Metals, Volume 14, Issue 5 (May 2024) – 58 articles

This work investigates the mechanical behavior under out-of-plane compression of the Al core and honeycomb sandwich at increasing temperatures of up to 300 °C. After the first introductive theoretical modeling on room-temperature compressive behavior, the experimental results at increasing temperatures up to 300 °C are presented and discussed. The analysis of the results shows that peak stress, plateau stress, and specific absorbed energy gradually decrease as the temperature increases. The final densification occurs always at the same strain level (around 75%). Sandwich honeycomb test temperatures have been limited to 200 °C for bonding problems of the skin to the sandwich due to the glue. The experimental and modeling results agree well at room temperature as well at increasing temperatures. The results can provide useful information to choose base materials for greater energy absorption at increasing temperatures. Full article

The corrosion behavior of copper was investigated in synthetic tap water with and without sodium hypochlorite (NaClO) at different temperatures during immersion for 70 d by using scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical measurement techniques. The weight loss corrosion rate and pit depth of copper first increase and then decrease with the change in solution temperature from 25 to 80 °C. This is mainly related to the corrosion products formed on the copper surface. The main corrosion products change from Cu₂O and Cu₂(OH)₂CO₃ to CuO with the increase in solution temperature. The presence of 3 ppm NaClO slightly increases the weight loss corrosion rate and pit depth of copper under all temperatures except for 50 °C and reduces the temperature of the maximum corrosion rate from 50 to 40 °C. Free chlorine reduction accelerates the cathodic reaction of the corrosion process. Full article

Aluminum and A356 alloy foam castings are produced using a melt-foaming method. Prior to foaming, the melt is modified with nano-sized particles (SiC, TiN, or Al₂O₃). The nano-sized particles are mixed with micro-sized Al particles, which are ultrasonically treated and hot-extruded. Thus, the so-called “modifying nano-composition” is obtained. The resulting compositions are introduced into the melt of the Al foam at the following mass concentrations of nanoparticles: SiC: 0.038 wt. %; TiN: 0.045 wt. %; and Al₂O₃: 0.046 wt. %. For the A356 foam, we use the following concentrations: SiC: 0.039 wt. %; TiN: 0.052 wt. %; and Al₂O₃: 0.086 wt. %. The macrostructure of the foam castings is investigated by CT scanning and 3D analysis. The pore size distributions and accumulative fraction dependencies are determined for all samples. The microstructure of the foam castings is investigated by SEM-EDS analysis. The results confirmed the presence of individual nano-sized particles, as well as clusters of particles in foam walls. The conducted compression tests show a significant increase in the plateau stress (up to 237%) of the modified aluminum foam castings compared to non-modified castings. However, a similar effect of the nano-compositions on A356 alloy foam castings is not observed. The obtained results show that the above-indicated concentrations of nanoparticles can positively influence the mechanical properties of aluminum foam castings. The novelty of the current study is two-fold: (1) such low concentrations of added nanoparticles have never been used before to alter Al foam’s properties, and (2) an original method of introducing the nanoparticles into the melt is applied in the form of nano-compositions. Full article

The strength–ductility mechanism of the low-carbon steels processed by laser cutting is investigated in this paper. A typical gradient-phased structure can be obtained near the laser cutting surface, which consists of a laser-remelted layer (LRL, with the microstructure of lath bainite + granular bainite) and heat-affected zone (HAZ). As the distance from the laser cutting surface increases, the content of lath martensite decreases in the HAZ, which is accompanied by a rise in the content of ferrite. Considering that the microstructures of the LRL and HAZ are completely different from the base metal (BM, ferrite + pearlite), a significant strain gradient can be inevitably generated by the remarkable microhardness differences in the gradient-phased structure. The hetero-deformation-induced strengthening and hardening will be produced, which is related to the pileups of the geometrically necessary dislocations (GNDs) that are generated to accommodate the strain gradient near interfaces. Plural phases of the HAZ can also contribute to the increment of the hetero-deformation-induced strengthening and hardening during deformation. Due to the gradient-phased structure, the low carbon steels under the process of laser cutting have a superior combination of strength and ductility as yield strength of ~487 MPa, tensile strength of ~655 MPa, and total elongation of ~32.7%. Full article

