Search Results (397)

In this study, the solidification behavior of 310S stainless steel was systematically investigated by combining high-temperature confocal laser scanning microscopy (HT-CLSM), microstructural characterization, and thermodynamic calculations. The focus was on the formation and transformation of ferrite, secondary-phase precipitation, and elemental segregation behavior, with comparisons made with 304 stainless steel. The effects of an Al addition and cooling rate were also explored. The results show that the solidification sequence of 310S stainless steel is L → L + γ → L + γ + δ → δ + γ, in which austenite nucleates early and grows rapidly, followed by the precipitation of a small amount of δ-ferrite in the later stages of solidification. In contrast, 304 stainless steel solidifies according to L → L + δ → L + δ + γ → δ + γ, with a rapid δ → γ transformation occurring after solidification. Compared with 304, 310S stainless steel exhibits a reduced ferrite fraction and a significantly increased σ phase content. The σ phase primarily precipitates directly from δ-ferrite (δ → σ), while M₂₃C₆ preferentially forms at grain boundaries and δ/γ interfaces, where δ-ferrite not only provides fast diffusion pathways for Cr but also nucleation sites. The solidification segregation sequence in 310S stainless steel is Cr > Ni > Fe, with Cr and Ni showing positive segregation and Fe showing negative segregation. The addition of Al does not alter the solidification mode of 310S stainless steel but refines austenite grains, reduces interdendritic solute enrichment, decreases segregation, lowers both the size and fraction of ferrite, and suppresses the precipitation of σ and M₂₃C₆ phases. This effect is mainly attributed to the reduction of δ/γ interfaces, which weakens the preferred nucleation sites for M₂₃C₆. Increasing the cooling rate enhances non-equilibrium solute segregation, promotes ferrite formation, inhibits the δ → γ transformation, and ultimately retains more ferrite; the intensified segregation further accelerates the δ → σ transformation. Full article

As 3D stacking technologies advance, low-temperature hybrid Cu bonding has become essential for fine-pitch integration. This study focuses on evaluating Pd nanolayers deposited by electroless plating (ELP) on Cu surfaces and compares them to electroplated (EP) Pd to assess their suitability for hybrid bonding. Pd nanolayers (5~7 nm) were deposited on Cu films, and their surface morphology, crystallinity, and chemical composition were characterized using AFM, TEM, GIXRD, and XPS. EP-Pd layers exhibited lower roughness and larger grain size, acting as effective Cu diffusion barriers. In contrast, ELP-Pd layers showed small grains, higher surface roughness, and partial Cu diffusion and oxidation. At 200 °C, both Pd layers enabled bonding, but ELP-Pd samples achieved more uniform and continuous interfaces with thinner copper oxide layers. Shear testing revealed that ELP-Pd samples exhibited higher average bonding strength (20.58 MPa) and lower variability compared to EP-Pd (16.47 MPa). The improved bonding performance of ELP-Pd is attributed to its grain-boundary-driven diffusion and uniform interface formation. These findings highlight the potential of electroless Pd as a passivation layer for low-temperature hybrid Cu bonding and underscore the importance of optimizing pre-bonding surface treatments for improved bonding quality. Full article

The grain boundary diffusion (GBD) process is currently the relatively effective method for utilizing heavy rare earth (HRE) elements in NdFeB magnets, especially for magnetic sheets. However, due to a highly uneven microstructure, the recovery of GBD magnets was considered difficult. In this work, our study prioritized short-loop recycling of GBD NdFeB sheet magnets to prepare block magnets. A comparative investigation was conducted between GBD-processed NdFeB magnets and the conventional sintered magnets, with particular emphasis on their recyclability characteristics. Among them, the Tb content of GBD magnets of 0.4 wt.% was significantly lower than sintered magnets of 1.73 wt.%. When two waste magnets were supplemented with the same amount of rare earth, it was found that the coercivity of the block magnets regenerated from GBD sheet magnets was higher. Microstructural analysis revealed that the core–shell grains originally located in the surface layer of GBD magnets were uniformly mixed and diffused with the ordinary particles originally located inside during the regeneration sintering process. The regenerated GBD magnets exhibited a more uniform core–shell microstructure with submicron shells of Tb elements along with reduced areas of RE-rich phase enrichment which facilitated the formation of a continuous and uniform thin-layer grain boundary, thereby enhancing the magnetic isolation effect. Apart from the significance of recycling, these block magnets regenerated from GBD magnets also provides a new approach to solving the challenge of high coercivity and low HRE elements in bulk magnets. Full article

