S. Fedosov (Samara State Technical University
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Galaktionovskaya 141
,
Samara 443010
,
Russia)
金属学报(英文版)
This paper Presents experimental data on effect of carbon concentration and laser processing regimes on retained austenite quantity. The data on retained austenite decomposition during subsequent temperings at various temperatures as well as after holding at room temperature during 3 years are given.Correla- tion between structural broadening of the X - ray lines of retained gamma - phase and the amount of the latter has been discovered.Mechanisms responsible for the increased quantity of the retained austen- ite in carbon and low alloyed steels after laser hardening are described.
关键词:
retained austenite
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null
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null
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Physical Review B
Calculating the S-state splitting of a d5 ion (Fe3+, Mn2+) in a crystal has been a long-standing difficult problem since 1934 when it was discussed by Van Vleck and Penney. Low and Rosengarten have concluded that crystal-field theory is not capable of providing a unified interpretation for the spectrum and for the S-state zero-field splitting of d5 6S ions. In the present paper, by utilizing a method of combined perturbation composed of the electrostatic, crystal-field, and spin-orbit-coupling energies, and by diagonalizing a set of complete energy matrices constructed for a d5 configuration and having a total order of 252, a reasonable interpretation is obtained for the d-d spectrum and the EPR cubic zero-field splitting of Fe3+ ions located at octahedral and tetrahedral sites in yttrium gallium garnet. This shows that crystal-field theory is as well suited for application to d5 ions and to other d(n) ions and that the earlier Low-Rosengarten conclusion is wrong. It is also shown that contributions to the ground-state splitting arising from various excited states of the d5 configuration or from various components of the crystal field do not obey a linear-superposition rule. In the Appendix, a detailed explicit description of the matrices is given.
关键词:
ion;spectra
Ming FANG
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Qinghui LI
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Fuxi GAN
材料科学技术（英文）
The optical absorption properties of phase-change optical recording thin films subjected to various initialization conditions were investigated. The effects of initialization power and velocity on optical constants of the Ge2Sb2Te5 thin films were also studied. The energy gap of Ge2Sb2Te5 thin films subjected to various initialization conditions was also obtained. It was found that the optical energy gap of the Ge2Sb2Te5 thin films increased with either increasing initialization laser power or decreasing initialization velocity, with peak of 0.908 eV at laser power of 1000 mW or initialization velocity of 4.0 m/s, but the continued increasing initialization laser power or decreasing initialization velocity resulted in the decrease of the optical energy gap. The change of the optical energy gap was discussed on the basis of amorphous crystalline transformation.
关键词:
Phase transformation
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null
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null
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null
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Physical Review B
Body-centered-cubic (bcc) iron is one of the most investigated solid-state systems. Using four different density-functional methods, we show that there is a magnetic transition close to the ground-state volume of bcc Fe, which originates from the particular magnetic band structure. The common equation of state functions, used to determine the basic ground-state physical quantities from the calculated total energies, cannot capture the physics of this magnetic transition leading to serious underestimation of the Fe bulk modulus. Ignorance of the magnetic transition found here is reflected by large scatter of the published theoretical bulk moduli of ferromagnetic bcc Fe. Due to the low performance of the exchange-correlation functionals, most of the erroneous results are accidentally in good agreement with the experimental values. The present finding is of fundamental importance, especially taking into account that bcc Fe is frequently used as a test system in assessing the performance of exchange-correlation approximations or total-energy methods.
关键词:
generalized-gradient-approximation;total-energy calculations;density-functional approximations;initio molecular-dynamics;magnetic;phase-stability;augmented-wave method;ab-initio;elastic-constants;electron-gas;ultrasoft pseudopotentials
Europhysics Letters
Noncollinear magnetic investigations of the ground state in PrFeAsO have been performed by the density-functional theory. We calculated the total energy and made structure optimization, and the electronic density of states of PrFeAsO was analyzed. There are three different magnetic structures in PrFeAsO defined by experiments. Based on these magnetic structures, we studied four collinear and four noncollinear cases. The ground state is found to take the ordering proposed by Zhao, in which the FeAs plane is of stripe antiferromagnetism and Pr spins are perpendicular to Fe spins. The electronic density of states indicates that for PrFeAsO the increase of the electron Coulomb interaction leads to a decrease in conductivity. Copyright (C) EPLA, 2011
关键词:
high-temperature superconductivity;phase-diagram;oxypnictides;instability
HAN Yafang M. C. Chaturvedi Institute of Aeronautical Materials
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Beijing
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Chi na. Department of Mechanical Engineering
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University of Manitoba
,
Canada.
材料科学技术（英文）
The steady state creep rate equdtion of a nickel base superalloy Inconel 718, strengthened by coherent ordered disc-shaped bct γ~(11) phase and coherent spherical fcc γ~1 phase precipitates, has been established in the stress and temperature ranges of 620-840 MN m~(-2) and 853-943K, respecti- vely. Constant stress tensile creep tests were used to medsure the values of steady state creep rate, ε_s, and the consecutive stress reduction method was used to measure the back stress during creep deformation. The values of effective stress exponent, n_e, were detemined from the slopes of the lgε_s vs. lg(σ_a-σ_0)/G plots. The effect of grain size, d, on steady state creep rdte has been also studied in this investigation, and the grain size sensitive exponents m were detemined from the slopes of lgε_s vs. lg(b/d) plots. The creep rate equations of Inconel 718, in the above stress and temperature ranges, have been proposed to be ε_s=1.6×10~(-5)(D_1Gb/KT) (b/d )~(0.19)[(σ_a-σ_0)/G]~(1.35) in diffusional creep region, and ε_s =75(D_1Gb/KT) (b/d)~(-0.42)[(σ_a-σ_0)/G]~(5.5) in dislocation power law creep region.
关键词:
Inconel 718
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null
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