Microstructural Tailoring and Enhancement in Compressive Properties of Additive Manufactured Ti-6Al-4V Alloy through Heat Treatment.

Among laser additive manufacturing, selective laser melting (SLM) is one of the most popular methods to produce 3D printing products. The SLM process creates a product by selectively dissolving a layer of powder. However, due to the layerwise printing of metal powders, the initial microstructure is fully acicular α'-martensitic, and mechanical properties of the resultant product are often compromised. In this study, Ti-6Al-4V alloy was prepared using SLM method. The effect of heat treatment was carried out on as-built SLM Ti-6Al-4V alloy from 650-1000 °C to study respective changes in the morphology of α/α'-martensite and mechanical properties. The phase transition temperature was also analyzed through differential thermal analysis (DTA), and the microstructural studies were undertaken by optical microscopy (OM) and scanning electron microscopy (SEM). The mechanical properties were assessed by microhardness and compressive tests before and after heat treatment. The results showed that heat treated samples resulted in a reduction in interior defects and pores and turned the morphology of the α'-martensite into a lamellar (α + ß) structure. The strength was significantly reduced after heat treatment, but the elongation was improved due to the reduction in columnar α'-martensite phase. An optimum set of strength and elongation was found at 900 °C.

Tailoring Compressive Strength and Absorption Energy of Lightweight Multi-Phase AlCuSiFeX (X = Cr, Mn, Zn, Sn) High-Entropy Alloys Processed via Powder Metallurgy.

The development of lightweight HEAs with high strength and low cost is an urgent requirement. In this study, equimolar AlCuSiFeX (X = Cr, Mn, Zn, Sn) lightweight HEAs were fabricated by advanced powder metallurgy. The mechanical alloying was performed for 45 h, and the powder compacts were densified at 650 °C. The final results revealed that AlCuSiFeSn lightweight HEA was composed of a single face-centered cubic (FCC) and Cu81Sn22, whereas AlCuSiFeZn showed a dual FCC and body-centered cubic (BCC) structures. Similarly, AlCuSiFeMn alloy contained a BCC + FCC phase with a µ-phase, whereas a σ-phase was present in AlCuSiFeCr in addition to FCC + BCC phases. We also calculated various thermodynamic parameters to predict the solid-solution phase stability of each of the above lightweight HEAs. It was found that lightweight HEAs with additive elements Sn and Zn tend to predominant FCC phases, whereas those with Cr and Mn result in major BCC with hard µ and σ phases, which further improve their mechanical strength. A maximum fracture strain of 23% was obtained for AlCuSiFeSn followed by 19% for AlCuSiFeZn HEA. The compressive fracture mechanisms of these lightweight HEAs are also discussed and reported here.

Vacuum brazing of Al2O3 and 3D printed Ti6Al4V lap-joints using high entropy driven AlZnCuFeSi filler.

In this work, we studied the brazing characteristics of Al2O3 and 3D printed Ti-6Al-4V alloys using a novel equiatomic AlZnCuFeSi high entropy alloy filler (HEAF). The HEAF was prepared by mechanical alloying of the constituent powder and spark plasma sintering (SPS) approach. The filler microstructure, wettability and melting point were investigated. The mechanical and joint strength properties were also evaluated. The results showed that the developed AlZnCuFeSi HEAF consists of a dual phase (Cu-Zn, face-centered cubic (FCC)) and Al-Fe-Si rich (base centered cubic, BCC) phases. The phase structure of the (Cu-Al + Ti-Fe-Si)/solid solution promises a robust joint between Al2O3 and Ti-6Al-4V. In addition, the joint interfacial reaction was found to be modulated by the brazing temperature and time because of the altered activity of Ti and Zn. The optimum shear strength reached 84 MPa when the joint was brazed at 1050 °C for 60 s. The results can be promising for the integration of completely different materials using the entropy driven fillers developed in this study.

Effect of Al2O3 Sandblasting Particle Size on the Surface Topography and Residual Compressive Stresses of Three Different Dental Zirconia Grades.