The present study focused on 10 wt.% TiB₂@Ti/AlCoCrFeNi_2.1 eutectic high-entropy alloy matrix composites (EHEAMCs), which were treated with furnace cooling (FC), air cooling (AC), and water cooling (WC) after being held at 1000 °C for 12 h, aiming to investigate the effect of cooling methods on their microstructure and mechanical properties. The results showed that the composites in all states consisted of FCC phase, BCC phase, TiB₂ phase, and Ti phase. The cooling methods did not change the phase types but affected the diffraction peak characteristics. With the increase in cooling rate, the diffraction peaks of FCC and BCC phases gradually separated from overlapping, and the diffraction peak of the FCC (111) crystal plane shifted to a lower angle (due to the increase in lattice constant caused by Ti element diffusion), while the diffraction peak intensity showed a downward trend. In terms of microstructure, all composites under the three cooling conditions were composed of eutectic matrix, solid solution zone, and grain boundary zone. The cooling rate had little effect on the morphology but significantly affected the element distribution. During slow cooling (FC, AC), Ti and B diffused sufficiently from the grain boundary to the matrix, resulting in higher concentrations of Ti and B in the matrix (Ti in FCC phase: 7.4 at.%, B in BCC phase: 8.1 at.% in FC state). During rapid cooling (WC), diffusion was inhibited, leading to lower concentrations in the matrix (Ti in FCC phase: 4.6 at.%, B in BCC phase: 4.3 at.%), but the element distribution was more uniform. Mechanical properties decreased with the increase in cooling rate: the FC state showed the optimal average hardness (627.0 ± 26.1 HV), yield strength (1574 MPa), fracture strength (2824 MPa), and fracture strain (24.2%); the WC state had the lowest performance (hardness: 543.2 ± 35.4 HV and yield strength: 1401 MPa) but was still better than the as-sintered state. Solid solution strengthening was the main mechanism, and slow cooling promoted element diffusion to enhance lattice distortion, achieving the synergistic improvement of strength and plasticity. Full article

Developing structural materials capable of maintaining integrity under extreme irradiation conditions is a cornerstone challenge for advancing sustainable nuclear energy technologies. The complexity and severity of radiation-induced microstructural changes—spanning multiple length and timescales—pose significant hurdles for purely experimental approaches. This review critically evaluates recent advancements in atomistic modeling, emphasizing its transformative potential to decipher fundamental mechanisms driving microstructural evolution in irradiated alloys. Atomistic simulations, such as molecular dynamics (MD), have successfully unveiled initial defect formation processes at picosecond scales. However, the inherent temporal limitations of conventional MD necessitate advanced methodologies capable of exploring slower, thermally activated defect kinetics. We specifically traced the development of powerful potential energy landscape (PEL) exploration algorithms, which enable the simulation of high-barrier, rare events of defect evolution processes that govern long-term material degradation. The review systematically examines point defect behaviors in various crystal structures—BCC, FCC, and HCP metals—and elucidates their characteristic defect dynamics, respectively. Additionally, it highlights the pronounced effects of chemical complexity in concentrated solid-solution alloys and high-entropy alloys, notably their sluggish diffusion and enhanced defect recombination, underpinning their superior radiation tolerance. Further, the interaction of extended defects with mechanical stresses and their mechanistic implications for material properties are discussed, highlighting the critical interplay between thermal activation and strain rate in defect evolution. Special attention is dedicated to the diverse mechanisms of dislocation–obstacle interactions, as well as the behaviors of metastable grain boundaries under far-from-equilibrium environments. The integration of data-driven methods and machine learning with atomistic modeling is also explored, showcasing their roles in developing quantum-accurate potentials, automating defect analysis, and enabling efficient surrogate models for predictive design. This comprehensive review also outlines future research directions and fundamental questions, paving the way toward autonomous materials’ discovery in extreme environments. Full article

