Microstructural Features Research Articles

(La0.8Sr0.2)0.95Mn0.5Fe0.5O3Perovskite as anEfficient Bi‐Functional Electrocatalyst for Oxygen‐Involved Reaction and Zn‐Air Batteries

AbstractThe perovskite‐type oxide (La0.8Sr0.2)0.95Mn0.5Fe0.5O3, synthesized using lanthanum resources recovered from polishing powder waste and manganese resources obtained from zinc anode mud, was obtained via a facile polymer‐assisted combustion method, and further applied in zinc‐air batteries.The crystal phase and microstructure features of the thus‐obtained nanoparticles were characterized using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X‐ray photoelectron spectroscopy (XPS), and nitrogen adsorption‐desorption measurements. The results showed that the (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 particles, with nanoscale size, possess a high specific surface area and a suitable Mn3+/Mn4+ molar ratio, which will benefit both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER). As expected, the thus‐fabricated (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 electrode exhibits a high current density of 71.2 and 85.2 mA cm−2 at −0.2 V and 0.6 V vs. Hg/HgO, respectively, which is superior to that of the commercial Pt/C catalyst (58 and 31 mA cm−2, respectively).Subsequently, this compound oxide can be an air electrode in a rechargeable zinc‐air battery. The assembled battery, using (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 as the cathode, exhibits a discharge voltage of 1.05~1.16 V and a charge voltage of 2.03~2.13 V under 15 mA cm−2 for 150 h.The excellent electrochemical results presented in this study highlight the potential of (La0.8Sr0.2)0.95Mn0.5Fe0.5O3 as a highly efficient and commercially viable bifunctional electrocatalyst for applications in rechargeable zinc‐air batteries.

Enhancing Ice Nucleation: The Role of Surface Roughness in Electrofreezing Using Laser Shock Processed Al6061 T6 Electrodes

The present study investigates the impact of the electrode surface roughness on the electrofreezing of water. This research focuses on how the electrode microstructure induced by a laser treatment affects the nucleation and growth of ice crystals under controlled electric fields. For this, electrofreezing experiments of deionized water over electrodes with varying surface roughnesses and crystalline textures were conducted. The electrodes of the Al6061 T6 alloy were microstructured via the Laser Shock Processing (LSP) method. For this purpose, the pulse densities during the LSP process were varied (900, 1600, and 2500 pulses/cm2). The increase in pulse density was correlated to the microstructural features and average roughness of the LSP-treated Al6061 alloy. A wave-like microstructure was induced upon the LSP treatment, with roughnesses between 3.5 and 6 µm at the selected pulse densities. The results indicate that electrode roughness significantly influences the electrofreezing process. Rougher electrodes were found to increase the nucleation temperature, suggesting enhanced ice nucleation activity. These findings are attributed to the increased electric field concentration at the asperities of the rough surfaces and the (111) planes of the Al6061 alloy, which may facilitate the alignment of water molecules and the formation of critical ice nuclei.

Effect of heat treatment on the microstructure and mechanical properties of AZ91D magnesium alloy fabricated via GTA wire arc additive manufacturing

This study aims to address elemental segregation and poor mechanical properties in as-deposited AZ91D magnesium alloy fabricated via wire arc additive manufacturing through heat treatment. Three distinct heat treatments are investigated: solution treatment (T4), artificial aging treatment (T5), and a combination of solution and aging treatment (T6). Microstructural analysis reveals equiaxed grains in all samples. In the T4 state, the eutectic phase along grain boundaries dissolvs into the matrix, reducing elemental segregation but increasing grain size. In the T5 state, elemental segregation is further reduced; however, due to the relatively low aging temperature, the microstructural features of the as-deposited state are largely retained. In the T6 state, solution treatment increases grain sizes, and the uneven distribution of the reprecipitated β phase leads variations in mechanical properties between vertical and horizontal directions. Compared to the as-deposited state, the T6 treatment achieves a synergistic improvement in both strength and ductility. The ultimate tensile strength increases to 262.3 MPa, and the elongation rises to 13.8%, representing improvements of 12.5% and 32.7%, respectively, compared to the as-deposited values of 233.2 MPa and 10.4%.