This study investigated the effect of sandblasting particle size on the surface topography and compressive stresses of conventional zirconia (3 mol% yttria-stabilized tetragonal zirconia polycrystal; 3Y-TZP) and two highly translucent zirconia (4 or 5 mol% partially stabilized zirconia; 4Y-PSZ or 5Y-PSZ). Plate-shaped zirconia specimens (14.0 × 14.0 × 1.0 mm3, n = 60 for each grade) were sandblasted using different Al2O3 sizes (25, 50, 90, 110, and 125 µm) under 0.2 MPa for 10 s/cm2 at a 10 mm distance and a 90° angle. The surface topography was characterized using a 3-D confocal laser microscopy and inspected with a scanning electron microscope. To assess residual stresses, the tetragonal peak shift at 147 cm-1 was traced using micro-Raman spectroscopy. Al2O3 sandblasting altered surface topographies (p < 0.05), although highly translucent zirconia showed more pronounced changes compared to conventional zirconia. 5Y-PSZ abraded with 110 µm sand showed the highest Sa value (0.76 ± 0.12 µm). Larger particle induced more compressive stresses for 3Y-TZP (p < 0.05), while only 25 µm sand induced residual stresses for 5Y-PSZ. Al2O3 sandblasting with 110 µm sand for 3Y-TZP, 90 µm sand for 4Y-PSZ, and 25 µm sand for 5Y-PSZ were considered as the recommended blasting conditions.

Pseudo-Anomalous Size-Dependent Electron-Phonon Interaction in Graded Energy Band: Solving the Fano Paradox.

Quantum size effects on interferons (electron-phonon bound states), confined in fractal silicon (Si) nanostructures (NSs), have been studied by using Raman spectromicroscopy. A paradoxical size dependence of Fano parameters, estimated from Raman spectra, has been observed as a consequence of longitudinal variation of nanocrystallite size along the Si wires leading to local variations in the dopants' density which actually starts governing the Fano coupling, thus liberating the interferons to exhibit the typical quantum size effect. These interferons are more dominated by the effective reduction in dopants' density rather than the quantum confinement effect. Detailed experimental and theoretical Raman line shape analyses have been performed to solve the paradox by establishing that the increasing size effect actually is accompanied by receding Fano coupling due to the weakened electronic continuum. The latter has been validated by observing a consequent variation in the Raman signal from dopants which was found to be consistent with the above conclusion.

Electrodeposited Silver Nanowire Transparent Conducting Electrodes for Thin-Film Solar Cells.

Silver nanowire (AgNW) networks have demonstrated high optical and electrical properties, even better than those of indium tin oxide thin films, and are expected to be a next-generation transparent conducting electrode (TCE). Enhanced electrical and optical properties are achieved when the diameter of the AgNWs in the network is fairly small, that is, typically less than 30 nm. However, when AgNWs with such small diameters are used in the network, stability issues arise. One method to resolve the stability issues is to increase the diameter of the AgNWs, but the use of AgNWs with large diameters has the disadvantage of causing a rough surface morphology. In this work, we resolve all of the aforementioned issues with AgNW TCEs by the electrodeposition of Ag onto as-spin-coated thin AgNW TCEs. The electrodeposition of Ag offers many advantages, including the precise adjustment of the AgNW diameter and wire-to-wire welding to improve the junction conductance while minimizing the increase in protrusion height because of the overlap of AgNWs upon increasing the diameter. In addition, Ag electrodeposition on AgNW TCEs can provide higher conductance than that of as-spin-coated AgNW TCEs at the same transparency because of the reduced junction resistance, which generates a superior figure of merit. We applied the electrodeposited (ED) AgNW network to a Cu(In,Ga)Se2 thin-film solar cell and compared the device performance to a device with a standard sputtered transparent conducting oxide (TCO). The cell fabricated by the electrodeposition method showed nearly equal performance to that of a cell with the sputtered TCO. We expect that ED AgNW networks can be used as high-performance and robust TCEs for various optoelectronic applications.

Design of Refolding DNA Aptamer on Single-Walled Carbon Nanotubes for Enhanced Optical Detection of Target Proteins.

