Search Results (1,164)

The steel industry is responsible for 7–9% of global CO₂ emissions. Shifting from primary iron ore to recycled scrap in electric arc furnace (EAF) steelmaking offers significant decarbonization potential, reducing carbon intensity by 60–70%. However, increased scrap use in EAF operations leads to higher nitrogen absorption, which can degrade mechanical properties. Nitrogen dissolves into molten steel, where it forms Cottrell atmospheres at dislocations in the following processing steps, intensifying strain aging and reducing ductility. This study establishes a precipitation criterion based on the TiN solubility product to prevent harmful liquid TiN formation, enabling effective nitrogen fixation via fine TiN precipitates (5–20 nm). Multiscale characterization techniques, such as TEM and EBSD, show that Ti reduces the number of mobile N atoms by 60–70%, evidenced by a 50–65% decrease in Snoek/SKK peak intensities. Excessive titanium can refine ferrite grain size and prevents harmful TiN inclusions. Titanium microalloying presents a cost-effective, sustainable strategy to reduce strain aging in scrap-rich EAF steels, enabling more sustainable steel production without sacrificing material properties. Full article

Al–Zn–Mg–Cu alloys are well known for their outstanding strength, toughness, and corrosion resistance, arising from the balanced addition of Mg, Zn, and Cu. However, conventional casting methods often lead to grain boundary segregation and the formation of coarse Fe-rich phases, which severely limit subsequent heat treatment and plastic processing. To overcome these drawbacks, this study systematically investigates the effects of the Continuous Rheo-Extrusion (CRE) process on the microstructure and mechanical performance of Al–Zn–Mg–Cu alloys using XRD, EBSD, SEM, and TEM analyses. The CRE process refines the average grain size from 53.5 μm to 16.1 μm and raises the fraction of high-angle grain boundaries to 88.8%. Moreover, coarse Fe-rich phases are fragmented to below 5 μm, while the elemental distribution of Zn, Mg, and Cu becomes more homogeneous, effectively reducing grain boundary segregation. The Al₂Cu precipitates are refined from 106.3 nm to 11.7 nm, corresponding to an 88.9% size reduction. These microstructural optimizations yield a remarkable increase in tensile strength (from 204.7 ± 23.7 MPa to 338.0 ± 9.3 MPa) and elongation (from 11.4 ± 2.4% to 13.8 ± 1.3%). Quantitative analysis confirms that dislocation and precipitation strengthening are the dominant contributors to this improvement. Overall, the CRE process enhances microstructural uniformity through the synergistic effects of shear deformation, continuous dynamic recrystallization (CDRX), and dynamic precipitation, thereby providing a solid theoretical and practical foundation for short-process fabrication of high-strength, high-ductility Al–Zn–Mg–Cu alloys. Full article

Grain refinement represents a critical approach in optimizing the as-cast microstructure of magnesium alloys, playing a pivotal role in the development of high-performance magnesium alloys. In the present research, a novel Al-Ce-C-O-Mg grain refiner was fabricated using an innovative rolling-assisted process, and the influence of the grain refiner on the grain size evolution of as-cast AZ91 alloy was systematically examined. The Al-Ce-C-O-Mg grain refiner prepared by the rolling-assisted process contains two types of effective refining particles—MgAl₂O₄ and Al₄C₃. These particles can act as potent nucleation sites for α-Mg in the melt, promoting efficient nucleation and achieving significant grain refinement. By adding 1.0 wt.% of the Al-Ce-C-O-Mg grain refiner to the AZ91 alloy, the grain size of the original AZ91 alloy was reduced by 73%. Moreover, adding a refiner facilitated the transformation of the coarse β-Mg₁₇Al₁₂ phase morphologies into a more uniformly distributed and dispersed form. The addition of 1.0 wt.% Al-Ce-C-O-Mg grain refiner to the AZ91 alloy resulted in significant improvements in its mechanical properties. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) increased from 158 MPa, 104 MPa, and 3.9% to 203 MPa, 121 MPa, and 6.3%, respectively. The grain refiner developed in this study demonstrates promising potential for application in Mg alloys. Full article

