Insup Lee
,
Kwang-Ho Jeong
材料科学技术（英文）
Plasma nitrocarburizing and plasma oxidizing treatments were performed to improve the wear and corrosion resistance of SKD 61 steel. Plasma nitrocarburizing was conducted for 12 h at 540℃ in the nitrogen, hydrogen and methane atmosphere to produce the ε-Fe2–3 (N,C) phase. The compound layer produced by plasma nitrocarburising was predominantly composed of ε-phase, with a small proportion of γ′-Fe4(N,C) phase. The thickness of the compound layer and the diffusion layer are about 10 μm and about 200 μm, respectively. Plasma post oxidation was performed on the nitrocarburized samples with various oxygen/hydrogen ratio at constant temperature of 500℃ for 1 h. The very thin magnetite (Fe3O4) layer of 1–2 μm in thickness on top of the compound layer was obtained. Anodic polarization test revealed that plasma nitrocarburizing process contributed a significant improvement of corrosion resistance of SKD 61 steel. However, the corrosion characteristics of the nitrocarburized compound layer was deteriorated by oxidation treatment.
关键词:
Plasma nitrocarburizing
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null
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Lixing HUO
,
Furong CHEN
,
Yufeng ZHANG
,
Li ZHANG
,
Fangjun LIU
,
Gang CHEN
材料科学技术（英文）
The electron beam local post-weld heat treatment (EBLPWHT) is a rather new method that provides the advantages of high precision, flexibility and efficiency, energy saving and higher productivity. This paper studies the effect of two post-weld heat treatment processes on the microstructure, mechanical properties and fracture toughness of an electron beam welded joints in 30CrMnSiNi2A steel. EBLPWHT, in a vacuum chamber, immediately after welding and a traditional furnace whole post-weld heat treatment (FWPWHT) were compared. The experimental results show that, after EBLPWHT treatment, the main microstructure of weld was changed from coarse acicular martensite into lath martensite, HAZ was changed from lath martensite, bainite into lower bainite, and base metal was changed from ferrite and pearlite into upper bainite and residual austenite. The microstructures of different zones of joints in FWPWHT condition were tempered sorbite. The properties of welded joints can be improved by the EBLPWHT in some extent, and especially largely for the fracture toughness of welded joints. However the value of fracture toughness of base metal is comparatively low, so appropriate heat treatment parameters should be explored in the future.
关键词:
Post-weld heat treatment
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null
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null
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Carbon
A combined in situ and post-synthesis gas phase oxidation approach for selective removal of metallic single-walled carbon nanotubes (m-SWCNTs) is reported. The in situ oxidation is performed by introducing a small amount of oxygen during the synthesis of SWCNTs by floating catalyst chemical vapor deposition, and the post-synthesis oxidation is conducted by heat-treating the synthesized SWCNTs in air at 400 C. A combination of characterization techniques shows that m-SWCNTs were selectively removed as a result of their higher reactive activity to oxygen compared to semiconducting SWCNTs, and the diameter distribution of the SWCNTs is narrowed to a range of 1.5-2.0 nm. The mechanism of the combined in situ and post-synthesis oxidation approach is discussed. (C) 2010 Elsevier Ltd. All rights reserved.
关键词:
field-effect transistors;preferential destruction;absorption-spectroscopy;fluorescence;irradiation;separation
Physica B-Condensed Matter
We have studied the effects of Si ion implantation and post-annealing on yellow luminescence (YL) from GaN. Two types of GaN samples grown by the metal-organic chemical vapor deposition method and labeled as GaN1 and GaN2 were studied. The PL spectrum of the as-grown GaN1 sample was dominated by a strong YL and that of the as-grown GaN2 sample was almost free from YL. After Si ion implantation with doses of both 1.3 x 10(13) and 1.0 x 10(16)cm(-2), the intensity ratios of YL to near band edge (NBE) emission (I-Y/I-NBE) for the GaN1 samples decreased markedly compared with those of the corresponding unimplanted ones both before and after post-annealing at temperatures up to 950degreesC. However, for the Si-ion-implanted GaN2 sample with a dose of 1.3 x 10(13)cm(-2), I-Y/I-NBE increased compared with that of the as-grown one both before and after post-annealing. Besides, the I-Y/I-NBE for Si-ion-implanted GaN1 with a dose of 1.3 x 10(13) cm(-2) increased monotonically with annealing temperature. Our results show that only the Si ion implantation being accompanied with high-temperature post-annealing could produce YL. The possible reasons for the marked reduction in I-Y/I-NBE for the GaN1 sample after Si-ion-implantation have been discussed. (C) 2002 Elsevier Science B.V. All rights reserved.
