Search Results (24)

The interface between dispersed compound nanoprecipitates and metal substrates can act as effective hydrogen traps, impeding hydrogen diffusion and accumulation, thus mitigating the risk of hydrogen embrittlement and hydrogen-induced coating failure. In this study, we considered the precipitation of vanadium carbide (VC) and vanadium nitride (VN) nanoprecipitates on a body-centered cubic Fe (α-Fe) substrate in the Kurdjumov–Sachs (K–S) orientation relationship. To evaluate the stability and hydrogen trapping ability of the interface, we used the first-principles method to calculate the interfacial binding energy and hydrogen solution energy. The results show that the stability of the interface was related to the type and length of bonding between atoms at the interface. The interface zone and the interface-like Fe zone have the best hydrogen trapping effect. We found that hydrogen adsorption strength depends on both the Voronoi volume and the number of coordinating atoms. A larger Voronoi volume and smaller coordination number are beneficial for hydrogen capture. When a single vacancy exists around the interface region, the harder it is to form a vacancy, and the more unstable the interface becomes. In addition to the C vacancy at the Baker–Nutting relationship interface found in previous studies being a deep hydrogen trap, the Fe and V vacancies at the α-Fe/VC interface and the V and N vacancies at the α-Fe/VN interface in the K–S relationship also show deep hydrogen capture ability. Full article

This study systematically investigates the energy and electronic properties of Si-segregated θ′(Al₂Cu)/Al semi-coherent and coherent interface systems in Al-Cu alloys using ab initio calculations. By evaluating the bonding strength at the interface, it has been revealed that Si segregated at the A1 site (Al slab) of the semi-coherent interface systems exhibits the most negative segregation energy, resulting in a noticeable decrease in total energy and an increase in interface adhesion. The electronic structure analysis indicates the presence of Al-Cu and Al-Al bonds, with Si occupying the A1 site. The strong bond formation between Al-Cu and Al-Al is essential for improving interface bonding strength. The results of the calculating analyses are consistent with the results of the previous experiments, and Si can be used as a synergistic element to reduce the θ′/Al interface energy and further reduce the coarsening drive of the θ′ precipitated phase, which can provide new perspectives and computational ideas for the compositional design of heat-resistant Al-Cu alloys. Full article

In this study, the rolling process of the warm-rolled duplex-phase Mg–8.3Li–3.1Al–1.09Si alloy and the strengthening mechanism of as-rolled Mg–Li alloy were investigated. The highest ultimate tensile strength (UTS, 323.66 ± 19.89 MPa) could be obtained using a three-pass rolling process with a 30% thickness reduction for each pass at 553 K. The strength of the as-rolled LAS831 alloy is determined by a combination of second-phase strengthening, grain refinement strengthening, dislocation strengthening, and load-transfer reinforcement. Of these factors, dislocation strengthening, which is caused by strain hardening of the α-Mg phase, can produce a good strengthening effect but also cause a decrease in plasticity. The Mg₂Si phase is broken up into particles or strips during the rolling process. After three passes, the AlLi particles were transformed into an AlLi phase, and the Mg₂Si particles and nanosized AlLi particles strengthened the second phase to form a hard phase. The average size of the DRXed β-Li grains decreased with each successive rolling pass, and the average size of recrystallized grains in the three-pass-rolled LAS831 alloy became as low as 0.27 μm. The interface between the strip-like Mg₂Si phase and the α-Mg phase is characterized by semicoherent bonding, which can promote the transfer of tensile and shear forces from the matrix to the strip-like Mg₂Si phase, thereby improving the strength of the matrix and thus strengthening the LAS831 alloy. Full article

