Controllable Liquid Crystal Micro Tube Laser

This study demonstrates controllable random lasing emissions in a dye-doped nematic liquid crystal (DDNLC)-infiltrated microcapillary. The emission wavelength of the micro tube laser can be adjusted by changing the focusing position of the pumped pulses on the center or the periphery of the liquid crystal region of the microcapillary. In addition, with doping azo-dyes in the DDNLC of the micro tube laser, optical controllability of the lasing intensity and wavelength can be further achieved. The controllable micro tube laser may find highly widespread photonic applications in multicolor emitting sources, and vibration and UV sensors.

Investigation on the Microporosity Formation of IN718 Alloy during Laser Cladding Based on Cellular Automaton

Porosity is one of the most common defects in the laser cladding of Inconel 718 (IN718) alloy, which can reduce the strength and fatigue performance of the components. However, the dynamic formation of microporosity is challenging to observe through experiments directly. In order to explore the formation mechanism of porosities and dynamically reproduce the competitive growth between porosities and dendrite, a multi-scale numerical model was adopted, combined with a cellular automaton (CA) and finite element method (FEM). The decentered square algorithm was adopted to eliminate crystallographic anisotropy and simulate dendrite growth in different orientations. Afterward, based on the formation mechanism of microporosity during solidification, equiaxed and columnar dendrites with porosities were simulated, respectively. Dendrite morphology, porosity morphology, and distribution of solute concentration were obtained during the solidification process. The simulation results were reasonably compared with experimental data. The simulation results of the equiaxed crystal region are close to the experimental data, but the columnar crystal region has a relative error. Finally, the interaction effects of porosities and dendrites under different environmental conditions were discussed. The results suggested that with the increase in the cooling rate, the quantity of porosity nucleation increased and the porosity decreased.

Study of Inconel 718 Welded by Bead-On-Plate Laser Welding under High-Frequency Micro-Vibration Condition

Inconel 718 alloy laser-welded joints have poor mechanical properties due to the presence of Laves phases and liquation cracks. This paper intends to solve the above problems by high-frequency micro-vibration-coupled bead-on-plate laser welding. According to the shape of the weld beam, the upper part of the weld is defined as the nail head, and the lower part is the nail body. The results showed that high-frequency micro-vibration can achieve grain refinement. The micro-vibration could break the primary dendrite arm to form secondary dendrite and reduce epitaxial growth of the cellular crystal region. Micro-vibration exacerbated the flow of Niobium (Nb) elements surrounded by dendrites and reduced dendritic segregation, which decreased the formation of Laves phases. The combination of interdendritic Nickel (Ni), Titanium (Ti), and Nb and the precipitation of strengthening phases γ′ and γ″ were promoted. When the vibration acceleration was 50.10 m/s2, it could inhibit the formation of Laves phases among dendrites and the size of the bulk Laves phase was effectively reduced. The cracks generated in the Inconel 718 alloy were distributed at three locations including the nail-head, the nail-body, and the junction of nail-head and nail-body. When the vibration frequency was 919 Hz, the length of the liquation crack reduced from 180 to 110 μm. While under 1331 Hz, the expansion of the liquation crack was extended, with the length of 200 μm.

Effect of Tungsten Inert Gas Remelting on Microstructure, Interface, and Wear Resistance of Fe-Based Coating

