Metals, Volume 13, Issue 4 (April 2023) – 186 articles

Quenching and partitioning (QP) steel has attracted much focus due to the effect of phase transformation induced plasticity (TRIP). However, the TRIP behavior makes it difficult to accurately predict the strain and stress distribution as well as the phase transformation behavior of QP steel. Scanning electron microscope (SEM) images of the QP980 microstructure were produced in this study, characterized by a combination of lath martensite, polygonal ferrite and retained austenite. The volume fraction evolution of retained austenite with equivalent plastic strain (EPS) of uniaxial tension was obtained by electron-backscatter diffraction. The phase transformation kinetics equations of QP980 were deduced based on the phase transformation model proposed by Olson and Cohen (simplified as O-C theory), considering the effects of strain rate, deformation temperature and stress state. A constitutive model on the dependence of the phase transformation was proposed to reveal the relation between metallographic characteristics and mechanical performance of QP980 steel during deformation. The User subroutine VUMAT in ABAQUS/Explicit was implemented to describe the volume fraction of retained austenite (VFRA) under different stress states. The established phase transformation and constitutive model were applied to three kinds of complex path loading tests. The variation in the retained austenite under complex strain paths was obtained and compared with the experimental results. Full article

A lightweight neural network fault diagnosis method based on Gramian angular field (GAF) feature map construction and efficient channel attention (ECA) optimization is presented herein to address the problem of the complex structure of traditional neural networks in bearing fault diagnosis. Firstly, a GAF is used to encode vibration signals into a temporal image. Secondly, the double-layer separation residual convolution neural network (DRCNN) is used to learn advanced features of the sample. The multi-branch structure is used as the receiving domain. ECA learns the correlation between feature channels. The extracted feature channels are adaptively weighted by adding a small additional computational cost. Finally, the method is tested and evaluated using wind turbine bearing data. The experimental results show that, compared with the traditional neural network, the DRCNN model based on GAF achieves higher diagnostic accuracy with less parameter calculation. Full article

The present study aims to explain how the incorporation of anatase TiO₂ nanoparticles at three different concentrations, i.e., 1, 3, and 5 g/L, into the ceramic-like oxide plasma electrolytic oxidation (PEO) coatings on pure titanium substrate can affect the friction and wear behavior of the coatings in simulated body fluid (SBF) aqueous solution. For this purpose, a ball-on-disk friction and wear tester was utilized to characterize the wear performance of the PEO coatings. The morphology and dimensions (width and depth) of wear tracks were analyzed by scanning electron microscopy (SEM) and 2D depth profilometry, respectively. The results indicated that abrasive wear was identified in all PEO coatings; however, the coefficient of friction (COF), wear volume loss, and wear rate were strongly affected by the concentration of TiO₂ nanoparticles. The coatings containing TiO₂ nanoparticles presented a lower COF, less wear volume loss, reduced wear rate, and improved wear resistance due to having smoother surfaces and the presence of hard TiO₂ nanoparticles on their surfaces and inside the pores. The coating with 3 g/L of TiO₂ nanoparticles demonstrated the lowest wear rate value of 1.33 × 10⁻⁶ mm³/Nm (about a 32% reduction compared with that of coating without TiO₂ nanoparticles) and the best wear protection properties among all coatings under investigation. The findings suggest TiO₂ nanoparticles incorporated PEO coatings as a promising choice of surface treatment wherein the load-bearing capacity of titanium implants is critical. Full article

Continuous casting production is an important stage in smelting high-quality steel, and automatic casting control based on artificial intelligence is a key technology to improve the continuous casting process and the product quality. By controlling the opening degree of the stopper rod reasonably, the mold can be filled with liquid steel stably in the specified time window, and automatic casting can be realized. In this paper, an automatic casting control method of continuous casting based on an improved Soft Actor–Critic (SAC) algorithm is proposed. Firstly, a relational model of the stopper rod opening degree and the liquid steel outflow velocity is established according to historical casting data. Then the Markov Decision Process (MDP) model of the automatic casting problem and the reinforcement learning framework based on the SAC algorithm are established. Finally, a Heterogeneous Experience Pool (HEP) is introduced to improve the SAC algorithm. According to the simulation results, the proposed algorithm can predict the stopper rod opening degree sequence under the constraint of the target liquid level curve. Under different billet specifications and interference conditions, an accuracy of 80% of liquid level in the mold and a stopper rod opening degree stability rate of 75% can be achieved, which is 4.29% and 3.17% higher than those for the baseline algorithms, respectively. Full article

