Search Results (577)

The limited ductility of conventional titanium alloys significantly limits their application in critical load-bearing components. To overcome this limitation, a Ti-6Al-2Mo-2Nb-2Zr-2Sn titanium alloy (TC21) was subjected to warm rolling at 500 and 600 °C and aging treatment. Subsequently, microstructural characterization was conducted using scanning electron microscopy, electron backscatter diffraction and transmission electron microscopy, while the mechanical properties were tested by uniaxial tensile tests and nanoindentation tests. The sample warm rolled at 600 °C exhibited an optimal combination of strength and ductility, with an ultrahigh yield strength of 1138 MPa and an elongation-to-fracture of 7.3%. Aging treatment further enhanced the yield strength to 1263 MPa, while retaining a good ductility of 9.6%. The improved mechanical properties are mainly associated with the formation of nanoscale secondary α phase (α_s) lamellae caused by the aging treatment. Interface strengthening is identified as the primary strengthening mechanism. In particular, the optimal volume fraction and decreasing texture intensity of the soft phase contribute to the enhanced ductility. This work provides a method for viable thermo-mechanical processing for achieving an excellent strength–ductility combination in titanium alloys. Full article

Iron tailings, steel slag (SS), and desulfurization ash (DA) are industrial solid wastes with high annual output and large stockpiles. To enhance their utilization rate in concrete and fully utilize the synergistic effect of iron tailings powder (ITP), SS, and DA, a multi-solid-waste ISD (ITP-SS-DA) concrete was prepared. In this study, ITP, SS, and DA were used as composite mineral admixtures to replace 30% of the cement, and iron tailings sand (ITS) and iron tailings waste rock (ITR) were used as aggregates. The effects of water/binder ratio (w/b), ITP fineness, and mineral admixture proportion on the compressive strength of ISD concrete were investigated. The influence of ITP fineness on the microstructure was analyzed based on mercury intrusion porosimetry (MIP) and backscattered electron (BSE) tests. The results show that the w/b has a significant effect on the early-age compressive strength, but its effect diminishes at mid-to-late ages. ISD composite mineral admixtures with properly ball-milled ITP enhance compressive strength, refine the pore structure, and increase the compactness of the interfacial transition zone (ITZ). Appropriately increasing the proportion of SS and adjusting the ratio of ITP to DA can promote the synergistic effect of mineral admixtures, thus enhancing compressive strength. Compared with cement concrete, ISD concrete exhibits slightly lower compressive strength but still meets the design requirements and presents a significantly superior microstructure when the w/b, ITP fineness, and admixture proportion are suitable. Full article

This study develops a multi-scale fiber-reinforced cementitious composite (MFRC) by hybridizing calcium carbonate whisker (CW), polyvinyl alcohol (PVA) fiber, and steel fiber. The interfacial micromechanical properties between steel fiber/matrix and PVA fiber/matrix under the influence of CW were systematically examined through single-fiber pull-out tests. The two-dimensional and three-dimensional distribution characteristics of fibers in the MFRC were analyzed using backscattered electron imaging (BSE) and X-ray computed tomography (X-CT), respectively. Based on the fiber distribution characteristics, flexural strength prediction models were developed with R² values of 0.79 (2D) and 0.82 (3D). Experimental validation via splitting tensile tests and three-point bending tests confirmed the model’s effectiveness in simultaneously predicting splitting tensile strength (R² = 0.89) and flexural strength (R² = 0.93). These findings demonstrate the reliability and universality of the proposed model for predicting flexural–tensile strength in an MFRC. Full article

