共查询到20条相似文献,搜索用时 31 毫秒
1.
D.J. Sordelet R.T. Ott M.Z. Li S.Y. Wang C.Z. Wang M.F. Besser A.C.Y. Liu M.J. Kramer 《Metallurgical and Materials Transactions A》2008,39(8):1908-1916
The structure of hyper-eutectic Zr
x
Pt100−x
(73 ≤ x ≤ 77) metallic glasses produced by melt spinning was examined with high-energy synchrotron X-ray diffraction (HEXRD) and
fluctuation electron microscopy. In addition, details of the amorphous structure were studied by combining ab initio molecular dynamics and reverse Monte Carlo simulations. Crystallization pathways in these glasses have been reported to vary
dramatically with small changes in compositions; however, in the current study, the structures of the different glasses were
also observed to vary with composition, particularly the prepeak in the total structure factor that occurs at a Q value of around 17 nm−1. Results from simulations and fluctuation electron microscopy suggest that the medium-range order of the amorphous structure
is characterized by extended groups of Pt-centered clusters that increase in frequency, structural order, or spatial organization
at higher Pt contents. These clusters may be related to the Zr5Pt3 structure, which contains Pt-centered clusters coordinated by 9Zr and 2Pt atoms.
This article is based on a presentation given in the symposium entitled “Bulk Metallic Glasses IV,” which occurred February
25–March 1, 2007 during the TMS Annual Meeting in Orlando, Florida under the auspices of the TMS/ASM Mechanical Behavior of
Materials Committee.
相似文献
D.J. Sordelet (Senior Scientist and Group Leader)Email: |
2.
The elastic properties of Ni x W1?x alloys up to x = 0.1875 have been determined from first principles calculations. We have used stress–strain relationships to calculate the C ij elastic coefficients and the Voigt–Reuss–Hill approximations to determine the bulk and shear moduli of polycrystals. The W alloying increases the compression modulus while the shear modulus remains almost constant. Furthermore, the W alloying has a minor effect on the elastic anisotropy and, therefore, on its contribution to the indentation modulus. 相似文献
3.
Yu. V. Verbovytskyy V. V. Shtender P. Ya. Lyutyi I. Yu. Zavaliy 《Powder Metallurgy and Metal Ceramics》2017,55(9-10):559-566
4.
5.
The ferromagnetic-antiferromagnetic concentration transition in Fe65(Ni1 − x
Mn
x
)35 alloys is studied by neutron diffraction and small-angle magnetic neutron scattering (SMNS). The Curie and Néel temperatures
are measured, and the antiferromagnetic moments and the cross sections of SMNS by magnetic heterogeneities are determined.
The parameters of spin density fluctuations in the heterogeneities are obtained. A cluster mechanism of the nucleation of
magnetic phases is revealed, and the spin-glass freezing temperatures are estimated. A low-temperature diagram is constructed
for the magnetic states of the alloys. 相似文献
6.
Yan Luo Lifeng Zhang Ming Li Seetharaman Sridhar 《Metallurgical and Materials Transactions B》2018,49(3):894-901
A complex nitride of Al x Mg(1?x)N was observed in silicon steels. A thermodynamic model was developed to predict the ferrite/nitride equilibrium in the Fe-Al-Mg-N alloy system, using published binary solubility products for stoichiometric phases. The model was used to estimate the solubility product of nitride compound, equilibrium ferrite, and nitride compositions, and the amounts of each phase, as a function of steel composition and temperature. In the current model, the molar ratio Al/(Al?+?Mg) in the complex nitride was great due to the low dissolved magnesium in steel. For a steel containing 0.52 wt pct Als, 10 ppm T.Mg., and 20 ppm T.N. at 1100 K (827 °C), the complex nitride was expressed by Al0.99496Mg0.00504N and the solubility product of this complex nitride was 2.95?×?10?7. In addition, the solution temperature of the complex nitride increased with increasing the nitrogen and aluminum in steel. The good agreement between the prediction and the detected precipitate compositions validated the current model. 相似文献
7.