This paper proposes a new silver nanoscale joining material, silver nanowire film, as an alternative joining approach for high-power and large-size chip packaging. The silver nanowire film was prepared by pressing filtration with silver nanowire that was synthesized using the polyol method. We found that the tensile strength of the film reached 3.40 MPa and the content of the silver reached up to 99.0 wt%. This paper further studies the influence of the size of silver nanowires on the performance of silver nanowire film. The experimental results show that the silver nanowire films prepared with silver nanowires with longer lengths and smaller diameters displayed better performances. The silver nanowire film with the best performance was prepared using silver nanowire with a diameter of 88 nm and a length of 29 μm. The thermal resistance of the sintered silver nanowire film that was hot-pressed at 250 °C 10 MPa was only 1.28 K∙W⁻¹. The shear strength of the sintered joint was 56.4 MPa, and the fracture that occurred in the sintered silver nanowire film displayed a good plasticity. Full article

For industrial processes in which refractory metals are necessary, hafnium carbonitride exhibits excellent performance due to its high thermal conductivity and resistance to oxidation. In this study, hafnium carbonitride was deposited on Inconel 718 steel and silicon (100) substrates. The objective was to characterize the wear properties as a function of temperature. The layers were deposited by physical vapor deposition (PVD) in an R.F. sputtering magnetron system from carbon targets and high-purity hafnium (99.99%). The wear tests were carried out at temperatures of 100 °C, 200 °C, 400 °C, and 800 °C in non-lubricated conditions. The coefficient of friction (COF) was recorded in situ. The heat treatment temperature on coatings is essential in determining anti-wear efficiency. It was determined that high temperatures (800 °C) improve resistance to wear. High-resolution XPS spectra were used to detect the chemical states of Hf 4f_5/2 and Hf 4f_7/2. The 4f_5/2 and 4f_7/2 binding energy indicates the presence of HfN and HfC. Using the TEM technique in bright field mode allowed us to know the orientation, crystallographic structure and interplanar distances of the HfCN. The topography of the coatings, by AFM, shows uniform grains and very small characteristics that determine the low surface roughness value. The SEM image of the cross-section of the HfCN coating shows homogeneity of the layer; no cracks or deformations are observed. Full article

SiC-particulate-reinforced aluminum matrix composites (SiCp/Al MMCs) are widely used in the aerospace field due to their high specific stiffness and strength, low thermal expansion coefficient, and good radiation resistance. In the process of application and promotion, there is a connection problem between the aluminum matrix composites and electronic glass. In this work, the lead-free SiO₂-B₂O₃-Na₂O glass filler was used to seal 65 vol.% SiCp/ZL102 composites and DM305 electronic glass in an atmospheric environment. The effects of the sealing temperature on the properties of the joints were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Additionally, the causes of defects and the fracture mechanisms of the joints were analyzed. The results showed that the glass filler and base material were connected through a dual mechanism of an Al, Na, Si, and O element diffusion reaction and a mechanical occlusion. At a sealing temperature of 540 °C and a holding time of 30 min, the joint interface was dense and crack-free. Meanwhile, the average shear strength reached 13.0 MPa, and the leakage rate of air tightness was 1 × 10⁻⁹ Pa·m³/s. The brittle fracture features were revealed by the step-like morphology of the fracture, which originated from the brazing seam and propagated into the pore. The crack gradually propagated into the base material on both sides as the fracture area expanded, ultimately resulting in a fracture. Full article

A digital-twin-model-based optimal control system is presented for the steel continuous casting process. The system is designed for the coordinated optimization and dynamic control of secondary cooling and final electromagnetic stirring (FEMS), and involves three related parts. Firstly, a three dimensional real-time heat transfer model is established as the digital twin of the heat transfer process of continuous casting; for high accuracy, it is calibrated offline and calibrated online using measurements of the surface temperatures and shell thicknesses (only offline). Secondly, according to metallurgical rules, cooling and stirring are optimized coordinatively, based on the established digital-twin model and chaos particle swarm optimization algorithm. Thirdly, cooling and stirring are further dynamically controlled for quality stability. Finally, the system is applied in a bloom caster with model errors ≤ ±10 °C and control errors ≤ ±4 °C, which reduces the macro-segregation over grade 1.5 from 11% to 3.3%. Full article

