Search Results (604)

Photovoltaic mounting structures operate in harsh environments, demanding high strength and elongation. However, a strength–graded product series within the same composition is lacking. Through Ti microalloying and heat treatment, we developed steels with strengths of 500–800 MPa and studied annealing effects at 640–740 °C. Scanning Electron Microscope (SEM) shows ferrite and cementite: with increasing temperature, ferrite changes from elongated to equiaxed via recovery and recrystallization, while cementite remains finely dispersed along grain boundaries. Transmission Electron Microscope (TEM) reveals TiC precipitates, which decrease in number but increase in size at higher temperatures. Grain refinement strengthening, dislocation strengthening, and precipitation strengthening are the primary strengthening mechanisms, contributing 91.2% and 94.4% to the yield strength after annealing at 640 °C and 720 °C, respectively. Within a wide annealing temperature range, the tensile strength fully covers the 550–650–750–800 MPa grades, with the corresponding elongation fluctuating between 12.4% and 25.3%, achieving a good strength–ductility balance. In summary, simply adding a single Ti element and adjusting the annealing temperature allows for the production of test steels with strengths ranging from 500 to 800 MPa and matched elongation. This approach not only reduces costs but also provides experimental evidence for the process development of a series of new steels for photovoltaic mounting brackets. Full article

Despite its excellent impact toughness and work-hardening capacity, high-manganese steel (HMS) suffers from low initial hardness, limiting its wear resistance under low-stress conditions. Conventional surface hardening methods for HMS involve high cost and intensive energy consumption and produce only shallow hardened layers; moreover, the understanding of laser transformation hardening in HMS remains insufficient. To address these gaps, this study employs a high-energy-density laser for rapid and precise surface modification of Mn13 HMS. The studied Mn13 steel contains 1.98 wt.% Cr, which contributes to solid-solution strengthening and influences the phase transformation behavior during laser transformation hardening. By optimizing the laser power, a well-defined laser-quenched layer with a gradient microstructure along the thickness direction is obtained. Microhardness at the surface treated by laser transformation hardening at 1.5 kW improved significantly, primarily due to grain refinement and a dense dislocation network. The small fraction of martensite contributes indirectly by generating geometrically necessary dislocations and acting as local barriers to dislocation glide. Along the depth direction, the microhardness varies with the gradient microstructure: coarse columnar grains at intermediate depths cause a slight decrease in microhardness, while the substrate restores it. Correspondingly, the laser-quenched surface exhibits improved wear resistance, as indicated by reduced friction coefficient, wear depth, and wear volume, and the dominant wear mechanism shifts from adhesive to abrasive wear. Importantly, this gradient configuration maintains a mechanically compatible transition between the quenched layer and the substrate, preserving impact toughness comparable to that of the untreated material. Full article

In this study, CoCrFeNiMn high-entropy alloys (HEAs) with different aluminum (Al) contents were fabricated, and the effects of Al content on the microstructure evolution and mechanical properties were systematically explored. The microstructural characterization results indicated that the Al content exerted a crucial regulatory effect on the crystal structure of the alloy. With increasing Al content, shifts in the characteristic XRD peaks indicate lattice expansion of the alloy. Meanwhile, the phase structure continuously evolved from a single face-centered cubic (FCC) structure to an FCC/body-centered cubic (BCC) dual-phase structure, and then finally transformed into a BCC-dominated structure. Appropriate Al element addition could produce localized stress fields near dislocations and achieve prominent solid-solution strengthening, which effectively inhibited dislocation movement and further improved the yield strength, tensile strength, and hardness of the alloy. In contrast, excessive Al addition would break through the solid solubility limit of the alloy matrix, causing obvious phase separation and the precipitation of brittle B2-ordered NiAl-type intermetallic secondary phases. These brittle secondary phases easily induced crack initiation in the plastic deformation process, which significantly deteriorated the ductility, work-hardening ability, and impact toughness of the alloys. Full article

