Search Results (495)

A detailed analysis of the effects of magnesium on the microstructure of hypereutectic Al–20Si alloys is provided in this study. Experimental results show that the addition of Mg significantly refines the primary silicon phase relative to the unmodified Al–20Si alloy, transforming its morphology from a complex form to a singular plate-like structure. Notably, for the first time, equiaxed aluminum grains appear in the aluminum matrix under conventional solidification conditions. The generation of these grains is closely related to the quenching effect caused by rapid cooling during metal mold casting, which promotes the generation of equiaxed aluminum grains within tightly constrained temporal and spatial parameters. The Al–Si eutectic structure exhibits a regular lamellar morphology, with an average eutectic silicon spacing of 930.97 nm. The phase analysis shows that the alloy mainly consists of Al, Si, and Mg₂Si phases after the addition of Mg. With the increase in Mg concentration, the diffraction peaks for Al(200) and Si(220) first shift to lower angles and then move to higher angles, along with significant peak broadening. Ambient temperature mechanical testing indicates that tensile strength first increases with increasing Mg concentration, then declines, with the highest tensile strength of 235.1 MPa at 3 wt.% Mg in the Al–20Si alloy. The fracture mechanism of the testing specimens changes from cleavage fracture to ductile fracture. Microhardness testing indicates a continuous increase in the hardness of the aluminum matrix with rising Mg concentration; the hardness of primary silicon declines first and then increases, whereas the hardness of the eutectic structure exhibits a first increase followed by a decline. Full article

Ontogenetic changes in bone microstructure provide key information on growth patterns and functional differentiation in birds. This study describes microanatomical and histological variation in the appendicular and axial skeleton across an ontogenetic series of Pygoscelis antarctica. Fifty-two thin sections were analyzed, representing five chicks of different ages, a juvenile, and an adult. Early stages are characterized by thin, highly vascularized cortices and extensive trabecular bone surrounding a large medullary cavity. The chick sequence shows progressive periosteal deposition, trabecular expansion, and increasing osteosclerosis. In the juvenile, secondary compaction and the initial development of the inner circumferential layer appear together with the onset of extensive remodeling. The adult specimen exhibits fully developed outer and inner circumferential layers, lamellar cortical tissue, and marked secondary remodeling, with differential medullary reduction among skeletal elements. Compared with Aptenodytes patagonicus, P. antarctica shows earlier and more pronounced medullary reduction and secondary trabecular compaction in the forelimbs, likely related to its shorter dependency period and earlier initiation of marine locomotion. In contrast, hindlimbs retain a medullary cavity and follow sex-linked pathways of medullary modification: males develop an inner circumferential layer, whereas females show trabecular bone followed by secondary compaction. Full article

In this study, sustainable polyurea greases were prepared using epoxidized soybean oil (ESO) as bio-based base oil, with octadecylamine (ODA) reacted with three diisocyanates: 4,4′-diphenylmethane diisocyanate (MDI), 1,6-hexamethylene diisocyanate (HDI), and toluene diisocyanate (TDI). The diisocyanate structure dominated the thickener microstructure: MDI-ODA formed a compact short-rod fibrillar network with strong hydrogen bonding and π–π stacking, endowing the grease with the highest consistency (256), dropping point (262 °C), lowest oil separation (2.7%), and optimal thermal stability (T5% = 278 °C). HDI-ODA showed a lamellar structure with moderate performance, while TDI-ODA presented a loose porous network. Rheological tests confirmed MDI-ODA/ESO possessed the highest yield stress and structural recovery (79.5%). Tribological tests showed MDI-ODA/ESO delivered the lowest friction coefficient and wear scar diameter. Compared with non-epoxidized soybean oil (SO), ESO significantly enhanced grease performance. This improvement is attributed to the ring-opening reaction between the N–H of the ureido group and the epoxy groups of ESO, which improves thickener–oil compatibility. In addition, the polar epoxy groups promote the formation of stable lubricating films. This work verifies that diisocyanate structure and base oil epoxidation are critical for high-performance sustainable polyurea greases. Full article

