Texturing by cooling a metallic melt in a magnetic field

Abstract

Processing in a magnetic field leads to the texturing of materials along an easy-magnetization axis when a minimum anisotropy energy exists at the processing temperature; the magnetic field can be applied to a particle assembly embedded into a liquid, or to a solid at a high diffusion temperature close to the melting temperature or between the liquidus and the solidus temperatures in a region of partial melting. It has been shown in many experiments that texturing is easy to achieve in congruent and noncongruent compounds by applying the field above the melting temperature T m or above the liquidus temperature of alloys. Texturing from a melt is successful when the overheating temperature is just a few degrees above T m and fails when the processing time above T m is too long or when the overheating temperature is too high; these observations indicate the presence of unmelted crystals above T m with a size depending on these two variables that act as growth nuclei. A recent model that predicts the existence of unmelted crystals above the melting temperature is used to calculate their radius in a bismuth melt.

Crystallization of Supercooled Liquid Elements Induced by Superclusters Containing Magic Atom Numbers

“…An energy saving per volume unit ε ls × ΔH m /V m is introduced in Equation (1); the new Gibbs free energy change is given by Equation (4), where σ 2ls is the new surface energy [15,27] …”

“…The Schrödinger equation depends only on the distance R of an s-state electron from the spherical potential center. The quantified solutions E q leading to the values of ε nm0 are given by the two equations in Equation (27), depending on U 0 which is equal to the complementary Laplace pressure Δp acting on an n-atom cluster having a volume equal to 4πR 3 /3 through an intermediate parameter called k: (27) where m 0 is the electron rest mass and ħ Planck's constant divided by 2π ([32], p. 135).…”

“…The value of U 0 is deduced from the atom number n which depends on molar volumes V m of solid elements extrapolated at T m from published tables of thermal expansion [16,33]. The values of ε nm0 are calculated as a function of R using Equation (28) instead of Equation (27) for n ≥ 147 because U 0 is assumed equal to E q :…”

“…The quantified and the potential energy saving coefficients ε nm0 of silver clusters have been calculated using Equations (27) and (28) and are represented in Figure 1 as a function of supercluster radius R nm which is assumed to continuously vary. These coefficients are equal for n ≥ 147.…”

4He glass phase: A model for liquid elements

“…This complementary enthalpy explains the presence of intrinsic long-lived metastable nuclei surviving above T m and disappearing as the applied superheating rate increases [27,28]. Crystallization and melting are initiated by the formation of these solid or liquid growth nuclei accompanied by a volume change that is expected to obey Lindemann's rule in pure liquid elements [29].…”