In this study, manual welding electrodes with varying niobium (Nb) contents (0, 0.05, and 0.1 wt%) were developed for 960 MPa grade low-alloy high-strength steel, and deposited metals were produced through multilayer multipass welding. Microstructural characterization and mechanical testing were performed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), and a universal testing machine to investigate the influence of Nb content and elucidate the strengthening mechanisms. The results demonstrate that under identical welding conditions, multipass thermal cycles induced a primary microstructural transformation from martensite to tempered martensite in all deposited metals, which predominantly comprised tempered martensite with minor fractions of bainite and second-phase particles. Increasing Nb content led to significant grain refinement. The second-phase particles exhibited sizes of 0.158 μm, 0.176 μm, and 0.168 μm, respectively, with volume fractions of 5.69%, 5.82%, and 5.90%. Nb addition substantially enhanced hardness and strength while causing a noticeable reduction in low-temperature impact toughness, though the values remained within acceptable limits. The deposited metal containing 0.05 wt% Nb exhibited optimal comprehensive mechanical properties, with a hardness of 386.7 HV, tensile strength of 1060 MPa, yield strength of 962 MPa, and Charpy impact energies of 41.95 J and 33.17 J at −40 °C and −60 °C, respectively. Theoretical calculations revealed that the dislocation strengthening contribution in martensite increased from 526 MPa to 600 MPa with increasing Nb content, representing the dominant strengthening mechanism, while grain refinement strengthening increased from 135.5 MPa to 157.6 MPa. Full article

Mg-Al-Ca alloys are attractive low-cost wrought Mg alloys. However, the distinct roles of Al and Ca in regulating deformation-processed microstructures and mechanical properties remain unclear. In this work, Mg–6Al–0.5Ca, Mg–9Al–0.5Ca, and Mg–9Al–1.3Ca (wt. %) alloys were extruded at 250 °C and 300 °C to clarify the composition-dependent microstructure evolution and strengthening mechanisms. Increasing the Al content from 6 to 9 wt. % markedly promoted the formation of fine Mg₁₇Al₁₂ (f-Mg₁₇Al₁₂) and coarse Mg₁₇Al₁₂ particles, whereas increasing the Ca content from 0.5 to 1.3 wt. % promoted the formation of coarse Al₂Ca particles while reducing the density of f-Mg₁₇Al₁₂. Quantitative analysis revealed that f-Mg₁₇Al₁₂ particles refined dynamically recrystallized grains by promoting recrystallization nucleation and pinning grain boundaries while also contributing to Orowan strengthening. The Mg–9Al–0.5Ca alloy exhibited the best strength–ductility balance, with a yield strength of 338 ± 4 MPa, ultimate tensile strength of 396 ± 5 MPa, and elongation of 8.7 ± 1.6% after extrusion at 250 °C. Strengthening calculations indicated that grain-boundary strengthening was the dominant strengthening contribution, while the strength advantage of Mg–9Al–0.5Ca originated from the dual role of f-Mg₁₇Al₁₂ in grain refinement and dislocation obstruction. These findings provide a practical strategy for designing high-strength non-rare-earth Mg–Al–Ca extrusion alloys. Full article

Developing low-cost, Co-free high-entropy alloys (HEAs) that retain both high strength and useful ductility at cryogenic temperatures remains challenging because hard strengthening phases usually intensify strain localization and accelerate plastic instability. In this work, a Fe-enriched Al₁₁Cr₁₄Fe₅₀Ni₂₅ HEA was designed and processed by heavy cold rolling followed by short-time annealing at 900 °C for 10 min to construct a hierarchical heterogeneous microstructure. The alloy consists of an FCC-dominated matrix and an ordered B2 phase distributed in recrystallized and unrecrystallized domains over multiple length scales. Tensile testing shows that the alloy achieves a yield strength of 953 MPa, an ultimate tensile strength of 1160 MPa, and an elongation of 21.1% at 298 K, while these values increase to 1268 MPa, 1686 MPa, and 28.6%, respectively, at 77 K. Load–unload–reload analysis at 77 K reveals that the hetero-deformation-induced stress reaches about 804 MPa at a true strain of 25%, contributing more than 52% of the total flow stress. The superior cryogenic strength–ductility synergy is attributed to strain partitioning between soft FCC and hard B2 phases and between recrystallized and unrecrystallized regions, which promotes geometrically necessary dislocation accumulation, back-stress strengthening, and sustained work hardening. This study demonstrates that hierarchical heterostructure design provides an effective route for developing cost-conscious Co-free HEAs for cryogenic structural applications. Full article

