Solidification Characteristics Research Articles

Spatial Structure and Vulnerability of Container Shipping Networks: A Case Study in the Beibu Gulf Sea Area

Ports play an important role in maintaining the effectiveness of maritime logistics. When ports encounter congestion, strikes, or natural disasters, the maritime container transportation network might be significantly affected. The Beibu Gulf sea area is a key channel to supporting China’s participation in international economic cooperation in the western region. It is highly susceptible to the influence of the political and economic instability. This study introduces a dual-component framework to analyze the inherent structure and potential vulnerabilities of the container transportation network in the Beibu Gulf Sea areas. The findings show that the core layer of the network exhibited circular solidification characteristics. The entire network heavily relies on some core ports, such as Haiphong Port, Ho Chi Minh Port, and Qinzhou Port, and it highlights the potential increases in vulnerability. The finding shows that deliberate attacks have a greater impact than random attacks on the normal operations of maritime networks. If ports with high intermediary centrality are attacked, the connectivity and transportation efficiency of the Beibu Gulf maritime network will be significantly affected. However, under such circumstances, redistributing cargo transportation through route adjustments can deal with the transmission of cascading failures and maintain the network’s resilience. Based on the existing knowledge and the data collected in a case study, this research stands out as the first to provide a critical examination of the spatial structure and vulnerability of container shipping networks in the Beibu Gulf sea.

Sub-rapid solidification microstructure characteristics and control mechanisms of twin-roll cast aluminum alloys: A review

Rapid growth in industrial sectors such as automotive and shipbuilding has highlighted the significance of strip casting technology to produce lightweight alloys, particularly aluminum alloys widely used in both industrial production and daily life. Twin-roll casting (TRC), as an economically and environmentally friendly method for slab/strip production and processing, has attracted significant interest from researchers. However, the development of TRC aluminum alloys faces many challenges due to limited understanding of microstructural characteristics and control mechanisms. To further enhance comprehension of TRC aluminum alloys, this article reviews the influencing parameters, control methods, and existing issues related to TRC sub-rapid solidification (SRS) microstructure. It firstly summarizes TRC equipment types and their solidification characteristics, followed by a detailed analysis on key parameters affecting the evolution of TRC microstructure including rolling speed, roll separation force (RSF), and heat transfer coefficient (HTC). Finally, solutions to TRC defects are summarized and evaluated alongside their underlying mechanisms. This article provides a comprehensive review of the characteristics and control mechanisms of TRC microstructure while offering valuable insights for the future production of high-quality TRC aluminum strips.

Laser-directed energy deposition of low-carbon, low-temperature ultra-fine bainitic multi-physical modeling, microstructure and performance studies

An innovative iron-based alloy powder characterized by reduced carbon content and elevated Mn content was developed, leading to the fabrication of iron-based ultrafine bainitic steel with exceptional mechanical properties utilizing laser-directed energy deposition (L-DED). The layers' morphology, microstructure, phase composition, and elemental distribution were analyzed, indicating that the melting depth of the layer was deep and ultra-fine dendrite formed in the top region. A multi-physical powder and melt pool simulation was conducted to analyze the melt flow and pool solidification characteristics, showing that the strong downward flow inside the molten pool caused by the powder impingement increased the melting depth. The cooling rate G × R, where G was the temperature gradient and R was the solidification rate, was higher at the top pool boundary, facilitating the ultra-fine dendrite formation at this location. Following subsequent low-temperature isothermal heat treatment, a refined bainitic microstructure emerged within the deposited layer. The bainitic plates in the 573 K isothermally transformed bainite were interspersed with film-retained austenite (RA). Conversely, the bainitic plates formed at a lower temperature (523 K) exhibited a coalesced morphology stemming from the diminished stability of super-cooled austenite. The bainite plates underwent growth and coalescence, ultimately giving rise to the bainitic microstructure. The 523 K transformed coatings demonstrated superior hardness (509.2 HV), strength (1435 MPa), and elongation (11.5 %) compared to the 573 K transformed coatings (456.5 HV, 1241 MPa, 10.1 %). This research holds significant implications for advancing low-carbon bainitic materials with remarkable comprehensive mechanical properties in additive manufacturing applications.