High-carbon hardline steels are primarily used for the manufacture of tire beads for both automobiles and aircraft, and vanadium (V) microalloying is an important means of adjusting the microstructure of high-carbon hardline steels. Using scanning electron microscopy (SEM), X-ray diffraction (XRD), and transmission electron microscopy (TEM), the microstructure and precipitation phases of continuous cooled high-carbon steels were characterized, and the vanadium content, carbon diffusion coefficient, and critical precipitation temperature were calculated. The results showed that as the V content increased to 0.06 wt.%, the interlamellar spacing (ILS) of the pearlite in the experimental steel decreased to 0.110 μm, and the carbon diffusion coefficient in the experimental steel decreased to 0.98 × 10⁻³ cm²·s⁻¹. The pearlite content in the experimental steel with 0.02 wt.% V reached its maximum at a cooling rate of 5 °C·s⁻¹, and a small amount of bainite was observed in the experimental steel at a cooling rate of 10 °C·s⁻¹. The precipitated phase was VC with a diameter of ~24.73 nm, and the misfit between ferrite and VC was 5.02%, forming a semi-coherent interface between the two. Atoms gradually adjust their positions to allow the growth of VC along the ferrite direction. As the V content increased to 0.06 wt.%, the precipitation-temperature-time curve (PTT) shifted to the left, and the critical nucleation temperature for homogeneous nucleation, grain boundary nucleation, and dislocation line nucleation increased from 570.6, 676.9, and 692.4 °C to 634.6, 748.5, and 755.5 °C, respectively. Full article

Microstructure and mechanical properties of in situ Cu-7.7Nb microcomposite (MC) wires manufactured by cold drawing with intermediate heat treatment (HT) have been studied. The evolution of Nb filaments morphology under various steps of deformation and modes of intermediate HT have been studied by the SEM and TEM methods. According to X-ray analysis, internal microstresses accumulate in the niobium filaments of the drawn MC, leading to a decrease in ductility. After heat treatment, the ductility of the wire increases significantly, since the microstresses in the niobium decrease even at the lowest HT temperature. The strength of the composite decreases under the HT because of negative changes in morphology and interface density of Nb filaments. The <110>Nb texture is stable under the HT up to 800 °C. The Nb filaments morphology and semi-coherent boundaries at Cu/Nb interfaces are restored under the post-HT cold drawing, leading to a sharp increase in the strength of the MC wire. Reducing the niobium concentration to 7.7%Nb relative to the traditional MC with 16–20%Nb and the recovery of the wire ductility under the HT makes it possible to obtain long-scale high-strength microwires with an extremely small diameter of 0.05 mm and high ultimate tensile strength of 1227 MPa. Full article

Nanometric multilayers composed of immiscible Ag and Ni metals were investigated by means of molecular dynamics simulations. The semi-coherent interface between Ag and Ni was examined at low temperatures by analyzing in-plane strain and defect formation. The relaxation of the interface under annealing conditions was also considered. With increasing temperature, a greater number of atomic planes participated in the interface, resulting in enhanced mobility of Ag and Ni atoms, as well as partial dissolution of Ni within the amorphous Ag. To mimic polycrystalline layers with staggered grains, a system with a triple junction between a silver single layer and two grains of nickel was examined. At high temperatures (900 K and 1000 K), the study demonstrated grain boundary grooving. The respective roles of Ni and Ag mobilities in the first steps of grooving dynamics were established. At 1100 K, a temperature close but still below the melting point of Ag, the Ag layer underwent a transition to an amorphous/premelt state, with Ni grains rearranging themselves in contact with the amorphous layer. Full article

The formation of coarse primary Si is the main scientific challenge faced in the preparation of high-Si Al matrix composites. The SiC/Al-50Si composites are prepared by high pressure solidification, which allows the primary Si to form a SiC–Si spherical microstructure with SiC, while the solubility of Si in Al is increased by high pressure to reduce the proportion of primary Si, thus enhancing the strength of the composites. The results show that the high melt viscosity under high pressure makes the SiC particles almost “fixed” in situ. The SEM analysis shows that the presence of SiC in the growth front of the primary Si will hinder its continued growth and eventually form SiC–Si spherical microstructure. Through aging treatment, a large number of dispersed nanoscale Si phases are precipitated in the α-Al supersaturated solid solution. The TEM analysis shows that a semi-coherent interface is formed between the α-Al matrix and the nanoscale Si precipitates. The three-point bending tests shows that the bending strength of the aged SiC/Al-50Si composites prepared at 3 GPa is 387.6 MPa, which is 18.6% higher than that of the unaged composites. Full article

