Search Results (1,383)

Friction stir welding (FSW) is a solid-state joining process widely used for aluminum alloys due to its low heat input, reduced distortion, and ability to produce high-quality joints. However, excessive tool forces generated during the welding process can increase machine loading, accelerate tool wear, and negatively affect the process efficiency. Therefore, understanding the relationship between welding parameters, tool forces, and the joint performance is essential for achieving high-quality welds while avoiding unnecessary mechanical loads. In this study, 4 mm thick AA5754 aluminum alloy plates were joined using the FSW process, and the feasibility of using tool force measurements for process optimization was investigated. A comprehensive experimental matrix consisting of nine different rotational speeds and ten different tool travel speeds was established based on preliminary studies and previous literature. During each welding operation, forces acting on the tool in the F_x, F_y, and F_z directions were continuously recorded. The welded joints were evaluated through tensile testing (Zwick Z300 universal testing machine, ZwickRoell, Ulm, Germany), hardness measurements, and microstructural characterization using scanning electron microscopy (SEM) (ZEISS Merlin scanning electron microscope, Carl Zeiss Microscopy GmbH, Oberkochen, Jena, and Göttingen, Germany). A Pearson correlation analysis and a two-way analysis of variance (ANOVA) were performed at a 95% confidence level to quantify the relationships and statistical significance of the process parameters. The results showed that F_z was the dominant force component during welding. The rotational speed had a statistically significant effect on the tensile strength, yield strength and hardness (p < 0.05), accounting for 99.39% of the total variation in hardness. For the mean tool force, both the rotational speed and the tool travel speed were statistically significant (p < 0.0001), contributing 38.48% and 47.16% of the total variation, respectively. The rotational speed also accounted for 81.55% of the variation in the maximum axial force. The Pearson correlation analysis showed a strong negative correlation between the rotational speed and hardness (r = −0.73), whereas the tool travel speed showed positive correlations with F_x (r = 0.61), F_z (r = 0.62), and the mean tool force (r = 0.68). Despite the increased tool loading associated with higher travel speeds, no corresponding improvement in the mechanical performance was observed. The results demonstrated that appropriately selected welding conditions produced joints with a yield strength and hardness exceeding 90% of the corresponding base material properties while maintaining relatively lower tool forces. SEM observations confirmed grain refinement in the stir zone. Overall, the combined correlation and ANOVA results demonstrate that real-time tool force monitoring can provide a quantitative basis for selecting FSW parameters that achieve an adequate mechanical performance while minimizing unnecessary machine and tool loading. Full article

7xxx series aluminum alloys exhibit high strength and low density; however, their high degree of alloying results in a pronounced hot-cracking tendency, making direct casting forming challenging. In this study, a rheo-squeeze-cast AA7075 alloy was investigated. Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and room-temperature tensile testing were employed to systematically examine the effects of the solution treatment window on the microstructure and mechanical properties of the castings. The distinctive contribution of this work is the quantitative correlation of solution-time-dependent second-phase evolution and porosity with the tensile behavior of ECSC-assisted rheo-squeeze-cast AA7075. The results show that, with increasing solution treatment time, the intergranular eutectic phases gradually dissolved, and their morphology evolved from lamellar structures into fine rod-like features. When the solution treatment time was extended to 12 h, a small number of pore defects appeared in the microstructure. Under the conditions of solution treatment at 470 °C for 8 h followed by aging at 120 °C for 24 h, uniformly distributed Zn–Mg-rich aging precipitates were observed in the matrix, resulting in the best comprehensive mechanical properties, with an ultimate tensile strength, yield strength, and elongation of 498.1 MPa, 413.7 MPa, and 8.2%, respectively. The optimized heat-treatment condition provides a practical route for achieving a favorable strength–ductility balance in rheo-squeeze-cast AA7075 components. Full article