Sunflower-like eutectic solidification in gas atomized Al0.3CrFeNiTi0.3 medium-entropy alloy powders: A comprehensive microstructural study

The addition of larger atomic size elements, such as Al and Ti, to CrFeNi medium-entropy alloys (MEAs) offers a strategic approach to overcome the strength-ductility trade-off. This study focuses on examining the morphological, solidification, phase, and elemental characteristics of Al0.3CrFeNiTi0.3 feedstock powders produced through gas atomization (GA). The rapid cooling rate inherent in GA results in sunflower-like eutectic solidification. This structure exhibits firstly solidified Cr-rich BCC phases filled with cuboidal-shaped L21-type precipitates, each measuring up to 20 nm. Their peripheral regions display outward and radial growth of L21 and Fe-rich BCC eutectic phases, while FCC phase develops at the remaining sites. Intermediate B2 layers between BCC and L21 phases are considered as kinetic buffers, which enhance the interfacial stability. The size and shapes of powders determine their cooling rates, leading to a transition from comparably large sunflower-like eutectic structures to finer equiaxed grains alongside reduced elemental segregation with decreasing powder size. Nano-hardness measurements demonstrate superior mechanical strength in the peripheral regions due to the higher volume fraction of the L21 phase and its optimal interfacial coherency with the Fe-rich BCC phase. Furthermore, the slightly higher concentrations of Al and Ti in Fe-rich BCC phase (compared to the Cr-rich BCC phase) induce a better lattice distortion effect.

Effect of Boron on the Solidification Characteristics and Constitutive Equation of S31254 Superaustenitic Stainless Steel

Solidification structure and segregation behavior of S31254 superaustenitic stainless steel ingot containing 0 wt% B and 0.005 wt% B are investigated. The results show that serious element segregation and massive eutectics are present in the center of the ingot. By contrast, the addition of boron reduces the secondary dendrite spacing, the degree of elemental segregation, and the σ phase. Further, the effect of boron on the solidification process is studied by using the high‐temperature confocal laser scanning microscope and combined with Thermo‐Calc thermodynamic simulation results. The results show that boron can widen the solidification temperature range and greatly retard the matrix solidification. The role of boron in refining dendrite structure and inhibiting precipitation is further confirmed. The effect of boron on the constitutive equation of S31254 superaustenitic stainless steel has also been researched through isothermal compression testing in the temperature range of 950–1200 °C and strain rate range of 0.01–10 s−1. The activation energy of the boron‐free and boron‐containing S31254 superaustenitic stainless steels based on the constitutive equation are 427.77 and 495.80 kJ mol−1, respectively. Processing maps indicate that the instability domain is significantly reduced and the hot ductility is improved after the addition of B.

Effects of Cooling Rate and Ti Content on the Solidification Characteristics of Al-Ti Alloys

Effects of Cooling Rate and Ti Content on the Solidification Characteristics of Al-Ti Alloys

In-situ intragranular multiple phases reinforced lamellar SiCp/Al-Cu joint induce excellent strength-plasticity without heat treatment

The intragranular second phase is expected to overcome the bottleneck of plasticity in metal matrix composites caused by grain boundary distribution induced stress concentration. In this study, Al3Ti fine second–phase-reinforced SiCp/Al joint was successfully prepared using the laser–friction stir technique. The mechanical properties and deformation mechanism of laminar s SiCp/Al joint was studied in detail. The second-phase particles were encapsulated inside the grains by the rapid solidification characteristic of laser metallurgy. Subsequently, the grains and the second phase underwent further refinement and violent deformation under the friction stir technology. Finally, Al3Ti and α-(Al,Mn) intragranular reinforcement phases were prepared. Tensile property tests results show that the maximum tensile strength of SiCp/Al joint attained is 325 ± 12 MPa and the fracture elongation is 4.49 % ± 0.44 %, which exceeds the reported properties of SiCp/Al joint. This study presents a new strategy for preparing fine second–phase-reinforced metal matrix composites.