GH4169 is one of the key materials used to manufacture high-temperature load-bearing parts for aero-engines, and the surface integrity of these parts in service conditions significantly affects their high-temperature fatigue performance. Under a coupling effect of high temperature and alternating load, the evolution process of the machined surface integrity index of superalloy GH4169 specimens was studied, and fatigue performance tests at 20 °C, 450 °C, and 650 °C were carried out to analyze the primary factors affecting the high-temperature fatigue performance of specimens. The results indicated that the surface roughness of specimens remained essentially unchanged. However, the value of surface residual stress decreased significantly, with a release of more than 60% at the highest temperature. At 650 °C, the surface microhardness increased, while the degree of surface plastic deformation decreased under alternating loads. Simultaneously, when the surface roughness was less than R_a 0.4 μm, surface microhardness was the main factor affecting the high-temperature fatigue performance of specimens. The influence of surface microhardness on low-cycle fatigue performance was not consistent with that on high-cycle fatigue performance. The latter increased monotonically, whereas the former initially increased and then decreased with increasing surface microhardness. Full article

The synthesis of silver nanoparticles (AgNPs) holds significant promise for various applications in fields ranging from medicine to electronics. Accurately predicting the particle size during synthesis is crucial for optimizing the properties and performance of these nanoparticles. In this study, we compare the efficacy of tree-based models compared with the existing models, for predicting the particle size in silver nanoparticle synthesis. The study investigates the influence of input features, such as reaction parameters, precursor concentrations, etc., on the predictive performance of each model type. Overall, this study contributes to the understanding of modeling techniques for nanoparticle synthesis and underscores the importance of selecting appropriate methodologies for accurate particle size prediction, thereby facilitating the optimization of synthesis processes and enhancing the effectiveness of silver nanoparticle-based applications. Full article

Objectives: Orthopedics and dentistry have widely utilized titanium alloys as biomaterials for dental implants, but limited research has been conducted on the fabrication of ceramic particle-reinforced Ti composites for further weight reductions. The current study compared titanium–titanium diboride metal composites (Ti-TiB₂) with pure titanium (processed by powder metallurgy) in terms of toxicity, corrosion resistance, and wettability. Methods: First, cell lines of a primary dermal fibroblast normal human adult (HDFa) were used to test the cytocompatibility (in vitro) of the composite and pure Ti using an indirect contact approach. Corrosion testing was performed for the materials using electrochemical techniques such as potentiodynamic polarization in a simulated bodily fluid (SBF) in conjunction with a three-electrode electrochemical cell. The entire set of experimental tests was conducted according to the ASTM F746-04 protocol. The contact angles were measured during wettability testing in accordance with ASTM D7334-08. An X-ray diffractometer (XRD) was used to catalog every phase that was visible in the microstructure. A scanning electron microscope (SEM) and energy-dispersive X-ray spectroscopy (EDS) were used to determine the chemical composition. Results: The cytotoxicity tests revealed that there was no detectable level of toxicity, and there was no significant difference in the impact of either of the two materials on the viability of human fibroblasts. An increase in the corrosion resistance of the composite (0.036 ± 0.0001 mpy (millimeters per year)) demonstrated the development of a passive oxide coating. According to the findings, the composites showed a greater degree of hydrophilicity (contact angle 44.29° ± 0.28) than did the pure titanium (56.31° ± 0.47). Conclusions/Significance: The Ti-TiB₂ composite showed no toxicity and better corrosion resistance and wettability than did pure Ti. The composite could be a suitable alternative to Ti for applications involving dental implants. Full article

This study presents an optimization of the process parameters for the effect of copper (Cu) donor material percentage on the friction stir welding (FSW) of AA6061-T6 alloy. Extensive factorial experiments were conducted to determine the significance of the rotational speed (ω), the transverse speed (v), the interface coefficient of friction (μ), and the Cu donor material percentage in the plunge, left, right, and downstream zones. Design Expert 13 software was used to identify the number of simulation experiments to be conducted using the Abaqus simulation software. From Design Expert 13, which is a thorough multi-objective optimization analysis software, we were able to identify ideal welding parameters such as a rotational speed of 1222 rpm, transverse speed of 1.1 mm/s, the coefficient of friction of 0.9, and a 19% donor material percentage for the plunge zone. Significant findings demonstrate that increasing the Cu donor material substantially reduced the temperature from 502 °C to 134 °C when the Cu content is increased from 0% to 50%. This integrated modeling and optimization approach provides a practical procedure to identify the best experimental parameters for the process and a new understanding to guide advances for high-quality FSW of aluminum alloys. This work offers a methodology for optimizing the FSW parameters aligned with multifaceted thermomechanical physics. Full article