The catalytic performance of copper-modified strontium titanate-based materials (SrTi_1−xCu_xO₃, where x = 0.02, 0.04, 0.06, and 0.10) in the NH₃-SCR and NH₃-SCO processes was studied. The catalytic materials were obtained by the modified Pechini method and characterized in terms of structural properties (XRD, XAS), surface composition (XPS), microstructural properties (SEM/EDS, SSA measurements), and reducibility (TPR). Catalytic activity, selectivity to N_2, and long-term stability in the NH₃-SCR and NH₃-SCO processes were experimentally verified. The catalytic materials consisted of agglomerates of nanocrystalline perovskite grains with homogeneously distributed copper, except for the material with the highest copper content. The catalytic activity of these materials was found to be highly dependent on copper loading, with STO_4Cu emerging as the optimal catalyst—the NO conversion in NH₃-SCR on the level of 88% and exceptional N₂ selectivity (>98%) was obtained at 275 °C, despite an extremely low Cu content (below 2 wt.%). Lower copper content (STO_2Cu) in catalysts appears to limit the low-temperature activity, which correlates with a higher Cu(I) contribution. On the other hand, the higher copper loading (STO_10Cu) triggers their aggregation. Twelve-hour isothermal stability tests confirmed robust long-term performance and stable N₂ selectivity for both the NH₃-SCR (at 250 °C) and NH₃-SCO (at 375 °C) reactions, demonstrating the potential of finely dispersed, low-loading copper perovskites for environmental catalysis. Full article

The dust generated during coal mining poses a significant threat to miners’ health and safety. Surfactants, as effective agents for improving coal wettability, require a deeper exploration of their microscopic action mechanisms. This study systematically investigates the micro-interaction behaviors and wetting regulation mechanisms of four types of surfactants—anionic (SDBS), cationic (CTAB), zwitterionic (BS-12), and nonionic (AEO-9)—with lignite, bituminous coal, and anthracite through molecular simulations and dynamic contact angle experiments. To correlate the wettability differences with the physical and chemical properties of different coal ranks, XRD and SEM observations were employed to analyze the mineral composition and surface microstructure. The results demonstrate that SDBS has the strongest adsorption capacity on coal, with the wettability capacity ranked as follows: SDBS > CTAB > BS-12 >AEO-9. This research reveals the regulation mechanism of surfactants on coal wettability, providing a theoretical basis for optimizing dust prevention technologies and fostering the development of green mining. Full article

Dissimilar friction stir welding (FSW) of titanium alloys offers a route to spatially optimized aerospace structures, but the asymmetric thermomechanical environment produces heterogeneous microstructures and textures whose interaction with mechanical performance is not well characterized. A near-α/α+β combination of titanium alloys, Ti–6242 SG (advancing side, ADV) and Ti–54M (retreating side, RET), was welded across a matrix of rotation speeds (225–325 rpm) and traverse speeds (100–150 mm·min⁻¹), spanning rotation-to-traverse-speed ratios N/v of 1.80–2.75, which was used throughout as an empirical processing index that orders the conditions of this matrix rather than as a measure of specific heat input. Microstructure, phase identification, relative diffracted-intensity trends, and crystallographic textures were characterized by 2D-XRD at three cross-section locations (ADV, weld nugget center [CEN], RET) and correlated with transverse tensile properties and fracture locations. Partial pole figures were plotted in the simple-shear reference frame with ideal-orientation overlays, intensities in multiples of a random distribution (m.r.d.). The CEN develops the strongest textures, dominated by a basal {002}_α component (20–31 m.r.d.) with poles near the normal direction; this concentration lies away from the ideal shear fiber loci and is more readily explained by orientation inheritance during the β→α transformation on cooling than by direct shear, although unambiguous identification of variant selection would require orientation-resolved measurements. The RET develops {101}_α and {100}_α pole concentrations clustering near the ideal P-fiber loci, consistent with deformation-related texture development, intensifying with both rotation and traverse speed. The ADV shows mixed textures varying non-monotonically with parameters. Two conditions of nearly identical N/v obtained from different parameter combinations (225 rpm/125 mm·min⁻¹ and 275 rpm/150 mm·min⁻¹) nevertheless develop measurably different streak morphologies, microstructures, textures, and tensile responses, showing directly that N/v orders but does not determine the thermomechanical state. Yield strength is uniform (≈900–940 MPa) across the full matrix, consistent with a Schmid-factor estimate in which the basal-near-ND CEN texture gives a very low resolved shear stress on basal systems under transverse loading; joint efficiencies reach ≈90–96%. Ductility, in contrast, tracks consolidation quality rather than texture severity: fracture strain rises almost monotonically with N/v, from ≈0.6–1.4% at N/v ≈ 1.8 (defect-driven, erratic failure) to ≈5.4–6.0% at N/v = 2.60, despite the latter condition carrying the strongest RET pyramidal texture. Full-field strain measurement shows the weld nugget to carry the lowest strain and the highest apparent stiffness of any zone in every condition for which the load record is reliable, with strain accumulating on the advancing side. Consolidated conditions fracture on the advancing side where deformation concentrates, whereas the lowest N/v and longest-exposure conditions fracture in the nugget center; all fracture surfaces are ductile, with the crack path following continuous α layers at prior-β grain boundaries. A favorable processing range within the investigated parameter matrix is N/v ≈ 2.2–2.6, with the best overall combination at 325 rpm and 125 mm·min⁻¹ (N/v = 2.60: UTS ≈ 1010 MPa, ≈5.4–6.0% elongation). Within the parameter range examined here, consolidation quality is the first-order design variable for this dissimilar system, with the zonal texture architecture setting the yield strength level. Full article

