S.C Liu(Research Institute for Fracture Technology Faculty of Engineering
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Tohoku University
,
Sendai
,
Japan
,
on leave from Dalian Railway Institute
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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
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null
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null
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null
CUI Juan
,
LIU Yazheng
,
PAN Hui
,
GAO Lifeng
钢铁研究学报(英文版)
The microsturctural transformation of austenite grain, pearlite interlamellar spacing, and lamellar cementite thickness of spring steel 60Si2MnA for railway were studied in the hotrolled and reheated states. Furthermore, the effect of microstructural characterization on its final mechanical properties was discussed. The results showed that as far as 60Si2MnA, the pearlite interlamellar spacing determined the hardness, whereas, the austenite grain determined the toughness. Compared with microstructure and mechanical properties in the hotrolled state, after reheating treatment at 950 ℃, its average grain sizes are apparently fine and the pearlite interlamellar spacing and lamellar cementite thickness coarsen to some extent, but both hardness and impact toughness increase to HRC 48 and 85 J, respectively. In the course of making spring, the optimum reheating austenitizing temperature for the 60Si2MnA steel is 950 ℃.
关键词:
austenitizing temperature;austenite grain;pearlite interlamellar spacing;hardness;toughness
MA Zongyi YAO Zhongkai Harbin Institute of Technology
,
Harbin
,
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
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composite
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null
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null
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null
Applied Physics Letters
The occurrence of deformation twinning in face-centered-cubic (fcc) crystals with medium to high stacking fault energy is normally very difficult. Through specially designing the orientation of Cu single crystal, the authors do not only observe profuse nanoscale deformation twins with a tower shape originating from grain boundary but also find some of them terminated in the interior of the grain. The observations clearly prove that the deformation twinning can nucleate through successively emitting partials from grain boundaries, indicating the ubiquity of deformation twinning even in those fcc single crystals deformed at suitable conditions. (C) 2008 American Institute of Physics.
关键词:
low strain-rate;nanocrystalline al;room-temperature;single-crystals;mechanism;metals;evolution;aluminum
Applied Physics Letters
The solidification behavior of germanium quenched from the melt at pressure of 2-7 GPa is presented. The solidification parameters of specimen were directly measured under high pressure. The microstructure of specimen was observed by electron microscopy. From the measured undercooling and average grain size, the interfacial free energy and activation energy of crystal growth under high pressures were estimated according to classical nucleation theory. Using high resolution transmission electron microscopy (HRTEM), crystals of sizes ranging from 5 to 100 nm surrounded by an amorphous matrix of germanium were found in those samples which quenched from deeply undercooled melt. (C) 1995 American Institute of Physics.
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Applied Physics Letters
The Si/Si oxynitride superlattices, with three periods, have been grown using the two-target alternation magnetron sputtering technique. The thicknesses of Si oxynitride layers and Si layers in the superlattices are 2.0 and 1.4 nm, respectively. Visible electroluminescence (EL) from a semitransparent Au film/(Si/Si oxynitride) superlattice/p-Si structure has been observed. Each EL spectrum of the structure has a dominant peak around 640 nm, a weaker peak around 520 nm, and a shoulder around 820 nm. By comparing the EL from the semitransparent Au film/(Si/Si oxynitride) superlattice/p-Si structure with that from a semitransparent Au film/Si oxynitride film/ p-Si structure, we found that the EL efficiency of the former structure is about 2-4 times of that of the latter one. (C) 1998 American Institute of Physics.
关键词:
chemical-vapor-deposition;silicon-nitride films;optical-properties;spectra
Applied Physics Letters
Ultraviolet (UV) light emission with almost the same peak wavelengths from thermally oxidized porous silicon (OPS) (340, 355, and 370 nm) and SiO2 powder (340, 350, and 370 nm) has been observed. Photoluminescence excitation spectra of OPS without Si nanoscale particles (SNP) and those of SiO2 powder are very similar, however, very different from those of the OPS with SNP. Three types of luminescence centers with luminescence wavelengths around 350 nm are responsible for UV light emission, and photoexcitation in OPS with SNP occurs in SNP-as well as in Si oxide layers covering SNP. (C) 1996 American Institute of Physics.
关键词:
light-emission;visible luminescence;optical-properties;photoluminescence;excitation;mechanism;centers;films
Journal of Applied Physics
Nanometer Ge particle (NGP) embedded Si oxide films were deposited on p-type Si substrates using the rf magnetron sputtering technique with a Ge-SiO2 composite target. The area ratio percentage of the Ge target to the composite target was 5%. These films were annealed in a N-2 ambient at 300, 600, 800, or 900 degrees C for 30 min. By fitting Raman scattering spectra, the average diameters of,the NGPs in the films were determined. They increased from 5.4 to 9.5 nm with increasing annealing temperatures from 600 to 900 degrees C. The photoluminescence (PL) peaks for all NGP embedded Si oxide films annealed at various temperatures are located at almost the same position around 580 nm (2.1. eV), although the average sizes of the NGPs in these films are very different from each other. After gamma-ray irradiation, the PL peak intensity increases by a factor of 2.3, with the peak position unchanged. The PL peak position does not show any evident shift when the measurement temperature increases from 10 to 300 K. All experimental facts indicate that Light emission originates mainly from the luminescence centers in the SiOx films covering the NGPs rather than from the NGPs. The role of NGPs in the PL process of the films is discussed. (C) 1998 American Institute of Physics.
关键词:
visible photoluminescence;porous silicon;luminescence;confinement;mechanism;matrix;raman
Applied Physics Letters
We use only nitrogen as the reaction gas to deposit on the cleaned Si wafer an extra-thin Si nitride film (similar to 40 Angstrom) by electron cyclotron resonance method. Electroluminescence (EL) with its peak wavelength at about 7000 Angstrom from the semitransparent Au/extra-thin Si nitride film/p-Si structure has been detected. The effects of forward bias and annealing on the EL have been studied. (C) 1996 American Institute of Physics.
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