DNA aptamer conjugated single-walled carbon nanotube (Aptamer-SWNT) hybrids have demonstrated effective optical biosensors because of their high selectivity and specificity to a target protein, however, the understanding of SWNT hybridization with an aptamer forming a secondary or tertiary structure is still lacking. We study wrapping methods dependent optical biosensing modulation by insulin and platelet-derived growth factor (PDGF) using the Aptamer-SWNT hybrids and the Aptamer-Anchor-SWNT hybrids with a periodically sequenced single-stranded DNA (ssDNA) as anchoring phases. We observe that the refolding nature of the aptamer and its combination with an anchoring phase are critical to the hybridization, where the remarkable optical sensing properties are attributed to the wrapping procedures including the direct wrapping with sonication and the indirect wrapping through dialysis. The tetrameric parallel-stranded G-quadrupole conformation of insulin binding aptamers (IBA) shows an enhanced fluorescence response quenching when using the directly wrapped Aptamer-Anchor-SWNT hybrids. In addition, helix-structural refolding of PDGF binding aptamers (PBA) indirectly wrapped on the SWNT vicinity is influenced by anchoring length for optical modulation. Furthermore, the consecutive centrifuging processes with the indirect wrapping demonstrate fluorescence response brightening, in which the diameter dependent brightening effect is observed by aptamer-protein interactions. This study provides an understanding the underlying conjugation nature of both the Aptamer-SWNT and the Aptamer-Anchor-SWNT hybrids formation, facilitating exceptional optical sensing modules with consideration of refolding feature of aptamers, selection of anchoring phases, wrapping methods and centrifuging process, and the hybridization voyage for DNA-SWNT platforms maneuvers their outcoming optical biosensing capabilities.

The Role of Charge Balance and Excited State Levels on Device Performance of Exciplex-based Phosphorescent Organic Light Emitting Diodes.

The design of novel exciplex-forming co-host materials provides new opportunities to achieve high device performance of organic light emitting diodes (OLEDs), including high efficiency, low driving voltage and low efficiency roll-off. Here, we report a comprehensive study of exciplex-forming co-host system in OLEDs including the change of co-host materials, mixing composition of exciplex in the device to improve the performance. We investigate various exciplex systems using 5-(3-4,6-diphenyl-1,3,5-triazin-2-yl)phenyl-3,9-diphenyl-9H-carbazole, 5-(3-4,6-diphenyl-1,3,5-triazin-2-yl)phenyl)-9-phenyl-9H-3,9'-bicarbazole, and 2-(3-(6,9-diphenyl-9H-carbazol-4-yl)phenyl)-4-phenylbenzo[4,5]thieno[3,2-d]pyrimidine, as electron transporting (ET: electron acceptor) hosts and 9,9'-dipenyl-9H, 9'H-3,3'-bicarbazole and 9-([1,1'-biphenyl]-4-yl)-9'-phenyl-9H,9'H-3,3'-bicarbazole as hole transporting (HT: electron donor) hosts. As a result, a very high current efficiency of 105.1 cd/A at 103 cd/m2 and an extremely long device lifetime of 739 hrs (t95: time after 5% decrease of luminance) are achieved which is one of the best performance in OLEDs. Systematic approach, controlling mixing ratio of HT to ET host materials is suggested to select the component of two host system using energy band matching and charge balance optimization method. Furthermore, our analysis on exciton stability also reveal that lifetime of OLEDs have close relationship with two parameters; singlet energy level difference of HT and ET host and difference of singlet and triplet energy level in exciplex.

Friction and Wear Reduction of Eccentric Journal Bearing Made of Sn-Based Babbitt for Ore Cone Crusher.

An anti-friction Babbitt alloy-coated bearing made by a casting process is a journal bearing, which is used in an ore cone crusher eccentric. The main purpose of the Babbitt coated eccentric is to provide a low friction to support and guide a rotating shaft. Despite the fact that the Babbitt-coated eccentric offers a low friction coefficient and can be operated without a continuous supply of lubricant, it suffers from mining environments and short service life. In this study, an ultrasonic nanocrystalline surface modification (UNSM) technique was used to further reduce the friction coefficient, to increase the wear resistance, and to extend the service life of the Sn-based Babbitt metal. The friction and wear behavior of the Sn-based Babbitt metal was investigated using a block-on-ring tester under both dry and oil-lubricated conditions. The results of the experiments revealed that the friction and wear behavior of Sn-based Babbitt metal could be improved by the application of the UNSM technique. The friction and wear mechanisms of the specimens were explained and discussed in terms of changes in surface properties-microstructure, surface hardness, surface roughness, etc.

Focused ion beam engineered whispering gallery mode resonators with open cavity structure.

