M.E.Abd El-Azim
,
H.M.Soliman (Metallurgy Dept.
,
Atomic Energy Authority Cairo
,
Egypt)
材料科学技术（英文）
Aluminizing of Cu by a pack cementation process was performed to improve its surface properties.The effect of variation of pack aluminizing temperature from 800 to 900℃ and aluminizing time from 1 to 6 h on the microstructure and the thickness of the aluminide coating of Cu was investigated. Pack aluminizing of Cu significantly improved the microhardness and the oxidation resistance. The microhardness was increased about seven times and the oxidation resistance,after 96 h exposure in air at 900℃, was extremely increased ten times by aluminizing Cu at 900℃ for 3 h.
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
Physical Review B
Triangle defect states of hexagonal boron nitride (h-BN) atomic layer were studied by a density functional theory calculation. N(B) triangle defect states of h-BN atomic layer with N(B) edge atoms have acceptor (donor) levels. A cohesive energy calculation indicates that the h-BN atomic layer with N triangle defects is more or less stable, respectively, than that with B triangle defects when it is negatively or positively charged, which is consistent with the recent experimental observation of N triangle defects in h-BN atomic layer. Charge population analysis shows that the edge N(B) atoms surrounding the N(B) triangle defect are negatively (positively) charged. Such a charged triangle defects in h-BN may serve as a potential nanolens for electron-beam focusing.
关键词:
energy
Modelling and Simulation in Materials Science and Engineering
The dynamical shear deformation-induced HCP -> FCC process in Ti(3)Al was systematically investigated using both molecular dynamics ( MD) and ab initio methods. The details of the dislocation initiation, the microstructure evolution and the velocity field effect were presented and discussed. The MD simulation reveals that, with the increment of the velocity field, the deformation-induced dislocation slide may happen by three modes based on the nucleation of an initial FCC core, i.e. the continued fault slipping may initiate every other three layers, every other one and then three layers and every other one atomic layer. The corresponding transformed structure is an alternate existence of the single FCC and HCP plate, 18R fault, and the FCC plate containing three ABC units or more. The mechanism was further explored based on ab initio calculations of the detailed energy variation at different fault transition modes. The results promote systematic understanding of the stress induced fault transition mechanism in experimental observations.
关键词:
tial based alloys;phase-transformation;1st-principles;dislocation;interfaces