This study focuses on the influence of chemically pure nanodiamonds produced by cavitation synthesis on structure formation and physical and mechanical properties of self-compacting concrete (SCC) using an analytical approach. The objective of this research was to develop a high-performance, self-compacting concrete with enhanced properties suitable for the construction sector. Chemically pure nanodiamonds produced by cavitation synthesis (KHA-HC) were added to SCC at weight percentages of 0%, 0.15%, 0.3%, 0.45%, 0.6%, and 0.75% of the binder mass. Fresh SCC modified with nanodiamonds was evaluated for density and cone spread diameter. Hardened SCC with KHA-HC was tested for density, water absorption, compressive strength, and axial compressive strength. The most effective KHA-HC content was established at 0.3%, correlating with 13.5% greater compressive strength, 15.1% higher axial compressive strength, and 19.6% lower water absorption. Incorporating KHA-HC into SCC resulted in a wider spread cone as the additive content was raised. The microstructure of SCC containing KHA-HC was found to be more homogeneous with a decrease in void content within the cement matrix. Polynomial relationships for changes in SCC properties as a function of nanodiamond content were proposed. The effectiveness of nanodiamond additives for modifying SCC was demonstrated. Highly effective self-compacting concretes with improved performance properties have been developed, which are suitable for construction. Full article

Wire arc additive manufacturing (WAAM) is increasingly being considered for large marine components because it offers design flexibility, reduced material waste, and potential benefits for manufacturing cost. However, the fatigue and fracture performance of WAAM materials in seawater remains insufficiently established for safety-critical applications such as marine propellers. This study evaluates the corrosion fatigue and fracture behavior of WAAM-manufactured 316L/316LSi austenitic stainless steel intended for propeller applications. A propeller-representative WAAM component was manufactured using gas metal arc welding, and fatigue specimens were extracted in both the weld and build directions. Axial fatigue testing was performed mainly in artificial seawater at stress ranges of 200, 250, 280, 300, and 330 MPa, with a test frequency of 5 Hz and a run-out criterion of 1 × 10⁶ cycles. Chemical composition, ferrite prediction, hardness, Charpy impact behavior, S–N response, and SEM/EDS fractography were assessed to evaluate the impact on structural integrity. The deposited material showed a chemical composition consistent with 316L/316LSi stainless steel and an estimated ferrite content of approximately 8%, indicating a generally sound austenitic weld–metal microstructure. Several specimens reached run-out at stress ranges up to 250–300 MPa, whereas valid gauge-section fatigue failures occurred in higher stress ranges. Premature failures outside the gauge section were attributed to fixture-related effects and were not considered representative of intrinsic material behavior. SEM/EDS examination of a valid fatigue fracture identified an aluminum- and oxygen-rich crack-initiation feature consistent with an aluminum oxide inclusion. This observation indicates that the fatigue response of WAAM 316L/316LSi should be interpreted not only based on stress-life data but also using principles of fracture mechanics and damage tolerance, where surface or near-surface discontinuities may act as initial flaws and promote ΔK-driven crack growth in seawater. The results demonstrate promising fatigue performance within the experimentally validated range, but they also show that bulk mechanical properties alone are insufficient for qualifying WAAM propeller components. For the investigated WAAM process route, specimen surface conditions, stress ratio (R = 0.053), artificial seawater environment, and experimentally validated cycle range of up to 1 × 10⁶ cycles, a preliminary engineering stress-range limit of Δσ = 200 MPa is recommended for pilot applications. This value should not be interpreted as a general design limit and should not be extrapolated to other WAAM processes, geometries, surface conditions, environments, stress ratios, or service-life regimes without additional qualification testing. Further high-cycle fatigue testing, mean-stress correction, fatigue crack-growth testing in seawater, fracture-toughness assessment, realistic defect-size characterization, non-destructive testing correlation, and component-scale validation are required before broader class acceptance of WAAM-manufactured propeller components. Full article

