Search Results (5,802)

In this study, a duplex treatment combining carburizing, nitriding, and subsequent induction hardening (IH) was applied to JIS-SCM420 low-alloy steel. A comprehensive evaluation was conducted to assess surface characteristics, including microstructure, hardness, residual stress, and fatigue performance. The IH process successfully produced a high-nitrogen-content ε-Fe_2-3(N,C) compound layer (2–3 μm thick) and fine acicular martensite at the surface, significantly enhancing surface hardness (950 HV0.03) and inducing beneficial compressive residual stress (−477 MPa). The IH-treated material exhibited a plane-bending fatigue strength of approximately 775 MPa, notably higher than that of conventionally carbonitrided specimens (700 MPa). This improvement was primarily attributed to the formation of the hard ε-Fe_2-3(N,C) compound layer and refined martensitic structure resulting from induction hardening. Additionally, IH activated residual interstitial elements, promoting the precipitation of stable surface nitrides. These microstructural changes effectively suppressed fatigue crack initiation and propagation, thereby extending fatigue life under cyclic loading conditions. Full article

Laser welding, a vital process in modern industry, offers significant technical and economic benefits, including improved part quality, precision, productivity, and cost reduction. This study significantly enhances our understanding of heat-treatable weldability (AA2024, AA2017, AA6061) and non-heat-treatable AA5083 aluminum alloys. It establishes a “weldability window” based on power density and interaction time, identifying three key domains: insufficient penetration, full penetration with regular weld, and irregular weld or cutoff. The study’s findings reveal that heat-treatable alloys soften in the fusion zone due to the dissolution of reinforcing precipitates during welding. In contrast, non-heat-treatable alloys exhibit hardening due to a fine dendritic microstructure. The fusion zone features fine dendrites, and in the heat-affected zone (HAZ), coarse particles and liquation at the fusion line are observed, particularly in AA6061 and 2024 alloys. The study also shows that the joint efficiency, a measure of the weld’s load-bearing capacity, is approximately 90% for the AA5083 alloy and 80% for the heat-treatable alloys. These findings significantly contribute to our understanding of welding processes. They can be used to optimize laser welding processes, thereby ensuring the production of high-quality and reliable joints in industrial applications. Full article

Film-cooling holes are the key cooling structures of turbine blades, and there are still great challenges in manufacturing high-quality film-cooling holes. Although abrasive flow machining can be used as a post-processing technique to optimize the quality of film-cooling holes, its action process and influence mechanism have not been systematically studied. Herein, the drilling method of femtosecond laser combined with abrasive flow is studied in detail. Moreover, for comparison, the drilling methods of single femtosecond laser, single electrical discharge machining, and electrical discharge machining combined with abrasive flow are also discussed. The microstructure and composition distribution of the hole walls before and after abrasive flow machining were systematically characterized, indicating that abrasive flow can effectively remove the recast layer and cause local plastic deformation. Due to the surface hardening and non-uniform residual stress caused by abrasive impact, abrasive flow machining can increase the high-temperature endurance time of film-cooling holes while reducing the elongation. The combination of femtosecond laser and abrasive flow machining demonstrates the best high-temperature mechanical properties, with the endurance time and elongation reaching 136.15 h and 12.1%, respectively. The fracture mechanisms of different drilling methods are further discussed in detail. The research results provide theoretical guidance for the manufacturing of high-quality film-cooling holes through the composite processing of femtosecond laser and abrasive flow. Full article

We explored the effects of different solution treatment temperatures on the microstructure, mechanical properties and wear resistance of alloyed high-manganese steel, as well as the correlations among the three parameters. The results indicated that the average grain size of high-manganese steel first decreases and then gradually increases with an increasing solution temperature. After solution treatment, the surface hardness of the high-manganese steel is lower than that of untreated steel. At a solution treatment temperature of 1050 °C, the surface hardness value is lowest, at 253.1 HV. In addition, the optimal combination of tensile strength, yield strength and work hardening rate is observed at a solution treatment temperature of 950 °C. The friction performance test results revealed that the average friction coefficient on the surface of the high-manganese steel first decreased and then increased with the increase in solution treatment temperature. After solution treatment at 950 °C, it reached a minimum value 0.273 due to oxidation friction. Meanwhile, the hardness of the steel after friction increased rapidly because of its excellent work hardening ability, so the wear rate was relatively low, approximately 0.223 × 10⁻¹³ m²/N, demonstrating optimal wear resistance. After solution treatment, the average grain size of high-manganese steel changed, and there was a transformation of the wear mechanism; the friction and wear mechanism shifted from a combination of particle wear and fatigue wear to adhesive wear, with particle wear as the auxiliary. Full article