The effect of proton irradiation on the structure, phase composition, defect state and nanohardness of Zr/Nb nanoscale multilayer coatings was investigated. Preservation of the Zr/Nb layered structure with 50 and 100 nm thick layers, was observed after irradiation with protons at 1720 keV energy and 3.4 × 10¹⁵, 8.6 × 10¹⁵ and 3.4 × 10¹⁶ ions/cm² fluences, and the interfaces remained incoherent. In the Zr/Nb nanoscale multilayer coatings with individual layer thicknesses of 10 and 25 nm, there were insignificant fluctuations in interplanar distance, which were influenced by changes in irradiation fluence, and the interfaces were partially destroyed and became semicoherent. Changing irradiation fluence in the investigated ranges led to a decrease in the nanohardness of the Zr/Nb nanoscale multilayer coatings with individual layer thicknesses of 10–50 nm. Variable-energy positron Doppler broadening analysis revealed that these changes are primarily caused by peculiarities of the localization and accumulation of the embedded ions and do not cause a significant increase in the S-parameters of Zr/Nb nanoscale multilayer coatings with a layer thickness less than 100 nm. Full article

Clarifying the deformation behaviors of microstructures could greatly help us understand the precipitation-strengthening mechanism in alloys. However, it is still a formidable challenge to study the slow plastic deformation of alloys at the atomic scale. In this work, the phase-field crystal method was used to investigate the interactions between precipitates, grain boundary, and dislocation during the deformation processes at different degrees of lattice misfits and strain rates. The results demonstrate that the pinning effect of precipitates becomes increasingly strong with the increase of lattice misfit at relatively slow deformation with a strain rate of 10⁻⁴. The cut regimen prevails under the interaction between coherent precipitates and dislocations. In the case of a large lattice misfit of 19.3%, the dislocations tend to move toward the incoherent phase interface and are absorbed. The deformation behavior of the precipitate-matrix phase interface was also investigated. Collaborative deformation is observed in coherent and semi-coherent interfaces, while incoherent precipitate deforms independently of the matrix grains. The faster deformations (strain rate is 10⁻²) with different lattice misfits all are characterized by the generation of a large number of dislocations and vacancies. The results contribute to important insights into the fundamental issue about how the microstructures of precipitation-strengthening alloys deform collaboratively or independently under different lattice misfits and deformation rates. Full article

The traditional Ag nanowire preparation means that it cannot meet the demanding requirements of photoelectrochemical devices due to the undesirable conductivity, difficulty in compounding, and poor heat resistance. Here, we prepared an Ag nanonetwork with superior properties using a special template method based on electrospinning technology. The transparent conductive films based on Ag nanonetworks have good transmittance in a wide range from ultraviolet to visible. It is important that the films have high operability and are easy to be compounded with other materials. After compounding with high-melting-point W metal, the heat-resistance temperature of the W/Ag composite transparent conductive films is increased by 100 °C to 460 °C, and the light transmission and electrical conductivity of the films are not significantly affected. All experimental phenomena in the study are analyzed theoretically. This research can provide an important idea for the metal nanowire electrode, which is difficult to be applied to the photoelectrochemical devices. Full article

The demand for high-strength aluminum alloys for the laser powder bed fusion (LPBF) process is still growing. However, to date, the crack susceptibility of conventional alloys as well as the high prices for specially developed alloys are the main obstacles for the use of high-strength aluminum alloys for LPBF. In this paper, crack-free LPBF samples with a relative density >99.9% were processed from AlMgSi1Zr (6182 series alloy) powder, to which 0.5 wt.-% Zr and 0.5 wt.-% Ti were added via mechanical mixing. No hot cracks were found in the µCT scans. Moreover, a fully equiaxed microstructure with a mean size of the α-Al grains of 1.2 µm was observed in the as-built parts. Al₃(Zr,Ti) particles were observed, acting as efficient heterogeneous grain refiners for α-Al by building a semi-coherent interface. Unmolten Ti and Zr particles with sizes up to 80 µm were found in the α-Al phase. The resulting fine-grained microstructure led to a tensile strength of 329 ± 4 MPa and a total elongation at a break of 11.4 ± 0.9% after solution heat treatment, quenching in water, and subsequent artificial ageing. Full article