The effect of Ti content on the microstructure and mechanical properties of 1Cr10Co6MoVNbN steel was systematically investigated by comparing a low-Ti steel (LTS, 0.0066 wt.%) with a high-Ti steel (HTS, 0.02 wt.%). Increasing the Ti content was found to markedly alter the precipitate distribution and, consequently, the creep and high-temperature tensile behavior. In HTS, the higher Ti level promoted the preferential formation of (Ti,Nb)N inclusions during solidification; EDS analyses indicated that the matrix of HTS was substantially depleted of Nb, N, Mo, and V relative to LTS, consistent with this preferential nitride formation. In the tempered state, HTS exhibited larger NbC particles that were frequently attached to (Ti,Nb)N inclusions, whereas LTS contained finer, more uniformly dispersed NbC and abundant needle-like Cr₂N precipitates within martensitic laths. These microstructural differences correlated with a substantially higher 100 h creep strain in HTS compared with LTS at 550 °C and 325 MPa, and with a 550 °C tensile strength in HTS that fell below the aerospace standard requirement. Post-creep examination further revealed void formation around (Ti,Nb)N inclusions in HTS, suggesting that these inclusions act as stress concentrators that reduce the effective load-bearing area during creep. The results indicate that strict control of Ti content is essential in Nb–N-strengthened martensitic steels to avoid excessive (Ti,Nb)N formation and the associated degradation of high-temperature mechanical performance. Full article

The physical, mechanical, and microstructural degradation that occurs in concrete elements exposed to high temperatures constitutes an important research topic in terms of the fire safety and service performance of structures. In this study, the behavior of plaster mortars produced with cement-based and ground granulated blast furnace slag (GGBFS)-based binders, as well as normal concrete (interior concrete) specimens coated with these mortars, under high-temperature exposure was experimentally investigated. After the prepared mortars and plastered concrete specimens were exposed to temperatures of 100, 300, 500, and 700 °C, changes in compressive strength, ultrasonic pulse velocity (UPV), water absorption, mass loss, and bulk density were evaluated. Analysis of the experimental results showed that high temperatures, particularly 300 °C and above, caused significant performance losses in all binder systems. Although calcium aluminate cement-based mortars developed high early-age strength, they exhibited more pronounced strength losses under elevated temperatures, whereas geopolymer-based binders demonstrated more stable performance at low and medium temperatures. Additionally, a strong correlation (R² ≈ 0.89) was observed between UPV and compressive strength in the plastered interior concrete specimens. At 500 and 700 °C, the plastered concrete specimens exhibited 9.8–13.3% and 10.4–18.1% higher residual compressive strength, respectively, compared with the unplastered control specimens. At 700 °C, the PC-based plaster provided the highest improvement in residual compressive strength (18.1%), while the G-Na system exhibited the lowest water absorption, which was 19.5% lower than that of the control concrete. Plastered concrete specimens retained their mechanical and physical properties better than the control (unplastered) concrete specimens at all temperature levels, and this finding was further supported by microstructural analyses. The results indicate that plaster systems produced with different binders are effective in limiting thermal damage to the interior concrete. Full article

