Additive manufacturing (AM), also known as 3D printing or rapid prototyping, is gaining increasing attention due to its ability to produce parts with added functionality and increased complexities in ...geometrical design, on top of the fact that it is theoretically possible to produce any shape without limitations. However, most of the research on additive manufacturing techniques are focused on the development of materials/process parameters/products design with different additive manufacturing processes such as selective laser melting, electron beam melting, or binder jetting. However, we do not have any guidelines that discuss the selection of the most suitable additive manufacturing process, depending on the material to be processed, the complexity of the parts to be produced, or the design considerations. Considering the very fact that no reports deal with this process selection, the present manuscript aims to discuss the different selection criteria that are to be considered, in order to select the best AM process (binder jetting/selective laser melting/electron beam melting) for fabricating a specific component with a defined set of material properties.
The lithium–sulfur (Li–S) battery is regarded as the most promising rechargeable energy storage technology for the increasing applications of clean energy transportation systems due to its remarkable ...high theoretical energy density of 2.6 kWh kg−1, considerably outperforming today's lithium‐ion batteries. Additionally, the use of sulfur as active cathode material has the advantages of being inexpensive, environmentally benign, and naturally abundant. However, the insulating nature of sulfur, the fast capacity fading, and the short lifespan of Li–S batteries have been hampered their commercialization. In this paper, a functional mesoporous carbon‐coated separator is presented for improving the overall performance of Li–S batteries. A straightforward coating modification of the commercial polypropylene separator allows the integration of a conductive mesoporous carbon layer which offers a physical place to localize dissolved polysulfide intermediates and retain them as active material within the cathode side. Despite the use of a simple sulfur–carbon black mixture as cathode, the Li–S cell with a mesoporous carbon‐coated separator offers outstanding performance with an initial capacity of 1378 mAh g−1 at 0.2 C, and high reversible capacity of 723 mAh g−1, and degradation rate of only 0.081% per cycle, after 500 cycles at 0.5 C.
A functional mesoporous carbon‐coated separator is developed for lithium–sulfur batteries, which exhibit significant enhancements in their performance: high capacities, long cycle life, and low capacity fading at different current rates. These improvements highlight the importance of the rational design of modified separators with mesoporous carbon structures and this proof of concept will bring reliability for advanced high‐performance lithium–sulfur batteries.
Cobalt-based metallic glasses have stimulated widespread interest due to their excellent mechanical properties and soft magnetic behavior. In the present work, a new Co51Fe15Hf6.5B27.5 glassy alloy ...was designed based on the ternary eutectic Co66Hf6.5B27.5 composition and its microstructure, thermal behavior and magnetic properties were examined. Partial substitution of Co with Fe in the new alloy systematically changes the crystallization behavior, enhances the fraction of complex (Co,Fe)21Hf2B6 phase upon crystallization and increases the extension of the supercooled liquid region from 26 K to 48 K. The improved thermal stability is in line with an increased activation energy of crystallization from 523 ± 20 kJ/mol for the Co66Hf6.5B27.5 glass to 573 ± 20 kJ/mol, corresponding to the Co51Fe15Hf6.5B27.5 glass. Magnetic studies revealed that the addition of Fe noticeably increases the saturation magnetization, Curie temperature, and slightly increases the coercive force from 19 A m2/kg to 57 A m2/kg, 315 K–515 K and 0.5 A/m to 1.5 A/m, respectively. It was found that the Co51Fe15Hf6.5B27.5 glassy ribbons exhibit a high resistance against milling-induced crystallization under cryogenic condition. The prepared cryomilled glassy particles show adequate thermal stability and thermoplastic forming ability for hot consolidation into a high density (96%) bulk metallic glass (BMG) with 10 mm diameter. The Co51Fe15Hf6.5B27.5 BMG exhibits a saturation magnetization of 57 A m2/kg, a Curie temperature of 527 K and a very low coercivity of 7 A/m, indicating its superior soft magnetic performance compared to most Co/Fe-based BMGs fabricated via powder metallurgy techniques. The evolution of microstructure, thermal behavior and magnetic properties upon cryomilling, hot consolidation and subsequent annealing was discussed.
•New Co–Fe-Hf-B bulk metallic glass (BMG) was prepared by powder metallurgy.•Iron addition increased thermal stability, saturation magnetization and Curie point.•The activation energy of crystallization was enhanced by iron addition.•The cryomilled glassy powders showed excellent thermoplastic forming behavior.•The new BMG exhibited very low coercivity and superior soft magnetic performance.
We propose a detailed mechanism for the growth of vertical graphene by plasma-enhanced vapor deposition. Different steps during growth including nucleation, growth, and completion of the ...free-standing two-dimensional structures are characterized and analyzed by transmission electron microscopy. The nucleation of vertical graphene growth is either from the buffer layer or from the surface of carbon onions. A continuum model based on the surface diffusion and moving boundary (mass flow) is developed to describe the intermediate states of the steps and the edges of graphene. The experimentally observed convergence tendency of the steps near the top edge can be explained by this model. We also observed the closure of the top edges that can possibly stop the growth. This two-dimensional vertical growth follows a self-nucleated, step-flow mode, explained for the first time.
