Search Results (61)

This study elucidates the influence of rapid heating (300 °C/s) on martensitic transformation pathways, crystallographic variant selection, and the resulting mechanical performance in a medium-carbon steel. Compared with conventional heating, rapid heating markedly refines the prior austenite grain (PAG) and martensitic substructures, reducing the mean PAG size from 16.08 μm to 5.06 μm and the martensitic block size from 4.24 μm to 2.41 μm. The accelerated austenitizing and quenching promote a higher density of high-angle grain boundaries (HAGBs) and favor variant selection dominated by the closely packed (CP) group. Σ3 twin boundaries are also found to assist variant nucleation and contribute to microstructural complexity. Despite a marginal decrease in tensile strength, rapid-heated steels exhibit significantly enhanced ductility and a 28.3% increase in the product of strength and elongation (PSE) compared to their conventionally treated counterparts. These findings demonstrate that rapid heating not only enables effective refinement of martensitic substructures but also offers a powerful means of controlling variant evolution, thereby achieving a superior strength–ductility synergy in martensitic steels. Full article

Controlling multiple phases by adjusting elemental ratios and applying heat treatments effectively balances the strength and ductility of refractory high-entropy alloys. In this study, five types of V-Ti-Cr-Nb-Mo alloys were designed by varying the contents of V, Ti, and Nb, followed by annealing at 1200 °C for 8 h. The alloys’ crystal structures, microstructure evolution, and mechanical properties were systematically investigated. The V-Ti-Cr-Nb-Mo alloys exhibited a typical dendritic structure with a dual-phase (BCC + HCP) matrix. When the Nb content was maintained at 35 at.% with increasing V content, the volume fraction of the HCP phase increased, and the C14 Laves phase emerged. The as-cast alloy V₁₅Ti₃₀Cr₅Nb₃₅Mo₁₅, with a triple-phase (BCC + HCP + Laves) structure, exhibited excellent mechanical properties, including a compressive strength of 1775 MPa and a ductility of 18.2%. After annealing, the HCP phase coarsened and partially dissolved, the Laves phase precipitation reduced, and while the hardness and strength decreased, the ductility improved significantly. The annealed alloy V₅Ti₃₅Cr₅Nb₄₀Mo₁₅, with a dual-phase (BCC + HCP) structure, achieved a ductility of 26.9% under a compressive strength of 1530 MPa. This work demonstrates that multi-phase refractory high-entropy alloys can significantly enhance the strength–ductility synergy, providing an experimental foundation for the compositional design and performance optimization of refractory high-entropy alloys. Full article

As an eco-efficient short-process manufacturing technique for aluminum alloys, twin-belt continuous casting and direct rolling (TBCCR) demonstrates significant production advantages. In this study, an Al-Fe-Si alloy system with different Fe-rich intermetallics (α-AlFe(Mn)Si and β-AlFe(Mn)Si) via TBCCR was developed for new energy vehicle batteries, utilizing the Computer Coupling of Phase Diagrams and Thermochemistry (CALPHAD) technique. Comprehensive microstructure and surface segregation analyses of continuous casted ingots and direct-rolled sheets revealed that the Al-Fe-Si alloy with a combined Fe + Si content of 0.7% and an optimal Fe/Si atomic ratio of 3:1 (FS31) presents optimized mechanical properties: ultimate tensile strength of 145.8 MPa, elongation to failure of 5.7%, accompanied by a cupping value of 6.64 mm. Notably, Mn addition further refined the grain structure of casting ingots and enhanced the strength of both ingots and rolled sheets. Among the experimental alloys, FS14 (optimal Fe/Si atomic ratio of 1:4) sheets displayed the least surface segregation upon Mn incorporation. Through systematic optimization, an Al-Fe-Si-Mn alloy composition (Fe + Si = 0.7%, Fe/Si = 1:4 atomic ratio, 0.8 wt.% Mn) was engineered for TBCCR processing, achieving enhanced comprehensive performance: ultimate tensile strength of 189.4 MPa, elongation to failure of 7.32%, and cupping value of 7.71 mm. This composition achieves an optimal balance between grain refinement, mechanical properties (strength–plasticity synergy), formability (cupping value), and corrosion resistance (corrosion current density). The performance optimization strategy integrates synergistic improvements in strength, ductility, and corrosion resistance, providing valuable guidance for developing high-performance aluminum alloys suitable for the TBCCR process. Full article