Overcoming the strength–ductility trade-off in conventional aluminum matrix composites (AMCs) remains a significant challenge. This study employs dual-scale hybrid reinforcement particles comprising micron-sized Cu and nano-sized Ti, alongside bimodal micro-sized pure Al powders as matrix fillers. The AMCs were fabricated through ball milling (BM) combined with multi-pass friction stir processing (FSP). The homogenously distributed hybrid reinforcement particles generate an integrated composite region consisting of both coarse-grained (CG) and fine-grained (FG) structures, demonstrating enhanced material characteristics. The interwoven network of coarse- and fine-crystalline domains constructs a heterogeneous architecture that enables simultaneous improvement in both strength and ductility properties. The micron-Cu acts as a skeletal support within the matrix, enhancing load transfer efficiency and effectively hindering dislocation motion. The nano-Ti and in situ intermetallics facilitate grain refinement via the pinning effect and promote heterogeneous nucleation, which contributes to stress dispersion and dislocation obstruction. The addition of dual-scale micron-sized pure Al powder particles promotes the formation of the heterogeneous architecture, which enhances the balancing of strength and ductility in the composite. Following compositing (Al₁₀-5Cu-10Ti-10Al₂₀), the alloy exhibits an ultimate tensile strength (UST) of 267 MPa, a hardness of 98 HV, and an elongation of 16.7%, representing increases of 193.4%, 226.7%, and 9.9%, respectively, relative to the base metal. Full article

In this study, a biodegradable Mg-Zn-Nd-Gd alloy was processed via multi-directional forging (MDF) to evaluate its microstructural evolution, mechanical performance, and corrosion behavior. Electron backscattered diffraction (EBSD) analysis was conducted to evaluate the influence of grain size and texture on mechanical strength and corrosion resistance. The average grain size decreased significantly from 118 ± 5 μm in the homogenized state to 30 ± 10 μm after six MDF passes, primarily driven by discontinuous dynamic recrystallization (DDRX). Remarkably, this magnesium (Mg) alloy exhibited a rare synergistic enhancement in both strength and ductility, with ultimate tensile strength (UTS) increasing by ~59%, yield strength (YS) by ~90%, while elongation improved by ~44% unlike conventional severe plastic deformation (SPD) techniques that often sacrifice ductility for strength. This improvement is attributed to grain refinement, dispersion strengthening from finely distributed Mg₁₂Nd and Mg₇Zn₃ precipitates, and texture weakening, which facilitated the activation of non-basal slip systems. Despite the mechanical improvements, electrochemical corrosion testing in Hank’s balanced salt solution (HBSS) at 37 °C revealed an increased corrosion rate from 0.1165 mm/yr in homogenized condition to 0.2499 mm/yr (after six passes of MDF. This was due to the higher fraction of low-angle grain boundaries (LAGBs), weak basal texture, and the presence of electrochemically active fine Mg₇Zn₃ particles. However, the corrosion rate remained within the acceptable range for bioresorbable implant applications, indicating a favorable trade-off between mechanical performance and degradation behavior. These findings demonstrate that MDF processing effectively enhances the strength–ductility synergy of Mg-rare earth alloys while maintaining a clinically acceptable degradation rate, thereby presenting a promising route for next-generation biomedical implants. Full article

This study employs a multi-technique approach to elucidate how graphene incorporation affects phase formation, microstructure, and thermal behavior in PVA-assisted sol–gel synthesized Ca_2.95Eu_0.05Co₄O_x nanomaterials. XRD confirms the preservation of the primary phases (hexagonal CaCO₃ and cubic CoO) alongside a distinct graphene (002) reflection; a systematic low-angle shift of the calcite (104) peak evidences partial relaxation of residual lattice strain with increasing graphene content, while Scherrer analysis indicates tunable crystallite size. Raman spectroscopy corroborates graphene incorporation through pronounced D (~1300 cm⁻¹) and G (~1580 cm⁻¹) bands and supports the XRD-identified phase coexistence via cobalt-oxide and calcite vibrations in the 200–700 cm⁻¹ region, also indicating increased defect/disorder with graphene loading. SEM shows grain refinement, denser/bridged lamellar textures, and reduced porosity at low–moderate graphene contents (1–3 wt.%), contrasted by agglomeration-driven heterogeneity at higher loadings (5–7 wt.%). EDX reveals increasing carbon with Ca/Co redistribution at accessible surfaces, and TG–DSC corroborates the removal of oxygen-containing groups and oxidative combustion of graphene at mid temperatures. Collectively, Raman–XRD-consistent evidence demonstrates that graphene provides a tunable handle over lattice strain, crystallite size, and grain-boundary architecture, establishing a processing–composition basis for optimizing functional (e.g., electrical/thermoelectric) performance. Full article

