Book•
The theory of transformations in metals and alloys
01 Jan 1965-
TL;DR: In this paper, the authors present a general introduction to the theory of transformation kinetics of real metals, including the formation and evolution of martensitic transformations, as well as a theory of dislocations.
Abstract: Part I General introduction. Formal geometry of crystal lattices. The theory of reaction rates. The thermodynamics of irreversable processes. The structure of real metals. Solids solutions. The theory of dislocations. Polycrystalline aggregates. Diffusion in the solid state. The classical theory of nucleation. Theory of thermally activated growth. Formal theory of transformation kinetics. Part II Growth from the vapour phase. Solidification and melting. Polymorphic Changes. Precipitation from supersaturated solid solution. Eutectoidal transformations. Order-disorder transformations. Recovery recrystalisation and grain growth. Deformation twinning. Characteristics of martensic transformations. Crystallography of martensitic transformations. Kinetics of martensitic transformations. Rapid solidification. Bainite steels. Shape memory alloys.
Citations
More filters
TL;DR: The structure and hyperfine fields of Fe1−xCrx (x=0.0236 −0.803) nanoparticles were studied at room temperature by combined x-ray diffraction and Mossbauer spectroscopy techniques as discussed by the authors.
Abstract: The structure and hyperfine fields of Fe1−xCrx (x=0.0236–0.803) nanoparticles (average size of 27±2 nm) are studied at room temperature by combined x-ray diffraction and Mossbauer spectroscopy techniques. They are produced by fast evaporation of bulk alloys at 3 Torr Ar pressure. The bulk alloys of any composition are shown to exhibit a bcc structure, whereas the nanoparticles demonstrate a mixture of bcc and tetragonal σ phases in the Cr range from 24.4 to 83.03 at. %. At the Cr content of 2.36 at. % the lattice constant for nanoparticles is larger than that of the bulk alloy, though the values of hyperfine fields on Fe nuclei do not differ. The Mossbauer spectrum of nanoparticles contains an oxide doublet in addition to the sextet specific to that of the bulk alloy. In both cases the width of the sextet lines is rather narrow. However, even at ∼8 at. % Cr the lines of the sextet are broadened so much that it can be decomposed by two-three components. This is explained by freezing the high-temperature ferromagnetic fcc phase regions in the bcc lattice. As the Cr content increases, the Mossbauer spectra become more complex, transforming finally into a paramagnetic singlet. A complete ferromagnetic→paramagnetic transition is observed for the bulk alloy at 68 at. % Cr and for nanoparticles at 35 at. % Cr. The results are discussed under the assumption that at high temperatures the alloys are not homogeneous and exhibit fluctuations of the composition. With decrease of temperature these fluctuations result in decomposition of the alloy into two phases for nanoparticles whereas they are frozen at the cluster level in the bulk alloys holding a macroscopic homogeneity.
34 citations
15 Jul 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the static recrystallization in deformed copper specimens with different initial grain sizes is carried out based on a previous dislocation-grain size interaction model and a Monte Carlo simulation.
Abstract: Modeling of the static recrystallization in deformed copper specimens with different initial grain sizes is carried out based on a previous dislocation–grain size interaction model and a Monte Carlo simulation. From the dislocation–grain size interaction model, the stored energy of the deformed copper is calculated considering the interaction of the dislocations due to the different initial grain sizes. Then, utilizing the stored energy and Monte Carlo simulation the kinetic of recrystallization and recrystallized grain sizes are obtained. The JMAK plots of the modeling results show that, in conditions of 2D modeling and site-saturated nucleation, the Avrami exponent is 2 ± 0.1. The time for 50% recrystallization and recrystallized grain size increase by increasing the initial grain size at a specific strain and are consistent with the experimental data.
34 citations
31 May 2001-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, structural relaxation in transition metal based metallic glasses has been studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), electrical resistivity, acoustic emission and Mossbauer spectroscopy techniques.
