共查询到20条相似文献,搜索用时 15 毫秒
1.
Interdiffusion coefficient matrices,
have been experimentally measured at 31 points in the αδFe phase field of the Fe-Cr-AI ternary equilibrium phase diagram
at 900 °C (1173 K). Analyses of the computed matrices were carried out by subjecting each measured -D n
ij to two consistency tests comprised of Onsager’s and Kirkaldy’s relations. Good consistency with these relationships was obtained
in the central region of the ternary phase field, but there were significant deviations near the phase boundaries. These may
beattributable to systematic uncertainties in the analytical procedure. The results indicate that
falls quickly with increasing C Cr, with C Al > 0.2, but is not a strong function of C Al. Conversely,
is not a strong function of C Al but decreases with increasing C Cr.
formerly with the Lawrence Berkeley Laboratories of the University of California, Berkeley
At the time of this research, Dr. Stringer was on sabbatical leave at the Lawrence Berkeley Laboratories, Department of Materials
Science and Mineral Engineering, University of California, Berkeley, CA 94720. 相似文献
2.
Coefficients for the interdiffusion of Sn in Pb-rich alloys and Pb in Sn-rich alloys were established using 1.5-mm-diameter
capillaries and the semi-infinite rod technique. Interdiffusion coefficients are presented for the entire concentration range
from pure Pb to pure Sn, for temperatures from 668 to 1031 K. The concentration dependence of the interdiffusion coefficients
was determined by establishing the concentration along the length of the capillaries and calculating the coefficients using
a finite-difference technique. The interdiffusion of Sn in Pb, extrapolated to 0 at, pct Sn, is given by and that for Pb in Sn, extrapolated to 0 at. pct Pb, by The “average” value for the interdiffusion of Sn in Pb, for the concentration range from 0 to 74 at. pct Sn, is given by
and the average value for the interdiffusion of Pb in Sn, for the concentration range from 0 to 26 at. pct Pb, is given by
The values obtained for the coefficients agree reasonably well with previous results for the diffusion of Sn in Pb-rich alloys
and are consistent with solvent self-diffusion coefficients for pure Pb and pure Sn. However, while the diffusion coefficients
obtained from these Arrhenius equations are likely of the right order of magnitude, it is concluded that the results are affected
by fluid flow in the capillaries, resulting in higher than actual activation energies. It is suggested that, for the capillary-reservoir
technique, convective flow in the reservoir across the open end of the capillaries induces “lid-driven” flow in the upper
portions of the capillaries, resulting in higher than actual diffusion coefficients, particularly for the Sn-rich alloys,
since the Sn-rich end of the capillaries was open to the reservoir. Because of fluid motion induced in the capillaries, all
of the results for solute and self-diffusion in Pb, both present and previous, are likely erroneous because they were obtained
using the capillary-reservoir technique.
Some previous results for solvent self-diffusion in liquid Sn were obtained using either the thin disk or the semi-infinite
rod technique and, since these results agree with results obtained in microgravity, it is concluded that the nonreservoir
methods may provide a means of obtaining more accurate liquid diffusion data. 相似文献
4.
Recently, Tiwari and Mehrotra asserted that the vacancy flux in interdiffusion is driven by a vacancy concentration gradient and also that interdiffusion in intermetallics cannot proceed by the six-jump cycle, triple defect, and antistructural bridge mechanisms. It is shown that those authors’ arguments are incorrect according to classical diffusion theory, by the numerous simulations that have been performed, and by analysis of these mechanisms. 相似文献
6.
Diffusion-couple experiments are conducted in the Fe-Pt system. The phase boundary compositions of the phases measured in
this study are found to be different than the compositions published previously. In the γ-FePt solid solution, the interdiffusion coefficient increases with the Pt content up to 25 at. pct Pt. Fe is the faster diffusing
species in this phase. The trend in the interdiffusion coefficient is explained with the help of calculated driving force
for diffusion. To reduce errors, the average interdiffusion coefficients are calculated in the FePt and FePt 3 compounds. 相似文献
8.
The V-Al system between 16 and 39 at. pet Al was studied at 1400°C under pressures of 0, 30, and 47 kbar. Electron microprobe
analysis, X-ray diffraction, microhardness readings, and metallographic examination revealed only a single solid solution.
Inter diffusion coefficients were determined as a function of composition and pressure. Concentration gradients were measured
with an electron microprobe analyzer and the diffusion coefficients were calculated by the Matano analysis. At 1400°C, the
value of the interdiffusion coefficient varied from 1 to 12 × 10 -9 sq cm per s, increasing with aluminum content and decreasing with increasing pressure.
