材料期刊网

HARDENING OF L1_2-ORDERED Co_3Ti BY PRECIPITATION OF FCC-Co PHASE

W. H. Tian , S.L. Hu and M. Nemoto(Department of Materials Physics , University of Science and Technology Beijing , Beijing 100083 , China)(Department of Materials Forming , University of Science and Technology Beijing , Beijing 100083 , China)(Department of Materials Science and Engineering , Faculty of Engineering , Kyushu University , Fukuoka 812 , Japan)

金属学报(英文版)

The Co3 Ti phase hardens appreciably by the fine precipitation of disordered fcc Co-rich phase upon aging after quenching from solution annealing temperature. Transmission electron microscope (TEM)observations revealed that the precipitates are platelet in shape, lying nearly parallel to the {100} planes of the L12-ordered matrix, and perfectly coherent with the matrix lattice at the beginning of aging. The high temperature strength increases appreciably with the fine precipitation of disondered Co-rich phase over the whole temperature range investigated. TEM observations of the deformed alloys after underaging revealed that saperdislocations are pinned by precipitates indicating an attractive interaction between dislocations and precipitates.

关键词: Co_3 Ti , null , null , null , null

EFFECT OF Cr ADDITION ON MICROSTRVCTURES AND MECHANICAL PROPERLIES OF β-NiAl ALLOYS

W.H. Tian , S.L. Hu and M. Nemoto(1) Department of Materials Physics , University of Science and Technology Beijing , Beijing 100083 , China 2) Department of Materials Forming , University of Science and Technology Beijing , Beijing 100083 , China 3) Department of Materials Science and Engineering , Faculty of Engineering , Kyushu University , Fukuoka 812 , Japan)Manuscript received in revised form 12 October 1998

金属学报(英文版)

The effect of Cr addition on the microstructures and mechanical properties of NiAl inermetallic alloys containing 4 to 8 mol% Cr has been characterized. It is shown that Cr is not only an efficient soild solution strengthener in NiAl, it is also an efficient precipitation Strengthener by fine dispersion of α-Cr particles. Transmission electron microscope observations have revealed that fine spherical particles of α-Cr appeared homogeneously in the NiAl matrix by aging at temperatures around 1073K after solution annealing at 1563K. The aging behavior was investigated by microhardness measurements and the temperature dependence of the yield stress of NiAl containing α-Cr particles was investigated by compression tests over the tempemture range from 298 to 1173K. NiAl alloys happened appreciably by the precipitation of α-Cr particles.Dislocations bypass the particles during deformation and typical Orowan loops were observed surrounding the α-Cr particles after deformation. Although the dispersion Of α-Cr particles increases the yield strength of NiAl at intermediate temperutre, the strength decreases appreciably at higher temperatures.

关键词: NiAl , null , null , null , null

EVALUATION OF EMBRITTLEMENT BEHAVIOR DUE TO SENSITIZATION IN A CRYOGENIC AUSTENITIC STAINLESS STEEL BY MEANS OF SMALL PUNCH AND FRACTURE TOUGHNESS TESTS

S.C Liu(Research Institute for Fracture Technology Faculty of Engineering , Tohoku University , Sendai , Japan , on leave from Dalian Railway Institute , Dalian 116028 , China)II-Hyun Kown , T Hashida and H Takahashi(Research Institute for nacture Technology , Faculty of Engineering , Tohoku Univeristy , Sendai , Japan)

金属学报(英文版)

In order to evaluate the tendency of mechanical properties degrudation due to weld-ing and other processing in materials used for supporting coils in super conducting rnaguets utilized in thermonuclear jusion reactore, a small punch (SP) test was used.This test, which was originally developed to study irradiation damage using miniatursized specimens was performed at 77 and 4 K for solution treated and sensitized JN1 austenitic stainless steel, a candidate cryogenic structural material. The area under the load-deflection curve up to the maximum applied load in SP test was defined as the SP enerpy, to characterize the resistance to fracture. Although solution treated material exhibited ductile fracture mode with high SP enerpy, embrittlement behavior due to sensitization at 650-800°for 1-5 h was shown clearlg by SP test with brittle intergranular fracture and decreased SP enerpy. Comparison of the results obtained by SP test with those by fracture toughness test showed the usefulness of SP test for evaluation of sensitization induced embrittlement at cryogenic temperature. The re-sults obtained in this study can be very usefol in predicting the degradation due to welding and other processing in cryogenic materials.