Cost-effective β-titanium alloys were developed via the hydrogenation–dehydrogenation (HDH) process using low-cost β-stabilizers Mo and Fe. Ti-5Mo-xFe (x = 2, 4 wt%) alloys were fabricated by powder metallurgy and subjected to six post-heat treatment conditions to reduce porosity and improve properties. The as-sintered alloys exhibited high porosity (15–20%), which adversely affected mechanical and corrosion performance. Heat treatment above the β-transus significantly reduced porosity, with Ti-5Mo-4Fe treated at 900 °C for 2 h showing the greatest reduction. Microstructures evolved from α + β lamellar Widmanstätten to equiaxed β with TiFe precipitates. Increased Fe content and heat-treatment temperature enhanced strength, while TiFe precipitates degraded corrosion resistance. Thus, optimized post-heat treatment improves strength and corrosion performance, although Fe content must be controlled. Full article

Island reef road construction faces a complex marine service environment characterized by high salinity and high humidity. Meanwhile, rapid construction and prompt subgrade repair are urgently required, creating a strong demand for novel calcareous-sand-based stabilization materials that combine excellent mechanical performance with resistance to seawater erosion. To this end, this study developed an early-strength cemented calcareous-sand reinforcement material for road base construction. Sulfoaluminate cement (SAC) and ferrite-aluminate cement (FAC), both featuring rapid setting/early strength development and superior corrosion resistance, were used to cement calcareous sand (CS) and to investigate its mechanical and microstructural characteristics under different water environments. Unconfined compressive strength tests (UCS) showed that SC-CS and FC-CS could meet subgrade requirements at 1 d and 7 d, with SC-CS and FC-CS reaching 3.12 MPa and 3.44 MPa at 1 d, and 3.26 MPa and 3.67 MPa at 7 d, respectively, under seawater SS conditions. Seawater mixing and immersion were found to promote the early strength and stiffness development of both SC-CS and FC-CS, with a more pronounced effect observed for FC-CS. Based on experimental results, a damage model for the stabilized specimens was established with a fitting accuracy of R² > 0.97. This constitutive model accurately describes the stress–strain relationship of the material and quantitatively characterizes its damage evolution. Microscopic XRD and SEM analyses indicated that the main hydration product in freshwater-cured specimens was ettringite, and the interparticle connection of CS was dominated by bridging through rod-like ettringite. In contrast, under seawater conditions, the ettringite content decreased, while hydrotalcite and calcium aluminate hydrate increased, forming massive and lamellar bridging products. Compared with SC-CS, the bridging structure in FC-CS was denser. Moreover, the compactness of the bridging structure not only affected its mechanical properties but also governed the movement mode of CS particles, thereby influencing the damage evolution and failure mode of the specimens. The findings provide theoretical support for the construction needs of island road. Full article

This study compares the microstructural evolution and mechanical properties of TC4 (Ti-6Al-4V) titanium alloy joints welded by Tungsten Inert Gas (TIG) and laser processes, following a post-weld annealing treatment at 650 °C for 2 h. Distinct microstructures were obtained: the TIG-welded joint developed a heterogeneous mixture of short-rod α and lamellar β, while the laser-welded joint formed a more homogeneous equiaxed α structure with uniformly distributed β-phase nanoparticles. Electron backscatter diffraction (EBSD) results confirmed that the annealing treatment significantly weakened the strong welding-induced texture and disrupted the epitaxial growth mode of columnar grains. Mechanical testing demonstrated that annealing improved the strength-toughness balance, but the extent and mechanism differed between the two processes. For the TIG-welded joint, the ultimate tensile strength slightly decreased, while elongation and impact toughness increased by 18% and 10.4%, respectively. In contrast, the laser-welded joint maintained its original strength while achieving greater improvements in ductility and toughness, with elongation and impact toughness increasing by 20% and 15.2%, respectively. This divergence is attributed to insufficient recrystallization and the persistence of residual coarse grains, limiting the TIG joint’s performance. However, in the laser-welded joint, the pinning effect of β-phase nanoparticles and associated grain refinement enhanced ductility without compromising strength. Full article