To address the demand for lightweight, high-performance Al-Si-Mg alloys in aerospace and automotive industries, this work proposes a novel synergistic strengthening strategy by combining rare-earth Y microalloying and in situ synthesized ZrB₂ nanoparticles to construct a hybrid reinforcement architecture. The effects of Y-ZrB₂ additions on the microstructure, crystallographic orientation evolution, and mechanical properties of Al-Si-Mg alloys were systematically investigated via XRD, SEM, EBSD, and tensile/hardness tests. Results show that compared with the base alloy and single-modified alloys, the co-addition of Y and ZrB₂ simultaneously enhances mechanical properties and optimizes grain structure. The optimal comprehensive performance is achieved at 0.3 wt.% Y + 2 wt.% ZrB₂ after T6 heat treatment, with ultimate tensile strength of 332.87 MPa, yield strength of 271.35 MPa, elongation of 16.24%, and Vickers hardness of 153.9 HV. Phase analysis and SEM-EDS confirm a synergistic coupling relationship between Y-rich phases and ZrB₂ nanoparticles. EBSD characterization reveals that Y-ZrB₂ modification has negligible effect on the morphology and crystallographic orientation stability of primary α-Al grains, but effectively regulates the lattice rotation, texture redistribution, and growth behavior of eutectic Si. At the optimal composition, the fraction of high-angle grain boundaries (HAGBs) reaches a maximum of 34.3%. Furthermore, the synergistic effect significantly increases the geometrically necessary dislocation (GND) density and reduces the Schmid factor of the dominant {111}⟨110⟩ slip system, thus enhancing dislocation strengthening and plastic deformation resistance. This work clarifies the intrinsic strength-ductility synergy mechanism of Y-ZrB₂ co-modified Al-Si-Mg alloys, paving a new pathway for the development of advanced lightweight aluminum alloys. Full article

Poor consolidations and the strength–conductivity trade-off limit the performance of copper alloys fabricated by laser powder bed fusion (LPBF). To address this, this study developed a strategy combining the response surface methodology (RSM) with direct ageing treatment (DAT) to achieve a favorable strength–conductivity synergy. The results showed that under the optimal process parameters, a high relative density of 99.25% (8.95 g/cm³ for theoretical density) was obtained. After direct ageing treatment at 490 °C for 60 min, the CuCrZr exhibited an ultimate tensile strength of 399.31 MPa and a thermal conductivity of 326.53 W/(m·K). To reveal the underlying mechanisms, this study employed a combination of systematic characterization via high-resolution transmission electron microscopy (HRTEM) and quantitative modeling. HRTEM characterized the uniformly dispersed nanoscale body-centered cubic (BCC) Cr precipitates that form semi-coherent interfaces with the face-centered cubic (FCC) Cu matrix, showing a crystallographic misorientation of approximately 10.5° intermediate between the classic Nishiyama–Wassermann and Kurdjumov–Sachs orientation relationships. Quantitative modeling indicates that the high strength arises from a synergistic effect: coherent strain fields exerted by the precipitates effectively pin retained dislocations, coupling Orowan and dislocation strengthening. Meanwhile, solute precipitation reduces lattice distortion, restoring notable thermal conductivity. Full article

In this work, to address the limitation of low strength and hardness of single-phase CoCrFeNi high-entropy alloy, SiC particles were introduced as a reinforcing phase to prepare CoCrFeNi matrix composites with SiC contents of 0 wt%, 1 wt%, 2.5 wt% and 5 wt% via spark plasma sintering (SPS). It was preliminarily predicted that SiC particles would be uniformly distributed along grain boundaries of the CoCrFeNi matrix. During sintering, partial SiC decomposes at high-temperature, high-activity interfaces, regulating carbide precipitation and phase structural evolution, while residual undecomposed SiC remains at grain boundaries to pin boundaries and refine grains, thereby synergistically enhancing mechanical properties and wear resistance. Microstructural characterization reveals that all samples maintain a face-centered cubic (FCC) solid-solution matrix, and samples with non-zero SiC addition contain Cr₇C₃ carbides, which are mostly distributed at grain boundaries. With the increase in SiC content, mechanical performance is remarkably improved compared with the unreinforced CoCrFeNi matrix: the hardness rises from 198.8 HV to 321.7 HV, the yield strength is greatly enhanced from 242.5 MPa to 673.4 MPa, and the tensile strength increases from 557.9 MPa to 755.7 MPa. The improved yield strength originates synergistically from grain refinement, solid-solution strengthening, grain-boundary strengthening and dislocation strengthening. By clarifying the influence of microstructural defects on critical shear stress (τ₀) and normal fracture stress (σ₀), the intrinsic mechanism governing tensile mechanical performance and ductile–brittle fracture transition was revealed. This optimized CoCrFeNi/SiC composite exhibits excellent strength–hardness comprehensive performance, showing promising application potential for high-load, wear-resistant and structural service components under severe tribological and pressure conditions. Full article