Calculation and experimental study of reactivity between CaO–BaO–Al2O3–CaF2–Li2O mould slag and low density and high strength steel

In the continuous casting of low-density and high-strength steel, minimising or eliminating steel–slag reactions is imperative to ensure stable slag properties and a smooth casting process. This study conducted steel–slag contact experiments at 1400 °C, based on thermodynamic calculations predicting the reaction trends of the proposed CaO–BaO–Al2O3–CaF2–Li2O mould slag with low-density and high-strength steel containing 8 wt-% Al. The changes in compositions, rheological, and solidification characteristics of slags pre- and post-reaction are analysed. The findings reveal that only Li2O reacts with Al in the steel, forming LiAlO2 rather than Al2O3. Reactivity is affected by component activity and the partial pressure of Li vapour at the reaction interface, established to vary between 0.154 and 0.253 atm. Within the current range of slag composition, increasing Al2O3 and reducing Li2O content in the slag inhibits the slag–metal reaction. Specifically, Li2O remains unreactive with Al when 2.5 wt-% < Li2O < 5 wt-% and Al2O3 > 27 wt-%. Conversely, the reaction occurs when Li2O > 4.5 wt-% and Al2O3 < 18 wt-%. In conclusion, low- and non-reactive mould slags suitable for casting low-density and high-strength steel are proposed, considering both reactivity and stable slag properties.

Research on flow, heat transfer, and solidification characteristics of flow distribution process in the twin-roll casting

Twin-roll casting (TRC) has seen a significant interest in recent years due to its short process, low energy consumption, and low emission. The research included both numerical simulation and experimental validation to examine the flow and temperature field distribution of the TRC process. The “U-shaped” buffer groove is identified as beneficial for maintaining a stable liquid level distribution in the molten pool through comparison with various flow distributor structures. The solidified billet shell dispersion around the casting roller in the molten pool is observed to undergo three distinct stages: stable growth, thickness fluctuation, and rapid growth. The inclusion of two circular side outlets, each with a diameter ranging from 8 to 10 mm, proves advantageous in maintaining a stable distribution of the liquid level within the molten pool. The edge outlet size ranges from 7 to 9 mm, and ensuring a U-shaped buffer groove width/flow distribution of 1.25–1.58 aids in enhancing casting stability.

Predicting rapid growth behavior in solidified eutectic ceramic composites using infrared thermal imaging and thermal field simulation during laser directed energy deposition

Cylindrical Al2O3/GdAlO3 binary in situ oxide eutectic ceramic composite, with a glossy surface and high relative density, has been fabricated using the laser directed energy deposition method (LDED) with optimized process parameters. In a novel and innovative approach, infrared thermal imaging and the finite element method (FEM) have been combined for the first time to capture the temperature field distribution across different regions of the molten pool during the LDED processing of the binary oxide eutectic ceramic composite, thereby synergistically obtaining the solidification characteristics. With an increase in the scanning rate, the temperature gradient within the molten pool decreases from 3.38 × 105 K/m to 1.62 × 105 K/m, while it shows minimal variation with fluctuations of the laser power. Under the conditions of high temperature gradients and rapid non-equilibrium solidification characteristic of LDED, the Al2O3/GdAlO3 (GAP) binary eutectic ceramic composites, which exhibit typical high melting entropy and faceted/non-faceted growth modes, exhibit complex and variable microstructure morphology. A combination of regular/irregular models, including JH (Jackson-Hunt), MK (Magnin-Kurz), GK (Guzik-Kopyciński) and TMK (Trivedi-Magnin-Kurz), is employed to investigate and predict the growth and transformation of microstructures. The JH and TMK models fairly predict the rod-like regular eutectic microstructure inside the colony and lamellar regular eutectic within adjacent layers, respectively. The “Chinese-script” irregular microstructure at the interface between the colony and the layers is consistent with the MK and GK models. The as-deposited eutectic ceramic composite presents ultra-fine microstructures, clear and strongly bonded phase interfaces with low strain energy, contributing to its microstructure stability after high temperature heat treatment at 1773 K for 200 h, and achieving a minimum microstructure coarsening rate of 0.0005 μm/h.

Solidification and Release Characteristics of Heavy Metals in Gypsum from Coal-Fired Power Plants

Heavy metals in flue gas desulfurization (FGD) gypsum from coal-fired power plants are at risk of releaching during the processes of stockpiling and resource utilization. In this study, the effects of organosulfur chelators dithiocarbamate (DTC) and trisodium trithiocyanate-15 (TMT-15) on the solidification characteristics of heavy metals in desulphurized gypsum under different mass fractions, pH values, water contents and reaction times were investigated. The chemical composition and morphology were analyzed by inductively coupled plasma atomic emission spectrometer (ICP-AES) and scanning electron microscope (SEM). The experiments showed that both DTC and TMT-15 were effective at stabilizing the heavy metals in the FGD gypsum, with more than a 50% curing effect for all the heavy metals except Pb. DTC showed a better stabilization for Pb, Hg, Cu, Zn, and Cr, and TMT-15 showed a better curing effect for Cd. The solidified gypsum had good heavy metal stability in low-water-content environments. Increasing the mass fraction, reaction time, and pH decreased the heavy metal leaching, and the mass fraction had the greatest effect on the total heavy metal leaching concentration, followed by the reaction time and pH value.

Characteristic analysis of high-speed steel powder prepared by gas atomisation

The performance of high-speed steel (HSS) powder is a prerequisite for the preparation of high-performance powder metallurgy HSS. The physical properties, microstructure, and solidification characteristics of HSS powder prepared by nitrogen gas atomisation were systematically studied and analysed in detail. For the atomised TPM558 HSS powder, the morphology is spherical and the particle size distribution is wide. The smooth small particles of satellite powder attach to the surface of large particles. Shrinkage pits caused by solidification shrinkage exist on the surface of large particles. The average cooling rate is between 104 and 106 K·s−1, with the increase of cooling rate, the powder surface tends to be smooth, and the grain structure is transformed in the order of cellular to dendritic to radial. The single powder particle surface shows fine-equiaxed grains, while the internal presents columnar grains. The crystalline phases of the powder are austenite, ferrite, martensite, and carbide, and the carbide includes MC carbide with face-centred structure and M2C carbide with hexagonal structure. The average nano-hardness of the powder is 9.93 GPa, resulting in poor formability, and it can be pressed and formed only after adding binder.

Melting and Solidification Characteristics of PCM in Oscillated Bundled-Tube Thermal Energy Storage System

Phase change material (PCM) based thermal energy storage (TES) is an important solution to the waste of heat and intermittency of new energy sources. However, the thermal conductivity of most PCMs is low, which severely affects the thermal energy storage performance. Oscillation of the tube bundles in a TES unit can intensify the convection of liquid PCM and, therefore, enhance heat transfer. However, the energy storage performance of bundled-tube TES systems in response to oscillation at different amplitudes and frequencies has not been well understood yet, and the optimum time to apply the oscillation during phase transition remains unexplored. To address this issue, this present study was carried out. First, the melting behaviour of PCM with oscillation starting at different times was investigated. Then, the influences of oscillation frequency and amplitude on the melting performance were explored. Finally, the solidification behaviour of PCM with oscillation starting at different times was examined. Results show that the oscillation can accelerate the phase transition process by enhancing convective heat transfer. Compared to the case without oscillation, the complete melting and solidification times are reduced by 8.2 and 6.7% for the case with oscillation starting at 200 s, respectively. The effect of oscillation frequency on the melting enhancement is negligible, while the oscillation amplitude has an important effect on the melting enhancement.

Effect of Co on Solidification Characteristics and Microstructural Transformation of Nonequilibrium Solidified Cu-Ni Alloys

Effect of Co on Solidification Characteristics and Microstructural Transformation of Nonequilibrium Solidified Cu-Ni Alloys

Effect of grooving on the inner surface of the spherical capsule filled with DI water for rapid heat transfer in cool thermal energy storage applications.

The demand for cooling applications increases severalfold; the integration of the CTES system will mitigate the demand and pollution caused by the building sectors. The objective of this study is to investigate the effect of grooving on the inner surface of the spherical capsule on the solidification characteristics of deionized (DI) water, which finds widespread use in the bed of cool thermal energy storage applications. Eight hemispheres made of mild steel of 100-mm diameter and 1-mm thickness are used to make four spherical capsules by the welding process for the study. Among the four capsules, one with a plain surface and the remaining with a groove depth of 0.3mm, 0.5mm, and 0.7mm are made. The grooving in the hemispherical capsule is obtained by the turning operation. The experiments are conducted at various bath temperatures of - 6°C, - 9°C, and - 12°C. The experimental result reveals that the surface modification leads to a significant reduction in solidification time, and in particular, the maximum percentage reduction in solidification time is achieved at - 6°C. The provision of grooves makes the evaporator operate at - 6°C instead of - 12°C till the solidification of 75% mass and the predicted energy saving is 18 to 24%. As the enhancement of heat transfer rate techniques is carbon-free, the recycling of the PCM will have zero impact on environmental pollution.