Formerly Visiting Scientist, Metallurgy Division, Institute for Materials Research, National Bureau of Standards, Washington,
D.C. 相似文献
9.
Interdiffusion in couples consisting of pure copper and a Cu-12.2 at. pet A1 alloy has been studied in the temperature range
between 977 and 1277 K. Concentration of aluminum was determined by EPMA. The interdiffusion coefficient increased with the
atomic fraction of aluminum, N ai, in solid solution: D 0(m 2/s) = 0.43 × 10 -4 and Q (kJ/tool) =194000 — 180000 N a1 The Kirkendall effect has also been studied in the temperature range from 977 to 1277 K. The markers moved toward the aluminum-rich
side. The ratio of the tracer-diffusion coefficient of aluminum, D
*
Al
, to that of copper, D
*
Cu
, at the marker position where N a1 = 0.073, was estimated at 1.7 to 3.7; this ratio showed a tendency to increase with temperature. 相似文献
10.
Interdiffusion was studied in the temperature between 974 and 1273 K, using conventional sandwich-type diffusion couples consisting
of pure copper and Cu-2.1 at. pct Ag alloy. The interdiffusion coefficient,
, increased slightly with increasing the atomic fraction of silver, N Ag. Values of
were well represented by the parameters of
0 = 0.21 x 10 -4 (m 2/s) and ≈
= 184.5 - 143.0 N Ag (kJ/g-atom) up to NAg = 0.02. The Kirkendall effect during diffu-sion treatments at 1174 K for up to 1.4724 x 10 6 s was also studied. The marker moved always toward the silver-rich side. The ratio, D* Ag / D* Cu,was 5.6 for N Ag = 0.011, while it was 4.2 for N Ag = 0. 相似文献
11.
Interdiffusion in Ni-rich, Ni-Cr-Al diffusion couples was studied after annealing at 1100 and 1200 °C. Recession of γ′ (Ni 3Al structure), β (NiAl structure), or α (bcc) phases was also measured. Aluminum and chromium concentration profiles were
measured in the γ (fcc) phase for most of the diffusion couples. The amount and location of Kirkendall porosity suggests that
Al diffuses more rapidly than Cr which diffuses more rapidly than Ni in the γ phase of Ni-Cr-Al alloys. The location of maxima
and minima in the concentration profiles of several of the diffusion couples indicates that both cross-term diffusion coefficients
for Cr and Al are positive and that D CrAl has a greater effect on the diffusion of Cr than does D A1Cr on the diffusion of Al. The γ/γ + β phase boundary has also been determined for 1200 °C through the use of numerous γ/γ + β diffusion couples. 相似文献
12.
Conclusions In an experimental investigation, the partial heterodiffusion coefficients of cadmium and nickel were determined for an annealing temperature of 270°C. It was established that the diffusion rate of cadmium markedly exceeds that of nickel. This difference accounts for the appearance of pores, inand an increase in volume of, compacts from mixed nickel and cadmium powders during sintering.Translated from Poroshkovaya Metallurgiya, No. 5 (149), pp. 87–92, May, 1975. 相似文献
13.
Interdiffusion between dissimilar solids can change the properties of joined materials. Although much work has been done to study experimentally and theoretically interdiffusion in one-dimensional (1-D) diffusion couples, studying interdiffusion in two-dimensional (2-D) or three-dimensional (3-D) solids remains a challenge. In this article, we report an experiment and develop a model to study interdiffusion in a multicomponent system of 2-D geometry. The results (concentration maps and profiles) are compared with data obtained by modeling and numerical simulations. It is assumed that the system satisfies Vegard’s rule and diffusion coefficients are composition dependent. To model the multidimensional diffusion with a drift, we take benefit of the concept of the drift potential. A nonlinear parabolic-elliptic system of strongly coupled differential equations is formulated and the implicit difference method, preserving Vegard’s rule, is applied in the simulations. 相似文献
15.
Interdiffusion coefficients in Nb 2C and NbC 1−x were measured using bulk diffusion couples in the temperature range from 1400 °C to 1700 °C. Marker experiments were used
to show that carbon is the only component undergoing significant diffusion in both carbides. Carbon concentrations were measured
by difference using electron probe microanalysis, and interdiffusion coefficients were taken from Boltzmann-Matano analyses
of the resulting concentration profiles. This analysis clearly showed that, in NbC 1−x, interdiffusion coefficient varies with carbon concentration, and is expressed by where x is the site fraction of vacancies on the carbon sublattice. The interdiffusion coefficient in Nb 2C is given by Parabolic layer growth coefficients were estimated from the Nb|C diffusion couples as well. They are given by The value of
in NbC 1−x was found to be consistent with literature values for the tracer diffusivity of C in NbC 1−x
via the thermodynamic factor, which was determined in two ways. 相似文献
17.
