S.M.Morsy (Metallurgy Dept. Nuclear Research Center
,
Atomic Energy Authority
,
Cairo
,
Egypt) I.Z.Selim (Physical Chemistry Dept.
,
National Research Center
,
Dokki
,
Cairo
,
Egypt)S. H. Tantawi (Building Research Institute
,
Dokki
,
Cairo
,
Egypt)
材料科学技术（英文）
Electrochemical techniques of the corrosion measurements of reinforcing steeI in concrete have been evaluated. These techniques include half-cell potential measurements, impressed voltage method, impressed current method and potentiostatic polarization technique. The results of corrosion behaviour of the steel in both 5%NaCl and 5%MgSO4 show that each electrochemical technique provides some information about the condition of the steel bar or the corrosivity of the environment being evaluated, yet none provides a complete data regarding the corrosion resistance of reinforcing steel in aggressive media
关键词:
A.F.Waheed and H.M.Soliman(Dept. of Metallurgy
,
Nuclear Research Center
,
Atomic Energy Authority
,
Cairo
,
Egypt)
材料科学技术（英文）
The beginning of failure of a (ZrO2-7%Y2O3)/(Ni-22%Co-17%Cr-12.5%Al-0.6%Y) duplex andgraded coating systems on lnconel 617 and IN738LC in burner rig tests has been characterized.The test conditions are 40 s heating up to 75O℃ substrate temperature followed by 80 s aircooling. Failure is considered at the appearance of the first bright spot during heating period.Stresses due to thermal expansion mismatch strains on cooling are the probable cause of life-limiting in this conditions of testing.
关键词:
H.M.Soliman
,
K.E.Mohamed
,
M.E.Abd El-Azim and F.H.Hammad(Metallurgy Dept.
,
Atomic Energy Authority
,
Cairo
,
Egypt)
材料科学技术（英文）
Low and medium carbon steels were aluminized by the pack aluminizing technique using halideactivated pure-Al and Fe-Al packs. The effect of mixture composition, aluminizing temperatureand time and C content of the steel substrate on the structure and thickness of the aluminidelayer, and on the oxidation resistance was investigated. The optimum oxidation resistance canbe achieved with a low carbon steel substrate when the intermetallic phases Fe3Al and FeAlform the surface of the aluminide layer. In this case, the Al concentration at the surface of thealuminide coating is at least ≥15 wt pct. Formation of high Al concentration phases (FeAl3 andFe2Al5) during aluminizing should be avoided as they tend to embrittle the aluminide layer andreduce its oxidation resistance.
关键词:
材料科学技术（英文）
The results of molecular dynamics calculations on the interfacial energies and atomic structures of Ag/Ni and Cu/Ni interfaces are presented. Calculation on Ag/Ni interfaces with low-index planes shows that those containing the (111) plane have the lowest energies, which is in agreement with the experiments. Comparing surface energy with interfacial energy, it is found the order of the interfacial energies of Ag/Ni and Cu/Ni containing the planes fall in the same order as solid-vapor surface energies of Ag, Cu and Ni. In this MD simulation, the relaxed atomic structure and dislocation network of (110)(Ag)parallel to(110)(Ni) interface are coincident to HREM observations.
关键词:
molecular dynamics;interfacial energy;atomic structure;heterophase;boundary;fcc metals;model;boundaries;liquid;nickel
Haijiang LIU
,
Shaoqing WANG
,
An DU
,
Caibei ZHANG
材料科学技术（英文）
The results of molecular dynamics calculations on the interfacial energies and atomic structures of Ag/Ni and Cu/Ni interfaces are presented. Calculation on Ag/Ni interfaces with low-index planes shows that those containing the (111) plane have the lowest energies, which is in agreement with the experiments. Comparing surface energy with interfacial energy, it is found the order of the interfacial energies of Ag/Ni and Cu/Ni containing the planes fall in the same order as solid-vapor surface energies of Ag, Cu and Ni. In this MD simulation, the relaxed atomic structure and dislocation network of (110) Ag||(110) Ni interface are coincident to HREM observations.
关键词:
Molecular dynamics
,
null
,
null
,
null
Shuwang DUO
,
Meishuan LI
,
Yaming ZHANG
材料科学技术（英文）
In order to study the atomic oxygen corrosion of spacecraft materials in low earth orbit environment, an atomic oxygen simulator was established. In the simulator, a 2.45 GHz microwave source with maximum power of 600 W was launched into the circular cavity to generate ECR (electron cyclotron resonance) plasma. The oxygen ion beam moved onto a negatively biased Mo plate under the condition of symmetry magnetic mirror field confine, then was neutralized and reflected to form oxygen atom beam. The properties of plasma density, electron temperature, plasma space potential and ion incident energy were characterized. The atomic oxygen beam flux was calibrated by measuring the mass loss rate of Kapton during the atomic oxygen exposure. The test results show that the atomic oxygen beam with flux of 1016~1017 atoms•cm-2•s-1 and energy of 5~30 eV and a cross section of Φ80 mm could be obtained under the operating pressure of 10¬-1~10-3 Pa. Such a high flux source can provide accelerated simulation tests of materials and coatings for space applications.
关键词:
Atomic oxygen
,
null
,
null
,
null
材料科学技术（英文）
In order to study the atomic oxygen corrosion of spacecraft materials in low earth orbit environment, an atomic oxygen simulator was established. In the simulator, a 2.45 GHz microwave source with maximum power of 600 W was launched into the circular cavity to generate ECR (electron cyclotron resonance) plasma. The oxygen ion beam moved onto a negatively biased Mo plate under the condition of symmetry magnetic mirror field confine, then was neutralized and reflected to form oxygen atom beam. The properties of plasma density, electron temperature, plasma space potential and ion incident energy were characterized. The atomic oxygen beam flux was calibrated by measuring the mass loss rate of Kapton during the atomic oxygen exposure. The test results show that the atomic oxygen beam with flux Of 10(16)similar to10(17) atoms(.)cm(-2.)s(-1) and energy of 5similar to30 eV and a cross section of phi80 mm could be obtained under the operating pressure of 10(-1)similar to10(-3) Pa. Such a high flux source can provide accelerated simulation tests of materials and coatings for space applications.
关键词:
atomic oxygen;low earth orbit space environment;ECR plasma;microwave;surfaces;erosion
Journal of Spacecraft and Rockets
An amorphous silicon carbonitride (Si(1-x-y)C(x)N(y), x = 0.43, y = 0.31) coating was deposited on polyimide substrate using the magnetron-sputtering method. Exposure tests of the coated polyimide in atomic oxygen beam and vacuum ultraviolet radiation were performed in a ground-based simulator. Erosion kinetics measurements indicated that the erosion yield of the Si(0.26)C(0.43)N(0.31) coating was about 1.5 x and 1.8 x 10(-26) cm(3) /a tom during exposure in single atomic oxygen beam, simultaneous atomic oxygen beam, and vacuum ultraviolet radiation, respectively. These values were 2 orders of magnitude lower than that of bare polyimide substrate. Scanning electron and atomic force microscopy, X-ray photoelectron spectrometer, and Fourier transformed infrared spectroscopy investigation indicated that during exposures, an oxide-rich layer composed of SiO(2) and minor Si-C-O formed on the surface of the Si(0.26)C(0.43)N(0.31) coating, which was the main reason for the excellent resistance to the attacks of atomic oxygen. Moreover, vacuum ultraviolet radiation could promote the breakage of chemical bonds with low binding energy, such as C-N, C = N, and C-C, and enhance atomic oxygen erosion rate slightly.
关键词:
atomic oxygen;films;radiation;polymers;beam;sicn
Science in China Series a-Mathematics Physics Astronomy
Based on the coincidence site lattice model and by use of the molecular dynamics method, the relaxation calculations on the atomic structures of the grain boundaries of various generating functions (SIGMA3, SIGMA5, ..., SIGMA19, ..., SIGMA33) in the transition metal Ni are performed. The features of atomic structures corresponding to the grain boundaries arid the effects of the pre-parameter on the interface structures are given. To study the doping response relating to the properties of materials, the SIGMA3 tilt grain boundary is selected. Based on the interstice and vacancy mechanisms, the interface responses doping boron, nitrogen and phosphorus for the grain boundary are investigated. According to the criterion of the energy in molecular dynamics simulation, the most probable positions of doping impurities and effect of doping impurities on the interface structure are given, and the dependence of the fine structure on doping type and the order of the impurity amount are obtained. The analysis of the local energy for the relaxation region shows that the light impurities, boron, nitrogen arid phosphorus, all have a tendency to segregate on the grain boundary and change the feature of the atomic configuration of the interface to a distinct extent. Then the effects of doping impurities on the interface can be predicted.
关键词:
atomic structure of grain boundary;doping response;molecular dynamics;method;austenitic stainless-steel;scale segregation behavior;electronic-structure;intergranular fracture;boron