We report the realization of an open cavity whispering gallery mode optical resonator, in which the circulating light traverses a free space gap. We utilize focused ion beam microfabrication to precisely cut a 10 µm wide notch into the perimeter of a crystalline disc. We have shown that this modified resonator structure supports high quality modes, and demonstrated qualify factor, Q ~/= 10(6), limited by the notch surface roughness due to the ion milling process. Furthermore, we investigated the spatial profile of the modes inside the open cavity with a microfabricated probe mechanism. This new type of resonator structure facilitates interaction of the cavity's optical field with mechanical resonators as well as individual atoms or molecules.

InGaN/GaN multiple quantum wells grown on nonpolar facets of vertical GaN nanorod arrays.

Uniform GaN nanorod arrays are grown vertically by selective area growth on (left angle bracket 0001 right angle bracket) substrates. The GaN nanorods present six nonpolar {1⁻100} facets, which serve as growth surfaces for InGaN-based light-emitting diode quantum well active regions. Compared to growth on the polar {0001} plane, the piezoelectric fields in the multiple quantum wells (MQWs) can be eliminated when they are grown on nonpolar planes. The capability of growing ordered GaN nanorod arrays with different rod densities is demonstrated. Light emission from InGaN/GaN MQWs grown on the nonpolar facets is investigated by photoluminescence. Local emission from MQWs grown on different regions of GaN nanorods is studied by cathodoluminescence (CL). The core-shell structure of MQWs grown on GaN nanorods is investigated by cross-sectional transmission electron microscopy in both axial and radial directions. The results show that the active MQWs are predominantly grown on nonpolar planes of GaN nanorods, consistent with the observations from CL. The results suggest that GaN nanorod arrays are suitable growth templates for efficient light-emitting diodes.

[Herbal preparation-induced liver injury].

Recently the use of herbal preparations as remedies for various medical conditions, has been rapidly increasing in Korea. In our previous study, 38.9% of patients with chronic liver disease were found to use some sorts of herbal preparations. They believe herbal preparations are safe although the ingredients has never been rigorously substantiated. Toxicities of certain herbal preparations are caused by their contaminants and adulterated ingredients or concurrently used conventional drugs rather than specific components of the herbal preparations. Furthermore, in most instances, multiple herbal ingredients are used by the prescribers of oriental medicine. All of these conditions frequently impose diagnostic difficulties. There are myriads of plant-derived hepatotoxic substances which may or may not cause liver injury in individuals. The severity of liver injury depends largely on the toxicity of the substance, the amount of exposure and the individual's susceptibility. These toxic substances cause liver injury not only through the mechanism of intrinsic hepatotoxicity but also through the idiosyncrasy as in conventional drug-induced injury. Therefore, theoretically, it is possible to apply pre-existing CAMs (Causality Assessment Methods) to the assessment of causality in cases with diagnostic difficulties.

Increased microfilaments in hepatocytes and biliary ductular cells in cholestatic liver diseases.

To assess the extent of microfilaments in cholestatic liver diseases we examined the cytoplasmic microfilaments in intrahepatic and extrahepatic cholestasis in man by electron microscopy. Study subjects were two patients with drug-induced intrahepatic cholestasis, three patients with intrahepatic cholestasis due to viral hepatitis, four patients with extrahepatic cholestasis due to stones of the common bile duct and two patients with primary biliary cirrhosis. Two biopsied specimens from patients without clinical or histological evidence of liver disease served as noncholestatic controls. The microfilaments in hepatocytes and biliary ductular cells were significantly increased in cholestasis compared with those in non-cholestatic controls. Well developed bundles of microfilaments were noted around the pericanalicular ectoplasm and seemed to be parallel to plasma membrane of the hepatocytes in cholestasis. In cholestasis, there were increased bundles of microfilaments around the periluminal region, lateral cell wall, and nucleus of biliary ductular cells. Two patterns of microfilaments bundles (fine microfilamentous network and spindle-shaped dense or clusters of microfilaments) were associated with cholestasis. The clustered form of microfilaments also seemed to be clearly associated with intracytoplasmic vacuoles containing bile salts. In conclusion, the increase of microfilaments in hepatocytes and biliary ductular cells may be the consequence of various forms of cholestasis. Further studies are needed to clarify the functional significance of increased microfilaments in cholestasis.