The present study investigated microstructural evolution and changes in tensile properties of an Al-Si piston alloy subjected to thermal exposures at 250 and 350 °C for 150, 300, and 500 h. Microstructural and nanoscale precipitates were characterized using a combination of high-angle annular dark field-scanning transmission electron microscopy (HAADF-STEM) images and scanning electron microscopy (SEM). The tensile testing was performed. The results demonstrated that the thermal exposure induced granulation of the δ-Al₃CuNi particles, alongside precipitation of the θ-Al₂Cu phase particles and AlCu clusters within the matrix. Specifically, an increase in the size and number density of the θ-Al₂Cu phase particles was observed with exposure time at 250 °C. Conversely, at 350 °C, the θ-Al₂Cu particles exhibited a gradual increase in size with prolonged thermal exposure, coupled with a decrease in their number density. AlCu clusters precipitated solely at a thermal exposure temperature of 350 °C, with precipitation intensifying over time. Moreover, a decrease in the alloy’s tensile strength and an increase in elongation were noted after thermal exposure. Finally, the present study discussed the precipitation mechanisms of θ-Al₂Cu particles and AlCu clusters within the grains, suggesting that the AlCu clusters exerted a more effective strengthening effect compared to the θ-Al₂Cu particles. Full article

This research addresses the escalating need for lightweight materials, such as aluminum and magnesium alloys, in the aerospace and automotive sectors. The study explores friction stir welding (FSW), a cost-efficient process known for producing high-quality joints in these materials. The experiment involved the welding of dissimilar aluminum alloys (AA5086-H111 to AA6061-T6) using a novel pin tool design with welding parameters such as holding time, pin tool length, tool spindle speed, and linear speed fine-tuned through a design of experiment (DOE) approach. A comparative analysis of two tool designs revealed that the newly introduced design substantially improved mechanical properties, particularly tensile strengths, by 18.2% relative to its predecessor. It is noteworthy that FSW joint efficiency is 83% when using a normal tool design in comparison with 92.2% when using a new tool design at similar FSW parameters. The new tool achieved the parameter values leading to the maximum tensile strength of 317 MPa with 3 mm thickness (Th), 25 s holding time (Tt), 0.1 mm dimension (L), 1600 rpm spindle speed (SS), and 30 mm/min feed velocity (Fr). In comparison, the normal tool achieved a maximum UTS of 285 MPa, 5 mm Th, 25 s Tt, 0.3 mm L, 800 rpm SS, and 90 mm/min Fr. The new tool design, with longitudinal and circular grooves, improves heat input for plastic deformation and alloy mixing during welding. Subsequent analysis of the joint’s microstructure and microhardness shows its similarity to the original alloys. Full article

The microstructure characteristics of TiAl alloy prepared by laser-directed energy deposition (L-DED) are coarse columnar grains parallel to the building direction, which results in serious mechanical properties and anisotropy and limits its application. In the present study, TiB₂ can be used as an effective grain refiner due to the extremely high Q value (growth inhibition factor; the larger the Q value of an alloying element, the stronger its grain refinement effect.) of B. With TiB₂ addition, TiAl alloys prepared by laser-directed energy deposition with the microstructure of full equiaxed grains were obtained, and the grain size was significantly reduced by about 30% with 0.45 wt.% TiB₂. This value has been further increased to 45% when adding 0.9 wt.% TiB₂. Moreover, the γ_m phase was nearly eliminated and the width of (α2 + γ) lamellar was significantly decreased, which has positive effects on mechanical properties. Meanwhile, TiB₂ precipitates uniformly distribute in the matrix, as a reinforced particle to increase the hardness and compressive strength of the alloys. The microhardness of the TiAl alloy increased with the increasing content of TiB₂. The addition of TiB₂ improved the room and high-temperature compressive properties of TiAl alloy while slightly increasing its ductility. These findings have important guiding significance for expanding the application of TiAl alloys. Full article