In the light of increasing research into amorphous composites and their applications, as-cast specimens of multicomponent Ti₄₈Zr₁₈V₁₂Cu₅Be₁₇ amorphous composites were prepared via water-cooled copper mold suction casting. Subsequently, the as-cast specimens were subjected to semi-solid isothermal treatment to obtain semi-solid specimens. Taking the semi-solid specimens as the research object, room temperature compressive deformation behavior was investigated by analyzing the shear band characteristics on the side surfaces of the compressed specimens. The evolution of shear bands at various stages of plastic deformation was investigated via scanning electron microscopy (SEM). Additionally, significant work hardening was observed after yielding. Surface deformation morphologies indicate that the work-hardening behavior is associated with plastic deformation, interactions between shear bands, and interactions between shear bands and β-Ti crystals. Experiments have demonstrated that at a specific deformation extent, shear bands preferentially initiate at the crystal–amorphous matrix interface. In the final stage of plastic deformation, shear bands propagate through work-hardened β-Ti crystals into the amorphous matrix, with their propagation retarded by the β-Ti crystals. When shear bands in the amorphous matrix are obstructed by β-Ti crystals and can no longer propagate, some evolve into cracks. These cracks then propagate exponentially, leading to eventual fracturing of the specimens and termination of plastic deformation. The research findings provide a theoretical basis for analyzing the deformation capacities of various amorphous composites. Full article

To enhance surface hardness, laser surface remelting (LSR) was performed to treat the surface of a novel nuclear-grade Zr-1.0Sn-1.0Nb-0.3Fe zirconium alloy. A combination of advanced characterization techniques was used to systematically analyze the microstructural features of the samples before and after the LSR treatment, and their correlation with hardness variations was studied. Results show that the LSR-treated surface consists of two distinct microstructural regions: (i) the remelted zone (RZ), characterized by fine lath structures and precipitates distributed along the lath boundaries; and (ii) the heat-affected zone, comprising blocky α phase, α laths, and precipitates. The surface of the LSR-treated samples exhibits a random texture, which is attributed to the selection suppression of α variants during the laser-induced rapid transformation. The average hardness of the RZ reaches 285.7 ± 8.3 HV, ~40% higher than the substrate. This hardness enhancement is ascribed to LSR-induced grain refinement. Full article

The present study explores the sustainable potential of volcanic ash sourced from the active Sakurajima volcano (Japan) as an eco-friendly alternative to Portland cement—a binder known for its high carbon emissions—in concrete and mortar production. The abundant pyroclastic material, currently a waste burden for the residents of Sakurajima and the Kagoshima Bay region, presents a unique opportunity for valorization in line with circular economy principles. Rather than treating this ash as a disposal problem, the research investigates its transformation into a valuable supplementary cementitious material (SCM), contributing to more sustainable construction practices. The investigation focused on the material characterization of the ash (including chemical composition, morphology, and PSD) and its pozzolanic activity index, which is a key indicator of its suitability as a cement replacement. Mortars were prepared with 25% of the commercial binder replaced by volcanic ash—both in its raw form and after mechanical activation—and tested for compressive strength after 28 and 90 days of water curing. Additional assessments included workability of the fresh mix (flow table test), apparent density, and flexural strength of the hardened composites. Tests results showed that the applied volcanic ash did not influence the workability of the mix and showed negligible effect on the apparent density (changes of up to 3.3%), although the mechanical strength was deteriorated (decrease by 15–33% after 7 days, and by 25–26% after 28 days). However, further investigation revealed that the simple mechanical grinding significantly enhances the pozzolanic reactivity of Sakurajima ash. The ground ash achieved a 28-day activity index of 81%, surpassing the 75% threshold set by EN 197-1 and EN 450-1 standards for type II mineral additives. These findings underscore the potential for producing low-carbon mortars and concretes using locally sourced volcanic ash, supporting both emissions reduction and sustainable resource management in construction. Full article

This study investigates the impact of arc-hardening parameters on a groove-shaped S45C steel tube, with a focus on surface hardness and microstructure. According to the findings, when arc quenching occurs, the tube’s surface hardness increases significantly compared to its original hardness. The surface layer hardness can increase to 50.3 HRC, which is 3.4 times greater than the untreated surface. Changing arc quenching parameters such as current intensity, gas flow rate, arc length, scan speed, heating angle, and cooling angle causes a variation in surface hardness due to the balance of heat input and cooling value. Moreover, the microhardness distribution is divided into three zones: the hardened zone (with a high hardness value), the heat-affected zone (HAZ), which has rapidly declining hardness, and the base metal (with a low hardness value). The hardened zone could have a hardness with a load of 0.3 N of 440 HV and a case depth of about 900 μm. The next zone is the HAZ, where the hardness with a load of 0.3 N drops significantly. The hardness in the base metal zone recovers to its original value of 152 HV. Interestingly, the microstructure, under the hardness distribution, illustrates the relationship between the hardness value and its phases. The hardened zone consists of martensite and residual austenite phases, resulting in a high hardness value. The bainite phase constitutes the HAZ, which correlates to the zone of rapid hardness reduction. Finally, the base metal zone has ferrite and pearlite microstructures, indicating the softest zone. The investigation’s findings may increase our understanding of the arc-hardening process and widen its industrial applications. Full article