FeCrMnNi-based alloys, derived from the well-known Cantor high-entropy alloy, have attracted increasing attention due to their excellent strength–ductility balance. Additively manufactured FeCrMnNi variants are characterized by superior hardness compared to their conventionally processed counterparts. In the present study an optimized composition of the FeCrMnNi medium-entropy alloy was additively manufactured via laser-based powder bed fusion and subsequently subjected to systematic heat treatments. CALPHAD simulations were applied to select the specific composition and post-processing heat treatment conditions, where the latter aimed at promoting the evolution of a dual-phase microstructure. Experimental characterization included X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction, as well as Vickers hardness and tensile testing. A microstructure could be established dominated by a face-centered cubic (FCC) phase with minor fractions of a secondary phase in the non-treated condition. The evolution of an additional body-centered cubic (BCC) phase upon heat treatment at and above 700 °C was observed. The emerging BCC phase as well as increasing fractions of the secondary phase were accompanied by significantly increased hardness and strength, surpassing the literature values of similar compositions. However, a heat treatment at 1000 °C resulted in recrystallization and an increase in grain size, while the decreasing fraction of the secondary phase eventually led to a reduction in strength. These findings underscore the combined potential of composition optimization and targeted post-processing to enhance the mechanical performance of additively manufactured FeCrMnNi alloys. Full article

Aluminum alloy composites are widely used in various high-end fields due to their ability to give full play to the advantages of each layer. However, the traditional three-layer aluminum alloy composite sheet cannot meet the current demand. In this study, composite rolling technology is adopted to combine three different alloys (4045, 3003, and 6061) for fabricating a 2.0 mm thick four-layer aluminum alloy composite sheet (4045/3003/6061/3003). The microstructure and properties of the composite sheet were analyzed by simulating the vacuum brazing process (595 °C/10 min) and artificial aging treatment (175 °C for 12 h), combined with characterization techniques including scanning electron microscopy (SEM), electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). The results show that the four-layer composite sheet exhibits lower Si diffusion after brazing, where the intermediate 3003 aluminum alloy layers effectively prevent the combination of magnesium (Mg) and the 4045 alloy. Compared with the brazed three-layer composite sheet the ultimate tensile strength and yield strength of the four-layer composite sheet after aging are increased by 139.7% and 326.6%, respectively, indicating significant improvement in its mechanical properties. This study provides a reference for the production of four-layer aluminum alloy composite sheet and contributes to the development of rail transit. Full article

In fundamental physics, sensors operating below liquid helium temperatures are highly vulnerable to vibrations, which can affect the sensitivity, for example, of high-performance particle detectors. Pulse-tube refrigerators, while generating vibrations lower than those of conventional systems, may still introduce several disturbances. Hence, flexible thermal connections are a commonly used mechanical solution to mitigate these undesirable effects. Among the materials that can be used, ultra-high-purity aluminum (UHP-Al) has attracted the attention for low-amplitude-vibration cryogenic applications, including gravitational wave interferometry, quantum information systems, precision space instrumentation, and cryogenic resonators. Thus, the aim of the paper is the characterization of the mechanical and microstructure properties of three UHP-Als (i.e., 5N—99.999 wt%, 5N5—99.9995 wt% and 6N—99.9999 wt%) intended for the production of thermal flexible connections with low stiffness, specifically designed to reduce vibration transmission in cryogenic environments. Mechanical properties were evaluated through standard tensile tests from room (+25 °C) to low temperature (i.e., −150 °C), providing insights into yield strength, ultimate tensile strength, elongation and elastic modulus. In addition, the dynamic elastic modulus of material loads, at cryogenic conditions (i.e., about −180 °C), was determined by measuring the natural resonance frequency, thereby assessing the material’s response to vibrational. Moreover, an extensive microstructural analysis was conducted using electron backscatter diffraction and x-ray diffraction. The correlation between the observed microstructure and the elastic properties was systematically examined. The results underscore the pivotal role of microstructural characteristics in dictating the elastic behavior of UHP Als. Eventually, the analysis provides valuable guidelines for the materials employment inside cryogenic systems, where severe vibration control is critical to maintain high operational performance. Full article

A Cu-containing FeCrMnNiAl multi-principal element alloy was processed by laser-based and electron beam-based powder bed fusion (PBF-LB/M and PBF-EB/M) to investigate processing–microstructure–property relationships. In focus were alloy variants with a relatively high Cu content. Two PBF-LB/M scan strategies, employing a Gaussian beam with and without a re-scan with a laser featuring a flat-top profile, were compared to PBF-EB/M processing, followed by heat-treatments between 300 °C and 1000 °C. The phase constitution, elemental partitioning and grain boundary characteristics were analyzed by X-ray diffraction, electron backscatter diffraction and energy-dispersive X-ray spectroscopy. Mechanical behavior was assessed by hardness and tensile testing. Both manufacturing routes promoted the evolution of stable multi-phase microstructures composed of face-centered-cubic (FCC)- and body-centered-cubic (BCC)-type phases across all heat-treatment conditions. PBF-LB/M processing resulted in finer, dendritic microstructures and suppressed formation of a Cu-rich FCC phase due to higher cooling rates, whereas PBF-EB/M promoted the evolution of Cu-rich FCC segregates and equiaxed grain morphologies. Heat-treatment above 700 °C led to recrystallization, accompanied by an increase of the FCC phase fraction, grain coarsening, and recovery. At lower heat-treatment temperatures, the changes in microstructure are different. Here, it is assumed that small, non-clustered Cu-rich precipitates formed at the grain and sub-grain boundaries, although this assumption is only based on the assessment of the mechanical properties. The size of these precipitates is below the resolution limit of the techniques applied for analysis in the present work. Additional structures seen within the Cu-rich areas of PBF-EB/M-manufactured samples treated at lower temperatures also seem to have an influence on the hardness and yield strength. All of the conditions investigated exhibited pronounced brittleness, limiting reliable tensile property evaluation and indicating the need for further optimization of processing strategies and microstructural control for high-Cu-fraction-containing multi-principal element alloys. Full article

The effects of different finishing rolling temperatures on the microstructure and mechanical properties of a 580HE hole expansion steel were systematically investigated using optical microscopy, scanning electron microscopy, electron backscatter diffraction, and transmission electron microscopy. The results show that the yield strength increases with decreasing finishing rolling temperature, whereas the tensile strength and total elongation exhibit relatively small variations. Significant changes in phase fraction, grain size, spatial distribution, and NbC precipitation behavior are observed under different finishing rolling temperatures. The microstructure mainly consists of polygonal ferrite and granular bainite, while acicular ferrite is formed at higher finishing rolling temperatures. With decreasing finishing rolling temperature, the ferrite and bainite grains are markedly refined and become more uniformly distributed. Meanwhile, the ferrite fraction slightly increases, the crystallographic texture is weakened, and, more importantly, the number density of precipitates increases while their size is significantly reduced. The hole expansion ratio increases noticeably with decreasing finishing rolling temperature, which is mainly attributed to grain refinement, improved microstructural and strain homogeneity, and the selective strengthening effect of fine NbC precipitates. These factors effectively reduce stress concentration and hardness mismatch between soft and hard phases, thereby delaying crack initiation during hole expansion. Full article

Eutectic alloys stand out for their ability to combine high strength and good ductility; a behaviour rooted in their characteristic two-phase microstructure—lamellar or globular—formed at a constant solidification temperature that minimizes segregation and suppresses brittle phases. Their low interfacial energy limits microcrack propagation, while interfacial sliding and dislocation blocking at phase boundaries enhance both strength and toughness. In this work, we investigate how controlled microstructural modifications influence the behaviour of the eutectic high-entropy alloy AlCoCrFeNi2.1, composed of B2 (Ni–Al-rich) and L12 (Co–Fe–Ni-rich) phases. Because these phases exhibit distinct mechanical responses, microconstituent morphology becomes a design parameter. Powder metallurgy is the only processing route capable of providing the level of microstructural control required in this study. It preserves the rapidly solidified eutectic architecture of gas-atomised powders while allowing its intentional transformation during consolidation. Two strategies were implemented: (i) tuning the thermal–electrical input in Spark Plasma Sintering (SPS) and Electrical Resistance Sintering (ERS), and (ii) engineering the particle size distribution, including a bimodal design that enhances surface-energy-driven morphological transitions. SPS enables a gradual lamellar-to-globular evolution, whereas ERS induces ultrafast transformations governed by current intensity. The bimodal PSD significantly accelerates globularisation at lower energy input. EBSD-KAM (Electron Backscatter Diffraction—Kernel Average Misorientation) mapping identifies the lamellar B2 phase as metastable and highly strained, while globular B2 domains show reduced dislocation density. Nanoindentation confirms that intrinsic phase properties remain unchanged, whereas microhardness scales with morphology and lamellar spacing. These results demonstrate that the macroscopic mechanical response is governed by microstructure, establishing powder metallurgy as a uniquely powerful pathway for microstructure-driven design in eutectic HEAs. Full article

