Search Results (110)

A 2014Al matrix composite reinforced with 0.8 wt.% graphene nanoplatelets (GNPs) was prepared by pre-dispersion and ultrasonic melt casting. Subsequently, the as-cast 2014Al-GNP composite was subjected to hot extrusion under different parameters, followed by a comparative analysis of the microstructure and properties of the various alloys. Microstructure and phase composition of the prepared samples were characterized using OM, SEM, EDS, EBSD and TEM inspections. The results indicate that the addition of GNPs effectively promoted the refinement of the as-cast matrix alloy microstructure, while hot extrusion with appropriate parameters further refined the microstructure of the as-cast matrix alloy. At an extrusion ratio of 16, the Al₂Cu, Al₂CuMg, and GNPs in the microstructure displayed a band-like distribution along the extrusion direction, with reduced size and enhanced uniformity. Concurrently, the dislocation density and Kernel Average Misorientation (KAM) values of the composite increased significantly, dynamic recrystallization intensified, and the texture was further enhanced. The tensile strength reached 572.1 MPa, hardness was 369.6 HV, and elongation was 11.9%, representing improvements of 89.0%, 92.0%, and 142.9%, respectively, compared to the as-cast matrix alloy. Fracture surface analysis exhibited brittle fracture characteristics in the matrix alloy, while the extruded composite with optimal parameters displayed distinct ductile fracture features. In the extruded aluminum matrix composite, the interface between GNPs and the matrix was clean, with mutual diffusion of Al and C atoms, achieving an excellent interfacial bonding state. The significant enhancement in mechanical properties of the extruded alloy was primarily attributed to grain refinement strengthening, dislocation strengthening, and load transfer strengthening by GNPs. Full article

Solvent processing hampers the reliability and energy density of self-healing binders for energetic materials. We report a solvent-free curing route for a Diels–Alder self-healing furanyl-terminated polybutadiene enabled by a functional external plasticizer, dibutyl phthalate (DBP), which acts not only to lower the viscosity of the binder but to disperse the high-melting bismaleimide, thereby driving crosslinked network formation. The 50 wt% DBP-plasticized film healed a pre-cut crack in 5 min at 120 °C and recovered nearly full mechanical properties after 24 h at 60 °C. Based on this binder system, a self-healing solid propellant with 80 wt% solid content was solvent-free cast into a dense and void-free grain that healed surface cracks within 5 min at 120 °C. This solvent-free approach overcomes the limitations of solvent-based processing and offers a viable fabrication route for self-healing energetic materials. Full article

HVAF WC-10Co-4Cr coating has been applied to the extreme wear protection of lightweight titanium alloy workpieces. However, the new generation of lightweight titanium alloy inner bore wear-resistant workpieces is faced with strong wear and instantaneous high-temperature airflow erosion during service, which requires a WC-10Co-4Cr wear-resistant coating with low surface roughness, high thickness and high toughness. In addition, its small diameter inner hole also requires the rapid heating, melting and acceleration performance of sprayed powder during spraying. At present, the finest spraying powder used in this system is generally in the range of 5–15 μm, which faces difficulties in meeting the above requirements. In order to solve this problem, the preparation of 2–10 μm spherical spray powder was studied though a spray granulation experiment, and the change law of powder morphology with the solid content of pre-spray slurry was explored. The suitable binder was selected through a slurry sedimentation test and viscosity test, so that the gunable solid content of the pre-sprayed slurry was reduced from 60 wt.% to 12.5% by weight, which significantly reduces the particle size of the powder obtained by spray granulation. When the solid content of pre-sprayed slurry is 12.5 wt.%, sodium carboxymethyl cellulose (CMC-Na) is selected as the binder, and the binder content is 2 wt.%, the particle size range of powder obtained by spray granulation process reaches 2–10 μm, and the median particle size reaches 5 μm. After heat treatment, the powder is spherical and dense inside. The research results provide technical support for preparing high-performance ultrafine WC-10Cr-4Co spherical powder with wear-resistant coating for light titanium alloy. Full article

