H.S. Fang and C. Zhang Departmentof Materials Science and Engineering
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Tsinghua University
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Beijing 100084
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China
金属学报(英文版)
The viewpoints aboutthe formation mechanism of bainite are described asfollowing aspects: ①Ultra finestructureof bainitein ferrous and nonferrousalloysis discovered by scanningtunneling microscopy (STM) .②STMstudies discoveredthatthesurface relief of bainiteissubstantiallycomposed of groupsofsmallrelieves which correspond of ultra fineunits,theirsurfacereliefistent shaped.③The frequency and mobility of 3 dimensionalsuperledgesinferrousand nonferrousareproved by TEMand STM.④Thebainitecarbide nucleateinthe ∪ sideof α/γinterfaceand grow toward austenite,thegrowth of carbide and ferrite arecom petitive.⑤STMstudies on surface relief of grain boundary allotriomorph ( GBA) andWidmansttten ferrite( WF) . They aretent shaped.⑥Theformation of bainiteisthroughsympathetic nucleation ledgewisegrowth mechanism .And both processesarecompetitive.⑦3 dimensional morphology of upper bainitetransformscontinuously to lower bainite, and noabruptlychange.
关键词:
bainite
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Andrej Atrens
材料科学技术（英文）
Corrosion research by Atrens and co-workers has made significant contributions to the understanding of the service performance of engineering materials. This includes: (1) elucidated corrosion mechanisms of Mg alloys, stainless steels and Cu alloys, (2) developed an improved understanding of passivity in stainless steels and binary alloys such as Fe-Cr, Ni-Cr, Co-Cr, Fe-Ti, and Fe-Si, (3) developed an improved understanding of the melt spinning of Cu alloys, and (4) elucidated mechanisms of environment assisted fracture (EAF) of steels and Zr alloys. This paper summarises contributions in the following: (1) intergranular stress corrosion cracking of pipeline steels, (2) atmospheric corrosion and patination of Cu, (3) corrosion of Mg alloys, and (4) transgranular stress corrosion cracking of rock bolts.
关键词:
Stress corrosion cracking
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null
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LIU Guoquan Department of Materials Science and Engineering
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University of Science and Technology Beijing
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100083
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China.
材料科学技术（英文）
Quantitative analysis of populations having a geometric structure,which has developed into a special scientific subject called microstructology or stereology,is of great importance to the characterization and evaluation of microstructures and their evolution in various processes.This paper, besides a brief discussion on those topics such as the recent developments of computer assisted image analysis,mathematical morphology,and fractal analysis,will mainly focus on the scope,fundamen- tals,present status,and perspectives of classical stereology.Several case examples of its application to materials science will also be given.
关键词:
stereology
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Materials Science & Engineering C-Biomimetic Materials Sensors and Systems
Bamboo, one of the strongest natural structural composite materials, has many distinguishing features. It has been found that its reinforcement unit, hollow, multilayered and spirally-wound bast fiber, plays an extremely important role in its mechanical behavior. In the present work, on the basis of the study on bamboo bast fiber and wood tracheid, a biomimetic model of the reinforcing element, composed of two layers of helically wound fiber, was suggested. To detect the structural characteristics of such a microstructure, four types of macro fiber specimens made of engineering composites were employed: axially aligned solid and hollow cylinders, and single- and double-helical hollow cylinders. These specimens were subjected to several possible loadings, and the experimental results reveal that only the double-helical structural unit possesses the optimum comprehensive mechanical properties. An interlaminar transition zone model imitating bamboo bast fiber was proposed and was verified by engineering composite materials. In our work, the transition zone can increase the interlaminar shear strength of the composite materials by about 15%. These biomimetic structural models can be applied in the design and manufacture of engineering composite materials.
关键词:
bamboo;bast fiber;biomimetics;engineering composites
Science
Strengthening materials traditionally involves the controlled creation of internal defects and boundaries so as to obstruct dislocation motion. Such strategies invariably compromise ductility, the ability of the material to deform, stretch, or change shape permanently without breaking. Here, we outline an approach to optimize strength and ductility by identifying three essential structural characteristics for boundaries: coherency with surrounding matrix, thermal and mechanical stability, and smallest feature size finer than 100 nanometers. We assess current understanding of strengthening and propose a methodology for engineering coherent, nanoscale internal boundaries, specifically those involving nanoscale twin boundaries. Additionally, we discuss perspectives on strengthening and preserving ductility, along with potential applications for improving failure tolerance, electrical conductivity, and resistance to electromigration.
