다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

X-ray analysis of ZnO nanoparticles by Williamson–Hall and size–strain plot methods

ZnO nanoparticles were prepared by coprecipitation method at 450C. X-ray diffraction result indicates that the sample is having a crystalline wurtzite phase. Transmission electron microscopy (TEM) result reveals that the ZnO sample is spherical in shape with an average grain size of about 50nm. X-ray peak broadening analysis was used to evaluate the crystalline sizes and lattice strain by the Williamson-Hall (W-H) analysis. All other relevant physical parameters such as strain, stress, and energy density values were also calculated using W-H analysis with different models, viz, uniform deformation model, uniform deformation stress model and uniform deformation energy density model. The root mean square strain was determined from the interplanar spacing and strain estimated from the three models. The three models yield different strain values; it may be due to the anisotropic nature of the material. The mean particle size of ZnO nanoparticles estimated from TEM analysis, Scherrers formula and W-H analysis is highly intercorrelated.

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Williamson-Hall analysis in estimation of lattice strain in nanometer-sized ZnO particles

The stability of two-dimensional (2D) layers and membranes is subject of a long standing theoretical debate. According to the so called Mermin-Wagner theorem, long wavelength fluctuations destroy the long-range order for 2D crystals. Similarly, 2D membranes embedded in a 3D space have a tendency to be crumpled. These dangerous fluctuations can, however, be suppressed by anharmonic coupling between bending and stretching modes making that a two-dimensional membrane can exist but should present strong height fluctuations. The discovery of graphene, the first truly 2D crystal and the recent experimental observation of ripples in freely hanging graphene makes these issues especially important. Beside the academic interest, understanding the mechanisms of stability of graphene is crucial for understanding electronic transport in this material that is attracting so much interest for its unusual Dirac spectrum and electronic properties. Here we address the nature of these height fluctuations by means of straightforward atomistic Monte Carlo simulations based on a very accurate many-body interatomic potential for carbon. We find that ripples spontaneously appear due to thermal fluctuations with a size distribution peaked around 70 \AA which is compatible with experimental findings (50-100 \AA) but not with the current understanding of stability of flexible membranes. This unexpected result seems to be due to the multiplicity of chemical bonding in carbon.

Intrinsic ripples in graphene

Welding Metallurgy of

The pulsed d.c plasma in industrial scale chamber for plasma nitriding and plasma enhanced chemical vapor deposition was measured with a single-langmuir probe. The plasma density was increased with the increasing of the pulse voltage in plasma nitriding process, but decreased in an initial stage and than increased sharply when the voltage is beyond 700V in TiN coatings deposition. Such different behavior of pulse d.c plasma was due to the addition of TiCl 4 , which has a great effect on suppression of plasma density. However, a quality TiN coating was usually obtained at low density, which needs a relatively low voltage below 700V. It has also been shown that the deposition rate depends strongly on the N 2 flow.

Diagnostics of TiN coatings process in pulsed D.C plasma enhanced chemical vapor deposition

Under specific manufacturing processes and heat treatments, the gamma titanium Aluminide Ti- 47Al-2Cr-2Nb presents a nearly lamellar microstructure with coarse lamellar grains (with alternating g and a2 lamellae) and dispersed small g grains. The obtained microstructure gives a relatively coarse grain size (approximately 0.4 mm x 3 mm). Residual stresses can then be generated between g and a2 lamellae inside the lamellar grain and also between different grains because of the lattice mismatch between tetragonal structure of g phase and hexagonal structure of a2 phase. A specific single crystalline XRD method is applied on these two non-cubic phases to determine the local residual stresses in two grains on each side of a grain boundary.

XRD Stress Analysis in a TiAl Based Intermetallic Multicrystal

The microstructures and tensile properties of Mg-4∼6Al-2∼4Zn-2∼3Ca-0∼1RE (in wt.%) extruded alloys have been investigated. C15 and C36 Laves phases, Ca2Mg6Zn3, Al2REZn2, and Al11RE3 phases were formed as networks during solidification in different alloys. After extrusion, coarse dendritic were significantly refined due to dynamic recrystallization, second phases were fragmented into pieces arranged as stripes, and typical basal fiber texture {0002} <10-10> with the extrusive direction paralleled to (0001) were formed in all studied alloys. Laves phase particles were prone to be crushed into nanoparticles, which appeared more easily to hinder the recrystallized grain growth and could bring about more than 30 vol % ultra-fine grains after extrusion. During extrusion, twinning-induced dynamic recrystallization occurred at first, and both discontinuous and continuous dynamic recrystallization dominated the microstructural evolution. The volume fraction of second phases had critical roles in recrystallization process, and a nearly complete recrystallization degree could be obtained in alloys containing more than 9 vol% second phases. The strengthening mechanisms were evaluated based on classic strengthening models, which agreed well with the experimental results. It was found that grain boundary strengthening, second phase strengthening, and texture strengthening contributed around 60%, 30%, and 10%, respectively, to yield strengthening, except for Mg-4Al-4Zn-2Ca alloy because of the high percentage of unrecrystallized region. Moreover, the overestimate of second phase strengthening happened in alloys having more than 9 vol% second phases, which revealed that too many second phases had limited influence on microstructures and the resulting mechanical properties. 

Vincent Ji

Papers

Diagnostics of TiN coatings process in pulsed D.C plasma enhanced chemical vapor deposition

XRD Stress Analysis in a TiAl Based Intermetallic Multicrystal

The microstructural features and strengthening mechanisms of Mg-Al-Zn-Ca-(RE) extruded alloys having high-volume fractions of second-phase particles