Structure and nonlinear spectra of the basal surface of ice Ih were investigated by molecular dynamics simulations. At a temperature significantly lower than the melting temperature $T_m$, the ice structure at the interface is only weakly perturbed by the presence of surface. The computed nonlinear spectrum of the interface well agrees with the experimental data and the results of the calculations provide the molecular-level interpretation of spectral features. In particular, the ice surface specific positive peaks in the Im[${\chi }^{\left(2\right)}$] spectrum at ∼3180 cm⁻¹ and at ∼3420 cm⁻¹ were found to result from the low- and high-frequency vibrational modes of quadruply H-bonded surface molecules, respectively. The spectrum of the crystalline ice interface is significantly affected by intermolecular interactions. Upon increasing the temperature, the structural disorder extends to the second water bilayer. The thickness of the premelted water layer of 6–8 Å can be estimated at the temperature by ca. 5 K below $T_m$. The increase in the temperature results in a change in the intensity and shape of the nonlinear spectrum of the ice Ih interface. The changes can be explained by the interconversion between different H-bonded surface species and by an increase in disordering of water molecules that reduces strength of intermolecular interactions. Results of the present work contribute to our understanding of the structure–spectrum relationship of the ice/air interface, and shed light on the origins of features in the nonlinear spectra of the system. Full article

This study develops a machine learning potential (MLP) based on the Moment Tensor Potential (MTP) method for the TaN-Ce system. This potential is employed to investigate the interfacial structure and wetting behavior between liquid Ce and solid TaN. Molecular dynamics (MDs) simulations reveal that liquid Ce exhibits significant wetting on the TaN surface at high temperatures. The interfacial region undergoes pre-melting and component interdiffusion, forming an amorphous transition layer. Nitrogen atoms display high diffusivity, leading to surface mass loss, while tantalum atoms demonstrate excellent thermal stability and penetration resistance. These findings provide theoretical support for the design of interfacial materials and corrosion control in high-temperature metallurgy. Full article

Snow cover constitutes a medium that can be used as a way of assessing air pollution. The chemical composition of snow layers from the same snowfall event reflects the composition of atmospheric aerosols and dry precipitates, depending on the properties of the adsorbing surface and prevailing weather conditions. Analyzing snow samples provides reliable insights into anthropogenic pollution accumulated in soil and groundwater of different land use type areas, as well as allows the evaluation of the degree and sources of environmental pollution. The aim of the research was to determine the distribution of polycyclic aromatic hydrocarbons in various sites of Zawoja village and identify their possible sources and factors influencing their differentiation. A total of 15 surface snow samples of the same thickness and snowfall origin were collected from different locations in the village in the winter of 2024. The samples were pre-concentrated by solid phase extraction and analyzed by gas chromatography—tandem mass spectrometry. The sampling set was invented, and the extraction procedure and analysis parameters were optimized. A spatial distribution map of PAHs was created. The contamination of ∑16PAHs varied from 710 to 2310 ng/L in melted snow with the highest concentrations detected in Zawoja Markowa by the border of the Babia Góra National Park, which is interpreted mainly as a result of the topographical setting. Medium molecular weight PAHs were the dominant fraction, which, combined with specific PAH ratios, indicate the combustion of biomass and coal as the main source of contamination. Full article

Parts fabricated by laser powder bed fusion (LPBF) contain oxide inclusions, which can be detrimental to fatigue resistance. Under typical LPBF conditions, the atmosphere contains enough oxygen to oxidize reactive elements such as aluminum and titanium, forming oxides in the parts. In this work, mechanisms of oxide formation and oxide alteration were studied by laser-remelting the surfaces of bulk specimens of IN718 and AlSi10Mg, without the addition of metal powder. Calculations based on the mass transfer of oxygen to the melt pool surface indicated that direct oxidation of the melt pool did not play a major role. Rather, both the oxidation of hot spatter and reworking of the pre-existing oxide affected the concentration and morphology of oxides on the metal surface. Full article

Residual stress (RS) is one of the main reasons for component failure during an additive manufacturing (AM) process, especially using selective laser melting (SLM) technology. This paper reviews RS’s investigation methods, formation mechanisms and regularities of distribution. When considering recent research progress, studies indicate that the dominant stress is primarily attributed to thermal stress induced by significant laser temperature gradients during the rapid melting and forming process, which subsequently transforms into RS upon cooling to room temperature, as verified by simulation and experiments. Then, the distribution regularities of RS are analyzed. SLM RS gradually increases when it is measured from the surface layer to the substrate. In the plane direction, at the center and edge of the part, tensile stresses are found; as for the middle area, which is the transition area of compressive stress, the whole plane stress remains in an equilibrium state. Based on the forementioned conclusions, the three-dimensional distribution diagram of RS on the sample was constructed. Finally, the strategic approaches for stress mitigation are briefly discussed. The excessive stress in forming can be reduced by process parameter matching, and the RS can be greatly remitted by pre-treatment/post-treatment, so as to improve the quality of formed parts. This review provides a valuable theoretical basis for practical applications of SLM. Full article