The quality of underwater laser welds is strongly dependent on the flow rates of the shielding and drainage gases. This study investigated the effect of argon and drainage gas flow rates on the formation, microstructure and mechanical properties of 304NG stainless steel using local dry underwater laser welding. At a water depth of 100 mm, with a laser power of 3.0 kW and a welding speed of 8 mm/s, the optimal conditions within the tested range were a shielding gas flow rate of 30 L/min and a drainage gas flow rate of 80 L/min. These conditions produced a continuous weld bead with an attractive surface and yielded the highest average maximum tensile load of 4.31 kN. Metallographic observations revealed that the weld metal primarily consisted of austenite alongside skeletal and lamellar ferrite, while the hardness along the weld depth remained relatively consistent at around 180 HV. These results demonstrate that matching the flow rates of the shielding and drainage gases properly is essential for stabilising the local dry cavity and improving weld quality and joint performance. Full article

Cr₂O₃-based ceramic coatings are widely used in wear-critical applications; however, their tribological performance under dry sliding conditions can be limited by brittleness and frictional instability. In heavy-duty vehicles, the king pin–bushing contact operates under severe dry sliding conditions, motivating the investigation of composite Cr₂O₃–nTiO₂ coatings as a potential surface engineering solution. In this study, Cr₂O₃–TiO₂ coatings containing 0, 10, 20, 30, and 40 wt% TiO₂ were deposited by atmospheric plasma spraying (APS) from mechanically mixed powders. Phase composition was analyzed by X-ray diffraction using an X’Pert PRO MRD diffractometer, while microstructure and elemental distribution were examined by scanning electron microscopy (SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) on a FEG Quattro C microscope. Mechanical properties were evaluated by Vickers microhardness, instrumented indentation and scratch testing, while dry sliding wear behavior was assessed by pin-on-disc tests performed on a CETR UMT-2 tribometer against a bronze counterbody, with continuous monitoring of the coefficient of friction (COF). The results show that plasma spraying produces lamellar composite coatings with intrinsic porosity and locally modified phase composition. Cr₂O₃-rich coatings exhibit higher hardness (1198 HV2 compared with 877 HV2 for Cr₂O₃–40TiO₂ corresponding to an increase of approximately 36%) and improved resistance to indentation, reflected by lower penetration depths and higher elastic modulus values (134 GPa for S0 compared with 77 GPa for S2). These coatings also exhibit a more stable friction response and reduced material transfer from the bronze counterbody, as confirmed by the lower mass loss of the pins (0.0295 g for S0 compared with 0.0473 g for S4, corresponding to a reduction of about 38%). Increasing TiO₂ content leads to changes in friction stability and wear behavior associated with microstructural heterogeneity. These findings indicate that the sliding wear performance of Cr₂O₃–nTiO₂ coatings is governed by elastic–plastic stability under localized contact loading and support their applicability for dry sliding king pin–bushing systems in heavy-duty vehicles. Full article

The rapid advancement and widespread application of telecommunication technologies have significantly increased human exposure to electromagnetic waves, thereby intensifying the demand for effective electromagnetic shielding materials. Beyond potential health concerns, ensuring the stable performance of highly integrated electronic devices also necessitates protection against electromagnetic interference (EMI). In this study, the effects of processing conditions on the EMI shielding effectiveness (SE) of AZ61 magnesium alloy sheets were systematically investigated. Aging treatment of rolled AZ61 alloy promoted the formation of Mg₁₇Al₁₂ lamellae. Transmission Kikuchi diffraction analysis revealed that plate-like Mg₁₇Al₁₂ precipitates preferentially formed on the (0001) planes of the Mg matrix, contributing to improved EMI shielding. The rolled AZ61 sheet exhibited the highest SE in both the as-rolled state (83.1 dB at 900 MHz) and after aging for 131 h at 250 °C (76.2 dB at 900 MHz). The superior shielding performance of the as-rolled sheet is attributed to its high density of deformation-induced defects such as dislocations and twins, which induce lattice distortions and impede wave propagation. Meanwhile, the enhanced SE from the 131 h-aged condition results from multiple reflections of incident electromagnetic waves facilitated by the matrix–precipitate lamellar microstructure. Full article