Magnesium alloys, characterized by high specific strength and low density, have high potential for applications in transportation and aerospace. Nevertheless, ensuring the reliable joining of thin-walled components remains a major technical challenge. This study examines how rotational speed affects the microstructure and mechanical properties of friction stir welded AZ61 magnesium alloy hollow profiles (3 mm thick), with particular focus on the underlying mechanisms. The results show that higher rotational speed during friction stir welding promotes dynamic recrystallization and weakens the basal texture. It also affects microstructural homogeneity, where an optimal rotational speed produces a relatively uniform hybrid microstructure consisting of refined recrystallized and un-recrystallized regions. This balance enhances both texture strengthening and microstructural optimization. The weld joint fabricated at a rotational speed of 1500 rpm showed the best overall mechanical properties, with ultimate tensile strength, yield strength, and elongation reaching peak values of 286.7 MPa, 154.7 MPa, and 9.7%, respectively. At this speed, the average grain size in the weld nugget zone was 4.92 μm, and the volume fraction of second-phase particles was 0.67%. This study establishes a critical process foundation for the reliable joining of thin-walled magnesium alloy structures. The optimized parameters serve as valuable guidelines for engineering applications in lightweight transportation equipment and aerospace manufacturing. Full article

This study investigates the microstructure and mechanical properties of copper (Cu) and graphene/Cu (Gr/Cu) composites produced via high-pressure torsion (HPT) under 5 GPa at room temperature. Microstructural analysis revealed significant grain refinement, with average grain sizes of 0.39 μm for pure Cu and 0.35 μm for Gr/Cu composite. The Gr/Cu composite exhibited slightly higher microstrains and effective stacking fault energy (SFE). Tensile tests showed ultimate tensile strengths of 689 MPa (pure Cu) and 674 MPa (Gr/Cu), with the latter demonstrating improved ductility (~10% elongation). Ab initio calculations confirmed a 27% increase in SFE for Gr/Cu, aligning with experimental results. These findings highlight the potential of Gr/Cu composites for applications requiring high strength and efficient heat dissipation. Full article

The low-temperature impact properties of high-heat-input steels, particularly low-carbon Nb–Ti steel, are significantly influenced by the coarse-grained heat-affected zone (CGHAZ) in welded joints. The microstructure predominantly consists of granular bainitic ferrite (GBF), ferrite side plate (FSP), degenerate pearlite (DP), coarse plate-like ferrite (PF), and limited acicular ferrite (AF). This study investigates the effect of lanthanum (La) addition to Nb–Ti steel, leading to the formation of composite inclusions with a LaAlO₃·TiN core surrounded by MnS/MnC precipitates. Unlike conventional Al₂O₃·MnS inclusions in Nb–Ti steel, these La-modified inclusions promote enhanced AF nucleation. This not only refines prior austenite grains but also reduces detrimental microstructural constituents such as GBF and FSP. As a result, the impact energy at −40 °C significantly improves from 23 J (Nb–Ti steel) to 137 J (Nb–Ti–La steel). Moreover, the inclusions exhibit an increase in size but a decrease in number density. The Nb–Ti–La variant demonstrates a higher AF volume fraction and increased AF density within the CGHAZ. The refined grain structure, along with an increased proportion of high-angle grain boundaries, effectively impedes secondary crack propagation. These microstructural modifications contribute to a substantial improvement in the low-temperature impact toughness of welded joints. Full article

The cold-rolled 2024 aluminum alloy sheets were subjected to solution treatments at different temperatures followed by artificial aging. The microstructure and mechanical properties were investigated using Vickers microhardness testing, tensile testing, optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results indicate that as the solution temperature increases, the coarse particles gradually dissolved into the matrix. At a solution temperature of 500 °C, the grains become nearly equiaxed with an average size of ~16.47 μm, and no significant grain growth is observed compared to the as-rolled condition. The refined microstructure contributes to excellent mechanical properties. In contrast, when the solution temperature increases to 550 °C, the microstructure shows severe grain coarsening (up to ~61.39 μm), which indicates that overburning occurs, resulting in a drastic deterioration in mechanical performance. As the aging time increases, precipitates become more uniformly and densely distributed throughout the matrix, and the hardness initially increases and reaches a peak after approximately 6 h of aging at 180 °C. The optimal mechanical performance, characterized by a favorable combination of strength and ductility, is achieved at an aging time of 6 h. In summary, the optimal heat treatment condition for the cold-rolled 2024 aluminum alloy sheet is solution treatment at 500 °C for 1 h followed by aging at 180 °C for 6 h, resulting in a hardness of 154 HV, a tensile strength of 465 MPa and an elongation of 13%. Full article

