Coarsening of aligned Cu-In eutectoid

Abstract

The coarsening behaviour of a unidirectionally transformed Cu-In eutectoid alloy has been studied at 829 K (0.98T _e where T_e is the eutectoid temperature). The as-transformed microstructure consisted of nearly perfect alternating lamellae of α-and δ-phases aligned generally in the growth direction, but contained lamellae terminations and fault lines, or mismatch surfaces; a characteristic zig-zag lamellar structure was also occasionally observed. Ageing the as-transformed structure resulted in two mechanisms of microstructural coarsening: a continuous reaction within the grains, and a discontinuous reaction at the grain boundaries. The kinetics of the continuous coarsening reaction were consistent with a diffusion-controlled fault migration mechanism. Only a limited amount of discontinuous coarsening occurred at 0.98T. The coarsening ratio, the ratio of the interlamellar spacing of the discontinuously coarsened lamellae to the original lamellae, was measured as 3.3 ± 0.4.