Experimental Study cn Dissolution of a Phase in γ/α/γ Diffusion Couples of the Fe-Cr-Ni System

Abstract

The dissolution kinetics of body-centered-cubic (bcc) a-ferrite in face-centered-cubic (fcc) y-austenite matrix was experimentally studied using four sets of r/r diffusion couples of the ternary Fe-Cr-Ni system in order to understand the general characteristics of the dissolution reaction of a solid-solution phase in multicomponent systems. The y/a/y diffusion couples consisting of an A-phase sheet with thicknesses of 0.07 to 0.19 mm and y-phase plates with a thickness of 2 mm were annealed at 1373 K for various times between 3.6 103; and 3.6 106s. Although the a phase should completely dissolve in the y phase after sufficiently long annealing, the thickness of the phase transiently increased with increasing annealing time at an early stage of the reaction. After reaching a maximum value, the thickness of the a phase decreased with increasing annealing time. The composition of the moving a/y interface changed with annealing time after overlap of diffusion zones took place in the a phase. The change in the interface composition and the transient thickening of the a phase were qualitatively explained using approximate solutions of the diffusion equations for the semi-infinite a/y diffusion couples. © 1993, The Iron and Steel Institute of Japan. All rights reserved.