The fabrication of Ce3+-doped lutetium oxyorthosilicate (Lu2SiO5:Ce, LSO:Ce) scintillation ceramics was investigated by pressureless sintering starting from synthetic submicrometer polycrystalline LSO:Ce powder. It was found that translucent LSO ceramics were densified successfully with relative density of 99.5% under sintering condition of 1720 °C for 4 h. As-sintered LSO ceramics were pore-free with average grain size of 5 μm and exhibited a translucent state. The broad emission spectra centered at 419 nm of the LSO:Ce ceramics under vacuum ultraviolet (VUV) and UV excitation at room temperature. Under x-ray excitation, the overall emission intensity of obtained LSO ceramics achieved twice of that of bismuth germanium oxide (also known as bismuth germanate) single crystal at room temperature. Under excitation of 356 nm and emission of 420 nm, the luminescence decay time of the obtained LSO scintillation ceramics reached only 21.2 ns. The light yield of the LSO ceramics was 21,300 ph/MeV, which reached 91% of that of LSO single crystal.

Additive manufacturing technologies, also known as 3D printing, have demonstrated the potential to fabricate complex geometrical components, but the resulting microstructures and mechanical properties of these materials are not well understood due to unique and complex thermal cycles observed during processing. The electron beam melting (EBM) process is unique because the powder bed temperature can be elevated and maintained at temperatures over 1000 °C for the duration of the process. This results in three specific stages of microstructural phase evolution: (a) rapid cool down from the melting temperature to the process temperature, (b) extended hold at the process temperature, and (c) slow cool down to the room temperature. In this work, the mechanisms for reported microstructural differences in EBM are rationalized for Inconel 718 based on measured thermal cycles, preliminary thermal modeling, and computational thermodynamics models. The relationship between processing parameters, solidification microstructure, interdendritic segregation, and phase precipitation (δ, γ′, and γ″) are discussed.

High energy laser (HEL) systems are currently being evaluated for various land, sea, and air based platforms. Some of these systems operate in or have to withstand harsh environment of sand storm, hurricane, and rain. The exit aperture on a HEL system operating in harsh environment can become the single point of failure. Current HEL systems operating in 1–2 µm wavelength use fused silica windows which are at risk of damage in the theater. Rugged window materials such as sapphire, ALON, and spinel are currently being evaluated as a potential replacement. One of the major parameters in window selection apart from its ruggedness is its absorption loss coefficient at laser wavelength. This paper reports on 3 different methods to reduce absorption loss in spinel ceramic from 100,000 ppm/cm down to 75 ppm/cm. The results are compared with ALON and sapphire.

Using phase separation, alumina-based porous ceramics with three-dimensional frameworks were prepared, with fine structural roughness created by subsequent hot-water treatment. The pore volume of the porous alumina and its specific surface area increased concomitantly with increasing hot-water treatment time. Porous alumina/fluorinated oil bulk composites were prepared by coating hydrophobic silane onto the porous ceramic surface and subsequently impregnating fluorinated oil. A wetting ridge formed at the bottom of the water droplets on the composites. Partial contact between the water and solid surface was inferred from a comparison of interface energies in the system. The composites provided a smaller sliding angle (SA) than that of the sample without impregnating fluorinated oil. The composite with fine roughness exhibited longer sustainability of a small SA than that without fine roughness. Particle image velocimetry revealed that the dominant sliding mode for water droplets on this composite was slipping. The droplets moved on the surface under an external electric field. Coulombic force contributes to this motion.

Material extrusion 3D printing (ME3DP) based on fused deposition modeling (FDM) technology is currently the most commonly used additive manufacturing method. However, ME3DP suffers from a limitation of compatible materials and typically relies upon amorphous thermoplastics, such as acrylonitrile butadiene styrene (ABS). The work presented here demonstrates the development and implementation of binary and ternary polymeric blends for ME3DP. Multiple blends of acrylonitrile butadiene styrene (ABS), styrene ethylene butadiene styrene (SEBS), and ultrahigh molecular weight polyethylene (UHMWPE) were created through a twin screw compounding process to produce novel polymer blends compatible with ME3DP platforms. Mechanical testing and fractography were used to characterize the different physical properties of these new blends. Though the new blends possessed different physical properties, compatibility with ME3DP platforms was maintained. Also, a decrease in surface roughness of a standard test piece was observed for some blends as compared with ABS.

An attempt to reduce the effect of major toxic components namely phosphine ligands and unsaturated solvents as being used in conventional nanocrystal synthesis, has been made with a new binary ligand, and a reusable solvent N-octadecane for a smokeless and clean synthesis procedure. The optimized effects of the two ligands oleic acid and octadecyl amine on the nucleation rate and growth of CdSe nanocrystals (NCs) are reported and substantiated by AFM analysis. Oleic acid accelerates particle ripening and nuclei growth, but inhibits nucleation whereas octadecyl amine catalyses nucleation and very gradually improves growth to obtain small stable NCs. Another important feature of the present study is the replacement of 1-octadecene by a competitive N-octadecane as a solvent in such ligand mediated nanocrystal synthesis. The GCMS analysis reports a recovery of 95% of solvent after reuse, thus opening a scope for environmental friendly processes.

