Microstructure and mechanical performances of CGHAZ for oil tank steel during high heat input welding

Microstructure and mechanical performances of the coarse grain heat-affected-zone （CGHAZ） for oil tank steel with different Ti content were investigated through Gleeble-3500, scanning electron microscopy, transmission electron microscopy, and energy dispersive spectrometer. The results show that the strength and low- temperature toughness of base material are significantly improved for the high titanium content steel, but the impact toughness of CGHAZ is seriously deteriorated after the high heat input welding and declined sharply with the heat input increasing, while the effects of heat input on impact toughness are very weak for the low titanium content steel, impact toughness of which is gradually larger than that of high titanium content steel with the welding heat input increasing because of the granular bainite increasing, TiN particle coarsening, and （Ti, Nb） N composition evolution during the high input welding for high titanium content steel.

Theoretical prediction and experimental realization of transition metal doped rutiles as diluted magnetic semiconductors

First principle calculations have been performed to study the electron structures and magnetic properties of transition metal doped ruilles in order to predict room temperature diluted magnetic semiconductors. Different doping configurailons have been calculated to find the preferred doping site. The ground state energies of both FM and AFM states have been calculated to study the magnetic coupling between the dopants. The calculation results show the Co doped mutile has a Curie temperature of 1438 K. Co doped mille films have been prepared on Si substrate by magnetron sputtering. X-ray diffraction results show that the deposited film is ruille. Hysteresis loop curves measured by vibration sample magnetization show that the film is ferromagnetic at root temperature.

Effects of post-annealing on crystalline and transport properties of Bi_(2)Te_(3) thin films

A well-established method is highly desirable for growing topological insulator thin films with low carrier density on a wafer-level scale. Here, we present a simple, scalable method based on magnetron sputtering to obtain high-quality Bi_(2) Te_(3) films with the carrier density down to 4.0 × 10^(13) cm^(-2). In contrast to the most-used method of high substrate temperature growth, we firstly sputtered Bi_(2) Te_(3) thin films at room temperature and then applied post-annealing. It enables the growth of highly-oriented Bi_(2) Te_(3) thin films with larger grain size and smoother interface. The results of electrical transport show that it has a lower carrier density as well as a larger coherent length(~ 228 nm, 2 K). Our studies pave the way toward large-scale, cost-effective production of Bi_(2) Te_(3) thin films to be integrated with other materials in wafer-level scale for electronic and spintronic applications.

PMMA with Long-Persistent Phosphors and Its Behavior of Luminescence

A new kind of rare earth material with high efficient long-persistent phosphors, such as SrAl2O4:Eu, Dy, has been developed in recent years. The PMMA with long-persistent phosphors is typical one of applications for the phosphors. In this work, we try to probe into the affection of the manufacture process on the PMMA with long-persistent phosphors, to analyze its performance, and its luminescence behavior, especially to study the self-excitation of the PMMA with long-persistent phosphors.

Upconversion emission enhancement of TiO_2 coated lanthanide-doped Y_2O_3 nanoparticles

To investigate the upconversion emission, this paper synthesizes Tm^3＋ and Yb^3＋ codoped Y2O3 nanoparticles, and then coats them with TiO2 shells for different coating times. The spectral results of TiO2 coated nanoparticles indicate that upconversion emission intensities have respectively been enhanced 3.2, 5.4, and 2.2 times for coating times of 30, 60 and 90 min at an excitation power density of 3.21× 10^2 W. cm^-2, in comparison with the emission intensity of non-coated nanoparticles. Therefore it can be concluded that the intense upconversion emission of Y2O3：Tm^3＋, Yb^3＋ nanoparticles can be achieved by coating the particle surfaces with a shell of specific thickness.

Nonlinear Optical Properties of Porphyrin Derivatives with Electron-donating or Electron-withdrawing Substituents

To investigate photoelectric properties of meso-extended porphyrin derivatives with electron-donating or elec- tron-withdrawing substituents, a series of functionalized porphyrin materials have been designed and synthesized by Suzuki coupling reaction. The meso-extended structures were fully characterized by IH NMR, IR spectroscopy and mass spectrometry. The photophysical properties of porphyrin derivatives were carefully examined by UV-Visible and fluorescence spectra, and the solvatochromic effect was observed and discussed. In particular, Z-scan technique was employed to characterize the third-order nonlinear optical （NLO） properties of the products such as nonlinear absorption and refraction, the third-order nonlinear refractive indexes （x（3）-value） of these porphyrin derivatives achieved 3.9 × 10-12 esu. In addition, the compounds could be self-assembled into highly organized morphologies through phase-exchange method. All the results indicated that the discotic materials have the potential for optoelec- tronic applications.