Numerical Simulation and Machine Learning Prediction of the Direct Chill Casting Process of Large-Scale Aluminum Ingots.

The large-scale ingot of the 7xxx-series aluminum alloys fabricated by direct chill (DC) casting often suffers from foundry defects such as cracks and cold shut due to the formidable challenges in the precise controlling of casting parameters. In this manuscript, by using the integrated computational method combining numerical simulations with machine learning, we systematically estimated the evolution of multi-physical fields and grain structures during the solidification processes. The numerical simulation results quantified the influences of key casting parameters including pouring temperature, casting speed, primary cooling intensity, and secondary cooling water flow rate on the shape of the mushy zone, heat transport, residual stress, and grain structure of DC casting ingots. Then, based on the data of numerical simulations, we established a novel model for the relationship between casting parameters and solidification characteristics through machine learning. By comparing it with experimental measurements, the model showed reasonable accuracy in predicting the sump profile, microstructure evolution, and solidification kinetics under the complicated influences of casting parameters. The integrated computational method and predicting model could be used to efficiently and accurately determine the DC casting parameters to decrease the casting defects.

Influence of various surfactants on the stability and solidification characteristics of DI water-based CuO NFPCM for cool thermal energy storage system

The current study goals to investigate the stability and solidification characteristics of deionized water (DI water) based copper oxide (CuO) nanofluid phase change materials (NFPCMs) with a nucleating agent, different types of surfactants (SBDS, CTAB, and GA) and different weight concentration of surfactant for cool thermal energy storage systems (CTES). The stability of NFPCMs was assessed through average particle size distribution, zeta potential, and UV–vis absorbance. Among all NFPCMs, 0.1 wt% SDBS - CuO NFPCM showed prolonged stability with −42.7 mV and 212.6 nm of zeta potential and average particle size value. The heat transfer properties of NFPCMs were studied with differential scanning calorimetry (DSC), Thermogravimetric analysis (TGA) and thermal conductivity measurements. The introduction of 0.05 wt% SDBS to NFPCM resulted in a notable 17.84 % and 7.64 % increase in thermal conductivity in solid and liquid states, with a slight decrease in latent heat by 5.2 % and 6.01 % during melting and crystallization as compared to DI water. The solidification experiments of NFPCMs were investigated in a spherical encapsulation at a surrounding bath temperature of −8 °C and − 10 °C. Comparing various surfactants in NFPCMs, the SDBS–CuO NFPCM was the most efficient in reducing the solidification time by 26.3 % and 28.4 % at −8 °C and − 10 °C respectively, compared to the nucleating agent PCM (NAPCM). Further, the different concentrations of SDBS in NFPCM demonstrated that 0.05 wt% SDBS–CuO NFPCM displayed the greatest reduction in solidification time, achieving 29.4 % and 27.7 % at −10 °C and − 8 °C, respectively, compared to the NAPCM.

Automatic Detection of Cast Billet Dendrite Based on Improved Hough Transform

Primary dendrite information is one of the most important metrics to measure the quality of continuous cast slabs. The contrast of low magnification images is very low under the influence of illumination and sampling devices, so the traditional dendrite detection method has the problem of missed detections. We propose an automatic dendrite detection method based on an improved Hough transform, which effectively improves the accuracy and efficiency of primary dendrite detection. By using the local grayscale features of the image, a genetic algorithm-based local contrast enhancement algorithm is proposed. Compared with the traditional contrast enhancement algorithm, it can retain all the information of the dendrites. Combined with the image binarization method based on Hessian matrix, we can obtain more detailed information about the dendrites. According to the continuity and solidification characteristics of dendrites, the Hough transform is improved to extract dendrite information, which effectively reduces the computational cost of the Hough transform. The experimental results show that the method of this paper has versatility, and the error is four pixels compared with the manual method, which can provide a reliable basis for the subsequent judgement of the quality of cast billets.