Al₃BC, with its remarkably high modulus of elasticity (326 GPa) and hardness (14 GPa), coupled with a low density (2.83 g/cc), stands out as a promising reinforcement material for Al matrix composite. To study feasibility of solid-solid reaction (SSR) by forming an in situ Al₃BC reinforcing phase within the matrix, this study developed an Al₃BC/Al composite via mechanical alloying, followed by sintering at 1000 °C/1 h, and subsequent hot pressing at 400 °C/40 MPa. The reaction kinetics and corresponding electron microscopy images suggest that the aluminum (Al)-boron (B) reacts with graphene nanoplates (GNPs) to form both clusters and a heterogeneous multi-structured Al₃BC reinforcements network dispersed within the fine-grain (FG) Al matrix. The heterostructure contributes to a good balance between strength (~284 MPa) and ductility (~17%) and stiffness (~212 GPa). Superior strain hardening ability (n = 0.3515) endorses remarkable load-bearing capacity (σ_c = 1.63) and thereby promotes excellent strength-ductility synergy in the composite. The fracture morphology reveals that reasonable ductility primarily relies on the crack deflection by the FG-Al matrix, playing a critical role in delaying fracture. The potential importance of the matrix microstructure in the overall fracture resistance of the composite has been highlighted. Full article

This study introduces a novel gradient dual-phase structure design in brass, achieved through ultrasonic severe surface rolling (USSR) processing, which enables an unconventional asymmetric bilayer structure—comprising a hardened surface layer (>1 mm thick) and a ductile substrate—distinct from conventional hard-soft-hard sandwich configurations in gradient nanostructured materials. Microstructural characterization reveals a gradient dual-phase (α + β′) structure in the hardened layer, progressively transitioning into a homogenized dual-phase structure in the substrate. This unique architecture endows the USSR brass with exceptional mechanical properties, including a yield strength of 582.4 ± 31.0 MPa, ultimate tensile strength of 775.3 ± 33.9 MPa, and retained ductility (9.3 ± 1.0%), demonstrating an outstanding strength-ductility synergy. The USSR brass also demonstrates superior wear resistance with a 42.32% reduction in wear volume and 40.82% decrease in coefficient of friction compared to its as-received counterpart under oil lubrication. This architectural paradigm establishes a robust framework for engineering high-performance brass that simultaneously achieve an exceptional strength-ductility balance and enhanced wear resistance. Full article

The generalized stacking fault energy (GSFE) and shear modulus (G) are critical parameters in determining the strength and ductility balance of Fe-based alloys, playing a significant role in alloy design and performance optimization. This study focuses on FeNiAl alloys and proposes a composition optimization method based on molecular dynamics simulations. The results reveal that Fe₉₀Ni₉Al alloy exhibits the best synergy between strength and ductility, achieving a yield strength of up to 16.33 GPa and a yield strain of 10.4%. During tensile deformation, this alloy demonstrates a complex microstructural evolution, including dislocation slip, phase transformations, and deformation twinning. These mechanisms collectively contribute to the significant enhancement of its mechanical properties. This study not only elucidates the profound influence of GSFE and G on the micro-deformation mechanisms and macroscopic mechanical properties of FeNiAl alloys but also establishes an efficient composition design and screening system. This system provides theoretical support and practical guidance for the rapid development of novel alloy materials with balanced strength and ductility. The proposed method is broadly applicable to the design and optimization of high-performance structural materials, offering critical insights for advancing the application of lightweight and high-strength metallic materials in aerospace, automotive manufacturing, and other fields. Full article

Thermomechanical processing by applying deformation-induced ferrite transformation (DIFT) is an effective method of producing ultrafine-grained (UFG) ferritic steels, which usually present high yield strength but low strain hardening. In this study, we explored the concept of DIFT in the processing of UFG dual-phase (DP) steel, in order to improve its strain hardening capability and thus its ductility. The processing temperature was reduced to enhance the dislocation storage in austenite. It was found that the warm deformation of austenite induced a dramatic occurrence of DIFT, resulting in the formation of UFG-DP microstructures along the whole thickness of the specimen. In the UFG-DP microstructure, the average ferrite grain size was 1.2 μm and the ferrite volume fraction was 44 vol.%. The observation of twinned martensite suggests the occurrence of carbon partitioning during the DIFT process. The UFG-DP microstructure exhibited a good combination of strength and ductility, which was enabled by the synergy of the ultrafine ferrite grains and the efficient composite effect. The outcome of this study provides a novel pathway to develop advanced hot-rolled steels with a UFG-DP microstructure and which are associated with the advantages of their readiness to be scaled up and low costs. Full article