Effects of annealing and cold rolling on microstructural features, magnetic properties, tensile behavior and electrical resistance of FeCoNi(MnAl)x high entropy alloys

In this study, the microstructure, magnetic properties, and tensile behavior of high entropy alloys of FeCoNi(MnAl)x (x = 0–0.6, in molar ratios) were investigated after casting, cold rolling and annealing. X-ray diffractometry (XRD), field emission scanning electron microscope (FE-SEM), vibrating sample magnetometer (VSM), and also tensile tests were used to evaluate phase formation, microstructure, magnetic behavior and tensile properties of the samples, respectively. The results showed that as the indices of x value increase to 0.6, crystallographic structures transform from FCC to FCC + BCC. This in turn decreased the magnetic saturation of FeCoNi(MnAl)0.6 from 151 to 36 emu/g. Increasing x to 0.6, also raised the values of Hc from 3 to 16 Oe. This behavior was also observed in annealed and cold rolled alloys. Annealing treatment also released the residual stresses and resulted in reduction of Hc values. However, the highest values of Hc was observed in cold rolled samples which ranged from 5 to 25 Oe. The tensile strength of cold rolled and annealed alloys for x values of 0, 0.2, and 0.4, were 510, 635, and 910 Mpa, respectively. Furthermore, the electrical resistance augmented monotonously with an increasing value of x. It is therefore concluded that cold rolled and annealed high entropy alloys of FeCoNi(AlMn)x can present a variety combinations of tensile, magnetic, and electrical behavior when compared to other soft magnetic materials.

Investigation of the microstructural, surface, and optical properties of WO3-doped ZnO thin films

The paper investigates the microstructural characteristics, surface features, and optical properties of WO3-doped ZnO thin film. The deposited samples exhibit polycrystalline characteristics, with reflections corresponding to bimetal oxides and metals. Specifically, ZnO shows (101) and (200) reflections, while (400) reflections are observed in the WO3 phase of the deposited sample. The crystallite sizes of the ZnO metal oxide phase in the film are 85 nm and 55 nm, while the crystallite size of the Zn nanoparticles is found to be 47 nm. The atomic concentrations of W and Zn are 53.4 % and 46.6 % for films deposited on uncoated glass, and 41.2 % and 58.8 %, for films deposited onto ITO-coated glass, respectively. An optical band gap value of 3.40 eV was obtained for both films. It was found that certain properties remain relatively unchanged despite variations in the substrate.

Micro- and Macrostructural Language Features in Vertebrobasilar or Carotid System Stroke Without Diagnosis of Aphasia.

This study aimed to investigate the macro- and microstructural features of language in patients with ischemic stroke without aphasia. Participants were grouped according to arterial system damage and given the Aphasia Language Assessment Test (ADD) to detect aphasia. A narrative sample was obtained and analyzed for macrostructural and microstructural features of the language. The study sample consisted of 31 participants with ischemic stroke (15 vertebrobasilar system [VBS] involvement and 16 carotid system [CS] involvement) and 31 healthy participants, totaling 62 individuals. The healthy control group scored higher than the stroke group on the microstructural feature type-token ratio and mean length of utterance in the narrative analysis and on the auditory comprehension, repetition, naming, grammar, speech act, and writing subtests in ADD. Effort behavior, errors, edits, repetitions, and pauses among microstructural features and uncertainty, filler expression, and anomia among macrostructural features were significantly higher in the vertebrobasilar and CS groups than in the healthy control group. The total ADD score and speech fluency and reading subtest scores were significantly higher in individuals with VBS damage than in individuals with CS lesions (p < .05). Language components may be impaired differently in patients with carotid and vertebrobasilar lesions. Speech and language disorders in individuals who have experienced cerebrovascular accidents should be evaluated in the subacute and chronic phases, and the therapeutic needs of patients with ischemic stroke should be determined, regardless of the presence of a clinical aphasia diagnosis.

