1993 Volume 33 Issue 4 Pages 498-507
The dissolution kinetics of body-centered-cubic (bcc) α-ferrite in face-centered-cubic (fcc) γ-austenite matrix was experimentally studied using four sets of γ/α/γ 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 γ/α/γ diffusion couples consisting of an α-phase sheet with thicknesses of 0.07 to 0.19 mm and γ-phase plates with a thickness of 2 mm were annealed at 1373 K for various times between 3.6×103 and 3.6×106 s. Although the α phase should completely dissolve in the γ phase after sufficiently long annealing, the thickness of the α phase transiently increased with increasing annealing time at an early stage of the reaction. After reaching a maximum value, the thickness of the α phase decreased with increasing annealing time. The composition of the moving α/γ interface changed with annealing time after overlap of diffusion zones took place in the α phase. The change in the interface composition and the transient thickening of the α phase were qualitatively explained using approximate solutions of the diffusion equations for the semi-infinite α/γ diffusion couples.