This study investigates the use of nanocrystalline Cu (NC-Cu) to suppress interfacial voids in low-temperature Cu-Cu bonding for 3D IC packaging. We quantitatively compared the void characteristics of electrodeposited NC-Cu (grain size ~89.3 nm) and (111)-oriented nanotwinned Cu (NT-Cu, ~621.8 nm) bonded at 200 °C. Plan-view STEM-HAADF analysis revealed that NC-Cu achieved a much lower void area ratio (1.8%) than NT-Cu (4.0%), attributed to its high grain boundary density, which enhances atomic diffusion and grain boundary migration. At 250 °C, typical Ostwald ripening was observed, with fewer but larger voids. However, a rise in total void area fraction suggests a competing mechanism—possibly new void nucleation at grain boundaries triggered by residual defects from the electroplating process. These results highlight the superior void-mitigating capability of NC-Cu under low thermal budgets. Full article

This study systematically investigates the homogenization-induced Laves phase dissolution kinetics and recrystallization mechanisms in laser powder bed fusion (L-PBF) processed IN718 superalloy. The as-built material exhibits a characteristic fine dendritic microstructure with interdendritic Laves phase segregation and high dislocation density, featuring directional sub-grain boundaries aligned with the build direction. Laves phase dissolution demonstrates dual-stage kinetics: initial rapid dissolution (0–15 min) governed by bulk atomic diffusion, followed by interface reaction-controlled deceleration (15–60 min) after 1 h at 1150 °C. Complete dissolution of the Laves phase is achieved after 3.7 h at 1150 °C. Recrystallization initiates preferentially at serrated grain boundaries through boundary bulging mechanisms, driven by localized orientation gradients and stored energy differentials. Grain growth kinetics obey a fourth-power time dependence, confirming Ostwald ripening-controlled boundary migration via grain boundary diffusion. Such a study is expected to be helpful in understanding the microstructural development of L-PBF-built IN718 under heat treatments. Full article

Aluminum (Al) alloys exhibit exceptional mechanical properties, seeing widespread use in various industrial fields. Here, we use a multiscale simulation method combining phase field method, dislocation dynamics, and crystal plasticity finite element method to reveal the evolution law of precipitates, the interaction mechanism between dislocations and precipitates, and the grain-level creep deformation mechanism in 7A09 Al alloy under creep loading. The phase field method indicates that Al alloys tend to form fewer but larger precipitates during the creep process, under the dominant effect of stress-assisted Ostwald ripening. The dynamic equilibrium process of precipitate is not only controlled by classical diffusion mechanisms, but also closely related to the local strain field induced by dislocations and the elastic interaction between precipitates. Dislocation dynamics simulations indicate that the appearance of multiple dislocation loops around the precipitate during the creep process is the main dislocation creep deformation mechanism. A crystal plasticity finite element model is established based on experimental characterization to investigate the macroscopic creep mechanism. The dislocation climb is hindered by grain boundaries during creep, and high-density dislocation bands are formed around specific grains, promoting non-uniform plastic strain and leading to strong strain gradients. This work provides fundamental insights into understanding creep behavior and deformation mechanism of Al alloy for deep-sea environments. Full article

By applying different heat treatment processes (furnace cooling, air cooling, and water cooling), the stress–strain behavior of the localized interfacial region in weathering steel–stainless steel clad plates was investigated using nanoindentation, along with an analysis of interfacial microstructure formation and strengthening mechanisms. The results show that samples in the as-rolled (R), furnace-cooled (FC), air-cooled (AC), and water-cooled (WC) conditions exhibit distinct interfacial morphologies and local mechanical properties. A well-defined interfacial layer forms between the base and cladding materials, where a high density of dislocations, grain boundaries, precipitates, and nanoscale oxides significantly enhances interfacial strength, resulting in a yield strength (R_p0.2) much higher than that of either adjacent metal. Across the transition from weathering steel to stainless steel, the interfacial region consists of ferrite—interfacial layer—“new austenite”—stainless steel austenite. Its formation is predominantly governed by element diffusion, which is strongly influenced by the applied heat treatment. Variations in diffusion behavior significantly affect the microstructural evolution of the dual-phase transition zone at the interface, thereby altering the local mechanical response. Full article