Effect of sawdust fillers loaded on Cucumis sativus fiber‐reinforced polymer composite: a novel composite for lightweight static application

AbstractThis research investigates the impact of sawdust fillers on Cucumis sativus fiber‐reinforced polymer composites through a conventional hand layup process. The objective is to develop a novel material suitable for static applications that is both lightweight and environmentally sustainable. A range of analytical techniques including X‐ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, mechanical testing, thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and energy‐dispersive X‐ray (EDX) analysis were employed to thoroughly characterize the resulting composite material. By integrating Cucumis sativus fibers and sawdust fillers into a polymer matrix, the study demonstrates the potential to create materials with improved mechanical properties due to addition of sawdust filler, including tensile strength (27.61 MPa), flexural strength (32.84 MPa), impact resistance (14.7 J cm−2) and hardness (42). These enhancements, averaging at 16.2%, are attributed to the addition of sawdust filler, which opens new avenues for environmentally conscious engineering solutions. XRD analysis reveals the composite's crystalline structure, indicating a crystallinity index of 64.5% and the orientation of crystalline planes. FTIR spectroscopy identifies chemical bonding and CO and CO functional groups present in the material with major peaks at 2123 and 2438 cm−1. TGA assesses the composite's thermal stability and decomposition behavior up to 380 °C. Additionally, SEM imaging elucidates the microstructural features and distribution of Cucumis sativus fibers and sawdust fillers within the epoxy matrix, while EDX analysis provides quantitative data on elemental composition. © 2024 Society of Chemical Industry.

Real-Time Simulation of the Reaction Kinetics of Supported Metal Nanoparticles.

A common issue with supported metal catalysts is the sintering of metal nanoparticles, resulting in catalyst deactivation. In this study, we propose a theoretical framework for realizing a real-time simulation of the reactivity of supported metal nanoparticles during the sintering process, combining density functional theory calculations, microkinetic modeling, Wulff-Kaichew construction, and sintering kinetic simulations. To validate our approach, we demonstrate its feasibility on α-Al2O3(0001)-supported Ag nanoparticles, where the simulated sintering behavior and ethylene epoxidation reaction rate as a function of time show qualitative agreement with experimental observation. Our proposed theoretical approach can be employed to screen out the promising microstructure feature of α-Al2O3 for stable supported Ag NPs, including the surface orientation and promoter species modified on it. The outlined approach of this work may be applied to a range of different thermocatalytic reactions other than ethylene epoxidation and provide guidance for the development of supported metal catalysts with long-term stability.

Structural disruption in subjective cognitive decline and mild cognitive impairment.

Subjective cognitive decline (SCD) marks the initial stage in Alzheimer's disease continuum. Nonetheless, current research findings regarding brain structural changes in the SCD are inconsistent. In this study, 37 SCD patients, 28 mild cognitive impairment (MCI) patients, and 42 healthy controls (HC) were recruited to investigate structural alterations. Morphological and microstructural differences among the three groups were analyzed based on T1- and diffusion-weighted images, correlating them with neuropsychological assessments. Additionally, classification analysis was performed by using support vector machines (SVM) categorize participants into three groups based on MRI features. Both SCD and MCI showed decreased volume in left inferior parietal lobe (IPL) compared to HC, while SCD showed altered morphologies in the right inferior temporal gyrus (ITG), right insula and right amygdala, and microstructures in fiber tracts of the right ITG, lateral occipital cortex (LOC) and insula relative to MCI. Moreover, the volume in the left IPL, right LOC, right amygdala and diffusivity value in fiber tracts of right LOC were significantly correlated with cognitive functions across all subjects. The classification models achieved an accuracy of > 0.7 (AUC = 0.8) in distinguishing the three groups. Our findings suggest that SCD and MCI share similar atrophy in the IPL but show more differences in morphological and microstructural features of cortical-subcortical areas.

Nonlinear viscoelasticity of filamentous fungal biofilms of Neurospora discreta

The picture of bacterial biofilms as a colloidal gel composed of rigid bacterial cells protected by extracellular crosslinked polymer matrix has been pivotal in understanding their ability to adapt their microstructure and viscoelasticity to environmental assaults. This work explores if an analogous perspective exists in fungal biofilms with long filamentous cells. To this end, we consider biofilms of the fungus Neurospora discreta formed on the air-liquid interface, which has shown an ability to remove excess nitrogen and phosphorous from wastewater effectively. We investigated the changes to the viscoelasticity and the microstructure of these biofilms when the biofilms uptake varying concentrations of nitrogen and phosphorous, using large amplitude oscillatory shear flow rheology (LAOS) and field-emission scanning electron microscopy (FESEM), respectively. A distinctive peak in the loss modulus (G″) at 30–50 % shear strain is observed, indicating the transition from an elastic to plastic deformation state. Though a peak in G″ has been observed in several soft materials, including bacterial biofilms, it has eluded interpretation in terms of quantifiable microstructural features. The central finding of this work is that the intensity of the G″ peak, signifying resistance to large deformations, correlates directly with the protein and polysaccharide concentrations per unit biomass in the extracellular matrix and inversely with the shear-induced changes in filament orientation in the hyphal network. These correlations have implications for the rational design of fungal biofilms with tuneable mechanical properties.