Indium-tin-oxide (ITO) thin films were prepared by reactive magnetron sputtering; their optical constants and thickness were determined by spectral reflectometry (SR) in the wavelength range from 400 nm to 800 nm and spectroscopic ellipsometry (SE) in the wavelength range from 191 nm to 1690 nm. A comparative evaluation of the measured data from SR and SE has been made using the same single layer optical model based on the Cauchy dispersion relation. The introduction of a surface roughness layer into the optical model considerably improved the fit quality during evaluation of SE data. Vertical inhomogeneity of the ITO thin films was assessed using a multilayer optical model describing porosity gradient and the three-layer optical model suggested by Jung [Y.S. Jung, Thin Solid Films467, 36 (2004)] from the SE data.

Bulk metallic glasses (BMGs) exhibit high yield strength but little tensile ductility. For this class of materials, damage tolerance is a key mechanical design parameter needed for their engineering use. Recently we have discovered a correlation between the local structural characteristics in the glass and the propensity for shear transformations. Based on the dependence of glass structure on alloy composition, zirconium (Zr)-rich Zr–titanium (Ti)–copper (Cu)–aluminum (Al) compositions are predicted to be more prone to spread-out plastic deformation and hence profuse shear banding. This structural perspective has guided us to locate a Zr61Ti2Cu25Al12 (ZT1) BMG that exhibits a record-breaking fracture toughness, on par with the palladium (Pd)-based BMG recently developed at Caltech. At the same time, the new BMG consists of common metals and has robust glass-forming ability. Interestingly, the ZT1 BMG derives its high toughness from its high propensity for crack deflection and local loading-mode change (from mode I to substantially mode II) at the crack tip due to extensive shear band interactions. A crack-resistance curve (R-curve) has been obtained following American Society for Testing and Materials (ASTM) standards, employing both “single-specimen” and “multiple-specimen” techniques as well as fatigue precracked specimens. The combination of high strength and fracture toughness places ZT1 atop all engineering metallic alloys in the strength–toughness Ashby diagram, pushing the envelop accessible to a structural material in terms of its damage tolerance.

The defense mechanism that nacre (mother-of-pearl) uses to protect its living organism against high-speed predatory attack can provide lessons for engineered armor design. However, the underlying physics responsible for nacre's dynamic energy dissipation has hitherto remained a mystery to be uncovered. Here we demonstrate a new energy dissipation mechanism hidden in nacre and activated only upon dynamic loading, where the crack terminates its propagation along nacre's biopolymer interlayers but straightly impinges the aragonite platelets (95 vol%) in a transgranular manner. This intergranular–transgranular transition promotes the fracture energy dissipation, far exceeding that of the currently-used engineered ceramics. The mechanistic origin accounting for the enhancement of fracture energy dissipation is attributed to the unique nanoparticle architectured aragonite platelets. The dynamic manifestation in nacre can inspire a new route to design stronger-and-tougher engineered ceramic armors.

Ultrasonic consolidation is a rapid manufacturing process for metal matrix composite (MMC) preimpregnated composite (prepreg) tapes or foils. One of the main advantages of this manufacturing technique over traditional MMC methods is the ability to produce multimaterial structures through the layer-by-layer build-up procedure. The interface of an ultrasonically consolidated bimaterial interface has not been studied on the nanometer scale through transmission electron microscopy (TEM), which can help better understand the bonding mechanisms. An ultrasonically consolidated copper–aluminum (Cu–Al) interface was explored through TEM, through which a 1-µm recrystallized subgrain region was observed on the aluminum side and dislocation pile-up was viewed between the subgrain and bulk aluminum interface. Phase changes were suspected due to varying contrast bands parallel to the Cu–Al interface and were confirmed through an x-ray energy dispersive spectroscopy (XEDS) linescan. An apparent diffusion coefficient was calculated, which supported bulk diffusion at the measured welding temperature of 493 °C and subgrain size of 20–50 nm.

Ti–6Al–4V parts made by the additive manufacturing (AM) technique selective laser melting (SLM) generally show poor ductility due to their fine martensitic microstructure. This study was designed to assess whether a more suitable microstructure can be obtained when long laser/material interaction times are used. As-fabricated components with an α + β microstructure were produced and characterized with various microscopy techniques. The microstructural evolution was discussed in relation to the build platform temperature, the cyclic reheating, and the thermal stresses that developed during the process. The hardness of the samples was also evaluated and discussed. The hardness varied in relation to the different microstructure morphologies observed in the samples and different partitioning of the alloying elements. This study indicates a methodology through SLM to obtain Ti–6Al–4V with an as-deposited α + β microstructure which is more desirable than that the typical fully martensitic microstructure typically obtained after SLM.