Materials with enhanced wear resistance are constantly in high demand. Nickel-based self-fluxing materials deposited by atmospheric plasma spraying (APS) have feasible wear resistance performance. This study aimed to evaluate the results of a nickel-based self-fluxing alloy coating deposited on AISI 4340 steel substrate using APS. Additionally, the temperature at which the remelting process achieved optimal results was investigated. The AISI 4340 steel substrate samples were coated with a self-fluxing NiCrBSiCFe powder by APS. The post-coating remelting process was performed in a controlled atmosphere tube furnace at 900, 1000, and 1100 °C. Microstructural analysis was carried out by Scanning Electron Microscopy (SEM) before and after remelting. The estimated porosity of the as-sprayed sample was 3.28%, while the remelted coating sample at 1100 °C had only 0.22% porosity. Furthermore, a microhardness measurement was conducted, and the best condition yielded an average value of 750 HV_0.5. Tribological tests were performed to evaluate the coefficient of friction and wear rates, revealing that at 1100 °C, the as-sprayed coating had a wear rate of 9.16 × 10⁻⁵ [mm³/(N*m] and the remelted coating had 4.106 × 10⁻⁵ [mm³/(N*m]. The wear-loss volume was determined to be 14.1 mm³ for the as-sprayed coating sample and 3.6 mm³ for the remelted coating at 1100 °C. Full article

The damage properties in the shear-punched surface layer, such as the strain-hardening increment, strain-induced martensite fraction, and initiated micro-crack/void characteristics at the shear and break sections, were experimentally evaluated to relate to the stretch-flangeability in three types of low-carbon high-strength TRIP-aided steel with different matrix structures. In addition, the surface layer damage properties were related to the mean normal stress developed on shear-punching and microstructural properties. The shear-punched surface damage of these steels was experimentally confirmed to be produced under the mean normal stress of negative to 0 MPa. TRIP-aided bainitic ferrite (TBF) steel had the smallest surface layer damage, featuring a significantly suppressed micro-crack/void initiation. This was due to the fine bainitic ferrite lath matrix structure, a low strength ratio of the second phase to the matrix structure, and the high mechanical stability of the retained austenite. On the other hand, the surface layer damage of TRIP-aided annealed martensite (TAM) steel was suppressed next to TBF steel and was smaller than that of TRIP-aided polygonal ferrite (TPF) steel. The surface layer damage was also characterized by a large plastic strain, a large amount of strain-induced martensite transformation, and a relatively suppressed micro-crack/void formation, which resulted from an annealed martensite matrix and a large quantity of retained austenite. The excellent stretch-flangeability of TBF steel might be caused by the suppressed micro-crack/void formation and high crack propagation/void connection resistance. The next high stretch-flangeability of TAM steel was associated with a small-sized micro-crack/void initiation and high crack growth/void connection resistance. Full article

A suitable heat treatment in the Mg₉₇Gd₂Zn₁ (at.%) alloy in the as-cast condition results, after extrusion at high temperature, in a two-phase lamellar microstructure consisting of magnesium grains with thin lamellar shape precipitates and long fibers of the 14H-Long-Period Stacking Ordered (LPSO) phase elongated in the extrusion direction. The magnesium matrix is not fully recrystallized and highly oriented coarse non-dynamically recrystallized (non-DRXed) grains (17% volume fraction) elongated along the extrusion direction remain in the material. The deformation mechanisms of the extruded alloy have been studied measuring the evolution of the internal strains during in situ tension and compression tests using synchrotron diffraction radiation. The data demonstrate that the macroscopic yield stress is governed by the activation of the basal slip system in the randomly oriented equiaxed dynamic recrystallized (DRXed) grains. Non-DRXed grains, due to their strong texture, are favored oriented for the activation of tensile twinning. However, the presence of lamellar-shape precipitates strongly delays the propagation of lenticular thin twins through these highly oriented grains and they have no effect on the onset of the plastic deformation. Therefore, the tension–compression asymmetry is low since the plasticity mechanism is independent of the stress mode. Full article