In-situ revealing the degradation mechanisms of Pt film over 1000℃

Degradation of a metallic film under harsh thermal-mechanical-electrical coupling field conditions determines its service temperature and lifetime.In this work,the self-heating degradation behaviors of Pt thin films above 1000℃were studied in situ by TEM at the nanoscale.The Pt films degraded mainly through void nucleation and growth on the Pt-SiN_(x)interface.Voids preferentially formed at the grain boundary and triple junction intersections with the interface.At temperatures above 1040℃,the voids nucleated at both the grain boundaries and inside the Pt grains.A stress simulation of the suspended membrane suggests the existence of local tensile stress in the Pt film,which promotes the nucleation of voids at the Pt-Si Nxinterface.The grain-boundary-dominated mass transportation renders the voids grow preferentially at GBs and triple junctions in a Pt film.Additionally,under the influence of an applied current,the voids that nucleated inside Pt grains grew to a large size and accelerated the degradation of the Pt film.

Ultra-high strength yet superplasticity in a hetero-grain-sized nanocrystalline Au nanowire

Nanocrystalline metals often display a high strength up to the gigapascal level,yet they suffer from poor plasticity.Previous studies have shown that the development of hetero-sized grains can efficiently overcome the strength-ductility trade-off of nanocrystalline metals.However,whether this strategy can lead to the fabrication of nanocrystalline nanowires exhibiting both high strength and superplasticity is unclear,similar to the atomistic deformation mechanism.In this paper,we show that ultra-small nanocrystalline Au nanowires comprising grains in both the Hall–Petch and inverse Hall–Petch grain-size regions can exhibit extremely high uniform elongation(236%)and high strength(2.34 gigapascals)at room temperature.In situ atomic-scale observations revealed that the plastic deformation underwent two stages.In the first stage,the super-elongation ability originated from the intergrain plasticity of small grains via mechanisms such as grain boundary migration and grain rotation.This intergrain plasticity caused the grains in the heterogeneous-structured nanowires to grow very large.In the second stage,the superelongation ability originated from intragrain plasticity accompanied by the diffusion of surface atoms.Our results show that the hetero-grain-sized nanocrystalline nanowires,comprising grains with sizes both in the strongest Hall–Petch effect region and the inverse Hall–Petch effect region,were simultaneously ultrastrong and ductile.They displayed neither a strength-ductility trade-off nor plastic instability.

Investigation on high magnetoresistance Ni_(0.81)Fe_(0.19) films grown on (Ni_(0.81)Fe_(0.19))_(1-x)Cr_(x) underlayers

We have fabricated Ni0.81Fe0.19 films with (Ni0.81Fe0.19)1-xCrx films as underlayers by dc magnetron sputtering, the results show that larger anisotropic magnetoresistance (△R/R) values of Ni0.81Fe0.19 films are observed using the underlayers with Cr concentration of ~36 at.% at an optimum underlayer thickness of ~4.4 nm, the maximum AMR value is 3.35%. The results of atomic force microscope (AFM) and X-ray diffraction (XRD) show that the △R/R enhancement is attributed to the formation of large average grain size and the strong(111) texture in the Ni0.81Fe0.19 films.

Microstructure change in deuterium implanted CLAM steel induced by electron irradiation

As Reduced Activation Ferritic/Martensitic (RAFM) steel is considered the primary candidate for use as a structural material in fusion power reactors,many countries are developing different kinds of RAFM.China is developing new CLAM (China Low Activation Martensitic) steel.The study investigates microstructural changes in CLAM steel implanted with deuterium ions induced by 1250 keV electron irradiation from R.T.to 873 K,and observes both the growth and shrinkage of the defect clusters produced by deuterium ion implantation under the electron irradiation.

AuAg合金纳米晶去孪晶机制的原位原子尺度研究

去孪晶是影响金属力学性能的重要塑性变形机制.本文对平均晶粒尺寸为15 nm的AuAg合金纳米晶进行了原位拉伸试验,首次在原子尺度上研究了合金纳米晶的去孪晶机制.结果表明合金纳米晶中存在三种去孪晶机制,第一种是晶界发生相向迁移的结果,这在小尺寸晶粒中更容易发生;第二种是通过孪晶逐层减薄和非共格孪晶界迁移相结合的方式进行,在去孪晶过程中,去孪晶速率会由于位错与共格孪晶界相互作用的影响而减缓,这仅在以往的经典建模中预测到;第三种是由非共格孪晶界迁移控制,这是多个偏位错集体滑移的结果.前两种类型的去孪晶过程在过去很少被报道,这表明固溶体合金纳米晶中的去孪晶机制不同于纯金属.