To address the issues of numerous influencing factors on material quality, difficulty in determining the optimal mix proportion, and the need to clarify the formation mechanism when foam concrete is used as an internal mold for prefabricated components, this study conducted orthogonal tests to investigate the influence laws of fly ash content, foam content, foaming agent dilution ratio, and water–binder ratio on the dry density and compressive strength of foam concrete, and determined the optimal mix proportion via analysis of variance (ANOVA). Additionally, scanning electron microscopy (SEM) tests were performed to analyze the effects of these four factors on the microscopic pore morphology of foam concrete from a microscopic perspective, thereby revealing its formation mechanism, and engineering applications were carried out. The results show that the primary-to-secondary order of factors affecting the dry density and compressive strength of foam concrete is as follows: foam content (B) > water–binder ratio (D) > foaming agent dilution ratio (C) > fly ash content (A). The optimal mix proportion is 5% fly ash content, 18% foam content, a 30-fold foaming agent dilution ratio, and a water–binder ratio of 0.55. Under this mix proportion, the pore size of foam concrete ranges from 200 μm to 500 μm with uniform distribution, and the pore spacing is between 20 μm and 30 μm, with almost no connected pores. When the foam concrete slurry sets and hardens, hydration products such as calcium silicate hydrate (C-S-H) gel, calcium hydroxide, ettringite (AFt), and monosulfate aluminate (AFm) are generated around the bubbles. The mechanical properties of foam concrete are afforded by the combined action of these hydration products and the pore structure. Full article

This paper deals with a method for producing gypsum concrete by vibropressing ultra-stiff concrete mixtures with a water–gypsum ratio (W/G) of 0.25–0.35 (stiffness 50–55 s according to Vebe), as well as the method of designing the composition of such concrete. The research was carried out using mathematical experimental design. Experimental and statistical polynomial models of strength and average density dependences on technological factors such as moisture content in the gypsum concrete mixture, aggregate consumption, and vibropressing parameters (dynamic punch pressure during vibration and process duration) were obtained. Models of the aggregate quantity and granulometric composition influence on the gypsum concrete strength at constant compaction parameters and changes in the mixture moisture content were obtained. Based on the obtained models, a method for designing the composition of vibropressed gypsum concrete on dense aggregate was developed. According to the proposed method, the aggregate-to-gypsum ratio (A/G) is first found, taking into account the given strength and quality of the materials. Next, the optimal W/G ratio, which ensures maximum compaction, is calculated and, after that, the residual air volume and the component consumption are obtained. The method allows determining the composition of gypsum concrete on dense aggregate, compacted by vibropressing of superhard mixtures according to a given compressive strength after 1 day of hardening in the range from 15 to 44 MPa. It also allows you to take into account the operating parameters of the molding plant, the aggregate grain composition, and determine the optimal moisture content of the gypsum concrete mixture. Full article

This study investigates the influence of key heat treatment parameters on the microstructure and mechanical properties of the powder metallurgy tool steel Vanadis 60. A fractional factorial design of experiments was applied to evaluate the effects of austenitising temperature, quenching medium, tempering temperature, and number of tempering cycles on hardness, flexural strength, and microstructure, using detailed phase characterisation by X-ray diffraction. The results reveal two distinct processing routes tailored to different performance objectives. Maximum hardness was achieved by combining austenitisation at 1180 °C, rapid oil quenching, and tempering at 560 °C. These conditions enhance the solubility of carbon and other alloying elements, promote secondary hardening, and reduce retained austenite. Conversely, higher toughness and ductility were obtained by austenitising at 1020 °C, air cooling, and tempering at 560 °C. These parameters favour the formation of a bainitic microstructure, together with lower martensite tetragonality and minimal retained austenite. A statistically significant interaction was identified between the austenitising temperature and the number of tempering cycles; three temperings were sufficient to compensate for the lower hardness associated with reduced austenitising temperatures. The results provide a robust guidance for optimising thermal processing in highly alloyed tool steels, enabling the precise tailoring of microstructure and properties in accordance with specific mechanical service requirements. Full article

