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High entropy alloys (HEAs) are promising multi-component alloys with unique combination of novel microstructures and excellent properties. However, there are still certain limitations in the fabrication of HEAs by conventional methods. Additive manufactured HEAs exhibit optimized microstructures and improved properties, and there is a significantly increasing trend on the application of additive manufacturing (AM) techniques in producing HEAs in recent years. This review summarizes the additive manufactured HEAs in terms of microstructure characteristics, mechanical and some functional properties reported so far, and provides readers with a fundamental understanding of this research field. We first briefly review the application of AM methods and the applied HEAs systems, then the microstructure including the relative density, residual stress, grain structure, texture and dislocation networks, element distribution, precipitations and the influence of post-treatment on the microstructural evolution, next the mechanical properties consisting of hardness, tensile properties, compressive properties, cryogenic and high-temperature properties, fatigue properties, creep behavior, post-treatment effect and the strengthening mechanisms analysis. Thereafter, emerging functional properties of additive manufactured HEAs, namely the corrosion resistance, oxidation behaviors, magnetic properties as well as hydrogen storage properties are discussed, respectively. Finally, the current challenges and future work are proposed based on the current research status of this topic.

High quality van der Waals chalcogenides are important for phase change data storage, thermoelectrics, and spintronics. Using a combination of statistical design of experiments and density functional theory, we clarify how the out-of-equilibrium van der Waals epitaxial deposition methods can improve the crystal quality of Sb2Te3 films. We compare films grown by radio frequency sputtering and pulsed laser deposition (PLD). The growth factors that influence the crystal quality for each method are different. For PLD grown films a thin amorphous Sb2Te3 seed layer most significantly influences the crystal quality. In contrast, the crystalline quality of films grown by sputtering is rather sensitive to the deposition temperature and less affected by the presence of a seed layer. This difference is somewhat surprising as both methods are out-of-thermal-equilibrium plasma-based methods. Non-adiabatic quantum molecular dynamics simulations show that this difference originates from the density of excited atoms in the plasma. The PLD plasma is more intense and with higher energy than that used in sputtering, and this increases the electronic temperature of the deposited atoms, which concomitantly increases the adatom diffusion lengths in PLD. In contrast, the adatom diffusivity is dominated by the thermal temperature for sputter grown films. These results explain the wide range of Sb2Te3 and superlattice crystal qualities observed in the literature. These results indicate that, contrary to popular belief, plasma-based deposition methods are suitable for growing high quality crystalline chalcogenides.

Cracking limits the formability of Mg-alloyed zinc coatings on steel substrates. Unfavorable crystal orientations and brittle microstructural components serve as the main sources of cracks in these coatings. In this study, we overcome the deformation-induced cracking and substantially enhance the formability of Zn-Al-Mg coatings by controlling their crystallographic texture. To demonstrate this, in-situ scanning electron microscopy uniaxial tensile tests and thorough orientation image microscopy have been employed. Ultimately, we validate our findings by implementing quantitative plastic deformation-based criteria, namely local strain hardening exponent and Schmid factor distributions within the examined coating microstructures. The approach and findings of the present work considerably resolve the long-lasting cracking problem of these coatings.

The effect of the mild detemplation method, based on Fenton chemistry (with and without previous solvent extraction), and calcination was evaluated by the drug uptake capacity of SBA-15 materials. A number of characterization techniques were applied for evaluation and comparison of the materials properties such as TGA, CNH, N-2 physisorption and Si-29 NMR. The mild Fenton detemplation method rendered a nearly pristine SBA-15 without structural shrinkage, low residual template, improved surface area, pore volume and silanol concentration. The drug (ibuprofen) adsorption experiments were carried out by solution immersion in powdery form. The mild detemplated samples experienced an enhanced uptake that could be explained by the enhanced density of silanols (mmol/g), originated from the absence of calcination in the Fenton approaches. (C) 2014 Elsevier B.V. All rights reserved.