M.J. Kramer Min Xu Y.Y. Ye D.J. Sordelet J.R. Morris 《Metallurgical and Materials Transactions A》2008,39(8):1847-1856
Since Ni and Cu differ by only one valence electron, yet have nearly identical atomic sizes (1.27 vs 1.28 Å for Cu and Ni, respectively), the amorphous Zr2Ni x Cu1?x system is ideal for isolating the effects of electronic structure on short- and medium-range order and the concomitant influence of both the structure and order on devitrification pathways. Thermal analysis, time-resolved high-energy X-ray diffraction (HEXRD), and transmission electron microscopy (TEM) were used to follow metastable and stable crystalline phase formation during devitrification. Using HEXRD, we observed that the first devitrification product in the Zr2Ni system is the C16 structure, if oxygen is kept sufficiently low, while the Zr2Cu system forms the C11b structure. For x = 0.25, the initial devitrification involves forming coexisting C11b and C16 phases. When Ni is increased to x ≥ 0.50, the initial devitrification only involves the C16 structure. These results are in complete accord with electronic structure calculations showing that the enthalpy of formation for the C11b phase is favored for x = 0, while enthalpies for C11b and C16 are nearly identical for x = 0.25; the C16 phase has the most negative enthalpy for all compositions in which x > 0.25. 相似文献
8.
Lithium–vanadium Li x V2O5 (x = 0.1–0.3) bronzes are synthesized by solid-phase and soft chemistry methods. Their electrical properties are studied. Cells with an Li x V2O5 cathode and a solid or liquid lithium anode are subjected to electrochemical cycling. The lithium–vanadium bronzes synthesized by the soft chemistry method are shown to have higher electrochemical characteristics. 相似文献
9.
Nanocrystalline Ni50Al50 ? x Mo x (x = 0, 0.5, 1, 2.5, and 5) intermetallic powders were synthesized by mechanical alloying (MA). Microstructural characterization and structural changes of powder particles during mechanical alloying were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results confirmed that the synthesis behavior of NiAl intermetallic depends on the Mo content and milling time. The SEM micrograph outcomes confirmed the specimen with longer milling time includes finer and more homogenous particles with attention to the ones with lesser milling time. Mo enhance has a considerable effect on the lowering of crystallite size. The TEM image showed that the Ni50Al45Mo5 nano-particles were less than 10 nm. 相似文献
10.
11.
The effect of the Li ion concentration on the phase composition, the electrical conductivity, and the thermoelectric power of the LaLi y Co1–yO3–δ (0 ≤ y ≤ 0.1) oxides synthesized by cocrystallization has been studied. It is found that the region of the perovskite-like solid solution LaLi y Co1–yO3–δ is no higher than y = 0.037. In the temperature range 300–1020 K, lithium alloying leads to an increase in the electrical conductivity and a decrease in the positive thermoelectric power of the single-phase samples compared to LaCoO3–δ. The results are discussed using the density of states model proposed by Senarus Rodriguez and Goodenough for LaCoO3–δ and La1–xSr x CoO3–δ and using the Mott theory of noncrystalline substances. 相似文献
12.
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14.
Yongmei M. Jin Armen G. Khachaturyan Yu U. Wang Chris R. Krenn Adam J. Schwartz 《Metallurgical and Materials Transactions A》2005,36(8):2031-2047
A new stress-accommodating crystallographic mechanism of the δ→α martensitic transformation in plutonium alloys is proposed. According to this mechanism, an orientation variant of the α phase is produced by a combination of a homogeneous strain and shuffling of the alternating close-packed (111)
δ
planes. It is shown that the formation of stable transformation-induced twins whose twin-plane orientations and twin-shear
directions do not depend on the small variations of the crystal-lattice parameters is the preferred stress-accommodating mode.
Only these stable twins have dislocation-free twin boundaries, while the twin boundaries of all others are decorated by an
ultradense distribution of partial dislocations. The theory predicts a crystal-lattice rearrangement mechanism involving the
(205)
α
stable twins. The corresponding invariant plane-strain (IPS) solutions, with special emphasis on the two simplest shuffling
modes (the single and double elementary modes), are presented and compared with the existing experimental observations. It
is shown that the habit-plane orientation is highly sensitive to the input values of the crystal-lattice parameters and, especially,
to the accuracy of the measured volume change in the δ→α transformation. An analysis of these effects on the habit-plane orientation and orientation relations is also presented. 相似文献
15.
