Search

Adding mixed K2TiF6-KBF4 salts into mechanical stirred molten A356 alloy (Al-7Si-0.3Mg) provides a simple method to fabricate in situ TiB2/A356 composites via salts-metal reaction. However, some issues, such as the loss of Mg element in A356 alloy and the clustering of TiB2 particles in the matrix, usually occur during the fabricating process. These issues easily result in the degradation of mechanical properties of composites. In this study, a quantitative analysis revealed that the Mg element was almost consumed after the reaction, and a thermodynamic analysis inferred that the loss of Mg resulted from the reaction between Mg and mixed salts. In order to fabricate in situ TiB2/A356 composites with high strength and good ductility, we proposed a developed approach that consisted of supplementing Mg and using ultrasound stirring during the fabricating process. The introduction of ultrasound into the melt could disperse TiB2 particles uniformly in the matrix, leading to more effective refinement of α-Al grains and modification of Si phase. Compared with the untreated A356, both the strength and ductility of the developed sample were improved significantly, and the coefficient of thermal expansion mismatch strengthening was found as the major contributor to the improvement in the yield strength. [ABSTRACT FROM AUTHOR]

Based on the available literature experimental phase equilibria, the Ti-RE (RE = Ce, Er, Tm, Y) binary systems have been critically reviewed and modeled by means of the CALPHAD (CALculation of PHAse Diagram) method. No compound exists in these binary systems. The solution phases, i.e., liquid, bcc(βTi, δCe, βY), hcp(αTi, Er, Tm, αY) and fcc(γCe, γY), are described by the substitutional solution model. A set of self-consistent thermodynamic parameters is finally obtained for each of these binary systems. Comparisons between the calculated and measured phase diagrams show that most of the experimental data are satisfactorily accounted for by the present thermodynamic descriptions. [ABSTRACT FROM AUTHOR]

Melamine and sodium chloroacetate were used as raw materials to synthesize a kind of quaternary ammonium salt (QAS) as potential clay swelling inhibitor and water-based drilling fluid additive, and the reaction conditions were screened based on the linear expansion rate of bentonite. The inhibitive properties of QASs were investigated by various methods, including montmorillonite (MMT) linear expansion test, mud ball immersing test, particle distribution measurement, thermogravimetric analysis and scanning electron microscopy etc. The results indicate that QAS can inhibit expansion and dispersion of clay in water effectively. At the same condition, the bentonite linear expansion rate in QAS-2 solution is much lower than those of others, and the hydration expansion degree of the mud ball in 0.5% QAS-2 solution is appreciably weaker than the control test. The compatibility test indicates QAS-2 could be compatible with the conventional additives in water-based drilling fluids, and the temperature resistance of modified starch was improved effectively. Meanwhile, the inhibitive mechanism was discussed through the particle distribution measurement, thermogravimetric analysis and scanning electron microscopy. [ABSTRACT FROM AUTHOR]

AlCoCrFeNi2.1+xwt.%TiC (x=3, 6, 9) coatings were prepared on H13 steel by laser cladding (LC) technology. It was characterized by a friction and wear test machine, optical microscope (OM), X-ray diffractometer (XRD), hardness tester, etc. The effects of different TiC contents on the microstructure and properties of AlCoCrFeNi2.1 coatings were analyzed. The results show that the coating microstructure without TiC addition is dominated by coarse columnar crystals and dendrites. After the addition of TiC, the coated massive crystals and equiaxed crystals become finer. XRD analysis reveals that the phase structure of the coating has FCC, B2 solid solution phase and TiC-reinforced phase. TiC phase can significantly improve the hardness of the coating. The microstructure reveals that fine TiC particles are widely distributed among the dendrites of the FCC matrix. The hardness and friction wear experiments revealed that the average hardness of the coatings with TiC has increased significantly compared to that of the substrate. The hardness of the AlCoCrFeNi2.1 with 9%TiC coating increased by 184.6% compared to that of the substrate. The friction coefficient was the smallest at 0.748. The lowest self-corrosion current was 9.040×10−7A⋅cm−2. The AlCoCrFeNi2.1 with 9%TiC coating had the best corrosion resistance. [ABSTRACT FROM AUTHOR]

The appearance of the ε phase during the welding process can severely weaken the welding strength of dissimilar metals of Mg-Zn-Al alloy systems. An understanding of the accurate phase diagram, especially the equilibrium phase relation around the ε phase, is thus of particular importance. However, the phase interrelation near the ε -Mg 23 (Al, Zn) 30 phase has not yet been fully studied. In this work, the local phase diagrams of the ε phase and its surrounding phases in the Mg-Zn-Al system are systematically determined by experimental investigation and thermodynamic verification. Five Mg-Zn-Al alloys and one diffusion couple were fabricated and analyzed to get accurate phase constituents and relationships adjacent to ε phase. The current experimental data obtained from Scanning Electron Microscope (SEM), X-ray diffraction (XRD), Differential Scanning Calorimetry (DSC), and Electron Probe Micro Analysis (EPMA) were further compared with the thermodynamically computed phase relations around ε phase for verification, showing good agreements. Several important conclusions are drawn based on current experimental work, which can provide supporting information for the follow-up studies on ε phase in the Mg-Zn-Al alloy systems.

We have described a concise construction of the pentacyclic benz[f]indolo[2,3-a]quinolizidine intermediate 3 (with an overall yield of 54% for three steps), featuring a tandem intermolecular formal aza-[3 + 3] cycloaddition/Pictet-Spengler cyclization. The present work can be considered as a formal synthesis of beta-carboline alkaloid (+/-)-tangutorine. Our strategy disclosed herein constitutes a new effective general synthetic approach toward the indoloquinolizidine family of alkaloids.