Diffusion of Al26 and Mn54 in Aluminum
01 May 1962-Journal of Applied Physics (American Institute of Physics)-Vol. 33, Iss: 5, pp 1671-1673
TL;DR: In this paper, the diffusion coefficients of Al26 and Mn54 in aluminum have been determined between 450° and 650°C. The exact solution to Fick's second law for the appropriate boundary conditions was used in treating the data.
Abstract: Diffusion coefficients of Al26 and Mn54 in aluminum have been determined between 450° and 650°C. Low specific activities of the isotopes necessitated use of a thick layer technique. The exact solution to Fick's second law for the appropriate boundary conditions was used in treating the data. Temperature dependence of the diffusion coefficients may be expressed by the following equations: DAl26=1.71 exp−(34 000/RT)DMn54=0.22 exp−(28 800/RT).
Citations
More filters
TL;DR: In this paper, a review of the fabrication, microstructure and mechanical properties of in situ metal matrix composites reinforced with in situ ceramic phases is presented, with particular attention paid to the mechanisms responsible for the formation of the in situ reinforcements.
Abstract: During the past decade, considerable research effort has been directed towards the development of in situ metal matrix composites (MMCs), in which the reinforcements are formed in situ by exothermal reactions between elements or between elements and compounds. Using this approach, MMCs with a wide range of matrix materials (including aluminum, titanium, copper, nickel and iron), and second-phase particles (including borides, carbides, nitrides, oxides and their mixtures) have been produced. Because of the formation of ultrafine and stable ceramic reinforcements, the in situ MMCs are found to exhibit excellent mechanical properties. In this review article, current development on the fabrication, microstructure and mechanical properties of the composites reinforced with in situ ceramic phases will be addressed. Particular attention is paid to the mechanisms responsible for the formation of in situ reinforcements, and for creep failure of the aluminum-based matrix composites.
1,474 citations
TL;DR: In this paper, the mechanical behavior of crystalline solids at elevated temperatures is discussed, including the creep properties of metals, solid solutions and two phase alloys, and the properties of two-phase alloys.
832 citations
20 Dec 2003-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, the diffusion coefficients of several transition elements (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) and a few non-transition elements (Mg, Si, Ga, and Ge) in fcc and liquid Al are critically reviewed and assessed by means of the least-squares method and semi-empirical correlations.
Abstract: The diffusion coefficients of several transition elements (Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn) and a few non-transition elements (Mg, Si, Ga, and Ge) in fcc and liquid Al are critically reviewed and assessed by means of the least-squares method and semi-empirical correlations. Inconsistent experimental data are identified and ruled out. In the case of the elements, for which plentiful experimental data are available in the literature, the least-squares analysis gives rise to the activation energies and pre-exponential factors in an Arrhenius equation. For the elements with limited experimental data or no data at all, the diffusion parameters are estimated from two semi-empirical correlations. In one correlation, the logarithmic pre-exponential factors are plotted against the activation energies for various elements in Al. In the other correlation, the activation energies are shown as a function of valences relative to Al. The diffusion coefficients calculated by using the evaluated diffusion parameters agree reasonably with the reliable experimental data. The proposed semi-empirical correlations are used to predict the diffusion coefficients of a few elements in liquid Al. A satisfactory agreement between the predicted and measured diffusion coefficients is obtained.
693 citations
TL;DR: In this article, the authors derived a model for the onset of the Portevin-Le Chatelier effect in substitutional alloys, based on the solute locking of dislocations temporarily arrested at obstacles in the glide path.
570 citations
TL;DR: In this article, a statistical model of point defect disorder in ordered compounds is presented and applied to Ti3Al and TiAl using input data generated with embedded-atom potentials.
544 citations
References
More filters
TL;DR: In this article, the authors measured the nuclear spin-lattice relaxation times and phase memory times in 99.99% pure aluminum foil from 77\ifmmode^\circ\else\text degree\fi{}K to the melting point by the spin-echo method.
