Search Results (22)

The large-scale, open-air storage of coal gangue often leads to oxidation and decomposition due to natural weathering, resulting in decreased strength and instability, which limits its wider application in concrete pavement. To address these issues, this paper proposed a composite consolidation treatment for weathered coal gangue (WCG), assessing its effectiveness and enhancement mechanisms through aggregate performance tests, mixture performance tests, and microscopic visualization analyses. Results indicated that the initial and post-20 dry–wet cycle crushing values of WCG were 23.96% and 47.94%, respectively, failing to meet required standards. However, applying a composite consolidation treatment using a lithium curing agent and cement paste significantly improved WCG’s robustness and stability. After 4 days of treatment, the crushing value, impact value, and Vickers hardness of WCG had reached 18.3%, 6.58%, and 113.52 kgf/mm², respectively, fully meeting the standards for aggregate filling in mini concrete pavements. Furthermore, tests demonstrated that the lithium curing agent induced the formation of hydrated calcium silicate and calcium aluminate on both the surface and interior of the WCG, enhancing its structural stability. Approximately 5–12 wt.% of the curing agent penetrates and encapsulates the WCG, strongly bonding and reinforcing its internal weak surfaces. These findings offer potential solutions and technical insights for the large-scale management of weathered coal gangue. Full article

Reducing hot cracking is essential for ensuring seamless production of nickel superalloys, which are extensively used in welded structures for aircraft engines. The prevalence of hot cracking in precipitation-strengthened alloy 718 is primarily governed by two factors: firstly, the chemical composition and the coarse microstructure formed during solidification, and secondly, the activation of hot cracking mechanisms, which is particularly critical in mushroom-shaped welding morphologies. In this study, different nickel-based superalloys welded using laser beam welding (LBW), more specifically bead on plate welding (BoP), specimens are compared. The cracking susceptibility of both wrought and two investment casting 718 alloys with tailored chemical compositions is examined through the application of both continuous and pulsed LBW. Additionally, various pre-weld treatments, including with and without Pre-HIP (hot isostatic pressing), are analyzed. The influences of chemical composition, LBW parameters and pre- and post-welding treatments on both internal and external cracks determined by conventional and advanced non-destructive tests are studied. A clear reduction of hot cracking susceptibility and overall welding quality improvement was observed in a tailored 718 alloy with relatively high Ni (55.6% wt) and Co (1.11% wt) contents. Full article

Thin twin-roll cast strips from a model Al-Cu-Mg-Li-Zr alloy with a small addition of Sc were prepared. A combination of a fast solidification rate and a favorable effect of Sc microalloying refines the grain size and the size of primary phase particles and reduces eutectic cell dimensions to 10–15 $\mathsf{\mu }$m. Long-term homogenization annealings used in conventionally cast materials lasting several tens of hours followed by a necessary dimension reduction through rolling/extruding could be substituted by energy and material-saving procedure. It consists of two-step short annealings at 300 °C/30 min and 450 °C/30 min, followed by the refinement and hardening of the structure using constrained groove pressing. A dense dispersion of 10–20 nm spherical ${\mathrm{Al}}_3(\mathrm{Sc},\mathrm{Zr})$ precipitates intensively forms during this treatment and effectively stabilizes the structure and inhibits the grain growth during subsequent solution treatment at 530 °C/30 min. Small (3%) pre-straining after quenching assures more uniform precipitation of strengthening ${\mathrm{Al}}_2\mathrm{Cu}$ (${\theta }^{\prime }$), ${\mathrm{Al}}_2\mathrm{CuMg}$ ($S\prime$), and Al₂CuLi ($T_1$) particles during subsequent age-hardening annealing at 180 °C/14 h. The material does not contain a directional and anisotropic structure unavoidable in rolled or extruded sheets. The proposed procedure thus represents a model near net shape processing strategy for manufacturing lightweight high-strength sheets for cryogenic applications in aeronautics. Full article

Depending on operating conditions, metals and alloys are exposed to various factors: wear, friction, corrosion, and others. Plasma surface alloying of machine and tool parts is now an effective surface treatment process of commercial and strategic importance. The plasma surface alloying process involves adding the required elements (carbon, chromium, titanium, silicon, nickel, etc.) to the surface layer of the metal during the melting process. A thin layer of the compound is pre-applied to the substrate, then melted and intensively mixed under the influence of a plasma arc, and during the solidification process, a new surface layer with optimal mechanical properties is formed. Copper-based alloys—Cu-X, where X is Fe, Cr, V, Nb, Mo, Ta, and W—belong to an immiscible binary system with high mechanical strength, electrical conductivity, and magnetism (for Fe-Cu) and also high thermal characteristics. At the same time, copper-based alloys have low hardness. In this article, wear tests were carried out on coatings obtained by plasma alloying of CuSn10 and CrxCy under various friction conditions. The following were chosen as a modifying element: chromium carbide to increase hardness and iron to increase surface tension. It is noted that an increase in the chromium carbide content to 20% leads to the formation of a martensitic structure. As a result, the microhardness of the layer increased to 700 HV. The addition of CuSn10 + 20% CrxCy and an additional 5% iron to the composition of the coating improves the formation of the surface layer. Friction tests on fixed abrasive particles were carried out at various loads of 5, 10, and 50 N. According to the test results, the alloy layer of the Fe-Cr-C-Cu-Sn system has the greatest wear resistance under abrasive conditions and dry sliding friction conditions. Full article

Municipal solid waste incineration fly ash is classified as hazardous waste because it contains dioxins and a variety of heavy metals. It is not allowed to be directly landfilled without curing pretreatment, but the increasing production of fly ash and scarce land resources has triggered consideration of the rational disposal of fly ash. In this study, solidification treatment and resource utilization were combined, and the detoxified fly ash was used as cement admixture. The effects of thermal treatment in different atmospheres on the physical and chemical properties of fly ash and the effects of fly ash as admixture on cement properties were investigated. The results indicated that the mass of fly ash increased due to the capture of CO₂ after thermal treatment in CO₂ atmosphere. When the temperature was 500 °C, the weight gain reached the maximum. After thermal treatment (500 °C + 1 h) in air, CO₂, and N₂ atmospheres, the toxic equivalent quantities of dioxins in fly ash decreased to 17.12 ng TEQ/kg, 0.25 ng TEQ/kg, and 0.14 ng TEQ/kg, and the degradation rates were 69.95%, 99.56%, and 99.75%, respectively. The direct use of fly ash as admixture would increase the water consumption of standard consistency of cement and reduce the fluidity and 28 d strength of mortar. Thermal treatment in three atmospheres could inhibit the negative effect of fly ash, and the inhibition effect of thermal treatment in CO₂ atmosphere was the best. The fly ash after thermal treatment in CO₂ atmosphere had the possibility of being used as admixture for resource utilization. Because the dioxins in the fly ash were effectively degraded, the prepared cement did not have the risk of heavy metal leaching, and the performance of the cement also met the requirements. Full article

Increasing the strength of Al-based alloys is an important issue of physical metallurgy and industrial processing. Severe plastic deformation and related extension of solid solubility during mechanical alloying provide an opportunity for significant strengthening due to grain refinement, solid solution, and precipitation strengthening mechanisms. During mechanical alloying, an anomalous increase in the solid-state solubility of alloying elements occurs. The present study focuses on the investigation of the pre-milling treatment to the microstructure, phase composition, and solubility in Al-7.7 Mn-3.5 Cu (wt%) alloy processed by a high-energy ball milling of Al-14.3 Mn-6.5 Cu (wt%) master alloy diluted with Al powder. During milling, the mean granular size decreased to ~5 µm, and a strong grain refinement occurred. According to our TEM and XRD data, ball milling provided a mean grain size of 13–14 nm and a microhardness of 490–540 HV. The lattice parameter of the Al-based solid solution decreased with an increase in the milling time to 7.5–10 h, which suggested the dissolution of the alloying elements, and the lattice parameter increased at a higher milling time of 12.5–40 h, which suggested the decomposition of the solid solution. The XRD data revealed the dissolution of the Al₆Mn and Al₂₀Cu₂Mn₃ solidification-originated phases with a further precipitation of the Al₆Mn dispersoids. Pre-milling of the master alloy entailed a significant decrease in the minimal lattice parameter value from 0.4029 nm to 0.4023 nm due to an increase in the Mn solute content from 6.2 wt% (3.3 at%) to 7.5 wt % (4.0 at%) in the studied alloy during high-energy ball milling. Full article