Abstract: Structural relaxation in several transition metal based metallic glasses has been studied using differential scanning calorimetry (DSC), X-ray diffraction (XRD), electrical resistivity, acoustic emission and Mossbauer spectroscopy techniques Annealing of metallic glass below the crystallization temperature gives rise to discontinuous changes in electrical resistance These changes are accompanied by acoustic emissions The latter process provides an indication for the viscous flow in the matrix In diverse alloy compositions, it has been observed that changes in electrical resistivity which begin instantly with the onset on isothermal annealing do not follow diffusion kinetics Mossbauer experiments also show that neither long range diffusion nor the formation of a new phase occurs as a result of annealing It is concluded that viscous flow is the mechanism for structural relaxation induced by isothermal annealing and short range ordering during this process is also a consequence of the viscous flow process
34 citations
TL;DR: In this paper, the authors discuss how the self-assembly of InAs QDs in MBE InAs/GaAs(001) should be properly understood in atomic scale, and they point out that the process may be transient or the time required for a QD to grow to maturity may be significantly short, which is obviously inconsistent with conventional kinetic theories.
Abstract: Currently, the nature of self-assembly of three-dimensional epitaxial islands or quantum dots (QDs) in a lattice-mismatched heteroepitaxial growth system, such as InAs/GaAs(001) and Ge/Si(001) as fabricated by molecular beam epitaxy (MBE), is still puzzling. The purpose of this article is to discuss how the self-assembly of InAs QDs in MBE InAs/GaAs(001) should be properly understood in atomic scale. First, the conventional kinetic theories that have traditionally been used to interpret QD self-assembly in heteroepitaxial growth with a significant lattice mismatch are reviewed briefly by examining the literature of the past two decades. Second, based on their own experimental data, the authors point out that InAs QD self-assembly can proceed in distinctly different kinetic ways depending on the growth conditions and so cannot be framed within a universal kinetic theory, and, furthermore, that the process may be transient, or the time required for a QD to grow to maturity may be significantly short, which is obviously inconsistent with conventional kinetic theories. Third, the authors point out that, in all of these conventional theories, two well-established experimental observations have been overlooked: i) A large number of “floating” indium atoms are present on the growing surface in MBE InAs/GaAs(001); ii) an elastically strained InAs film on the GaAs(001) substrate should be mechanically unstable. These two well-established experimental facts may be highly relevant and should be taken into account in interpreting InAs QD formation. Finally, the authors speculate that the formation of an InAs QD is more likely to be a collective event involving a large number of both indium and arsenic atoms simultaneously or, alternatively, a morphological/structural transformation in which a single atomic InAs sheet is transformed into a three-dimensional InAs island, accompanied by the rehybridization from the sp
2-bonded to sp
3-bonded atomic configuration of both indium and arsenic elements in the heteroepitaxial growth system.
34 citations
01 May 1993-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the authors examined the phase stability and competitive kinetics of a metastable ferromagnetic τ phase in undercooled Mn 0.55 Al 0.433 C 0.017 alloy.
Abstract: The solidification of a metastable ferromagnetic τ phase in undercooled MnAlC alloys is examined in terms of the relative thermodynamic phase stability and competitive kinetics. The heat of transformation ΔH t τ → ϵ of the metastable τ phase to the equilibrium h.c.p. ϵ phase and the heat of fusion ΔH f ϵ → l of the h.c.p. ϵ phase in a Mn 0.55 Al 0.433 C 0.017 alloy were measured to determine the Gibbs free energy differences between the metastable and stable phases as a function of temperature. The results indicate that a minimum amount of undercooling of ΔT = 87 K is required to form the metastable ferromagnetic τ phase over the equilibrium phases in a Mn 0.55 Al 0.433 C 0.017 alloy. The thermodynamic evaluation was applied further to develop a complete temperature-time-transformation (TTT) diagram of the Mn 0.55 Al 0.433 C 0.017 alloy based on a solid-state transformation kinetics analysis of the ϵ → τ reaction during isothermal treatments. This analysis reveals the critical cooling rate of the order of 20 K s −1 to bypass the metastable τ phase nucleation during solid state transformation in agreement with empirical observations. The combined thermodynamic and competitive kinetics analysis provide a unified guide for the processing of near equiatomic MnAl alloys.
34 citations