The hydrogenation of a dichloromethane soluble fraction of flash pyrolysis oil (bio-oil, BO), obtained by treatment of BO with a water–dichloromethane solvent mixture, was investigated using a water-soluble homogeneous ruthenium catalyst (RuCl3·3H2O/tris(msulfonatophenyl)phosphine, TPPTS). The catalyst is active at mild conditions (

This work aimed at studying the effect of a Ti interlayer and the alloying with carbon and nitrogen of W-S-C(N) films on the mechanical and tribological properties. The W-S-C and W-S-N films were deposited by r.f. magnetron reactive sputtering with CH4 or N2 as reactive gases and analysed by high resolution electron microscopy techniques. The hardness showed an improvement with the addition of the alloying element, which was attributed to the densification of the morphology, the decrease of the grain size, and the precipitation of new phases harder than WS2. The formation of either TiC or TiN at the interface between the Ti interlayer and the W-S-C(N) films promoted the enhancement of adhesion in the alloyed films. These improvements led to an enhanced tribological behaviour, in particularly the lowering of the wear coefficients. http://www.sciencedirect.com/science/article/B6TW0-4G0YT89-1/1/43c87d747e277f938d8dff3f03dd5e34

The effectiveness of pyrolysis as a possible technique for disposing of CCA (chromium, copper and arsenic oxide)-treated wood was studied. A CCA-treated sample given an extra heat treatment at 450 degreesC for 10 min was thoroughly investigated in order to establish the details of the reaction in which arsenic is captured in the pyrolysis residue prior to volatilization. Composition and structure of the metal compounds in the pyrolysis residue were examined by transmission electron microscopy (TEM). A large number of particles were found of variable diameter between 10 and 100 nm. The smaller ones were mostly spherical, sometimes faceted. The larger ones were lumpy. CCA compounds and their reaction products like Cr2As4O12 and As2O3 were identified in conventional TEM by selected area electron diffraction. In high resolution, the nanoparticles exhibited lattice fringes as indication of their monocrystalline character, fitting, e.g., the d(210) = 0.204 nm of Cr. The volatility of arsenic during pyrolysis of CCA-treated wood was measured by XRF (X-ray fluorescence) analysis at temperatures up to 500 degreesC and at times up to I h. Weight change and arsenic content of the pyrolysis residue were measured after dissolution in HNO3. More than 20% of arsenic was already lost at 300 degreesC, which may have been caused mainly by the volatilization of the unreacted arsenic compound after reduction of As(V) in As2O5 to As(III) in As2O3. Arsenic is probably released as As4O6, which is very difficult to capture and toxic. By an additional heat treatment, this reduction can be prevented and the dry separation of the metals may be allowed. (C) 2003 Elsevier Science B.V. All rights reserved.

The microstructure of a TiB/Ti composite coating, obtained by laser cladding a Ti–6Al–4V substrate with a Ti/TiB2 powder mixture, was scrutinized using transmission electron microscopy. TiB showed three different morphologies: fine needles (200 nm diameter, 15 μm length); plates (thickness 1 μm, short length 3 μm and long length 15 μm); and coarse needles (diameter 3 μm and length of 50 μm). All TiB is composed of both the stable B27 and the metastable Bf crystal structures. Intimate mixing of B27 and Bf is possible because B27(200) planes fit excellently on Bf(110) or ( 1 1 0 ) planes (with B27[010]//Bf[001]) that easily leads to stacking disorder. Aspects of disorder are quantitatively analyzed using high-resolution transmission electron microscopy (HRTEM). Throughout the fine needles, extensive stacking disorder occurs. In the plates a core of B27 (with relatively low stacking-fault (SF) density) is present, with faulted Bf on the outer surfaces that has a rough but fully faceted interface with the Ti matrix. The coarse needles consist predominantly of nearly defect-free B27. It is noteworthy about the coarse needles that they have a large core composed of Ti. On a much finer scale Ti is also dispersed in the plates and fine needles. It will be shown that the differences in microstructure among the three types of TiB morphologies provide important clues about the evolution of the TiB under the conditions of rapid growth.

The continuous precipitation of D019 Co3W from a highly supersaturated Co-rich fcc matrix has been investigated. A detailed analysis of planar defects generated in the precipitates has been carried out using conventional and high-resolution transmission electron microscopy. The spatial arrangement of stacking faults and antiphase boundaries revealed the actual defect formation mechanisms and disclosed important aspects of the phase transformation at an atomic level. The results point to a displacive/diffusional Widmanstätten type of transformation, which is not simply based on a common ledge growth and, furthermore, follows the path: fcc→hcp→D019. The α' + Co7W6→Co3W peritectoid transformation has also been studied.