Blast furnace (BF) ironmaking is a key process in iron and steel production. Because BF ironmaking is a dynamic time series process, it is more appropriate to use a recurrent neural network for modeling. The long short-term memory (LSTM) network is commonly used to model time series data. However, its model performance and generalization ability heavily depend on the parameter configuration. Therefore, it is necessary to study parameter optimization for the LSTM model. The sparrow search algorithm (SSA) holds advantages over traditional optimization algorithms in several aspects, such as no need for prior knowledge, fewer parameters, fast convergence, and high scalability. However, the algorithm still faces some challenges, such as the tendency to become trapped in the local optimum and the imbalance between global search ability and local search ability. Therefore, on the basis of SSA, this study examined the Levy flight strategy, sine search strategy, and step size factor adjustment strategy to improve it. This algorithm, improved by three strategies, is called the improved sparrow search algorithm (ISSA). Then, the ISSA-LSTM model was established. Furthermore, considering the limitations of SSA in dealing with multi-objective problems, the fast non-dominated sorting genetic algorithm (NSGAII) was introduced, and the ISSA-NSGAII model was established. Finally, experimental validation was performed using real blast furnace operation data, which demonstrated the proposed algorithm’s superiority in parameter optimization for the LSTM model and prediction for real industrial data. Full article

Estimates of physical and mechanical characteristics of materials at high strain rates play a key role in enhancing the accuracy of prediction of the stress–strain state of structures operating in extreme conditions. This article presents the results of a combined experimental–numerical study on the mechanical response of a thin-sheet rolled Ti-5Al-2.5Sn alloy to dynamic penetration. A specimen of a titanium alloy plate underwent punching with a hemispherical indenter at loading rates of 10, 5, 1, and 0.5 m/s. The evolution of the rear surface of specimens and crack configuration during deformation were observed by means of high-speed photography. Numerical simulations were performed to evaluate stress distribution in a titanium plate under specified loading conditions. To describe the constitutive behavior and fracture of the Ti-5Al-2.5Sn alloy at moderate strain rates, a physical-based viscoplastic material model and damage nucleation and growth relations were adopted in the computational model. The results of simulations confirm a biaxial stress state in the center of specimens prior to fracture initiation. The crack shapes and plate deflections obtained in the calculations are similar to those observed in experiments during dynamic punching. Full article

The mechanical characteristics and sliding friction behaviors of AA7075 samples were studied in regard to structural states formed in them by ECAP and depending on the ECAP pass number. In addition, the effect of a counterbody’s material on the tribological characteristics of the samples was investigated by the examples of AISI 52100 steel, alumina Al₂O₃ and silicon nitride Si₃N₄. Vibration acceleration and acoustic emission signals with parameters such as acoustic emission energy and median frequency were used for characterizing the sliding regimes. The structural state and mechanical properties of the ECAPed AA7075 samples significantly affected their wear behaviors in dry sliding. The counterbody material had a significant influence on the formation of a transfer layer and the subsurface deformation of samples. The dynamic behavior of the tribosystem was studied and the relationship between the sliding parameters, vibrometry and acoustic emission signals was established. Full article

Considering that Einstein’s relation between the diffusion coefficient and the drift mobility of free randomly moving charge carriers in homogeneous materials including metals is always valid, it is shown that the effective electric force acting on free electrons in metal depends on the ratio between the kinetic free electron energy at the Fermi surface to the classical particle energy 3 kT/2. The electrical resistivity of elemental metals dependence on very low temperatures has the quadratic term, which has been explained by electron–electron scattering. In this paper, it is shown that the quadratic term of the electrical resistivity at low temperatures is caused by scattering of the free randomly moving electrons by electronic defects due to linear effective free electron scattering cross-section dependence on temperature, but not by electron–electron scattering. Full article

As a recently developed high-strength aluminium alloy used specifically for laser additive manufacturing, AlMgMnSc alloy possesses superior mechanical properties and excellent processability. Extreme high-speed laser deposition (EHLD) is a novel surface-modification technique, which is characterised by high depositing speed, rapid cooling, rate and minimal dilution rate. To offer a new method for surface repairing high-strength aluminium alloys, an AlMgMnSc alloy coating, containing two deposition layers, is prepared on a 6061 aluminium-alloy axle using the EHLD technique. Meanwhile, the microstructure, composition distribution, and microhardness variation of the fabricated coating are studied. The results reveal that the coating is dense and crack-free, which is well-bonded with the substrate. Additionally, layer 1 is mainly composed of large columnar and equiaxed grains, while layer 2 consists of a fully equiaxed grain structure with an average grain size of about 4.5 μm. Moreover, the microhardness of the coating (about 104~118 HV) is similar to the substrate (about 105 HV), proving the feasibility of repairing high-strength aluminium alloys using AlMgMnSc alloy powders through the EHLD technique. Full article

