WR. Chen
,
J.Triantafillou
,
J. Beddoes and L. Zhao(Dept. of Mech. & Aero. Eng.
,
Carleton University
,
Ottawa
,
Canada Structures
,
Materials & Propulsion Laboratory
,
National Research Council
,
Ottawa
,
Canada Manuscript received 26 August 1996)
金属学报(英文版)
Creep of a polycrystalline near γ-TiAl alloy in two fully lamellar conditions is presented. A lamellar structure with fine interface spacing and planar grain boundaries provides improved creep resistance. The lamellar structure with wide interface spacing and interlocked grain boundaries has <1/2 the creep life, five times the minimum strain rate and greater tertiary strain.Creep strain is accommodated by dislocation motion in soft grains, but the strain rate is controlled by hard grains. The resistance to fracture is controlled by the grain boundary morphology, with planar boundaries causing intergranular fracture.To maximize the creep resistance of near γ-TiAl with a lamellar microstructure requires narrow lamellar interface spacing and interlocked lamellae along grain boundaries.
关键词:
:creep
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null
,
null
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null
,
null
L. M. Lobanov (The E. O. Paton Electric welding Institute of the National Academy of Sciences of Ukraine
,
kiev
,
Ukraine)
金属学报(英文版)
A package of work is presented on development of highly effective welded structures, currently conducted by the E. O. Paton Electric Welding Institute. New types of cost - effective and reliable welded struc- tures have been developed, including light - weight building structures, bridge frameworks, TV tow- ers, heavy - duty structures from high - strength steels, large-sized stringer panels and shells, unique structures of a transformable volume. A series of methods of investigations of welding stresses and strains have been created, they being characterized by a high accuracy and information content. The physical and mathematical fundamentals of optical simulation of welded stresses have been estab- lished and the theory of their similarity has been constructed. Holographic methods of investigation of the quality and stressed - strained state of welded joints have been advised. Portable holographic sys- tems for been been developed which allow investigations to be conducted without the vibration - insulation facilities. A non-destructive testing method of residual stresses determination has been elaborated based on ultrasonic probing of the appropriate sections of the welded structure. A new trend has been formed, namely the distortion - free welding of structures, which is based on regulation of the thermal processes during welding with the aim of reduction of the heat input and inducing the preliminary stressed - strained states optimized in terms of welding stresses and strains. Specialized procedures and equipment based on the acoustic emission effect have been developed for diagnostics of welded structures. The technology and equipment have been for ultrasonic impact treatment of welded joints in or- der to improve their fatigue resistance, as well as computerized methods for design of welded joints and structures.
关键词:
welded structure
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null
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null
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null
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null
CHAI Huifen WANG Liqin Xi'an Jiaotong Uuiversity
,
Xi'an
,
ChinaLAIRD Campell University of Pennsylvania
,
U.S.A.[Originally published in ACTA METALL SIN(CHINESE EDN)25(3)1989 pp A201—A206
,
Associate professor
,
Xi'an Jiaotong University
,
Xi'an
,
China
金属学报(英文版)
The evolution of dislocation structures in 6% prestrained steel 1018 during fatigue has been studied by TEM.The dislocations are quite movable,the loose cells quickly change to “checkboard”structures,in which the main cell walls lie about {100}.Then,the low energy dislocation structures i.e.dipolar walls and abyrinth structures are evolved.The characteristic of labyrinth and the orientation of dipolar walls are quite similar to fcc crystal.This indicates the energy state of system and the moving ability of dislocations are important factors affect- ing softening process,rather than the slip geometric characteristic of dislocations and details of dislocations.The decreasing in misorientation between adjoining cells and internal stress are discussed.
关键词:
steel 1018
,
null
,
null
Acta Materialia
The deformation structures of copper powder induced by ball milling were studied in detail by using high resolution electron microscopy. It was found that copper powder after 20 h of milling shows the formation of shear bands and a number of mechanical twins. The observed twins belong to two types, i.e. multiple twins and high-order ones. It is suggested that Venables' model on mechanical twins in face-center-cubic metals is reasonable in this case. The generation of mechanical twins could be explained as follows: the shear stress (P-max) induced by ball milling exceeds the critical shear stress for twinning (tau); the grain size decreases to a critical value below which twinning rather than slip is the preferred mode of deformation as well as the high strain rates induced by ball milling. The formation of subgrains was found to occur via two routes: they were formed both in the shear bands and at the tip of them or at the tip of the twin boundaries, or at the edge of the larger grains. The subgrains formed via the two ways are in nanometer scale (10-100 nm), and their orientations are completely random. The as-received nanograins contained high density of dislocations. The grain boundaries (GBs) of nanocrystalline (NC) Cu are usually ordered, curved and strained, and disordering, lattice distortion and nanovoids in local regions were observed too.