While self-healing of metals and alloys facilitated by electromagnetic pulse (EMP) energy introduced by electropulsing has been widely reported, the in-depth mechanism is still ambiguous. Here, an approximate in-situ observation was designed to explore the effect of EMP energy induced by electropulsing on the alloy interface self-healing. Electromagnetic shocking treatment (EST) utilizing EMP energy was demonstrated to promote metallic interface bridging and self-healing. At local regions, flat surfaces turn into wavy ones, especially, while local interface bridging and self-healing are commonly observed, indicating a nonlinear surface pre-melting. Based on the assumed mass–spring–damping system of the pre-melted interfaces, the mechanisms of local interface bridging and self-healing under the EST are explored. This work provides new understanding about the interface self-healing mechanism by electropulsing, as well as new insights about the effect of pulse energy (such as EMP) on metallic interface complexion. Full article

This paper investigated and experimentally analyzed the penetration behavior of liquid copper along austenite grain boundaries (GBs) at high temperatures. The microstructure of the liquid copper channel network along GBs and triple junctions (TJs), as well as the TJ wetting, was observed and interpreted through diffusion-controlled premelted GB formation. The concentration distribution results along GBs show that copper diffusion in both the near-surface premelted GBs and the non-surface-layer solid-state GBs conform to the diffusion equation, though the diffusion coefficients differ by approximately one order of magnitude. However, the copper concentration at premelted GBs cannot be fully described by an error solution. Using a modified diffusion equation when considering the concentration dependence of the GB diffusion coefficient provides a more accurate description, aligning better with experimental characteristics. Electron backscatter diffraction measurements indicate that the copper orientation at premelted GBs remains consistent with that of surface copper coating, whereas that at solid-state GBs undergoes significant changes. This finding is consistent with the argument that the corresponding material states at premelted GBs are different from those at solid-state GBs, thus providing experimental evidence for the diffusion equation solutions presented above. It provides a theoretical reference for understanding and preventing liquid metal embrittlement. Full article

Gas hydrate systems display complex structural arrangements in their bulk and interfacial configurations. Controlling nucleation and growth in the context of potential applications requires a characterization of these structures such that they can be manipulated at the atomic and molecular scale to fine tune macroscale applications. This work uses molecular dynamics to show the different methods of identifying interface location and thickness, the drawbacks of certain methods, and proposes improved methodology to overcome sampling issues. We characterize the interfacial position and thickness using structure and dipole-based methods at different conditions for water/sII natural gas hydrate mixtures. We find that phases with similar densities are particularly sensitive to the regression technique employed and may not resolve the thickness of the complex pre-melting layer adequately, while the dipole moments may provide better resolution. The dipole shows the complex natural of the small and compressed layer that presents on the hydrate surface. These results show that the interface is thin but dynamic and careful characterization required analysis of multiple molecular phenomena. Full article

The present study was focused on assessing the molten salt-induced hot corrosion resistance of selective laser melting (SLM) manufactured Inconel 625 at 900 °C for 96 h and investigating the possibility of improving the superalloy’s corrosion resistance by applying a pre-oxidation heat treatment. The material’s hot corrosion properties were assessed in a heat-treated state (heat treatments performed at 1000 °C/1 h and 1150 °C/1 h, respectively) with and without pre-oxidation. The heat treatment at 1000 °C promoted the columnar dendrite morphology evolution, while the heat treatment at 1150 °C promoted the equiaxed dendrite morphology evolution. At 1150 °C, microstructural features specific to conventional manufactured material developed (annealing twin boundaries). They are considered a sign of anisotropy reduction due to equiaxed grains forming and it is believed that the internal stress in the material is reduced. High-temperature pre-oxidation heat treatment at 900 °C for 96 h ensured the formation of protective oxide scales with a reduced thickness (1.74 μm in the case of samples’ heat-treated at 1000 °C, and 2.22 μm in the case of samples’ heat-treated at 1150 °C, respectively). Experimentally, based on weight gain and oxide scale analysis, it was proven that pre-oxidation can improve the hot corrosion resistance of SLM manufactured Inconel 625 by forming a stable and protective oxide scale on the surface of the alloy before exposure to molten salts. The preformed oxide layer acts as a barrier for the corrosive species, reducing the formation of detrimental compounds, especially Mo-rich sulfides. Based on the tests, an improvement in corrosion resistance of up to 33.94% was observed in samples heat-treated at 1150 °C with pre-oxidation compared to samples heat-treated at 1000 °C without pre-oxidation. Full article