The objective of the presented work was to develop a new forging process for a pinion shaft as a component of a wind turbine. A study of near-net-shape forming using Deform 3D software was performed to reduce operational cost, time, and material scrap; enhance specific properties; increase productivity. Near-net forged products have good dimensional accuracy and continuous metal flow lines, which are characteristic of improved mechanical properties. To avoid the traditional trial-and-error experimental method, the process and tool design were accomplished with a careful and detailed numerical simulation approach. In the present work, the Finite Element Method was used to develop a process model for the existing hot forging process of the 18CrNiMo7-6 steel pinion shaft used in a wind turbine. The developed numerical process model was validated via experiment including a comparison of the metal flow lines from the FEM model with the metallography results of the forged part. Two new die designs were proposed, and the simulation results were compared to the actual process to achieve improved geometry. The results for the new geometries showed improvements in terms of the die cavity filling for the new proposed dies and better results in grain flow orientation. Compared to the initial non-optimized die, the new designs improved the mechanical properties and savings associated with the lower volume of required raw material and fewer finishing operations. Considering the applied stresses and wear in the new near-net shape, the die geometry shall be updated to accommodate more severe solicitations. Naturally, all the improvements carried out are dependent on other factors such as the conditions of the equipment, operator skills, lubrication, and other variables. A surface heat treatment is also suggested for stress relief as a reliability improvement. Full article

This research investigates the tribological behavior of advanced open-cell porous AlSi10Mg-SiC composites fabricated using the novel replication method of NaCl space holders. These composite materials have potential applications in lightweight and high-strength structures that require high resistance to friction and wear. The composites were tested using a pin-on-disk method under dry sliding-friction conditions at ambient temperature, with a sliding velocity of 1.0 m∙s⁻¹ and an applied load of 50 N. The resulting wear parameters, including the coefficient of friction (COF) and mass wear, provided quantitative measures of the tribological behavior. Microstructural observations of the worn composite surfaces were carried out using scanning-electron microscopy (SEM) to study the wear mechanisms, and an elemental analysis was performed using X-ray energy-dispersive spectroscopy (EDS) to examine the elemental composition. The results showed that the AlSi10Mg-SiC composites had lower mass wear and COF than the open-cell porous AlSi10Mg material under the same experimental conditions. Three different machine learning (ML) models were employed to predict the COF of the composites, and their performances were evaluated using the R2, MSE, RMSE, and MAE metrics on the validation and test sets. Full article

FeSiCr soft magnetic composites (SMCs) were fabricated by the sol-gel method, and an Al₂O₃/resin composite layer was employed as the insulation coating. By the decomposition of boehmite (AlOOH) gel into Al₂O₃ in the temperature range of 606–707 °C, a uniform Al₂O₃ layer could be formed on the FeSiCr powder surface. The Al₂O₃ insulation coating not only effectively reduced the core loss, increased the resistivity, and improved the quality factor, but it also increased the thermal conductivity of SMCs. The best overall properties with saturation magnetization M_s = 188 emu/g, effective permeability μ_e = 39, resistivity ρ = 8.28 × 10⁵ Ω·cm, quality factor Q = 94 at 1 MHz, and core loss = 1173 mW/cm³ at 200 kHz and 50 mT were obtained when the SMC was prepared with powders coated by 0.5 wt.% Al₂O₃ and resin. The optimized SMC exhibited the lowest core loss with 27% reduction compared to the resin only-insulated sample and 71% reduction compared to the sample without insulation treatment. Importantly, the thermal conductivity of the SMCs is 5.3 W/m·K at room temperature, which is higher than that of the samples prepared by phosphating and SiO₂ coating owing to the presence of a high thermal conductive Al₂O₃ layer. The high thermal conductivity is beneficial to enhancing the high temperature performance, lifetime, and reliability of SMCs. This work is expected to be a valuable reference for the design and fabrication of SMCs to be applied in high-temperature and high-frequency environments. Full article