Three-dimensional atom-probe (3DAP) microscopy has been applied to the study of segregation at ceramic/metal (C/M) interfaces. In this article, results on the MgO/Cu(X) (where X = Ag or Sb) systems are summarized. Nanometer-size MgO precipitates with atomically clean and atomically sharp interfaces were prepared in these systems by internal oxidation. Segregation of the ternary component (Ag or Sb) at the MgO/Cu heterophase interface was enhanced by extended low-temperature anneals. Magnesia precipitates in the 3DAP reconstructions were delineated as isoconcentration surfaces, and segregation of each ternary component at the C/M interfaces was analyzed with the proximity histogram method developed at Northwestern University. This method allows the direct extraction of the Gibbsian interfacial excess of solute at the C/M interfaces from the experimental data. A value of (3.2+/-2.0) x 10(17)m(-2) at 500 degrees C is obtained for the segregation of Ag at a MgO/Cu(Ag) interface, while a value of (2.9+/-0.9) x 10(18) m(-2) at 500 degrees C is obtained for the segregation of Sb at a MgO/Cu(Sb) interface. The larger Gibbsian excess for Sb segregation at this ceramic/metal heterophase interface is most likely due to the so-called pdeltaV effect.

The objective of the present work is the in-situ study of the transformation of small oxide precipitates in a metal matrix by conventional and high-resolution transmission electron microscopy (HRTEM). As an example the reduction of Mn 3 O 4 into MnO for nano-sized oxide precipitates in a silver matrix was studied in detail. A convenient method for monitoring the reduction process is shown for a large number of precipitates simultaneously. It is based on two-beam dark-field images showing distinct Moire patterns for the MnO and the various types of Mn 3 O 4 precipitates embedded within an Ag matrix. A controlling factor of the transformation kinetics appeared to be the rate in which the system can relax the strains due to the accompanying volume reduction of the precipitates. Other interesting aspects of the Mn 3 O 4 to MnO transformation scrutinized and explained were the shape change of the precipitates upon reduction and the fact that mixed Mn 3 O 4 /MnO precipitates were only detected within a small temperature/time interval. Ostwald ripening of the MnO precipitates was observed as well.

Under appropriate aging treatments Ni–Sn supersaturated solutions (α') decompose at an advancing reaction front into alternating lamellae of Sn-depleted face-centered cubic (fcc) α and DO19 Ni3Sn. This precipitation and the typical defect structures generated within the DO19 compound were investigated by using conventional and high-resolution transmission electron microscopy (CTEM and HRTEM). Complete characterization of defects lying on the basal planes of Ni3Sn lamellae was achieved by HRTEM imaging and iterative digital image matching. The spatial arrangement of stacking faults, rotation interfaces and antiphase boundaries revealed important aspects of the defect formation mechanisms.

Transmission electron microcopy (TEM) revealed Mn 3 O 4 precipitates with two types of dominant shape in Pd–3 at.% Mn that was internally oxidized in air at 1000°C. One type is octahedrally shaped and bounded by {111} planes of the Mn 3 O 4 . These observations were compared with earlier observations in the Ag/Mn 3 O 4 system and the octahedrons show a relatively larger truncation by (002) in Pd than in Ag. Further, the second type of precipitate shape, comprising about 1/3 of all of the precipitates in Pd, was not observed in Ag. It corresponds to a plate-like structure, showing an orientation relationship where the tetragonal axes of Mn 3 O 4 are parallel to the cube axes of Pd, with the c -axis of Mn 3 O 4 as habit plane normal. High-resolution TEM observations revealed the presence of a square misfit dislocation network with line direction 〈110〉 and Burgers vector 1/2〈110〉 at these interfaces with (002)Mn 3 O 4 ‖{200}Pd. The general conclusions of the present analysis are: (1) the anisotropy in interface energy for oxide precipitates in a metal matrix is substantial due to the ionic nature of the oxide, giving well-defined shapes associated with the Wulff construction; (2) the influence of misfit energy on the precipitate shape as bounded by semi-coherent interfaces is important only if sufficient anisotropy in mismatch is present and if the matrix is sufficiently stiff; and (3) the stronger coupling strength due to electronic binding effects across the interface in Pd compared with Ag is responsible for formation of the dislocation network structures at larger misfit.