Abstract
Ultracentrifuge experiments were performed on a miscible alloy of In-Pb system to study the sedimentation of atoms and phase equilibrium under a strong gravitational field (maximum acceleration: 106 g level, temperature: below melting point (solid), starting state: intermediate α-phase (fct, c0⁄a0<1), time duration: 30–150 h). All centrifuged samples formed graded structure. The Pb content continuously increased, and conversely, the In content decreased in the direction of gravitational field. For the centrifuged sample of 100 hours in time duration, Pb-rich phase (fcc) and In-rich phase (fct, c0⁄a0>1) appeared at the strong- and weak-gravitational field sides of the sample, respectively, from starting state of α-phase, and the continuous changes in lattice parameters were observed in each phases. These observation results showed that the graded structure was continuous in atomic scale, and was formed by the sedimentation of substitutional solute atoms. Composition profiles of the centrifuged samples for 31.3 h, 60 h and 150 h showed that the composition change reached the steady state within 60 hours. As a result of the simulation of sedimentation process, the diffusion coefficient for sedimentation was estimated to be about 8 times larger than that for usual diffusion. The present result indicated that the diffusion mechanism of the sedimentation in this system was different from the conventional ones.