While gas nitriding of steel is currently used in industry, nitriding of aluminum alloys remains an open challenge. The main obstacle is aluminum’s high susceptibility to passivation. The oxide film provides an effective barrier to nitrogen diffusion. Attempts to overcome this problem have mainly focused on glow discharge nitriding using cathode sputtering of an oxide layer. The produced AlN layers exhibit no diffusion zone and show limited performance properties. In this work, the effect of hybrid treatment aimed at producing diffusion layers of nitrides other than AlN on aluminum alloys was investigated on the model system of iron nitride–aluminum substrate. Hybrid treatment combines an electrochemical process involving the removal of the aluminum oxide layer from the substrate, its subsequent iron plating, and a further gas nitriding in high-purity ammonia. The obtained results prove that the hybrid treatment allows the production, at 530 °C/10 h, of diffusion layers of Fe₃N iron nitrides on aluminum substrates with a nitrogen diffusion zone range in aluminum of ca. 12 µm. In alloys containing magnesium, its unfavorable effect on the nitrogen diffusion and the functional properties of the layers was observed. An interesting direction for further research is hybrid treatment of precipitation-hardened alloys without magnesium. Full article

This purpose of this paper is to examine the relationship between crack growth equations based on Elber’s original plastic wake induced crack closure concept and the fatigue threshold as defined by the American Society for Testing and Materials (ASTM) fatigue test standard ASTM E647-15el. It is shown that, for a number of conventionally manufactured metals, the function U(R), where R is the ratio of the minimum to maximum applied remote stress, that is used to relate the stress intensity factor ΔK to the effective stress intensity factor ΔK_eff is inversely proportional to the fatigue threshold ΔK_th(R). This finding also results in a simple closed form equation that relates the crack opening stress intensity factor K_o(R) to ΔK, K_max, and the fatigue threshold terms ΔK_th(R) and ΔK_eff,th. It is also shown that plotting da/dN as function of ΔK/ΔK_th(R) would appear to have the potential to help to identify the key fracture mechanics parameters that characterise the effect of test temperature on crack growth. As such, for conventionally manufactured metals, plotting da/dN as function of ΔK/ΔK_th(R) would appear to be a useful addition to the tools available to assess the fracture mechanics parameters affecting crack growth. Full article

Micropores are one of the critical factors affecting materials’ performance and service life. As the need for a deeper understanding of micropore evolution and damage mechanisms grows, assessing the mechanical properties of materials containing micropores and predicting the lifespan of related metal structural components becomes increasingly complex. This paper focuses on the evolution process, regularities, and research methods of micropores in metal materials. Based on recent research and practical applications, the key stages of micropore evolution are discussed, encompassing nucleation, growth, coalescence, collapse, interaction, and the influence of other microstructures. Firstly, the advantages and limitations of commonly used characterization methods such as scanning electron microscopy, transmission electron microscopy, and X-ray computed tomography are introduced in the study of micropore evolution. Subsequently, critical theoretical models for micropore evolution, such as the Gurson model and its extensions, are summarized. By using a multiscale approach combining the crystal plasticity finite element method, dislocation dynamics, and molecular dynamics, the factors influencing the micropore evolution, such as external stress conditions, internal microstructures, and micropore characteristics, are specifically elaborated, and the basic physical mechanisms of micropore evolution are analyzed. Finally, a comprehensive review and summary of current research trends and key findings are provided, and a forward-looking perspective on future research directions is presented. Full article