AbstractInterdiffusion was studied in copper (rich)-chromium solid solutions in the composition range approximately 0.2 to 0.8 at% Cr and in the temperature range 852°C – 1050°C. Diffusion couples consisted of cylindrical sections of OFHC copper electroplated with pure chromium. The concentration profiles of the diffusion couples were determined using an electron probe micro analyzer, and the diffusion coefficients were determined by fitting the error function solution of the diffusion equation to the experimental curves. The Arrhenius plot of the diffusion coefficients obtained for five different temperatures gives 48.4 ± 1.2 kcal/mole and 1.11 ?0.44+0.78 cm 2/sec for the activation energy (E D) and frequency factor (D o) respectively (where the limits given are standard deviations for a 99 per cent confidence level), and approximate published chromium tracer diffusion and copper self diffusion results. Résumé Les auteurs ont étudié l'interdiffusion dans des solutions solides, riches en cuivre et con tenant environ 0.2 à 0.8% atomique de chrome, pour une gamme de temp;amp;#x00E9;ratures de 852 agrave; 1050°c. Les couples de diffusion étaient des sections cylindriques de cuivre OFHC électroplaqués avec du chrome pur. Les profils de concentration des couples ont été mesurés par microsonde électronique et les coefficients de diffusion ont été déterminés en lissant les courbes expérimentales grâce à la solution de la fonction erreur pour l'équation de diffusion. La courbe déArrhenius des coefficients de diffusion obtenus à cinq températures différentes donne une énergie d'activation (ED) de 48.4 ± 1.2 kcal/mole et un facteur de fréquence (Do) de 1.11 ?0.44+0.78 cm 2/sec. (oú les limites indiquées sont les déviations standards pour un niveau de con fiance de 99%). Ces valeurs sont approximativement égales à celles publiées pour la diffusion de traceur de chrome et pour l'autodiffusion du cuivre. 相似文献
18.
Interdiffusion was investigated with solid-solid diffusion couples in the α (fcc) region of the quaternary Ni-Cr-Co-Mo system at 1300 °C for the determination of diffusion paths and diffusional interactions
among the components. The concentration profiles for a given couple exhibited a common cross-over composition, Y c, which reflected the relative depths of diffusion in the terminal alloys. Interdiffusion fluxes were calculated directly
from the concentration profiles, and the quaternary interdiffusion coefficients were calculated at selected compositions.
Ni and Co exhibited uphill diffusion against their individual concentration gradients in a direction opposite to the interdiffusion
of Cr. Quaternary diffusion paths were presented as a set of partial diffusion paths on the basis of relative concentration
variables. 相似文献
19.
To better understand fuel-cladding compatibility issues as affected by diffusion processes in Argonne National Laboratory’s
Integral Fast Reactors, interdiffusion studies were carried out with solid-solid diffusion couples assembled with a U-23 at.
pct Zr alloy and cladding steels, such as 316, D9, and HT9. All diffusion couples were annealed at 700 °C and examined metallographically
and by scanning electron microscopy-energy-dispersive spectroscopy analysis for diffusion structure development. The development
of diffusion layers in the couples for various cladding steels is compared and discussed in light of the relative diffusion
behavior of the individual elements, intermetallic formation, and experimental diffusion paths. In the context of fuel-cladding
compatibility, HT9 is considered superior to 316 and D9, as it develops the smallest diffusion zone with the fewest number
of phases.
Formerly Graduate Student, School of Materials Engineering, Purdue University 相似文献
20.
从扩散机制、扩散动力学、热力学以及相结构等方面,总结了室温范围内Au/Sn互扩散的主要特点。给出了Au/Sn互扩散中生成的AuSn,AuSn2,AuSn4等金属间化合物的主要性质。详细总结了不同Sn含量的Au/Sn扩散中,初始态、中间态和最终态的金属间化合物的形成次序、形貌、分布、演化等特征。采用热力学方法定量计算了不足量的Au或Sn的条件下Au/Sn扩散中各中间相的生成吉布斯自由能,较好地解释了中间相的演化规律。给出了Au/Sn扩散的扩散数据,以及主要中间相的生长特点,介绍了Kirkendall效应导致的相关效应。 相似文献
|