C.C. Liu
,
Z. Liu and G.X. Chen (Department of Mechanical Engineering
,
Tsinghua University
,
Beijing 100084
,
China)(Department of Mechanical Engineering
,
Tsinghua University
,
Beijing 100084
,
China)(Department of Mechanical Engineering
,
Tsinghua University
,
Beijing 100084
,
China)
金属学报(英文版)
ZBainitic transformation is analyzed in detail according to the factors such as morphology,crystallography,mechanical property of bainite and transformation kinetics,and conclusion is drawn that bainitic transformation is controlled by displacive mechanism and self-fempering of displacive microstructure.That is to say,bainite is the product of such procedure during which undercooled austemite first transforms into one certain displacive microstructure by displacive mechanism and then this microstructure experiences self-fempering.With this idea,several questions,which cannot be illustrated only by displacive transformation mechanism,can be explained successfully.
关键词:
bainitic transformation
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null
,
null
J.L. Huang
,
X.G. Cao
,
E. Sukedai
,
S. Yamasaki
,
and H.C.Gu(Department of Materials Engineering
,
Luoyang Institute of Technology
,
Luoyang 471039
,
China)(Department of Mechanical Engineering
,
Okayama University of Science
,
1-1 Ridai-Cho
,
Okayama City
,
Okayma 700
,
Japan)(Institute of Materials Science and Engineering
,
Xi'an Jiaotong University
,
Xi'an 710049
,
China)
金属学报(英文版)
The direct observations of the atomic arrangements in both conventional furnace annealed and electric pulse rapid annealed Fe78B13Si9 amorphous alloy have been conducted by the lattice imaging technique in a higt resolution electron microscope. The results showed that the embrittlement of the alloy was related to the extent of atomic rearrangements during the annealing processes. The embrittlement of the alloy after 1hour conventional furnace annealing at about 270℃ is caused by the sufficient atomic rearrangements which are characterized by the growth of some bct Fe3B-like atomic short range ordering regions already existed in the as-quenched structure. Electric pulse rapid annealing can effectively retard the above-mentioned atomic rearrangements and thus restrain the embrittlement. The embrittlement only occurs when certain amount of bcc α-Fe nanocrystals are precipitated in the amorphous matrix during electric pulse rapid annealing.
关键词:
Fe_(78)B_(13)Si_9 amorphous alloy
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null
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null
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null
Y. P. Zhang
,
J.X. Zhu
,
Y. Q. Wang and J.Y.Su(Institute of Cast Iron Research
,
Xi'an University of Technology
,
Xi'an 710048
,
China)(Department of Mechanical Engineering
,
Xi'an Jiaotong University
,
Xi'an 710049
,
China)
金属学报(英文版)
This paper deals with an important role of silicon in producing ductile iron with quenched complex structure of bainite and martensite. The samples are cast in permanent mold and quenched in solution of sodium silicate. The result of thc experiments shows that the austenizing temperature should rise with increasing silicon content, otherwise much undissolved ferrite is present in the matrix after quenching. However the undissolvec ferrite can be decreased greatly or even eliminated by adding appropriate amount of ooron. On this condition, the amount of bainite gets increasing and the amount of residual austenite decreasing with the silicon cortent increasing. An approach has also been made to the mechanism of the effect of silicon on the transformation of bainite in ductile iron. The T.T.T. curves measured show that the increase of sllicon content causes the curve to shift to the left. This is quite different from the fact in steel.
关键词:
ductile iron
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null
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null
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null
Mehdi Ebrahimian-Hosseinabadi Fakhredin Ashrafizadeh Mohammadreza Etemadifar Subbu S. Venkatraman
材料科学技术（英文）
In this paper, preparation of nano-biphasic calcium phosphate (nBCP), mechanical behavior and load-bearing of poly (lactide-co-glycolide) (PLGA) and PLGA/nBCP are presented. The nBCP with composition of 63/37 (w/w) HA/β-TCP (hydroxyapatite/β-tricalcium phosphate) was produced by heating of bovine bone at 700°C. Composite scaffolds were made by using PLGA matrix and 10-50 wt% nBCP powders as reinforcement material. All scaffolds were prepared by thermally induced solid-liquid phase separation (TIPS) at -60°C under 4 Pa (0.04 mbar) vacuum. The results of elastic modulus testing were adjusted with Ishai-Cohen and Narkis models for rigid polymeric matrix and compared to each other. PLGA/nBCP scaffolds with 30 wt% nBCP showed the highest value of yield strength among the scaffolds. In addition, it was found that by increasing the nBCP in scaffolds to 50 wt%, the modulus of elasticity was highly enhanced. However, the optimum value of yield strength was obtained at 30 wt% nBCP, and the agglomeration of reinforcing particles at higher percentages caused a reduction in yield strength. It is clear that the elastic modulus of matrix has the significant role in elastic modulus of scaffolds, as also the size of the filler particles in the matrix.
关键词:
Scaffold
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
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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null
Biomedical Materials
In this work, porous magnesium (Mg) with a three-dimensional open-cellular structure, potentially employed as bone tissue engineering scaffolds, was fabricated by the mechanical perforation method. The influences of porosity, pore size and pore arrangement on compressive behavior and the anisotropy of new porous Mg were analyzed theoretically using orthogonal arrays and the finite element method (FEM). The results showed that the parameters of porosity, pore size and pore arrangement had different effects on the compressive properties. The compressive strength could be improved by optimizing these parameters. The anisotropy of porous Mg was also verified in this study. The theoretical results showed good agreement with the experimental ones before the strain reaches 0.038.
关键词:
unidirectional solidification;pore-size;hydroxyapatite;replacement;cartilage;porosity;matrix