Guowei Chang Shuying Chen Xudong Yue Qingchun Li 《Metallurgical and Materials Transactions A》2017,48(4):1551-1561
The morphological changes of the δ-ferrite/γ interphase boundary have been observed in situ with a high-temperature confocal scanning laser microscope (HTCSLM) during δ/γ transformations (δ → γ and γ → δ) of Fe-0.06 wt pct C-0.6 wt pct Mn alloy, and a kinetic equation of morphological stability of δ-ferrite/γ interphase boundary has been established. Thereafter, the criterion expression for morphological stability of δ-ferrite/γ interphase boundary was established and discussed, and the critical migration speeds of δ-ferrite/γ interphase boundaries are calculated in Fe-C, Fe-Ni, and Fe-Cr alloys. The results indicate that the δ-ferrite/γ interphase boundary is very stable and nearly remains absolute planar all the time during γ → δ transformation in Fe-C alloy. The δ-ferrite/γ interphase boundary remains basically planar during δ → γ transformation when the migration speed is lower than 0.88 μm/s, and the interphase boundary will be unstable and exhibit a finger-like morphology when the migration speed is higher than 0.88 μm/s. The morphological stability of δ-ferrite/γ interphase boundary is primarily controlled by the interface energy and the solute concentration gradient at the front of the boundary. During the constant temperature phase transformation, an opposite temperature gradient on both sides of δ-ferrite/γ interphase boundary weakens the steady effect of the temperature gradient on the boundary. The theoretical analysis of the morphological stability of the δ-ferrite/γ interphase boundary is coincident with the observed experimental results utilizing the HTCSLM. There is a good agreement between the theoretical calculation of the critical moving velocities of δ-ferrite/γ interphase boundaries and the experimental results. 相似文献
16.
The in-situ continuous cooling β-to-α transformation kinetics of extra-pure (EP) Ti and of grade-4 commercially pure (CP) Ti were investigated using a fully computer-controlled
resistivity-temperature realtime measurement apparatus and transmission electron microscopy. The β-to-α′ martensitic transformation occurs under near pure shear condition, and the habit plane of lath-type martensite was determined
to be
parallel to
, which is in good agreement with the prediction of the crystallographic theory. The M
s
temperature of EP-Ti was measured as 800 °C and can be raised by up to about 40 °C due to the generation of thermal stress
and local deformation during rapid cooling. The massive transformation was, for the first time, observed to occur over a wide
range of cooling rates in an EP-Ti. The massive start temperature and its occurrence were, unlike the martensitic transformation,
hardly affected by the generation of thermal stress and local deformation during rapid cooling. The stable regime of massive
transformation in a grade-4 CP-Ti was considerably shifted toward a slower cooling rate side and was significantly contracted
at the same time. This is because the presence of iron impurity not only largely suppresses the massive transformation but
also significantly delays a long-range diffusional transformation. 相似文献
17.
Shenyan Huang Ke An Yan Gao Akane Suzuki 《Metallurgical and Materials Transactions A》2018,49(3):740-751
Constrained γ/γ′ lattice misfit as a function of temperature (room temperature, 871 °C, 982 °C, 1093 °C, and 1204 °C) is measured by neutron diffraction on the first-generation Ni-based single-crystal superalloy René N4 and second-generation superalloys René N5, CMSX4, and PWA1484. All the alloys studied show negative misfit at temperatures above 871 °C. For René N4, René N5, and PWA1484, the misfit becomes less negative at temperatures above 1093 °C, possibly due to either the chemistry effect or internal stress relaxation. The magnitude of the misfit shows a qualitative agreement with Caron’s misfit model based on Vegard’s coefficients. The Re-free alloy René N4 was found to have a larger γ lattice parameter and γ/γ′ misfit due to higher fractions of Cr, Ti, and Mo. After 100 hours of annealing at high temperatures, René N5 shows a more negative misfit than the misfit after the standard heat treatment. 相似文献
18.
P. Sahu A.S. Hamada R.N. Ghosh L.P. Karjalainen 《Metallurgical and Materials Transactions A》2007,38(9):1991-2000
19.