Dynamic strain ageing of austenitic Ni-based alloy during cyclic loading at 350 °C: Mechanism and its evolution

Dynamic strain ageing (DSA) in an austenitic Ni-based alloy was investigated by symmetric/asymmetric low cycle fatigue tests with different strain amplitudes at 350 °C. A quantitative analysis of DSA activity was provided in terms of the characteristic parameters (DSA transient and serration length), and associated microstructural features were explored. Particular attention was paid to the comparison in the DSA domain between Ni- and Fe-based austenite with different strain ratios. Results showed that DSA existed throughout life and led to the continuous cyclic hardening in austenitic Ni-based alloy. The DSA activity first decreased and remained almost constant under symmetric loadings. A gradual increase in DSA activity was observed for the asymmetric loadings before the final failure. In addition, a physical model was presented to explore the DSA mechanisms of austenitic Ni-based alloys in different temperature ranges. Specifically, at 350 °C, DSA is caused by C diffusion in austenite, while at higher temperatures, it may be caused by Cr diffusion. Moreover, for a given mechanism, the DSA occurred at a higher temperature range in Ni-based alloy than in Fe-based alloy.

Interactions between geometrical forms and microstructural features in culm of square bamboo

Bamboo culms can alter the bamboo’s geometric shape by adjusting the hierarchical organization of anatomical components as a means of adapting to different living conditions. Therefore, a square-like culm has been found commonly in the Chimonobambusa bamboo species. However, the underling mechanism for how these anatomical components assemble into a square culm in the species remains to be considered. Furthermore, the relationship between the geometrical construction of culm and its corresponding organization of anatomical components within also needs clarification. Therefore, the geometrical construction of cross-sections was examined in this work. A super-ellipse based on the Lamé curve was confirmed. Additionally, the transitional zone, at 3/4 in the radial direction, was detected as an inflection point where the geometric parameters clearly changed. Meanwhile, anatomical observation also suggested that the transitional zone can be identified as an inflection point because the fibre morphology difference in circumferential regions becomes more apparent in this area. It is worth mentioning that there is a coherence between the geometrical and microstructural features in circumferential and radial variation. These findings are meaningful to manifest the controlling mechanism of hierarchical structures on the geometrical shape of bamboo culm.

Evolution of microstructure and tensile behavior in an interstitial strengthened high entropy alloy

The microstructural evolution and mechanical properties of Fe61.5Cr17.5Ni11.5Al8C1.5 high-entropy alloys (HEAs) were investigated to establish an optimal set of annealing conditions that would result in reasonable recrystallized fractions across the different temperatures and durations. The evolution of the microstructure was analyzed, tracking the transformation from the rolling texture to the recrystallization texture, as well as any phase transformations that occurred. The grain size distribution, overall microstructural features, and the effects of annealing temperature and time on the tensile properties of the HEAs were examined and discussed. The alloy was subjected to cold rolling and subsequent annealing treatments, revealing a single FCC phase after homogenization at 1260 °C. The cold-rolled samples retained the FCC structure at lower annealing temperatures (400 °C and 500 °C) but underwent a phase transformation to BCC at higher temperatures (600 °C to 900 °C). Microstructural characterization demonstrated that cold rolling introduced a high density of dislocations, while annealing facilitated recrystallization and grain growth. The tensile tests indicated that HEA samples exhibited a yield strength of 570 MPa and ductility of ∼36 % with large grain size after a long annealing at elevated temperature. In contrast, after being heat-treated at 1200 °C for 2 min, HEAs restrict FCC-to-BCC phase transformation and exhibit small grain size (3.2 µm) with M23C6-like carbide precipitation in the FCC matrix. Smaller grains provide additional boundaries, which restrict dislocations to bypass these boundaries. While carbide precipitates at grain boundaries and inside grains, it strengthens the material by pinning grain boundaries and restricting dislocation movement, resulting in a yield strength of 610 MPa and ductility of ∼41 %.