关键词:
strain-rate sensitivity;stacking-fault energy;nano-scale twins;cu-al;alloys;nanocrystalline metals;mechanical-properties;activation;volume;copper;deformation;behavior
Corrosion Science
The sulphidation of two copper-silver alloys containing 5 and 10 wt.% silver (Cu-5Ag and Cu-10Ag, respectively) was investigated over the temperature range 550-750 degrees C in H-2/H2S mixtures under sulphur pressures below the dissociation of Ag2S. External scales, composed mainly of cuprous sulphide, often containing some (Cu,Ag)(2-x)S islands, formed on both alloys. The corrosion kinetics were significantly affected by the detachment of the outer scales at temperature, as a consequence of the significant volume increase due to sulphidation. After scale detachment, sulphidation proceeded through a dissociative transport of sulphur in voids between the outer sulphide layer and the alloy substrate, yielding an abrupt decrease of the corrosion rate in all cases and modifying the composition of the reaction products in the case of Cu-10Ag. An increase of the volume fraction of the silver-rich solid solution in the subscale region with respect to the original alloy was observed in all cases. The silver islands coalesced to a continuous subscale layer only in the sulphidation of Cu-5Ag at 650 and 750 degrees whereas, in all the other cases, they remained as particles in a Cu2S matrix. The peculiar corrosion behaviour of these alloys is attributed to the low solubility of silver in copper. (C) 1999 Elsevier Science Ltd. All rights reserved.
关键词:
sulphidation;copper;silver;two-phase alloys;state corrosion kinetics;2-phase binary-alloys;most-stable oxide;internal oxidation
Oxidation of Metals
The sulfidation behavior of a Co-Ce alloy containing approximately 15 wt.% Ce has been studied at 600-800 degrees C in H-2-H2S mixtures providing a sulfur pressure of 10(-8) atm, but also of 10(-7) atm at 800 degrees C. At 600 and 700 degrees C the alloy corrodes more slowly than pure cobalt, but more rapidly than pure cerium. At 800 degrees C under 10(-8) atm S-2, which is below the stability of the cobalt sulfides, the alloy corrodes quite slowly, bur under 10(-7) atm S-2 it corrodes very rapidly and practically at the same rate as pure cobalt. The sulfidation kinetics are generally il regular, except for a few cases of nearly parabolic behavior. The sulfidation of the alloy produces duplex scales, containing an outermost layer of practically pure cobalt sulfide and an inner complex layer where the two components are simultaneously present. Cerium is not able to diffuse out of the alloy-consumption region, where it forms a cerium sulfide mixed with cobalt sulfide and an innermost region where cerium sulfide is mixed with cobalt metal. The cobalt sulfide forms a continuous network which allows the growth of the external CoSy layer, even though at rates reduced with respect to pure cobalt. Thus, a cerium content of 15 wt.% is not sufficient to prevent the sulfidation of the base metal. These results as well as the details of the microstructure of the scales grown on the alloy are interpreted by taking into account the limited solubility of cerium in the base metal and the presence in the alloy of an intermetallic compound rich in cerium.
关键词:
cobalt;cerium;sulfidation;high-temperature sulfidation;2-phase binary-alloys;low oxidant;pressures;fe-nb alloys;internal oxidation;h2-h2s mixtures;mo alloys;600-degrees-c-800-degrees-c;corrosion;ni
材料科学技术（英文）
The corrosion of an Fe-based alloy containing 15 wt pet Y in H-2-H2S mixtures under 10(-3) Pa S-2 was studied at 600 similar to 800 degrees C in an attempt to find materials with improved sulphidation resistance with respect to pure Fe. The presence of Y has been shown to be beneficial, but not sufficient to the level expected. In fact, the alloy is able to form at all tested temperatures an external FeS layer, beneath which a zone containing a mixture of the two sulphides is also present. Thus, Fe can still diffuse through this region to form the outer FeS layer with non-negligible rate. The corrosion rate of Fe is considerably reduced by the Y addition, but the alloy corrodes still much more rapidly than Y. The sulphidation kinetics is generally rather irregular for both the pure metals, while the corrosion rate of the alloy decreases with time and tends to become parabolic after an initial period of 12 similar to 17 h. The sulphidation behaviour of the alloys is discussed by taking into account the presence of an intermetallic compound Fe17Y2 and the limited solubility of Y in Fe.
关键词:
high-temperature sulfidation;most-reactive component;ni-nb alloys;h2-h2s mixtures;behavior;600-degrees-c-800-degrees-c;oxidation