The development and implementation of the methods for designing amorphous metal alloys with desired mechanical properties is one of the most promising areas of modern materials science. Here, the machine learning methods appear to be a suitable complement to empirical methods related to the synthesis and testing of amorphous alloys of various compositions. In the present work, a method is proposed a method to determine amorphous metal alloys with mechanical properties closest to those required. More than 50,000 amorphous alloys of different compositions have been considered, and the Young’s modulus E and the yield strength ${\sigma }_y$ have been evaluated for them by the machine learning model trained on the fundamental physical properties of the chemical elements. Statistical treatment of the obtained results reveals that the fundamental physical properties of the chemical element with the largest mass fraction are the most significant factors, whose values correlate with the values of the mechanical properties of the alloys, in which this element is involved. It is shown that the values of the Young’s modulus E and the yield strength ${\sigma }_y$ are higher for amorphous alloys based on Cr, Fe, Co, Ni, Nb, Mo and W formed by the addition of semimetals (e.g., Be, B, Al, Sn), nonmetals (e.g., Si and P) and lanthanides (e.g., La and Gd) than for alloys of other compositions. Increasing the number of components in alloy from 2 to 7 and changing the mass fraction of chemical elements has no significantly impact on the strength characteristics E and ${\sigma }_y$. Amorphous metal alloys with the most improved mechanical properties have been identified. In particular, such extremely high-strength alloys include Cr${}_{80}$B${}_{20}$ (among binary), Mo${}_{60}$B${}_{20}$W${}_{20}$ (among ternary) and Cr${}_{40}$B${}_{20}$Nb${}_{10}$Pd${}_{10}$Ta${}_{10}$Si${}_{10}$ (among multicomponent). Full article

Metallic Mg is an important strategic metal and its properties are greatly affected by impurities. Silicothermic reduction and electrolysis are the most used approaches to prepare metallic Mg. The products of these processes need to be further refined to obtain high-purity Mg metal. However, previous research has mainly focused on refining the crude Mg (CM) produced via silicothermic reduction, whereas no in-depth investigations have been conducted on refining the CM produced via electrolysis. Here, vacuum distillation was used to refine electrolytically produced CM. The content and morphological characteristics of the impurity elements in CM were studied via glow discharge mass spectrometry, mineral dissociation analysis, and electron probe microanalysis. The effect of different distillation temperatures and times on the quality of the refined Mg was investigated. The results show that the main impurity elements are Al, Fe, Si, Ti, Cr, S, Cl, and Ni. The content of impurities, such as Si, Al, Fe, Ni, Ti, and Cr, in the refined Mg is significantly reduced at a temperature of 1023 K and a time of 120 min, and the purity of the refined Mg reaches 99.99%, which meets the Mg9999 national standard for primary Mg ingots in China (GB/3499-2011). Full article

The effects of different strain levels applied through high-pressure torsion (HPT) deformation following annealing on the microstructural evolution, thermal stability, and mechanical properties of Al-4Mg-0.3Cu alloy were investigated. The results reveal that Cu-segregated grain boundaries (GBs) were generated in the ultrafine-grained Al-4Mg-0.3Cu alloy with high angle grain boundaries. By contrast, the phenomenon of Cu segregation was not found in micron-scale and submicron-scale grains with low-angle grain boundaries. The mechanism of Cu segregation in ultrafine-grained Al-4Mg-0.3Cu alloy was discussed. After heat treatment, Cu segregation induced the precipitation of the dense Al₂CuMg phase at GBs, which strongly inhibit grain growth and improve thermal stability. Stress–strain curves of as-cast, 5-turn, and 10-turn HPT samples showed that fracture strength significantly increased, attributed to grain size refinement, dislocation density increase, and Cu segregation at GBs. After heat treatment, 5-turn and 10-turn HPT samples demonstrate an enhanced elongation to fracture with a slight reduction of fracture strength. Full article

Wear tends to shorten tool life, reduce component quality. To prevent or postpone the wear of tool steel forming tools, methods to increase wear resistance, such as increasing the material hardness, optimizing the carbide distribution and application of surface coatings, are often used. However, the formation of lubricating phases in steels leading to anti-attrition is less investigated. The friction behavior of three steels were investigated thoroughly by a tribo test with different normal loads. A Field-emission scanning electron microscope (FE-SEM) along with energy dispersive X-ray spectroscopy (EDS) were used to characterize the microstructure as well as the influence of the precipitated phases on the wear mechanisms. Results showed the friction coefficient decreased with increasing normal load, whereas the wear rate increased with increasing normal load. Compared with SKD11 and DC53 steels, the friction coefficient and wear volume of SLD-MAGIC steel were reduced by 0.1 to 0.3 and 10% to 30%, respectively. With the increase of normal load, the wear mechanism changed in order from abrasive wear, adhesive wear to oxidation wear. The more carbide contents, the rounder the carbide, the better the wear resistance of the tool steel. It can be shown that, under different normal loads, SLD-MAGIC exhibits better wear performance than SKD11 and DC53 tool steels, which is mainly due to the self-lubricating phenomenon of SLD-MAGIC steel. The self-lubricating mechanism was due to the fact that the exfoliated sulfide during wear formed a lubricating film to reduce wear. Full article

