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1.
The quality of the fit between the precipitates occurring in Al–Zn alloys and the matrix of the Al host is considered taking into account the positions of the atoms in the lattice planes forming the possible faces of the precipitates and the neighboured lattice planes of the matrix. The quality of the fit depends on the number of (pseudo-)coincidence sites of both planes, the density of Al atoms in the matrix plane and the misfit in the spacings of the atoms in the adjoining planes in consideration. The effect of the misfit is taken into account by means of two different models. Based upon the obtained results many of the experimentally observed features about the preferred shapes and orientations of the faces of the growing precipitates can be explained. It turned out that in both of the applied models most probably the effect of the density of the coincidence sites on the interfacial energy is underestimated. 相似文献
2.
On the basis of
- 1 the experimental observation of dislocation loops by means of TEM,
- 2 the conclusion from this that the concentration of vacancies in the dislocation loops exists at the cost of the vacancy concentration primarily present at Tq, and
- 3 the inversion of the decomposition kinetics of Al–Zn–Mg alloys found out by means of resistivity and microhardness measurements, the effective vacancy concentration cv.eff being at disposal for the GP-zone formation was found out by means of the relation tR,max (tR,max being the time required to reach the maximum of resistivity) and the Arrhenius plot In tR,max = f(1/Tq) of the isothermal resistivity measurements. From the comparison of cv.eff with the theoretical V concentration at Tq it is possible to derive statements about the loss of vacancies during and after the quench through loop formation, building-in of vacancies in GP-zones and annealing of vacancies at lattice defects. From this comparison follows:
- The ideal ZnV concentration at Tq (calculated by means of the Lomer equation) is sufficiently great to account for the effective vacancy concentration.
- The part of cMgV in the loss concentration is rising with increasing cMg.
3.
The effect of Sb on the dissolution of Si single crystals (face {111}) in Al–Si melts is studied. The dissolution isotherms at three temperatures and fixed undersaturation are obtained. The experimental data are treated according to the Bliznakov's ratio. Some conclusions are made with reference to the crystal growth process. A probable mechanism of the influence of Sb on the structure of Al–Si alloys is given. 相似文献
4.
The size distribution of approximately spherical incoherent precipitations of Zn in AlZn-alloys is calculated and experimentally tested by means of neutron small angle scattering (NSAS) at a double-crystal diffractometer (DCD). The scattering curves can be approximated by a Gaussian function, so that the size distribution is directly calculated for the experimentical scattering curves under application of a particular LAPLACE-transformation. The size distributions of the α′m-phase of AlZn(16)-samples of different averaged radii of precipitations are calculated by means of FWHM which are determined by the fitting procedure of a computer programme and compared with TEM micrographs. 相似文献
5.
The structures of microcrystalline AlSiMg alloys during heat treatment were studied using optical microscope Reichert MeF2 equipped with a monochrome TV camera VS-700. The average size of the silicon particles was determined. The significant influence of magnesium on the microstructure at high temperatures was demonstrated. Magnesium accelerates the structure coarsening process and a decrease of the effective activation energy of the silicon particles growth was found. 相似文献
6.
Creep tests under the effect of cyclic stress reduction were conducted to Al‐16 wt%Ag and Al‐16 wt%Ag‐0.1 wt%Zr alloys aged at 548 and 673 K. The steady state creep rate was found to be higher under cyclic stress reduction condition than that under static creep condition for the same maximum stress. An expression for the temperature dependence of the threshold stress for cyclic creep acceleration is offered. Cyclic creep acceleration is interpreted using the dislocation cross‐slip model. TEM investigations confirmed that the addition of Zr to Al‐Ag alloy accelerates the formation and coarsening of γ′ and γ‐phases. The mean value of activation energy for both alloys aged at 548 K was found to be 35±0.3 kJ/mol, and 58±0.4 kJ/mol for alloys aged at 673 K. 相似文献
7.
