Experimental Study on Dissolution of .ALPHA. Phase in .GAMMA./.ALPHA./.GAMMA. Diffusion Couples of the Fe-Cr-Ni System.

Abstract

The dissolution kinetics of body-centered-cubic (bcc) oc-ferrite in face-centered-cubic (fcc) y-austenite matrix was experimentally studied using four sets of y/c(/y 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/c(/y diffusion couples consisting of an oc-phase sheet with thicknesses of 0,07 to 0.1 9 mm and y-phase plates with a thickness of 2 mm were annealed at 1 373 K for various times between 3.6x I O' and 3,6xlO's. Although the c( phase should completely dissolve in the y phase after sufficiently long annealing, the thickness of the a phasetransiently increased with increasing annealing time at an early stage of the reaction, After reaching a maximum value, the thickness of the c( phase decreased with increasing annealing time, The composition of the moving oc/y interface changedwith annealing time after overlap of diffusion zones took place in the oe phase. The change in the interface composition and the transient thickening of the c( phase were qualitatively explained using approximate solutions of the diffusion equations for the semi-infinite a/y diffusion couples.