Transparent glazing systems are increasingly required to provide simultaneous control over light transmission, solar heat gain, thermal losses, surface contamination, and environmental durability, creating new challenges for the development of multifunctional coating technologies. This review critically examines advanced optical and self-cleaning coatings developed for transparent glass and polymeric substrates, with particular emphasis on the relationships between materials chemistry, surface/interface chemistry, microstructure, and functional performance. Dielectric multilayers, metal oxides, ceramic coatings, sol-gel-derived hybrid systems, and emerging chromogenic materials are discussed in terms of their chemical compositions, structural characteristics, and mechanisms governing optical, thermal, and surface properties. Particular attention is given to structure–property relationships associated with photosynthetically active radiation (PAR) transmission, near-infrared (NIR) management, thermal emissivity, solar modulation, wettability, and self-cleaning behavior, together with their implications for energy-efficient transparent glazing and greenhouse environments. The influence of coating architecture, porosity, surface roughness, interfacial interactions, and deposition conditions on functional performance and long-term stability is critically evaluated. The advantages and limitations of representative deposition strategies are further compared, considering scalability, process compatibility, substrate sensitivity, and application to heat-sensitive polymeric films. Environmental degradation mechanisms induced by ultraviolet irradiation, moisture, thermal cycling, and mechanical stresses are analyzed to identify the key factors governing coating durability and sustainability. Finally, current knowledge gaps and emerging research directions are identified, highlighting the need for rational materials design, multifunctional integration, scalable fabrication, and improved structure-property-durability correlations for next-generation transparent glazing and greenhouse applications. Full article

In traditional gangue backfilling mining, the use of gangue as backfill material often leads to issues such as supply–demand imbalance, low crushing efficiency, and insufficient early strength. To address these challenges, a novel gangue-cemented high-porosity backfill material (GCBM) was developed, using coal gangue (CG, 15–20 mm) as aggregates bonded with an alkali-activated modified coal gangue powder and slag-based fast-setting cementitious material (FCM). The effects of alkali equivalent on the workability and mechanical properties of FCM were investigated to determine the optimal composition. The influence of FCM proportion on the porosity and strength of GCBM was analyzed, and a strength–porosity correlation model was established. The microstructure and bonding mechanism of the interfacial transition zone (ITZ) between FCM-CG aggregates were revealed through multiple microscopic techniques. Results indicate an optimal alkali equivalent of FCM is 6%. The FCM proportion is positively correlated with the compressive and flexural strengths of GCBM, with a critical proportion of 24% at which flexural strength increased by 172% compared with 22%, reflecting enhanced interfacial bonding. Microscopic observations further show that increasing the FCM proportion optimizes the ITZ structure and promotes secondary hydration products, thereby improving interfacial bonding density and the overall mechanical performance of the backfill material. Full article

To meet the demands for lightweight design and high-conductivity connections in new energy vehicles, the high-quality joining of dissimilar Al/Cu metals has emerged as a critical research focus. In this study, laser welding was performed on 2 mm-thick 1060 pure aluminum and T2 copper plates. The effects of laser power (3.6–4.0 kW) and welding speed (0.9–1.5 m/min) on the interfacial microstructural evolution and mechanical properties of the lap joints were systematically investigated. The results demonstrate that the macroscopic morphology of the weld is primarily governed by heat input: excessive laser power induces transverse cracking, whereas an overly low welding speed promotes porosity. Microstructural analysis revealed that intermetallic compounds (IMCs), such as Al₂Cu, AlCu, and Al₄Cu₉, predominantly form at the interface, with their morphology and distribution varying significantly depending on the heat input. Under the optimized parameters of a 3.8 kW laser power and a 1.2 m/min welding speed, sufficient mixing of the molten Al and Cu was achieved. This promoted the formation of fine, dispersed IMCs accompanied by a continuous Al–Cu eutectic layer at the interface, yielding a maximum tensile-shear load of 1561 N. This research elucidates the intrinsic relationship between heat input and the microstructure–property correlation of Al/Cu laser-welded joints, identifying a viable process window for 2 mm-thick sheets and providing theoretical and practical guidance for joining dissimilar medium-thickness metal plates. Full article