V. Syne
ek M. Simmerska P. Bartuka H. Lffler R. Gerlach 《Crystal Research and Technology》1983,18(10):1261-1276
The results of TEM investigations are presented of the effects of various solutions and ageing treatments, cooling and quenching rates as well as of tensile stress at elevated temperatures on the microstructure of the grain boundary (GB) region of the examined Al Zn and Al Zn Mg alloys. A pronounced influence was found of partial coherency of GB stable β(Zn) precipitates with the α matrix in the Al Zn alloy on the asymmetry of Zn depleted GB region and on the shape of GB precipitates. The role of GB's as sources and sinks of vacancies and the effect of stress gradients in GB regions were emphasized in the establishment of differences in the nucleation and decomposition characteristics within the GB region as compared to those within the grain interior. The existence of a negative stress gradient towards the GB has been suggested to lead to the observed gradual retardation of transformation kinetics within the GB region in Al Zn alloys. A rapid quench from annealing to ageing temperature introduced large local stresses close to GB giving rise to “band of precipitates” on subsequent ageing within the former precipitate free region (PFZ) in Al Zn Mg alloy. Similar enhancement of local stresses accompanied by acceleration of decomposition kinetics was also observed in the aged Al Zn sample subjected to a prior tensile creep exposure within the one-phase region. 相似文献
8.
Lei Wang Yanhong Wei Fengyi Yu Qi Zhang Qingyu Peng 《Crystal Research and Technology》2016,51(10):602-609
A quantitative phase‐field model for directional solidification is applied to study dendrite growth under forced flow conditions in an Al‐Cu Gas Tungsten Arc (GTA) welding molten pool. Evolution of the dendrite morphology and the solute field under forced flow conditions is simulated. Growth of columnar grains goes through three periods, including the initial instability period, the competitive growth period and the relatively stable period. The solute segregation, the solute redistribution and the solute concentration in the liquid side of the interface are investigated, respectively. For the given conditions, simulation results are in good agreement with experimental findings. 相似文献
9.
The microstructure of periodic fluctuant dendritic θ in a matrix of +θ eutectic was obtained in an Al–38 wt% Cu alloy processed by ACRT-B method grown at growth velocities (V) ranging from 5 to 60 μm/s and crucible rotating in a trapezoidal way with maximum rotation rates (Ωmax) ranging from 100 to 400 rpm. Formation of this structure is explained by the influence of the periodical Ekman flow on the growth of dendritic θ during the spin-up and spin-down process. It was also observed that the +θ eutectic between the primary dendrites of θ (CuAl2) is not periodic and fluctuant during ACRT-B process. This is quite different from our previous observation of periodic eutectic in Al–Cu eutectic processed by similar ACRT-B method. 相似文献
10.
The effect of a vertical high magnetic field (up to 10 T) on the dendrite morphology has been investigated during Bridgman growth of Al–4.5 wt%Cu alloys experimentally. It is found that the field causes disorder in dendrites and their tilt in orientation. Along with the increase of the magnetic field and decrease of the growth velocity, the dendrites became broken and orientated in 1 1 1 along the direction of solidification instead of 1 0 0. The field also enlarged the primary dendrite spacing and promoted the branching of the dendrites to form high-order arms. Above phenomena are attributed to the thermoelectromagnetic convection effect and orientation caused by the high magnetic field. 相似文献
11.
H. Neumann B. Schumann E. Nowak A. Tempel G. Kühn 《Crystal Research and Technology》1983,18(7):895-900
Using CuIn2Se3.5 as source material epitaxial layers are obtained on (111)A- und (100)-oriented GaAs substrates by flash evaporation in the substrate temperature range Tsub = 720—870 K. The composition of the films is between CuInSe2 and CuIn2Se3.5. The structural properties of the films are similar to those for CuInSe2 epitaxial layers and refer to a chalcopyrite-like structure. The films are always p-type conducting but different acceptor states are found in dependence on the substrate temperature. 相似文献
12.
In the present work investigations on the effect of stoichiometric variations on the Occurrence and stabilization of quasicrystalline (qc) and related phases have been carried out. Based on the explorations of several Al-deficient and Al-rich versions of the ideal nominal composition i.e. Al65Cu20Cr15, it has been found that the alloy compositions corresponding to Al62Cu23Cr15 (Al-deficient) and Al68Cu17Cr15 (Al-rich) exhibit several structural subtleties. The Al-deficient alloy, has been found to exhibit crystalline bcc and fcc phases with a = 8.90 Å and a = 17.98 Å respectively. In addition to these phases, a new crystalline bcc variant (a = 15.42 Å) originating from the bcc (a = 8.90 Å) phase has been found. Also a curious superstructure of the fcc (a = 17.98 Å) has been observed. The Al-rich alloy typified by Al68Cu17Cr15, on the other hand, does not exhibit any structural variants, instead it shows nearly pure i-phase. 相似文献
13.