Due to the low hydration activity of steel slag, its mechanical properties are insufficient, which limits its strategic application in steel slag based cementitious composite. In this study, the promoting effect of calcined layered double hydroxide (CLDH) on the hydration process, mechanical properties, and microstructure of high-volume steel slag cementitious materials was systematically investigated. The results showed that the addition of CLDH significantly optimized the material’s performance. When the mass fraction of steel slag was 70 wt% and the CLDH dosage was 2.0 wt%, the 7-day compressive strength reached 42.5 MPa, indicating an increase of 23.9% compared with the control group. Microscopic characterization suggested that CLDH slightly enhanced the hydration reaction of steel slag and increased the generation of hydration products through the nucleation effect. The addition of CLDH demonstrated a change in the composition of C-(A)-S-H to a higher Al/Ca ratio. Meanwhile, the lamellar structure of CLDH effectively filled the pores and promoted the densification of the matrix. This research provides valuable insights for the high-value utilization of steel slag and the design of high-performance cementitious materials. Full article

The application of microalloying technology has significantly improved the mechanical properties, oxidation resistance, and corrosion resistance of the Sn-9Zn-xAl-series solder. The effects of Al addition on microstructural evolution and service-related performance of the solders were systematically investigated using a combination of characterization techniques, including scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDX), differential scanning calorimetry (DSC), tensile testing, spreading testing, thermogravimetry (TG), and potentiodynamic polarization measurements. Microstructural characterization reveals that an optimal content of Al reacts with the Sn-Zn matrix to form AlZnSn intermetallic compounds (IMCs), which effectively refines the Zn-rich precipitates and eutectic lamellar structure. Concomitantly, the formation of second-phase strengthening contributes to a significant enhancement in the tensile strength of the solder alloys. Specifically, the Sn-9Zn-0.8Al solder exhibits a tensile strength of 87 MPa, corresponding to a 37% increment compared to the base Sn-9Zn alloy, whereas the elongation is reduced to 14.1%. Moreover, the in situ-formed Al₂O₃ passive film provides effective protection for the solder matrix, inhibiting oxidation induced by oxygen atoms and corrosion caused by chlorine ions, thereby remarkably improving the oxidation and corrosion resistance of the alloy. Collectively, these findings demonstrate that Al microalloying can substantially enhance the strength, oxidation resistance, and corrosion resistance of Sn-9Zn solder; however, a trade-off between wettability and ductility needs to be carefully considered for practical applications. Full article

To give more insight into the microstructural evolution and deformation mechanisms governing the long-term service performance of additively manufactured TiAl-based composites at elevated temperatures, this study investigated the high-temperature compressive creep behavior of a laser powder bed-fused LaB₆ reinforced high-Nb TiAl-based composite after hot isostatically pressing (HIP), with emphasis on the creep response and dynamic recrystallization (DRX) mechanisms under different applied stress levels. The results showed that, as the applied stress increased from 200 MPa to 450 MPa, the steady-state creep rate rose from 2.88 × 10⁻⁸ s⁻¹ to 3.85 × 10⁻⁷ s⁻¹. Stress exponent analysis indicated that creep deformation was predominantly controlled by dislocation climb, and no tertiary creep stage was observed within the investigated stress range. At 200 MPa and 300 MPa, a certain fraction of recrystallized grains formed during prolonged creep exposure. When the stress increased to 400 MPa, the recrystallization process was restricted due to the limited creep duration. In contrast, at 450 MPa, the accelerated accumulation of strain energy significantly promoted recrystallization. Both continuous dynamic recrystallization (CDRX) and discontinuous dynamic recrystallization (DDRX) were identified, jointly governing the microstructural evolution. Superior creep resistance can be attributed to multiple synergistic strengthening mechanisms, including the refined α₂/γ lamellar structure induced by HIP treatment, the strong pinning effect of dispersed La₂O₃ nanoparticles on dislocation motion, and the suppression of diffusion-controlled dislocation climb by Nb addition. These combined effects enhance the high-temperature creep performance of the TiAl composite and provide important insights for the application of LPBF-fabricated TiAl-based composites under elevated-temperature service conditions. Full article