Alkali-activated binders (AABs) represent eco-friendly alternatives to ordinary Portland cement. Nevertheless, the synergistic influences of calcium dosage and aluminosilicate stoichiometry on phase assemblage, gel nanostructure, and mechanical properties have not been fully elucidated. Herein, AAB samples with graded CaO contents were fabricated, and the co-regulatory mechanisms of CaO dosage and Si/Al molar ratio on compressive strength and microstructural evolution were systematically explored through compressive strength tests, XRD, TG-DTG, FTIR, and SEM-EDS. In addition, pure reference C-S-H and N-A-S-H gels were synthesized by using the sol–gel method for comparison with AAB pastes. The results reveal that CaO dosage acts as the primary parameter dictating gel phase transition and strength level, categorizing the prepared AABs into three distinct zones: low-calcium region (CaO < 10 wt.%), medium-calcium region (10–20 wt.%), and high-calcium region (CaO > 20 wt.%). Combined grey relational and partial correlation analyses clarify the collinearity-induced false correlations and reveal the stage-dependent independent effects of oxide molar ratios on AABs’ compressive strength. Low-calcium AAB matrices are dominated by N-A-S-H gel networks coexisting with abundant low-strength zeolite crystals, which deteriorate thermal stability and retard strength gain. Increasing CaO content triggers a progressive phase transformation from N-A-S-H gel to high-strength C-(A)-S-H gel. Abundant Ca-rich chabazite and C-S-H gel form in high-calcium systems, which fill internal pores and microcracks and greatly enhance matrix densification and thermal resistance. This work clarifies the multiscale regulatory mechanism of calcium species over gel polycondensation, crystalline phase development, and mechanical performance of AABs, offering fundamental theoretical guidance for the customized design and property optimization of high-strength alkali-activated binders. Full article

Steel/tin bimetallic components fabricated using traditional casting processes have inherent drawbacks, including complicated preparation procedures and a relatively low interfacial bonding strength. To efficiently create metallurgical composite steel/tin bimetallic structures under complex service conditions, we utilized TIG-based additive manufacturing with front wire feeding to prepare the components. The effects of the substrate inclination angle on the macroscopic morphology of the deposited layer, interfacial phase composition, the growth behavior of intermetallic compounds (IMCs) at the bimetallic interfaces, and interfacial mechanical properties were investigated. Our results show that macro-structural defects like cracks, voids and pores were not observed at the steel/tin interfaces. The grains of the interface IMCs were mainly composed of Fe₃Sn, FeSn₂ and FeSb₂ phases; Fe-rich microspheres were dispersed inside the deposited tin layer. Under horizontal substrate conditions, deposited layer morphology and IMC layer thickness presented symmetric distributions. When the inclination angle of the substrate reached 30°, the deposited layers exhibited an asymmetric teardrop morphology, resulting in an increased layer height and width and penetration depth. Meanwhile, tin alloy grains were significantly refined; more high-angle grain boundaries (HAGBs) were formed at the spreading fronts of molten droplets. Tin alloy hardness was improved via synergistic dispersion and grain boundary strengthening. This work reveals the inclination–morphology–microstructure–property correlation, fills the research gap in inclined substrate arc additive manufacturing of steel/tin bimetals, and provides a theoretical foundation for engineering applications. Full article

Taro (Colocasia esculenta) stems are promising bio-based feedstocks for composite materials, textile fibres and adsorbents; however, a quantitative understanding of how their microstructure governs mechanical behaviour remains lacking, constraining their application. This study conducted mechanical tests and scanning electron microscopy (SEM) tests on stems harvested from different ground elevations. The results show that axial tensile strength (σ_t) and nominal radial compressive stress (σ_c) increase first and then decrease with height above ground. σ_t (2.67 MPa) and σ_c (7.64 MPa) both peak at 50–100 mm above ground level. Furthermore, the ultimate nominal compressive strength (σ_c) is significantly higher than the ultimate tensile strength (σ_t) at all heights above ground. Correlation analysis revealed that cross-sectional area A_c (r = 0.83), fibre bundle area fraction P_c (r = 0.78) and fibre wall thickness T_c (r = 0.77) were significantly positively correlated with σ_t, while A_c (r = 0.62) and T_c (r = 0.70) were positively correlated with σ_c. The tensile and compressive properties are closely associated with three microstructural parameters: cross-sectional area, fibre bundle area fraction, and fibre wall thickness—whereas fibre cell area shows only weak correlations with all mechanical indicators (r < 0.5) and is not a key regulatory factor. The stem cross-section transitions from crescent at the base to near-circular at the apex, with the reduction in bearing area underlying the decline in mechanical properties. These results offer a fundamental basis for tailoring mechanical preprocessing parameters and for selective utilisation of stem segments with distinct mechanical performance, thereby supporting the efficient conversion of this abundant biomass into value added materials. Full article