Comparison of phases observed in air at 900–980°C in the Ln–Ba–Cu–O (Ln = Lanthanoid) systems is reported. On the basis of the occurrence of compounds found in these Ln2O3–BaCO3–CuO systems they must be divided into at least three subgroups: the first is characteristic of La, Pr and Nd, the second specific for Sm and Eu, and the third common to the smaller lanthanoids, the Y-type elements, with some variation within the groups. 相似文献
14.
We present for the first time, direct and clear experimental evidence of Al–O–Al and Si–O–Si linkages in charge-balanced aluminosilicate glasses with Si/Al=1, such as NaAlSiO4 (nepheline) and LiAlSiO4 (β-eucryptite) compositions using 17O triple quantum MAS (3QMAS) NMR and quantify the extent of disorder in framework cations (Si/Al). The degree of Al avoidance in NaAlSiO4 glass is 0.942 at 1050 K, and in LiAlSiO4 glass is 0.928 at 930 K (0.902 at 1050 K), which demonstrates the effect of cation field strength on the extent of disorder. In addition, we find a remarkable similarity between the ordering state of the liquid and that of the first, disequilibrium phase to crystallize. 相似文献
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17.
Copper iron oxides, Cu1‐xFe2+xO4 (0 ≤ x ≤ 0.5), have been synthesized by thermal oxidation of copper ‐ iron mixtures. In this process, the phase formation and the phase stability were investigated as function of the temperature (800°C – 1200°C) and the oxygen partial pressure (1.013 x 101 – 1.013 x 105 Pa). The phase formation starts with the reaction of the metallic components to simple oxides (Fe3O4, Fe2O3, CuO). From these simple oxides, the formation of complex oxides requires a minimum temperature of 800°C. The synthesis of single phase spinel compounds Cu2+1‐2x Cu1+xFe2+xO4±δ is realized for 0.1 ≤ x ≤ 0.5, using specific temperature – p(O2) – conditions for a given value of x. Remarkably, to achieve our goal, we found that the increase of x implies that of the reaction temperature and/or a decrease of the p(O2) in the reaction gas stream. Besides, a single phase spinel CuFe2O4 does not exist in the temperature / p(O2)‐field investigated. Using the results of XRD ‐ phase analysis, T ‐ p(O2) – x – diagrams were constructed. These diagrams allow the prediction of phase compositions expected for different synthesis conditions. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
18.
A detailed analysis of the relationship of the Kohlrausch–Williams–Watts relaxation function to its recently proposed approximation resulting from the Rajagopal log-relaxation-time distribution is presented. Our considerations are based on the interpretation of the relaxation function as a survival probability of the initial state of a relaxing system expressed by means of the weighted average of an exponential decay with respect to the distribution of the effective relaxation time. Such an interpretation of the relaxation function enforces certain framework of analysis in which the basic probabilistic rules have to be fulfilled. In our approach, to compare the properties of the relaxation function resulting from the Rajagopal relaxation-time distribution and the Kohlrausch–Williams–Watts relaxation function, we use the strict relationship of the latter to the one-sided stable relaxation-rate distribution. 相似文献
19.
Violeta Vassileva 《Crystal Research and Technology》1995,30(3):339-343
The solubility in the Cu(HCOO)2–Sr(HCOO)2–H2O system has been studied by the method of physico-chemical analysis at 25 and 50 °C. It has been established that two double salts are formed in the system: CuSr2(HCOO)6 · H2O at 25 °C and CuSr(HCOO)4 · 4 H2O at 50 °C. The latter salt has not yet been described in the literature. It has been characterized by X-ray powder diffraction and DT and TG analysis. CuSr(HCOO)4 · 4 H2O crystallizes in the triclinic system with lattice parameters a = 12.376(6) Å, b = 13.394(4) Å, c = 11.508(6) Å, α = 93.38(3)°, β = 94.01(3)°, γ = 75.04(3)°. Dehydration proceeds in two stages. 相似文献