Additive manufacturing using laser powder bed fusion (LPBF) has been widely used to produce nickel-based superalloy components with complex shapes for high-temperature applications requiring creep resistance. In this research, the creep behavior of LPBF Inconel 718 under solution and double-aging heat treatments, performed at 590–650 °C under stresses of 450–550 MPa, is studied. The characterization included optical microscopy, scanning electron microscopy (SEM), porosity analysis, Vickers microhardness tests, and fracture surface examination. The findings revealed that even after heat treatment, the material maintained a mainly directional, columnar microstructure, with an average porosity below 1%, which was unevenly distributed and contained critical defects related to lack-of-fusion (LOF) and trapped powder. Fracture after creep presents regions of ductile failure alongside facets indicative of quasi-cleavage. Kinetic analysis revealed a high stress exponent (n = 18.26) and an activation energy (Qc = 410–538 kJ/mol), indicating that the deformation operates within the power-law breakdown (PLB) regime, where dislocation–precipitate interactions govern the creep rate in this precipitation-strengthened superalloy. Overall, the results highlight that the directional microstructure and residual defects typical of LPBF can reduce the creep resistance of Inconel 718, underscoring the importance of post-processing methods and internal defect control specifically tailored for additively manufactured materials. Full article

In pursuit of a composite coating for tunnel boring machine (TBM) disc cutters that offers both high wear resistance and self-lubricating functionality, we fabricated Fe-based composite coatings reinforced with WC and MoS₂ through laser cladding. Seven coating compositions with systematically tailored MoS₂ contents were prepared to investigate the concentration-dependent effects of MoS₂ on microstructural evolution and tribological properties, and to evaluate their performance under various rock-contact conditions. XPS results reveal that MoS₂ decomposed during laser cladding, leading to the in situ formation of metal sulfides in the Fe-based matrix. These sulfides, characterized by low shear strength, readily form a continuous and stable lubricating tribofilm at the hob–rock interface. The tribofilm effectively lowers the coefficient of friction (COF), curtails friction-induced energy dissipation and surface degradation, and ultimately enhances the wear resistance of the disc cutter. Simultaneously, the rapid non-equilibrium solidification inherent in laser cladding stabilizes metastable phases, which refine the microstructure, improve densification, and bolster phase stability. Among the tested compositions, the coating containing 4 wt.% MoS₂ exhibited the most favorable dry-sliding tribological performance, as evidenced by an average coefficient of friction of 0.409, a hardness of 749.5 HV1, and consistently low wear mass losses below 2.1 × 10⁻³ g under different rock-contact conditions. Mechanistically, XRD and SEM analyses further attributed the superior performance of the 4 wt.% MoS₂ coating to concurrent strengthening mechanisms: grain refinement, dispersion strengthening from uniformly distributed second-phase particles, and increased dislocation density. Collectively, these effects substantially improve the wear resistance of the disc cutter, thereby extending its durability and service life under complex operating conditions. Full article

Nanodefect engineering has emerged as an effective strategy to address the inherent strength–ductility trade-off and limited damage tolerance of wrought and cast magnesium alloys through controlled manipulation of their defect structures. Recent advances demonstrate that introducing and tailoring nanoscale defects can significantly enhance mechanical performance and, under appropriate defect architectures and processing conditions, may enable improved strength–ductility balance. This review provides a concise, mechanism-oriented overview of nanodefect-mediated strengthening in Mg alloys, focusing on the roles of nanograins, nanoprecipitates, nanotwins, and nano-stacking faults. Grain refinement via severe plastic deformation and other processing routes enhances strength through Hall–Petch effects while modifying texture and activating non-basal slip. Concurrently, nanoscale precipitates contribute through dislocation shearing and Orowan bypassing, whereas planar defects such as nanotwins and stacking faults introduce high-density interfaces that both impede dislocation motion and facilitate plastic accommodation. Emphasis is placed on the synergistic interactions among these defect populations, which govern strain hardening, deformation stability, and the overall strength–ductility balance. The review underscores that tailored defect architectures, achieved through integrated processing and alloy design, provide a viable pathway for developing next-generation Mg alloys with improved and tunable mechanical performance. Full article