This study systematically investigates the effects of heat treatment at 800–1000 °C on the microstructure and mechanical properties of 10 wt.% TiB₂@Ti/AlCoCrFeNi_2.1 eutectic high-entropy alloy matrix composites (EHEAMCs) prepared by vacuum hot-pressing sintering. The results show that the materials consist of FCC, BCC, TiB₂, and Ti phases, with a preferred orientation of the (111) crystal plane of the FCC phase. As the temperature increases, the diffraction peak of the BCC phase separates from the main FCC peak and its intensity increases, while the diffraction peak positions of the FCC and BCC phases shift at small angles. This is attributed to the diffusion of TiB₂@Ti from the grain boundaries into the matrix, where the Ti solid solution increases the lattice constant of the FCC phase. Microstructural observations reveal that the eutectic region transforms from lamellar to island-like structures, and the solid solution zone narrows. With increasing temperature, the Ti concentration in the solid solution zone increases, while the contents of elements such as Ni decrease. Element diffusion is influenced by binary mixing enthalpy, with Ti and B tending to solidify in the FCC and BCC phase regions, respectively. The mechanical properties improve with increasing temperature. At 1000 °C, the average hardness is 579.2 HV, the yield strength is 1294 MPa, the fracture strength is 2385 MPa, and the fracture strain is 19.4%, representing improvements of 35.5% and 24.9% compared to the as-sintered state, respectively, without loss of plasticity. The strengthening mechanisms include enhanced solid solution strengthening due to the diffusion of Ti and TiB₂, improved grain boundary strength due to the diffusion of alloy elements to the grain boundaries, and synergistic optimization of strength and plasticity. Full article

Corrosion poses a critical challenge to the durability and performance of metals and alloys, particularly steel, with significant economic, environmental, and safety implications. The corrosion susceptibility of steel is influenced by aggressive chemical species, intrinsic material defects, and environmental factors. Understanding the atomic-scale mechanisms governing corrosion is essential for developing advanced corrosion-resistant materials. Density functional theory (DFT) has become a powerful computational tool for investigating these mechanisms, providing insight into the adsorption, diffusion, and reaction of corrosive species on iron surfaces, the formation and stability of metal oxides, and the influence of defects such as vacancies and grain boundaries in localised corrosion. This review presents a comprehensive analysis of recent DFT-based studies on iron and steel surfaces, emphasising the role of solvation effects and van der Waals corrections in improving model accuracy. It also explores defect-driven corrosion mechanisms and the formation of protective and reactive oxide layers under varying oxygen coverages. By establishing accurate DFT modelling approaches, this review provides up-to-date literature insights that support future integration with machine learning and multiscale modelling techniques, enabling reliable atomic-scale predictions. Full article

This study systematically investigates the influence mechanism of the element Cr on the mechanical properties of the heat-affected zone in pipeline steels for supercritical CO₂ transportation. Microstructural evolution in the heat affected-zone was characterized through thermal simulation tests, Charpy impact testing (−10 °C), and microhardness measurements, complemented by multiscale microscopic analyses (optical microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy). The results demonstrate that Cr addition enhances the base metal’s resistance to supercritical CO₂ corrosion but reduces its low-temperature impact toughness from 277 J to 235 J at −10 °C. Notably, the intercritical heat-affected zone exhibits severe embrittlement, with impact energy plummeting from 235 J (base metal) to 77 J. Microstructural analysis reveals that Cr interacts with carbon to form stable carbonitride particles, which reduce the free carbon concentration and diffusion coefficient in austenite, thereby inducing heterogeneous austenitization. Undissolved carbonitrides pin grain boundaries, creating carbon concentration gradients. During rapid cooling, these localized carbon-enriched microregions preferentially transform into core–shell-structured M-A constituent, characterized by a micro-twin containing retained austenite core encapsulated by high hardness lath martensite. The synergistic interaction between micro-twins and interfacial thermal mismatch stress induces localized stress concentration, triggering microcrack nucleation and subsequent toughness degradation. Full article