关键词:
photoluminescence;yellow luminescence;ion implantation;GaN;detected magnetic-resonance;vapor-phase epitaxy;laser-diodes;undoped;gan;photoluminescence;vacancies;layers;origin
Acta Materialia
The post-dynamic transformation that takes place during the subsequent isothermal holding for the case when dynamic strain-induced transformation (DSIT) from austenite to ferrite occurs during hot deformation is investigated by cellular automaton modeling. The simulation provides a better understanding of carbon diffusion in retained austenite and the resulting microstructure evolution during the post-dynamic transformation. The predictions reveal that continuing transformation from retained austenite to ferrite and the reverse transformation can occur simultaneously in the same microstructure during post-deformation isothermal holding owing to the locally acting chemical equilibrium conditions. Competition between forward and reverse transformation exists during the early stage of post-dynamic heat treatment. It is also revealed that increasing the final strain of DSIT might promote the reverse transformation, whereas the continuous austenite-to-ferrite transformation yields a diminishing effect. The influence of the DSIT final strain on the grain size of ferrite and the characteristics of the resultant microstructure is also discussed. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
关键词:
Strain-induced transformation;Post-dynamic transformation;Cellular;automaton;Modeling;Low-carbon steel;strain-induced transformation;deformation-induced ferrite;ultrafine-grained steels;c-mn steel;phase-transformation;mechanical-properties;microalloyed steel;microstructure;simulation;alloys
Douxing LI and Hengqiang YE (Laboratory of Atomic imaging of Solids
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Institute of Metal Research
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Chinese Academy of Sciences
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Shenyang
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110015
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China)
材料科学技术（英文）
The present paper summarizes the current status of high resolution electron microscopy (HREM)and the applications of HREM to materials science and condensed matter physics. This review recounts the latest development of high resolution electron microscope, progress of HREM and the applications of HREM, including the crystal structure determination of microcrystalline materials and characterization of the local structure of the defects and nanostructured materials as well as qualitative and quantitative analysis of the grain boundaries, interfaces and interfacial reactions in the advanced materials by means of HREM in combination with electron diffraction,subnanometer level analysis, image simulation and image processing.
关键词:
Journal of Materials Chemistry
The introduction of a secondary phase is an efficient and effective way to improve the electrochemical performance of graphene towards energy storage applications. Two fundamental strategies including pre-graphenization and post-graphenization were widely employed for graphene-based hybrids. However, there is still an open question of which way is better. In this contribution, we investigated the differences in the structure and electrochemical properties of pre- and post-graphenized graphene-SnO2 hybrids. The pre-graphenization is realized by synthesis of thermally reduced graphene and subsequent impregnation of SnO2, while the post-graphenization is realized by introducing a Sn-containing phase onto GO sheets followed by chemical reduction. The pre-graphenization process provides a large amount of pores for ion diffusion, which is of benefit for loading of SnO2, fast ion diffusion for supercapacitors, and higher capacity for Li-ion batteries, but poor stability, while the post-graphenization process offers compact graphene and good interaction between the SnO2 and graphene, which provides stable structure for long term stability for supercapacitor and Li-ion battery use.
关键词:
performance anode materials;lithium ion batteries;2-dimensional;nanomaterial;supercapacitor electrodes;sno2/graphene composite;carbon;materials;mass-production;fabrication;capacitors;graphite