Carbonized polymer dots (CPDs) have been paid a lot of attention by researchers because of their excellent properties due to their unique structure. However, few studies have researched the impact of the CPD structure on composite applications. Herein, CPD and heat-treated CPD (h-CPD) are used to fabricate a reinforced Cu matrix composite. There was a semi-coherent interface between h-CPD and Cu. However, functional groups and polymer chains of CPDs decomposed during heat treatment, weakening the mechanical and electrical properties of the composites. These findings show that CPD structural integrity is vital to composites. Full article

Objectives: to quantitatively analyze macrophage-like cells (MLCs) at the vitreoretinal interface in retinal vein occlusion (RVO) using swept-source optical coherence tomography angiography (SS-OCTA) and en face optical coherence tomography (OCT). Methods: The study included 72 RVO patients, with 43 acute patients and 29 chronic patients. For a normal control, 64 fellow eyes were included. MLCs were visualized in a 5 μm en face OCT slab above the vitreoretinal interface centered on the fovea. After semi-automatic binarization and quantification, we evaluated the MLC count and density among groups. We also investigated the MLC density and distribution relative to retinal edema. Results: Morphological changes and congregation of MLCs appeared in RVO eyes. The MLC density of both the acute and chronic groups was significantly higher than that of the control eyes (p < 0.001). In the acute group, the MLC density of the edematous region was lower than both the non-edematous region (p < 0.001) and the whole image (p < 0.01). The MLC density in acute eyes was negatively correlated to central fovea thickness (CFT) (r = −0.352, p < 0.05). The MLC density in chronic eyes was positively correlated to CFT and mean retina thickness (MRT) (r = 0.406, p < 0.05; r = 0.412, p < 0.05, respectively). Conclusions: SS-OCTA is a viable and simple method for the characterization of MLCs at the vitreoretinal interface. A significant increase in the MLC density in both acute and chronic eyes implicates the activation and recruitment of MLCs in RVO and that the MLC density and distribution can be affected by retinal edema. Full article

Continuous innovation in the design of metallic materials is essential for further progress in aerospace, automotive, construction, and shipping. Fine grain strengthening is considered to increase the strength of metals without losing plasticity. However, many fabrication techniques are restricted to very small sizes. Recently, the introduction of in situ nanoparticles with coherent or semi-coherent interfaces in the metallic matrix achieves simultaneous enhancement of the strength and ductility of metallic materials. In this review, the focus is on fabrication techniques and the formation mechanism of nanoparticles and nanoclusters in metal materials. The effects of nanoparticles on grain refinement, inhibiting segregation, second phase, and inclusion refinement are discussed, and the mechanism of simultaneous improvement in the strength and ductility of nanostructured metal materials is briefly covered. Finally, we provide a summary and outline of the possible direction for further advances in this research field. Full article

Ferritic materials consisting of a disordered matrix and a significant volume fraction of ordered intermetallic precipitates have recently gained attention due to their favorable properties regarding high-temperature applicability. Alloys strengthened by Heusler-type precipitates turned out to show promising properties at elevated temperatures, e.g., creep resistance. The present work aims at developing a fundamental understanding of the microstructure of an alloy with a nominal composition of 60Fe–20Al–10Ni–10Ti (in at. %). In order to determine the microstructural evolution, prevailing phases and corresponding phase transformation temperatures are investigated. Differential thermal analysis, high-temperature X-ray diffraction, and special heat treatments were performed. The final microstructures are characterized by means of scanning and transmission electron microscopy along with hardness measurements. Atom probe tomography conducted on alloys of selected heat-treated conditions allows for evaluating the chemical composition and spatial arrangement of the constituent phases. All investigated sample conditions showed microstructures consisting of two phases with crystal structures A2 and L2₁. The L2₁ precipitates grew within a continuous A2 matrix. Due to a rather small lattice mismatch, matrix–precipitate interfaces are either coherent or semicoherent depending on the cooling condition after heat treatment. Full article