Understanding the mechanical behavior of materials under various strain-rate regimes is critical for many scientific and engineering applications. Accordingly, this study investigates the strain-rate-dependent compressive mechanical behavior of B2-containing (TiZrNb)_79.5(TaAl)_20.5 refractory high-entropy alloy (RHEA) at room temperature. The RHEA is prepared by vacuum arc melting and is tested over intermediate (1.0 × 10⁻¹ s⁻¹, 1.0 s⁻¹) and dynamic (1.0 × 10³ s⁻¹, 2.0 × 10³ s⁻¹, 2.8 × 10³ s⁻¹, 3.2 × 10³ s⁻¹, and 3.5 × 10³ s⁻¹) strain rates. The alloy characterized as hybrid body-centered-cubic (BCC)/B2 nanostructure reveals an exceptional yield strength (YS) of ~1437 MPa and a fracture strain exceeding 90% at an intermediate (1.0 s⁻¹) strain rate. The YS increases to ~1797 MPa under dynamic strain-rate (3.2 × 10³ s⁻¹) loadings, which is a ~25 % improvement in strength compared with the deformation at the intermediate strain rate. Microstructural analysis of the deformed specimens reveals the severity of dislocation activity with strain and strain rate that evolves from fine dislocation bands to the formation of localized adiabatic shear bands (ASBs) at the strain rate 3.5 × 10³ s⁻¹. Consequently, the RHEA fracture features mixed ductile–brittle morphology. Overall, the RHEA exhibits excellent strength–ductility synergy over a wide strain-rate domain. The study enhances understanding of the strain-rate-dependent mechanical behavior of B2-containing RHEA, which is significant for alloy processes and impact resistance applications. Full article

The difficulty in enhancing both tensile strength and ductility is limiting the development of high-performance Mg alloys. The “plastic deformation + electropulsing (EP) treatment” is an effective process for modifying the microstructure and enhancing the mechanical properties of metals. In this work, the influence of the current density of EP treatment on the microstructure and tensile property evolution of the as-extruded Mg-6Al-1Zn alloy was systematically investigated. The microstructure of the as-extruded sample was predominantly composed of an α-Mg matrix and a minor quantity of the β-Mg₁₇Al₁₂ phase on grain boundaries. After EP treatments, the microstructure underwent recrystallization, resulting in the formation of fine recrystallized grains. Meanwhile, the distribution and volume fraction of the β-Mg₁₇Al₁₂ phase demonstrated minor changes. After the 60 cycles of EP with a current density of 1050 A·mm⁻² for a duration of 60 s, the tensile strength and elongation of the as-extruded Mg-6Al-1Zn alloy improved from 260 ± 2.6 MPa and 22 ± 1.3% to 319 ± 3.6 MPa and 23 ± 1.1%, respectively. The results prove the effectiveness of EP treatment in tailoring recrystallization via changing current density. Full article

In this research, as-built Ti–6Al–4V anatomical plates were successfully fabricated using laser powder bed fusion (LPBF). This study thoroughly examines the microstructural evolution and its role in enhancing the mechanical properties of clavicle bone plates under sub-β-transus heat treatment for medical application. Scanning electron microscope (SEM) images of the as-built specimens reveal a dense formation of a hard α’ hcp martensite structure, which decomposes during annealing at 650 °C and ultimately transforms into an α + β lamellar structure at 950 °C. Additionally, coarse grains resulting from recrystallization and reduced dislocation density were observed through electron backscatter diffraction (EBSD) following heat treatment. Due to these microstructural evolutions, the desired mechanical properties of as-built Ti64 parts for surgical applications were achieved. Heat treatment of the anatomical plates at 950 °C demonstrated an excellent strength–ductility synergy under tensile deformation and the highest energy absorption capability under bending deformation, indicating sufficient durability for medical implantation applications. Full article

In recent years, prefabricated components have been widely used in the construction of substation superstructures, while cast-in-place foundations remain the primary method for substation foundations. This paper presents and evaluates a novel prefabricated foundation design aimed at enhancing construction efficiency and load-bearing performance. The foundation features a modular design, with each module weighing only half that of a cast-in-place foundation of the same size, significantly improving construction convenience and transportation efficiency. The load-bearing performance of the foundation was validated through static load tests and finite element modeling. The results indicate that the foundation demonstrates excellent ductility, with flexural failure as the primary mode, characterized by multiple cracks across the mid-span and complete yielding of longitudinal reinforcing steels. Further parametric analysis shows that increasing the plate thickness ratio (λ) improves the ultimate bearing capacity of the foundation significantly. Additionally, enlarging the cross-sectional size of the shear key or increasing the strength of the wet joint material enhances overall structural synergy, reduces local deformation, and improves load distribution efficiency. Overall, the sensitivity order of factors influencing the bearing capacity of the new prefabricated foundation is plate thickness ratio (λ) > wet joint strength > shear key cross-sectional size. Full article