The Nd-Fe-B hot-deformation magnet with high resistivity was successfully prepared by hot-pressing and hot-deformation of Nd-Fe-B fast-quenched powder with amorphous glass fiber. After the process optimization, the resistivity of the magnet was increased from 0.383 mΩ·cm to 7.2 mΩ·cm. Therefore, the eddy current loss of magnets can be greatly reduced. The microstructure shows that the granular glass fiber forms a continuous isolation layer during hot deformation. At the same time, the boundary of Nd-Fe-B quick-quenched the flake and glass fiber from the transition layer, which improves the binding of the two, and which can effectively prevent the spalling of the isolation layer. In addition, adding glass fiber improves the orientation of the hot deformation magnet to a certain extent. The novel design concept of insulation materials provides new insights into the development and application of rare earth permanent magnet materials. Full article

Firstly, the properties and the microstructure evolution of the solid-solution process of Mg-5 wt.%Sn were studied. From the motion analysis of resistivity and microhardness during solution treatment, the reasonable solution technology of Mg-5 wt.%Sn should be 12–16 h at 480 °C. After solution treatment at 480 °C for 16 h, the precipitating behavior in supersaturated solid solution. Mg-5 wt.%Sn alloy was investigated. In the aging process, it was observed that there were precipitated phases in the both grain and grain boundaries, and continuous inhomogeneous precipitation occurred along the grain boundaries, and continuous homogeneous precipitation happened in the grain. Transmission Electron Microscope (TEM) analysis indicated the plate- and lath-shaped precipitates within the grains and only the plate-shaped precipitates along the grain boundary. High-Resolution Electron Microscopy (HRTEM) studies have shown that metastable precipitates may occur during aging, coherently or semi-coherent with the matrix. Energy Dispersive Analysis by X-ray (EDAX) analysis showed that the Mg/Sn ratio was not actually constant, and the Sn content of the metastable phase was lower than that of the Mg₂Sn equilibrium phase. X-ray diffraction (XRD) studies confirm the existence of this metastable phase, which is supposed to be GP zone and metastable Mg₃Sn phase. Full article

The corrosion performance of P91, 304SS and IN625 alloys was evaluated in simulated Solar Salt at 565 °C for up to 15 days. Results revealed that IN625 exhibited the best corrosion resistance with the evolution of thin and compact dual-structured oxide scales. 304SS experienced a great corrosion rate at the initial stage, but showed protective behavior in the later period. A linear mass gain rate was observed for P91, which may result in breakaway corrosion during prolonged immersion time. Finally, the underlying corrosion mechanisms were revealed, providing important guidelines for selecting applicable materials for corrosion mitigation in thermal energy storage (TES) system. Full article

Flexible pipelines connect offshore platforms to subsea production systems due to their high flexibility, applicability, and recycling. Flexible armor layers in flexible pipelines are constructed using the parallel helical wrapping of several rectangular wires. The complex stress modes to which pipelines are subjected provide complex failure modes that are mostly unpredictable, requiring expensive pipeline integrity verification methods. This work investigates texture and microstructure evolution in pearlite-drawn wires due to different heat treatments. The material was subjected to annealing and isothermal heat treatments to obtain changes in its microstructure and texture. The changes were characterized using SEM, XRD, and EBSD techniques. Samples were subjected to tensile testing to evaluate their mechanical properties. This work revealed that annealing and isothermal treatments mainly modify the material microstructure, whereas annealing provides a material with grains with ease of deformation. In contrast, isothermal treatment provides grain growth with high internal energy and more deformation resistance. Annealing increases the intensity of all texture components, while isothermal treatment reduces intensity. These findings provide insights into the relationship between material properties and heat treatments, which can be used to optimize the design and performance of flexible pipelines, thereby reducing the need for expensive integrity verification methods. Full article

For weathering steel used in building, it is necessary not only to ensure weather resistance, but also to improve the strength and yield ratio. This study investigates the strengthening effect of Ti microalloying on the tested steel by conducting continuous cooling transformation tests of undercooled austenite and comparative tests of microstructure and performance at different coiling temperatures, with 0.07 wt.% Ti added to the weathering building test steel. The results show that, with an increase in cooling rate (0.1~50 °C/s), the room temperature microstructure of different cooling rates gradually transitions as follows: F + P, F + P + B, F + B and B + M; in addition, the hardness increases. Polygonal ferrite and pearlite were obtained by coiling at 650 °C; quasi-polygonal ferrite, acicular ferrite, pearlite and a small amount of bainite were obtained by coiling at 600 °C; and bainite was obtained by coiling at 550 °C. With a decrease in coiling temperature, the strength of the test steel increased, the yield ratio increased, the elongation after fracture decreased and the elongation at the yield point decreased. Compared with those observed at 650 °C, the nano precipitation phases observed in the sample at 600 °C were smaller in size, higher in number and higher in dislocation density. The combined action of second-phase precipitation strengthening and dislocation strengthening increased the strength and yield ratio of the test steel. This study will be helpful in guiding the improvement of strength grades for weathering steel used in building and industrial production. Full article