Tungsten inert gas arc (TIG) process was employed to remelt Fe-based coating deposited by plasma spraying. Subsequently, the microstructure, interface, and the wear resistance of the coatings before and after remelting were studied. The results showed that the lamellar structure, pores, and inclusions of Fe-based coating were eliminated and the porosity significantly decreased from 4% to 0.4%. The as-sprayed coating contained microcrystalline region, nanocrystalline region, and transition region, while single crystal region and rod-shaped (Fe,Cr)23C6 were observed in the remelted coating. There was no element diffusion and dissolution phenomenon at the interface; thus, the bonding form between the as-sprayed coating and substrate mainly was mechanical bonding. On the contrary, the diffusion transfer belt (DTB) emerged at the interface of the remelted coating and substrate, the remelted coating was bonded with the substrate metallurgically. Additionally, the average microhardness and elastic modulus of the remelted coating increased by 33.4% and 53.2%, respectively, compared with the as-sprayed coating. During wear process, the as-sprayed coating exhibited obvious brittle fracture characteristics, while the remelted coating appeared typical plastic deformation characteristics and its weight loss reduced by 39.5%. Therefore, TIG remelting process significantly improved the microstructure, mechanical properties, and wear resistance of Fe-based coating.

Degradation of Synthetic Reactive Dye Wastewater Based on Amine-Functionalized Polyacrylonitrile Fiber

A series of functional fibers have been prepared by modifying a commercially available polyacrylonitrilefiber (PANF) with polyamines such as ethylenediamine, tetraethylenepentamine and hyperbranched polyethylenimine (HPEI), and then used to coordinate with Fe3+, respectively, to produce Fe-modified PAN fiber complexes. The chemical structures of modified PANFs were verified by Fourier transform infrared spectroscopy (FT-IR). X-ray Diffraction (XRD) characterization showed that the inner crystal region of PANF was damaged during the introduction of amine groups.. Organic elemental analysis results to a certain extent demonstrate the success of modification. The coordination of Fe3+ was verified by Energy Dispersive Spectroscopy (EDS). The Fe-modified PAN fiber complexes were were used to eliminate the color from synthetic reactive dye wastewater (SRDW, including Reactive Red 195, RR 195) under normal conditions. This study presents a valuable route towards wastewater treatment in dyeing and finishing.

Degradation of PBS Introducing Crosslink by Glycerol

A series of poly (butylenes succinate) with low Glycerol (GL) fraction ranging from 0 to 6‰ were synthesized by two step melting condensation. By this method, some three-dimentional branch or crosslink structure was introduced to the linear aliphatic chain of PBS. The sequence distribution, GL fraction, crystal structure and degradability were investigated. The degrability of PBS enhanced when GL was led into polymer chain as the crystalline (χc) decreased with GL increasing. And the degradation first happened in amorphous region and then crystal region.

Effect of the Seed Polarity for High Quality 4H-SiC Crystal Grown on 6H-SiC Seed by PVT Method

The single crystal ingots by using a sublimation technique were grown on 6H-SiC dual-seed crystals with opposite face polarities and then SiC crystal wafers sliced from the SiC ingot were systematically investigated to find out the polarity dependence of the crystal quality. The growth rate of the SiC crystal grown in this study was about 0.2mm/hr. N-type 2’’ SiC crystals exhibiting the 4H- and 6H-SiC polytype were successfully fabricated on C-face and Si-face, respectively. The incorporation of nitrogen donors in the SiC crystals grown on the C-face seed crystal was exhibited to be higher than in SiC crystals grown on a Si-face crystal. When the SiC crystal ingot proceeded to grow, the SiC crystal region grown on the C-face seed crystal was enlarged compared to the SiC crystal region on the Si-face seed crystal.

Effects of Impurities Distribution on the Crystal Structure and Electrical Properties of Multi-Crystalline Silicon Ingots

Multi-crystalline silicon ingots were prepared by directional solidification using vacuum induction melting furnace. The content of aluminum and iron deeply decreased in the columnar crystal region of the multi-crystalline silicon ingots. The columnar crystal growth broke off corresponded to the iron contents sharply increased. The height of columnar crystal in the silicon ingots related to the pulling rates had been clarified by the constitutional supercooling theory. The maximum of the resistivity and the minority carrier lifetime closed to the transition zone where the conductive type changed from p-type to n-type in silicon ingots. Further analysis suggested that the electrical properties were related to the contents of shallow level impurities aluminum, boron and phosphorus.