MA Zongyi YAO Zhongkai Harbin Institute of Technology
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Harbin
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China
金属学报(英文版)
The SiC_w/Al composite prepared by squeeze casting has a combination of superior room temperature specific strength and modulus together with excellent thermal properties.The extrusion can make an improvement on the strength and ductility of the composite from 582 MPa as squeeze casted up to 639 MPa,and on the transformation from isotropic to the anisotropic structure.This seems to be explained by the orientation of whiskers and the densification of dislocations in matrix.TEM observation indicates that the stacking fault is the usual planar defect on the SiC_w surface. composite;;SiC whisker;;Al alloy;;microstructure
关键词:
composite
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null
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null
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null
Applied Physics Letters
The dielectric resonance and multiple magnetic resonances which correspond to multiple microwave absorptions in the 2-18 GHz range have been studied in the composite Fe/TiO(2). The Fe grain size is found to have great impact on the dielectric resonance in this metal-semiconductor composite. The polarization mechanism is attributed to interfacial polarization. The multiple magnetic resonances can be ascribed to the natural resonance and exchange resonances, which can be explained by Aharoni's exchange resonance theory. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3496393]
关键词:
ferromagnetic particles;carbon nanotubes;absorption;permeability
材料科学技术（英文）
Molecular structures of adsorbed waters at metal surfaces are essential to understanding the widespread processes ranging from ice nucleation, to water involved catalytic surface reactions, to many phenomena of biological and astrochemical importance. Instead of providing a comprehensive literature survey, we focus in this review on detailed structural information, such as water orientations and occupation sites, of intact waters at low temperatures and ultrahigh vacuum conditions investigated by various surface techniques. Despite progresses made in direct imaging the surface waters at high resolutions, as exemplified in a close-packed (e.g. Pd(111)) and an open metal surfaces (e.g. Cu(110)) supported waters, structural mysteries remain at diverse metal surfaces. We highlight experimental challenges and discuss structural mysteries in elucidating surface water structures at molecular levels.
关键词:
Water monolayer;Surface structure;Transition metal surfaces;scanning-tunneling-microscopy;density-functional theory;vibrational-spectra;ice;pt(111);adsorption;dissociation;ru(0001);excitation;molecules
Jibiao Li Shenglong Zhu Fuhui Wang
材料科学技术（英文）
Molecular structures of adsorbed waters at metal surfaces are essential to understanding the widespread processes ranging from ice nucleation, to water involved catalytic surface reactions, to many phenomena of biological and astrochemical importance. Instead of providing a comprehensive literature survey, we focus in this review on detailed structural information, such as water orientations and occupation sites, of intact waters at low temperatures and ultrahigh vacuum conditions investigated by various surface techniques. Despite progresses made in direct imaging the surface waters at high resolutions, as exemplified in a close-packed (e.g. Pd(111)) and an open metal surfaces (e.g. Cu(110)) supported waters, structural mysteries remain at diverse metal surfaces. We highlight experimental challenges and discuss structural mysteries in elucidating surface
water structures at molecular levels.
关键词:
Water monolayer
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surface structure
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transition metal surfaces
J.Q.ZHANGD.J.YOUNG
中国腐蚀与防护学报
Metaldusting attacks iron, low and high alloy steels and nickel-or cobalt-base alloys by disintegrating bulk metals and alloys into metal particles in a coke deposit. It occurs in strongly carburising gas atmospheres (carbon activity aC>1) at elevated temperatures (400 ℃~1000 ℃). This phenomenon has been studied for decades, but the detailed mechanism is still not well understood. Current methods of protection against metal dusting are either directed to the process conditions-temperature and gas composition-or to the development of a dense adherent oxide layer on the surface of the alloy by selective oxidation. However, metal dusting still occurs by carbon dissolving in the base metal via defects in the oxide scale. The research work at UNSW is aimed at determining the detailed mechanism of metal dusting of both ferritic and austenitic alloys, in particular the microprocesses of graphite deposition, nanoparticle formation and underlying metal destruction. This work was carried out using surface observation, cross-section analysis by focused ion beam and electron microscopic examination of coke deposits at different stages of the reaction. It was found that surface orientation affected carbon deposition and metal dusting at the initial stage of the reaction. Metal dusting occurred only when graphite grew into the metal interior where the volume expansion is responsible for metal disintegration and dusting. It was also found that the metal dusting process could be significantly changed by alterations in alloy chemistry. Germanium was found to affect the iron dusting process by destabilising Fe3C but increasing the rate of carbon deposition and dusting, which questions the role of cementite in ferritic alloy dusting. Whilst adding copper to iron did not change the carburisation kinetics, cementite formation and coke morphology, copper alloying reduced nickel and nickel-base alloy dusting rates significantly. Application of these fundamental results to the dusting behaviour of engineering alloys is discussed.
关键词:
metal dusting
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null
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null
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null
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null
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null
Journal of Applied Physics
To date, high compressive ductility and energy absorption have been achieved in amorphous metal foams based on high-toughness Pd- and Zr-based metallic glasses and are known to result from two extrinsic toughening mechanisms: bending of struts and shear band arrest by pores. We study here a syntactic amorphous metallic foam produced by infiltration of a bed of hollow crystalline iron spheres with a low-toughness Mg-based metallic glass (Mg60Cu21Ag7Gd12). After quenching to vitrify the matrix, this foam exhibits much higher compressive failure strain and energy absorption than the monolithic metallic glass, an improvement which is assigned to an intrinsic mechanism, i.e., composite toughening by the network of hollow ductile iron spheres.(C) 2007 American Institute of Physics.
关键词:
glass matrix composites;mechanical-properties;enhanced plasticity;syntactic foams;alloys;fabrication;damage
Applied Physics Letters
The magnetotransport behaviors of a series of rare earth manganites with the same A-site cational mean radius and different A-site ionic radii variance (A-site disorder) are investigated. It is found that the system's ground state transforms from ferromagnetic metal to cluster-glass insulator with increasing A-site disorder. In the cluster-glass state, the magnetization shows the steplike behavior, indicating the existence of short-range magnetically ordered clusters. The significant effect of the A-site disorder on the electronic phase separation is revealed by detecting the cluster-glass ground state at low temperature. (c) 2006 American Institute of Physics.
关键词:
manganese oxide perovskites;phase-separation;cation disorder;double-exchange;magnetoresistance;resistivity
Journal of Applied Physics
Magnetic and transport properties of SrRuO(3) film grown on SrTiO(3) at different substrate temperatures have been investigated. Metallic behavior over the temperature range from 5 to 300 K is observed in the film grown at 750 degrees C. With a decrease in the growth temperature, a metal-insulator transition occurs for films grown at 700 and 650 degrees C, with transition temperatures of 15 K and 250 K, respectively, and a complete insulator behavior shows up in the film grown at 600 degrees C. Correspondingly, out-of-plane (OOP) magnetic anisotropy is gradually weakened, leading to complete magnetic isotropy in the film grown at 600 degrees C. The OOP lattice constant increases from 0.395 nm, for the film grown at 750 degrees C, up to 0.403 nm for the film grown at 600 degrees C. The correlation between the magnetic properties, transport properties, and the lattice constants indicates that the magnetic anisotropy and the metal-insulator transition (or insulator behavior) are caused mainly by strain in the SRO films, with correspondingly larger strain in films grown at lower temperatures. (C) 2010 American Institute of Physics. [doi: 10.1063/1.3431459]
关键词:
internal stresses;lattice constants;magnetic anisotropy;magnetic thin;films;metal-insulator transition;pulsed laser deposition;strontium;compounds;electronic-structure;transport-properties;001 srtio3