关键词:
microstructures;films
Physica B-Condensed Matter
Three kinds of structures precipitated from the A gall of a patient were observed on the same samples by a field emission gun-scanning electron microscope (FEG-SEM). They were branching fractal structures, dendritic structures, and irregular crystalline grains. The fractal structures consisted of numerous granules that mostly disconnected each other. The dendrites were connected basically together. The tiny crystalline grains were of complicated shapes. A precipitation-aggregation-branching (PAB) model was used to explain growth mechanism of the fractal structure. Energy dispersive X-ray spectroscopy (EDS) was employed to measure chemical composition of three kinds of precipitates, as well as the A gall matrix. The experimental results reveal that saline or salt played an important role to the formation of the fractal structure, and also to that of the dendritic structure and crystalline grain. There may be relationship between the fractal in the A gall sample and fractal in gallstones. (c) 2005 Elsevier B.V. All rights reserved.
关键词:
fractal structure;dendrite;A gall;precipitation;tear;growth
Journal of Physics-Condensed Matter
The electronic energy subbands and minigaps in lateral-surface superlattices (LSSLS) produced by deposition of AlAs and GaAs fractional layers on (001) vicinal GaAs substrates were calculated variationally. The results were compared with those calculated with other theories. It was found that energy minigaps induced by periodic structures on LSSL interfaces are much smaller than those induced by periodic structures inserted in the middle of LSSLS, and the approximation of infinitely high potential barriers between GaAs and AlAs interfaces is not as good in calculating the energy subbands in LSSLs as it is in the case of quantum wells.
关键词:
optical-properties
Anti-Corrosion Methods and Materials
Purpose - The objective of the present work was to study the influence of chemical compositions of five naphthenic acids (NAs) extracted from Liaohe crude oil on their corrosivity. Design/methodology/approach - Fourier-transform infrared spectrometry and electron impact mass spectrometry were used to characterize the chemical structures and compositions if five NAs. The corrosivities of the NAs were assessed by stagnant NA corrosion (NAC) tests. An attempt was made to identify any correlation between the chemical composition of the NAs and their corrosiveness. Findings - The acidic species in all five NA samples were saturated aliphatic and naphthenic acids and the amount of aromatic and unsaturated acids was negligible. A relationship between the carboxylic acid distribution and the molecular weight was obtained. Most of the carboxylic acids in five NAs contained 0-3 ring structures. NAs with lower molecular weight and fewer ring structures usually were more corrosive. Originality/value - The findings have important implications for assessing the corrosivity of acidic crude oils from various resources.
关键词:
acids;corrosion;mass spectrometry;oils;chromatography-mass spectrometry;erosion-corrosion;high-temperature;crude-oil;steels;q235
材料科学技术（英文）
Conductance behaviours of resonant tunneling junction with elementary, second and third Sierpinskii structures are considered. Numerical calculation shows that a tunneling junction with higher order fractal structure possesses more meticulous resonant behaviour. it provides the possibility of fabricating exact energy selecting tunneling devices. The structure of tunneling junction can be determined by experimental observation. The energetic spectrum of such device is supposed to be a fractal one. The effect of electrode is alteration of the shape and maximum of conductance peaks.
关键词:
Rouli FU
,
Junhao CHU
,
Rongtang FU
,
Lei LI
,
Xin SUN
材料科学技术（英文）
The effects of the electric field on the electronic structures in electroluminescent polymers were studied with the tight-binding model including electron-phonon interactions plus an applied electric field. It is found that the applied electric field changes both the energy levels and the electronic wavefunctions in electroluminescent polymers: applied field induces two localized electronic states near the midgap, and also polarizes these localized electronic states, so the polarization occurs at weak or moderate fields. In addition, the strong field will dissociate a bipolaron exciton and lead to photoluminescence quenching.
关键词:
Guanghou WANG(National Lab. of Solid State Microstructures
,
Nanjing University
,
Nanjing 210093
,
China)Fengqi LIU(Center for Advanced Studies in Science and Technology of Microstructures
,
Nanjing 210093
,
China)
材料科学技术（英文）
We have studied structures and properties of nanostructured films prepared with nanometersized lithium fluoride(LiF) clusters by inert gas condensation method, and then characterized by transmission electron microscope, Fourier transform infrared spectra and Raman scattering spectra, etc. Following important results are obtained: Multi-order-like Raman scatterings from LiF clusters are obtained, including the fine structure of the spectra. The observed Raman peaks are discussed in terms of surface optical modes, Lo. To, LA modes and their combination form.As the cluster size decreases, the phonons are confined in nanoscale so that the q vector selection rule is relaxed or even totally free of q conservation, and prohibition at the first- and third-order scatterings in the bulk LiF crystal is relaxed. The sudece modes appear and play an important role in Raman scattering processes. The infrared absorption spectra are obtained with different deposition conditions. When the clusters are in the medium size range from ～7 to 15 nm, most infrared absorption peaks are second-order feature, and no single surface mode emerges. For the smaller clusters, molecular-like vibration is observed whereas the broad band of long wavelength transverse-optical modes appear from 580 to 400 nm-1 for the clusters larger than 19 nm
关键词:
