N.S.Stoloff Department of Materials Engineering
,
Rensselaer Polytechnic Institute
,
Troy
,
New York
,
USAC.T.Liu Metals and Ceramics Division
,
Oak Ridge National Laboratory
,
Oak Ridge
,
Tennessee
,
USA
材料科学技术(英文)
A comprehensive review of low temperature environmental embrittlement in intermetallics is pres- ented. Moisture and hydrogen are shown to severely embrittle many intermetallics, including iron, nickel and titanium aluminides. The roles of composition, microstructure and external test variables are emphasized. Several methods to reduce or avoid embrittlement are described.
关键词:
environmental embrittlement
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null
,
null
吴垠
,
李凤生
,
白华萍
,
姜炜
材料导报
采用激光粒度分析法测定超细OAK木炭及竹炭粉粒度,探讨了分散剂种类、分散时间、搅拌速度、超声时间等因素对超细OAK木炭及竹炭粉粒度的影响.结果表明:以六偏磷酸钠为分散剂时分散效果最佳,其用量为0.06g/(100mlOAK木炭及竹炭粉乳液);在测定时选择循环搅拌泵速为2200~2400r/min较好;超声时间为200s左右时,可达到最佳分散效果.
关键词:
超细OAK
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木炭及竹炭粉
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粒度
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激光粒度分析法
LIANG Sizu LIANG Yaoneng LIU Zhengyi South China University of Technology
,
Guangzhou
,
China Lecturer
,
Department of Mechanical Engineering No.2
,
South China University of Technology
,
Guangzhou 510641
,
China
金属学报(英文版)
The fracture surface of the normalized steel 55SiMnMo was observed,under tensile device at- tached on the SEM,to be of ductile dimple feature on the bainite which is composed of lath ferrite and austenite platelet.The dimple is essentially nucleated in the ferrite.Because the austenitic plastic deformation is remarkable during fracturing,the tear ridge of dimple is very sharp.
关键词:
dimple
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null
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null
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null
ZHANG Zuo-tai
,
ZHANG Ying-yi
钢铁研究学报(英文版)
The recrystallization and oxidation of a Mn-containing interstitial free (IF) steel were investigated simultaneously using confocal scanning laser microscope (CSLM) under controlled atmosphere of Ar 95% and H2 5% (in volume percent) at different temperatures. It was found that the grain boundary played a significant role in controlling recrystallization and oxidation in overall oxidation kinetics of the steel. The surface morphology was composed of two networks along the original and new grain boundaries respectively, which did not coexist. The grain boundary moved in different directions with different velocities during annealing process. The recrystallization processes were studied by CSLM motion video through observing the moving grain boundary to estimate the time for 50% recrystallization, and the activation energy for recrystallization was therefore calculated. The oxidation mechanism was discussed through comparison of the fluxes among mass transfer of water vapor, dissociation of water vapor and outward diffusion alloying elements. The results indicated that the oxidation was controlled by the mass transfer from the bulk gas to the surface, or dissociation rate, or outward diffusion of manganese, which depended on the temperature to form a grain boundary ridge or groove.
关键词:
IF steel
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oxidation
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recrystallization
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grain boundary
Semiconductor Science and Technology
A systematic investigation has been undertaken on the growth, characterization and performance of tensile-strained multiple-quantum-well (MQW) lasers emitting at 1.34 mum. Two photoluminescence peaks corresponding to n = 1 electron-light hole (E1-LH1) and n = 1 electron-heavy hole (E1-HH1) transitions are clearly observed in MQW structures. The improvements of tensile strained MQW lasers such as the internal quantum efficiency, internal loss and threshold current are attributed to the increased energy separation between LH1 and HH1 when the tensile strain and well width are larger. The relatively thick barrier layer is required to mitigate the strain relaxation between the quantum wells. The degradation of device performance by the excessive barrier height could be attributed to the exacerbated spatial non-uniformity of the carrier distribution in the valence band. The optimized tensile strained MQW lasers with 300 mum cavity length and ridge waveguide (RWG) structure exhibit a lower threshold current of 13 mA and a higher external differential efficiency per facet of 0.29 mWmA(-1) at 25 degreesC.
关键词:
differential gain;lasers;amplifiers;1.3-mu-m
Semiconductor Science and Technology
Polarization insensitive 13 10 nm InGaAsP-InP multi-quantum-well (MQW) semiconductor optical amplifiers (SOAs), with 7degrees tilted ridge waveguide and buried-window end facets, have been fabricated and fully characterized on chip and module level. SOAs chips with an optimized complex strained MQW active region exhibited less than 1 dB polarization dependence of amplified spontaneous power in the drive current range of 50-200 mA. The amplifier module, having a residual facet reflectivity of 2.8 x 10(-5), achieved 25 dB fibre-to-fibre unsaturated gain, for both transverse electric and transverse magnetic polarization states, 11.2 dBm saturation output power, and 7.6 dB noise figure at 1310 nm. The polarization dependence of gain was less than 0.6 dB in the 3 dB gain bandwidth of 56 nm. Coupling efficiency played a significant role in the gain, saturation output power and noise figure of a SOA module. Spot-size-converter integrated SOAs with buried heterostructures are expected to exhibit further improved performances.
关键词:
wavelength conversion;tensile;transmission;modulation;lasers;fiber;gain
材料科学技术(英文)
The dynamic tensile deformation and fracture behavior of the Zr-based metallic glass/porous W phase composite were investigated at room temperature by means of the Split Hopkinson Tension Bar (SHTB) It was found that the composite exhibited no appreciable macroscopic plastic deformation prior to catastrophic fracture and the fracture surface was perpendicular to the axial direction Substantive micro cracks were observed along the interface between W grains or the interface between the metallic glass phase and the W phase Scanning electron microscopy (SEM) observations revealed that vein-like patterns dimple-like patterns and substantive ridge-like structures were the typical fracture morphologies on the fracture surface for the metallic glass phase and the morphology of the W phase is a mixture of intergranular and transgranular fracture Based on those results referred above the dynamic tensile deformation and fracture mechanism of the Zr-based metallic glass/porous W phase composite were discussed in detail
关键词:
Metallic glasses;Porous W;Composite;Dynamic tension;Fracture;behavior;glass matrix composites;bulk amorphous-alloys;mechanical-properties;deformation-behavior;fracture-toughness;shear bands;propagation;tungsten;failure
Intermetallics
The phase transformation of alumina formed during oxidation of beta-NiAl coating prepared on M38G alloy by pack cementation was investigated. Oxidation experiments were conducted at 950 degrees C for various times from 2 to 180 min. The phase composition and microstructure of the oxide scales were investigated by using glancing angle XRD, AFM and SEM. The results showed that at the initial oxidation stage needle-like theta-Al2O3 was formed and then it covered the sample surface rapidly. The formation of alpha-Al2O3 grains beneath the theta-Al2O3 layer was favored by depletion of Al in the beta-NiAl coating during oxidation. alpha-Al2O3 preferred growing on the top (ridge) of beta-NiAl grains, which resulted in the formation of net-like alpha-Al2O3 inner layer. With increasing time, theta-Al2O3 transformed to alpha-Al2O3 gradually. After 180 min oxidation, most of alpha-Al2O3 grains transformed into alpha-Al2O3. A mechanism of excessive voids' formation at the oxide/coating interface was also proposed in this paper. (c) 2007 Elsevier Ltd. All rights reserved.
关键词:
nickel aluminides, based on NiAl;oxidation;phase transformations;coatings, intermetallic and otherwise;high-temperature oxidation;theta-alpha-al2o3 transformation;behavior;coatings;superalloy;transition;layers