The square steel tube–timber–concrete composite L-shaped columns are lighter in weight due to the inclusion of wood and exhibit superior seismic performance. This combination not only reduces transportation and labor costs but also enhances earthquake resistance. The wood contributes lightness and flexibility, the steel provides strength, and the concrete offers excellent compressive performance, thereby achieving an optimized design for performance. To investigate the axial compression performance of square steel tube–timber–concrete composite L-shaped short columns, axial compression tests were conducted on eight groups of L-shaped columns. The study examined ultimate load, failure modes, load–displacement relationships, initial stiffness, ductility, and bearing capacity improvement factors under different slenderness ratios, steel tube wall thicknesses, and wood content rates. The results show that the mechanical performance of the composite columns is excellent. Local buckling of the steel tube is the primary failure mode, with ‘bulging bands’ forming at the middle and ends. When the wood content reaches 25%, the synergy between the steel tube, concrete, and wood is optimal, significantly enhancing ductility and bearing capacity. The ductility of the specimen increased by 31.1%, and the bearing capacity increased by 4.14%. The bearing capacity increases with the steel tube wall thickness but decreases with increasing slenderness ratio. Additionally, based on the Mander principle and considering the partitioned constraint effects of concrete, a simplified calculation method for the axial compressive bearing capacity was proposed using the superposition principle. This method was validated to match well with the test results and can provide a reference for the design and application of these composite L-shaped columns. Full article

By tailoring different microstructural features, this study verifies that the laser powder bed fusion (LPBF)-fabricated Ti-6Al-4V titanium alloy with a fully α/β lamellar structure exhibits excellent ductility at liquid nitrogen temperature. HT-800 was obtained by holding at 800 °C for two hours and then furnace-cooled, resulting in a microstructure consisting of residual martensitic α’ phase, lamellar α phase, and particulate β phase. The HT-900 was obtained by holding at 900 °C for two hours and then furnace-cooled, completely eliminating the multi-level martensitic α’ phase generated during the LPBF process and resulting in an α/β lamellar structure. HT-900 achieved an elongation of 11% at liquid nitrogen temperature, a 47% improvement over the HT-800. After low-temperature strain fracture, the proportions of 61.38°<11–20> twin boundaries in the HT-800 and HT-900 were 21.4% and 26.4%, respectively, indicating that a substantial amount of deformation twinning is activated at liquid nitrogen temperature. Twinning induces the activation of slip systems by altering the orientation of surrounding grains. The coordinated plastic deformation of twinning and slip enhances the ductility of the HT-900 at 77 K. The results show that the LPBF-TC4 titanium alloy with a fully α/β lamellar structure exhibits superior, coordinated plastic deformation capabilities at 77 K, maintaining high strength while achieving greater ductility and fracture toughness. Full article

The trimodal grain-structured (TGS) carbon nanotube-reinforced aluminum matrix composites (CNT/Al) exhibit better strength–ductility synergy compared to bimodal grain-structured (BGS) composites. The addition of fine grain (FG) to the TGS composites effectively facilitates strain hardening and reduces strain/stress concentrations. In order to address the strain incompatibility in TGS composites, a significant accumulation of geometrically necessary dislocations (GNDs) occurs at the hetero-zone boundaries. This accumulation serves as the key factor in generating additional strengthening and work hardening. By utilizing a multi-mechanism strain gradient model, a quantitative analysis of the contributions made by Hall–Petch, Taylor, and back stress strengthening was conducted. Furthermore, effects of each domain volume fraction on the GND density at the boundaries between heterogeneous domains were carefully and extensively investigated and compared. It is found that the strengthening effect of back stress significantly surpasses that of the Hall–Petch and Taylor strengthening accounting. Compared to BGS composites, the TGS composites are more effective in facilitating strain hardening and reducing strain/stress concentrations, which may lead to a better balance between strength and ductility. Full article

Cold spray is a solid-state additive manufacturing technology and has significant potential in component fabrication and structural repair. However, the unfavourable strength–ductility synergy in cold spray due to the high work hardening, porosity and insufficient bonding strength makes it an obstacle for real application. In recent years, several methods have been proposed to improve the quality of the cold-sprayed deposits, and to achieve a balance between strength and ductility. According to the mechanism of how these methods work to enhance metallurgical bonding, decrease porosity and reduce dislocation densities, they can be divided into four groups: (i) thermal methods, (ii) mechanical methods, (iii) thermal–mechanical methods and (iv) optimisation of microstructure morphology. A comprehensive review of the strengthening mechanism, microstructure and mechanical properties of cold-sprayed deposits by these methods is conducted. The challenges towards strength–ductility synergy of cold-sprayed deposits are summarised. The possible research directions based on authors’ research experience are also proposed. This review article aims to help researchers and engineers understand the strengths and weaknesses of existing methods and provide pointers to develop new technologies that are easily adopted to improve the strength–ductility synergy of cold-sprayed deposits for real application. Full article