The lithium–sulfur (Li–S) battery is one of the most promising candidates for the next generation of rechargeable batteries owing to its high theoretical energy density, which is 4- to 5-fold greater ...than those of state-of-the-art Li–ion batteries. However, its commercial applications have been hampered due to the insulating nature of sulfur and the poor cycling stability caused by the polysulfide shuttle phenomenon. In this work, we show that Li–S batteries with a mesoporous carbon interlayer placed between the separator and the sulfur cathode not only reduces the internal resistance of the cells but also that its intrinsic mesoporosity provides a physical place for trapping soluble polysulfides as well as to alleviate the negative impact of the large volume change of sulfur. This improvement of the active material reutilization allows one to obtain a stable capacity of 1015 mAh g–1 at 0.2 C after 200 cycles despite the use of a conventional sulfur–carbon black mixture as cathode. Furthermore, we observe an excellent capacity retention (∼0.1% loss per cycle, after the second cycle), thus making one step closer toward feasible Li–S battery technology for applications in electric vehicles and grid-scale stationary energy storage systems.
This study presents results of selective laser melting (SLM) processing of in situ Ti–TiB composites from optimally milled Ti–TiB2 powder. Optimized tuning of the SLM manufacturing parameters was ...applied to obtain almost fully dense (>99.5%) Ti–TiB composites. X-ray diffraction and electron diffraction patterns as well as microstructural investigations indicate a chemical reaction during SLM in which irregular-shape titanium diboride (TiB2) particles react with pure Ti to form needle-shape titanium monoboride (TiB) particles. Transmission electron microscopy investigations reveal that Ti grains are refined significantly due to the existence of B. The microhardness, yield stress and compressive strength of the SLM-produced Ti–TiB composites increase to 402 Hv, 1103MPa and 1421MPa, respectively, compared to 261 Hv, 560MPa and 1136MPa, respectively, for the SLM-produced commercially pure Ti. These improvements are mainly due to strengthening and hardening effects induced by TiB particles and refinement of Ti grains. Fractography analyses show that a mixture of splitting/shearing and smooth/rough zones covers the fracture surfaces of failed composite samples after compression testing.
Nanocomposites have the potential for novel material properties that significantly exceed the capabilities of their individual constituent phases, thereby enabling the exploration of gaps in material ...property charts. In this book, we aim to provide an overview of the current state of the art, enabling the investigation of novel structural and functional material properties through better understanding and implementation of nanocomposite design. The covered properties of interest encompass the whole material usage span, starting from the structural modifications of nanocomposites by employing different synthesis routes, to assessing their microstructure-dependent mechanical properties such as strength, ductility, and high-temperature stability. Furthermore, we address the functional characteristics of nanocomposites, such as soft magnetic properties or thermoelectricity, as well as tailored property adjustment through design strategies (bioinspired design, chemical sensitivity, bio sensing). Thus, the included contributions detail methods for the synthesis, characterization, modeling, and in-depth understanding of the mechanisms governing the outstanding properties of this fascinating material class.
The laser-based powder bed fusion (LBPF) process or commonly known as selective laser melting (SLM) has made significant progress since its inception. Initially, conventional materials like 316L, ...Ti6Al4V, and IN-718 were fabricated using the SLM process. However, it was inevitable to explore the possible fabrication of the second most popular structural material after Fe-based alloys/steel, the Al-based alloys by SLM. Al-based alloys exhibit some inherent difficulties due to the following factors: the presence of surface oxide layer, solidification cracking during melt cooling, high reflectivity from the surface, high thermal conductivity of the metal, poor flowability of the powder, low melting temperature, etc. Researchers have overcome these difficulties to successfully fabricate the different Al-based alloys by SLM. However, there exists no review dealing with the fabrication of different Al-based alloys by SLM, their fabrication issues, microstructure, and their correlation with properties in detail. Hence, the present review attempts to introduce the SLM process followed by a detailed discussion about the processing parameters that form the core of the alloy development process. This is followed by the current research status on the processing of Al-based alloys and microstructure evaluation (including defects, internal stresses, etc.), which are dealt with on the basis of individual Al-based series. The mechanical properties of these alloys are discussed in detail followed by the other important properties like tribological properties, fatigue properties, etc. Lastly, an outlook is given at the end of this review.
This work studied the preparation of starting powder mixture influenced by milling time and its effect on the particle morphology （especially the shape） and, consequently, density and compression ...properties of in situ Ti-TiB composite materials produced by selective laser melting （SLM） technology. Starting powder composite system was prepared by mixing 95 wt% commercially pure titanium （CP-Ti） and 5 wt% titanium diboride （TiB2） powders and subsequently milled for two different times （i.e. 2 h and 4 h）. The milled powder mixtures after 2 h and 4 h show nearly spherical and irregular shape, respectively. Subsequently, the resultant Ti-5 wt% TiB2 powder mixtures were used for SLM processing. Scanning electron microscopy image of the SLM-processed Ti-TiB composite samples show needle-shape TiB phase distributed across the Ti matrix, which is the product of an in-situ chemical reaction between Ti and TiB2 during SLM. The Ti-TiB composite samples prepared from 2 h and 4 h milled Ti-TiB2 powders show different relative densities of 99.5% and 95.1%, respectively. Also, the compression properties such as ultimate strength and compression strain for the 99.5% dense composite samples is 1421 MPa and 17.8%, respectively, which are superior to those （883 MPa and 5.5%, respectively） for the 95.1% dense sample. The results indicate that once Ti and TiB2 powders are connected firmly to each other and powder mixture of nearly spherical shape is obtained, there is no additional benefit in increasing the milling time and, instead, it has a negative effect on the density （i.e. increasing porosity level） of the Ti-TiB composite materials and their mechanical properties.
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