High-purity copper features excellent electrical conductivity but generally low mechanical properties. Adding a three-dimensional graphene network as reinforcement to make a copper–graphene metal matrix composite is promising for a wide range of applications with better mechanical performance and functional capabilities. However, direct application in a metal matrix is difficult due to unfavorable wetting, which causes poor dispersion and weak interfacial bonding in the graphene–metal system. Here, the powder metallurgy method was used to construct a three-dimensional continuous graphene network in the copper matrix combined with high-pressure torsion. Optimized deformation/thermomechanical treatment enhanced the microstructural development processed by the severe plastic deformation method of high-pressure torsion. The primary advantage of this hybrid process is that it enables us to achieve grains with a size in the ultra-fine or even nanoscale. A homogeneous equiaxed nanostructure without segregation was observed during microstructural characterization, with a grain size of ~300 nm. This study investigated structural development during progressive deformation, and the samples were evaluated from the viewpoint of grain size and grain boundaries. The process significantly increased the microhardness of the copper–graphene composite. The tensile strength reached ~500 MPa at room temperature. The interpenetrating structural feature of graphene promoted interfacial shear stress to a high level, whereas plastic deformation increased the dislocation density and grain boundaries, thus resulting in significantly enhanced load transfer strengthening and crack-bridging toughness simultaneously. Full article

To address the erosion-induced failure of large-caliber gun barrels under extreme thermochemical coupling, this study systematically investigates the microstructural evolution of multi-layered gradient regions along the radial direction of 32CrNi3MoV steel under extreme thermochemical cycling. Leveraging SEM, EBSD, TKD, and double-beam aberration-corrected TEM, combined with JMatPro thermodynamic simulations, the phase transitions, crystallographic characteristics, and substructural evolution spanning from the bore surface to the matrix are elucidated. The results demonstrate that a three-layer gradient structure forms along the radial direction. The topmost layer is a chemically stabilized metastable austenite diffusion layer with a thickness of 1.5–4.0 μm. which is attributed to the suppression of martensitic transformation due to C/N interstitial diffusion lowering the MS temperature. The observed high-density dislocation tangles and stacking faults within this austenite diffusion layer result from thermal mismatch stresses during rapid thermal cycling. The subsurface region is a martensitic transformation layer with a thickness of 70–97 μm, exhibiting a substructural gradient from nanostructured high-density twinned martensite to refined lath martensite. Thermodynamic analysis indicates that rapid heating (≈10⁵ °C/s) facilitates significant austenite nucleation and growth during the reverse phase transformation, subsequently forming nanostructured martensitic grains via non-equilibrium transformation during rapid cooling. Adjacent to this is a matrix tempering layer extending approximately 160 μm. Nanoindentation hardness profiling reveals that the peak radial hardness (≈1000 HV) occurs within the fine-grained martensitic zone approximately 40 μm from the surface. In contrast, the tempered layer exhibits reduced hardness (≈400 HV) compared to the original matrix (≈500 HV). This is primarily attributed to transient high-temperature over-tempering effects, which induces carbide coarsening and the loss of solid solution strengthening, alongside the softening of prior austenite grain boundaries. This study clarifies the micro-to-nanoscale evolution of the barrel microstructure, providing critical theoretical insights for understanding erosion mechanisms and improving lifetime predictions. Full article

Laser powder bed fusion (LPBF) of aluminum matrix tribological composites holds high potential for advanced bearing applications, yet its widespread implementation is often constrained by high porosity and severe residual stresses. In this work, the influence of hot pressing (HP) temperature (100–400 °C) on the microstructure, substructural evolution, mechanical properties, and fracture mechanisms of the LPBF Al-10Sn-10Pb alloy was investigated to achieve simultaneous densification and matrix optimization. Processing was carried out at 300 MPa with a 30 min holding time. It was established that at temperatures >200 °C, near-full consolidation is achieved through liquid-assisted pore closure. Increasing the temperature leads to the coarsening of Sn and Pb inclusions and the disruption of the initial dispersed network of soft phases. Williamson–Hall analysis revealed a transition from dislocation accumulation at 100 °C (~15 × 10¹³ m⁻²) to dynamic recovery at 200 °C, followed by matrix recrystallization at higher temperatures. A combination of strength (up to 127 MPa) and ductility (~11%) is realized at 200 °C due to the synergy between remaining substructural strengthening and pore healing. At 300–400 °C, the strength decreases to 108–113 MPa with a concomitant increase in ductility to 34–44%. A shift in fracture mechanisms from quasi-brittle to ductile is shown; at 400 °C, the development of intergranular fracture associated with the influence of liquid phases is possible. Full article