The grain size of the full lamellae TiAl-based alloy changes from ~400 μm to ~40 μm through the precipitation of metastable structures by cyclic heat treatment. Based on this, two kinds of variant selection processes—coherent metastable γ variants precipitated during the air-cooling process and α_s variants precipitated during the holding at a single α phase region process—are identified to promote the formation of refined Type I and Type II coherent grain boundaries. The oxidation tests at 1000 °C for 100 h show that the formation of refined coherent grain boundaries can greatly improve oxidation resistance by inducing the continuous multi-layer protective barrier consisting of (Ti, (Nb, Ta))O₂, TiN, and Al(Nb,Ta)₂. This protective barrier inhibits the inward diffusion of oxygen and nitrogen. Full article

While conventional die manufacturing techniques often lead to limitations in production speed and design intricacy due to labour-intensive procedures like machining and casting, Additive Manufacturing (AM) emerges as a key player offering substantial potential for cost reduction and process improvement in mass production. This study benchmarks four leading Laser Powder Bed Fusion (L-PBF) systems for producing maraging steel (EN 1.2709) dies. Despite the shared material and technology, variations in dimensional accuracy, surface finish, and microstructure were observed among the maraging steel parts. SEM/EDS, EBSD, hardness testing, and dimensional analysis revealed system-specific performance differences. Additionally, select parts underwent heat treatment and tensile testing, demonstrating the impact of post-processing on mechanical properties. These results offer valuable guidance for industrial stakeholders considering AM, highlighting the importance of supplier selection and process optimisation for achieving consistent part quality and unlocking the full potential of AM technologies. Full article

In this study, the response surface method is used to develop a model for analyzing and optimizing zinc leaching experiments. An investigation into the leaching kinetics of smithsonite in ammonium citrate solution is also conducted. A model of kinetics is studied in order to represent these effects. The experimental data show that an increase in the solution temperature, concentration, and stirring speed has a positive impact on the leaching rate, while an increase in the particle size has a negative impact on it. The optimal experimental conditions consist of a leaching temperature of 70 °C, ammonium citrate concentration of 5 mol/L, particle size of 38 µm, and rotational speed of 1000 rpm. Under these optimal conditions, the leaching rate of zinc from smithsonite is 83.51%. It is speculated that the kinetic model will change when the temperature is higher than 60 °C. When the temperature is lower than 60 °C, the leaching process is under the control of the shrinking core model of the surface chemical reactions. The calculated activation energy of the leaching reaction is equal to 42 kJ/mol. The model of the leaching process can be described by the following equation: $1-{\left(1-\left.x\right)\right.}^{1/3}=\left[k_0\right.\cdot {\left(C\right)}^{0.6181}\cdot {\left(r_0\right)}^{-0.5868}\cdot {\left(SS\right)}^{0.6901}\mathit{exp}\left(-42/RT\right)]t$. This demonstrates that an ammonium citrate solution can be used in the leaching process of zinc in smithsonite as an effective and clean leaching agent. Full article

This paper presents a study on the effectiveness of two turbulence models, the large eddy simulation (LES) model and the k-ε turbulence model, in predicting mixing time within a ladle furnace using the computational fluid dynamics (CFD) technique. The CFD model was developed based on a downscaled water ladle from an industrial ladle. Corresponding experiments were conducted to provide insights into the flow field, which were used for the validation of CFD simulations. The correlation between the flow structure and turbulence kinetic energy in relation to mixing time was investigated. Flow field results indicated that both turbulence models aligned well with time-averaged velocity data from the experiments. However, the LES model not only offered a closer match in magnitude but also provided a more detailed representation of turbulence eddies. With respect to predicting mixing time, increased flow rates resulted in extended mixing times in both turbulence models. However, the LES model consistently projected longer mixing times due to its capability to capture a more intricate distribution of turbulence eddies. Full article