Laser welding (sealing) is a promising technology for joining metal to glass, but it shows poor joint strength in existing studies. This study conducted the laser sealing of a 304 stainless steel alloy to high-alumina glass using pre-oxidation and laser surface melting as an interlayer. The present investigation aimed to determine the influence of this surface modification strategy on the mechanical behavior of glass-to-metal sealing joints made via laser welding. An experimental campaign was conducted on 304 stainless steel and high-alumina glass. Pre-oxidation and laser surface melting treatment were performed on the 304 steel alloy surface before joining to improve the mechanical interlock and chemical bonding between the substrates. The microstructures of the 304 steel alloy/glass interface were investigated by using scanning electron microscopy (SEM) and an energy-dispersive spectrometer (EDS), and the interface evolution mechanism and the correlation between the steel/glass joining strength and the interface morphology were discussed. Finite element analysis software simulated the temperature field and stress field in the welding process, and the reasons for the differences in the welding strengths of different surface treatment samples were analyzed in depth. The results showed that the laser surface melting strategy used significantly influenced the mechanical behavior of the joints and the failure mode. Adopting a higher number of scans improved the mechanical interlock and, consequently, the mechanical behavior of the joints. Full article

The difference in the crystallization kinetics during growth from the melt between II–VIs (CdTe, Cd_1−xZn_xTe, ZnSe, and ZnTe) and III–Vs (GaAs and InP) is discussed. At the melt growth of II–VI crystals, the most important difference is the lack of controllability of seeding and achievement of a desired growth orientation. A pronounced tendency of self-orientation toward <111>, <110>, and sometimes <112> and <122>, but almost never toward <100> direction, has been observed regardless of whether a seed has been used or not. The main reason proves to be the tetrahedral coordination due to the high binding ratio of ionicity remaining in the II–VI melts but not occurring in III–Vs. As a result, the general effect of pre-ordering into density layers, forced by the solid surface, is in the II–VI liquids superimposed by a {111} self-orientation via tetrahedral in-plane alignment. Fitting growth kinetics seem to only be possible when this melt configuration conforms to the crystal structure, like the {111} but hardly the {100}. Otherwise, the liquid self-orientation determines the continuing crystal orientation. Additionally, an <100>-oriented seed abruptly changed into an <122> direction via a congruent twin plane. Although such considerations still need verifying atomistic simulations, they are helpful to optimize the growth methodology even for larger crystal diameters. Full article

The simulation of additive manufacturing has become a prominent research area in the past decade. Process physics simulations are employed to replicate laser powder bed fusion (L-PBF) manufacturing processes, aiming to predict potential issues through simulated data. This study focuses on calculating surface roughness by utilizing 3D surface topology extracted from simulated data, as surface roughness significantly influences part quality. Accurately predicting surface roughness using a simulation remains a persistent challenge. To address this challenge, the L-PBF technique with two different cases (pre- and post-contouring) was simulated using two-step process physics simulations. The discrete element method was utilized to simulate powder spreading, followed by the Flow-3D melting simulation. Ten layers were simulated at three different linear energy density (LED) combinations for both cases, with samples positioned at a 30-degree angle to accommodate upskin and downskin effects. Furthermore, a three-dimensional representation of the melted region for each layer was generated using the thermal gradient output from the simulated data. All generated 3D layers were stacked and merged to consolidate a 3D representation of the overall sample. The surfaces (upskin, downskin, and side skins) were extracted from this merged sample. Subsequently, these surfaces were analyzed, and surface roughness (Sa values) was calculated using MATLAB. The obtained values were then compared with experimental results. The downskin surface roughness results from the simulation were found to be within the range of the experimental results. This alignment is attributed to the fact that the physics simulation primarily focuses on melt pool depth and width. These promising findings indicate the potential for accurately predicting surface roughness through simulation. Full article