Seizure during ironing negatively affects the quality of parts and die life. To prevent seizures, lubrication has to be improved. In this study, laser-textured dies with lubricant pockets were utilized to improve seizure resistance in the ironing of aluminum alloy sheets and stainless steel cups. The effects of array patterns of micro-pockets, such as grid and crossing array patterns with circular pockets, as well as a grooved array patterns on seizure resistance, were experimentally examined by strip ironing. The sheet and die materials were the A1050-O aluminum alloy and JIS SKD11 tool steel, respectively. Moreover, the underlying physics of the lubricant flow influencing the load-carrying capacity were investigated using three-dimensional computational fluid dynamics simulations. The optimum array patterns of the micro-pockets were then utilized on a tungsten carbide-cobalt (WC-Co) die surface for ironing SUS430 stainless steel cylindrical cups. The strip ironing results showed that the grid array pattern was successful in ironing sheets with a high ironing ratio. The grid array pattern increased the load-carrying capacity of the lubricant more than the crossing pattern, as demonstrated by the simulations, thereby improving the ironing limit. The subsequent ironing of stainless steel cups revealed that when using a textured die with a grid array pattern and lubricant without the extreme pressure additive in comparison to an untextured die, the ironing limit increased by 6% and the average ironing load decreased by 35%. The seizure resistance was improved because the pockets on the surface structured by laser surface texturing improved the load-carrying capacity during ironing. Full article

The structure of the new ternary eutectic Al-Ca-Cu system considered as a replacement for the ternary eutectic system Al-Ce-Cu widely used for additive manufacturing has been studied using experimental techniques. The liquidus projection of the Al-Ca-Cu system in the aluminum corner has been suggested based on experiential studies of the microstructure and phase composition of model alloys. The suggested structure of the diagram has two quasi-binary sections: (Al)-Al₂₇Ca₃Cu₇ and (Al)-Al₈CaCu₄ and three invariant eutectic transformations: L→(Al) + (Al,Cu)₄Ca + Al₂₇Ca₃Cu₇ (at 5.6 wt.% Ca, 4.5 wt.% Cu, 595 °C), L→(Al) + Al₂₇Ca₃Cu₇ + Al₈CaCu₄ (at 2.2 wt.% Ca, 13.5 wt.% Cu, 594 °C) and L→(Al) + Al₈CaCu₄ + Al₂Cu (at 0.5 wt.% Ca, 34 wt.% Cu, 544 °C). The limit solubility of copper in aluminum solid solution (Al) at 530 °C reaches ~5.1 wt.% in the ternary phase field (Al) + Al₈CaCu₄ + Al₂Cu and drops to ~2.4 wt.% in the (Al) + Al₈CaCu₄ + Al₂₇Ca₃Cu₇ ternary phase field. For the example of the model ternary hypoeutectic alloys with a predominant content of the eutectic (Al,Cu)₄Ca phase, it has been shown that the system is promising for designing new eutectic-type alloys with a natural composite structure. Full article

More and larger blast furnaces have been constructed for ironmaking across the world in recent years due to the advantages of high productivity, high energy efficiency and low cost. Slag plays important role in a blast furnace to produce high-quality hot metal and maintain smooth operations. Liquidus temperatures are the essential information of the slag to avoid the formation of the solid phase during the ironmaking process and slag tapping. The principal components of the iron blast furnace slags can be described by the system CaO-MgO-Al₂O₃-SiO₂. With the significant changes in the raw materials and different requirements of the blast furnace operations, phase equilibria in this slag system have been extensively investigated from different directions. Phase diagrams were presented in various pseudo-ternary and pseudo-binary forms to meet the requirements of wide applications. Reliable thermodynamic modelling is the target of the researchers which can predict accurate liquidus temperatures of the slag. Development of the reliable thermodynamic modelling relies on systematic and accurate experimental data including liquidus temperatures and compositions of the solid solutions. Experimental data on the phase equilibria of the system CaO-MgO-Al₂O₃-SiO₂ are summarised and compared with the thermodynamic predictions which can provide systematic information for the researchers and blast furnace operators. Full article