2-D Microstructure Modeling based on Micrographs of Laser Powder Bed Fusion Melted Specimens

2D microstructural modeling based on the optical micrographs was successfully carried out. Creating a realistic microstructural model containing microstructural features such as fusion boundaries and phases makes it possible to analyze the relationship between the microstructure and property. We implemented this method to the 316 stainless steel (SS) laser powder bed fusion melted specimens. The optical micrographs were meshed and imported into finite element (FE) software. According to the results, the orientation of the fusion boundaries significantly influenced the mechanical properties of the printed parts. Stress localization was significant when the fusion boundaries were parallel to the loading direction. The situation differed when the fusion boundaries were perpendicular to the loading direction. In this case, the large amount and size of fusion boundaries showed significant ductility with homogenously distributed straining.

Crystallization behavior of BOF slag during the cooling process towards leaching for CO2 sequestration

This work addresses the crystallization behavior and microstructure feature of the molten basic oxygen furnace (BOF) slag during a slow cooling process. The aim is to provide a reference for the modification of BOF slag for subsequent leaching of Ca as part of CO2 sequestration. Integrated analysis of XRD, SEM-EDS, and thermodynamic calculations suggest a crystallization behavior of BOF slag during the cooling process. RO phases ((Mg, Fe, Mn) O) was the equilibrium phase at a high temperature of around 1600 °C, followed at lower temperatures by the formation of Ca3SiO5 (C3S) and α-Ca2SiO4 (α-C2S). The Ca2Fe2O5 (C2F) phase forms during the latter stages of melt solidification. On the basis of the combined analysis of the leaching test results and crystallographic analysis, a future direction of modification of BOF slag is suggested that enriches Ca into the C2S and hinders the formation of C2F. However, inhibiting the generation of C2F by adjusting the cooling process alone is difficult since its crystallization rate is fast. The phase of C2F was observed in XRD and SEM even if the BOF slag was quenched from 1600 °C. Furthermore, the chemical characterization and morphological evolution of the crystalline phase of molten BOF slag during the slow cooling process was observed.

Optimized synthesis and characterization of La(OH)3 and LaB6 nanostructures for enhanced NIR optical filters

The present study describes a method for synthesizing nanostructured La(OH)3 and LaB6 materials with efficient field emission properties using the spin coating technique. The study was motivated by the significant demand for the optical properties of LaB6 with efficient field emission properties using the spin coating technique in the near-infrared (NIR) region. The optimization of the LaB6 synthesis process for economic and reproducible results is highlighted, showcasing a systematic approach starting from La(OH)3 formation through chemical mixing and high-temperature heating, followed by boron incorporation. The systematic methodology includes forming La(OH)3 through chemical mixing and high-temperature heating, followed by combining it with boron to achieve the LaB6 structure. Characterization methods such as XRD, FTIR, SEM, AFM, and SIMS validated the successful synthesis and uniformity of the materials. Optical analyses showed increased visible transmittance and reduced infrared transmittance for the LaB6 thin film. Optical analyses showed increased visible transmittance and decreased infrared transmittance in the 110 nm thick LaB6 film, with an absorption valley at 1000 nm. SEM images revealed microstructural features and AFM analysis indicated a homogeneous distribution of La and B atoms with an RMS value of 0.87 nm. SIMS analysis confirmed uniform atomic distribution throughout the film thickness. The optimized recipes contribute to the efficiency and controllability of the synthesis process. The presented results provide valuable insights into material synthesis methodologies and serve as a crucial reference for utilizing LaB6 materials in infrared devices.

Predicting creep behavior in composites from microstructural features using deep learning

This study uses a multilayer perceptron deep learning model to predict creep strain vs time curves in composite materials based on their microstructural features. Finite element simulations generate ground truth data for model training and validation. The multilayer perceptron model, trained on this comprehensive dataset, effectively captures the complex relationships between the microstructure and creep behavior, achieving high accuracy. Comparative analysis with traditional models shows the multilayer perceptron model’s superior performance. This demonstrates the model’s potential for reliable application in various engineering fields, offering improved predictions of composite material behavior under creep conditions.