Abstract: Nuclear spin-lattice relaxation times ${T}_{1}$ and phase memory times ${T}_{2}$ have been measured in 99.99% pure aluminum foil from 77\ifmmode^\circ\else\textdegree\fi{}K to the melting point by the spin-echo method. At high temperature the line narrows due to self-diffusion, as previously observed by Seymour. The temperature dependence of the narrowing gives an activation energy of self-diffusion ${E}_{D}$ of 1.4\ifmmode\pm\else\textpm\fi{}0.1 ev. From the measured "narrowing temperature" and Nowick's theoretical estimate of ${D}_{0}$, the same value of ${E}_{D}$ is found. As predicted theoretically, measurements show that ${T}_{1}$ arises from interaction with conduction electrons and is inversely proportional to temperature from 1\ifmmode^\circ\else\textdegree\fi{}K to 930\ifmmode^\circ\else\textdegree\fi{}K. At the highest temperatures, an unknown line broadening mechanism is found which is believed to represent quadrupole coupling to strain fields of dislocations. The measurements were made feasible only through the use of a phase-coherent detection system, a description of which is given.
116 citations
TL;DR: In this article, it was shown that the rate of vacancy annealing depends on the vacancy concentration and the temperature but is independent of the temperature of the injection of vacancy injection per se.
Abstract: It is shown that in very high-purity aluminum, ${\mathrm{Al}}_{\mathrm{II}}$, the rate of vacancy annealing depends on vacancy concentration and annealing temperature but is independent of the temperature ${T}_{i}$ of vacancy injection per se. The rate can be described as the sum of first and second order components. The first order component becomes most prominent at a monovacancy concentration estimated to be ${10}^{\ensuremath{-}6}$ atom fraction. It is shown that the results are consistent with the Koehler-Seitz-Bauerle dissociative mechanism. The activation energy for diffusion of monovacancies in ${\mathrm{Al}}_{\mathrm{II}}$ is found to be 0.65\ifmmode\pm\else\textpm\fi{}0.06 ev. This, combined with earlier results on the formation energy of vacancies, gives 1.44\ifmmode\pm\else\textpm\fi{}0.11 ev for the activation energy for self-diffusion in aluminum by a monovacancy mechanism.In zone-refined aluminum, ${\mathrm{Al}}_{\mathrm{I}}$, of lesser purity the rate of vacancy annealing depends upon ${T}_{i}$ per se and falls off more rapidly with decreasing vacancy concentration than in ${\mathrm{Al}}_{\mathrm{II}}$. Two hypotheses for the impurity effects are considered, namely: (1) trapping of vacancies by impurity atoms and (2) inhibition of dislocation climb by adsorbed impurities.
91 citations
TL;DR: In this paper, a more detailed study of the so-called stage II of the annealing out of the quenched-in resistivity in 99.995 % aluminium has been carried out.
Abstract: A more detailed study of the so-called stage II of the annealing out of the quenched-in resistivity in 99.995 % aluminium (whose existence was established in a preceding paper) has been carried out. The process is found to be a single activated one, the activation energy being Q=1.33±0.05 ev; the analytical shape of the isothermal curves is given by f= 1 –(t/τ)m where m∼0.55 and τ = 2.6 10−8 exp (Q/kt)sec. Several considerations leave little doubt that Q is to be identified with the activation energy for self-diffusion in aluminium, although the nature of the defects and the mechanism of annealing out are yet not clearly understood.
38 citations
19 citations
TL;DR: In this article, the main decay observed is through a 1.15 Mev positron in coincidence with 1.82-Mev gamma ray, and gamma rays of 0.717 Mev and 2.91 Mev have been found.
Abstract: Long-lived ${\mathrm{Al}}^{26}$ has been chemically purified from aluminum targets used in the 86-in. cyclotron. The main decay observed is through a 1.30\ifmmode\pm\else\textpm\fi{}0.15 Mev positron in coincidence with a 1.82-Mev gamma ray. In addition, gamma rays of 0.717 Mev and 2.91 Mev have been found.
10 citations