Conventional book casting of Sm₂TM₁₇-type alloys (where TM = Co, Fe, Cu, Zr) leads to a coarse, highly segregated microstructure, predominantly due to the slow, variable cooling rate from the mould surface towards the centre of the ingot. These cast alloys require a long homogenisation treatment to remove this segregation and develop a super-saturated, metastable SmTM₇-type hexagonal phase. This SmTM₇ phase is a vital precursor phase required during magnet production to develop the complex cellular structure responsible for high magnetic properties. In this work, strip casting was employed to facilitate rapid solidification to develop thin flakes (<0.5 mm thick) with a columnar grain structure. Rapid cooling has the potential to produce a homogenous microstructure consisting predominantly of the metastable SmTM₇ phase. This could remove or significantly reduce the need for the energy-intensive homogenisation treatment usually required in conventional magnet manufacture. This paper investigates the effect of wheel speed (and hence cooling rate) on flake thickness, microstructure, and phase balance of the cast alloys. It was shown that for wheel speeds between 1.1 and 3.0 m/s, the microstructure showed large variation; however, in all cases, evidence of the columnar SmTM₇ phase was presented. The adhesion between the melt and the wheel was deemed to be critical for the nucleation and subsequent columnar growth of SmTM₇ grains, where the wheel speed controlled both the flow of the alloy onto the wheel and the thickness of the resultant flake. It was determined that in order to achieve a homogenous columnar SmTM₇ structure, the maximum flake thickness should be limited to 270 μm to avoid the formation of equiaxed Sm₂TM₁₇ grains through insufficient cooling. Full article

KR (Kanbara Reaction) desulfurization slag is a solid waste that is not sufficiently utilized. This is because the KR desulfurization slag contains 1–2.5% sulfur, which is directly used in steel smelting to increase the sulfur content in molten steel. Therefore, the possibility of oxidation desulfurization of KR desulfurization slag was studied in this study. Experiments were conducted to investigate the possibility of removing sulfur from used KR (Kambara Reaction) slag with oxidation. The KR slag samples were treated with oxidative desulfurization in the oxygen partial pressure range of 0.05 bar–1.00 bar, with a gas flow rate ranging from 2 L min⁻¹ to 6 L min⁻¹, and at a temperature of 1420 °C. X-ray diffraction (XRD), an infrared carbon sulfur analyzer, and scanning electron microscopy–energy dispersive X-ray spectrometry (SEM–EDS) analysis were used to reveal the oxidative desulfurization mechanism of KR desulfurization slag. At low oxygen pressure ($P_{{\mathrm{O}}_2}$ < 0.20 bar), the desulfurization rate of slag oxidized for 120 min increased with the increase in oxygen partial pressure. At high oxygen pressure ($P_{{\mathrm{O}}_2}$ ≥ 0.20 bar), the desulfurization rate of slag samples did not change with the change in oxygen partial pressure, and the desulfurization rate was higher than 93.5%. At low oxygen pressure ($P_{{\mathrm{O}}_2}$ < 0.20 bar), the residual sulfur in the slag after oxidation still existed in the slag as the CaS phase. At high oxygen pressure ($P_{{\mathrm{O}}_2}$ ≥ 0.20 bar), the residual sulfur in the slag oxidized from the CaS phase to the 11CaO·7Al₂O₃·CaS phase in the slag. The sulfur removal rate was directly correlated with the slag surface area and the flow rate of the reaction gas, and it increased with an increase in both surface area and gas flow rate. Full article

Surface modifications for titanium, a material of choice for dental implants, can greatly alter the surface micro/nanotopography and composition of implants, leading to notable enhancements in their hydrophilicity, mechanical properties, osseointegration performance, and antibacterial performance, as well as their impacts on osteoblast activity and bone formation processes. This article aims to update titanium surface modification techniques for dental implants from the past to the present, along with their effects on osteoblasts and bone formation, by thoroughly summarizing findings from published studies. Peer-reviewed articles published in English consisting of in vitro, in vivo, and clinical studies on titanium dental implant surface treatments were searched in Google Scholar, PubMed/MEDLINE, ScienceDirect, and the Scopus databases from January 1983 to December 2023 and included in this review. The previous studies show that implant surface roughness, condition, and hydrophilicity are crucial for osteoblast adhesion and growth. While various techniques enhance osseointegration comparably, one of the most common approaches to accomplishing these properties is sandblasting large-grit acid etching surface treatment and coating with hydroxyapatite or chitosan. In conclusion, this review points out the efficacy of different subtraction and addition techniques in enhancing the surface properties of titanium dental implants, promoting favorable outcomes in terms of osteoblast activity and bone formation in various degrees. However, most existing studies predominantly compare treated and non-treated titanium, revealing a need for more comprehensive studies comparing the effects of various modification techniques. Moreover, further investigation of factors playing a role in the dynamic osseointegration process in addition to osteoblasts and their functions, as well as improved surface modification techniques for the treatment of compromised patients, is greatly required. Full article