Hybrid nanocomposites based on Aluminum 6061 (Al 6061) reinforced with carbon nanotubes (CNTs) and aluminum oxide (Al₂O₃) emerge as promising materials due to their ability to achieve simultaneous improvements in strength, thermal stability, and tribological performance. This study examines the structure–property relationships of CNT–Al₂O₃ nano-reinforced hybrid Al 6061, with particular emphasis on microstructural evolution and mechanical properties. The nanocomposites are fabricated via a powder metallurgy route, which enables optimized dispersion and homogeneous distribution of CNTs and Al₂O₃ within the aluminum matrix. Microstructural characteristics, interfacial bonding, and grain refinement are systematically analyzed using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Mechanical characterization demonstrates a marked enhancement in mechanical properties compared to Al 6061. The observed property improvements are attributed to synergistic strengthening mechanisms, including effective load transfer from the matrix to Al₂O₃ particles, CNT-induced grain refinement, and increased resistance to dislocation motion. These results establish a direct correlation between microstructural features and mechanical performance, highlighting the potential of CNT–Al₂O₃ reinforced Al 6061 hybrid nanocomposites for lightweight, high-strength applications in aerospace, automotive, and structural engineering industries. Full article

Distributed acoustic sensing sends laser pulses along a fiber optic cable and analyzes the backscattered light to identify acoustic signals along the entire fiber. Liquid slugs were produced in a 427 m vertical test well using surface-controlled gas lift valves. To enhance DAS monitoring, pressure pulses were induced by multiple acoustic shots from a fluid level gun. Visualization of the responses through frequency band energy plots and unfiltered phase shift measurements permitted tracking slug movement and estimating parameters such as velocity, location, and body length. The results demonstrate that DAS stimulated with acoustic pulses can effectively track liquid slugs in real-time. We observe that relying solely on flow-induced noise in multiphase flow environments may not provide sufficient signal strength for slug detection. Applications include real-time detection of liquid slugs for improved well monitoring and flow management. Full article

The strategic balance between strength and electrical conductivity in Al-Mg-Si alloys is a critical challenge that must be overcome to enable their widespread adoption as viable alternatives to copper conductors in power transmission systems. To address this, the present study comprehensively investigates model alloys with Mg/Si ratios ranging from 1.0 to 2.0. A multi-faceted experimental approach was employed, combining tailored thermo-mechanical treatments (solution treatment, cold drawing, and isothermal annealing) with comprehensive microstructural characterization techniques, including electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM). The results elucidate a fundamental competitive mechanism governing property optimization: excess Mg atoms concurrently contribute to solid-solution strengthening via the formation of Cottrell atmospheres around dislocations, while simultaneously enhancing electron scattering, which is detrimental to conductivity. A critical synergy was identified at the Mg/Si ratio of 1.75, which promotes the dense precipitation of fine β″ phase while facilitating extensive recovery of high dislocation density. Furthermore, EBSD analysis confirmed the development of a microstructure comprising 74.1% high-angle grain boundaries alongside a low dislocation density (KAM ≤ 2°). This specific microstructural configuration effectively minimizes electron scattering while providing moderate grain boundary strengthening, thereby synergistically achieving an optimal balance between strength and electrical conductivity. Consequently, this work elucidates the key quantitative relationships and competitive mechanisms among composition (Mg/Si ratio), processing parameters, microstructure evolution, and final properties within the studied Al-xMg-0.5Si alloy system. These findings establish a clear design guideline and provide a fundamental understanding for developing high-performance aluminum-based conductor alloys with tailored Mg/Si ratios. Full article

