum value at ~100 μm. As the depth continues to increase, the value begins to decrease gradually. Dislocation accumulation near grain boundaries, interacting with θ’-Al2Cu, contributes to strength enhancement. The main strengthening mechanisms enhanced by LSP involve creating a gradient microstructure through significant plastic deformation, pore closure, and the presence of high-density dislocations. Post-T6 treatment, θ’-Al2Cu significantly restricts dislocation slip, pins dislocations, and encourages the emergence of new dislocation sources, thereby enhancing the strengthening effect and stability induced by LSP.

Research on hot deformation behavior and microstructure evolution mechanism of GH4169 superalloy

The hot deformation behavior and microstructure evolution of GH4169 superalloy were investigated through hot compression experiments with a temperature range of 900–1100 °C and strain rates ranging from 0.01 to 5 s−1. Concurrently, the flow stress curve of the alloy was obtained and constitutive equations were established. Based on the dynamic material model, a hot working diagram was established and the hot working window was optimized. The findings demonstrate that the high-temperature softening mechanism of this alloy primarily involves dynamic recrystallization (DRX), while both discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) exist. According to the hot processing map, the process parameters corresponding to the unstable areas are low temperatures and medium-high strain rates (900–985 °C, 0.15–5 s−1), and high temperatures and high strain rates (1025–1100 °C, 2.5–5 s−1). The reason is that the appearance of deformation bands and flow localization in the microstructure. The optimal hot working parameters for GH4169 are 1000 °C/0.01 s−1 and 1050–1100 °C/0.01–0.1 s−1, where the microstructure consists of uniformly distributed DRX grains. The volume fraction of DRX in GH4169 alloy rises with higher temperatures or lower strain rates. In addition, the reduction of intergranular dislocations promotes the migration of grain boundaries from low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs).

Structural evolution and mechanical response of multiple Al Σ5(210) grain boundaries with segregation of solute atoms: First-principles study

Grain boundary (GB) segregation of solute atoms is a key factor affecting the microstructure and macroscopic properties of materials. In this study, first-principles calculations were carried out to investigate the effect of solute atoms (Mg and Cu) segregation on the structural evolution and mechanical response of Al ground-state Σ5(210) GB (GB-Ⅰ) and metastable Σ5(210) GBs (GB-Ⅱ and GB-Ⅲ). The GB energy, segregation energy, and the theoretical tensile strength of the multiple Σ5(210) GBs were calculated. The results show that both Mg and Cu atoms tend to segregate in the boundary plane, thus reducing GB energy and improving GB stability. The segregation of Cu atoms reduced the GB energy more significantly than that of Mg atoms. The segregation of solute atoms can change the symmetric GB structure into an asymmetric one or induce GB phase transformation. The theoretical strength of GB-I is weaker than that of the metastable GB-II with higher GB energy, suggesting that grain boundaries with higher energy are not necessarily unstable. In addition, the effect of solute atom segregation on the GB strength depends not only on the type of element but also on the specific GB structure. The weakening effect of Mg segregation in GB-I and GB-II is due to the weak MgAl bond which enlarges the low charge density region of GB and increases the free volume of GB. The strengthening of GB-I and GB-II by Cu segregation mainly depends on the stronger AlCu bond than AlAl bond along the GB fracture path. The enhanced strength of GB-III with Mg and Cu segregation is attributed to the GB structural phase transformation caused by the segregation of solute atoms. The calculation results further elucidate the relationship between element segregation and grain boundary characteristics.

Phase-Field Simulation of Grain Growth in Uranium Silicide Nuclear Fuel

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.

One-pot hydrothermal synthesis of transition metal sulfides-decorated CuS microflower-like structures for electrochemical CO2 reduction to CO

Electrochemical CO2 reduction (ECR) to value-added products is regarded as a sustainable strategy to mitigate global warming and energy crisis, and designing highly efficient and robust catalysts is essential. In this work, transition metal sulfides (TMS)-decorated CuS microflower-like structures were prepared via the one-pot hydrothermal synthesis method for ECR to CO, and the influence of TMS doping on ECR performance was demonstrated. Characterization of the catalysts was performed using XRD, FESEM-EDS, N2 physisorption, and XPS, revealing the successful loading of TMS, the formation of microflower-like architectures and the generation of sulfur vacancies. Electrochemical tests demonstrated that doping ZnS, Bi2S3, CdS and MoS2 improved the intrinsic CO2 reduction activity of the CuS catalyst. Particularly, the MoS2-CuS composite catalyst with imperfect petal-like structure showed uniform distribution of edge Mo sites, which worked synergistically with the formed grain boundaries (GBs) and undercoordinated S vacancy sites in promoting CO2 activation, stabilizing *COOH adsorption, facilitating *CO desorption, and lowering the energy barrier of the potential-limiting step for improved CO selectivity. The MoS2-CuS catalyst achieved a maximum CO selectivity of 83.2% at –0.6 V versus the reversible hydrogen electrode (RHE) and a high CO cathodic energetic efficiency of 100%. At this potential, the catalyst maintained stable catalytic activity and CO selectivity during a 333-min electrolysis process. The findings will offer a promising avenue for the development of efficient and stable catalysts for CO production from ECR.