Many sandy soil foundations need to be solidified during traffic construction in Guangxi, China. Because it has a similar chemical composition as cement, municipal solid waste incineration fly ash (MSWIFA) can strengthen sandy soil. However, the chloride ions and heavy metals in MSWIFA may have a negative influence on the solidification of sandy soil. Thus, FA resource use faces great challenges. This study evaluates the feasibility of using MSWIFA to solidify sandy soil. The acetic acid buffer solution method was used in the leaching test to simulate the weak acid groundwater environment in the Guangxi karst landform. The effects of the treatment methods (washing with ferrous sulphate solution, pre-treatment of organics via chelation, and adding sugarcane ash) on the strength and environmental characteristics of fly ash cement-stabilised soil (FACS) are discussed in detail. The results indicate that the FACS unconfined compressive strength (UCS) decreased by 24.82–46.64% when 5% cement was replaced with FA. Sugarcane ash effectively improved the strength of FACS by more than 10%. The leaching concentrations of Zn and Cu in the FACS meet the concentration limit set by GB 16889-2008. The leaching concentrations of Cr and Pb after washing with 6% ferrous sulphate solution were reduced by more than 30%. Meanwhile, the FACS strength developed faster. Organic chelating agents solidified most heavy metals. Full article

The nickel-based superalloy, Haynes 230 (H230), is widely used in high-temperature applications, e.g., heat exchangers, because of its excellent high-temperature mechanical properties and corrosion resistance. As of today, H230 is not yet in common use for 3D printing, i.e., metal additive manufacturing (AM), primarily because of its hot cracking tendency under fast solidification. The ability to additively fabricate components in H230 attracts many applications that require the additional advantages leveraged by adopting AM, e.g., higher design complexity and faster prototyping. In this study, we fabricated nearly fully dense H230 in a laser powder bed fusion (L-PBF) process through parameter optimization. The efforts revealed the optimal process space which could guide future fabrication of H230 in various metal powder bed fusion processes. The metallurgical analysis identified the cracking problem, which was resolved by increasing the pre-heat temperature from 80 °C to 200 °C. A finite element simulation suggested that the pre-heat temperature has limited impacts on the maximum stress experienced by each location during solidification. Additionally, the crack morphology and the microstructural features imply that solidification and liquation cracking are the more probable mechanisms. Both the room temperature tensile test and the creep tests under two conditions, (a) 760 °C and 100 MPa and (b) 816 °C and 121 MPa, confirmed that the AM H230 has properties comparable to its wrought counterpart. The fractography showed that the heat treatment (anneal at 1200 °C for 2 h, followed by water quench) balances the strength and the ductility, while the printing defects did not appreciably accelerate part failure. Full article

This study aims to investigate the possibilities of municipal waste incineration bottom ash (MSWIBA) utilization in the construction sector. MSWIBA development fits into the European Green Deal, Sustainable Development Goals (SDGs), and the Circular Economy (CE). This manuscript describes current MSWIBA treatment such as solidification, ceramization, vitrification, chemical activation (NaOH, CaOH₂, NA₂SiO₃ + NaOH, Na₂CO₃ + NaOH, NH₄OH), acid treatment with diluted solutions (HCl, H₂SO₄), chemical stabilization (FeSO₄, PO₄³⁻), chelation, etc. For the purpose of comparative research, MSWIBA before valorization, after valorization, and after NaOH pre-treatment was investigated. In terms of their physico-chemical properties, the tested samples were examined. Three kinds of MSWIBA were used as a substitute for 30% of cement in mortars. The mortars were tested for 28-day strength. Leachability tests were performed in acid, aggressive, alkali, and neutral water environments. Life Cycle Assessment (LCA) analysis was carried out, which presented the environmental benefits of MSWIBA management in construction. Full article