To address the performance deficiencies in welded joints in 2507 duplex stainless-steel pipes under demanding service conditions such as deep-sea operation, this study investigates drawn 2507 duplex stainless-steel pipes. Vacuum-fusion welding coupled with ER2507 wire filling is employed to fabricate the joints. The joint microstructure and tensile behavior are systematically analyzed using microstructural characterization techniques (electron backscatter diffraction and transmission electron microscopy) and uniaxial tensile testing. The results indicate that the joint exhibits a graded microstructure along the welding direction: base metal-heat affected zone-weld metal. The austenite phase fraction in the fusion zone decreases to 27.6%. The joint achieves an ultimate tensile strength of 833.3 MPa and a total elongation of close to 23%, demonstrating an excellent combination of strength and ductility. During tensile deformation, the ferrite and austenite phases undergo coordinated deformation. Strain is distributed relatively uniformly at low strain levels but localized preferentially within the fusion zone at high strain levels. Fractographic analyses reveal a ductile fracture mode. This research provides theoretical support and technical reference for optimizing welding processes and assessing the service safety of 2507 duplex stainless-steel pipes in deep-sea pipeline-engineering applications. Full article

The use of flawed excavated-mass aggregates produced from crushing and screening hydraulic engineering waste in concrete projects can reduce natural resource extraction, increase waste utilization rates, and minimize environmental pollution. However, the direct application of flawed excavated-mass aggregates is limited due to their high crushing index and water absorption rate. Therefore, this paper measures the multi-dimensional physical and mechanical properties of defective aggregates. A strengthening slurry is prepared by comprehensively modifying the crystallization strength and penetration path of sodium silicate solution using various chemical reagents. The strengthening mechanism of the slurry on flawed excavated-mass aggregates is analyzed using SEM and MIP tests. Concrete tests are designed to investigate the workability and mechanical properties of flawed excavated-mass aggregate concrete. The pore structure of the ITZ (Interfacial Transition Zone) in defective aggregate concrete is analyzed through BSE (Backscattered Electron) imaging to elucidate the strengthening mechanism of secondary crystallization reactions on the ITZ. The research findings can provide technical support for repairing aggregates with defects. Full article

The laser welding of 4 mm thick Ti80 alloy under different powers was analyzed, and the weld morphology, microstructure, and mechanical properties were studied. A simulation model was established based on ABAQUS, and laser welding simulations were conducted using 2520 W and 3000 W laser welding power sources to analyze the temperature field and stress field, which were verified by experiments. The increase in power changed the weld morphology from Y-shaped to X-shaped and affected the number of pores in incomplete and complete penetration. The microstructure in the weld zone presented fine acicular α′ phase. Subsequently, grain boundary distribution maps, Kernel Average Misorientation (KAM) maps, and geometrically necessary dislocation (GND) density maps were generated through electron backscatter diffraction (EBSD) analysis. These comprehensive data visualizations enabled multi-dimensional investigation, establishing and analyzing correlations between laser welding parameters, microstructural evolution, and mechanical properties in Ti80 titanium laser welding. The hardness of the base material was 320 HV to 360 HV, and it increased from 420 HV to 460 HV in the weld zone. At 3000 W, the tensile strength reached 903.12 MPa, and the elongation was 10.40%, indicating ductile fracture. The simulation results accurately predicted the maximum longitudinal residual stress in the weld zone, with an error of 1.65% to 1.81% of the measured value. Full article