During the heat treatment of stainless steel (SS)/carbon steel (CS) bimetal composites, the carbon in the CS diffuses into the SS, and carbides precipitate on the grain boundary and in the grains, affecting the microstructure and properties of the composite steel. In order to change the precipitation and distribution of the carbides seen on hot-rolled 304/Q235 after cold drawing (HR), the microstructure and properties of composite round steel were investigated by optical microscopy, SEM/EDS, and hardness, tensile, fatigue, and electrochemical tests while changing the temperature of the full annealing and aging treatments. The results showed that dispersed chromium carbide particles precipitated at the grain boundaries, and intragranular and slip lines promoted simultaneous dispersion strengthening and fine-grain strengthening and greatly improved the hardness, yield strength, tensile strength, and fatigue strength of the composite round steel. However, the increase in chromium carbide particles leads to the formation of stress concentration points and accelerates the creation of fatigue cracks, resulting in a decrease in the fatigue strength of the steel. Simultaneously, the corrosion resistance of the composite round steel samples was reduced due to the precipitation of a large amount of chromium carbide. Full article

The novel pyridine oxime-based complexing agents 2-pyridinecarboxaldehyde oxime, 2-acetylpyridine ketoxime and 2-pyridine amidoxime were synthesized for alkaline Zn-Ni alloy electrodeposition, outperforming conventional citrate/TEPA systems in corrosion resistance and microstructural control. The N,O-bidentate chelation mechanism governs metal ion reduction kinetics via diffusion-limited pathways, enabling γ-phase Ni₅Zn₂₁ intermetallic formation and nanocrystalline refinement. Electrochemical and microstructural analyses demonstrate suppressed random nucleation and hydrogen evolution side reactions, leading to enhanced charge transfer resistance and reduced corrosion current density. Notably, 2-pyridine amidoxime achieves ultrasmooth surfaces through defect-free nanocluster growth, while 2-pyridinecarboxaldehyde oxime maximizes γ-phase crystallinity. The synergy between grain boundary density and surface integrity establishes a dual protection mechanism combining barrier layer formation and active dissolution suppression. This work advances microstructure engineering via coordination chemistry, offering a breakthrough over traditional zincate electroplating for high-performance anti-corrosion coatings. Full article

During the high-temperature preparation of stainless steel cladding plate, carbon atoms from carbon steel diffused into stainless steel. When temperatures were within 450–850 °C, carbides precipitated at grain boundaries, which initiated intergranular sensitization and thereby reduced the corrosion resistance of stainless steel. This study designed NiP and NiCuP interlayer alloys to effectively block carbon diffusion in stainless steel cladding plates. The effect of adding interlayers on the microstructure of stainless steel cladding plate was studied by using optical microscopy and scanning electron microscopy. Electrochemical tests were subsequently conducted to evaluate the impact of interlayer incorporation on the corrosion resistance of stainless steel cladding. The results demonstrated that 304/45 specimens exhibited severe carbon diffusion, resulting in the poorest corrosion resistance. The addition of interlayers improved the corrosion resistance of stainless steel cladding to varying degrees. Among these, the 304/NiCuP/45 specimen showed the best performance. It had an intergranular corrosion susceptibility of only 0.25% and pitting potential as high as 0.336 V, which indicated its superior corrosion resistance. The passive film of stainless steel cladding exhibited n-type semiconductor characteristics. And 304/NiCuP/45 specimen demonstrated the lowest carrier density of 3.02 × 10¹⁸ cm⁻³, which indicated the formation of the densest passive film. Full article