Municipal solid waste incineration (MSWI) fly ash has been classified as hazardous waste in China because of the leachable toxic heavy metals and high concentrations of chlorides and polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs). Currently, the main treatment method is still landfilling after chemical treatment or cement solidification, and an effective approach to realize fly ash utilization is still lacking. In the present work, the fly ash was firstly water-washed to remove the soluble chlorine salts, which can improve the performance of the produced cement mortar in later work. Mechanochemical pre-treatment was adopted to destroy the PCDD/Fs and improve the heavy metals’ stabilization. The results show that 75% of PCDD/Fs can be degraded and that most of the heavy metals are stabilized. After the mechanochemical pre-treatment, the average particle size of the fly ash decreases to 2–5 μm, which is beneficial for promoting the activation energy and accelerating the hydration process in cement mortar production. The compressive and flexural strengths of the fly ash cement mortar improve to 6.2 MPa and 32.4 MPa, respectively, when 35% of the OPC is replaced by treated fly ash. The similarity in the 3-day and 28-day strength with or without the addition of the treated ash shows the light influence of the fly ash addition. Thus, the mechanochemical process can stabilize the heavy metals and activate the fly ash, allowing it to partly substitute ordinary Portland cement in building materials, such as cement raw materials and concrete. Full article

Manganese-bearing intermetallic compounds (IMCs) are important for ensuring adequate corrosion performance of magnesium-aluminium alloys and can be deleterious to mechanical performance if they are large and/or form clusters. Here, we explore the formation of Al-Mn IMCs in Mg-9Al-0.7Zn-0.2Mn produced by two industrial casting processes, high-pressure die casting (HPDC) and direct chill (DC) casting. As Al₈Mn₅ starts forming above the α-Mg liquidus temperature in this alloy, we consider its formation during melt handling as well as during casting and heat treatment. In HPDC, we focus on sludge formation in the holding pot, partial solidification of IMCs in the shot chamber, and Al-Mn IMC solidification in the die cavity. In DC casting, we focus on interactions between Al-Mn IMCs and oxide films in the launder system, Al-Mn IMC solidification in the billet, and the partial transformation of Al₈Mn₅ into Al₁₁Mn₄ during solution heat treatment. The results show that minimising pre-solidification in the shot sleeve of HPDC and controlling pouring and filtration in DC casting are important for ensuring small Al-Mn intermetallic particles in these casting processes. Full article

Considering transient processes where liquid/solid phase change occurs, this paper focuses on the associated modeling and numerical treatment in the frame of “Computational Fluid Dynamics” simulations. While being of importance in many industrial applications involving solidification and melting of mixed materials, including power and manufacturing engineering, the first application of this work pertains to the analysis of severe accidents in a nuclear reactor. Indeed, in this context, the molten core materials (a.k.a. corium) can form a high-temperature multiphase liquid pool at the boundary of which fusion and solidification phenomena are of prime importance. In this context, even if materials at play are treated as pure components, it is mandatory to distinguish two different phase change temperatures with a solid fusion temperature and a liquid solidification temperature. Accordingly, in the frame of a sharp interface representation, the paper introduces non-classical heterogeneous conditions at the liquid/solid boundary in such a way that both moving interface (through Stefan conditions associated with fusion or solidification) and static interface (imposing heat flux continuity) are supported at the same time on different spatial locations along this boundary. Within a monolithic resolution of Navier–Stokes and heat conduction equations, this interface is explicitly tracked with combined Front-Tracking and VOF methods. In order to ensure zero velocity in the solid phase, an Immersed Boundary Method and a direct forcing penalization are also introduced. The main relevant features of this combination of numerical methods are discussed along with their implementation in the TrioCFD code taking advantage of the pre-existing code capabilities. Numerical simulations including both verification tests and a case of interest for our industrial application are reported and demonstrate the applicability of the proposed triptych model+methods+code to treat such problems. The numerical tools and the simulation code developed in this work could be used not only in the several accident context but also to simulate melting, solidification and fusion processes occurring in aerodynamics, hypersonic reentry vehicles and laser applications to cite but a few. Full article

