This paper obtained an additively manufactured high-strength Al-Li alloy by laser powder bed fusion (LPBF) based on a third generation AA2195 alloy powder raw material. The relationship between the process optimization, microstructure evolution, and mechanical properties of the as-printed (AP) and heat-treated (HT) specimens was established for the first time to explain the intergranular fracture sensibility during LPBF and reveal the dominant precipitation strengthening mechanism induced by the subsequent heat treatment. The precipitation order of AP Al-Li alloy at the last stage of the solidification process was: L (Liquid phase) →T2 (Al6CuLi3) + θ′(Al2Cu) + δ′/β′ (Al3(Li,Zr)) + T (LiAlSi) + Ω (AlCuMgAg). The micro-cracks caused by a relatively high grain boundary coverage of interconnected film-like eutectic phases, as well as micro-voids caused by the localized slip between the coarse T2-phases and soft precipitate-free zones, resulted in the high intergranular fracture sensibility. The well-designed T6 heat treatment of 515 °C/60 min solution treatment and 170 °C/6 h aging treatment was conducted to maximize the precipitation strengthening by T1-phases. The precipitation order of HT Al-Li alloy was supersaturated solid solution → GP zone + δ′/β′ → θ′ + T1 (Al2CuLi) + ω (Al7Cu2Fe) + β′. The presence of continuously distributed T1-cells along the grain boundaries was not only capable of providing a pinning effect on dislocations movement and boundary migration, but also able to shorten the pile-up distance on the slip plane. Such phenomena improved the resistance ability of Al-Li alloys to mechanical damage and permitted a significant strength enhancement.
The accurate detection of fiber bundle orientation is vital to ensure the mechanical performance of composite manufacturing. However, the weak texture, high reflectivity and non-contactable properties of fiber bundle surfaces present challenges for existing inspections. In this work, a novel measurement method based on binocular vision reconstruction technology is proposed to measure fiber bundle with high accuracy in a simple way. This approach includes a "coarse-to-fine" target-free stereo matching strategy to reduce the mismatch and enhance the reconstruction accuracy. The strategy is proven to match the homologous points correctly in the numerical simulation. Experiments in the filament winding results show the dimensional accuracy error is less than 0.3% and the winding angle deviation is 1°. As a conclusion, the proposed method is validated for its efficiency and high precision in obtaining fiber bundle trajectories and winding angles.
Liquid metals have garnered significant attention from researchers in recent years, which possess fascinating characteristics originating from their simultaneous metallic and liquid qualities. The great fluidity and conductivity make liquid...
Engineering applications of carbon nanofibers and nanotubes require their alignment in specific directions. Single-walled carbon nanotubes can be aligned in a magnetic field due to the presence of small amounts of catalyst elements, such as Ni and Co. However, for carbon nanofibers, their extremely low magnetic susceptibility is not sufficient for magnetically induced alignment. We present a method of solution-coating of NiO and CoO onto the surface of the carbon nanofibers. Due to the NiO- and CoO-coating, these nanofibers can be well aligned in the polymer composites under moderate magnetic field (3 T). Both transmission electron microscopy and scanning electron microscopy results show the well-aligned nanofibers in a polymer matrix. Mechanical testing shows a pronounced anisotropy in tensile strength in directions normal (12.1 MPa) and parallel (22 MPa) to the applied field, resulting from the well-aligned nanofibers in the polymer matrix. The mechanism of magnetic alignment due to coating of NiO and CoO on the nanofiber surface is discussed.
Ultrathin films of polystyrene were deposited on the surfaces of carbon nanofibers using a plasma polymerization treatment. A small percent by weight of these surface-coated nanofibers were incorporated into polystyrene to form a polymer nanocomposite. The plasma coating greatly enhanced the dispersion of the nanofibers in the polymer matrix. High-resolution transmission-electron-microscopy (HRTEM) images revealed an extremely thin film of the polymer layer (∼3 nm) at the interface between the nanofiber and matrix. Tensile test results showed considerably increased strength in the coated nanofiber composite while an adverse effect was observed in the uncoated composites; the former exhibited shear yielding due to enhanced interfacial bonding while the latter fractured in a brittle fashion.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Inorganic Crystal Structure Database, the world’s repository for inorganic crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the joint CCDC and FIZ Karlsruhe Access Structures service and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
We have developed a molecular mechanics approach to study surface modification and its effect on the mechanics of interfaces in nanocomposites. Investigation of this topic is motivated by the exceptional mechanical properties that have been demonstrated in a new generation of nanomaterials. The systems studied mainly include polystyrene polymers that are reinforced by carbon nanotubes subjected to different surface modifications. The interactions among the atoms in the system are governed by the empirical potentials in the form of force fields. To directly probe the interfacial mechanics, a nanotube pull-out test is simulated. The interfacial properties between the carbon nanotube and polystyrene matrix are evaluated from the numerical experiments under different surface modification conditions. The simulation results show that both the interfacial energy and interfacial shear stress can be improved significantly by introducing a functional group on the surface of the carbon nanotube. Interfacial strength up to 486 MPa can be achieved with the employed surface modification. The simulation also indicates the existence of an optimum functional ratio in terms of the energy barrier for interfacial sliding.
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