The effects and solidification characteristics of municipal solid waste incineration fly ash-slag-tailing based backfill blocks in underground mine condition

Currently, there is a limited understanding of the material performance effects and hydration mechanisms of solidified waste-based binder filling materials containing municipal solid waste incineration fly ash in the actual underground filling environment. This study utilized the Circulating Fluidized Bed (CFB) and Grate Furnace (GF) techniques to produce quadri-component uncalcined binder fill materials from municipal solid waste incineration fly ash (MSWI FA), blast furnace slag (BFS), flue gas desulfurization (FGD) gypsum, and tailings. The solidified test blocks were then cured in-situ in a void space of a certain iron underground mine in Hebei with conditions (temperature: 25-30℃, humidity: 18-19%, mine water influx: annual average of 150m3/h). The research results indicate that the mechanical performance and heavy metal solidification outcomes of these blocks surpassed those samples cured under laboratory conditions (temperature: (20±1)℃, humidity: not less than 90%), demonstrating the feasibility of using MSWI FA for underground binding and backfilling in mines. Building upon preliminary research, a binder mix proportion was established: 20wt.% MSWI FA, 70wt.% BFS, and 10wt.% FGD gypsum. Test blocks were fabricated using lead-zinc tailings sand and iron mine tailings as aggregates. All blocks met the 28-day strength requirements for typical mine backfills ranging from 1 to 6.5MPa, with the strength of the XB-M group reaching 24MPa (when cured underground). The leaching concentrations of heavy metals were all below the limits set for class III groundwater standards, with Pb, Zn, Cr, and As achieving a solidification rate of over 98% at 28 days. Microscopic hydration mechanisms indicate that the primary hydration products in the solidified body were ettringite, Friedel's salt, and C-S-H gel. The high content of reactive Al2O3 in the CFB fly ash enables the [AlO4]5- to substitute [SiO4]4-, leading to the formation of a long-chain, high polymerization C-A-S-H phase. Additionally, the abundant Cl- in GF fly ash readily reacted with [Al(OH)6]3−, forming Friedel's salt. The hydration products in the blocks cured under mine conditions significantly increased in their degree of polymerization. This provides a practical application approach for the future treatment and reuse of MSWI FA. Environmental implicationMSWI FA is classified as hazardous waste (HW18) due to its content of harmful components such as chlorides, dioxins, and soluble heavy metals, which pose potential environmental pollution risks. This study, for the first time, solidified test specimens were sent to an underground mining void in a certain iron mine in Hebei, China, for on-site curing (temperature range: 25-30°C, humidity: 18-19%, annual average mine water inflow rate: 150m3/h). The mechanical properties and the solidification performance of heavy metals in the test specimens were superior to those under laboratory curing conditions (temperature: (20±1)°C, humidity not less than 90%).

Role of Cr in Mn-rich precipitates for Al–Mn–Cr–Zr-based alloys tailored for additive manufacturing

Novel alloy concepts enabled via additive manufacturing processes have opened up the possibility of tailoring properties beyond the scope of conventional casting and powder metallurgy processes. The authors have previously presented a novel Al–Mn–Cr–Zr-based alloy system containing three times the equilibrium amounts of Mn and Zr. The alloys were produced via a powder bed fusion-laser beam (PBF-LB) process taking advantage of rapid cooling and solidification characteristics of the process. This supersaturation can then be leveraged to provide high precipitation hardening via direct ageing heat treatments. The hardening is enabled with Zr-rich and Mn-rich precipitates. Literature study confirms that Mn-rich precipitates have a notable solubility of Cr, for example, the Al12Mn precipitate. This study aims to clarify the effect of Cr solubility in the thermodynamics and kinetics simulation and compare the precipitation simulations with samples subject to >1000 h isothermal heat treatment, thus creating an equilibrium-like state. The results show that Cr addition to the precipitates stabilizes the Al12Mn precipitate while slowing the precipitation kinetics thus producing a favourable hardening response. Such observations could be insightful while designing such alloys and optimising heat treatments of the current or even a future alloy system.