Drying Strawberry Slices: A Comparative Study of Electrohydrodynamic, Hot Air, and Electrohydrodynamic‐Hot Air Techniques

ABSTRACTThe investigation encompassed an examination of the drying durations, modeling, and quality attributes (color, rehydration capacity, microstructural features, total soluble solid [TSS], and pH values) of strawberry slices subjected to diverse drying methodologies, namely electrohydrodynamic (EHD), EHD‐hot air, and hot air processes. Furthermore, 10 distinct thin‐layer drying models were applied, and their goodness‐of‐fit was assessed to identify the most suitable model for the drying process. This analysis encompassed applying two distinct temperatures (50°C and 55°C), and voltage levels (20 and 30 kV). The EHD method yielded the lengthiest drying durations for the strawberry samples, with hot air and EHD‐hot air drying techniques subsequent in descending order of drying time. The outcomes of the modeling analyses demonstrated that the thin‐layer drying behaviors of used drying methods were best described by the Midilli et al. and Wang and Singh models in terms of their goodness‐of‐fit. A decline in the L* values was noted with the elevation of temperature in the hot air drying method and with the escalation of voltage in the EHD drying. The minimum a* value was detected in the hot air drying method conducted at 55°C. The rehydration capacity of strawberry samples subjected to the EHD and EHD‐hot air combination drying methods (except 20 kV‐55°C) did not exhibit any statistically significant variation in response to different voltage settings. Although the structure of strawberry samples dried with 20 kV application was observed as smoother, cracks occurred on the product surface in other drying applications. In hot air and EHD methods, varying temperature and volt applications did not show a significant effect on TSS and pH values. As a result, it has been seen that EHD technology, which is a promising drying method used in this study, is a suitable method in terms of processing efficiency and consumer acceptability of dried strawberry products.

Microstructure and mechanical properties of laser powder bed fusion Ti-6Al-4V after HIP treatments with varied temperatures and cooling rates

This work investigated non-standard HIP cycles for PBF-L Ti-6Al-4V and characterized microstructure and tensile properties to compare between material that originated from the same build. For 920°C, faster cooling rates (100°C/min, 2000°C/min) were found to promote bi-lamellar α microstructure, while the 2000°C/min cooling rate improved the strength. For HIP with lower temperature (800°C, 200 MPa), coarsening was minimized resulting in strength improvement. The slow cooling rate (12°C/min) showed the highest strength as faster rates increased the amount of orthorhombic martensite (α″). For HIP with higher temperature (1050°C), the as-built crystallographic texture was reduced and equiaxed prior-β grain morphology resulted, leading to more isotropic tensile properties. However, the cooling rate (2000°C/min) was not enough to prevent formation of grain boundary α, which reduced strength and elongation. Machine learning was carried out on the dataset via Principal Component Analysis (PCA) to reduce the dimensionality of the parameters and microstructural features.

Crystallographic Study of Transformation Products of Heat-Affected Zone and Correlation with Properties of FH690 Heavy-Gauge Marine Steel by Multi-Pass Submerged Arc Welding

In this work, the microstructure–property relationship of the heat-affected zone (HAZ) of a FH690 ultra-heavy marine steel plate was investigated based on insight of microstructure and crystallographic features. After multi-pass welding with a heat input of ~30 kJ/cm, an ~8 mm wide HAZ was obtained with a coarse grain HAZ (CGHAZ) of ~3.8 mm, fine grain HAZ (FGHAZ) of ~3.4 mm, and intercritical HAZ (ICHAZ) of ~1 mm. High impact toughness values of ~120 and 140 J at -60 °C were obtained for coarse grain HAZ and fine grain HAZ, respectively. The microstructure of the CGHAZ and FGHAZ was fine lath bainite. Although the average prior austenite grain size for the CGHAZ was ~75 μm, which was five times that of the FGHAZ (15 μm), a high density of high-angle grain boundaries (HAGBs) with misorientation higher than 45° was obtained in the CGHAZ. This is the underlying reason for the excellent low-temperature toughness of the HAZ. Thermo-dynamic calculations indicated that the high density of HAGBs in the CGHAZ was attributed to the decreased bainitic transformation temperature due to the reduced phase transformation driving force via the high nickel addition, leading to weak variant selection. In addition, the high nickel addition offered high hardenability for high hardness in the FGHAZ. The outcome of this study could provide an experimental and fundamental basis for designing high-strength ultra-heavy steel plates with excellent weldability.