The content of active components in traditional Chinese medicine is relatively small, and it is difficult to detect some trace components with modern analytical instruments, so good pretreatment and extraction are very important in the experiment. Graphene was introduced by a dispersive liquid–liquid microextraction method based on solidification of floating organic drop (DLLME-SFO) with graphene/1-dodecyl alcohol used as the extractant, and this method, combined with quantitative proton nuclear magnetic resonance spectroscopy (¹H-qNMR), was used to simultaneously qualitative and quantitative osthole, columbianadin and isoimperatorin in Angelicae Pubescentis Radix. In this experiment, a magnetic stirrer was used for extraction, all NMR spectra were recorded on a Bruker Advance III 600 MHz spectrometer with dimethyl sulfoxide-d₆ (DMSO-d₆) as deuterated solvent and pyrazine as the internal standard. The influencing factors and NMR parameters in the extraction process were investigated and optimized. In addition, the methodology of the established method was also examined. The quantitative signals of osthole, columbianadin and isoimperatorin were at a chemical shift of δ6.25–δ6.26 ppm, δ6.83–δ6.85 ppm, and δ6.31–δ6.32 ppm. The linear ranges of osthole, columbianadin and isoimperatorin were all 0.0455–2.2727 mg/mL, and R² were 0.9994, 0.9994 and 0.9995, respectively. The limits of detection of osthole, columbianadin and isoimperatorin were 0.0660, 0.0720, 0.0620 mg, and the limits of quantification of osthole, columbianadin and isoimperatorin were 0.2201, 0.2401, 0.2066 mg/mL. The solution had good stability and repeatability within 24 h. The recoveries of osthole, columbianadin and isoimperatorin were 102.26%, 99.89%, 103.28%, respectively. The established method is simple and easy to operate, which greatly reduces the cumbersome pretreatment of samples and has high extraction efficiency. Full article

Titanium additions are often used for boron factor and primary austenite grain size control in boron high- and ultra-high-strength alloys. Due to the risk of formation of coarse TiN during solidification the addition of titanium is limited in respect to nitrogen. The risk of coarse nitrides working as non-metallic inclusions formed in the last solidification front can degrade fatigue properties and weldability of the final product. In the presented study three microalloying systems with minor additions were tested, two without any titanium addition, to evaluate grain size evolution and mechanical properties with pre-defined as-cast, hot forging, hot rolling, and off-line heat-treatment strategy to meet demands for S1100QL steel. Microstructure evolution from hot-forged to final martensitic microstructure was observed, continuous cooling transformation diagrams of non-deformed austenite were constructed for off-line heat treatment, and the mechanical properties of Nb and V–Nb were compared to Ti–Nb microalloying system with a limited titanium addition. Using the parameters in the laboratory environment all three micro-alloying systems can provide needed mechanical properties, especially the Ti–Nb system can be successfully replaced with V–Nb having the highest response in tensile properties and still obtaining satisfying toughness of 27 J at –40 °C using Charpy V-notch samples. Full article

In this work, weldability and hot cracking susceptibility of five alloy 718 investment castings in laser beam welding (LBW) were investigated. Influence of chemical composition, with varying Si contents from 0.05 to 0.17 wt %, solidification rate, and pre-weld heat treatment were studied by carrying out three different weldability tests, i.e., hot ductility, Varestraint, and bead-on-plate tests, after hot isostatic pressing (HIP) and solution annealing treatment. Onset of hot ductility drop was directly related to the presence of residual Laves phase, whereas the hot ductility recovery behaviour was connected to the Si content and γ grain size. LBW Varestraint tests gave rise to enhanced fusion zone (FZ) cracking with much more reduced heat-affected zone (HAZ) cracking that was mostly independent of Si content and residual Laves phase. Microstructural characterisation of bead-on-plate welding samples showed that HAZ cracking susceptibility was closely related to welding morphology. Multiple HAZ cracks were detected in nail or mushroom welding shapes, typical in keyhole mode LBW, irrespective of the chemical composition and thermal story of castings. In all LBW welds, Laves phase with a composition similar to the eutectic of the pseudo-binary equilibrium diagram of alloy 718 was formed in the FZ. The composition of this regenerated Laves phase matched with the continuous Laves phase film observed along HAZ cracks. This was strong evidence of backfilling mechanism, which is described as wetting and infiltration of terminal liquid along γ grain boundaries of parent material. The current results suggest that this cracking mechanism was activated in three-point intersections resulting from perpendicular crossing of columnar grain boundaries with fusion line and was enhanced by nail or mushroom weld shapes and narrow and columnar γ grain characteristics of castings. Neither Varestraint nor hot ductility weldability tests can reproduce this particular cracking mechanism. Full article