Three-dimensional concrete printing (3DCP) is an emerging technology that improves design flexibility and material efficiency in construction. However, widespread adoption of 3DCP requires overcoming key material challenges. These include controlling rheology for pumpability and buildability and achieving sufficient mechanical strength. This paper provides a comprehensive review of the application of nanoclays (NCs) as a key admixture to address these challenges. The effects of three primary NCs (attapulgite (ATT), bentonite (BEN), and sepiolite (SEP)) on the fresh- and hardened-state properties of printable mortars are systematically analyzed. This review summarize findings on how NCs enhanced thixotropy, yield stress, and cohesion, which are critical for shape retention and the successful printing of multilayered structures. Quantitative analysis reveals that optimized dosages of NCs can increase compressive strength by up to 34% and flexural strength by up to 20%. For enhancing rheology and printability, a dosage of approximately 0.5% by binder weight is often suggested for ATT and SEP. In contrast, BEN can be used at higher replacement levels (up to 20%) to also function as a supplementary cementitious material (SCM), though this significantly impacts workability. This review consolidates the current knowledge to provide a clear framework for selecting appropriate NCs and dosages to develop high-performance, reliable, and sustainable materials for 3DCP applications. Full article

This study investigates the strain hardening and dislocation structure in the surface layers of C45 steel subjected to precision grinding at various depths. The aim was to assess how different grinding conditions influence the mechanical response and defect structure of ferrite. Nanoindentation was used to evaluate mechanical properties, while X-ray diffraction analysis provided data on the microstrain, crystallite size, and residual stress. The character and density of dislocations were further examined using modified Williamson–Hall and q-parameter analysis. The results revealed that the sample ground to a depth of 2 μm exhibited the highest density of statistically stored dislocations, as well as the lowest dislocation mobility. This condition also corresponded to the highest residual stresses and the greatest share of screw dislocations, indicating intense strain localization. In contrast, deeper grinding depths resulted in lower dislocation densities and reduced the strain energy. The observed trends highlight the formation of a dislocation-rich nanostructured layer in the shallowest ground region. These findings provide new insights into the mechanisms of surface hardening in ferritic steels and demonstrate how the depth of material removal during grinding governs the subsurface microstructure and strengthening effects. Full article

This paper discusses the potential of adding a self-made super-early-strength agent to produce quick-setting, quick-hardening, and high-strength concrete. A super-early-strength agent is prepared by mixing triethanolamine (TEA), aluminum sulfate (Al₂(SO₄)₃·18H₂O), formic acid (HCOOH), and sodium fluoride (NaF) with a water-reducing agent in different proportions. In this paper, the effects of super-early-strength agent ratio and dosage, water–binder ratio, silica fume content, and cementitious material content on the setting time and compressive strength of high-strength concrete were studied. The hydration characteristics were evaluated by X-ray diffraction (XRD) and TG-DSC thermal analysis. The results show that the high-strength concrete prepared by 42.5R ordinary Portland cement mixed with appropriate amount of silica fume and self-made super-early-strength agent has a compressive strength of 10 MPa in 6 h, a compressive strength of 40 MPa in 1 day, a compressive strength of not less than 80 MPa in 28 days, and a compressive strength of not shrinking in 180 days. Using conventional raw materials and general process methods, the concrete prepared according to the preparation method of this experiment can significantly shorten the setting time and improve the compressive strength. However, it is difficult to form concrete when the amount of super-early-strength agent is too large. Nevertheless, this study provides a theoretical basis for large-scale and high-value utilization of the potential of super-early-strength agents and development to improve efficiency. At the same time, it provides a reference for the application of coating technology in rapid repair engineering. Full article

This study investigated the effects of preheat hardening on the egg-laying capacity of honeybee queens and the flight performance of their daughter workers. A honeybee queen was confined in a cage with a two-section frame for 12 h. Then, 48 h old eggs from one section were incubated for 15 min at 41 °C and 70% relative humidity (RH). The queens (n = 12) raised in this section were named the pre-heat-treated queens (pH-TQs). Eggs from the second section were exposed to 34.5 °C and 70% RH for 15 min, and the queens raised in this section were named the non-heat-treated queens (nH-TQs) (n = 12). After mating, both groups were introduced to queenless hives in order to produce workers. The results show that, during the study period (2021 and 2022), the colonies headed by the pH-TQs reared significantly more brood cells and worker adults (especially during the summer), collected and stored more pollen, had less tendency to rear drone brood, and constructed fewer swarm cells than the colonies headed by the nH-TQs. Preheat hardening can be a promising method for improving honeybee workers’ reproductive potential and adaptability, allowing for better adaptation to environmental changes, thus compensating for the mass fatalities of honeybees globally. Full article