A scanning magnetometer based on a magnetoimpedance sensor with a 1 mm spatial resolution and 10 nT sensitivity was used to study stray magnetic fields of Fe₇₄B₁₃Si₁₁C₂ amorphous ferromagnetic microwires. Spatial magnetic images and vertical component profiles of stray magnetic fields of the studied microwires were obtained in a longitudinal homogeneous magnetic field of Helmholtz coils with a strength in the range of ±600 A/m. A magnetic calculation method is suggested that allows for using the measured magnetic fields to determine the magnitude and pattern of magnetization for the microwire. Characteristic values of the microwires’ average magnetization and width of closure domains for various values of bias fields were found. Full article

Electrocatalytic nitrate reduction into ammonia is promising for its restricted activity and selectivity in wastewater treatment, however, it remains challenging. In this work, Co₃O₄ nanosheet electrodes with rich oxygen vacancies (OVs) (Co₃O_4−x/NF) are prepared and then applied as efficient catalysts for selective electrocatalytic reduction of nitrate to ammonia. The resulting Co₃O_4−x/NF electrodes exhibit high NO₃⁻-N removal efficiency and NH₄⁺-N selectivity, at 93.7% and 85.4%, respectively. X-Ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance spectra (EPR) results clearly reveal the formation of OVs in Co₃O_4−x/NF. The electrochemical characterization results confirm that OVs can effectively improve electron transfer as well as the electrochemically active area. The Co²⁺/Co³⁺ ratio of Co₃O_4−x/NF increases after the electrocatalytic reduction of nitrate, highlighting the crucial role played by Co²⁺ in mediating ammonia production via the Co²⁺/Co³⁺ cycle. These findings offer valuable guidelines for the development of more efficient and sustainable approaches for nitrate-contaminated wastewater treatment and ammonia synthesis. Full article

Welding deformation occurs due to non-uniform thermal expansion, thermal contraction, restraint, and phase transformation in a metal by a local welding heat source. This causes problems such as low buckling strength and the reduced workability of the production process. Correcting welding deformations in stainless steel using heat—such as by linear heating—causes metal sensitization, which should be avoided. Herein, welding deformation was reduced by applying tension stress instead of correcting the deformation by heating. A deformation-prevention jig was used to reduce welding deformation during the manufacturing of a cylinder made of STS304 by laser welding. The tensile stress was induced by pushing the cylinder shell outward using the deformation-prevention jig. A thermo-elastoplastic analysis was performed to investigate the effects of the magnitude of the tensile stress on welding deformation. Furthermore, the parametric results—which indicated a reduction in welding deformation—were verified through experiments. The thermo-elastoplastic analysis suggested that deformation did not occur when the magnitude of tensile stress was approximately 50% of the yield stress of the base metal. Moreover, the deformation was experimentally reduced by 11–20% when a tensile stress of 30 MPa was applied to the cylinder, compared with that in the absence of tensile stress. Full article

In this work, two compounds of isonicotinohydrazide organic class, namely (E)-N′-(1-(4-(dimethylamino)phenyl)ethylidene) isonicotinohydrazide (MAPEI) and (Z)-N′-(2-oxo-2, 3-dihydro-1H-inden-1-ylidene) isonicotinohydrazide (OHEI) were synthesized and evaluated for corrosion protection of N80 steel in a concentrated acidic medium (15 wt.% HCl) at a temperature of 303 K. The weight loss method (gravimetric method) and electrochemical techniques, i.e., electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization curves (PPC), were used to evaluate the inhibition and adsorption characteristics of tested compounds. Further, surface characterization using a scanning electron microscope (SEM) was used to assess the surface morphology of steel before and after inhibition. Weight loss experiments at 303 K and 363 K showed that tested compounds’ performance decreased with the increase in temperature, particularly at low concentrations of inhibitors whereas they exhibited good stability at higher concentrations. Electrochemical tests showed that MAPEI and OHEI inhibitors were effective at 5 × 10⁻³ mol/L, reaching an inhibition efficiency above 90%. It was also determined that the adsorption of both inhibitors followed the Langmuir adsorption isotherm model. Furthermore, SEM analysis showed that the investigated compounds can form a protective layer against steel corrosion in an acidic environment. On the other hand, the corrosion inhibition mechanism was established from density functional theory (DFT), and the self-consistent-charge density-functional tight-binding (SCC-DFTB) method which revealed that both inhibitors exerted physicochemical interactions by charge transfer between the s- and p-orbitals of tested molecules and the d-orbital of iron. The results of this work are intended to deepen the research on the products of this family to control the problem of corrosion. Full article