It is widely accepted that modern humans display distinctive vertebral and intervertebral disc (IVD) morphologies that evolved to meet the biomechanical demands of habitual terrestrial bipedalism. This study synthesizes macro- and microstructural differences in the lumbar spine to clarify how human specializations compare with those of extant apes. The skeletal sample consisted of 240 humans, 20 chimpanzees, and 25 gorillas. The CT scan sample comprised 180 humans and eight chimpanzees. Histological analysis of the IVD was performed on 10 humans and four ape specimens. Vertebral bodies and discs were measured. Histological analyses employed hematoxylin–eosin, Von Kossa, and Van Gieson staining. Statistical analyses included ANOVA with Bonferroni-corrected t-tests or Welch’s ANOVA and Games–Howell post hoc tests. Regression analyses were performed using ordinary least-squares estimation, and differences between regression lines were assessed using ANCOVA. Humans and chimpanzees differed significantly in vertebral body proportions, bone volume fraction, IVD thickness, apophyseal ring thickness, annulus fibrosus lamellar organization, endplate and subchondral bone thickness, and vascularization at the bone–endplate interface. These results indicate substantial evolutionary modification of the human vertebral body and IVD, enhancing rotational mobility and resistance to axial loading, key functional requirements for maintaining upright posture and efficient bipedal locomotion. Full article

This study examines the effect of vanadium addition on the microstructure and mechanical properties of low-cost powder metallurgy Ti-4Al-2Fe-3Cu alloys. Alloys with and without 6 wt.% V were fabricated by hot extrusion of blended elemental powders followed by vacuum heat treatment. Microstructural analysis revealed that the base alloy exhibits a coarse lamellar α/β structure, while vanadium addition promotes a refined basketweave morphology with a significantly higher β-phase fraction, increasing from 28.1% to 46.2%. Energy-dispersive spectroscopy confirmed preferential partitioning of Fe, Cu, and V into the β phase. Mechanical testing showed that the addition of 6 wt.% V markedly enhances strength, increasing yield strength and ultimate tensile strength from 1122 MPa and 1214 MPa to 1291 MPa and 1349 MPa, respectively, while maintaining comparable tensile ductility (~3.5%). The strength improvement is attributed to α-plate refinement, increased β-phase fraction, and solid-solution strengthening of the β phase. These results demonstrate that vanadium addition is an effective approach for improving the strength of low-cost PM titanium alloys without compromising ductility. Full article

This study systematically investigated the chemical composition, microstructure, and mechanical properties of HR3C steel tubes that have been in service. The results indicate that, after nearly 70,000 h of operation, continuous lamellar M₂₃C₆ precipitates formed along grain boundaries in the HR3C steel, with needle-like or rod-like M₂₃C₆ phases extending from the grain boundaries into the grain interiors. Additionally, NbCrN and σ-phase precipitates were observed in the regions adjacent to the grain boundaries. Mechanical testing revealed a slight increase in hardness following service exposure, while the tensile strength remained largely unchanged; the yield strength, however, increased by approximately 15%. In contrast, the elongation at fracture decreased significantly—ductility declined by 64–73% relative to the as-received condition—and impact toughness dropped dramatically by 96%. These findings collectively indicate pronounced embrittlement of the HR3C steel after long-term service at 620 °C. Microstructural analysis confirms that the precipitation of M₂₃C₆ and σ phases is the primary contributor to the observed deterioration in toughness and ductility. Full article