关键词: small punch test , null , null , null

DEFORMATION AND FRACTURE OF TiAl PST CRYSTALS UNDER MONOTONIC AND CYCLIC LOADING

Y.Umakoshi , T. Nakano and H .Y. Yasuda (Department of Materials Science and Engineering , Faculty of Engineering , Osaka University , 2-1 , Yamada-Oka , Suita , Osaka 565 Japan)

金属学报(英文版)

Plastic behaviour of TiAl polysynthetically twinned (PST) crystals is reviewed to show our knowledge and understanding for receiving a good combination of strength and ductility of two phase TiAl alloys under monotonic and cyclic loading conditions. Anisotropy and mechanism of strength, ductility, toughness. cyclic hardening and fatigue life are described focusing on the effect of lamellar structure.

关键词: :Fatigue. Deformation , null , null

PRECIPITATION BEHAVIOUR AND HARDENING OF B2-ORDERED Ni(Al, Ta)

W.H. Tian and M. Nemoto2(Department of Materials Physics , University of Science and Technology Beijing , Beijing 100083 , China)(Department of Materials Science and Engineering , Faculty of Engineering , Kyushu University , 812 , Fukuoka , Japan)

金属学报(英文版)

Precipitation of Ni2Al in supersaturated NiAl containing Ta and corresponding hardening have been investigated by hardness measurements and by transmission electron microscope observations. Selected area electron diffraction, high resolution electron microscopy and energy dispersive X-ray spectrometer analysis have shown that the Ni2Al with a hexagonal structure precipitates coherently in the B2-NiAl matrix. Ni2Al is an ordered phase with a. unit cell parameter, aNi2All=aNiAl and CNi2Al= aNiAl. The orientation relationship between the Ni2Al precipitate and the B2-NiAl matrix is (0001)Ni2Al (111)NiAl and [1120]Ni2Al[110]NiAl. NiAlhardens appreciably by the precipitation of Ni2Al phase.

关键词: intermetallic compound , null , null , null , null

Service Performance of Engineering Materials

Andrej Atrens

材料科学技术（英）

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 , null , null

Biomimicry of bamboo bast fiber with engineering composite materials

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

Strengthening Materials by Engineering Coherent Internal Boundaries at the Nanoscale

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

Crystal facet engineering of semiconductor photocatalysts: motivations, advances and unique properties

Chemical Communications

Crystal facet engineering of semiconductors has become an important strategy for fine-tuning the physicochemical properties and thus optimizing the reactivity and selectivity of photocatalysts. In this review, we present the basic strategies for crystal facet engineering of photocatalysts and describe the recent advances in synthesizing faceted photocatalysts, in particular TiO(2) crystals. The unique properties of faceted photocatalysts are discussed in relation to anisotropic corrosion, interaction dependence of adsorbates, photocatalytic selectivity, photo-reduction and oxidation sites, and photocatalytic reaction order. Ideas for future research on crystal facet engineering for improving the performance of photocatalysts are also proposed.

关键词: shape-controlled synthesis;exposed 001 facets;rutile tio2 nanorods;visible-light photocatalysis;solvent-solute interactions;anatase;titanium(iv) oxide;low-temperature synthesis;ordered solid-phases;platinum nanocrystals;hydrogen-production

Study on compression behavior of porous magnesium used as bone tissue engineering scaffolds

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