Inconel 625 (IN625) superalloys can be easily fabricated by the laser-based powder bed fusion (PBF-LB/M) process, allowing the production of components with a high level of design freedom. However, one of the main drawbacks of the PBF-LB/M process is the control over thermally induced stresses and their mitigation. A standard approach to prevent distortion caused by residual stress is performing a stress-relieving (SR) heat treatment before cutting the parts from the building platform. Differently from the cast or wrought alloy, in additively manufactured IN625, the standard SR at 870 °C provokes the early formation of the undesirable δ phase. Therefore, this unsuitable precipitation observed in the PBF-LB/M material drives the attention to develop a tailored SR treatment to minimise the presence of undesirable phases. This work investigates SR at lower temperatures by simultaneously considering their effects on residual stress mitigation, microstructural evolution, and mechanical properties. A multiscale approach with cantilever and X-ray technologies was used to investigate how the residual stress level is affected by SR temperature. Moreover, microstructural analyses and phase identifications were performed by SEM, XRD, EBSD, and DSC analyses. Finally, mechanical investigations through microhardness and tensile tests were performed as well. The results revealed that for the additively manufactured IN625 parts, an alternative SR treatment able to mitigate the residual stresses without a massive formation of δ phase could be performed in a temperature range between 750 and 800 °C. Full article

Two kinds of alloys with and without the addition of Cu, Al-7%Si-0.3%Mg-0.3%Cr and Al-7%Si-0.3%Mg-0.3%Cr-1.5%Cu, are studied in this work. The addition of Cu can notably improve notably the strength of Al alloy but it reduces its corrosion resistance. In this study, the electrochemical workstation is used to measure the open circuit potential and polarization curve of alloys and immersion corrosion is carried out. SEM and TEM images are taken before and after immersion corrosion to observe the pitting and intergranular corrosion of the alloy. Results show that the addition of Cu accelerates the immersion corrosion rate of Al alloy by 26.8% to 269.2%. This affects the peak ageing and overageing samples the most. The influence is less evident for underaged samples. At the same time, the addition of Cu aggravates the aggregation of pitting corrosion in the primary step of corrosion of Al alloy and the intergranular corrosion around and within the pitting hole. ${\beta }^{″}$-Mg₅Si₆ precipitates and ${\theta }^{″}$-Al₃Cu precipitates are observed in Al-7%Si-0.3%Mg-0.3%Cr-1.5%Cu alloy. The Cu atoms occupy Si3/Al site of ${\beta }^{″}$ and segregate at the edge of ${\beta }^{″}$. It is believed that the deterioration of corrosion performance essentially is attributed to the Si-enriched particles, Al₁₃Cr₄Si₄ phase and the Cu-enriched precipitates, ${\beta }^{″}$-Mg₅Si₆ precipitates and ${\theta }^{″}$-Al₃Cu precipitates. Full article

Sulfide precipitation has been widely applied to remove arsenic from acidic wastewater containing As(III) and As(V), due to its simple process and high efficiency. However, the characteristics and composition of the precipitates are also of importance for its further treatment and disposal. To explore the characteristics of elemental S formed by reduction and the combined form of the generated S and As₂S₃, the characteristics of precipitates sulfurized from As(III) and As(V) and the effects of temperature, the S(-II) to As ratio (S/As), Cl⁻ concentration (c_Cl−), and the volume fraction of H₂SO₄ (φ_H2SO4(v)) on the sulfurization of As(III) and As(V) were investigated in detail. The results showed that the contents of As and S were 60.37% and 39.73% in precipitate-As(III), while they accounted for 47.46% and 52.64% in precipitate-As(V); both precipitate-As(III) and precipitate-As(V) were mainly composed of amorphous As₂S₃, while the latter contained elemental S. Temperature and S(-II)/As(III) slightly affected the sulfurization process of As(III), while for As(V), as the temperature increased, the content of As₂S₃ in precipitate-As(V) increased significantly. Additionally, with the S(-II)/As(V) increasing, the content of A₂S₃ increased continuously. This study provides a further clarification of the specific composition and structure of the complex precipitates of arsenic sulfide, which will benefit the efficient stabilization of the arsenic sulfide sludge. Full article