Polycrystalline copper optics are widely utilized in infrared systems due to their exceptional electrical and thermal conductivity combined with favorable machining characteristics. The grain size profoundly influences both surface quality consistency and fundamental material removal behavior during processing. This investigation employs multiscale numerical modeling to simulate nanoscale cutting processes in polycrystalline copper with controlled grain structures, coupled with experimental ultra-precision machining validation. Comprehensive analysis of stress distribution, subsurface damage formation, and cutting force evolution reveals that refined grain structures promote more homogeneous plastic deformation, resulting in superior surface finish with reduced roughness and diminished grain boundary step formation. However, the enhanced grain boundary density in fine-grained specimens necessitates increased cutting energy input. These findings establish critical process–structure–property relationships essential for advancing precision manufacturing of copper-based optical systems. Full article

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

In this paper, 316 stainless steel/TiC coatings with different LaB₆ contents (0%, 2%, 4%, 6%) were prepared on the surface of 45 steel by laser cladding technology. The effects of the LaB₆ content on the phase composition, microstructure, microhardness, and wear resistance of the coatings were studied. The results show that without the LaB₆ addition, the coating is composed of Austenite and TiC phases, with defects such as pores and cracks, and the microstructure is mainly equiaxed grains. With the addition of LaB₆, Fe-Cr phases are formed in the coating, and the microstructure transforms into columnar grains and dendritic grains. The grains are first refined and then coarsened, among which the coating with 4% LaB₆ (C4) has the smallest grain size. The experimental results indicate that the microhardness of the coatings first increases and then decreases with the increase in the LaB₆ content, and the C4 coating has the highest microhardness (594HV_0.2). The wear rate shows the same variation trend. The C4 coating has the lowest wear rate and the best wear resistance. This is attributed to the synergistic effect of the fine grain strengthening and TiC particle dispersion strengthening. Full article

In this study, a novel casting–forging hybrid forming technique, introducing torsional shear during squeeze casting, was investigated. This approach enhances the forming efficiency and refines the grain size. Using a finite element method coupled with a viscoplastic self-consistent model, a macro-microscopic simulation model of the squeeze casting torsional forming process was established. The introduction of torsional shear in SQ results in a more uniform distribution and lower equivalent stress, thereby improving the forming efficiency. Additionally, the shear force is increased during the forming process, the shear force is greater with the distance from the torsional axis increasing, and the great shear force could be maintained for a long time. Ultimately, this leads to a thinner wall thickness, finer secondary dendrites, and eutectic Si in the workpiece. During the SQT process, for introducing $(1\overline{1}1)[10\overline{1}]$ slip during the late stage of deformation, a significant shift in grain rotation directions happens and the grain rotation angles increase, finally attributed to the development of the $(1\overline{1}\overline{1})[0\overline{1}1]$ texture. Full article

This study examines the effects of laser pulse duration on the structural, morphological, optical, and gas-sensing characteristics of ${\mathrm{Al}}_2{\mathrm{O}}_3$/AgO thin films deposited on glass substrates using pulsed laser deposition (PLD). Pulse durations of 10, 8, and 6 nanoseconds were achieved through optical lens modifications to control both energy density and laser spot size. X-ray diffraction (XRD) and atomic force microscopy (AFM) analyses showed a distinct reduction in both crystallite and grain sizes with decreasing pulse width, along with significant improvements in surface morphology refinement and film compactness. Hall effect measurements revealed a transition from n-type to p-type conductivity with decreasing pulse width, demonstrating increased hole concentration and reduced carrier mobility attributed to grain boundary scattering. Furthermore, current-voltage (I-V) characteristics demonstrated improved photoconductivity under illumination, with the most pronounced enhancement observed in samples prepared using longer pulse durations. Gas sensing measurements for ${\mathrm{NO}}_2$ and ${\mathrm{H}}_2$S revealed enhanced sensitivity, improved response/recovery characteristics at 250 °C, with optimal performance achieved in films deposited using shorter pulse durations. This improvement is attributed to their larger surface area and higher density of active adsorption sites. Our results demonstrate a clear relationship between laser pulse parameters and the functional properties of ${\mathrm{Al}}_2{\mathrm{O}}_3$/AgO films, providing valuable insights for optimizing deposition processes to develop advanced gas sensors. Full article